Identification of Novel Crk-associated Substrate (p130Cas) Variants with Functionally Distinct Focal Adhesion Kinase Binding Activities [Signal Transduction]

March 24th, 2015 by Kumbrink, J., Soni, S., Laumbacher, B., Loesch, B., Kirsch, K. H.

Elevated levels of p130Cas (Crk-associated substrate)/BCAR1 (breast cancer antiestrogen resistance 1 gene) are associated with aggressiveness of breast tumors. Following phosphorylation of its substrate domain (SD), p130Cas promotes the integration of protein complexes involved in multiple signaling pathways and mediates cell proliferation, adhesion and migration. In addition to the known BCAR1-1A (wild-type) and 1C variants, we identified four novel BCAR1 mRNA variants, generated by alternative first exon usage (1B, 1B1, 1D, and 1E). Exon 1A and 1C encode for four amino acids (aa), whereas 1D and 1E for 22 aa and 1B1 for 50 aa. Exon 1B is non-coding resulting in a truncated p130Cas protein (Cas1B). BCAR1-1A, 1B1 and variant 1C mRNAs were ubiquitously expressed in cell lines and a survey of human tissues, while 1B, 1D and 1E expression were more restricted. Reconstitution of all isoforms but of 1B in p130Cas deficient murine fibroblasts induced lamellipodia formation and membrane ruffling, which was unrelated to the SD phosphorylation status. The longer isoforms exhibited increased binding to focal adhesion kinase (FAK), a molecule important for migration and adhesion. The shorter 1B isoform exhibited diminished FAK binding activity and significantly reduced migration and invasion. In contrast the longest variant 1B1 established the most efficient FAK binding and greatly enhanced migration. Our results indicate that the p130Cas exon 1 variants display altered functional properties. The truncated variant 1B and the longer isoform 1B1 may contribute to the diverse effects of p130Cas on cell biology and therefore will be the target of future studies.
  • Posted in Journal of Biological Chemistry, Publications
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