A Negative Feedback Loop Between NAMPT and TGF-β Signaling Pathway in Colorectal Cancer Cells

Nicotinamide phosphoribosyltransferase (NAMPT) and the transforming growth factor-β (TGF-β) signaling pathway play important roles in colorectal tumorigenesis and progress. However, the underlying regulatory mechanisms between NAMPT and TGF-β signaling in colorectal cancer (CRC) remain poorly understood.

Public data were extracted from the Oncomine database and the PrognoScan database to investigate the mRNA expression and the prognostic value of NAMPT, respectively, in CRC. Western blot tests were performed to detect Smad2, Smad3, p-Smad2, p-Smad3, Smad4 expression in CRC cells transfected with human NAMPT-siRNA or NAMPT-overexpressing plasmid. TGF-β1 concentrations in culture supernatants were assayed using ELISA kits. The effect of TGF-β1 on NAMPT expression was evaluated by quantitative real-time PCR and Western blot. The dual-luciferase reporter assay was employed to confirm the binding of miR-1-3p to NAMPT 3'-UTR. Subsequently, NAMPT levels in HCT116 cells transfected with the mimics and inhibitors of miR-1-3p were detected by quantitative real-time PCR and Western blot.

NAMPT was overexpressed in human CRC and was correlated with short overall survival. NAMPT increased the protein expression levels of components in the TGF-β signaling pathway including Smad2, Smad3, and Smad4. Moreover, NAMPT promoted TGF-β1 secretion. Intriguingly, the TGF-β1 treatment down-regulated NAMPT expression at mRNA and protein levels in CRC cells which were partly through the up-regulation of miR-1-3p that directly bound to the NAMPT 3'-UTR. These outcomes demonstrated that NAMPT was a downstream target of miR-1-3p and there was a negative association between NAMPT and miR-1-3p in CRC.

There is a negative feedback loop between NAMPT and the TGF-β signaling pathway in CRC cells, providing new insight into the mechanism underlying the regulatory pathways in CRC.