Identification of HS1 protein as a major substrate of protein-tyrosine kinase(s) upon B-cell antigen receptor-mediated signaling.

Abstract

Crosslinking of membrane-bound immunoglobulins, which are B-cell antigen receptors, causes proliferation and differentiation of B cells or inhibition of their growth.The receptor-mediated signaling involves tyrosine phosphorylation of cellular proteins and rapid activation of Src-like kinases. The amino acid sequences of five proteolytic peptides of p75, a major substrate of protein-tyrosine kinase(s) in the signaling, showed that p75 is the human HS1 gene product. The HS1 gene is expressed specifically in hematopoietic cells and encodes p75HSl, which carries both helix-turhelix and Src homology 3 motifs. p75HSl showed rapid tyrosine phosphorylation and association with a Src-like kinase, Lyn, after crosslinking of membrane-bound IgM. Thus, p75HS1 may be an important substrate of Lyn and possibly other protein-tyrosine kinases upon B-cell antigen receptor-mediated signaling.Membrane-bound immunoglobulin (mIg) forms an antigen receptor complex on the plasma membrane of B cells with at least two transmembrane proteins, MB-1 and B29 (1-3). In general, crosslinking of the receptor complex of resting B cells by antigens or antibodies to the immunoglobulins activates B cells to enter the G1 phase of the cell cycle, in which they become susceptible to proliferative signals provided by helper T cells. These responses are preceded by phosphatidylinositol turnover, activation of phospholipase C, and Ca2+ mobilization, which are apparently dependent on the functions of a GTP-binding protein(s), protein-tyrosine kinase(s), and protein-tyrosine-phosphatase(s) (1, 2). The tyrosine phosphorylation of proteins after mlg crosslinking is thought to be an initial intracellular signaling event. As mlg, MB-1, and B29 carry no catalytic domain, the receptor must regulate protein-tyrosine kinase(s) as an intracytoplasmic signal transducer(s) (1-3).Src-like kinases are intracytoplasmic protein-tyrosine kinases of 55-60 kDa that are thought to be localized on the inner part of the plasma membrane via myristic acid (4, 5).

Syk-mediated Tyrosine Phosphorylation Is Required for the Association of Hematopoietic Lineage Cell-specific Protein 1 with Lipid Rafts and B Cell Antigen Receptor Signalosome Complex

“…2, right panels). This result is consistent with a previous report by others (17). To determine the tyrosine phosphorylation status of HS1 in rafts, we analyzed by phosphotyrosine immunoblot the HS1 associated with raft and high density fractions of the cells with and without anti-IgM antibody treatment.…”

“…Biochemical studies have established HS1 as a prominent substrate of protein-tyrosine kinases Syk and Src family proteins including Lyn, Fgr, Fyn, and Lck (17)(18)(19)(20). Direct association of HS1 with Lyn or Lck is evident in T and B lymphocytes and erythroid cells during the differentiation mediated by erythropoietin (21)(22)(23).…”

SDF1α‐induced interaction of the adapter proteins Nck and HS1 facilitates actin polymerization and migration in T cells

“…An SH3 domain forms the C-terminal part of the molecule [3,22]. Moreover, HS1 contains several tyrosine motifs and is a substrate of Src and Syk kinases in several hematopoietic cell types [23][24][25][26][27][28].…”

Cloning and characterization of APS, an adaptor molecule containing PH and SH2 domains that is tyrosine phosphorylated upon B-cell receptor stimulation

“…Lnk is a 38 kDa tyrosine-phosphorylated protein which also binds to PLCg1, PI3K and Grb2 in response to T cell activation (Huang et al, 1995). HS1 has shown to be tyrosine phosphorylated in response to BCR stimulation and to play a role in apoptosis (Yamanashi et al, 1993;Fukuda et al, 1995). All these signal transduction proteins contain Src homology 2 (SH2) or SH3 domains which lead to protein ± protein interactions.…”