Regulation of ceramide synthases in tumor cells and their effects on proliferation and apoptosis

神经酰胺是细胞膜的重要分子，在细胞内信号传导中起着关键作用，通过靶向不同的蛋白质，如激酶和磷酸酶。它们由神经酰胺合成酶（CerS）合成。到目前为止，已经报道了六种不同的哺乳动物cer (CerS1-6)，它们在组织表达水平和产生不同链长神经酰胺的特异性上存在差异。先前已经证明，人类乳腺癌组织中CerS 2、4和6的活性增加，同时它们的产物C16:0、C24:0和C24:1的生成也增加。在体外，用雌二醇处理MCF-7和MDA-MB-231细胞导致CerS 2、4和6的mrna表达增加，但神经酰胺的表达没有类似的增加。TGF-处理的结肠癌细胞（HCT-116/Caco-2）也是如此。TGF-处理后Caco-2细胞的CerS mrna表达水平升高，但与Caco-2细胞的神经酰胺水平无关。此外，可以证明神经酰胺合成酶4和6在MCF-7（乳腺癌）和HCT-116（结肠癌）细胞中的过表达伴随着短链神经酰胺C16:0、C18:0和C20:0的增加，并诱导这些细胞凋亡。而神经酰胺合成酶2的过表达导致C24:0-和C24:1-Cer的产生增加，促进了这些细胞的增殖。在后续的应用中，需要研究TGF-/雌二醇处理后诱导CerS表达或活性水平的转录、转录后和翻译后机制。此外，通过使用特异性抑制剂和分子生物学方法，应该分析长链或超长链神经酰胺分别导致细胞凋亡或促进细胞增殖的信号通路。最后，这些研究应该阐明一个问题，即CerS是否是开发新化疗疗法的有用靶点。

Ceramides are important molecules of membranes and are known to be key players in intracellular signaling by targeting different proteins like kinases and phosphatases. They are synthesized by ceramide synthases (CerS). So far, six different mammalian CerS (CerS1-6) have been described, which differ in their tissue expression level and their specificity to produce ceramides of various chain length. Previously, it has been demonstrated that human breast cancer tissue displays increased activity of CerS 2, 4, and 6, together with enhanced generation of their products, ceramides C16:0, C24:0, and C24:1. In vitro, treatment of MCF-7 and MDA-MB-231 cells with estradiol led to an increase in mRNA-expression of CerS 2,4 and 6 but not to an similarly increase in ceramides. The same was true for colon carcinoma cells (HCT-116/Caco-2) treated with TGF-. Caco-2 cells demonstrated an enhanced CerS mRNA-expression level after TGF- treatment which could not be correlated to the ceramide levels in these cells. Furthermore, it could be demonstrated that overexpression of ceramide synthases 4 and 6 in MCF-7 (breast cancer) and HCT-116 (colon cancer) cells was accompanied by elevated generation of short chain ceramides C16:0, C18:0 and C20:0 and induction of apoptosis in these cells. While overexpression of ceramide synthase 2 led to an increase in C24:0- and C24:1-Cer production and promoted proliferation of these cells. In this follow-up application transcriptional, post-transcriptional as well as post-translational mechanisms should be investigated leading to the induction of CerS on expression or activity level after TGF-/estradiol treatment. Furthermore, by using specific inhibitors and molecular biological methods, the signaling pathways should be analysed, that are targeted by long chain or very long chain ceramides leading to apoptosis or enhances proliferation, respectively. At the end, these investigations should shed light on the question, if CerS are useful targets for the development of new chemo therapeutics.