Growth hormone (GH) induces the formation of protein complexes involving Stat5, Erk2, Shc and serine phosphorylated proteins

The aim of this study was to investigate the interaction of Stat5 with hey effector proteins Erk2 and She after activation by growth hormone (GH), usi ng Chinese Hamster Ovary (CHO) cells stably expressing the wild type rabbit growth hormone receptor (GHR). In coimmunoprecipitation experiments. we sh ow GH-induced formation of complexes consisting of Stat5a and Erk?, and Sta t5a and Stat5b association with the protein adaptor. She. In CI-IO cells tr eated with GH, a rapid association of tyrosine and serine phosphorylated Sl at5a with activated Erk2 is observed. In contrast, She proteins interact wi th non-phosphorylated forms of Stat5. Using truncated and tyrosine mutants of the GI-TR, we identify a carboxy-terminal domain of the receptor, which is critical for serine phosphorylation of Stat5a and Stat5a/Erk2 complex Fo rmation. In addition, tyrosine residues of this region of the GHR are not r equired for Stat5/Erk2 interaction but are essential for Stat5a serine phos phorylation, Moreover, we detect serine phosphorylated proteins associated with Erk2, She and Stat5: both Stat5 isoforms interact with ii serine phosp horylated protein of 63 kDa, which is shown to be related to the serine-thr eonine kinase Akt-1. Our results support the importance of serine phosphory lation cascades in GH signaling and open another pathway of GH signal trans duction. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.