UBXN2A enhances CHIP‐mediated proteasomal degradation of oncoprotein mortalin‐2 in cancer cells

Abstract

Overexpression of oncoproteins is a major cause of treatment failure using current chemotherapeutic drugs. Drug‐induced degradation of oncoproteins is feasible and can improve clinical outcomes in diverse types of cancers. Mortalin‐2 (mot‐2) is a dominant oncoprotein in several tumors, including colorectal cancer (CRC). In addition to inactivating the p53 tumor suppressor protein, mot‐2 enhances tumor cell invasion and migration. Thus, mot‐2 is considered a potential therapeutic target in several cancer types. The current study investigated the biological role of a ubiquitin‐like protein called UBXN2A in the regulation of mot‐2 turnover. An orthogonal ubiquitin transfer technology followed by immunoprecipitation, in vitro ubiquitination, and Magnetic Beads TUBE2 pull‐down experiments revealed that UBXN2A promotes carboxyl terminus of the HSP70‐interacting protein (CHIP)‐dependent ubiquitination of mot‐2. We subsequently showed that UBXN2A increases proteasomal degradation of mot‐2. A subcellular compartmentalization experiment revealed that induced UBXN2A decreases the level of mot‐2 and its chaperone partner, HSP60. Pharmacological upregulation of UBXN2A using a small molecule, veratridine (VTD), decreases the level of mot‐2 in cancer cells. Consistent with the in vitro results, UBXN2A+/− mice exhibited selective elevation of mot‐2 in colon tissues. An in vitro Anti‐K48 TUBE isolation approach showed that recombinant UBXN2A enhances proteasomal degradation of mot‐2 in mouse colon tissues. Finally, we observed enhanced association of CHIP with the UBXN2A‐mot‐2 complex in tumors in an azoxymethane/dextran sulfate sodium‐induced mouse CRC model. The existence of a multiprotein complex containing UBXN2A, CHIP, and mot‐2 suggests a synergistic tumor suppressor activity of UBXN2A and CHIP in mot‐2‐enriched tumors. This finding validates the UBXN2A‐CHIP axis as a novel and potential therapeutic target in CRC.

Heat Shock Proteins: Agents of Cancer Development and Therapeutic Targets in Anti-Cancer Therapy

“…In breast cancer, the treatment of embelin, therefore, reduced cancer cell growth and metastatic ability by activation of p53 [185]. Veratridine (VTD) has shown efficacy in selectively suppressing the expression of Mortalin (HSP70) by increasing the expression of a ubiquitin-like protein called UBXN2A that degrades Mortalin (HSP70) [186]. In addition, knockdown of GRP78 (HSP70) prompts 5-FU-induced apoptosis through deterioration of ER stress [108].…”

“…Embelin-inhibition of Mortalin and p53 interaction, decrease of cell growth and metastasis [185] Colon cancer Veratridin (VTD)-inhibition of Mortalin through upregulation of UBXN2A [186] Breast and oral cancer stem cells…”

Hsp70 inhibitors: Implications for the treatment of colorectal cancer

“…UBXN2A in turn increases CHIP‐mediated proteasomal degradation of mortalin‐2. These findings indicate that UBXN2A/CHIP axis is negative regulator of mortalin‐2 and Veratridine could be entered in preclinical setting for the treatment of CRC …”

Salvianolic Acid B Targets Mortalin and Inhibits the Migration and Invasion of Hepatocellular Carcinoma via RECK/STAT3 Pathway

“…However, it is not clear whether Sal B can affect mortalin expression. Current studies have shown that ubiquitin-like protein UBXN2A promotes hydroxyl-terminal-dependent mortalin ubiquitination of HSP70 interacting protein (CHIP), and UBXN2A can increase mortalin proteasome degradation (Sane et al, 2018). Therefore, we speculated whether Sal B degraded mortalin protein through ubiquitination.…”