Submitted on November 19, 2007
Accepted on May 2, 2008
Rho-ROCK Signaling Differentially Regulates Chondrocyte Spreading on Fibronectin and Bone Sialoprotein
Kamal Singh Gill1, Frank Beier2, and Harvey A Goldberg3*
1 CIHR Group in Skeletal Development and Remodeling, University of Western Ontario, London, Canada; Biochemistry, University of Western Ontario, London, Canada; Schulich School of Medicine & Dentistry, University of Western Ontario, London, Canada
2 CIHR Group in Skeletal Development and Remodeling, University of Western Ontario, London, Canada; Physiology and Pharmacology, University of Western Ontario, London, Canada; Schulich School of Medicine & Dentistry, University of Western Ontario, London, Canada
3 CIHR Group in Skeletal Development and Remodeling, University of Western Ontario, London, Canada; Biochemistry, University of Western Ontario, London, Canada; Division of Oral Biology, University of Western Ontario, London, Canada; Schulich School of Medicine & Dentistry, University of Western Ontario, London, Canada
* To whom correspondence should be addressed. E-mail: hagoldbe{at}uwo.ca.
The mammalian growth plate is a dynamic structure rich in extracellular matrix (ECM). Interactions of growth plate chondrocytes with ECM proteins regulate cell behaviour. In this study, we compared chondrocyte adhesion and spreading dynamics on fibronectin (FN) and bone sialoprotein (BSP). Chondrocyte adhesion and spreading were also compared to fibroblasts to analyze potential cell type-specific effects. Chondrocyte adhesion to BSP is independent of post-translational modifications but is dependent on the RGD sequence in BSP. While chondrocytes and fibroblasts adhered at similar levels on FN and BSP, cells displayed more actin-dependent spread on FN despite a 16X molar excess of BSP adsorbed to plastic. To identify intracellular mediators responsible for this difference in spreading, we investigated focal adhesion kinase (FAK)-Src and Rho-ROCK signaling. Although activated FAK localized to the vertices of adhered chondrocytes, levels of FAK activation did not correlate with the extent of cell spreading. Furthermore, Src inhibition reduced chondrocyte adhesion and spreading on both FN and BSP suggesting that FAK-Src signaling is not responsible for less cell spreading on BSP. In contrast, inhibition of Rho and ROCK in chondrocytes increased cell spreading on BSP and membrane protrusiveness on FN but did not affect cell adhesion. In fibroblasts, Rho inhibition increased fibroblast spreading on BSP while ROCK inhibition changed membrane protrusiveness of FN and BSP. In summary, we identify a novel role for Rho-ROCK signaling in regulating chondrocyte spreading and demonstrate both cell- and matrix molecule-specific mechanisms controlling cell spreading.
