Albi Elisabetta, Cataldi Samuela, Bartoccini Elisa, Magni Mariapia Viola, Marini Francesca, Mazzoni Francesca, Rainaldi Giuseppe, Evangelista Monica, Garcia-Gil Mercedes
Department of Clinic and Experimental Medicine, Physiopathology, Policlinico Monteluce, Perugia, Italy.
J Cell Physiol. 2006 Jan;206(1):189-95. doi: 10.1002/jcp.20448.
Sphingomyelin (SM) cycle has been involved in the regulation of proliferation, differentiation, and apoptosis. Increases in ceramide have been found after a larger number of apoptotic stimuli including cytokines, cytotoxic drugs, and environmental stresses. Accumulating evidence suggest that the subcellular localization of ceramide generation is a critical factor in determining the cellular behavior. Since recently enzymes involved in ceramide metabolism such as sphingomyelinase, SM synthase, sphingosine kinase and ceramidase have been found in the nucleus of hepatocyte cells, we have studied first the presence and the physicochemical characteristics of SM metabolism enzymes in nuclei isolated from embryonic hippocampal cells (cell line HN9.10e). The activities of sphingomyelinase and SM-synthase have been assayed and the ceramide production evaluated at different times after serum deprivation in these neurones cultivated in serum-deficient medium. We report that both enzymes are present in the nucleus of embryonic hippocampal cells and differ from those present in the homogenate in optimum pH. After serum deprivation, that induces a time-dependent decrease in cell viability and increase of the cell percentage in G1 phase of the cell cycle, a nuclear sphingomyelinase activation together with SM-synthase inhibition and a consequent increase of nuclear ceramide pool have been demonstrated. No similar enzyme activity modifications in homogenate have been identified. The possible role of nuclear sphingomyelinase/sphingomyelin-synthase balance in serum deprivation-induced apoptosis in the embryonic hippocampal cell is discussed.
鞘磷脂（SM）循环参与了细胞增殖、分化和凋亡的调节。在包括细胞因子、细胞毒性药物和环境应激等大量凋亡刺激后，已发现神经酰胺增加。越来越多的证据表明，神经酰胺生成的亚细胞定位是决定细胞行为的关键因素。由于最近在肝细胞的细胞核中发现了参与神经酰胺代谢的酶，如鞘磷脂酶、SM合成酶、鞘氨醇激酶和神经酰胺酶，我们首先研究了从胚胎海马细胞（细胞系HN9.10e）分离的细胞核中SM代谢酶的存在情况及其物理化学特性。在缺乏血清的培养基中培养的这些神经元中，测定了鞘磷脂酶和SM合成酶的活性，并在血清剥夺后的不同时间评估了神经酰胺的产生。我们报告，这两种酶都存在于胚胎海马细胞的细胞核中，并且在最适pH值方面与匀浆中的酶不同。血清剥夺后，这会导致细胞活力随时间下降以及细胞周期G1期细胞百分比增加，已证明细胞核鞘磷脂酶激活以及SM合成酶抑制，进而导致细胞核神经酰胺池增加。在匀浆中未发现类似的酶活性改变。本文讨论了细胞核鞘磷脂酶/鞘磷脂合成酶平衡在血清剥夺诱导的胚胎海马细胞凋亡中的可能作用。
