Southampton Cancer Research UK Centre (MP824), University of Southampton School of Medicine, Southampton General Hospital, Southampton SO16 6YD, UK.
Biol Cell. 2010 Jan;103(1):1-19. doi: 10.1042/BC20100067.
CtBPs [C-terminal (of E1A) binding protein] have roles in the nucleus as transcriptional co-repressors, and in the cytoplasm in the maintenance of vesicular membranes. CtBPs are expressed from two genes, CTBP1 and CTBP2, mRNA products of which are alternatively spliced at their 5'-ends to generate distinct protein isoforms. Extensive molecular and cellular analyses have identified CtBPs as regulators of pathways critical for tumour initiation, progression and response to therapy. However, little is known of the expression or regulation of CtBP isoforms in human cancer, nor of the relative contributions of CTBP1 and CTBP2 to the tumour cell phenotype.
Expression of CtBP proteins and CTBP1 and CTBP2 mRNA splice forms in breast cancer cell lines and tumour tissue was examined. CtBP1 proteins are identifiable as a single band on Western blots and are ubiquitously detectable in breast tumour samples, by both Western blotting and immunohistochemistry. CtBP1 is present in six of six breast cancer cell lines, although it is barely detectable in SKBr3 cells due to reduced CTBP1 mRNA expression. In the cell lines, the predominant CTBP1 mRNA splice form encodes CtBP1-S protein; in tumours, both major CTBP1 mRNA splice forms are variably expressed. CtBP2 proteins are ubiquitously expressed in all lines and tumour samples. The predominant CTBP2 mRNA encodes CtBP2-L, although an alternatively spliced form that encodes CtBP2-S, previously unidentified in humans, is expressed at low abundance. Both CtBP2-L and CtBP2-S are readily detectable as two distinct bands on Western blots; here we show that the CTBP2-L mRNA is translated from two AUG codons to generate both CtBP2-L and CtBP2-S. We have also identified an autoregulatory feedback mechanism whereby CtBP protein abundance is maintained in proliferating breast cancer cells through the post-transcriptional regulation of CtBP2. This feedback is disrupted by UV-C radiation or exposure to cisplatin. Finally, we demonstrate that CtBP1 and CtBP2 both have p53-dependent and -independent roles in suppressing the sensitivity of breast cancer cells to mechanistically diverse cancer chemotherapeutic agents.
These studies support recent evidence that CtBP family proteins represent potential targets for therapeutic strategies for the treatment of cancer in general, and breast cancer in particular.
CtBPs（E1A 羧基末端结合蛋白）在核内作为转录共抑制因子发挥作用，并在细胞质中维持囊泡膜。CtBPs 由两个基因 CTBP1 和 CTBP2 表达，其 mRNA 产物在 5'端被选择性剪接，生成不同的蛋白异构体。广泛的分子和细胞分析表明，CtBPs 是肿瘤起始、进展和对治疗反应的关键途径的调节剂。然而，人们对 CtBP 异构体在人类癌症中的表达或调节知之甚少，也不知道 CTBP1 和 CTBP2 对肿瘤细胞表型的相对贡献。
在乳腺癌细胞系和肿瘤组织中检测了 CtBP 蛋白和 CTBP1 和 CTBP2 mRNA 剪接形式的表达。CtBP1 蛋白在 Western 印迹上可识别为单一条带，并通过 Western 印迹和免疫组织化学在乳腺癌样本中普遍存在。CtBP1 存在于六种乳腺癌细胞系中，但由于 CTBP1 mRNA 表达减少，在 SKBr3 细胞中几乎检测不到。在细胞系中，主要的 CTBP1 mRNA 剪接形式编码 CtBP1-S 蛋白；在肿瘤中，两种主要的 CTBP1 mRNA 剪接形式均可变表达。CtBP2 蛋白在所有细胞系和肿瘤样本中普遍表达。主要的 CTBP2 mRNA 编码 CtBP2-L，但以前在人类中未发现的另一种剪接形式 CtBP2-S 以低丰度表达。CtBP2-L 和 CtBP2-S 都可以在 Western 印迹上很容易地检测到两条不同的带；在这里，我们表明 CTBP2-L mRNA 从两个 AUG 密码子翻译生成 CtBP2-L 和 CtBP2-S。我们还发现了一种自身反馈机制，通过这种机制，CtBP 蛋白丰度在增殖的乳腺癌细胞中通过 CtBP2 的转录后调节得以维持。这种反馈被 UV-C 辐射或顺铂暴露破坏。最后，我们证明 CtBP1 和 CtBP2 都具有 p53 依赖性和非依赖性作用，可抑制乳腺癌细胞对机制不同的癌症化疗药物的敏感性。
这些研究支持了最近的证据，即 CtBP 家族蛋白代表了治疗癌症的一般治疗策略的潜在靶点，尤其是乳腺癌。
