Section of Microbial Pathogenesis, Yale University School of Medicine, New Haven, CT 06536, USA.
J Cell Biol. 2010 Jun 14;189(6):1027-38. doi: 10.1083/jcb.201003053. Epub 2010 Jun 7.
Rapid plasma membrane resealing is essential for cellular survival. Earlier studies showed that plasma membrane repair requires Ca(2+)-dependent exocytosis of lysosomes and a rapid form of endocytosis that removes membrane lesions. However, the functional relationship between lysosomal exocytosis and the rapid endocytosis that follows membrane injury is unknown. In this study, we show that the lysosomal enzyme acid sphingomyelinase (ASM) is released extracellularly when cells are wounded in the presence of Ca(2+). ASM-deficient cells, including human cells from Niemann-Pick type A (NPA) patients, undergo lysosomal exocytosis after wounding but are defective in injury-dependent endocytosis and plasma membrane repair. Exogenously added recombinant human ASM restores endocytosis and resealing in ASM-depleted cells, suggesting that conversion of plasma membrane sphingomyelin to ceramide by this lysosomal enzyme promotes lesion internalization. These findings reveal a molecular mechanism for restoration of plasma membrane integrity through exocytosis of lysosomes and identify defective plasma membrane repair as a possible component of the severe pathology observed in NPA patients.
快速的质膜修复对于细胞存活至关重要。早期的研究表明，质膜修复需要依赖 Ca(2+)的溶酶体胞吐作用和一种快速的内吞作用来去除膜损伤。然而，溶酶体胞吐作用和随后发生的膜损伤后的快速内吞作用之间的功能关系尚不清楚。在这项研究中，我们发现当细胞在 Ca(2+)存在的情况下受到损伤时，溶酶体酶酸性鞘磷脂酶 (ASM)会被释放到细胞外。溶酶体胞吐作用发生在缺乏 ASM 的细胞（包括来自尼曼-匹克 A 型（NPA）患者的人类细胞）中，但这些细胞在损伤依赖性的内吞作用和质膜修复方面存在缺陷。外源性添加重组人 ASM 可恢复 ASM 耗竭细胞的内吞作用和再封闭，表明这种溶酶体酶将质膜鞘磷脂转化为神经酰胺可促进损伤内化。这些发现揭示了通过溶酶体胞吐作用恢复质膜完整性的分子机制，并确定了缺陷的质膜修复可能是 NPA 患者严重病理表现的一个组成部分。
