Identification of Novel Crk-associated Substrate (p130Cas) Variants with Functionally Distinct Focal Adhesion Kinase Binding Activities |
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Authors: | Joerg Kumbrink Shefali Soni Barbara Laumbacher Barbara Loesch Kathrin H Kirsch |
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Institution: | From the ‡Department of Biochemistry, Boston University School of Medicine, Boston, Massachusetts 02118.;the §Immunotherapy Research Center, Pettenkoferstrasse 8, 80336 Munich, Germany, and ;¶Immunis e.V., Pettenkoferstrasse 8, 80336 Munich, Germany |
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Abstract: | 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. |
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Keywords: | cancer biology cell migration cell signaling PTK2 protein tyrosine kinase 2 (PTK2) (focal adhesion kinase) (FAK) signal transduction SH3 domain binding alternative splice variants N-terminal SH3 domain extensions exon 1 p130Cas |
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