Trk receptor binding and neurotrophin/fibroblast growth factor (FGF)-dependent activation of the FGF receptor substrate (FRS)-3.

We have investigated the signaling properties of the fibroblast growth factor (FGF) receptor substrate 3 (FRS3), also known as SNT-2 or FRS2beta, in neurotrophin-dependent differentiation in comparison with the related adapter FRS2 (SNT1 or FRS2alpha). We demonstrate that FRS3 binds all neurotrophin Trk receptor tyrosine kinases and becomes tyrosine phosphorylated in response to NGF, BDNF, NT-3 and FGF stimulation in transfected cells and/or primary cortical neurons. Second, the signaling molecules Grb2 and Shp2 bind FRS3 at consensus sites that are highly conserved among FRS family members and that Shp2, in turn, becomes tyrosine phosphorylated. While FRS3 over-expression in PC12 cells neither increases NGF-induced neuritogenesis nor activation of Map kinase/AKT, comparable to previous reports on FRS2, over-expression of a chimeric adapter containing the PH/PTB domains of the insulin receptor substrate (IRS) 2, in place of the PTB domain of FRS3 (IRS2-FRS3) supports insulin-dependent Map kinase activation and neurite outgrowth in PC12 cells. Collectively, these data demonstrate that FRS3 supports ligand-induced Map kinase activation and that the chimeric IRS2-FRS3 adapter is stimulating sufficient levels of activated MapK to support neurite outgrowth in PC12 cells.

Genomic organization and comparative sequence analysis of the mouse and human FRS2, FRS3 genes.

The signaling adapter proteins FRS2 and FRS3 are implicated in the transmission of extracellular signals from nerve growth factor (NGF) or fibroblast growth factor (FGF) receptors to the Ras/mitogen-activated protein kinase signaling cascade. This study presents the genomic sequence and exon-intron organization of the mouse FRS2 and FRS3 loci as well as their evolutionary conservation with their human counterparts. Both FRS2 and FRS3 contain 5 coding exons spanning over 7 kb of genomic sequence with similar exon sizes and organization. Comparative genomic sequence analyses show a highly conserved genomic organization between mouse and human in both FRS2 and FRS3 genes. Non-coding sequences, highly conserved between mouse and human, were identified in the FRS3 introns that may potentially function as regulatory elements. To assay potential differences in their patterns of expression, RT-PCR analysis was used to assay FRS2 and FRS3 expression in the developing embryo and neural tube (NT) during the time of neurogenesis.