Frontiers in Oncology (Sep 2020)
Role of Ubiquitination in PTEN Cellular Homeostasis and Its Implications in GB Drug Resistance
Abstract
Glioblastoma (GB) is the most common and aggressive brain malignancy, characterized by heterogeneity and drug resistance. PTEN, a crucial tumor suppressor, exhibits phosphatase-dependent (PI3K-AKT-mTOR pathway)/independent (nucleus stability) activities to maintain the homeostatic regulation of numerous physiological processes. Premature and absolute loss of PTEN activity usually tends to cellular senescence. However, monoallelic loss of PTEN is frequently observed at tumor inception, and absolute loss of PTEN activity also occurs at the late stage of gliomagenesis. Consequently, aberrant PTEN homeostasis, mainly regulated at the post-translational level, renders cells susceptible to tumorigenesis and drug resistance. Ubiquitination-mediated degradation or deregulated intracellular localization of PTEN hijacks cell growth rheostat control for neoplastic remodeling. Functional inactivation of PTEN mediated by the overexpression of ubiquitin ligases (E3s) renders GB cells adaptive to PTEN loss, which confers resistance to EGFR tyrosine kinase inhibitors and immunotherapies. In this review, we discuss how glioma cells develop oncogenic addiction to the E3s-PTEN axis, promoting their growth and proliferation. Antitumor strategies involving PTEN-targeting E3 ligase inhibitors can restore the tumor-suppressive environment. E3 inhibitors collectively reactivate PTEN and may represent next-generation treatment against deadly malignancies such as GB.
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