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cGMP-dependent protein kinase Iβ regulates breast cancer cell migration and invasion via interaction with the actin/myosin-associated protein caldesmon
Raphaela Schwappacher, Hema Rangaswami, Jacqueline Su-Yuo, Aaron Hassad, Ryan Spitler, Darren E. Casteel


The two isoforms of type I cGMP-dependent protein kinase (PKGIα and PKGIβ) differ in their first ∼100 amino acids, giving each isoform unique dimerization and autoinhibitory domains. The dimerization domains form coiled-coil structures and serve as platforms for isoform-specific protein–protein interactions. Using the PKGIβ dimerization domain as an affinity probe in a proteomic screen, we identified the actin/myosin-associated protein caldesmon (CaD) as a PKGIβ-specific binding protein. PKGIβ phosphorylated human CaD on serine 12 in vitro and in intact cells. Phosphorylation on serine 12 or mutation of serine 12 to glutamic acid (S12E) reduced the interaction between CaD and myosin IIA. Because CaD inhibits myosin ATPase activity and regulates cell motility, we examined the effects of PKGIβ and CaD on cell migration and invasion. Inhibition of the NO/cGMP/PKG pathway reduced migration and invasion of human breast cancer cells, whereas PKG activation enhanced their motility and invasion. siRNA-mediated knockdown of endogenous CaD had pro-migratory and pro-invasive effects in human breast cancer cells. Reconstituting cells with wild-type CaD slowed migration and invasion; however, CaD containing a phospho-mimetic S12E mutation failed to reverse the pro-migratory and pro-invasive activity of CaD depletion. Our data suggest that PKGIβ enhances breast cancer cell motility and invasive capacity, at least in part, by phosphorylating CaD. These findings identify a pro-migratory and pro-invasive function for PKGIβ in human breast cancer cells, suggesting that PKGIβ is a potential target for breast cancer treatment.


  • Author contributions

    D.E.C. conceived the project. D.E.C., R. Schwappacher and H.R. designed the experiments, analyzed and interpreted the data, and wrote the manuscript. D.E.C. performed the overlay experiments and the proteomic screen. R. Schwappacher performed immunofluorescent staining and cell migration studies. H.R. constructed the adenoviral vectors and performed the cell invasion assays. J. S.-Y., A.H. and D.E.C. performed the protein-protein interaction, co-immunoprecipitation and phosphorylation experiments. R. Spitler performed the cell velocity measurements.

  • Funding

    This work was supported by the National Institutes of Health [grant number K22-CA124517 to D.E.C.]; the Deutsche Forschungsgemeinschaft [a research fellowship (SCHW1352\2-1) to R. Schwappacher]; and the UCSD Neuroscience Microscopy Shared Facility [grant number NS047101]. Deposited in PMC for release after 12 months.

  • Supplementary material available online at

  • Accepted January 21, 2013.
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