The role of Parf, a novel partner of ARF, in pancreatic ductal adenocarcinoma and in ARF signaling

Pancreatic ductal adenocarcinoma (PDAC) is an incurable, highly metastatic cancer resistant to current treatments. A better understanding of the genetic basis of PDAC progression is urgently needed to improve treatment options. The ARF tumor suppressor is inactivated in ~45% of PDAC. My thesis lab identified a new, uncharacterized ARF binding protein, Partner of ARF isoform 1A (Parf-1A). This thesis explores the hypothesis that Parf-1A plays an important role in PDAC and ARF tumor suppressor signaling

Initial studies sought to develop a novel mouse xenograft model of PDAC metastasis that would expedite testing of putative PDAC genes. Human PDAC cell lines stably expressing luciferase were generated and introduced by intracardiac injection into immunodeficient mice to model hematogenous dissemination of cancer cells. Tumor development was monitored non-invasively by bioluminescence imaging and found to recapitulate PDAC tumor formation and metastatic distribution. The model was validated by the ability of ARF to suppress PDAC cancer cell migration in vitro and reduce tumor cell colonization in vivo; establishing a new bioluminescent mouse model for rapidly assessing the significance of suspected PDAC genes.

Using human PDAC cell lines and tumor specimens, we investigated the role and significance of Parf-1A to PDAC. RNAi analyses demonstrated Parf-1A is required for PDAC cell survival, proliferation and resistance to the PDAC therapeutic, oxaliplatin. PDAC cells are ARF-null; therefore these tumor promoting activities of Parf-1A were independent of ARF. Notably, immunohistochemical analyses of Parf-1A in human PDAC tumors showed Parf-1A expression is a prognostic marker of poor survival in PDAC patients. These data suggest Parf-1A is a novel biomarker of PDAC and potential target for anticancer therapy.

Other studies tested how Parf-1A influenced ARF signaling. Parf-1A depletion and overexpression showed it inhibits ARF anti-proliferative activity by mobilizing ARF from the nucleus (where it is functional) into the cytoplasm. These data show Parf-1A is a new inhibitor of ARF. Considered with findings that Parf-1A can act independent of ARF to promote PDAC tumorigenesis, such results suggest Parf-1A is a novel oncoprotein that acts through multiple pathways to facilitate tumorigenesis. Thus, Parf-1A may have broad relevance to many types of human cancers.