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，通过靶向不同的蛋白，如激酶和磷酸酶，在细胞内信号转导中发挥关键作用。它们是由神经酰胺合成酶(CERs)合成的。到目前为止，已经描述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。已有研究表明，人乳腺癌组织CER2、CER4和CER6活性增强，其产物神经酰胺C16：0、C24：0和C24：1生成增加。在体外，雌激素处理MCF-7和MDA-MB-231细胞后，CER2、CER4和CER6的mRNA表达增加，但神经酰胺的表达没有类似的增加。转化生长因子-β处理的结肠癌细胞(HCT-116/Caco-2)也是如此。Caco-2细胞经转化生长因子处理后CERs基因表达增强，但与神经酰胺水平无关。此外，在MCF-7(乳腺癌)和HCT-116(结肠癌)细胞中神经酰胺合成酶4和6的过度表达伴随着短链神经酰胺C16：0、C18：0和C20：0的产生增加，并诱导这些细胞的凋亡。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，促进了细胞的增殖。在这一后续应用中，应研究转录、转录后和翻译后的机制，导致在转化生长因子-雌二醇处理后CERs在表达或活性水平上的诱导。此外，通过使用特定的抑制剂和分子生物学方法，应分析长链或超长链神经酰胺分别靶向的导致细胞凋亡或促进增殖的信号通路。最后，这些调查应该会阐明CER是否是开发新的化疗疗法的有用目标的问题。

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.