Knauer D J, Smith G L
Proc Natl Acad Sci U S A. 1980 Dec;77(12):7252-6. doi: 10.1073/pnas.77.12.7252.
Multiplication-stimulating activity (MSA) produced by Buffalo rat liver cells (BRL-3A) in culture is related to the somatomedin family of growth regulatory polypeptides. MSA will stimulate glucose transport and DNA synthesis in normal chicken embryo fibroblasts (CEF) at concentrations of 10-200 ng/ml. MSA found in BRL-3A-conditioned medium, like the somatomedins in serum, does not exist as the free hormone but is bound to a specific high molecular weight carrier protein. In this report we demonstrate that purified MSA carrier protein (MCP) inhibits the biological activity of MSA on CEF as measured by the stimulation of glucose transport and DNA synthesis. In addition, purified MCP competitively inhibits the binding of 125I-labeled MSA to these cells. In control experiments in which insulin was used as the mitogenic agent, MCP had no effect on these biological responses. These results indicate that the inhibitory effect of MCP is the result of specific interaction with MSA and support the hypothesis that cells may be unresponsive to somatomedins bound to their serum carrier proteins.
水牛大鼠肝细胞（BRL-3A）在培养过程中产生的增殖刺激活性（MSA）与生长调节多肽的生长介素家族有关。MSA在浓度为10 - 200 ng/ml时可刺激正常鸡胚成纤维细胞（CEF）中的葡萄糖转运和DNA合成。在BRL-3A条件培养基中发现的MSA，与血清中的生长介素一样，不是以游离激素形式存在，而是与一种特定的高分子量载体蛋白结合。在本报告中，我们证明，通过刺激葡萄糖转运和DNA合成来衡量，纯化的MSA载体蛋白（MCP）可抑制MSA对CEF的生物学活性。此外，纯化的MCP竞争性抑制125I标记的MSA与这些细胞的结合。在以胰岛素作为促有丝分裂剂的对照实验中，MCP对这些生物学反应没有影响。这些结果表明，MCP的抑制作用是与MSA特异性相互作用的结果，并支持细胞可能对与其血清载体蛋白结合的生长介素无反应这一假说。
