SHP2 and cbl participate in α-chemokine receptor CXCR4–mediated signaling pathways

Abstract

Stromal cell-derived factor (SDF)-1␣ and its receptor, CXCR4, play an important role in cell migration, embryonic development, and human immunodeficiency virus infection. However, the cellular signaling pathways that mediate these processes are not fully elucidated. We and others have shown that the binding of SDF-1␣ to CXCR4 activates phosphatidylinositol-3 kinase (PI-3 kinase), p44/42 mitogen-associated protein kinase, and the transcription factor nuclear factor-B, and it also enhances the tyrosine phosphorylation and association of proteins involved in the formation of focal adhesions. In this study, we examined the role of phosphatases in CXCR4-mediated signaling pathways. We observed significant inhibition of SDF-1␣-induced migration by phosphatase inhibitors in CXCR4-transfected pre-B lymphoma L1.2 cells, Jurkat T cells, and peripheral blood lymphocytes. Further studies revealed that SDF-1␣ stimulation induced robust tyrosine phosphorylation in the SH2-containing phosphatase SHP2. SHP2 associated with the CXCR4 receptor and the signaling molecules SHIP, cbl, and fyn.Overexpression of wild-type SHP2 increased SDF-1␣-induced chemotaxis. Enhanced activation of fyn and lyn kinases and the tyrosine phosphorylation of cbl were also observed. In addition, SDF-1␣ stimulation enhanced the association of cbl with PI-3 kinase, Crk-L, and 14-3-3␤ proteins. Our results suggest that CXCR4-mediated signaling is regulated by SHP2 and cbl, which collectively participate in the formation of a multimeric signaling complex. ( IntroductionChemokines and their receptors play important roles in immune and inflammatory responses through the regulation of cell migration and growth. In addition, chemokines participate in the pathogenesis of several diseases. [1][2][3][4][5] Chemokine receptors act as coreceptors for the human immunodeficiency virus (HIV), and the expression of both chemokines and chemokine receptor homologues by Kaposi's sarcoma herpes virus (KSHV/HHV-8) has been implicated in the development of Kaposi's sarcoma. 6,7 The ␣-chemokine, stromal cell-derived factor (SDF), is a widely expressed ligand of the CXCR4 receptor. [8][9][10][11] It is a potent chemotactic factor for mature leukocytes such as monocytes and T lymphocytes as well as for CD34 ϩ progenitors. 12-14 CXCR4 is a 7-transmembrane G protein-coupled receptor that is expressed by a variety of cells, including peripheral blood lymphocytes (PBLs), monocytes, thymocytes, pre-B cells, dendritic cells, and endothelial cells. 15-17 CXCR4 serves as a coreceptor for T-cell tropic HIV-1 strains and plays an important role in HIV pathogenesis. 1,17,18 In addition, CXCR4 and SDF-1␣ are critical for embryonic development. Targeted disruption of either protein leads to severe defects in mice embryos that are lethal. [19][20][21][22] Although CXCR4 and/or SDF-1␣ play important roles in both physiologic and pathologic processes, the cellular signaling pathways that mediate these effects are not fully elucidated.Previously, we and others have shown that the association of...

The tyrosine phosphatase SHP‐2 regulates differentiation and apoptosis of individual primary T lymphocytes

“…The interaction between SHP-2 and c-Cbl has been described earlier [44,45], but effects of this interaction for T cell function has not been shown to date. Potential target molecules of SHP-2/Cbl complex in T cells that are located upstream of PKC in the TCR signal transduction cascade are CD3-e, CD3-f, Lck, ZAP-70 or in particular PI3K [52][53][54][55][56][57].…”

“…In this context, dephosphorylation of the target protein should either produce an activating signal or could lead to the inactivation of an inhibitory signal. SHP-2 is able to directly interact with the receptor CXCR4 in Jurkat cells [44], which could be mediated by an ITIM in the fourth intracellular domain of CXCR4. In Jurkat as well as in breast cancer cells, receptor stimulation leads to the association of SHP-2 with Cbl, PI3K, 14-3-3b and Crk-L [44,45].…”

“…SHP-2 is able to directly interact with the receptor CXCR4 in Jurkat cells [44], which could be mediated by an ITIM in the fourth intracellular domain of CXCR4. In Jurkat as well as in breast cancer cells, receptor stimulation leads to the association of SHP-2 with Cbl, PI3K, 14-3-3b and Crk-L [44,45]. However, we additionally show that SHP-2 signals for migration mainly depend on the activity of G i -proteins, since pertussis toxin is able to block the enhanced migration.…”

Regulation of CXCR4-mediated chemotaxis and chemoinvasion of breast cancer cells

“…Cbl acts as an adaptor protein in tyrosine-dependent signaling, and has been shown to be phosphorylated upon CXCL12 stimulation in T cells (Chernock et al, 2001). Stimulation with CXCL12 increased the tyrosine phosphorylation of Cbl in DU4475 cells (Figure 7a,upper panel).…”

“…There has been considerable interest regarding signaling events induced by CXCL12 that regulate chemotaxis in T cells. Our laboratory and others have shown that CXCR4 ligation leads not only to G proteincoupled receptor events but also to induction of protein tyrosine kinases of the src family, as well as to induction of the RAFTK/Pyk2 platform kinase, and protein tyrosine phosphatases in T cells (Ganju et al, 1998a;Hatch et al, 1998;Wang et al, 2000;Chernock et al, 2001;Zhang et al, 2001). CXCR4-mediated chemotactic signaling is also regulated by the nitric oxide pathway (Cherla and .…”