Abstract
Objective: MUC1 is a transmembrane mucin glycoprotein expressed on the surface of lymphocytes and epithelial cells. Its cytoplasmic COOH‐terminus (CT) is evolutionarily conserved and mediates intracellular signaling. The objective of this study was to identify proteins involved in MUC1 CT signaling.Methods: We searched for proteins binding to the MUC1 CT using a yeast two‐hybrid system and confirmed the results by coimmunoprecipitation (coIP) analysis.Results: Of the positive clones encoding proteins that interacted with the MUC1 CT, the majority coded for CAML (calcium modulating cyclophilin ligand), a protein involved in Ca2+ signaling. The MUC1 CT interacted with CAML as revealed by growth on selective media and in situ X‐alpha‐galactosidase activity of yeast double transformants or progeny from matings of single transformants. Binding of the MUC1 CT to CAML was confirmed by reciprocal coIPs (MUC1 CT IP + CAML IB and CAML IP + MUC1 CT IB). By deletion mutagenesis, only the MUC1 CT and not its extracellular tandem repeat region or SEA domain interacted with CAML. Likewise, the region of CAML binding to MUC1 was localized to its NH2‐terminus.Conclusion: Our results have identified CAML as a novel binding partner of the MUC1 CT and suggest that MUC1 plays a role in Ca2+ signaling.
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