| Research Abstract |
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
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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
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