title: Identification of Novel Crk-associated Substrate (p130Cas) Variants with Functionally Distinct Focal Adhesion Kinase Binding Activities.
abstract: Elevated levels of p130(Cas) (Crk-associated substrate)/BCAR1 (breast cancer antiestrogen resistance 1 gene) are associated with aggressiveness of breast tumors. Following phosphorylation of its substrate domain, p130(Cas) 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 p130(Cas) 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 p130(Cas)-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 p130(Cas) exon 1 variants display altered functional properties. The truncated variant 1B and the longer isoform 1B1 may contribute to the diverse effects of p130(Cas) on cell biology and therefore will be the target of future studies.
authors: From the Department of Biochemistry, Boston University School of Medicine, Boston, Massachusetts 02118.
authors: Joerg
authors: J
authors: Kumbrink
authors: From the Department of Biochemistry, Boston University School of Medicine, Boston, Massachusetts 02118.
authors: Shefali
authors: S
authors: Soni
authors: the Immunotherapy Research Center, Pettenkoferstrasse 8, 80336 Munich, Germany, and.
authors: Barbara
authors: B
authors: Laumbacher
authors: Immunis e.V., Pettenkoferstrasse 8, 80336 Munich, Germany.
authors: Barbara
authors: B
authors: Loesch
authors: From the Department of Biochemistry, Boston University School of Medicine, Boston, Massachusetts 02118, kirschk@bu.edu.
authors: Kathrin H
authors: KH
authors: Kirsch
mesh_terms: D017398:Alternative Splicing; D000818:Animals; D001483:Base Sequence; D002448:Cell Adhesion; D002465:Cell Movement; D050719:Crk-Associated Substrate Protein / Q000235:genetics* / Q000378:metabolism*; D005091:Exons; D005347:Fibroblasts / Q000378:metabolism; D051416:Focal Adhesion Protein-Tyrosine Kinases / Q000378:metabolism*; D015971:Gene Expression Regulation, Enzymologic; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D009361:Neoplasm Invasiveness; D020033:Protein Isoforms; D017434:Protein Structure, Tertiary; D012333:RNA, Messenger / Q000378:metabolism; D012689:Sequence Homology, Nucleic Acid; D015398:Signal Transduction; D018909:src Homology Domains
chemical_list: C493841:BCAR1 protein, human; D050719:Crk-Associated Substrate Protein; D020033:Protein Isoforms; D012333:RNA, Messenger; D051416:Focal Adhesion Protein-Tyrosine Kinases
keywords: N-terminal SH3 domain extensions; PTK2 protein tyrosine kinase 2 (PTK2) (focal adhesion kinase) (FAK); SH3 domain binding; alternative splice variants; cancer biology; cell migration; cell signaling; exon 1; p130Cas; signal transduction