Phosphorylation‐Regulated Degradation of the Tumor‐Suppressor Form of PED by Chaperone‐Mediated Autophagy in Lung Cancer Cells

Abstract

PED/PEA‐15 is a death effector domain (DED) family member with a variety of effects on cell growth and metabolism. To get further insight into the role of PED in cancer, we aimed to find new PED interactors. Using tandem affinity purification, we identified HSC70 (Heat Shock Cognate Protein of 70 kDa)—which, among other processes, is involved in chaperone‐mediated autophagy (CMA)—as a PED‐interacting protein. We found that PED has two CMA‐like motifs (i.e., KFERQ), one of which is located within a phosphorylation site, and demonstrate that PED is a bona fide CMA substrate and the first example in which phosphorylation modifies the ability of HSC70 to access KFERQ‐like motifs and target the protein for lysosomal degradation. Phosphorylation of PED switches its function from tumor suppression to tumor promotion, and we show that HSC70 preferentially targets the unphosphorylated form of PED to CMA. Therefore, we propose that the up‐regulated CMA activity characteristic of most types of cancer cell enhances oncogenesis by shifting the balance of PED function toward tumor promotion. This mechanism is consistent with the notion of a therapeutic potential for targeting CMA in cancer, as inhibition of this autophagic pathway may help restore a physiological ratio of PED forms. J. Cell. Physiol. 229: 1359–1368, 2014. © 2014 Wiley Periodicals, Inc.

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

“…7 Thus, CMA inhibition in malignant cells lowers cellular proliferation and reduces tumorigenic and metastatic capacity. 7,19 Later reports have confirmed this dependence on CMA for cancer cell growth and attribute it to a diversity of mechanisms including: protection against oxidative damage, 19 removal of negative regulators of cell proliferation 20 and antioncogenes 21 or maintenance of the metabolic switch favorable for cancer cell growth. 22,23 However, the role of CMA on early stages of tumor development such as transformation of normal cells into cancerous cells has not been elucidated.…”

Development of PEA-15 using a potent non-viral vector for therapeutic application in breast cancer

“…We have shown that the double-unphosphorylated form (PEA-15-AA), strongly inhibited tumor growth and Ki-67 expression in an ovarian cancer xenograft model[8; 9]. Several other studies also have shown that unphosphorylated form of PEA-15 acts as a tumor suppressor in cervical cancer and lung cancer cells [26; 27]. Moreover, recent studies indicate that serous ovarian cancer has a genomic pattern very similar to that of triple-negative breast cancer [28] which may indicate that potent form of PEA-15, such as PEA-15-AA, can be selectively targeted for TNBC using breast cancer-specific promoter.…”

Cerebrovascular Atherosclerosis: Cognitive Dysfunction Progress and Autophagic Regression

“…This reaction works the same way on a responsible disassembly of clathrin from coated vesicles, and is needed to fold the unfolded cytosolic proteins upon recognition of exposed hydrophobic regions [28]. Once the substrate is translocated into the lysosomal lumen, LAMP-2A is rapidly dissembled from the complex into monomers, which endows LAMP-2A to bind with other substrates again [27]. LAMP-2A is one of the three splice variants of the lamp2 gene [9], and is a single-span membrane protein.…”

“…When the substrate proteins are recognized by a cytosolic chaperone, it results in targeting substrates to lysosomes [26]. CMA proceeds in sequential multi-steps: (i) recognition of substrate proteins; (ii) binding and unfolding of substrates; (iii) translocation of substrates inside the lysosomes; and (iv) degradation of substrates in the lysosomal lumen through its cellular functions [27].…”