With an annual incidence and mortality of ~38,000 people, pancreas cancer or pancreatic ductal adenocarcinoma (PDA) is the fourth leading cause of cancer-related death in the United States. The 5-year overall survival for patients with PDA is less than 3%. The gap junction protein connexin43 (Cx43) is a tumor suppressor gene that is expressed in pancreatic ductal cells, the putative site of cancer origin. We have preliminary evidence that Cx43 expression, localization and phosphorylation is dysregulated during pancreas cancer. This proposal focuses on how these events interplay in vivo to affect carcinogenesis of the pancreas. Gap junctions (GJ) are specialized membrane domains that contain channels that allow exchange of small molecules (<1000 Da) including ions, metabolites, and second messengers (e.g., Ca2+ and IP3) between neighboring cells. Connexins, like other junctional proteins, also play critical signaling and growth control roles that are independent of channel function. Very extensive correlative evidence in vivo and cell lines indicates that gap junctional intercellular communication (GJC) and connexin expression regulate proliferation and play key tumor prevention roles. Cx43, by far the most widely expressed connexin (>34 tissues and 46 cell types), is phosphorylated at multiple serine residues found in the cytoplasmic, C-terminal region. Cx43 phosphorylation can modulate the levels of protein trafficking, stability of the junctional complex, gap junctional communication (GJC) and the interaction with other proteins. We have found that homozygous "knock-in" (KI) of mutant Cx43 bearing an S to A amino acid substitutions at casein kinase 1 (CK1) phosphorylation sites S325, S328 and S330 (termed CK3*) leads to dramatically reduced Cx43-dependent GJC and sustained increased MAPK activity and decreased apoptosis in tissues in response to different acute stimuli. Our collaborator has recently developed the first models of preinvasive and invasive pancreatic ductal adenocarcinoma through the targeted physiologic expression of oncogenic KrasG12D to the pancreas. Resected pancreata demonstrate the full spectrum of preinvasive lesions seen in patients, and the lesions progress histologically over time culminating in fully invasive and metastatic disease. However, like in humans with pancreas cancer, disease progression, symptom presentation and speed of progression varies even in these syngeneic models. We hypothesize that Cx43 phosphorylation is critical for the control of cell growth and is modulated during pancreas carcinogenesis affecting its progression. Consequently, prevention of these regulatory events will result in an altered course of carcinogenesis in pancreas cancer.
We hypothesize that Cx43 phosphorylation is critical for the control of cell growth and is modulated during pancreas carcinogenesis affecting its progression. Since drugs that affect Cx43 activity and gap junctional communication are under development, understanding how these factors affect progression could ultimately lead to better treatment of this lethal disease.