Background: Pancreatic cancer (PC) is an extremely fatal disease due to late diagnosis and a lack of efficient therapy. Identification of aberrantly expressed proteins which are functionally involved in the pathobiology of PC is critical to achieve early diagnosis and the development of effective therapeutic strategies. Mucins are a group of glycoproteins that under normal conditions protect mucosal surfaces, but have tumor promoting properties when over-expressed in neoplastic conditions. We have previously shown that mucin 13 (MUC13) is aberrantly overexpressed in pancreatic cancer tissues and promotes the growth and invasion of pancreatic cancer cell lines, indicating the importance of MUC13 in pancreatic cancer pathogenesis and the potential utilization of MUC13 for diagnostic and therapeutic applications. Here, we report a novel microRNA (miRNA)-mediated mechanism underlying aberrant expression of MUC13 in pancreatic cancer. miRNAs have been implicated in cancer initiation and progression via their ability to affect expression of genes and proteins that regulate cell proliferation and/or cell death.

Methods: To investigate whether the expression of MUC13 is regulated by miRNAs, we searched the MUC13 sequence for potential miRNA binding sites using Target Scan and miRanda. In silico analysis revealed a putative 8 mer-binding site for miRNA-145 (miR-145) in the 3UTR of MUC13 transcript, suggesting that miR-145 may target and inhibit the expression of MUC13. MUC13 expressing pancreatic cancer cell lines (HPAF-II and Capan-1) were used for the study. Following transient transfection of mature miR-145 RNAs and miR-145 inhibitors, Western blotting and immunofluorescence techniques were used to investigate the effects of miR-145 on MUC13 expression and on additional proteins known to be affected by MUC13 expression. Additionally, functional studies of the effects of miR-145 included cell proliferation, colony formation, cell migration, and cell invasion assays.

Results: We demonstrate that the overexpression of miR-145 significantly downregulates endogenous MUC13 protein levels (by 80%). Of interest, overexpression of miR-145 inhibits cell proliferation, clonogenicity, migration, and invasion and enhances intercellular adhesion in pancreatic cancer cells. Exogenous expression of miR-145 also causes a reduction of HER2, P-AKT, and PAK1 and an increase in p53. Similar results are found when MUC13 is specifically inhibited by shRNA directed at MUC13. Additionally, the miR-145 inhibitor abrogated the effects induced by miR-145. Interestingly, we detected only a low level of miR-145 in pancreatic cancer cells with high MUC13 protein levels, suggesting an inverse association between miR-145 and MUC13 expression.

Conclusions: These findings demonstrate that miR-145 is a novel regulator of MUC13 and acts as a tumor suppressor miRNA in PC.

Citation Format: Sheema Khan, Diane Maher, Mara Ebeling, Deepak Kumar, Meena Jaggi, Subhash C. Chauhan. MicroRNA-145 targets MUC13 and suppresses invasion and metastasis of pancreatic cancer cells . [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4184. doi:10.1158/1538-7445.AM2013-4184