Condition-dependent functional shift of two <i>Drosophila</i> Mtmr lipid phosphatases in autophagy control

Myotubularin (MTM) and myotubularin-related (MTMR) lipid phosphatases catalyze the removal of a phosphate group from certain phosphatidylinositol derivatives. Because some of these substrates are required for macroautophagy/autophagy, during which unwanted cytoplasmic constituents are delivered into lysosomes for degradation, MTM and MTMRs function as important regulators of the autophagic process. Despite its physiological and medical significance, the specific role of individual MTMR paralogs in autophagy control remains largely unexplored. Here we examined two <i>Drosophila</i> MTMRs, EDTP and Mtmr6, the fly orthologs of mammalian MTMR14 and MTMR6 to MTMR8, respectively, and found that these enzymes affect the autophagic process in a complex, condition-dependent way. EDTP inhibited basal autophagy, but did not influence stress-induced autophagy. In contrast, Mtmr6 promoted the process under nutrient-rich settings, but effectively blocked its hyperactivation in response to stress. Thus, Mtmr6 is the first identified MTMR phosphatase with dual, antagonistic roles in the regulation of autophagy, and shows conditional antagonism/synergism with EDTP in modulating autophagic breakdown. These results provide a deeper insight into the adjustment of autophagy. <b>Abbreviations</b>: Atg, autophagy-related; BDSC, Bloomington <i>Drosophila</i> Stock Center; DGRC, <i>Drosophila</i> Genetic Resource Center; EDTP, Egg-derived tyrosine phosphatase; FYVE, zinc finger domain from Fab1 (yeast ortholog of PIKfyve), YOTB, Vac1 (vesicle transport protein) and EEA1 cysteine-rich proteins; LTR, LysoTracker Red; MTM, myotubularin; MTMR, myotubularin-related; PI, phosphatidylinositol; Pi3K59F, Phosphotidylinositol 3 kinase 59F; PtdIns3P, phosphatidylinositol-3-phosphate; PtdIns(3,5)P₂, phosphatidylinositol-3,5-bisphosphate; PtdIns5P, phosphatidylinositol-5-phosphate; ref(2)P, refractory to sigma P; Syx17, Syntaxin 17; TEM, transmission electron microscopy; UAS, upstream activating sequence; Uvrag, UV-resistance associated gene; VDRC, Vienna <i>Drosophila</i> RNAi Center; Vps34, Vacuolar protein sorting 34.肌管蛋白（Myotubularin, MTM）及肌管蛋白相关（myotubularin-related, MTMR）脂质磷酸酶可催化特定磷脂酰肌醇衍生物脱去磷酸基团。由于部分此类底物对于巨自噬（macroautophagy/自噬，autophagy）至关重要——巨自噬过程中，异常细胞质组分被运送至溶酶体进行降解——因此MTM与MTMR家族蛋白是自噬过程的重要调控因子。尽管该过程具有重要的生理与医学意义，但单个MTMR旁系同源基因在自噬调控中的具体功能仍未得到充分探索。本研究对两种果蝇（Drosophila）MTMR蛋白——EDTP与Mtmr6——进行了分析，二者分别为哺乳动物MTMR14与MTMR6至MTMR8的果蝇同源基因。研究发现，这两种酶以复杂的条件依赖性方式影响自噬过程：EDTP可抑制基础水平自噬，但不影响应激诱导的自噬。与之相反，Mtmr6在营养充足的条件下可促进自噬过程，但在应激响应时则有效阻断自噬的过度激活。综上，Mtmr6是首个被发现具有双重拮抗性功能的MTMR家族磷酸酶，可在自噬调控中发挥双向作用，且在调节自噬降解过程中与EDTP呈现条件性的拮抗/协同关系。本研究结果为自噬的调控机制提供了更深入的认知。**缩写说明**：Atg，自噬相关（autophagy-related）；BDSC，布卢明顿果蝇种质中心（Bloomington Drosophila Stock Center）；DGRC，果蝇遗传资源中心（Drosophila Genetic Resource Center）；EDTP，卵源性酪氨酸磷酸酶（Egg-derived tyrosine phosphatase）；FYVE，源自Fab1（PIKfyve的酵母同源蛋白）、YOTB、Vac1（囊泡转运蛋白）与EEA1的半胱氨酸富集型锌指结构域；LTR，LysoTracker Red（红色荧光染料LysoTracker Red）；MTM，肌管蛋白（myotubularin）；MTMR，肌管蛋白相关蛋白（myotubularin-related）；PI，磷脂酰肌醇（phosphatidylinositol）；Pi3K59F，磷脂酰肌醇3激酶59F（Phosphotidylinositol 3 kinase 59F）；PtdIns3P，磷脂酰肌醇-3-磷酸（phosphatidylinositol-3-phosphate）；PtdIns(3,5)P₂，磷脂酰肌醇-3,5-二磷酸（phosphatidylinositol-3,5-bisphosphate）；PtdIns5P，磷脂酰肌醇-5-磷酸（phosphatidylinositol-5-phosphate）；ref(2)P，σP抗性蛋白（refractory to sigma P）；Syx17，突触融合蛋白17（Syntaxin 17）；TEM，透射电子显微镜（transmission electron microscopy）；UAS，上游激活序列（upstream activating sequence）；Uvrag，紫外线抗性相关基因（UV-resistance associated gene）；VDRC，维也纳果蝇RNAi中心（Vienna Drosophila RNAi Center）；Vps34，液泡蛋白分选34（Vacuolar protein sorting 34）。