Bio


I thrive to understand the roles of lysosomes in physiological and pathological conditions. Lysosomes are both degradation compartment and metabolic controlling hub, and dysregulation of lysosomal functions are frequently implicated in a vast number of diseases including neurodegenerative diseases, however, the systematic knowledge of the molecular mechanism by which lysosomal contributes to these diseases is lacking. Ion channels are the primary mediators of neuronal activity, defects in neuronal ion channel activity are linked with many kinds of neurodegenerative diseases. Interestingly, besides typical ion channels that are involved in the neuronal activity, defects in lysosomal ion channels, such as TRPML1, CLN7 and CLC-7 are also implicated in neuropathy. My previous work as Ph.D student in University of Texas MD Anderson Cancer Center focused on regulation of lysosomal function by ion channels and metabolites. I discovered a mechanism of lysosomal Na+ channel regulate mTORC1 activation by regulating lysosomal amino acid accumulation. I also discovered role of glutamine in controlling lysosomal degradation capacity. In the meantime, I developed novel methods to isolate organelles. My ultimate research goal is to understand the key developmental pathways and how alterations in gene sequences and expression contribute to human disease, therefore, I am pursuing independent academic researcher as my career goal. Starting Feb 2022, I work with Dr. Monther Abu-Remaileh at Stanford University on role of lysosomes in neurodegenerative diseases. I use genetics, chemical biology and omics approaches to study lysosome function under various physiological and pathological conditions, especially age-associated neurodegenerative disorders, and monogenic neurodegenerative lysosome storage diseases. In Stanford, I aim to integrate ionic regulation, metabolomic regulation and functional proteomic regulation to systematically understand the biology of lysosome in physiological conditions and pathological conditions.

Professional Education


  • B.S., Wuhan University, Biological Science and Biotechnology (2010)
  • M.S, University of Texas MD Anderson Cancer Center, Cell and Regulatory Biology (2014)
  • Ph.D, University of Texas MD Anderson Cancer Center, Biochemistry and Cell Biology (2020)

Stanford Advisors


All Publications


  • The Three Two-Pore Channel Subtypes from Rabbit Exhibit Distinct Sensitivity to Phosphoinositides, Voltage, and Extracytosolic pH. Cells Feng, X., Xiong, J., Cai, W., Tian, J. B., Zhu, M. X. 2022; 11 (13)

    Abstract

    Two pore channels (TPCs) are implicated in vesicle trafficking, virus infection, and autophagy regulation. As Na+- or Ca2+-permeable channels, TPCs have been reported to be activated by NAADP, PI(3,5)P2, and/or high voltage. However, a comparative study on the function and regulation of the three mammalian TPC subtypes is currently lacking. Here, we used the electrophysiological recording of enlarged endolysosome vacuoles, inside-out and outside-out membrane patches to examine the three TPCs of rabbit (Oryctolagus cuniculus, or Oc) heterologously expressed in HEK293 cells. While PI(3,5)P2 evoked Na+ currents with a potency order of OcTPC1 > OcTPC3 > OcTPC2, only OcTPC2 displayed a strict dependence on PI(3,5)P2. Both OcTPC1 and OcTPC3 were activatable by PI3P and OcTPC3 was also activated by additional phosphoinositide species. While OcTPC2 was voltage-independent, OcTPC1 and OcTPC3 showed voltage dependence with OcTPC3 depending on high positive voltages. Finally, while OcTPC2 preferred a luminal pH of 4.6-6.0 in endolysosomes, OcTPC1 was strongly inhibited by extracytosolic pH 5.0 in both voltage-dependent and -independent manners, and OcTPC3 was inhibited by pH 6.0 but potentiated by pH 8.0. Thus, the three OcTPCs form phosphoinositide-activated Na+ channels with different ligand selectivity, voltage dependence, and extracytosolic pH sensitivity, which likely are optimally tuned for function in specific endolysosomal populations.

    View details for DOI 10.3390/cells11132006

    View details for PubMedID 35805090

    View details for PubMedCentralID PMC9265530

  • Ameliorating cancer cachexia by inhibiting cancer cell release of Hsp70 and Hsp90 with omeprazole. Journal of cachexia, sarcopenia and muscle Liu, Z., Xiong, J., Gao, S., Zhu, M. X., Sun, K., Li, M., Zhang, G., Li, Y. P. 2022; 13 (1): 636-647

    Abstract

    Cancer cachexia, characterized by muscle and fat tissue wasting, is a major determinant of cancer-related mortality without established treatment. Recent animal data revealed that cancer cells induce muscle wasting by releasing Hsp70 and Hsp90 as surface proteins on extracellular vesicles (EVs). Here, we test a therapeutic strategy for ameliorating cancer cachexia by inhibiting the release of Hsp70 and Hsp90 using proton pump inhibitor omeprazole.Omeprazole effect on Hsp70/90 release through EVs by Lewis lung carcinoma (LLC) cells in vitro, serum levels of Hsp70/90 and Hsp70/90-carrying EVs in LLC tumour-bearing mice, and LLC-induced muscle protein degradation pathways in C2C12 myotubes and mice were determined. Omeprazole effect on endolysosomal pH and Rab27b expression in LLC cells were analysed.Omeprazole treatment of LLC cells inhibited Hsp70/90 and Hsp70/90-carrying EV release in a dose-dependent manner (1 to 10 μM) and attenuated the catabolic activity of LLC cell-conditioned medium on C2C12 myotubes. Systemic omeprazole administration to LLC tumour-bearing mice (5 mg/kg/day subcutaneously) for 2 weeks blocked elevation of serum Hsp70, Hsp90, and Hsp70/90-carrying EVs, abrogated skeletal muscle catabolism, and prevented loss of muscle function as well as muscle and epididymal fat mass without altering tumour growth. Consequently, median survival increased by 23.3%. Mechanistically, omeprazole increased cancer cell endolysosomal pH level dose-dependently (0.1 to 1 μM) by inhibiting vacuolar H+ -ATPase. Further, omeprazole suppressed the highly elevated expression of Rab27b, a key regulator of EV release, in LLC cells.Omeprazole ameliorates cancer cachexia by inhibiting cancer cell release of Hsp70 and Hsp90.

    View details for DOI 10.1002/jcsm.12851

    View details for PubMedID 34729960

    View details for PubMedCentralID PMC8818607

  • Rapid affinity purification of intracellular organelles using a twin strep tag. Journal of cell science Xiong, J., He, J., Xie, W. P., Hinojosa, E., Ambati, C. S., Putluri, N., Kim, H. E., Zhu, M. X., Du, G. 2019; 132 (24)

    Abstract

    Cells are internally organized into compartmentalized organelles that execute specialized functions. To understand the functions of individual organelles and their regulations, it is critical to resolve the compositions of individual organelles, which relies on a rapid and efficient isolation method for specific organellar populations. Here, we introduce a robust affinity purification method for rapid isolation of intracellular organelles (e.g. lysosomes, mitochondria and peroxisomes) by taking advantage of the extraordinarily high affinity between the twin strep tag and streptavidin variants. With this method, we can isolate desired organelles with high purity and yield in 3 min from the post-nuclear supernatant of mammalian cells or less than 8 min for the whole purification process. Using lysosomes as an example, we show that the rapid procedure is especially useful for studying transient and fast cellular activities, such as organelle-initiated signaling and organellar contents of small-molecular metabolites. Therefore, our method offers a powerful tool to dissect spatiotemporal regulation and functions of intracellular organelles.

    View details for DOI 10.1242/jcs.235390

    View details for PubMedID 31780580

    View details for PubMedCentralID PMC6955222

  • Regulation of lysosomal ion homeostasis by channels and transporters. Science China. Life sciences Xiong, J., Zhu, M. X. 2016; 59 (8): 777-91

    Abstract

    Lysosomes are the major organelles that carry out degradation functions. They integrate and digest materials compartmentalized by endocytosis, phagocytosis or autophagy. In addition to more than 60 hydrolases residing in the lysosomes, there are also ion channels and transporters that mediate the flux or transport of H(+), Ca(2+), Na(+), K(+), and Cl(-) across the lysosomal membranes. Defects in ionic exchange can lead to abnormal lysosome morphology, defective vesicle trafficking, impaired autophagy, and diseases such as neurodegeneration and lysosomal storage disorders. The latter are characterized by incomplete lysosomal digestion and accumulation of toxic materials inside enlarged intracellular vacuoles. In addition to degradation, recent studies have revealed the roles of lysosomes in metabolic pathways through kinases such as mechanistic target of rapamycin (mTOR) and transcriptional regulation through calcium signaling molecules such as transcription factor EB (TFEB) and calcineurin. Owing to the development of new approaches including genetically encoded fluorescence probes and whole endolysosomal patch clamp recording techniques, studies on lysosomal ion channels have made remarkable progress in recent years. In this review, we will focus on the current knowledge of lysosome-resident ion channels and transporters, discuss their roles in maintaining lysosomal function, and evaluate how their dysfunction can result in disease.

    View details for DOI 10.1007/s11427-016-5090-x

    View details for PubMedID 27430889

    View details for PubMedCentralID PMC5147046

  • Pharmacological Validation of ASIC1a as a Druggable Target for Neuroprotection in Cerebral Ischemia Using an Intravenously Available Small Molecule Inhibitor. Frontiers in pharmacology Qi, X., Lu, J. F., Huang, Z. Y., Liu, Y. J., Cai, L. B., Wen, X. L., Song, X. L., Xiong, J., Sun, P. Y., Zhang, H., Zhang, T. T., Zhao, X., Jiang, Q., Li, Y., Krishtal, O., Hou, L. C., Zhu, M. X., Xu, T. L. 2022; 13: 849498

    Abstract

    Acidosis is a hallmark of ischemic stroke and a promising neuroprotective target for preventing neuronal injury. Previously, genetic manipulations showed that blockade of acid-sensing ion channel 1a (ASIC1a)-mediated acidotoxicity could dramatically alleviate the volume of brain infarct and restore neurological function after cerebral ischemia. However, few pharmacological candidates have been identified to exhibit efficacy on ischemic stroke through inhibition of ASIC1a. In this work, we examined the ability of a toxin-inspired compound 5b (C5b), previously found to effectively inhibit ASIC1a in vitro, to exert protective effects in animal models of ischemic stroke in vivo. We found that C5b exerts significant neuroprotective effects not only in acid-induced neuronal death in vitro but also ischemic brain injury in vivo, suggesting that ASIC1a is a druggable target for therapeutic development. More importantly, C5b is able to cross the blood brain barrier and significantly reduce brain infarct volume when administered intravenously in the ischemic animal model, highlighting its systemic availability for therapies against neurodegeneration due to acidotoxicity. Together, our data demonstrate that C5b is a promising lead compound for neuroprotection through inhibiting ASIC1a, which warrants further translational studies.

    View details for DOI 10.3389/fphar.2022.849498

    View details for PubMedID 35401212

    View details for PubMedCentralID PMC8988055

  • CAMK2/CaMKII activates MLKL in short-term starvation to facilitate autophagic flux AUTOPHAGY Zhan, Q., Jeon, J., Li, Y., Huang, Y., Xiong, J., Wang, Q., Xu, T., Li, Y., Ji, F., Du, G., Zhu, M. X. 2022; 18 (4): 726-744

    Abstract

    MLKL (mixed lineage kinase domain like pseudokinase) is a well-known core component of necrosome that executes necroptotic cell death upon phosphorylation by RIPK3 (receptor interacting serine/threonine kinase 3). Recent studies also implicate a role of MLKL in endosomal trafficking, which is not always dependent on RIPK3. Using mouse Neuro-2a and L929 as well as human HEK293 and HT29 cells, we show here that MLKL is phosphorylated in response to serum and amino acid deprivation from the culture medium, in a manner that depends on CAMK2/CaMKII (calcium/calmodulin dependent protein kinase II) but not RIPK3. The starvation-induced increase in MLKL phosphorylation was accompanied by decreases in levels of lipidated MAP1LC3B/LC3B (microtubule associated protein 1 light chain 3 beta; LC3-II) and SQSTM1/p62 (sequestosome 1), markers of autophagosomes. These changes were prevented by disrupting either MLKL or CAMK2 by pharmacology and genetic manipulations. Moreover, disrupting MLKL or CAMK2 also inhibited the incorporation of LC3-II into autolysosomes, demonstrating a role of the CAMK2-MLKL pathway in facilitating autophagic flux during short-term starvation, in contrast to necroptosis which suppressed autophagic flux. Furthermore, unlike the necroptotic pathway, the starvation-evoked CAMK2-mediated MLKL phosphorylation protected cells from starvation-induced death. We propose that upon nutrient deprivation, MLKL is activated by CAMK2, which in turn facilitates membrane scission needed for autophagosome maturation, allowing the proper fusion of the autophagosome with lysosome and the subsequent substance degradation. This novel function is independent of RIPK3 and is not involved in necroptosis, implicating new roles for this pseudokinase in cell survival, signaling and metabolism.Abbreviations: CAMK2/CaMKII: calcium/calmodulin dependent protein kinase II; DIABLO/SMAC: direct inhibitor of apoptosis-binding protein with low pI/second mitochondria-derived activator of caspase; ECS: extracellular solution; ESCRT: endosomal sorting complexes required for transport; FBS: fetal bovine serum; GSK3B: glycogen synthase kinase 3 beta; HBSS: Hanks' balanced salt solution; KO: knockout; LC3-II: lipidated microtubule associated protein 1 light chain 3 beta; LDH: lactate dehydrogenase; MLKL: mixed lineage kinase domain like pseudokinase; MTOR: mechanistic target of rapamycin kinase; MTORC1: MTOR complex 1; N2a: Neuro-2a neuroblastoma; Nec-1: necrostatin-1; NSA: necrosulfonamide; PBS: phosphate-buffered saline; PI: propidium iodide; PK-hLC3: pHluorin-mKate2-human LC3; RIPK1: receptor interacting serine/threonine kinase 1; RIPK3: receptor interacting serine/threonine kinase 3; ROS: reactive oxygen species; RPS6KB1/S6K: ribosomal protein S6 kinase B1; shRNA: short hairpin RNA; siRNA: small interference RNA; SQSTM1/p62: sequestosome 1; TBS: Tris-buffered saline; TNF/TNF-α: tumor necrosis factor; TSZ, treatment with TNF + DIABLO mimetics + z-VAD-FMK.

    View details for DOI 10.1080/15548627.2021.1954348

    View details for Web of Science ID 000675113300001

    View details for PubMedID 34282994

    View details for PubMedCentralID PMC9037428

  • mTORC1 controls lysosomal Ca2+ release through the two-pore channel TPC2. Science signaling Ogunbayo, O. A., Duan, J., Xiong, J., Wang, Q., Feng, X., Ma, J., Zhu, M. X., Evans, A. M. 2018; 11 (525)

    Abstract

    Two-pore segment channel 2 (TPC2) is a ubiquitously expressed, lysosomally targeted ion channel that aids in terminating autophagy and is inhibited upon its association with mechanistic target of rapamycin (mTOR). It is controversial whether TPC2 mediates lysosomal Ca2+ release or selectively conducts Na+ and whether the binding of nicotinic acid adenine dinucleotide phosphate (NAADP) or phosphatidylinositol 3,5-bisphosphate [PI(3,5)P2] is required for the activity of this ion channel. We show that TPC2 is required for intracellular Ca2+ signaling in response to NAADP or to mTOR inhibition by rapamycin. In pulmonary arterial myocytes, rapamycin and NAADP evoked global Ca2+ transients that were blocked by depletion of lysosomal Ca2+ stores. Preincubation of cells with high concentrations of rapamycin resulted in desensitization and blocked NAADP-evoked Ca2+ signals. Moreover, rapamycin and NAADP did not evoke discernable Ca2+ transients in myocytes derived from Tpcn2 knockout mice, which showed normal responses to other Ca2+-mobilizing signals. In HEK293 cells stably overexpressing human TPC2, shRNA-mediated knockdown of mTOR blocked rapamycin- and NAADP-evoked Ca2+ signals. Confocal imaging of a genetically encoded Ca2+ indicator fused to TPC2 demonstrated that rapamycin-evoked Ca2+ signals localized to lysosomes and were in close proximity to TPC2. Therefore, inactivation of mTOR may activate TPC2 and consequently lysosomal Ca2+ release.

    View details for DOI 10.1126/scisignal.aao5775

    View details for PubMedID 29636391

    View details for PubMedCentralID PMC6055479

  • Loss of Smooth Muscle α-Actin Leads to NF-κB-Dependent Increased Sensitivity to Angiotensin II in Smooth Muscle Cells and Aortic Enlargement. Circulation research Chen, J., Peters, A., Papke, C. L., Villamizar, C., Ringuette, L. J., Cao, J., Wang, S., Ma, S., Gong, L., Byanova, K. L., Xiong, J., Zhu, M. X., Madonna, R., Kee, P., Geng, Y. J., Brasier, A. R., Davis, E. C., Prakash, S., Kwartler, C. S., Milewicz, D. M. 2017; 120 (12): 1903-1915

    Abstract

    Mutations in ACTA2, encoding the smooth muscle isoform of α-actin, cause thoracic aortic aneurysms, acute aortic dissections, and occlusive vascular diseases.We sought to identify the mechanism by which loss of smooth muscle α-actin causes aortic disease.Acta2-/- mice have an increased number of elastic lamellae in the ascending aorta and progressive aortic root dilation as assessed by echocardiography that can be attenuated by treatment with losartan, an angiotensin II (AngII) type 1 receptor blocker. AngII levels are not increased in Acta2-/- aortas or kidneys. Aortic tissue and explanted smooth muscle cells from Acta2-/- aortas show increased production of reactive oxygen species and increased basal nuclear factor κB signaling, leading to an increase in the expression of the AngII receptor type I a and activation of signaling at 100-fold lower levels of AngII in the mutant compared with wild-type cells. Furthermore, disruption of smooth muscle α-actin filaments in wild-type smooth muscle cells by various mechanisms activates nuclear factor κB signaling and increases expression of AngII receptor type I a.These findings reveal that disruption of smooth muscle α-actin filaments in smooth muscle cells increases reactive oxygen species levels, activates nuclear factor κB signaling, and increases AngII receptor type I a expression, thus potentiating AngII signaling in vascular smooth muscle cells without an increase in the exogenous levels of AngII.

    View details for DOI 10.1161/CIRCRESAHA.117.310563

    View details for PubMedID 28461455

    View details for PubMedCentralID PMC5518614

  • Critical roles of Gi/o proteins and phospholipase C-δ1 in the activation of receptor-operated TRPC4 channels. Proceedings of the National Academy of Sciences of the United States of America Thakur, D. P., Tian, J. B., Jeon, J., Xiong, J., Huang, Y., Flockerzi, V., Zhu, M. X. 2016; 113 (4): 1092-7

    Abstract

    Transient Receptor Potential Canonical (TRPC) proteins form nonselective cation channels commonly known to be activated downstream from receptors that signal through phospholipase C (PLC). Although TRPC3/C6/C7 can be directly activated by diacylglycerols produced by PLC breakdown of phosphatidylinositol 4,5-bisphosphate (PIP2), the mechanism by which the PLC pathway activates TRPC4/C5 remains unclear. We show here that TRPC4 activation requires coincident stimulation of Gi/o subgroup of G proteins and PLCδ, with a preference for PLCδ1 over PLCδ3, but not necessarily the PLCβ pathway commonly thought to be involved in receptor-operated TRPC activation. In HEK293 cells coexpressing TRPC4 and Gi/o-coupled µ opioid receptor, µ agonist elicited currents biphasically, with an initial slow phase preceding a rapidly developing phase. The currents were dependent on intracellular Ca(2+) and PIP2. Reducing PIP2 through phosphatases abolished the biphasic kinetics and increased the probability of channel activation by weak Gi/o stimulation. In both HEK293 cells heterologously expressing TRPC4 and renal carcinoma-derived A-498 cells endogenously expressing TRPC4, channel activation was inhibited by knocking down PLCδ1 levels and almost completely eliminated by a dominant-negative PLCδ1 mutant and a constitutively active RhoA mutant. Conversely, the slow phase of Gi/o-mediated TRPC4 activation was diminished by inhibiting RhoA or enhancing PLCδ function. Our data reveal an integrative mechanism of TRPC4 on detection of coincident Gi/o, Ca(2+), and PLC signaling, which is further modulated by the small GTPase RhoA. This mechanism is not shared with the closely related TRPC5, implicating unique roles of TRPC4 in signal integration in brain and other systems.

    View details for DOI 10.1073/pnas.1522294113

    View details for PubMedID 26755577

    View details for PubMedCentralID PMC4743816

  • Differential mechanisms of action of the mucolipin synthetic agonist, ML-SA1, on insect TRPML and mammalian TRPML1. Cell calcium Feng, X., Xiong, J., Lu, Y., Xia, X., Zhu, M. X. 2014; 56 (6): 446-56

    Abstract

    Mucolipin synthetic agonist 1 (ML-SA1) was recently identified to activate mammalian TRPML channels and shown to alleviate lipid accumulation in lysosomes of cellular models of lysosome storage diseases, mucolipidosis type IV (MLIV) and Niemann-Pick's disease type C (NPC). Owning to its potential use in complimenting genetic studies in Drosophila melanogaster to elucidate the cellular and physiological functions of TRPML channels, we examined the effect of ML-SA1 on Drosophila TRPML expressed in HEK293 cells using whole-cell, inside-out, and whole-lysosome electrophysiological recordings. We previously showed that when expressed in HEK293 cells, Drosophila TRPML was localized and functional on both plasma membrane and endolysosome. We show here that in both inside-out patches excised from the plasma membrane and whole-lysosome recordings from enlarged endolysosome vacuoles, ML-SA1 failed to activate TRPML unless exogenous phosphatidylinositol 3,5-bisphosphate [PI(3,5)P2] was applied. At 1 μM ML-SA1, the sensitivity of TRPML to PI(3,5)P2 increased approximately by 10-fold and at 10 μM ML-SA1, the deactivation of PI(3,5)P2-evoked TRPML currents was markedly slowed. On the other hand, constitutive activation of TRPML by a mutation that mimics the varitint-waddler (Va) mutation of mouse TRPML3 rendered the insect channel sensitive to activation by ML-SA1 alone. Moreover, different from the insect TRPML, mouse TRPML1 was readily activated by ML-SA1 independent of PI(3,5)P2. Thus, our data reveal that while ML-SA1 acts as a true agonist at mouse TRPML1, it behaves as an allosteric activator of the Drosophila TRPML, showing dependence on and the ability to stabilize open conformation of the insect channels.

    View details for DOI 10.1016/j.ceca.2014.09.004

    View details for PubMedID 25266962

    View details for PubMedCentralID PMC4252876

  • Bimodal voltage dependence of TRPA1: mutations of a key pore helix residue reveal strong intrinsic voltage-dependent inactivation. Pflugers Archiv : European journal of physiology Wan, X., Lu, Y., Chen, X., Xiong, J., Zhou, Y., Li, P., Xia, B., Li, M., Zhu, M. X., Gao, Z. 2014; 466 (7): 1273-87

    Abstract

    Transient receptor potential A1 (TRPA1) is implicated in somatosensory processing and pathological pain sensation. Although not strictly voltage-gated, ionic currents of TRPA1 typically rectify outwardly, indicating channel activation at depolarized membrane potentials. However, some reports also showed TRPA1 inactivation at high positive potentials, implicating voltage-dependent inactivation. Here we report a conserved leucine residue, L906, in the putative pore helix, which strongly impacts the voltage dependency of TRPA1. Mutation of the leucine to cysteine (L906C) converted the channel from outward to inward rectification independent of divalent cations and irrespective to stimulation by allyl isothiocyanate. The mutant, but not the wild-type channel, displayed exclusively voltage-dependent inactivation at positive potentials. The L906C mutation also exhibited reduced sensitivity to inhibition by TRPA1 blockers, HC030031 and ruthenium red. Further mutagenesis of the leucine to all natural amino acids individually revealed that most substitutions at L906 (15/19) resulted in inward rectification, with exceptions of three amino acids that dramatically reduced channel activity and one, methionine, which mimicked the wild-type channel. Our data are plausibly explained by a bimodal gating model involving both voltage-dependent activation and inactivation of TRPA1. We propose that the key pore helix residue, L906, plays an essential role in responding to the voltage-dependent gating.

    View details for DOI 10.1007/s00424-013-1345-6

    View details for PubMedID 24092046

    View details for PubMedCentralID PMC4062818

  • Drosophila TRPML forms PI(3,5)P2-activated cation channels in both endolysosomes and plasma membrane. The Journal of biological chemistry Feng, X., Huang, Y., Lu, Y., Xiong, J., Wong, C. O., Yang, P., Xia, J., Chen, D., Du, G., Venkatachalam, K., Xia, X., Zhu, M. X. 2014; 289 (7): 4262-72

    Abstract

    Transient Receptor Potential mucolipin (TRPML) channels are implicated in endolysosomal trafficking, lysosomal Ca(2+) and Fe(2+) release, lysosomal biogenesis, and autophagy. Mutations in human TRPML1 cause the lysosome storage disease, mucolipidosis type IV (MLIV). Unlike vertebrates, which express three TRPML genes, TRPML1-3, the Drosophila genome encodes a single trpml gene. Although the trpml-deficient flies exhibit cellular defects similar to those in mammalian TRPML1 mutants, the biophysical properties of Drosophila TRPML channel remained uncharacterized. Here, we show that transgenic expression of human TRPML1 in the neurons of Drosophila trpml mutants partially suppressed the pupal lethality phenotype. When expressed in HEK293 cells, Drosophila TRPML was localized in both endolysosomes and plasma membrane and was activated by phosphatidylinositol 3,5-bisphosphate (PI(3,5)P2) applied to the cytoplasmic side in whole lysosomes and inside-out patches excised from plasma membrane. The PI(3,5)P2-evoked currents were blocked by phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2), but not other phosphoinositides. Using TRPML A487P, which mimics the varitint-waddler (Va) mutant of mouse TRPML3 with constitutive whole-cell currents, we show that TRPML is biphasically regulated by extracytosolic pH, with an optimal pH about 0.6 pH unit higher than that of human TRPML1. In addition to monovalent cations, TRPML exhibits high permeability to Ca(2+), Mn(2+), and Fe(2+), but not Fe(3+). The TRPML currents were inhibited by trivalent cations Fe(3+), La(3+), and Gd(3+). These features resemble more closely to mammalian TRPML1 than TRPML2 and TRPML3, but with some obvious differences. Together, our data support the use of Drosophila for assessing functional significance of TRPML1 in cell physiology.

    View details for DOI 10.1074/jbc.M113.506501

    View details for PubMedID 24375408

    View details for PubMedCentralID PMC3924289