Chaperone-mediated autophagy prevents cellular transformation by regulating MYC proteasomal degradation

Abstract

Chaperone-mediated autophagy (CMA), a selective form of protein lysosomal degradation, is maximally activated in stress situations to ensure maintenance of cellular homeostasis. CMA activity decreases with age and in several human chronic disorders, but in contrast, in most cancer cells, CMA is upregulated and required for tumor growth. However, the role of CMA in malignant transformation remains unknown. In this study, we demonstrate that CMA inhibition in fibroblasts augments the efficiency of MYC/c-Mycdriven cellular transformation. CMA blockage contributes to the increase of total and nuclear MYC, leading to enhancement of cell proliferation and colony formation. Impaired CMA functionality accentuates tumorigenesis-related metabolic changes observed upon MYC-transformation. Although not a direct CMA substrate, we have found that CMA regulates cellular MYC levels by controlling its proteasomal degradation. CMA promotes MYC ubiquitination and degradation by regulating the degradation of C330027C09Rik/KIAA1524/CIP2A (referred to hereafter as CIP2A), responsible for MYC stabilization. Ubiquitination and proteasomal degradation of MYC requires dephosphorylation at Ser62, and CIP2A inhibits the phosphatase responsible for this dephosphorylation. Failure to degrade CIP2A upon CMA blockage leads to increased levels of phosphorylated MYC (Ser62) and to stabilization of this oncogene. We demonstrate that this phosphorylation is essential for the CMA-mediated effect, since specific mutation of this site (Ser62 to Ala62) is enough to normalize MYC levels in CMA-incompetent cells. Altogether these data demonstrate that CMA mitigates MYC oncogenic activity by promoting its proteasomal degradation and reveal a novel tumor suppressive role for CMA in nontumorigenic cells.

Autophagy in the Immunosuppressive Perivascular Microenvironment of Glioblastoma

“…CMA blockage in cancer cells has anti-cancer activity, decreasing cell proliferation and tumorigenic/metastatic ability [4,5]. However, both reduced and increased CMA activity can be pro-oncogenic depending on the cellular context, as reduced CMA increases DNA damage and decreases proteostasis [94], providing an environment that facilitates malignant transformation [105]. However, once cells have undergone transformation, they up-regulate CMA to protect against oxidative damage [4], degrade negative regulators of cell proliferation [106] and anti-oncogenes [107] and maintain the metabolic switch favorable for cancer-cell growth [108,109].…”

Chaperone-mediated autophagy and endosomal microautophagy: Jointed by a chaperone

“…The presence of a KFERQ-like motif is required to classify a protein as bona fide CMA substrate but, as described in the following sections, it is no longer sufficient because the same motif is also used by hsc70 to target cytosolic proteins to late endosomes via eMI (8). Hence, validation of proteins as CMA substrates requires experimental validation (5,34).The list of experimentally validated CMA substrates continues to grow and includes a broad variety of proteins involved in diverse cellular processes such as glycolytic enzymes (18,30,35,36), lipogenic enzymes (18), lipid droplet structural proteins (32), RNA modifying enzymes (37), proteins involved in calcium biology (38,39), transcription factors and their regulators (40)(41)(42), cell cycle regulators (25), ubiquitin-proteasome components (43), proteins involved in immune function (39 ,44), and in cell survival/cell death decisions (45)(46)(47)(48), as well as a subset of proteins that contribute to the pathogenesis of known neurodegenerative disorders (23,(26)(27)(28)43,(49)(50)(51).…”

EBP50 suppresses the proliferation of MCF-7 human breast cancer cells via promoting Beclin-1/p62-mediated lysosomal degradation of c-Myc

“…Pietri et al reported CIP2A, an inhibitor of autophagy by stimulating mammalian target of rapamycin complex 1 (mTORC1), protects c-Myc against proteasome-mediated degradation, which suggests there is a strong correlation between the activation on autophagy and degradation of c-Myc [21] . Luciana et al found that chaperone-mediated autophagy promotes c-Myc ubiquitination and degradation [22] and our by macroautophagic lysosomal pathway directly. The above studies focused on the proteasome-mediated degradation of c-Myc and did not explored the autophagic lysosomal degra-dation of c-Myc.…”