Abstract
The predominant way in which conventional chemotherapy kills rapidly proliferating cancer cells is the induction of DNA damage. However, chemoresistance remains the main obstacle to therapy effectivity. An increasing number of studies suggest that epithelial-to-mesenchymal transition (EMT) represents a critical process affecting the sensitivity of cancer cells to chemotherapy. Zinc finger E-box binding homeobox 1 (ZEB1) is a prime element of a network of transcription factors controlling EMT and has been identified as an important molecule in the regulation of DNA damage, cancer cell differentiation, and metastasis. Recent studies have considered upregulation of ZEB1 as a potential modulator of chemoresistance. It has been hypothesized that cancer cells undergoing EMT acquire unique properties that resemble those of cancer stem cells (CSCs). These stem-like cells manifest enhanced DNA damage response (DDR) and DNA repair capacity, self-renewal, or chemoresistance. In contrast, functional experiments have shown that ZEB1 induces chemoresistance regardless of whether other EMT-related changes occur. ZEB1 has also been identified as an important regulator of DDR by the formation of a ZEB1/p300/PCAF complex and direct interaction with ATM kinase, which has been linked to radioresistance. Moreover, ATM can directly phosphorylate ZEB1 and enhance its stability. Downregulation of ZEB1 has also been shown to reduce the abundance of CHK1, an effector kinase of DDR activated by ATR, and to induce its ubiquitin-dependent degradation. In this perspective, we focus on the role of ZEB1 in the regulation of DDR and describe the mechanisms of ZEB1-dependent chemoresistance.
Highlights
Cancer is the second leading cause of death worldwide (Wang et al, 2016)
epithelial-mesenchymal transition (EMT) originally observed during embryogenesis (Hay, 1995), is a reversible, evolutionary conserved process that is tightly regulated through the interplay between environmental signals from Wnt, TGF, FGF family members, interleukins, and various EMT-transcription factors (EMT-TFs), including Zinc-finger Ebox binding protein 1 (ZEB1), ZEB2, Snail, Slug, and Twist (Kalluri and Weinberg, 2009)
With regards to clinical relevance, ZEB1 expression increases progressively through the different stages of cancer progression, e.g., ZEB1 expression dramatically increases in advanced castration-resistant prostate cancer (CRPC) and PCa metastasis compared to clinically localized prostate cancer (Figiel et al, 2017)
Summary
Cancer is the second leading cause of death worldwide (Wang et al, 2016). the basis of poor prognosis for cancer patients and the obstacle to a positive clinical outcome is not the primary tumor itself, but cancer cell plasticity, which enables local invasion, dissemination, and distant metastases. We outline recent studies on the molecular function of ZEB1 in cellular plasticity and metastasis and elucidate its role in DDR and therapy resistance in an EMT-dependent or EMTindependent manner. The feedback loop between ZEB1 and the miRNA-200 family is a well-described mechanism of the regulation of cellular plasticity, (de)differentiation, and EMT machinery (Tian et al, 2014; Zhang Y. et al, 2019).
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