Abstract 722: MYB promotes pancreatic tumor associated-desmoplasia by up-regulating Sonic hedgehog and adrenomedullin

Pancreatic cancer (PC) stands as the fourth leading cause of cancer-related death in the United States. Unfortunately, even with the emergence of tumor-targeted therapies, the 5-year survival rate of PC continues to remain very dismal (∼ 7.0%). The presence of dense desmoplastic region at the tumor site is a prominent pathological characteristic of PC, and tumor-associated desmoplasia is suggested to limit the therapeutic efficacy by acting as a physical barrier for drug delivery. In addition, it plays pivotal roles in promoting the survival and aggressive phenotypes of tumor cells. Therefore, it is of utmost importance that we identify novel gene targets and associated molecular mechanisms accountable for the development of desmoplasia in pancreatic tumors. Our recent study provided first evidence for a role of MYB, an oncogenic transcription factor, in pancreatic tumor growth and metastasis. Upon histological examination of orthotopic tumor xenografts derived from MYB-overexpressing and -silenced pancreatic tumor cells, we noticed a positive association of MYB expression with the extent of desmoplastic reaction. This finding was further confirmed by staining the tumor xenograft sections with Collagen-I, fibronectin and a-SMA, the well-characterized markers of desmoplasia. In a co-culture experiment, we observed that MYB-overexpressing pancreatic tumor cells promoted greater proliferation of pancreatic stellate cells (PSCs) as compared to the MYB-silenced cells further supporting a role of MYB in desmoplasia. From the mechanistic standpoint, we identified MYB to be novel direct regulator of Sonic hedgehog (SHH) and Adrenomedullin (ADM) expression in PC cells as confirmed by chromatin immunoprecipitation (ChIP) analysis. Treatments of pancreatic tumor (high or low MYB) and stellate cells co-culture with specific inhibitors and/or recombinant SHH and ADM demonstrated that both SHH and ADM cooperatively mediated the effect of MYB on PC and stellate cells via autocrine and/or paracrine mechanisms. Together, our studies suggest that MYB promotes malignant phenotype of PC not only by directly impacting the tumor cells, but also by altering the tumor microenvironment. Citation Format: Arun Bhardwaj, Sanjeev K. Srivastava, Nikhil Tyagi, Sumit Arora, Seema Singh, James E. Carter, Ajay P. Singh. MYB promotes pancreatic tumor associated-desmoplasia by up-regulating Sonic hedgehog and adrenomedullin. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 722.