Formation of STAT5-containing DNA Binding Complexes in Response to Colony-stimulating Factor-1 and Platelet-derived Growth Factor

Abstract

Colony-stimulating factor (CSF-1) activates several members belonging to the STAT (signal transducers and activators of transcription) family of transcription factors. We investigated the DNA binding complexes activated by CSF-1 in several cell lines and compared them with complexes activated by platelet-derived growth factor and interleukin 3. Our results indicate that the SIF-A complex activated by CSF-1 and platelet-derived growth factor may contain STAT3/STAT5 heterodimers binding to the high affinity SIF binding site, m67. In addition, both growth factors activate one or several STAT5-containing protein complexes binding to the prolactin-inducible element, PIE. The formation of these complexes was cell type and growth factor specific. Interleukin 3 activated only PIE binding complexes containing STAT5A and STAT5B and did not activate m67 binding complexes. It appears, therefore, that STAT5 cannot bind to m67 as a homodimer, but it can bind if it is dimerized with STAT3, whereas it can bind to the PIE element without being either complexed with STAT3 or any other known STAT protein, possibly as a homodimer or as STAT5A/STAT5B heterodimer. However, in addition, STAT5 may heterodimerize with other proteins and form novel PIE binding complexes.Over the past several years, a new group of transcription factors has been characterized and cloned (reviewed in Ref. 1). The first members of this family of transcription factors, known as STAT 1 proteins (signal transducers and activators of transcription) were identified as the factors mediating the response to IFN-␣ (2). Subsequently, it has been shown that a wide range of cytokines and growth factors lead to the activation of members of the STAT family. Thus far, six members of the family have been cloned. The STAT5 gene is the only one which has been duplicated (3). The levels of amino acid sequence identity between the different members of the STAT family range between about 50 and 18% (4). However, all known STAT proteins share several features, one SH2 and one SH3-like domain and one C-terminal tyrosine residue, which is phosphorylated upon activation. In addition, several of the STAT proteins require the phosphorylation of a C-terminal serine, located within a well conserved mitogen-activated protein kinase phosphorylation site, for DNA binding, and/or transactivation capacity (5-8). The mitogen-activated protein kinase phosphorylation site is present in STAT1, STAT3, and STAT4; however, the biological requirement for serine phosphorylation has, thus far, only been demonstrated for STAT1 and STAT3 (6).Binding of the STAT proteins to specific DNA sequences on the promoter of regulated genes requires prior dimerization, involving binding of a C-terminal phosphotyrosine of one STAT protein to the SH2 domain of the other. The formation of heterodimeric complexes has been observed, such as STAT1/ STAT2 binding to the interferon-␣/␤ response element via p48 (9), and STAT1/STAT3 binding to the sis-inducible element (SIE) (10). The composition of these complexes has bee...

Constitutive activation of FLT3 stimulates multiple intracellular signal transducers and results in transformation

“…In these reports, JAK 1, JAK 2, STAT 1, STAT 3 and /or STAT 5 were tyrosine-phosphorylated following receptor activation in response to EGF, PDGF, CSF-1 or SCF stimulation. [65][66][67][68][69][70] These studies, in conjunction with the findings reported here, imply a possible role for the JAK-STAT pathway in FLT3 receptor signaling. Whether this is a result of phosphorylation of JAKs by the activated receptor via a direct interaction of the two proteins or is indirect and results from phosphorylation and activation of other tyrosine kinases (eg SRC family members) or intermediate adaptor proteins is not known and will require further study.…”

Activation of Stat5 by platelet-derived growth factor (PDGF) is dependent on phosphorylation sites in PDGF β-receptor juxtamembrane and kinase insert domains

“…Stat5 was ®rst characterized in mammary gland tissue as a prolactin-inducible transcription factor (Wakao et al, 1994), but has been shown to be activated by numerous cytokines and growth factors in diverse cell types (Azam et al, 1995;Friedmann et al, 1996;Mui et al, 1995;Ru -Jamison et al, 1995;Gouilleux et al, 1995;Novak et al, 1996;. Two highly related Stat5 proteins, denoted Stat5a and Stat5b have been described, which are able to form homo-or heterodimers after phosphorylation.…”

Consequences of Stat6 deletion on Sis/PDGF- and IL-4-induced proliferation and transcriptional activation in murine fibroblasts

“…Stat1, 3 and 5 have also been shown to be activated by PDGF (Novak et al, 1996;Patel et al, 1996;Sadowski et al, 1993;Silvennoinen et al, 1993). Therefore, we investigated the consequences of deleting Stat6 on the activation of these other STAT family members.…”

“…Among the PDGF isoforms, PDGF BB is the human homolog of the v-sis oncogene product Doolittle et al, 1983;Water®eld et al, 1983). Jak1, Jak2 and Tyk2 (Vignais et al, 1996), as well as Stat1, Stat3 (Sadowski et al, 1993;Silvennoinen et al, 1993), Stat5 (Novak et al, 1996;Patel et al, 1996) and Stat6 (Patel et al, 1996) have been implicated among the many PDGFR downstream e ector molecules (Claesson-Welsh, 1996).…”