Calpain is required for macroautophagy in mammalian cells

Demarchi et al., J. Cell Biol. 175: 595-605 (2006)

Speaker: 張家綸                                                    Time: 13:10~14:00; Mar. 21, 2007

Commentator: 林以行 老師                                 Place: Room 601

Abstract

Calpains constitute a family of calcium-regulated cysteine proteases, mediating regulatory cleavages of specific substrates involved in processes during differentiation, life and death of the cell. Ubiquitously expressed micro- and millicalpain both require the calpain small 1 (CAPNS1) regulatory subunit for function ¹. Previous studies have shown that calpain inhibition sensitizes cells to apoptosis and calpain deficiency strengthens the proapoptotic effect of ceramide. Macroautophagy is a conserved process for turning over of macromolecules and organelles in eukaryotic cells and which plays diverse roles in cell survival and death ². Here the authors address the role of calpain in autophagy and the effect of calpain-related autopahgy on apoptosis. Autophagy is impaired in CAPNS1-defecient mouse embryonic fibroblasts (MEF), and the same phenomena were observed in CAPNS1-depleted human osteosarcoma cell line U2OS, in which CAPNS1 were knockdown by siRNA. Defects in lysosomal activity and long-lived protein degradation were also shown in CAPNS1-defeiceint MEFs. The authors also monitored autophagosome formation after exogenous LC3 constitutively formed discrete bodies in CAPNS1-defient MEFs and GAPNS1-depleted U2OS cells. Exogenous LC3 bodies constitutively presented in CAPNS1-depleted cells werecolocalized with endosome markers and accumulated in early endosome-like vesicles. Finally, the calpain-dependent impairment of autophagy sensitized cells to apoptosis in CAPNS1-deficient and CAPNS1-depleted cells. In conclusion, calpain function is required for autophagy in mammalian cells, and calpain may play a role in the delivery of membranes to the autophagosome.

References

1.      Goll DE, Thompson VF, Li H, Wei W, Cong J. The calpain system. Physiol. Rev. 83: 731-801 (2003).

2.      Levine B, and Yuan J. Autophagy in cell death: an innocent convict? J. Clin. Invest. 115: 2679-2688 (2005).