Mani Muralidharan, James Declan J, Martin Thomas F J
University of Wisconsin-Madison.
Res Sq. 2025 Sep 4:rs.3.rs-7349548. doi: 10.21203/rs.3.rs-7349548/v1.
Secretory granules (SGs) in endocrine cells store and release peptide hormones with their turnover tightly controlled to maintain cellular hormone levels. We found that crinophagy, a specialized autophagy process, is the prevalent pathway that degrades older unused SGs in resting cells by SG-lysosome fusion. siRNA screening with a live cell assay for SG-lysosome merge identified SG components Rab27A, Munc13-4 and VAMP2 and lysosomal components PLEKHM1, HOPS subunits, and SNAREs STX7, STX8, and VTI1B required for docking SGs to and fusion with lysosomes. Munc13-4 is a central regulator of crinophagy that associates with many proteins that are functionally essential for the merge of SGs with lysosomes, and regulates the docking and fusion of SGs with lysosomes. SG-lysosome fusion was regulated by local or global calcium through binding and activation of Munc13-4. The findings reveal the critical docking/fusion machinery for mediating SG turnover in mammalian endocrine cells, and indicate how its dysregulation could impair hormonal and metabolic regulation.
内分泌细胞中的分泌颗粒（SGs）储存并释放肽类激素，其更新过程受到严格控制，以维持细胞内激素水平。我们发现，胞噬作用（一种特殊的自噬过程）是静息细胞中通过SG-溶酶体融合降解陈旧无用SGs的主要途径。通过对SG-溶酶体融合进行活细胞检测的siRNA筛选，确定了SG成分Rab27A、Munc13-4和VAMP2以及溶酶体成分PLEKHM1、HOPS亚基和SNAREs STX7、STX8和VTI1B，这些是SG与溶酶体对接和融合所必需的。Munc13-4是胞噬作用的核心调节因子，它与许多对SG与溶酶体融合功能至关重要的蛋白质相关联，并调节SG与溶酶体的对接和融合。SG-溶酶体融合受局部或全局钙通过Munc13-4的结合和激活来调节。这些发现揭示了介导哺乳动物内分泌细胞中SG更新的关键对接/融合机制，并表明其失调可能如何损害激素和代谢调节。
