Barcia M G, Castro J M, Jullien C D, Freire M
Departamento de Bioquimica e Bioloxia Molecular, Facultade de Bioloxia, Universidade de Santiago, Santiago de Compostela, Galicia, Spain.
J Biol Chem. 1993 Mar 5;268(7):4704-8.
Prothymosin alpha is a widely distributed polypeptide whose function, though unknown, seems to be related to cell proliferation. In vitro, it is a substrate for casein kinase-2. In this work, extracts of mitogenically stimulated murine splenic lymphocytes labeled with [32P] orthophosphate were found to contain [32P]prothymosin alpha. Phosphorylation activity was highly dependent on mitogenic activation with concanavalin A plus interleukin-2. While cells remained viable, phosphorylation increased with stimulation time in the presence of [32P]orthophosphate. Structural analysis showed that prothymosin alpha was phosphorylated at Thr residues located among its first 14 amino acids, whereas its in vitro phosphorylation by casein kinase-2 affects both Ser and Thr residues in this fragment, apparently in similar proportions. Thus, casein kinase-2 seems not to be responsible for the phosphorylation of prothymosin alpha in vivo. Prothymosin alpha was also found to be phosphorylated in proliferating murine thymocytes and HeLa cells; the phosphorylation sites were the same as in splenic lymphocytes, but the rate of phosphorylation was about 5 times lower. In thymocytes and subconfluent HeLa cells, the [32P]prothymosin alpha concentrations of the cytosolic and nuclear fractions were similar; in splenic lymphocytes, [32P]prothymosin alpha was found mostly in cytosol.
前胸腺素α是一种广泛分布的多肽，其功能尚不清楚，但似乎与细胞增殖有关。在体外，它是酪蛋白激酶-2的底物。在这项研究中，发现用[32P]正磷酸盐标记的经有丝分裂原刺激的小鼠脾淋巴细胞提取物中含有[32P]前胸腺素α。磷酸化活性高度依赖于伴刀豆球蛋白A加白细胞介素-2的有丝分裂原激活。在细胞保持存活的情况下，在[32P]正磷酸盐存在下，磷酸化随刺激时间增加。结构分析表明，前胸腺素α在其前14个氨基酸中的苏氨酸残基处被磷酸化，而其在体外被酪蛋白激酶-2磷酸化会影响该片段中的丝氨酸和苏氨酸残基，比例显然相似。因此，酪蛋白激酶-2似乎不是体内前胸腺素α磷酸化的原因。还发现前胸腺素α在增殖的小鼠胸腺细胞和HeLa细胞中被磷酸化；磷酸化位点与脾淋巴细胞中的相同，但磷酸化速率约低5倍。在胸腺细胞和亚汇合的HeLa细胞中，胞质和核部分的[32P]前胸腺素α浓度相似；在脾淋巴细胞中，[32P]前胸腺素α主要存在于胞质溶胶中。
