Lung Cancer, Cigarette Smoke And Functional Study Of OLC1 Protein

Lung cancer is one of the most common malignant cancers with high morbidity and mortality around the world and cigarette smoke is the principal risk factor of estimated 90%of all lung cancers. Although growing researches about lung cancer have been reported and many implicated genes and proteins have been in-depth studied, the precise molecular mechanism underlying lung carcinogenesis remains unclear.OLCl (Overexpressed in Lung Cancer 1) gene was previously identified with high expression level in lung cancer tissues and cells and overexpression of OLCl was more common in lung cancer patients with a smoking history. Previous studies revealed that OLCl may play a vital role in lung carcinogenesis. In this research, we aimed to investigate the interaction between OLCl and BRCAI proteins and reveal the mechanism of how OLCl is regulated by cigarette smoke condensate (CSC) in vitro and in vivo.In the first part of study. GST pull-down and co-immunoprecipitation (CO-IP) assays were performed to characterize the interaction between OLCl and BRCAI protein in lung cancer cells. Their co-localization in cytoplasm was confirmed by immunofluorescence approach. Then we demonstrated that overexpression of OLCl decreased BRCAI protein level by promoting its ubiquitination and degradation without affecting BRCAI mRNA level in lung cancer cells. Additionally, the expression levels of OLCl and BRCAI protein detected by immunohistochemistry in lung cancer tissues were negatively correlated to each other just like that in vitro.In the second part of study, we demonstrated that CSC induced the elevation of OLCl protein without impacting on mRNA level of OLCl in lung cancer cells. Ubiquitination of OLCl protein was blocked upon CSC treatment, which accumulated OLCl protein. Furthermore, we showed that anaphase promoting complex (APC) was the E3 ligase responsible for ubiquitination of OLCl and CSC impaired the interaction between OLCl and APC, thus compromising OLCl ubiquitination and subsequent degradation.In summary, these results herein suggest that OLCl interacts with BRCAI, providing a new mechanism and pathway by which OLCl may exert tumor promoting function and contribute to lung tumorigenesis. Meanwhile, revealing the mechanisms responsible for the increase of OLCl protein upon cigarette smoke exposure is helpful to clarify the role of candidate oncogene OLCl in cigarette smoke-related lung carcinogenesis.