Major transcript variants of VAV3, a new member of the VAV family of guanine nucleotide exchange factors.

VAV3 is a new member of the VAV oncogene family with a strong homology to VAV and VAV2. A conceptual translation of the cDNA indicates that VAV3 is between 40 and 77% identical to VAV and VAV2 at the amino acid level in all identified functional motifs. This homology suggests that VAV3 occupies a similar position in signal transduction as the other family members. A major variant transcript, VAV3.1, found in both humans and mice, appears to encode only the 3' SH3-SH2-SH3 region, which suggests that it may substitute for the full-length isoform in functions mediated by this domain, or compete with the full-length isoform in functions mediated by more N-terminal motifs. VAV3.1 either is a partly unspliced mRNA or originates from a different promoter. VAV3 transcripts are found in cells of hematopoietic origin, where VAV is primarily expressed. However, unlike, VAV, the VAV3 and VAV3.1 transcripts are also found at varying levels in a wide variety of other tissues and cell lines. TGF-beta and EGF reversibly down-regulate the abundance of the VAV3. 1 transcript in HaCaT keratinocytes, representing the first observation of transcript regulation of a member of the VAV family by a growth factor.