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1.  Bcr is a substrate for Transglutaminase 2 cross-linking activity 
BMC Biochemistry  2011;12:8.
Breakpoint cluster region (Bcr) is a multi-domain protein that contains a C-terminal GTPase activating protein (GAP) domain for Rac. Transglutaminase 2 (TG2) regulates Bcr by direct binding to its GAP domain. Since TG2 has transglutaminase activity that has been implicated in the response to extreme stress, we investigated if Bcr can also act as a substrate for TG2.
We here report that activation of TG2 by calcium caused the formation of covalently cross-linked Bcr. Abr, a protein related to Bcr but lacking its N-terminal oligomerization domain, was not cross-linked by TG2 even though it forms a complex with it. A Bcr mutant missing the first 62 amino acid residues remained monomeric in the presence of activated TG2, showing that this specific domain is necessary for the cross-linking reaction. Calcium influx induced by a calcium ionophore in primary human endothelial cells caused cross-linking of endogenous Bcr, which was inhibited by the TG2 inhibitor cystamine. Treatment of cells with cobalt chloride, a hypoxia-mimetic that causes cellular stress, also generated high molecular weight Bcr complexes. Cross-linked Bcr protein appeared in the TritonX-100-insoluble cell fraction and further accumulated in cells treated with a proteasome inhibitor.
Bcr thus represents both an interacting partner under non-stressed conditions and a target of transglutaminase activity for TG2 during extreme stress.
PMCID: PMC3044668  PMID: 21310073
2.  The Fer tyrosine kinase regulates interactions of Rho GDP-Dissociation Inhibitor α with the small GTPase Rac 
BMC Biochemistry  2010;11:48.
RhoGDI proteins are important regulators of the small GTPase Rac, because they shuttle Rac from the cytoplasm to membranes and also protect Rac from activation, deactivation and degradation. How the binding and release of Rac from RhoGDI is regulated is not precisely understood.
We report that the non-receptor tyrosine kinase Fer is able to phosphorylate RhoGDIα and form a direct protein complex with it. This interaction is mediated by the C-terminal end of RhoGDIα. Activation of Fer by reactive oxygen species caused increased phosphorylation of RhoGDIα and pervanadate treatment further augmented this. Tyrosine phosphorylation of RhoGDIα by Fer prevented subsequent binding of Rac to RhoGDIα, but once a RhoGDIα-Rac complex was formed, the Fer kinase was not able to cause Rac release through tyrosine phosphorylation of preformed RhoGDIα-Rac complexes.
These results identify tyrosine phosphorylation of RhoGDIα by Fer as a mechanism to regulate binding of RhoGDIα to Rac.
PMCID: PMC3009610  PMID: 21122136

Results 1-2 (2)