Src family kinases are required for integrin but not PDGFR signal transduction

Abstract

Src family kinases (SFKs) have been implicated as important regulators of ligand-induced cellular responses including proliferation, survival, adhesion and migration. Analysis of SFK function has been impeded by extensive redundancy between family members. We have generated mouse embryos harboring functional null mutations of the ubiquitously expressed SFKs Src, Yes and Fyn. This triple mutation leads to severe developmental defects and lethality by E9.5. To elucidate the molecular mechanisms underlying this phenotype, SYF cells (deficient for Src, Yes and Fyn) were derived and tested for their ability to respond to growth factors or plating on extracellular matrix. Our studies reveal that while Src, Yes and Fyn are largely dispensable for platelet-derived growth factor (PDGF)-induced signaling, they are absolutely required to mediate specific functions regulated by extracellular matrix proteins. Fibronectin-induced tyrosine phosphorylation of focal adhesion proteins, including the focal adhesion kinase FAK, was nearly eliminated in the absence of Src, Yes and Fyn. Furthermore, consistent with previous reports demonstrating the importance of FAK for cell migration, SYF cells displayed reduced motility in vitro. These results demonstrate that SFK activity is essential during embryogenesis and suggest that defects observed in SYF triple mutant embryos may be linked to deficiencies in signaling by extracellular matrix-coupled receptors.

CUTL1 promotes tumor cell migration by decreasing proteasome-mediated Src degradation

“…Cells lacking Src, Yes and Fyn (SYF triplemutant cells) show reduced motility and reduced spreading in vitro (Lowell and Soriano, 1996;Parsons and Parsons, 1997;Thomas and Brugge, 1997;Klinghoffer et al, 1999). Our results suggest that Src has a crucial role in CUTL1-induced tumor cell migration: migration of SYF triple-mutant cells, which lack Src, Yes and Fyn was not noticeably affected by CUTL1 upregulation.…”

“…To address this issue, we used two different mouse embryonic cell lines derived from double or triple knockout mice: the src þ þ (yes À fyn À ) cell line shows normal expression of endogenous Src but lacks Yes and Fyn. In contrast, the SYF (src À yes À fyn À ) cell line lacks endogenous Src, Yes and Fyn through triple knockout mutations (Klinghoffer et al, 1999). It has been shown that SYF cells show significantly reduced cell migration compared with src þ þ cells (Klinghoffer et al, 1999) indicating the important role of Src in migration.…”

“…In contrast, the SYF (src À yes À fyn À ) cell line lacks endogenous Src, Yes and Fyn through triple knockout mutations (Klinghoffer et al, 1999). It has been shown that SYF cells show significantly reduced cell migration compared with src þ þ cells (Klinghoffer et al, 1999) indicating the important role of Src in migration. To assess the relevance of Src, we transiently upregulated CUTL1 in both SYF and src þ þ cell lines.…”

“…Upon activation of integrins by ECM proteins, Src family protein tyrosine kinases such as Src, Yes and Fyn (SFKs) get activated and localize to focal adhesions (Burridge and Chrzanowska-Wodnicka, 1996;Lowell and Soriano, 1996;Parsons, 1996;Parsons and Parsons, 1997;Thomas and Brugge, 1997). Cells lacking the Src family protein tyrosine kinases Src, Yes and Fyn (SYF triple mutant cells) show reduced motility and reduced spreading in vitro, indicating that Src, Yes and Fyn kinases play an important role as mediators of promigratory signals initiated by ECM proteins (Klinghoffer et al, 1999).…”

No requirement for Src family kinases for PDGF signaling in fibroblasts expressing SV40 large T antigen

“…Yet Klingho er and colleagues recently presented evidence that ®broblasts derived from mice null for Src, Fyn and Yes responded normally to PDGF (Klingho er et al, 1999, EMBO J., 18: 2459± 2471. What is the reason for this discrepancy?…”