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

• Published in: The Journal of biological chemistry 2015-05, Vol.290 (19), p.12247-12255
• Main Authors: Kumbrink, Joerg, Soni, Shefali, Laumbacher, Barbara, Loesch, Barbara, Kirsch, Kathrin H.
• Format: Article
• Language: English
• Subjects: alternative splice variants; Alternative Splicing; Animals; Base Sequence; cancer biology; Cell Adhesion; Cell Biology; cell migration; Cell Movement; cell signaling; Crk-Associated Substrate Protein - genetics; Crk-Associated Substrate Protein - metabolism; exon 1; Exons; Fibroblasts - metabolism; Focal Adhesion Protein-Tyrosine Kinases - metabolism; Gene Expression Regulation, Enzymologic; Humans; Mice; Molecular Sequence Data; N-terminal SH3 domain extensions; Neoplasm Invasiveness; p130Cas; Protein Isoforms; Protein Structure, Tertiary; PTK2 protein tyrosine kinase 2 (PTK2) (focal adhesion kinase) (FAK); RNA, Messenger - metabolism; Sequence Homology, Nucleic Acid; SH3 domain binding; Signal Transduction; src Homology Domains
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M115.649947

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, 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). Exons 1A and 1C encode for four amino acids (aa), whereas 1D and 1E encode for 22 aa and 1B1 encodes 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, whereas 1B, 1D, and 1E expression was more restricted. Reconstitution of all isoforms except for 1B in p130Cas-deficient murine fibroblasts induced lamellipodia formation and membrane ruffling, which was unrelated to the substrate domain 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. Background: The tumor promoter p130Cas utilizes its SH3 domain to control cell adhesion and migration. Results: We identified N-terminal extended p130Cas variants with enhanced SH3 domain binding activity which modulates cell migration and invasion. Conclusion: Naturally occurring p130Cas variants exhibit differential biological activities. Significance: Knowledge on these variants may explain how p130Cas controls cellular programs and drives carcinogenesis.