Epidermal growth factor induces the tyrosine phosphorylation and nuclear translocation of Stat 5 in mouse liver.

Abstract

Intraperitoneal injection of epidermal growth factor into mice results in the appearance of multiple tyrosine-phosphorylated proteins in liver nuclei within minutes after administration. We have previously identified three of these proteins as Stat la, Stat 113 (p91, p84), and Stat 3 (p89). In the present report we demonstrate that Stat 5 (p92), the recently described prolactin inducible transcription factor detected in mammary glands, is the major tyrosinephosphorylated protein translocated to the nucleus in mouse liver in response to epidermal growth factor. Furthermore, gel-shift analysis and affinity purification revealed that Stat 5, Stat la, and Stat 1p specifically bind to the prolactin inducible element upstream of the p-casein promoter.Epidermal growth factor (EGF) elicits a variety of biological responses when administered either to intact animals or added to cells growing in culture (1-3). These responses are mediated at the cell surface by the EGF receptor. Upon ligand binding, the intrinsic tyrosine kinase activity of the EGF receptor is augmented, resulting in its autophosphorylation, as well as the phosphorylation, of specific intracellular protein substrates (4-6). Some of these tyrosine-phosphorylated proteins are responsible for initiating signal transduction from the cell membrane to the nucleus and have been termed Stat (signal transducers and activators of transcription) proteins (7).The Stat proteins are members of a growing family of transcription factors that reside in the cytosol, are activated by tyrosine phosphorylation, and are translocated to the nucleus in response to various growth factors and cytokines. Stat la/1f3 (p91, p84) was shown to be tyrosine-phosphorylated and form specific binding complexes with the sis-conditioned medium inducible element (SIE) upstream of the c-fos promoter in response to both interferon y and EGF (8,9). Similarly, Stat 3 (p89) was shown to be tyrosine-phosphorylated and bind the SIE in response to both EGF and interleukin 6 or lipopolysaccharide (10,11). Recently, several reports have appeared that describe the induction in sheep mammary glands of DNA-binding activity specific for a prolactin (PRL)-inducible element (PIE). This PRL-induced DNA-binding activity was attributed to a 92-kDa protein that has been termed Stat 5 (or mammary gland factor) due to sequence homologies with conserved regions of known Stat proteins (12, 13).We previously reported that injection of EGF into mice leads to a rapid increase in the level of tyrosine phosphorylation of many proteins in all organs examined (14). Using this in situ system we were able to detect at least four tyrosinephosphorylated proteins (p92, p91, p89, and p84) in nuclear extracts from the livers of mice treated with EGF. Three of these proteins, p91, p89, and p84, were identified as Stat la, Stat 3, and Stat 1/3, respectively (8, 11). However, the identity of the major tyrosine-phosphorylated protein detected in the nucleus in response to EGF, p92, was unknown. In this report, we identify p92 ...

Mechanism of STAT3 Activation by Insulin-like Growth Factor I Receptor

“…Our results indicate that the in vivo protocol of IGF-I injection is effective in activating IGF-IR and its downstream signaling. A similar method has been used successfully to study substrate tyrosine phosphorylation in neonatal mice (45) as well as STAT5 tyrosine phosphorylation and nuclear translocation in mouse liver in response to EGF stimulation (46). We have chosen DBA mice here since we have previously demonstrated STAT5 activation by perfusion of insulin in liver (30).…”

The mouse waved-2 phenotype results from a point mutation in the EGF receptor tyrosine kinase.

“…In addition, GRB2, though apparently not a substrate of the EGFR tyrosine kinase, associates with phosphorylated receptors (Lowenstein et al 1992) serving as an SH2 adaptor protein in a ternary complex with Son of sevenless (SOS) that stimulates ras activity (Buday and Downward 1993;Chardin et al 1993;Egan et al 1993;Gale et al 1993;Li et al 1993;Rozakis-Adcock et al 1993). Another SH2 domaincontaining protein, SHC, associates with and is phosphorylated by EGFR in cultured cells ) and neonatal mouse tissues (Ruff-Jamison et al 1993) exposed to EGF. Furthermore, SHC also associates with GRB2 (Rozakis-Adcock 1992).…”

Requirement of STAT5b for sexual dimorphism of body growth rates and liver gene expression

“…Subsequently, two highly homologous STAT5 genes (17,18), STAT5a and STAT5b, were found to be expressed in a wide range of tissues (17)(18)(19)(20). These STATs can be activated by many growth factors and cytokines, including prolactin (21), GH (10,22,23), interleukins (20,24), epidermal growth factor (25,26), and erythropoietin (27). The high (Ϸ96%) sequence similarity between STAT5a and STAT5b suggests that there may be redundancy in their signaling pathways.…”