Molecular cloning of a novel rat salt-tolerant protein by functional complementation in yeast

Splicing variant of Cdc42 interacting protein-4 disrupts beta-catenin-mediated cell-cell adhesion: expression and function in renal cell carcinoma

We have identified an alternative splicing variant in the Cdc42-interacting protein 4 (CIP4) gene in patients with renal cell carcinoma (RCC); almost 50% of the RCCs examined showed an aberrant splicing event in reverse transcription-PCR and the insertion of 19 nucleotides derived from intron9 based on a sequence analysis. This variant (CIP4-V) encodes a premature stop codon, resulting in the loss of a tyrosine phosphorylation site, the Cdc42 binding domain, and the SH3 domain. In this report, we show that overexpression of CIP4-V causes the formation of ubiquitinated aggresomes and a loss of cell-cell adhesion. We determined that CIP4-V increased the beta-catenin tyrosine phosphorylation levels that mediate Fer/Fyn tyrosine kinases and induced beta-catenin mistrafficking from cell membrane to cytoplasmic aggresome. These results indicate that CIP4 is critical for beta-catenin-mediated cell-cell adhesion and may be an important aspect of its functional contribution to RCC, especially with regard to metastasis and invasiveness.

A new method for isolating tyrosine kinase substrates used to identify fish, an SH3 and PX domain-containing protein, and Src substrate

We describe a method for identifying tyrosine kinase substrates using anti-phosphotyrosine antibodies to screen tyrosine-phosphorylated cDNA expression libraries. Several potential Src substrates were identified including Fish, which has five SH3 domains and a recently discovered phox homology (PX) domain. Fish is tyrosine-phosphorylated in Src-transformed fibroblasts (suggesting that it is a target of Src in vivo) and in normal cells following treatment with several growth factors. Treatment of cells with cytochalasin D also resulted in rapid tyrosine phosphorylation of Fish, concomitant with activation of Src. These data suggest that Fish is involved in signalling by tyrosine kinases, and imply a specialized role in the actin cytoskeleton.