Abstract P4-07-11: Dual characteristics of microRNA-484 modulated cytidine deaminase (CDA) axis in breast cancer: Chemo-resistance and regulating cell proliferation
Authors: Hu X , Ye F , Cao Z , Ling H , Qiao F , Song C , Shao Z 
Published: August 2014

Abstract
Acquired resistance to chemotherapy is a major clinical obstacle to achieve successful treatment in breast cancer. Cancer cells could evolve a complicated sensory network to develop resistance to chemo treatment. Recently, microRNAs modulated chemo-resistance is investigated as a new paradigm in cancer biology and some acquired mis-expression of miRs confer cancer cells to escape chemotherapy. However, it is important to address whether these miRs also play various intrinsic roles in carcinogenesis. Here, our study demonstrated that miR-484 could modulate cytidine deaminase (CDA) axis, playing various roles in chemo-resistance and cell proliferation.
We have generated a chemo-resistant breast cancer cell line (MDA-MB-231 Gem) which has 10 fold higher IC50 value than MDA-MB-231 cells in response to gemcitabine (dFdC) treatment through molecular evolution. Gene ontology analysis showed that cytidine degradation pathway was activated in the resistant cells, and qPCR array confirmed that cytidine deaminase (CDA), which converts dFdC to dFdU, was significantly upregulated. Interestingly, microRNA array analysis implicated that miR-484, which might target the 3’UTR region of CDA gene was down-regulated in these resistant cells. Furthermore, 3’UTR luciferase reporter assay and western blot revealed that miR-484 directly regulates CDA gene expression. Over-expression of miR-484 can sensibilize the resistant cells to dFdC treatment. Remarkably, restoration of CDA gene strongly converts miR-484–mediated dFdC sensibilization. These results implicated that miR-484/CDA axis play a pivotal role in chemo-resistance. Unexpectedly, further studies implicated that miR-484/CDA axis could also regulate cell proliferation due to disrupting cell cycle. We found that the chemo-resistant cells had deficiency in cell cycle progression at the S-phase transition, and miR-484 could significantly promote cell growth and overcome cell cycle arrest with CDA down-regulation. Moreover, reintroduction of CDA gene could abrogate miR-484-induced effects on cell proliferation via reactivating S-phase checkpoint. Importantly, the Kaplan-Meier survival analysis supported that higher expression of CDA in breast cancer patients indicates better outcome in DFS model.
In summary, this study uncovers for a previously unknown axis that cytidine deaminase was a direct downstream target for miR-484. The miR484/CDA axis could modulate cells into stagnant status for promoting cellular resistance to DNA damage agents in chemotherapy. On the other hand, as CDA gene participates in cell cycle S-phase arrest, miR484/CDA axis could also contribute to cell proliferation. Taken together, our findings provided new evidences that miR-484/CDA axis has various functions in cell proliferation and chemo-resistance and might be considered as a candidate therapeutic target in breast cancer.
Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P4-07-11.