Role of miR-21 in Regulating TET I-Hydroxymethylcytosine and Chemotherapeutic Response in Colorectal Cancer (I)

DNA methylation at the 5-position of cytosine (5-mC) is a key epigenetic mark that is critical for various biological and pathological processes. Aberrant DNA methylation occurs in all tumor types and correlates with transcriptional silencing of tumor suppressor genes. DNA methylation is thought to be very stable, and active DNA demethylation remains a long-standing enigma. Recently, the ten-eleven translocation (TET) family of oxygenases are found to oxidize 5-mC to 5-hydroxymethylcytosine (5-hmC), which is prerequisite for active DNA demethylation. Colorectal cancer (CRC) is the second leading cause of cancer-related death in males and females in the world, as well as in Taiwan. Both TET1 expression and global 5-hmC content are significantly reduced in CRC. However, the involving molecular mechanisms are still unclear. The oncogenic microRNA (miRNA) miR-21 has recently identified as a diagnostic and prognostic biomarker in CRC. In addition, the upregulation of miR-21 is tightly correlated with the chemotherapeutic responses in various tumors. Our group have found that adenomatous polyposis coli (APC) inactivation in CRC is associated with APC mutation and miR-21 overexpression. In this project, we will further investigate how miR-21 downregulates APC gene expression. We found that the 3’-UTR region of TET1 gene contains a miR-21 target sequence. Transfection of a synthetic miR-21 inhibitor into the colorectal cancer cells could increase the TET1 protein expression, suggesting that TET1 may be the direct target of miR-21. In this proposal, we will investigate the molecular mechanism for the regulation of TET1 and 5-hmC by miR-21 and their roles in APC inactivation in CRC. In addition, the role of miR-21/TET1/5-hmc signaling axis in the chemotherapeutic responses of CRC will also be investigated. Three Specific Aims will be executed in three years: Aim 1: To investigate the regulation of TET1 and APC gene expression by miR-21. Aim 2: To investigate the regulation of DNA methylation/hydroxymethylation-associated gene expression by miR-21, especially the APC gene. Aim 3: To investigate the role of miR-21/TET1/5-hmC signaling axis in chemotherapeutic responses in CRC.