Expression and heterodimerization of Type A and B Cholecystokinin Receptors in Gallbladder cancer

e15655 Background: Gallbladder cancer is the most common malignancy of the biliary tract and endemic in Northern India. The prognosis of gallbladder cancer remains dismal despite any treatment because of late presentation and aggressive tumor biology. Cholecystokinin (CCK) is present in abundance in gallbladder tissue and mediates function through two structurally related receptors, the type A (CCKAR) and B (CCKBR) receptors. Previously, heterodimerization of CCKAR and CCKBR receptor has been demonstrated in vitro, and was shown to bind natural agonists normally but exhibited agonist stimulated cellular signaling, promoting cell growth. In this study we examined the expression level of CCKAR and CCKBR in resected gallbladder tissue samples and also attempted to determine the dimerization status of CCKAR and CCKBR receptors in gallbladder cancer comparing them to cholelithiasis and normal gallbladder tissue. Methods: Tissue samples from resected normal gallbladder (n = 10), cholelithiasis (n = 25) and gallbladder cancer (n = 25)) were evaluated for the expression of CCKAR and CCKBR by immunohistochemistry. Determination of CCKAR and CCKBR expression was also done by western blot in representative samples from each of these tissue types while their dimerization status was evaluated by immunoprecipitation. Results: By Immunohistochemistry technique, positive CCKAR expression was observed in 80% gallbladder cancer, 84% cholelithiasis, 90% normal gallbladder, P = 0.76. However significantly higher expression of CCKBR was noted in gallbladder cancer (60%) as compared to cholelithiasis (25%) and normal gallbladder (20%), P = 0.013. We also observed progressively increasing level of expression of CCKAR and CCKBR in gallbladder cancer as compared to cholelithiasis and normal gallbladder by western blot. In addition, we also observed a higher level of heterodimer formation in gallbladder cancer compared to cholelithiasis and normal gallbladder using immunoprecipitation technique. Conclusions: Our results provide the first evidence of increasing trend of heterodimerization of CCKAR and CCKBR in gallbladder cancer which has potential clinical and therapeutic significance.