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.
Rogers
M S
MS
Tumor Biology Program, Department of Biochemistry and Molecular Biology, Mayo Graduate School and Mayo Clinic Cancer Center, Mayo Clinic/Foundation, Rochester, Minnesota 55905, USA.
Strehler
E E
EE
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