Anticancer Res. 2013 Aug;33(8):3047-52.

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

 

Junaid Ansari MD1, Elba A Turbat-Herrera MD2, James Cotelingam MD2, Rodney E Shackelford DO, Ph.D.2*

1Feist Weiller Cancer Center, Shreveport, LA, USA

2Department of Pathology, LSU Health Shreveport, Shreveport, LA, USA

*Corresponding Author

 

ABSTRACT

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 mitochondrial deacetylase which functions in conjunction with 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); i.e., 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.

KEYWORDS: Follicular carcinoma; NAD+; SIRT3; nicotinamide phosphoribosyltransferase; papillary carcinoma

PMID: 23898059

 

SUPPLEMENT

The study by Shackelford et al. focused on the increased expression of Nampt and SirT3 in well-differentiated thyroid carcinomas. Intracellular Nampt is overexpressed in nearly twenty different human malignancies (1). Within cells Nampt catalyses NAD+ synthesis by transferring the phosphoribosyl group of 5-phosporibosyl-1-pyrophosphate to nicotinamide, forming nicotinamide mononucleotide (NMN). NAD+ synthesis is completed by NMN adenylyltransferase (Nmnat), which converts NMN into NAD+ (2). Nampt catalytic activity is ~46-fold lower than that of Nmnat, so small changes in Nampt protein levels, but not Nmnat levels, profoundly effects NAD+ metabolism and NAD-dependent events (2, 3). Increased NAD+ is known to promote malignant progression via increasing the activities of SirT1, CD38, CtBP1 and 2, and PARP-1. Each of these proteins function by degrading NAD+ into an ADP-ribose moiety and nicotinamide. Thus, high Nampt levels are required to synthesize the NAD+ needed for the malignancy-promoting actions of these proteins. SirT1 activity attenuates p53, PTEN, and retinoblastoma activities, stabilizes N-Myc, and promotes the epithelial to mesenchymal transition, while increasing cell migration. CtBP1 and 2 activities promote invasive behaviors in malignant cells, while suppressing apoptosis and several tumor suppressor genes. PARP-1 is overexpressed in many malignancies and its inhibition lowers cancer cell viability. CD38 regulates cell adhesion, calcium signaling, and signal transduction. Its role in cancer is poorly understood (Figure 1, for review 1).

Thyroid carcinomas are the most common endocrine malignancies, accounting for almost 95% of the total new endocrine cancers. Based on cancer statistics, 62,450 estimated new cases of thyroid cancer will be diagnosed in 2015 with a total of 2,890 estimated deaths due to the disease (4) Well-differentiated thyroid carcinomas (TCs) are mainly classified into papillary thyroid carcinoma (PTC) (most common), follicular carcinoma (FC) and Hurthle cell (oxyphillic; oncocytic) carcinoma (HCC). There are 7 different prognostic schemes and the most common and important prognostic factors in these schemes include age, extrathyroidal invasion and distant metastatic lesions (5). In the current times molecular markers like BRAF, RET/PTC and RAS are also being studied as indicators of prognosis (6, 7). The overall prognosis of well-differentiated thyroid carcinomas (TCs) is good with favorable long term survival in localized thyroid disease. Distant metastases at the time of presentation is a strong predictor of very poor outcome (8). The workup mainly includes thyroid function studies, thyroid suppression test, thyroid ultrasound and fine-needle aspiration biopsy (FNAB). In conjunction with standard imaging techniques like MRI and CT scanning, 18FDG-PET is increasingly being performed during initial as well as subsequent evaluation of patients with well-differentiated thyroid carcinomas (TCs) detecting skip metastases and reflecting risk of recurrence and prognosis. (9). Surgery is the main stay of treatment. Postoperative radioactive ablation and TSH suppression are being used as adjuncts in selected patients. Loco-regional or metastatic disease is managed with surgical excision in potentially curable patients, 131I therapy and external beam irradiation. Systemic therapies (such as cytotoxic chemotherapy or kinase inhibitors) are mainly considered in metastases and have shown to improve progression free survival in selected clinical trials. In loco-regional disease systemic therapy is only employed after all surgical and radiation therapy options have been exhausted. (10)

The molecular pathogenesis of thyroid cancer especially well-differentiated thyroid carcinomas (TCs) has been a recent field of interest owing to the discovery of genetic and epigenetic alterations, mainly involving the activation of RET-RAS-BRAF signaling pathway. BRAF mutations are the most common genetic alteration seen in PTCs and involves the activation of MAPK cascade which is critical for tumor development. The PI3K-AKT pathway have also a functional role in sporadic thyroid tumorigenesis. This was revealed by the increased expression and activation of AKT in thyroid cancers, especially FC (11). It has also been devised that simultaneous activation of MAPK and PI3K-AKT pathway becomes more frequent as the grade of thyroid tumors increases (12, 13). The identification of these driver mutations may provide a viable therapeutic target in future and have encouraged the development of BRAF inhibitors, MEK inhibitors, AKT and mTOR inhibitors. The simultaneous targeting of multiple signaling pathways may be a more effective way of treating these cancers especially in advanced stage and is a promising area in translational research in thyroid cancer. Sawicka-Gutaj et al. found that elevated expression of NAMPT is associated with more advanced tumor stage and metastatic disease. They suggested that NAMPT might be a molecular marker of poor prognosis and invasiveness. In their multiple comparison analysis, NAMPT expression was higher in cancers than in benign lesions and healthy tissues. It positively correlated with tumor stage and involvement of lymph nodes. They also found that NAMPT expression positively correlated with survivin splicing variant DEx3 whose overexpression is characteristic of aggressive thyroid cancers (7, 14). Many NAMPT inhibitors are already in research and development (APO866, GMX1777, and GMX1778).

The function of SirT3 in cancer is poorly understood. SirT3 is a mitochondrial NAD+-dependent histone deacetylase that exerts anti-cancer effects by destabilizing HIF-1a and promoting mitochondrial function and cell survival following genotoxin exposure. It also promotes carcinogenesis by attenuating p53 function and promoting metastasis (15, 16). In most studies SirT3 expression is cytoplasmic in benign tissue and is suppressed in malignancy (15-17). For example, Yang et al. found SirT3 cytoplasmic expression was suppressed in gastric cancer (17). We obtained the same results examining SirT3 in this malignancy (unpublished data). Our finding that SirT3 expression is increased in both the cytoplasm and nuclei of well-differentiated thyroid carcinomas indicates that: 1), SirT3 expression may be increased in malignancy, and 2) SirT3 expression can be nuclear and associated with malignancy.

Taken together the above data indicates that NAMPT and possibly SirT3 play an important role in well-differentiated thyroid cancer development and progression. Additionally, pharmacologic NAMPT inhibitors may potentially have therapeutic benefit in treating advanced thyroid cancers in future.

 

RS FIG1

Figure 1. Increased intracellular Nampt increases cellular NAD+ concentrations, increasing the activities of PARP-1, CD38, SirT1, and CtBP1 and 2, promoting malignancy (modified from 1). This present study indicates that SirT3 overexpression may also play a role in promoting malignancy in well-differentiated thyroid carcinoma.

 

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