Proline Dehydrogenase affects lung cancer cell proliferation by inducing ROS and cellular senescence

Proline dehydrogenase (PRODH) is a mitochondrial flavoenzyme that catalyzes proline oxidation. Its catabolism is linked to basic cellular metabolism. Moreover, the electrons generated from oxidation can be used to generate ATP or ROS, potentially affecting several cellular processes, such as survival, apoptosis, and senescence. PRODH is frequently expressed in lung adenocarcinoma (LUAD), yet little is known about the correlation between the expression of this enzyme and its role in lung cancer development. Lung cancer is one of the most frequent types of tumor and the leading cause of cancer-related deaths. Availability of biomarkers for early diagnosis, prognosis, and prediction of response to therapy would improve patients survival. Thus, we aim to investigate if PRODH could represent a diagnostic and prognostic marker. To do so, we are elucidating its role in LUAD cell lines. To investigate how PRODH affects growth and proliferation of lung cancer cells, we stably transfected the NCI-H1299 LUAD cell line, not expressing PRODH, with a PRODH expression construct or the empty vector (control). To compare the ability of PRODH expressing cells to survive and proliferate compared to control cells, we performed clonogenic assays and MTT assays. ROS production as well as apoptosis and cellular senescence were also investigated. We observed a decrease in survival and proliferation in PRODH clones compared to control clones. PRODH clones were found to produce higher levels of ROS using the 2′,7′-dichlorofluorescin diacetate assay. In order to identify the biological process(es) involved in the observed phenotype, we tested induction of apoptosis. We found no difference in the number of apoptotic cells between PRODH and control clones. Instead, a greater number of senescent cells was observed in PRODH clones with the senescence-associated β-galactosidase assay. Induction of cell senescence was confirmed by the increase in senescence markers. We conclude that PRODH promotes cellular senescence in LUAD cells via ROS production and that senescence is the mechanism underlying the decrease in proliferation observed in PRODH expressing cells. The results obtained from our study allow to better understand the role of PRODH in lung cancer development. Induction of cellular senescence by ROS production was shown to affect LUAD cell proliferation. We envisage that the senescent phenotype induced by PRODH may also affect the response to therapy of cancer cells.