Structural elements that regulate pp59c-fyn catalytic activity, transforming potential, and ability to associate with polyomavirus middle-T antigen

Abstract

Except for its unique amino-terminal region (residues 1 through 83), which possibly dictates substrate recognition, pp59c-fYbears a high degree of homology with other members of the src family of tyrosine kinases. Here we show that the carboxy terminus of pp59c-fyn is necessary for stable middle-T-antigen association, that pp59C-fyfis normally phosphorylated on both serine and tyrosine residues, and that Tyr-531 and Tyr-420 are phosphorylation sites in vivo and in vitro, respectively. Analysis of a spontaneously generated mutant encoding a truncated form of pp59c-fyn and of variants specifically mutated at the Tyr-531 and Tyr-420 phosphorylation sites indicates that pp59c-fyn has regulatory elements analogous to those that have already been identified for other src-like tyrosine kinases. However, further examination of the pp59clYfy variants suggests the likelihood of additional means by which its activities might be regulated. Although alteration of Tyr-531 to phenylalanine (531F) in pp59'-fy' results in a protein which is more active enzymatically that the wild type, the enhancement is much less than that for the analogous variant of pp6o-src. Furthermore, contrary to results of similar experiments on other src-like proto-oncogene products, 531F did not induce transformation of NIH 3T3 cells. Studies involving pp59c`fy-pp60csrc chimeras in which the unique amino-terminal sequences (residues 1 through 83) of the two kinases were precisely interchanged implied that the inability of 531F to induce transformation is probably not caused by the absence of substrates for pp59c fYnin NIH 3T3 cells but rather by the insufficient enhancement of pp59c-fyn kinase activity. It is therefore probable that the kinase and transforming activities of pp59C-fyf are repressed by additional regulatory elements possibly located in the amino-terminal half of the molecule.

Neuroprotective Effects of Inhibiting Fyn S-Nitrosylation on Cerebral Ischemia/Reperfusion-Induced Damage to CA1 Hippocampal Neurons

“…The catalytic function of Fyn is tightly regulated by phosphorylation [ 43 ]. When a tyrosine residue in Fyn at position 420 was dephosphorylated by tyrosine phosphatase, the enzymatic activity of this protein was inhibited [ 44 , 45 ].…”

The Fyn Tyrosine Kinase Binds Irs-1 and Forms a Distinct Signaling Complex during Insulin Stimulation

“…Both SH2 and SH3 domains are essential for regulation of the enzymatic activity, because deletion of either domain leads to constitutive activation of the kinase and an increased transformation potential (23)(24)(25)(26). An important role for p59 fyn during signal transduction by tyrosine kinase receptors has been implicated in a number of systems: the p59 fyn associates with middle T-antigen (27,28), the ligand-stimulated PDGF and colony-stimulating factor-1 receptors (29,30), and B and T cell antigen receptors during antigen stimulation (31,32). In these systems, p59 fyn may participate in the stimulation of cell proliferation.…”