Lysosomal membrane permeabilization during apoptosis ‐ involvement of Bax?

Abstract

Bcl-2 family members have long been known to control permeabilization of the mitochondrial membrane during apoptosis, but involvement of these proteins in lysosomal membrane permeabilization (LMP) was not considered until recently. The aim of this study was to investigate the mechanism underlying the release of lysosomal proteases to the cytosol seen during apoptosis, with special emphasis on the role of Bax. In human fibroblasts, exposed to the apoptosis-inducing drug staurosporine (STS), the release of the lysosomal protease cathepsin D to the cytosol was observed by immunocytochemistry. In response to STS treatment, there was a shift in Bax immunostaining from a diffuse to a punctate pattern. Confocal microscopy showed co-localization of Bax with both lysosomes and mitochondria in dying cells. Presence of Bax at the lysosomal membrane was confirmed by immuno-electron microscopy. Furthermore, when recombinant Bax was incubated with pure lysosomal fractions, Bax inserted into the lysosomal membrane and induced the release of lysosomal enzymes. Thus, we suggest that Bax is a mediator of LMP, possibly promoting the release of lysosomal enzymes to the cytosol during apoptosis.

Insights on a new path of pre-mitochondrial apoptosis regulation by a glycosaminoglycan mimetic

“…Importantly, in skin fibroblasts submitted to oxidative stress, only cathepsin D could mediate apoptosis through the activation of Bax and this by an unknown mechanism. 19,28,30 This resulted in the collapse of mitochondrial membrane potential independently of cathepsin B activity and Bid cleavage. 2,19 Even if there are many controversies on the involvement of cathepsin D and pro-cathepsin D in Bax activation, 31,32 our results show that treatment with Pepstatin A, a specific inhibitor of cathepsin D, protects cells from oxidative stress injuries to the same extent as the GAG-mimetic.…”

Lysosomal membrane permeabilization in cell death

“…In the outer mitochondrial membrane, proapoptotic proteins Bax and Bak may form transient pores that allow for the translocation of a number of molecules larger than 100 kDa without provoking a rupture of the membrane (Kuwana et al, 2005). According to some reports, Bax is also capable of inducing LMP by acting directly on the lysosomal membrane (Kagedal et al, 2005;Feldstein et al, 2006). Nonetheless, the implication of proteins from the Bcl-2 family in LMP has not been studied extensively thus far.…”

“…Recently, the proapoptotic Bcl-2 family member Bax has been shown to exert a direct effect on lysosomes. Thus, Bax can translocate from the cytosol to lysosomal membranes and induce LMP (Kagedal et al, 2005). Fibroblasts cultured in the presence of the proapoptotic pan-tyrosine kinase inhibitor staurosporine exhibit a conformational change in Bax and its translocation to lysosomes, resulting in LMP and CD translocation to the cytosol (Kagedal et al, 2005).…”

“…Thus, Bax can translocate from the cytosol to lysosomal membranes and induce LMP (Kagedal et al, 2005). Fibroblasts cultured in the presence of the proapoptotic pan-tyrosine kinase inhibitor staurosporine exhibit a conformational change in Bax and its translocation to lysosomes, resulting in LMP and CD translocation to the cytosol (Kagedal et al, 2005). The requirement of Bax for LMP has been demonstrated by comparing Bax þ / þ and Bax À/À hepatocytes exposed to long-chain fatty acids (Feldstein et al, 2006).…”

Cathepsin D—Many functions of one aspartic protease

“…In many instances, lysosomal permeabilization appears to be an early event in the apoptotic cascade, preceding other hallmarks of apoptosis like destabilizatin of mitochondria, cytochrom c release and caspase activation. Several mechanisms of lysosomal membrane permeabilization were proposed including the involvement of reactive oxygen species [109][110][111], members of Bcl-2 family [112], and intracellular sphingosine, a biologically active metabolite of ceramide [69,113].…”