Bandyopadhyay Sucharita, Zhan Rui, Wang Ying, Pai Sudha K, Hirota Shigeru, Hosobe Sadahiro, Takano Yukio, Saito Ken, Furuta Eiji, Iiizumi Megumi, Mohinta Sonia, Watabe Misako, Chalfant Charles, Watabe Kounosuke
Department of Medical Microbiology and Immunology, Southern Illinois University School of Medicine, Springfield, Illinois, USA.
Cancer Res. 2006 Jun 1;66(11):5934-40. doi: 10.1158/0008-5472.CAN-05-3197.
Fatty acid synthase (FAS) has been found to be overexpressed in a wide range of epithelial tumors, including breast cancer. Pharmacologic inhibitors of FAS cause apoptosis of breast cancer cells and result in decreased tumor size in vivo. However, how the inhibition of FAS induces apoptosis in tumor cells remains largely unknown. To understand the apoptotic pathway resulting from direct inhibition of FAS, we treated breast tumor cells with or without FAS small interfering RNA (siRNA) followed by a microarray analysis. Our results indicated that the proapoptotic genes BNIP3, tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), and death-associated protein kinase 2 (DAPK2) were significantly up-regulated on direct inhibition of the FAS gene. We also found that the knockdown of FAS expression significantly increased ceramide level in the tumor cells, and this increase was abrogated by acetyl-CoA carboxylase inhibitor. In addition, carnitine palmitoyltransferase-1 (CPT-1) inhibitor up-regulated the ceramide and BNIP3 levels in these cells, whereas treatment of tumor cells with FAS siRNA in the presence of a ceramide synthase inhibitor abrogated the up-regulation of BNIP3 and inhibited apoptosis. Furthermore, we found that treatment of cells with BNIP3 siRNA significantly counteracted the effect of FAS siRNA-mediated apoptosis. Consistent with these results, a significant inverse correlation was observed in the expression of FAS and BNIP3 in clinical samples of human breast cancer. Collectively, our results indicate that inhibition of FAS in breast cancer cells causes accumulation of malonyl-CoA, which leads to inhibition of CPT-1 and up-regulation of ceramide and induction of the proapoptotic genes BNIP3, TRAIL, and DAPK2, resulting in apoptosis.
脂肪酸合酶（FAS）已被发现在包括乳腺癌在内的多种上皮肿瘤中过表达。FAS的药理抑制剂可导致乳腺癌细胞凋亡，并在体内使肿瘤体积减小。然而，FAS抑制如何诱导肿瘤细胞凋亡在很大程度上仍不清楚。为了了解直接抑制FAS所导致的凋亡途径，我们用或不用FAS小干扰RNA（siRNA）处理乳腺肿瘤细胞，随后进行微阵列分析。我们的结果表明，直接抑制FAS基因后，促凋亡基因BNIP3、肿瘤坏死因子相关凋亡诱导配体（TRAIL）和死亡相关蛋白激酶2（DAPK2）显著上调。我们还发现，FAS表达的敲低显著增加了肿瘤细胞中的神经酰胺水平，而这种增加被乙酰辅酶A羧化酶抑制剂消除。此外，肉碱棕榈酰转移酶-1（CPT-1）抑制剂上调了这些细胞中的神经酰胺和BNIP3水平，而在神经酰胺合酶抑制剂存在的情况下用FAS siRNA处理肿瘤细胞则消除了BNIP3的上调并抑制了凋亡。此外，我们发现用BNIP3 siRNA处理细胞显著抵消了FAS siRNA介导的凋亡作用。与这些结果一致，在人类乳腺癌临床样本中观察到FAS和BNIP3的表达呈显著负相关。总体而言，我们的结果表明，抑制乳腺癌细胞中的FAS会导致丙二酰辅酶A积累，从而导致CPT-1受抑制、神经酰胺上调以及促凋亡基因BNIP3、TRAIL和DAPK2的诱导，进而导致凋亡。
