REGULATION AND FUNCTION OF TUMOR SUPPRESSOR ECRG2 IN RELATION TO DNA DAMAGE AND MICROTUBULE DYNAMICS IN HUMAN MALIGNANCIES

Abstract

phageal Cancer-Related Gene 2 (ECRG2) is a novel tumor suppressor which is frequently mutated or downregulated in multiple human cancers. Previous studies have demonstrated that ECRG2 inhibits growth of cancer cells by inducing apoptotic death. However, the molecular basis of its regulation and involvement in DNA damage response remain to be elucidated. The function of tumor suppressor p53 in cellular response to stress conditions, such as DNA damage, has been well-established. In the present study, we report for the first time, that ECRG2 is a novel pro-apoptotic transcriptional target of p53 and ECRG2 expression is induced by DNA damage in a p53-dependent manner. Moreover, we demonstrate that disruption of ECRG2 leads to reduced apoptosis and improved survival following the treatment with DNA damage-inducing anticancer agent despite p53 activation in cancer cells. Significantly, we characterized a natural variant in ECRG2promoter (rs3214447) that is found in the genomes of ~38.5% of world population and showed that ECRG2 promoter with rs3214447 variant is defective in responding to p53 and DNA damage. Thus, ECRG2 is an important executor of p53-mediated apoptosis in response to DNA damage. We also report a novel biological function of ECRG2 and demonstrate that ECRG2 interacts with and stabilizes microtubules. ECRG2 was shown to protect the microtubules against the destabilization induced by cold and nocodazole treatment. In addition, we show that ECRG2 increases acetylation of microtubules, which is associated with more stable microtubules. Importantly, we demonstrate that ECRG2 disruption give rise to increased cell proliferation by elevated activation of Akt. Taken together, our findings ascribe a novel function to ECRG2 in the regulation of microtubule dynamics and cancer cell proliferation. ECRG2-mediated tumor suppressor activities elucidated in this dissertation are clinically significant. Our database analyses reveal that cancer patients with lower ECRG2expression in their tumors had poor prognosis and reduced disease-free survival as compared to their counterparts. These observations suggest that loss of ECRG2 expression and function confers survival advantage to cancer cells. Collectively, this dissertation highlights novel aspects of ECRG2 regulation and function in cancer cell sensitivity to DNA damage-inducing anticancer therapy, microtubule dynamics and cell proliferation.