Neurotrophic interrelation between neuron and glia Molecular mechanism of a new glia-derived neurotrophic factor, gliostatin

Gliostatin是由Asai和Kato从人神经纤维瘤中纯化的神经胶质生长抑制因子。最近，我们已经证明其核苷酸序列与从人血小板中纯化的血小板衍生内皮细胞生长因子（PD-ECGF）的核苷酸序列完全相同。Gliostatin/PD-ECGF是一种Mr=100,000的多肽，具有同源二聚体结构，包括两个50 kda的亚基，其中一个含有482个氨基酸，但不含碳水化合物部分。氨基端没有信号序列，这是蛋白质分泌出细胞[5]所必需的。然而，已证实gliostatin/PD-ECGF具有多种生物学作用，但缺乏分泌信号序列，如1)体外对内皮细胞的趋化活性，2)体内血管生成活性，3)体外胶质细胞分化和神经营养活性，包括神经元存活活性和神经生成活性，以及4)体内关节生成活性。除了对胶质抑制素/PD-ECGF功能的分子机制了解较多外，对其基因表达的调控以及在人体组织中的分布和含量却知之甚少。缺乏信号序列的胶质抑制素/PD-ECGF是否在生理条件下细胞外分泌尚不清楚。因此，我们目前利用人肿瘤细胞系，通过敏感酶免疫分析法（EIA）研究胶质抑制素/PD-ECGF的组织特异性分布，并诱导其蛋白合成和与其分泌相关的基因表达。Gliostatin/PD-ECGF在人体组织和器官中普遍存在，在消化系统（食道和直肠）、脑、脾、膀胱和肺组织中含量较高，而在胆囊、主动脉、肌肉、脂肪和肾脏中含量较低。某些肿瘤细胞（A431和MKN74）似乎将其释放到条件培养基中。gliostation/PD-ECGF在表皮样癌细胞（A431）和胃癌细胞（MKN45）中表达是由二丁基环AMP和磷酯诱导的，而在MKN45中是由氢化可的松诱导的。特别是，这种氢化可的松特异性地引起MKN74的明显分泌增加，而没有细胞毒性作用，这表明可能在限制性而非通用细胞系中分泌胶质抑制素/PD-ECGF。少

Gliostatin is an scidic protein purified from human neurofibroma as glial growth inhibitory factor by Asai and Kato. Lately, we have demonstrated that its nucleotide sequence is completely identical to that of platelet-derived endothelial cell growth factor (PD-ECGF), which was purified from human platelets. Gliostatin/PD-ECGF is polypeptides of Mr=100,000 with a homodimeric structure comprising two 50-kDa subunits, one of which contains 482 amino acids but not carbohydrate moiety. The amino terminus has no signal sequence which is necessary for a protein to be secreted out of cells [5]. However, it has been confirmed that gliostatin/PD-ECGF has varied biological actions, but lacked the secretory signal sequence, such as 1) chemotactic activity for endothelial cells in vitro, 2) angiogenic activity in vivo, 3) glial differentiative and neurotrophic activities including neuronal surviving activity and neuritogenic activity in vitro, and 4) arthritogenic activity in vivo.Apart from much … More information of the molecular mechanism of its functions, little is known about the regulation of gene expression as well as the human tissue distribution and content of gliostatin/PD-ECGF in detail. And it is also not clear yet whether gliostatin/PD-ECGF lacking a signal sequence is extracellularly secreted in physiological conditions or not. Therefore, we have currently investigate the tissue-specific distribution of gliostatin/PD-ECGF by sensitive enzyme immunoassay (EIA), and the induction of its protein synthesis and gene expression with relevance to its secretion, using human tumor cell lines. Gliostatin/PD-ECGF was found to distribute in rather ubiquitous than specific human tissues and organs, with a relatively high levels in the tissues of digestive system (esophagus and rectum), brain, spleen, bladder and lung, but not in gall bladder, aorta, muscle, fat and kidney. Certain tumor cells (A431 and MKN74) appeared to release it into the conditioned medium. Expression of gliostation/PD-ECGF in epidermoid carcinoma cell (A431) and stomach cancer cell (MKN45) was induced by dibutyryl cyclic AMP and phorbol ester, and uniquely in MKN45 by hydrocortisone. In particular, this hydrocortisone specifically saused an increase of the apparent secretion of MKN74 without its cytotoxic effects, suggesting a possible secretion of gliostatin/PD-ECGF in the restricted but not universal cell line. Less