STAP-2/BKS, an Adaptor/Docking Protein, Modulates STAT3 Activation in Acute-phase Response through Its YXXQ Motif

Abstract

As a c-fms-interacting protein, we cloned a novel adaptor molecule, signal-transducing adaptor protein-2 (STAP-2), which contains pleckstrin homology-and Src homology 2-like (PH and SRC) domains and a prolinerich region. STAP-2 is structurally related to STAP-1/ BRDG1 (BCR downstream signaling-1), which we had cloned previously from hematopoietic stem cells. STAP-2 is a murine homologue of a recently identified adaptor molecule, BKS, a substrate of BRK tyrosine kinase. STAP-2 was tyrosine-phosphorylated and translocated to the plasma membrane in response to epidermal growth factor when overexpressed in fibroblastic cells. To define the function of STAP-2, we generated mice lacking the STAP-2 gene. STAP-2 mRNA was strongly induced in the liver in response to lipopolysaccharide and in isolated hepatocytes in response to interleukin-6. In the STAP-2 ؊/؊ hepatocytes, the interleukin-6-induced expression of acute-phase (AP) genes and the tyrosinephosphorylation level of STAT3 were reduced specifically at the late phase (6 -24 h) of the response. These data indicate that STAP-2 plays a regulatory role in the AP response in systemic inflammation. STAP-2 contains a YXXQ motif in the C-terminal region that is a potential STAT3-binding site. Overexpression of wild-type STAP-2, but not of mutants lacking this motif, enhanced the AP response element reporter activity and an AP protein production. These data suggest that STAP-2 is a new class of adaptor molecule that modulates STAT3 activity through its YXXQ motif.Tyrosine kinases play an important role in regulating cell growth, differentiation, and transformation. Activated receptor tyrosine kinases trans-phosphorylate several tyrosines in their cytoplasmic domains, which provide recognition sites for various adaptor and effector proteins in multiple signal transduction pathways (1, 2). These adaptor proteins utilize their Src homology-2 (SH2) 1 and SH3 domains to mediate the interactions that link different proteins involved in signal transduction. For example, the adaptor protein Grb2 links a variety of surface receptors to the Ras/MAP kinase signaling cascade. Grb2 interacts with activated receptor tyrosine kinases via its SH2 domain and recruits the guanine nucleotide-releasing factor, SOS (Son of Sevenless), close to its target protein, Ras, at the cell membrane. Phosphoinositide-3-OH kinase (PI3K) and phospholipase C␥ (PLC␥) are also recruited to receptor tyrosine kinases through their SH2 domains. Growth factor-induced membrane recruitment of signaling proteins is also mediated by a family of docking proteins. These docking proteins contain an N-terminal membrane-targeting domain, such as the PH domain, and C-terminal multiple tyrosine phosphorylation sites for recruiting SH2 domain-containing proteins. A significant effort has been made to search for novel adaptor and docking proteins, because these molecules will uncover the unique signal transduction and modulation mechanisms of receptor tyrosine kinases.Signal transducer and activator of transcription (STAT) fam...

Requirement of STAT3 activation for maximal collagenase-1 (MMP-1) induction by epidermal growth factor and malignant characteristics in T24 bladder cancer cells

“…An initial phosphorylation was quick and transient, while a secondary phosphorylation was late and prolonged at least 4 h. Biphasic phosphorylation was detectable in another cancer cell line and therefore not particular to T24 cells (data not shown). Recent study with hepatocytes showed that an adaptor protein, STAP-2, is necessary for the interleukin 6-induced phosphorylation of STAT3 at the late phase of the response (Minoguchi et al, 2003). The mechanism as to how EGF induces a biphasic activation of STAT3 is currently under investigation.…”

Leukemia inhibitory factor-induced phosphorylation of STAP-2 on tyrosine-250 is involved in its STAT3-enhancing activity

“…4A). Previously, we demonstrated mRNA expression of endogenous STAP-2 in LIF-treated M1 myeloid cells and murine macrophages [4].…”

“…Previous studies have demonstrated that STAP-2 is tyrosine-phosphorylated by several protein tyrosine kinases (PTKs), including Brk, v-src, Jak2, Syk and EGFR [4,5,12]. We identified four potential phosphorylation sites via substitution of tyrosine residues with phenylalanine ( Fig.…”

The protein content of an adaptor protein, STAP-2 is controlled by E3 ubiquitin ligase Cbl

“…Through these functional domains, STAP-2 can bind to a number of signaling molecules and regulate the activities of its binding partners. For example, STAP-2 interacts with STAT3 through its YXXQ motif [1] and with STAT5 through its PH and SH2-like domains [3], resulted in influencing their transcriptional activity. The SH2-like domain of STAP-2 binds to MyD88 and IKK-a/b, thereby modulating TLR4-mediated cytokine production and NFkB activation [4].…”

“…STAP-2 is tyrosine-phosphorylated by epidermal growth factor (EGF) in NIH-3T3 cells [1]. Cbl also plays a critical role in the EGF/EGF receptor signaling pathway [7,19].…”