Post-translational modification of OCT4 in breast cancer tumorigenesis

Abstract

Recurrence and drug resistance of breast cancer are still the main reasons for breast cancer-associated deaths. Cancer stem cell (CSC) model has been proposed as a hypothesis for the lethality of breast cancer. Molecular mechanisms underlying CSC maintenance are still unclear. In this study, we generated mammospheres derived from breast cancer MDA-MB231 cells and MCF7 cells to enrich CSCs and performed DNA microarray analysis. We found that the expression of carboxy terminus of HSP70-interacting protein (CHIP) E3 ubiquitin ligase was significantly downregulated in breast CSCs. CHIP depletion increased mammosphere formation, whereas CHIP overexpression reversed this effect. We identified interactomes by mass spectrometry and detected CHIP directly interacted with OCT4, a stemness factor. CHIP overexpression decreased OCT4 stability through proteasomal degradation. CHIP induced OCT4 ubiquitination, whereas H260Q, a catalytic CHIP mutant, did not. Interestingly, we determined that OCT4 was ubiquitinated at lysine 284, and CHIP overexpression did not degrade K284R mutant OCT4. CHIP overexpression decreased the proliferation and side population of breast cancer cells, but these were not occurred in K284R mutant OCT4 overexpressed cells. Only 1000 cells showing CHIP depletion or OCT4 overexpression sufficiently generated breast tumors and lung metastases in xenografted mice. Ubiquitination-defective mutant of OCT4(K284R) overexpressed cells drastically generated tumor burdens in mice. Patients with breast cancer who showed low CHIP expression had poor survival probability. Taken together, we suggest that CHIP-induced OCT4 ubiquitination is important in breast CSCs. Regulation of CHIP expression and OCT4 protein stability is a considerable approach for breast cancer therapy.

Molecular Chaperones in Cancer Stem Cells: Determinants of Stemness and Potential Targets for Antitumor Therapy

“…YL-109-induced CHIP upregulation in MDA-MB-231 cells resulted in attenuation of CSC properties, including the mammosphere-forming ability, expression of stemness markers, invasiveness, and metastatic potential [88]. In a similar model, CHIP was found to be significantly downregulated in breast CSCs and such a CHIP deficiency was correlated with mammosphere formation in vitro, lung metastases in xenografted mice, and poor outcome among patients with breast cancer exhibiting low CHIP expression [89]. The authors explained such effects of the CHIP depletion by a failure in CHIP-mediated ubiquitination and degradation of OCT4, a transcription factor promoting stemness that is a client protein of HSP90; in support of that, they demonstrated direct CHIP-OCT4 interactions and also the CHIP depletion-mimicking action of a ubiquitination-defective OKT4 mutant [89].…”

“…Those nestin-HSC71 interrelations seemed to maintain the CSC phenotype and such typical manifestations of the cancer stemness as tumorigenicity, invasion, and spheroid formation. Moreover, alterations in the CHIP expression/activity levels may affect the destiny of some stemness-regulating proteins bound to HSP70 and HSP90, as it was shown for breast CSCs [88,89].…”

“…Additionally, vice versa: The CHIP downregulation can preserve some proteins that otherwise undergo degradation. Both situations were modeled in human breast cancer [88,89]. YL-109-induced CHIP upregulation in MDA-MB-231 cells resulted in attenuation of CSC properties, including the mammosphere-forming ability, expression of stemness markers, invasiveness, and metastatic potential [88].…”

Human papillomavirus E7 binds Oct4 and regulates its activity in HPV-associated cervical cancers

“…Initial evidence suggests that Oct4 acts as a rheostat gene controlling the development and progression of malignancy in germ cells [6]. More recent evidence reports the expression of Oct4 in somatic malignancies, such as prostate [8], breast [9], ovarian [10], hepatocellular [11], head and neck [12] and cervical [13] cancers. As a cancer marker, Oct4 was recently associated with poor prognosis in hepatocellular carcinomas [14].…”

Mass spectrometry based immunopeptidomics leads to robust predictions of phosphorylated HLA class I ligands

“…Multiple studies have identified post-translational modifications (PTMs) showing aberrant behavior in cancer (8)(9)(10)(11), resulting for instance in abnormal cellular signaling, one of the hallmarks of cancer (12). Phosphorylation of serine, threonine, and tyrosine is one of the most frequent and best studied PTMs (13), and is carried out by different types of protein kinases, consisting mainly of serine/threonine-and tyrosine-specific protein kinases.…”