Nicotinamide phosphoribosyltransferase and SIRT3 expression are increased in well-differentiated thyroid carcinomas

Nicotinamide phosphoribosyltransferase (NAMPT) catalyzes the rate-limiting step of nicotinamide adenine dinucleotide (NAD(+)) synthesis. NAMPT expression promotes angiogenesis, DNA synthesis, cell growth and survival, and mitochondrial biogenesis and function. Sirtuin-3 (SIRT3) is an NAD(+)-dependent deacetylase which functions in conjunction with mitochondrial NAMPT to promote cell survival following genotoxic stress. NAMPT expression is increased in several human malignancies, while SIRT3 levels are increased in some malignancies and suppressed in others. Based on this, we hypothesized that NAMPT and SIRT3 expression might be increased in well-differentiated thyroid carcinomas (TCs), follicular carcinomas (FC) and papillary thyroid carcinomas (PTC). Immunohistochemical analysis for NAMPT and SIRT3 staining was performed on these tumors using tissue microarrays. NAMPT and SIRT3 expression was low in benign thyroid tissues, moderately increased in FC, and more highly expressed in PTC. Specifically we observed both NAMPT and SIRT3 to be highly expressed in well-differentiated TCs. The data suggest that mitochondrial alterations play a role in the development and maintenance of well-differentiated TC. Since an effective pharmacological NAMPT inhibitor is currently in clinical use, further studies of NAMPT overexpression in well-differentiated TCs may be useful in selecting patients for NAMPT inhibitor therapy, particularly for metastatic well-differentiated thyroid carcinomas refractory to other treatments.