Cigarette Smoke Suppresses the Ubiquitin-dependent Degradation of OLC1

The newly identified gene, overexpressed in lung cancer 1 (OLC1), is highly expressed as OLC1 protein in the tumor tissues of lung cancer patients with histories of cigarette smoking. However, the underlying mechanisms of how the gene is affected by cigarette smoke have been poorly characterized. In this study, we investigated how OLC1 is regulated in lung cancer cells by cigarette smoke condensate (CSC). Compared to the controls, CSC treatment increased OLC1 protein levels in a dose- and time-dependent manner without affecting OLC1 mRNA levels in lung cancer cells. Ubiquitination of OLC1 protein was blocked upon CSC treatment. Biochemical analysis revealed that the ubiquitin E3 ligase anaphase promoting complex (APC) and its activators cell-division cycle protein 20 (CDC20) and cadherin-1 (CDH1) are responsible for the degradation of OLC1. However, upon introducing CSC the binding of OLC1 to the proteins CDC20, CDH1, and APC2 was impaired. These results demonstrate that CSC regulates OLC1 expression in lung cancer cells by compromising its ubiquitination and subsequent degradation through the ubiquitin E3 ligase APC.