The FRK / RAK-SHB Signaling Cascade: A Versatile Signal- Transduction Pathway that Regulates Cell Survival, Differentiation and Proliferation
Recent experiments have unravelled novel signal transduction pathways that involve the SRC homology 2 (SH2) domain adapter protein SHB. SHB is ubiquitously expressed and contains proline rich motifs, a phosphotyrosine binding (PTB) domain, tyrosine phosphorylation sites and an SH2 domain and serves a role in generating signaling complexes in response to tyrosine kinase activation. SHB mediates certain responses in platelet-derived growth factor (PDGF) receptor-, fibroblast growth factor (FGF) receptor-, neural growth factor (NGF) receptor TRKA-, T cell receptor-, interleukin-2 (IL-2) receptor- and focal adhesion kinase- (FAK) signaling. Upstream of SHB in some cells lies the SRC-like FYN-Related Kinase FRK / RAK (also named BSK / IYK or GTK). FRK / RAK and SHB exert similar effects when overexpressed in rat phaeochromocytoma (PC12) and β-cells, where they both induce PC12 cell differentiation and β-cell proliferation. Furthermore, β-cell apoptosis is augmented by these proteins under conditions that cause β-cell degeneration. The FRK / RAK-SHB responses involve FAK and insulin receptor substrates (IRS) -1 and -2.
Besides regulating apoptosis, proliferation and differentiation, SHB is also a component of the T cell receptor (TCR) signaling response. In Jurkat T cells, SHB links several signaling components with the TCR and is thus required for IL-2 production. In endothelial cells, SHB both promotes apoptosis under conditions that are anti-angiogenic, but is also required for proper mitogenicity, spreading and tubular morphogenesis. In embryonic stem cells, dominant-negative SHB (R522K) prevents early cavitation of embryoid bodies and reduces differentiation to cells expressing albumin, amylase, insulin and glucagon, suggesting a role of SHB in development.
In summary, SHB is a versatile signal transduction molecule that produces diverse biological responses in different cell types under various conditions. SHB operates downstream of GTK in cells that express this kinase.
Document Type: Review Article
Publication date: June 1, 2003
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- Current Molecular Medicine is an interdisciplinary journal focused on providing the readership with current and comprehensive reviews on fundamental molecular mechanisms of disease pathogenesis, the development of molecular-diagnosis and/or novel approaches to rational treatment. The reviews should be of significant interest to basic researchers and clinical investigators in molecular medicine. Periodically the journal will invite guest editors to devote an issue on a basic research area that shows promise to advance our understanding of the molecular mechanism(s) of a disease or has potential for clinical applications.