- Pediatric Dermatology
- Genetic Skin Disease
- Cell-based Therapy
- Cutaneous Surgery
- General skin conditions including atopic dermatitis, acne, viral exanthem, hair and nail disorders etc
- Novel Therapeutic Drug Application
Director of Pediatric Dermatology, Stanford University (2012 - Present)
Director of Pediatric Dermatology Fellowship, Stanford University (2012 - Present)
Director of Pediatric Dermatology, University of Wisconsin-Madison (2007 - 2012)
Honors & Awards
Mentorship Award, Women's Dermatology Society (2006)
William Weston Research Award, Society of Pediatric Dermatology (2009)
Preceptorship Award, American Society of Dermatologic Surgery (2008, 2010)
Teaching Award, University of Wisconsin-Madison (2012)
Research Award, Dermatology Foundation (2009, 2012)
Boards, Advisory Committees, Professional Organizations
FAAD, American Academy of Dermatology (2002 - Present)
Member, American Society for Dermatologic Surgery (2002 - Present)
Member, Society of Pediatric Dermatology (2005 - Present)
Member, American Academy of Pediatrics (2012 - Present)
Member, Women’s Dermatologic Society (2005 - Present)
Member, American Medical Association (2002 - Present)
Member, Dermatology Foundation (2007 - Present)
Medical Education:Vanderbilt University School of Medicine (2001) TN
Residency:Vanderbilt University Medical Center (2005) TN
Board Certification: Pediatric Dermatology, American Board of Dermatology (2006)
Fellowship:University of Colorado Health Science Center (2006) CO
Board Certification: Dermatology, American Board of Dermatology (2005)
Internship:Vanderbilt University Medical Center (2002) TN
Postgraduate Fellowship, Memorial Sloan-Kettering Institute, Molecular Immunology (1997)
PhD, Medical College of Wisconsin, Cellular Immunology (1993)
Medical Education:Medical College Of Wisconsin (1993) WI
Topical Sirolimus for the Treatment of Pachyonychia Congenita (PC)
A study to evaluate safety and efficacy of topical sirolimus to treat plantar keratoderma in adults with PC. Subjects may receive either placebo or treatment with at least 1 foot receiving topical sirolimus at some time. For certain phases of the study treatment assignment to the right and left foot will be randomized in a double blind fashion. Blood levels will test systemic absorption of sirolimus. Other safety and efficacy measures will be taken through the 39-week study duration. Funding Source - FDA OOPD
Sildenafil for the Treatment of Lymphatic Malformations
A Phase 2 study to evaluate safety and efficacy of sildenafil taken orally to improve or resolve lymphatic malformations in children. Subjects may receive either placebo or treatment in an oral dosage with an open label extension for subjects who received placebo. The study treatment assignment will be randomized in a double blind fashion. MRI examination will evaluate change in lesion volume due to treatment. Other safety and efficacy measures will be taken through the 32-week study duration. Funding Source - FDA OOPD
Postdoctoral Faculty Sponsor
Graduate and Fellowship Programs
Treatment of complex periorbital venolymphatic malformation in a neonate with a combination therapy of sirolimus and prednisolone
2015; 28 (4): 218-221
Venolymphatic malformations (VLMs) are vascular anomalies consisting of both veins and lymph vessels. A 2-week-old newborn presented with large VLMs on the left forehead, temple, preauricular area, and orbit. Patient was at imminent risk for permanent vision loss due to a localized mass effect. Surgical excision or debulking was contraindicated due to its complexity and proximity to the left eye, and the patient failed to respond to the sildenafil treatment and sclerotherapy. Patient was subsequently started on oral sirolimus 0.8 mg/m(2) twice daily in combination with prednisolone 2 mg/kg daily. The patient had an excellent therapeutic outcome for 7 months with complete preservation of vision before treatment was discontinued. However, 2 months after the medical treatments were discontinued, her VLM rebounded. She responded to the combination therapy again after a failed treatment with the mTOR inhibitor alone. This case demonstrates that the sirolimus and prednisolone combination therapy could be beneficial for treatment of complex VLM intractable to other treatments.
View details for DOI 10.1111/dth.12208
View details for Web of Science ID 000358434400006
View details for PubMedID 25753853
Advances in the therapeutic use of mammalian target of rapamycin (mTOR) inhibitors in dermatology
JOURNAL OF THE AMERICAN ACADEMY OF DERMATOLOGY
2015; 72 (5): 879-889
Significant developments in the use of mammalian target of rapamycin (mTOR) inhibitors (mTORIs) as immunosuppressant and antiproliferative agents have been made. Recent advances in the understanding of the mTOR signaling pathway and its downstream effects on tumorigenesis and vascular proliferation have broadened the clinical applications of mTORIs in many challenging disorders such as tuberous sclerosis complex, pachyonychia congenita, complex vascular anomalies, and inflammatory dermatoses. Systemic mTORI therapy has shown benefits in these areas, but is associated with significant side effects that sometimes necessitate drug holidays. To mitigate the side effects of systemic mTORIs for dermatologic applications, preliminary work to assess the potential of percutaneous therapy has been performed, and the evidence suggests that percutaneous delivery of mTORIs may allow for effective long-term therapy while avoiding systemic toxicities. Additional large placebo-controlled, double-blinded, randomized studies are needed to assess the efficacy, safety, duration, and tolerability of topical treatments. The objective of this review is to provide updated information on the novel use of mTORIs in the management of many cutaneous disorders.
View details for DOI 10.1016/j.jaad.2015.01.014
View details for Web of Science ID 000353118400028
Pediatric Teledermatology: A Survey of Usage, Perspectives, and Practice
2015; 32 (3): 363-368
Pediatric dermatology is one of the smallest subspecialties, and expanding the availability of care is of great interest. Teledermatology has been proposed as a way to expand access and improve care delivery, but no current assessment of pediatric teledermatology exists. The objective of the current study was to assess usage and perspectives on pediatric teledermatology. Surveys were distributed electronically to all 226 board-certified U.S. pediatric dermatologists; 44% (100/226) responded. Nearly all respondents (89%) have experience with teledermatology. Formal teledermatology reimbursement success rates have increased to 35%. Respondents were positive about teledermatology's present and future prospects, and 41% want to use teledermatology more often, although they viewed teledermatology as somewhat inferior to in-person care regarding accuracy of diagnosis and appropriation of management plans. Significant differences were found between formal teledermatology users and nonusers in salary structure, practice environment, sex, and region. Substantial increases in pediatric teledermatology have occurred in the last 5 to 10 years, and there remains cause for optimism for teledermatology's future. Concerns about diagnostic confidence and care quality indicate that teledermatology may be best for care of patients with characteristic clinical presentations or management of patients with established diagnoses.
View details for DOI 10.1111/pde.12533
View details for Web of Science ID 000354820500035
- Dermatologic and Dental Aspects of the 2012 International Tuberous Sclerosis Complex Consensus Statements JAMA DERMATOLOGY 2014; 150 (10): 1095-1101
An open-label study to evaluate sildenafil for the treatment of lymphatic malformations
JOURNAL OF THE AMERICAN ACADEMY OF DERMATOLOGY
2014; 70 (6): 1050-1057
Lymphatic malformations can be challenging to treat. Mainstay interventions including surgery and sclerotherapy are invasive and can result in local recurrence and complications.We sought to assess the effect of 20 weeks of oral sildenafil on reducing lymphatic malformation volume and symptoms in children.Seven children (4 boys, 3 girls; ages 13-85 months) with lymphatic malformations were given oral sildenafil for 20 weeks in this open-label study. The volume of the lymphatic malformation was calculated blindly using magnetic resonance imaging performed before and after 20 weeks of sildenafil. Lymphatic malformations were assessed clinically on weeks 4, 12, 20, and 32. Both the physician and parents evaluated the lymphatic malformation in comparison with baseline.Four subjects had a lymphatic malformation volume decrease (1.0%-31.7%). In 2 subjects, despite a lymphatic malformation volume increase (1.1%-3.7%), clinical improvement was noted while on sildenafil. One subject had a 29.6% increase in lymphatic malformation volume and no therapeutic response. Lymphatic malformations of all 6 subjects who experienced a therapeutic response on sildenafil softened and became easily compressible. Adverse events were minimal.A randomized controlled trial will be necessary to verify the effects of sildenafil on lymphatic malformations.Sildenafil can reduce lymphatic malformation volume and symptoms in some children.
View details for DOI 10.1016/j.jaad.2014.02.005
View details for Web of Science ID 000336030400023
Pediatric Lichen Sclerosus: A Review of the Epidemiology and Treatment Options.
2015; 32 (5): 593-599
Lichen sclerosus (LS) is a rare, chronic, inflammatory disease of the skin that primarily affects postmenopausal women but may occur in men and children as well. Approximately 7% to 15% of cases are believed to occur in children. The epidemiologic data for LS have been limited and treatment options are not well studied, particularly in children. We reviewed new developments available in the current literature on the epidemiology and management of LS for children.
View details for DOI 10.1111/pde.12615
View details for PubMedID 25940739
- Treatment of keratitis-ichthyosis-deafness (KID) syndrome in children: a case report and review of the literature DERMATOLOGIC THERAPY 2015; 28 (2): 89-93
- Medicaid acceptance among pediatric dermatologists JOURNAL OF THE AMERICAN ACADEMY OF DERMATOLOGY 2015; 72 (1): 191-193
- Scabies infection in a neonate. journal of pediatrics 2014; 165 (6): 1266-1266 e1
- Proceedings of the Inaugural Pediatric Dermatology Research Alliance (PeDRA) Conference JOURNAL OF INVESTIGATIVE DERMATOLOGY 2014; 134 (11): 2671-2674
- Proceedings of the Inaugural Pediatric Dermatology Research Alliance (PeDRA) conference. journal of investigative dermatology 2014; 134 (11): 2671-2674
Dermatologic and dental aspects of the 2012 International Tuberous Sclerosis Complex Consensus Statements.
2014; 150 (10): 1095-1101
The 2012 International Tuberous Sclerosis Complex Clinical Consensus Conference was convened to update the last consensus statement in 1998. Skin and dental lesions are common in tuberous sclerosis complex (TSC) and are a frequent concern for patients. Recognition of these lesions is imperative for early diagnosis, given the treatment advances that may improve patient outcomes.To detail recommendations for the diagnosis, surveillance, and management of skin and dental lesions in TSC.The TSC Dermatology and Dentistry Subcommittee, 1 of 12 subcommittees, reviewed the relevant literature from 1997 to 2012.A consensus on skin and dental issues was achieved within the Dermatology and Dentistry Subcommittee before recommendations were presented, discussed, and agreed on in a group meeting of all subcommittees from June 14 to 15, 2012.Skin and dental findings comprise 4 of 11 major features and 3 of 6 minor features in the diagnostic criteria. A definite diagnosis of TSC is defined as the presence of at least 2 major features or 1 major and 2 or more minor features; in addition, a pathological mutation in TSC1 or TSC2 is diagnostic. Skin and oral examinations should be performed annually and every 3 to 6 months, respectively. Intervention may be indicated for TSC skin or oral lesions that are bleeding, symptomatic, disfiguring, or negatively affecting function. Options presented include surgical excision, laser(s), or use of a mammalian target of rapamycin inhibitor.
View details for DOI 10.1001/jamadermatol.2014.938
View details for PubMedID 25029267
Xanthoma striatum palmare associated with nonsyndromic paucity of the interlobular bile ducts.
2014; 93 (5): E6-8
View details for PubMedID 24897150
- Somatic HRAS p.G12S Mutation Causes Woolly Hair and Epidermal Nevi JOURNAL OF INVESTIGATIVE DERMATOLOGY 2014; 134 (4): 1149-1152
Familial Urticaria Pigmentosa: Report of a Family and Review of the Role of KIT Mutations
AMERICAN JOURNAL OF DERMATOPATHOLOGY
2013; 35 (1): 113-116
Cutaneous mastocytosis is a rare clinically heterogeneous disorder characterized by mast cell infiltration. Mastocytosis affects both children and adults and has been reported to occur in families. Recent data suggest that mutations in the c-kit proto-oncogene are causative of mastocytosis not only in adults but in children and familial cases as well; however, mutation analysis other than D816V is not widely available, making detection of causative mutations problematic. We present the case of a 33-year-old man with a 30-year history of persistent urticaria pigmentosa and his 2 affected children. Sequencing of KIT exons 8, 10, 11, and 17 was carried out on a skin biopsy specimen and mucosal swabs of the incident case and was negative for known KIT mutations. Additional work-up was deferred by the family. Presentation of this familial case of urticaria pigmentosa demonstrates the complexity of genetic evaluation in clinical settings. It suggests that mutations other than those reported in exons 8, 10, 11, and 17 may also result in familial mastocytosis. Presentation of this case also allows for review of the mechanism of action of causative KIT mutations and the recent literature supporting KIT mutations in childhood and familial mastocytosis.
View details for DOI 10.1097/DAD.0b013e31826330bf
View details for Web of Science ID 000314103600024
View details for PubMedID 22892471
Tuberous sclerosis complex diagnostic criteria update: recommendations of the 2012 international tuberous sclerosis complex consensus conference.
2013; 49 (4): 243-54.
View details for DOI 10.1016/j.
- Tuberous sclerosis complex surveillance and management: recommendations of the 2012 international tuberous sclerosis complex consensus conference. Pediatric Neurology 2013; 49 (4): 255-65
Dermatofibrosarcoma Protuberans in Children: an Update on the Diagnosis and Treatment
2012; 29 (6): 707-713
Dermatofibrosarcoma protuberans (DFSP) is a fibrohistiocytic tumor of low grade malignant potential. Although rare, pediatric cases pose a particular challenge in diagnosis and management. In children, the clinical appearance may be heterogeneous and a high index of suspicion is necessary to avoid delays in diagnosis which can lead to further morbidity. Histologic examination, often with the use of appropriate immunostains, is necessary for diagnosis. Advances in the understanding of the molecular genetics of DFSP have led to further diagnostic and therapeutic modalities. DFSP is thought to result from a translocation between platelet-derived growth factor beta (PDGFB, 22q13.1) and type 1 collagen (COL1A1, 17q21?22) leading to a fusion protein (PDGFB) which stimulates the PDGF receptor. Detection of this translocation in tissue via PCR or fluorescence in situ hybridization (FISH) can be helpful in difficult cases. While surgery with wide local excision or Mohs micrographic surgery is the mainstay of treatment, the use of targeted therapy with imatanib mesylate shows promise in large or unresectable tumors. Knowledge of the clinical features, histology, genetics, and treatment options is important for successful management of these tumors.
View details for DOI 10.1111/j.1525-1470.2012.01767.x
View details for Web of Science ID 000310565500001
View details for PubMedID 22780227
Effective Topical Combination Therapy for Treatment of Lichen Striatus in Children: A Case Series and Review
JOURNAL OF DRUGS IN DERMATOLOGY
2012; 11 (7): 872-875
Lichen striatus (LS) is an uncommon linear dermatosis that is primarily seen in children from 4 months to 15 years of age. While some of these eruptions are asymptomatic, others can be quite pruritic. In darker-skinned individuals, post-inflammatory hypopigmentation can be significant and may provide a cause for concern for the patients and/or their parents. In our case series of 4 patients, we observed rapid resolution of LS by combining a topical retinoid with a topical steroid. To our knowledge, this is the first report of successful treatment with this kind of combination therapy in the English literature. The patients not only achieved satisfying cosmesis, but also complete resolution of their pruritus. The most common side effect of topical tazarotene is localized irritation at treatment sites, but the patients in this particular series tolerated the treatment well.
View details for Web of Science ID 000306164100018
View details for PubMedID 22777233
Progress towards genetic and pharmacological therapies for keratin genodermatoses: current perspective and future promise
2012; 21 (7): 481-489
Hereditary keratin disorders of the skin and its appendages comprise a large group of clinically heterogeneous disfiguring blistering and ichthyotic diseases, primarily characterized by the loss of tissue integrity, blistering and hyperkeratosis in severely affected tissues. Pathogenic mutations in keratins cause these afflictions. Typically, these mutations in concert with characteristic features have formed the basis for improved disease diagnosis, prognosis and most recently therapy development. Examples include epidermolysis bullosa simplex, keratinopathic ichthyosis, pachyonychia congenita and several other tissue-specific hereditary keratinopathies. Understanding the molecular and genetic events underlying skin dysfunction has initiated alternative treatment approaches that may provide novel therapeutic opportunities for affected patients. Animal and in vitro disease modelling studies have shed more light on molecular pathogenesis, further defining the role of keratins in disease processes and promoting the translational development of new gene and pharmacological therapeutic strategies. Given that the molecular basis for these monogenic disorders is well established, gene therapy and drug discovery targeting pharmacological compounds with the ability to reinforce the compromised cytoskeleton may lead to promising new therapeutic strategies for treating hereditary keratinopathies. In this review, we will summarize and discuss recent advances in the preclinical and clinical modelling and development of gene, natural product, pharmacological and protein-based therapies for these disorders, highlighting the feasibility of new approaches for translational clinical therapy.
View details for DOI 10.1111/j.1600-0625.2012.01534.x
View details for Web of Science ID 000305508500001
View details for PubMedID 22716242
Treatment of Recalcitrant Excessive Granulation Tissue with Photodynamic Therapy in an Eight-Year-Old Patient with Focal Dermal Hypoplasia Syndrome
2012; 29 (3): 324-326
We report a pediatric patient with focal dermal hypoplasia syndrome who developed painful excessive granulation tissue refractory to traditional medical and surgical therapies. Complete response was achieved rapidly with a combination of photodynamic therapy and intralesional steroid injections. The patient has remained in remission for longer than a year.
View details for DOI 10.1111/j.1525-1470.2011.01436.x
View details for Web of Science ID 000304139900018
View details for PubMedID 21995324
Chemically defined conditions for human iPSC derivation and culture
2011; 8 (5): 424-U76
We re-examine the individual components for human embryonic stem cell (ESC) and induced pluripotent stem cell (iPSC) culture and formulate a cell culture system in which all protein reagents for liquid media, attachment surfaces and splitting are chemically defined. A major improvement is the lack of a serum albumin component, as variations in either animal- or human-sourced albumin batches have previously plagued human ESC and iPSC culture with inconsistencies. Using this new medium (E8) and vitronectin-coated surfaces, we demonstrate improved derivation efficiencies of vector-free human iPSCs with an episomal approach. This simplified E8 medium should facilitate both the research use and clinical applications of human ESCs and iPSCs and their derivatives, and should be applicable to other reprogramming methods.
View details for DOI 10.1038/NMETH.1593
View details for Web of Science ID 000289987100021
View details for PubMedID 21478862
A Case of Sclerodermatous Graft-versus-Host Disease Responsive to Imatinib Therapy
2011; 28 (2): 172-175
Sclerodermatous graft-versus-host disease (sGVHD) is a rare, late complication of hematopoietic cell transplantation. Classified as a variant of chronic graft-versus-host disease, sGVHD is thought to be predominantly an immune-mediated response characterized by aberrant T-cell function and dysregulation of tyrosine kinase cascades. Recently, the profibrotic cytokine transforming growth factor B and stimulatory autoantibodies against the platelet-derived growth factor receptor have been implicated in the pathogenesis of sGVHD. Treatment of sGVHD remains disappointing and largely limited by systemic side effects. Imatinib mesylate is a small molecule tyrosine kinase inhibitor that has been shown to selectively inhibit both the platelet-derived growth factor receptor and transforming growth factor-? signaling pathways. We report a case of sGVHD in a pediatric patient that was resistant to traditional therapy but showed improvement in cutaneous symptoms following daily treatment with 400 mg of imatinib mesylate. Due to its favorable side-effect profile, specificity for molecular pathways deranged in sGVHD and proven efficacy in other sclerodermoid diseases, imatinib mesylate is a promising new tool in the management of this challenging disease.
View details for DOI 10.1111/j.1525-1470.2010.01301.x
View details for Web of Science ID 000290381900017
View details for PubMedID 21504445
Lipoatrophic Panniculitis Case Report and Review of the Literature
ARCHIVES OF DERMATOLOGY
2010; 146 (8): 877-881
Lipoatrophic panniculitis (LP) is a rare disease of childhood characterized by eruption of tender erythematous nodules and plaques followed by circumferential bands of lipoatrophy often seen on the arms and legs. This condition has also been known as lipophagic panniculitis of childhood, annular atrophy of the ankles, and partial lipodystrophy.A previously healthy 8-year-old boy was evaluated for tender, raised plaques on the ankles, which progressed to circumferential atrophy of the distal lower extremities. Biopsy specimen analysis revealed a dense mixed infiltrate extending into the subcutaneous tissue as well as lipophages within the fatty lobules. A diagnosis of LP was made, and the patient began treatment with prednisone and hydroxychloroquine. Methotrexate was added later to the regimen as a steroid-sparing agent, and the dose was increased over the course of 3 months, by which time the cutaneous disease progression was nearly halted. However, the patient continued to have lower leg pain with bone changes demonstrated on magnetic resonance imaging.We report this case and review of the literature to call attention to the clinical features of LP and its association with skeletal changes. Our patient's response to combination therapy is of interest and contributes to the limited literature about management of this disease.
View details for Web of Science ID 000281249700010
View details for PubMedID 20713820
- Topical Rapamycin A Novel Approach to Facial Angiofibromas in Tuberous Sclerosis ARCHIVES OF DERMATOLOGY 2010; 146 (7): 715-718
Rapid Improvement in Digital Ischemia and Acral Contracture in a Collodion Baby Treated With Topical Tazarotene
JOURNAL OF DRUGS IN DERMATOLOGY
2010; 9 (6): 713-716
Collodion baby is a rare congenital disorder whereby affected infants are born encased in a thick, taut, shiny, translucent membrane. The majority of babies with collodion membrane have associated disorders, most commonly nonbullous congenital ichthyosiform erythroderma and lamellar ichthyosis. The authors report a case of collodion baby with rare complication of acral contracture, ischemia and nail dystrophy. Topical treatment with tazarotene 0.1% gel resulted in rapid improvement. The patient developed normal nail plates and full motor function in both hands and feet following treatment. To the authors' knowledge, this is the first report demonstrating the benefit of topical tazarotene for management of this rare condition in a neonate.
View details for Web of Science ID 000278572400022
View details for PubMedID 20645539
- Mohs Surgical Excision of a Granular Cell Tumor with Plexiform Features on the Arm of a 7-Year-Old Child DERMATOLOGIC SURGERY 2010; 36 (4): 546-550
- Sweet's panniculitis associated with metastatic breast cancer JOURNAL OF THE AMERICAN ACADEMY OF DERMATOLOGY 2007; 56 (2): S61-S62
CD2-mediated activation of the Tec-family tyrosine kinase ITK is controlled by proline-rich stretch-4 of the CD2 cytoplasmic tail
1998; 10 (7): 1009-1016
Ligation of the CD2 co-stimulatory receptor on human T lymphocytes induces tyrosine phosphorylation and activation of the Tec-family tyrosine kinase, ITK. To examine whether any of several proline-rich (PR) stretches of the CD2 cytoplasmic tail are necessary for ITK activation we introduced wild-type and mutated versions of rat CD2, each missing at least one PR stretch of the tail, into human Jurkat T leukemia cells. The influence of cytoplasmic tail mutations was then studied following stimulation of transfectants with the rat CD2 mAb pair, OX54/OX55. As predicted, wild-type rat CD2 was able to activate ITK in Jurkat cells. In addition, a truncation mutant, lacking the most membrane-distal PR stretch, PR6, was able to activate ITK. By contrast, all other studied truncation mutants, each of which is missing at least PR4-PR6, were unable to induce ITK activation. Of deletion mutants, deletion of the membrane-proximal PR stretches, PR1-PR3, did not impair rat CD2-mediated ITK activation. However, additional deletion of PR4 from a tail missing PR1 and PR2, deletion of PR2 and PR4, and deletion of PR4 alone from rat CD2 abrogated an ability to activate ITK. Thus, these results identify PR4 as an element of the CD2 tail that is required for activation of ITK. Furthermore, we show that, unlike wild-type rat CD2, PR4-deleted rat CD2 is unable to induce IL-2 secretion from Jurkat cells. This is consistent with the view that PR4-mediated activation of ITK is important for downstream signaling events induced by CD2 co-stimulation.
View details for Web of Science ID 000074974300017
View details for PubMedID 9701039
Analysis of CD28 cytoplasmic tail tyrosine residues as regulators and substrates for the protein tyrosine kinases, EMT and LCK
JOURNAL OF IMMUNOLOGY
1997; 158 (2): 580-590
The CD28 cell surface receptor provides an important costimulatory signal for T cells necessary for their response to Ag. Early events in CD28 signaling include recruitment and activation of phosphatidylinositol 3-kinase (PI3-kinase) and activation of the protein tyrosine kinases (PTKs), LCK and EMT. Recruitment and activation of PI3-kinase is known to be dependent upon phosphorylation of tyrosine 173 of the CD28 cytoplasmic tail contained within a YMNM motif. By contrast, little is known of which residues of the CD28 tail, including tyrosines, are required for the activation of PTKs. To address this we studied the ability of truncation mutants and tyrosine to phenylalanine substitution mutants of the CD28 cytoplasmic tail to activate LCK and EMT in Jurkat T leukemia cells. Our results indicate that 1) activation of EMT is partially dependent upon tyrosine 173 of the CD28 tail, although it does not require PI3-kinase activation; 2) activation of LCK is independent of CD28 cytoplasmic tail tyrosine residues; and 3) elements sufficient for the activation of both kinases are contained within the first half of the tail. In addition we studied the CD28 tail as a substrate for both PTKs in in vitro kinase assays. We demonstrate that EMT can phosphorylate all four tyrosines of the CD28 tail, in contrast to LCK, which phosphorylates only tyrosine 173. Together with evidence that in vivo, tyrosines other than tyrosine 173 become phosphorylated following CD28 stimulation, this finding suggests that, like LCK, one function of EMT during CD28 signaling is phosphorylation of the receptor.
View details for Web of Science ID A1997WC63800007
View details for PubMedID 8992971
The Tec family tyrosine kinases BTK and ITK in lymphocyte development and activation
MUNKSGAARD. 1997: 284-298
View details for Web of Science ID A1997BJ08M00021
Phosphorylation of each of the distal three tyrosines of the CD28 cytoplasmic tail is required for CD28-induced T cell IL-2 secretion.
1996; 48 (4): 255-264
Signaling by the CD28 T cell costimulatory receptor is known to involve recruitment and activation of phosphatidylinositol 3-kinase (PI3-kinase) which is dependent upon phosphorylation of tyrosine 173 of the CD28 cytoplasmic tail, present in a YMNM motif. However, whether this phosphorylation is required for CD28 costimulation and whether or not phosphorylation of any of the other three tyrosines of the CD28 cytoplasmic tail (tyrosines 188, 191 and 200) is also important for CD28 induced responses is unclear. To address this we examined the ability of chimeric receptors, consisting of the extracellular plus transmembrane membrane domain of human CD8 alpha linked to different mutated human CD28 cytoplasmic tails, to induce IL-2 secretion in Jurkat T leukemia cells in the presence of PMA and ionomycin. A receptor in which tyrosine 173 of the CD28 tail was mutated to phenylalanine was able to induce IL-2. By contrast, receptors which contained single tyrosine 188, 191 or 200 to phenylalanine substitutions were unable to induce IL-2. These results imply that in this system phosphorylation of tyrosine 173 and hence activation of PI3-kinase is not required for CD28 induced IL-2 secretion. Further, they imply that phosphorylation of each of tyrosines 188, 191 and 200 is necessary for this response. Despite an apparent requirement for phosphorylation of all three of these tyrosines, however, receptors which contain tyrosine only at positions 191 or 200 and a truncated receptor which does not contain tyrosine 200 induce normal IL-2. These last findings, therefore, illustrate the complexity of CD28 mediated activation signals.
View details for PubMedID 8946678
CD28-mediated cytotoxicity by the human leukemic NK cell line YT involves tyrosine phosphorylation, activation of phosphatidylinositol 3-kinase, and protein kinase C
JOURNAL OF IMMUNOLOGY
1996; 156 (9): 3222-3232
The human leukemic cell line YT displays spontaneous cytotoxicity against CD80+ and/or CD86+ and ICAM-1+ target cells. In this work, we report that CD28-mediated cytotoxicity of YT involves tyrosine phosphorylation and activation of phosphatidylinositol (PI) 3-kinase, the Tec kinase Itk/Emt, and protein kinase C (PKC). YT mediates lysis of CD80+/CD86+ B lymphoblastoid cell lines and the murine mastocytoma p815 transfected with CD80 or CD86. The lysis was inhibited by two different Pi 3-kinase inhibitors, wortmannin and LY294002. The PKC inhibitors calphostin C and bisindolylmaleimide GF109203X also abolished YT-mediated cytotoxicity. Furthermore, exocytosis of cytolytic effector molecules was also inhibited by PI 3-kinase inhibitors and PKC inhibitors. PMA together with Ionomycin did not induce granule exocytosis or cytotoxicity by YT cells. Treatment of YT cells with PMA for up to 20 h, which depleted PMA-responsive PKC isoforms, had no effect on the CD28-mediated cytotoxicity. This cytotoxicity displayed by PMA-treated YT cells, however, could still be inhibited by Pi 3-kinase inhibitors and PKC inhibitors. Taken together, these results are consistent with a model in which activation of CD28 and LFA-1 induces tyrosine phosphorylation of the CD28 cytoplasmic domain, recruitment and activation of PI 3-kinase, as well as the Tec kinase Itk/Emt, and the activation of PMA-nonresponsive PKC isoenzymes. Activation of PI 3-kinase and PMA-nonresponsive PKC isoenzymes is shown to be involved directly in cytolytic granule release by YT cells.
View details for Web of Science ID A1996UF74200018
View details for PubMedID 8617944
RESIDUES OUTSIDE OF THE HLA-A2 PEPTIDE-BINDING GROOVE CAN ABROGATE OR ENHANCE RECOGNITION OF INFLUENZA-VIRUS MATRIX PEPTIDE PULSED CELLS BY CYTOTOXIC T-LYMPHOCYTES
1994; 31 (6): 445-457
An examination of the crystal structure of HLA-A2.1 reveals two classes of residues on the class I MHC molecule that could affect CTL recognition: (1) those predicted to interact with the TCR directly; and (2) those that interact with bound peptides. To examine the role of individual TCR contacting residues, as well as residues not predicted to interact with bound peptide or the TCR, a panel of 28 HLA-A2 variants that differ from each other by a single amino acid substitution in either the alpha 1- or alpha 2-domain was utilized. Peptide titration, time course and cold target inhibition analysis of these targets showed that only the substitution of position 62 in the alpha 1-domain had a significant effect on recognition of the MHC-peptide complex by influenza matrix protein M1 (57-68) peptide-specific, HLA-A2.1-restricted CTL. In contrast, substitutions at positions 154, 162 and 163 in the alpha 2-domain abolished recognition by the same CTL. Additionally, substitutions at position 138 in the alpha 2-domain and positions 107 and 127 on the loops connecting the beta-strand in the alpha 2-domain were recognized in a more efficient, heteroclitic fashion. Overall, there was no direct correlation between the level of peptide binding to the variants and the level of T cell recognition of the variants. These results indicate that residues in the alpha 2-domain may be more important than residues in the alpha 1-domain in controlling TCR binding to the class I MHC molecule and suggest that the "footprint" of the TCR may be more extensive than previously predicted and encompass a broad region that extends beyond the alpha 2-helix. These findings also imply that the class I MHC molecule may exist in a "tipped" orientation on the cell surface during T cell recognition.
View details for Web of Science ID A1994NK03000005
View details for PubMedID 8183283
BOTH MAJOR AND MINOR PEPTIDE-BINDING POCKETS IN HLA-A2 INFLUENCE THE PRESENTATION OF INFLUENZA-VIRUS MATRIX PEPTIDE TO CYTOTOXIC T-LYMPHOCYTES
1994; 31 (6): 459-470
Most of the polymorphic residues in class I MHC molecules are concentrated in the alpha 1- and alpha 2-domains with their side chains pointing towards the antigen peptide site. Previous crystal structure analysis revealed six pockets inside the peptide-binding groove and the "extra" electron density in some of the pockets indicated that the pockets are involved in direct peptide binding. In order to investigate the functional role of individual positions from each pocket in antigen presentation, 37 HLA-A2 variants with single amino acid substitution in the peptide-binding groove were generated and used to analyse the specificity of influenza A virus matrix peptide-specific, HLA-A2-restricted CTL. The ability to present peptide by each variant was studied in detail by peptide titration, cold target inhibition, time course and limiting dilution analysis. The direct effect on peptide binding by these substitutions was determined by cell surface class I MHC molecule reconstitution analysis. The results demonstrated that each of the six peptide binding pockets plays a role in T cell recognition. Substitutions introduced into pocket F had less effect on CTL recognition than substitutions introduced in other pockets. With the exception of Tyr substitution for Phe9, single amino acid substitutions in the peptide-binding groove had only minor effects on peptide binding. Therefore, the impact of the substitutions in altering the epitopes recognized by CTL seems to be mediated through an alteration in the conformation of the bound peptide.
View details for Web of Science ID A1994NK03000006
View details for PubMedID 8183284