Study of Expression and Functional Mechanisms of Histamine N-Methyltransferase (HNMT) in Tumorigenesis and Correlation with Progression in Lung Cancer

Lung cancer is one the leading malignant tumors in Taiwan and also worldwide. The prevalence of lung cancer is significantly increased in both genders in last two decades in Taiwan. In 2010, lung cancer ranks first in major malignant tumors in Taiwan and the mortality rate of 19.7%. The tumorigenesis of lung cancer is still unknown although lifestyle, dietary, and perhaps other environmental factors are important risk factors. Molecular events involved in lung cancer are heterogenous and include genetic and epigenetic abnormalities. KRAS and EGFR pathways have been described in molecular events of lung cancer tumorigenesis. Both pathways involve the stepwise accumulation of multiple mutations, but the genes involved and the mechanism by which the mutations accumulate differ. But little is known about how many genes involved and detailed gene changes in tumorigenesis and in affecting the biologic behaviors of lung cancer. Recently, Histamine N-methyltransferase HNMT has been found to play as prognostic marker of cancer progression in some cancers. Histamine N-methyltransferase has been showed to be involved in tumorigenesis and progression of human cancers suggesting the important roles of histamine methylation in tumor cell behavior. However, recent evidences have shown paradoxical results as the expression levels of some histamine N-methyltransferase subgroups were found down regulated in tumorigenecity while other subgroups was overexpressed in distal metastasis. Histamine N-methyltransferase HNMT is the essential core subgroup of methyltransferase whose functions have never been defined in lung cancers and its cancer stem cells counterpart. Our preliminary data showed expression of HNMT protein in the tumor cells of lung cancer by immunohistochemistry and western blot. Meanwhile, the expression of HNMT seemed statistically correlated with patients’ outcome (in two cohorts from the Prognoscan database). However, the clinical significance of HNMT remains to be verified and its functional mechanisms in tumorigenesis of NSCLC are still not clear. In this two-year project, we propose comprehensive study to determine role of HNMT gene in tumorigenesis and progression as well its detailed functional mechanisms in lung cancer. We will also perform the experiment of therapeutic effect of HNMT inhibitor in lung cancer using animal model. In first year, the expression of HNMT protein and related up-stream and down-stream proteins in lung tumor tissues will be studied using primary tissue materials and immunohistochemical method in our cohort of lung tumor samples. The results of IHC will be collected and correlated with clinical data of the patients. In second year, functional mechanisms, including cell proliferation, caner stem cells self-renewal activity, migration and invasion abilities in vitro, colony forming capacity and soft agar colony forming ability of HNMT gene in lung cancer will be studied using knockdown and overexpression of HNMT gene in lung cancer cell lines. In third year, the effects of HNMT gene in tumor tissues of lung cancer in vivo, including abilities of tumor formation and metastasis, will be studied using stable clone of knockdown and overexpression of HNMT-transfeced lung cancer cell lines in NOD-SCID mouse. The therapeutic role of HNMT inhibitor will be tested in animal experiments. Through this study, we will understand and clarify the role and molecular mechanisms of HNMT gene in tumorigenesis of lung cancer and provide information for combined molecularly targeted therapy for lung cancer in the future.