Borror K C, Garabedian M J, DeFranco D B
Department of Biological Sciences, University of Pittsburgh, Pennsylvania 15260, USA.
Steroids. 1995 May;60(5):375-82. doi: 10.1016/0039-128x(94)00068-n.
Nucleocytoplasmic shuttling of glucocorticoid receptors (GRs) is disrupted in v-mos-transformed cells leading to the redistribution of hormone-bound receptors from the nuclear to cytoplasmic compartments. We show here that GRs from v-mos-transformed cells are hyperphosphorylated on a specific peptide and maintain hormone-induced phosphorylations upon a prolonged hormone treatment that is associated with disruptions in its nucleocytoplasmic shuttling. Since similar effects on GR nucleocytoplasmic shuttling and phosphorylation were exerted upon treatment of nontransformed cells with the protein phosphatase inhibitor okadaic acid, we examined whether hyperphosphorylation of GRs in v-mos-transformed cells resulted from inhibition of receptor dephosphorylation. Protein phosphatase activity, measured using various substrates in vitro, was identical in cell-free extracts prepared from v-mos-transformed and nontransformed cells. Analysis of phosphate turnover in vivo from either the sum of all GR phosphorylation sites or from individual sites using pulse-chase analysis, did not reveal any significant difference between v-mos-transformed cells versus nontransformed cells. Thus, hyperphosphorylation of GR in v-mos-transformed cells does not appear to result from inhibition of GR dephosphorylation, but rather from stimulation of GR phosphorylation.
糖皮质激素受体（GRs）的核质穿梭在v-mos转化细胞中受到破坏，导致激素结合受体从细胞核重新分布到细胞质区室。我们在此表明，来自v-mos转化细胞的GRs在特定肽段上过度磷酸化，并且在长时间激素处理后维持激素诱导的磷酸化，这与核质穿梭的破坏有关。由于用蛋白磷酸酶抑制剂冈田酸处理未转化细胞会对GR核质穿梭和磷酸化产生类似影响，我们研究了v-mos转化细胞中GRs的过度磷酸化是否源于受体去磷酸化的抑制。使用各种底物在体外测量的蛋白磷酸酶活性，在从v-mos转化细胞和未转化细胞制备的无细胞提取物中是相同的。使用脉冲追踪分析对所有GR磷酸化位点总和或单个位点的体内磷酸盐周转进行分析，未发现v-mos转化细胞与未转化细胞之间有任何显著差异。因此，v-mos转化细胞中GR的过度磷酸化似乎不是由GR去磷酸化的抑制引起的，而是由GR磷酸化的刺激引起的。
