Physiological role of neonatal brain-derived carcinostatic factor(NBCF) during the ontogenesis

小鼠的大脑，在新生儿阶段，而不是在成年或胎儿阶段，分泌一种蛋白质，这种蛋白质比正常细胞更优先抑制恶性细胞的生长和DNA合成，因此被称为新生儿脑源性癌静态因子（NBCF）。在本研究中，NBCF是从培养的新生儿脑的条件培养基中制备的，并通过高效液相色谱法获得为均匀蛋白（62 kDa, PI 9.1）；NBCF的物理、化学和生物学特性不同于已知的脑蛋白。1,2-顺式二醇亲和柱保留NBCF，然后用d -山梨醇洗脱；用神经氨酸酶处理的NBCF失去了部分活性，但没有出现新的n端氨基酸，这表明活性显示需要聚糖部分。低剂量的tunicamycin可以抑制NBCF分泌，这一点得到了支持。NBCF不水解靶蛋白；多种蛋白酶抑制剂不能抵消NBCF的细胞毒性作用。NBCF的醚萃取物没有细胞毒性，而醚不溶性残留物保留了部分初始活性。固定化胰蛋白酶或二硫苏糖醇联合胍使NBCF失活的效果比两种药物都明显。因此，通过蛋白水解以外的作用介导的NBCF的细胞毒性表现归因于蛋白质原理，而不是蛋白质结合的亲脂配体，并且需要保留蛋白质构象和分子内埋藏的SS键。

The mouse brain, at the neonatal stage but not at the adult or fetal stage, secretes a protein, which inhibits growth and DNA synthesis of malignant cells preferentially over those of normal cells, and so is termed neonatal brain-derived carcino- static factor (NBCF). In the present study NBCF was prepared from conditioned medium of the neonatal brain cultured, and was obtained by HPLC as a homogeneous protein (62 kDa, PI 9.1); physics-chemical and biological properties of NBCF differ from those of cerebral proteins known. A 1,2-cis-diol affinity column retained NBCF, which was thereafter eluted with D-sorbitol; NBCF treated with neuraminidase lost part of activity without emergence of new N-terminal amino acids, suggesting glycan moieties required for the activity exhibition. This is supported by repression of NBCF secretion by tunicamycin of doses as low as is not cytotoxic. NBCF did not hydrolize target proteins; cytotoxic action of NBCF was not counteracted by a diversity of protease inhibitors. An ether-extract of NBCF was not cytotoxic whereas the ether-insoluble residuum retained part of the initial activity. NBCF was inactivated with immobilized trypsin or with dithiothreitol combined with guanidine more markedly than with either agent. Thus cytotoxicity exhibition of NBCF, mediated through actions other than proteolysis, is attributed to the proteinic principle but not to protein-bound lipophilic ligands, and requires retention of the protein conformation and intramolecularly buried SS bonds.