Chaperone-mediated autophagy prevents apoptosis by degrading BBC3/PUMA

Abstract

Abbreviations: BBC3/PUMA, BCL2 binding component 3; BCL2L11/BIM, BCL2-like 11; CA, constitutively active; CDKN1A/ p21, cyclin-dependent kinase inhibitor 1A (p21, Cip1); CHUK/IKKa, conserved helix-loop-helix ubiquitous kinase; CMA, chaperone-mediated autophagy; CHX, cycloheximide; DOX, doxorubicin; IKBKB/IKKb, inhibitor of kappa light polypeptide gene enhancer in B-cells, kinase b; HSPA8/HSC70, heat shock 70kDa protein 8; LAMP2A, lysosomal-associated membrane protein type 2A; NFKB1/NF-kB, nuclear factor of kappa light polypeptide gene enhancer in B-cells 1; NFKBIA/IkBa, nuclear factor of kappa light polypeptide gene enhancer in B-cells inhibitor, a; PNS, postnuclear supernatant; shRNA, short hairpin RNA; TNF, tumor necrosis factor; TP53/p53, tumor protein 53.Autophagy is a potentially inimical pathway and together with apoptosis, may be activated by similar stress stimuli that can lead to cell death. The molecular cues that dictate the cell fate choice between autophagy and apoptosis remain largely unknown. Here we report that the proapoptotic protein BBC3/PUMA (BCL2 binding component 3) is a bona fide substrate of chaperone-mediated autophagy (CMA). BBC3 associates with HSPA8/HSC70 (heat shock 70kDa protein 8), leading to its lysosome translocation and uptake. Inhibition of CMA results in stabilization of BBC3, which in turn sensitizes tumor cells to undergo apoptosis. We further demonstrate that upon TNF (tumor necrosis factor) treatment, IKBKB/IKKb (inhibitor of kappa light polypeptide gene enhancer in B-cells, kinase b)-mediated BBC3 Ser10 phosphorylation is crucial for BBC3 stabilization via blocking its degradation by CMA. Mechanistically, Ser10 phosphorylation facilitates BBC3 translocation from the cytosol to mitochondria. BBC3 stabilization resulting from either Ser10 phosphorylation or CMA inhibition potentiates TNF-induced apoptotic cell death. Our findings thus reveal that the selective degradation of BBC3 underlies the prosurvival role of CMA and define a previously unappreciated proapoptotic role of IKBKB that acts through phosphorylation-mediated stabilization of BBC3, thereby promoting TNFtriggered apoptosis.

miR‐26b‐5p helps in EpCAM+cancer stem cells maintenance via HSC71/HSPA8 and augments malignant features in HCC

“…Furthermore, the relative expression of HSPA8 mRNA was increased in the cells transfected with anti‐miR‐26b‐5p, but was decreased in HuH7 cells overexpressing miR‐26b‐5p (Figure B). BBC3 is a proapoptotic protein, which is known to be post‐translationally regulated by HSPA8 . While there was no significant difference in the expression of BBC3 at the mRNA level (Figure C), the expression of BBC3 protein was markedly reduced in the HuH7 cells wherein miR‐26b‐5p expression was suppressed (Figure D).…”

“…Silencing of miR‐26b‐5p increased the EpCAM+ cell population as well as the expression of both EpCAM and HSPA8 transcripts. This was further accompanied by increased expression of stemness genes which are direct targets of EpCAM and reduced level of proapoptotic protein BBC3 which is known to be degraded by HSPA8 mediated autophagy …”

CMA down-regulates p53 expression through degradation of HMGB1 protein to inhibit irradiation-triggered apoptosis in hepatocellular carcinoma

“…In consideration of the declining apoptosis induced by radiotherapy, we thought there must exist some factors to reduce the irradiation-induced apoptosis. Studies showing that CMA pathway activation plays a role in regulating cancer cell proliferation or apoptosis gave rise to our attention[21]. To determine whether CMA pathway activation impacts on the irradiation-induced cancer cell apoptosis, we firstly detected the activation of the CMA pathway.…”

Acetylation targets HSD17B4 for degradation via the CMA pathway in response to estrone

“…49,50 It is reported that acetylation, phosphorylation and ubiquitylation are crucial for autophagy induction, regulation and fine-tuning. 33,34,51 We presently indicate that HSD17B4 acetylation at K669 stimulates its degradation via CMA, a selective degradation for proteins, especially those with a long-half-life.…”