Kastner P, Bocquel M T, Turcotte B, Garnier J M, Horwitz K B, Chambon P, Gronemeyer H
Laboratoire de Génétique Moléculaire des Eucaryotes, Centre National de la Recherche Scientifique Unité 184 de Biologie Moléculaire et de Génie Génétique, Strasbourg, France.
J Biol Chem. 1990 Jul 25;265(21):12163-7.
Two isoforms (A and B) of the human (hPR) and chicken (cPR) progesterone receptors originate from a single PR gene. cPR form A results from initiation of translation at a downstream ATG codon (ATG2) which in the cPR cDNA-deduced open reading frame is found 128 amino acids C-terminal to and in-frame with the first ATG codon (ATG1) that gives rise to form B. Our recent observation of an abundant cPR mRNA which encodes only form A suggested to us that the two isoforms are translated from different transcripts (Jeltsch, J. M., Turcotte, B., Garnier, J. M., Lerouge, T., Krozowski, Z., Gronemeyer, H., and Chambon, P. (1990) J. Biol. Chem. 265, 3961-3974). This view is, however, at variance with data obtained by transient transfection with expression vectors containing most of the cPR cDNA (downstream of nucleotide +53) since both isoforms were generated in transiently transfected COS cells (Conneely, O. M., Kettelberger, D. M., Tsai, J. J., Schrader, W. T., and O'Malley, B. W. (1989) J. Biol. Chem. 264, 14062-14064). To further support our above conclusion, vectors containing either hPR or cPR cDNAs were introduced into HeLa and COS-1 cells. Only hPR form B originated from a vector containing the entire cDNA (containing nucleotides 1 to approximately 4400), and form A was produced only from a vector expressing hPR transcripts (nucleotides 814 to approximately 4400) lacking ATG1. Vectors expressing the 5'-untranslated and coding region of the cPR mRNA (nucleotides 29-2921) generated only traces of form A in the two cell lines. Similar traces of form A were observed in COS-1 cells transfected with a vector lacking the 5'-untranslated region. Collectively, these results do not support the hypothesis that similar amounts of the two PR isoforms are generated by alternative initiation of translation on a single PR transcript. We discuss data indicating that for hPR and cPR, isoforms A and B are in fact translated from different mRNAs.
人（hPR）和鸡（cPR）孕酮受体的两种亚型（A和B）源自单一的PR基因。cPR A亚型是由下游ATG密码子（ATG2）起始翻译产生的，在cPR cDNA推导的开放阅读框中，该密码子位于产生B亚型的第一个ATG密码子（ATG1）的C端128个氨基酸处，且读码框一致。我们最近观察到一种仅编码A亚型的丰富的cPR mRNA，这使我们推测这两种亚型是从不同的转录本翻译而来的（耶尔茨克，J.M.，图尔科特，B.，加尼尔，J.M.，勒鲁热，T.，克罗佐夫斯基，Z.，格罗内迈尔，H.，以及尚邦，P.（1990年）《生物化学杂志》265卷，3961 - 3974页）。然而，这一观点与用包含大部分cPR cDNA（核苷酸 +53下游）的表达载体进行瞬时转染所获得的数据不一致，因为在瞬时转染的COS细胞中产生了两种亚型（康奈利，O.M.，凯特尔伯格，D.M.，蔡，J.J.，施拉德，W.T.，以及奥马利，B.W.（1989年）《生物化学杂志》264卷，14062 - 14064页）。为了进一步支持我们上述结论，将包含hPR或cPR cDNA的载体导入HeLa和COS - 1细胞。只有hPR B亚型源自包含完整cDNA（包含核苷酸1至约4400）的载体，而A亚型仅由表达缺失ATG1的hPR转录本（核苷酸814至约4400）的载体产生。表达cPR mRNA的5' - 非翻译区和编码区（核苷酸29 - 2921）的载体在这两种细胞系中仅产生痕量的A亚型。在用缺失5' - 非翻译区的载体转染的COS - 1细胞中也观察到了类似痕量的A亚型。总体而言，这些结果不支持在单一PR转录本上通过可变起始翻译产生等量的两种PR亚型这一假说。我们讨论了表明对于hPR和cPR，A和B亚型实际上是从不同mRNA翻译而来的数据。
