Carnitine palmitoyltransferase 1C (CPT1C), an enzyme located in the outer mitochondria membrane, has a crucial role in fatty acid transport and oxidation. It is also involved in cell proliferation and is a potential driver for cancer cell senescence. However, its upstream regulatory mechanism is unknown. Peroxisome proliferator activated receptor α (PPARα) is a ligand-activated transcription factor that regulates lipid metabolism and tumor progression. The current study aimed to elucidate whether and how PPARα regulates CPT1C and then affects cancer cell proliferation and senescence. Here, for the first time we report that PPARα directly activated CPT1C transcription and CPT1C was a novel target gene of PPARα, as revealed by dual-luciferase reporter and chromatin immunoprecipitation (ChIP) assays. Moreover, regulation of CPT1C by PPARα was p53-independent. We further confirmed that depletion of PPARα resulted in low CPT1C expression and then inhibited proliferation and induced senescence of MDA-MB-231 and PANC-1 tumor cell lines in a CPT1C-dependent manner, while forced PPARα overexpression promoted cell proliferation and reversed cellular senescence. Taken together, these results indicate that CPT1C is a novel PPARα target gene that regulates cancer cell proliferation and senescence. The PPARα-CPT1C axis may be a new target for the intervention of cancer cellular proliferation and senescence.

Background

Aberrant expression of Nicotinamide N-methyltransferase (NNMT) has been reported in pancreatic cancer. However, the role of NNMT in pancreatic cancer development remains elusive. Therefore, the present study was to investigate the impact of NNMT on pancreatic cancer cell proliferation, metastatic potential and survival under metabolic stress.

Methods

Pancreatic cancer cell line PANC-1 was transfected with NNMT expression plasmid or small interfering RNA of NNMT to overexpress or knockdown intracellular NNMT expression, respectively. Rate of cell proliferation was monitored. Transwell migration and matrigel invasion assays were conducted to assess cell migration and invasion capacity. Resistance to glucose deprivation, sensitivity to glycolytic inhibition, mitochondrial inhibtion and resistance to rapamycin were examined to evaluate cell survival under metabolic stress.

Results

NNMT silencing markedly reduced cell proliferation, whereas NNMT overexpression promoted cell growth moderately. Knocking down NNMT also significantly suppressed the migration and invasion capacities of PANC-1 cells. Conversely, NNMT upregulation enhanced cell migration and invasion capacities. In addition, NNMT knockdown cells were much less resistant to glucose deprivation and rapamycin as well as glycolytic inhibitor 2-deoxyglucose whereas NNMT-expressing cells showed opposite effects although the effects were not so striking.

Conclusions

These data sugguest that NNMT plays an important role in PANC-1 cell proliferation, metastatic potential and survival under metabolic stress.