The tumor-sensitive calmodulin-like protein is a specific light chain of human unconventional myosin X.
Human calmodulin-like protein (CLP) is an epithelial-specific Ca(2+)-binding protein whose expression is strongly down-regulated in cancers. Like calmodulin, CLP is thought to regulate cellular processes via Ca(2+)-dependent interactions with specific target proteins. Using gel overlays, we identified a approximately 210-kDa protein binding specifically and in a Ca(2+)-dependent manner to CLP, but not to calmodulin. Yeast two-hybrid screening yielded a CLP-interacting clone encoding the three light chain binding IQ motifs of human "unconventional" myosin X. Pull-down experiments showed CLP binding to the IQ domain to be direct and Ca(2+)-dependent. CLP interacted strongly with IQ motif 3 (K(d) approximately 0.5 nm) as determined by surface plasmon resonance. Epitope-tagged myosin X was localized preferentially at the cell periphery in MCF-7 cells, and CLP colocalized with myosin X in these cells. Myosin X was able to coprecipitate CLP and, to a lesser extent, calmodulin from transfected COS-1 cells, indicating that CLP is a specific light chain of myosin X in vivo. Because unconventional myosins participate in cellular processes ranging from membrane trafficking to signaling and cell motility, myosin X is an attractive CLP target. Altered myosin X regulation in (tumor) cells lacking CLP may have as yet unknown consequences for cell growth and differentiation.
Tumor Biology Program, Department of Biochemistry and Molecular Biology, Mayo Graduate School and Mayo Clinic Cancer Center, Mayo Clinic/Foundation, Rochester, Minnesota 55905, USA.
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MS
Rogers
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Strehler
D000595:Amino Acid Sequence; D001483:Base Sequence; D002135:Calcium-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D017931:DNA Primers; D006801:Humans; D008969:Molecular Sequence Data; D009218:Myosins / Q000737:chemistry / Q000378:metabolism*; D011485:Protein Binding; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism
D002135:Calcium-Binding Proteins; D017931:DNA Primers; C498718:MYO10 protein, human; D011994:Recombinant Proteins; D009218:Myosins