Fatty acid synthase expression associated with NAC1 is a potential therapeutic target in ovarian clear cell carcinomas

Abstract

Background: This study examined the clinical significance of NAC1 and the expression level of its potential downstream target fatty acid synthase (FASN) in ovarian clear cell carcinomas (OCCCs), and evaluated the NAC1/FASN pathway as a potential therapeutic target.

Methods: NAC1 and FASN expression and NACC1 gene amplification were assessed in ovarian cancers by immunohistochemistry, fluorescence in situ hybridisation, and clinical data collected by a retrospective chart review. C75, a FASN inhibitor, was used to assess whether this pathway represented a therapeutic target in OCCC.

Results: High NAC1 expression was most frequent in clear cell tumours (40.0%:24/60). NACC1 gene amplification was identified in none of the 58 OCCCs. The frequency of NACC1 gene amplification was significantly higher in the high-grade serous histology than in the clear cell histology (P<0.01). NAC1 expression was significantly correlated with FASN expression in both OCCC samples and OCCC cell lines. Either high NAC1 expression or high FASN expression significantly correlated with shorter progression-free and overall survival (P=0.002 and 0.0048). NAC1 overexpression stimulated FASN expression, and NAC1 silencing using siRNA decreased FASN expression in OCCC cell lines. Profound growth inhibition was observed in C75-treated carcinoma cells with FASN overexpression when compared with the response in carcinoma cells without FASN expression.

Conclusion: These findings indicate that NAC1/FASN overexpression is critical to the growth and survival of a subset of OCCC. The FASN silencing by the C75-induced phenotypes depends on the expression status of the targeted cell line. Therefore, NAC1/FASN pathway-targeted therapy may benefit selected OCCC patients.

Figure 1

Immunoreactivity of NAC1 and FASN in OCCC tissues. (A, D) Showing H&E staining of corresponding tissues in upper and lower panels, respectively. (B) Intense NAC1 immunoreactivity is present in the nuclei of OCCC cells (upper centre panel). (C) Intense FASN immunoreactivity is present in the cytoplasm of OCCC cells (upper centre panel). (E, F) An OCCC case with negative staining of both NAC1 and FASN respectively.

Figure 2

(A, B) NAC1 overexpression tended to correlate with shorter progression-free/overall survival in patients with OCCC who received cytoreductive surgery, followed by a standard platinum-based chemotherapy regimen (P=0.119 and 0.318 respectively, log-rank test). (C) Kaplan–Meier survival analysis showing that high expression of FASN was associated with a shorter progression-free survival in comparison to low FASN expression in OCCCs (P=0.021, log-rank test). (D) Kaplan–Meier survival analysis showing that high FASN expression tended to correlate with a shorter overall survival than low FASN expression in OCCC (P=0.075, log-rank test). (E, F) Either high NAC1 or high FASN expression correlated with shorter progression-free/overall survival in OCCC (P=0.004 and 0.037 respectively, log-rank test).

Figure 3

(A) Western blot analysis showing higher expression levels of NAC1 protein in OV207, OVTOKO, and JHOC9 cells than in OVISE and ES2 cells. Western blot analysis showing a higher expression level of FASN protein in OV207, OVTOKO, and JHOC9 cells than in OVISE and ES2 cells in which FASN protein is not detectable. (B) NAC1 protein expression is significantly correlated with FASN protein expression in OCCC cell lines (r=0.877, P<0.01). (C) Gene expression analysis showing a significant reduction of FASN gene expression in NAC1 siRNA-treated cells compared with control siRNA-treated cells in OV207 and JHOC9 cell lines. *P<0.05. (D) Gene expression analysis showing a significant induction of FASN gene expression in NAC1-transfected cells compared with control vector-treated cells in ES2 cell line. *P<0.05. (E) Western blot analysis showing a reduction of FASN in C75-treated cells compared with control DMSO-treated cells in JHOC9 cell line. (F) C75 suppresses cell growth depending on FASN expression levels in ovarian clear cell carcinomas. *P<0.05.