The Expression Of LKB1in Hilar Gholangiocarcinoma And Its Impact On Tumor Cellular Behaviours

Chapter I Expression and clinical significance of LKB1in hilarcholangiocarcinomaBackground and Aim: Hilar cholangiocarcinoma (HC) is a rare malignancy which arisingfrom the epithelium of perihilar bile ducts, and account for approximately60%of allcholangiocarcinoma cases. Hilar cholangiocarcinoma has been reported a annual incidenceof2/100,000in the United States and5.1/100,000in Korean. Hilar cholangiocarcinomawas first reported by Klatskin in1965, it still remains a challenging clinical problem with anextremely poor prognosis. Although more options are available for HC treatment, completeresection of the tumour with negative histological resection margins (R0) is still the onlyway for patient to obtain long time survive. Moreover, little is known about its pathogenesis,early diagnosis and nonsurgical treatment. Therefore, a better understanding of themolecular biological features of HC may help to improve its both diagnosis and therapy.The LKB1(or STK11) gene encodes a serine/threonine kinase that phosphorylates andactivates several targets, including adenosine monophosphate–activated protein kinase(AMPK) and the AMPK-related kinases. This study was aim to detect the expression ofLKB1in hilar cholangiocarinoma (HC) tissues, and to evaluate its clinical significance.LKB1expression in327HC tissues was detected by immunohistochemistry．Associations ofLKB1with clinicopathological characteristics were subsequently assessed.Immunohistochemistry showed the expression of LKB1in HC tissue was decreased.Immunohistochemistry showed the LKB1expression was associated with age ofpatients，differentiation, regional lymph, UICC stage. Furthermore decreased expression ofLKB1was correlated with poor prognosis. So we can got a conclusion that decreasedexpression of LKB1might be the feature of HC and benefit us in predicting the prognosis． Part II The mechanism of downregulation of LKB1and itsimpact on biological behaviour of Cholangiocarcinoma cellsIt is becoming clear that LKB1plays vey important roles tumorigenesis and tumoralprogression. The search for substrates of LKB1that mediate its tumor-suppressor functionled to the identification of the LKB1/AMPK/mTOR singling pathway. Adenosinemonophosphate-activated protein kinase (AMPK) is a direct LKB1substrate. Inactivationof LKB1cause constitutively downregulated AMPK activity, thus elevate mTOR level,finally promoting cell growth, proliferation, invasion, migration and resistance of drugtreatment through multiple downstream proteins.LKB1and AMPK negatively affect cell growth by inhibition of the protein kinase, mTOR(mammalian target of rapamycin), which functions in increasing cell growth and iscommonly deregulated in cancer. LKB1–AMPK regulation of mTOR occurs via AMPKactivation of the tuberous sclerosis complex (TSC1/2) tumor suppressors, which inhibitmTOR activation. Interestingly, stimuli that normally activate LKB1–AMPK fail to result indecreased mTOR activity in LKB1-null cells and can activate apoptosis. LKB1is the majorupstream kinase activating the energy-sensing kinase AMPK, making LKB1-deficient cellsunable to appropriately sense metabolic stress. For example, a most recent study has shownthat metabolic drugs phenformin, a mitochondrial inhibitor and analog of the diabetestherapeutic metformin selectively induced apoptosis in LKB1-deficient NSCLC cells.Recent basic and clinical researches have demonstrated that tumor cells have uniquelyaltered metabolisms, displaying increased glucose uptakes, increases in enzymes of theglycolytic pathway, and an increased sensitivity to inhibition of glycolysis.The critical roles of LKB1inactivation are becoming clearer, however, little isknown about status of LKB1gene in HC. In this study, we first examined LKB1geneticaberrations using fluorescence in situ hybridization (FISH) and exon sequencing. Wefound a high deletion rate of LKB1; however little mutations were found. Next, we testedLKB1protein expression level in HC tissues with HC tissue array, and found obviousdownregulation in many cases. More important is low expression of LKB1has significant correlation with patient survival time. And we discovered LKB1negatively regulatedcholangiocarcinoma cancer cell migration and invasion. Furthermore, we also examinedthe response of HC cell lines to metformin, a LKB1-AMPK activator, and the relationshipof the response to the function of the LKB1tumor suppressor gene. Results showed thatfenformin has stronger ability to induce cell apoptosis in LKB1-decreased HC cells thanin that of LKB1normal cells. This study may provide new strategies for HC diagnosis andtreatment.