Absence of SPARC in lens epithelial cells results in altered adhesion and extracellular matrix production in vitro.

The matricellular protein (also known as osteonectin and BM-40) is expressed abundantly in lens epithelium. That mice exhibit early cataractogenesis, indicates a role for duanyu1842RC in the maintenance of lens transparency. Comparison of cultured wild-type and duanyu1842RC-null lens epithelial cells revealed significant changes in adhesion to different substrates. duanyu1842RC-null lens cells displayed enhanced attachment and spreading, focal adhesion formation, and resistance to trypsin detachment in comparison to wild-type cells. In the absence of there was increased deposition of the ECM protein laminin-1 (LN-1). Proteins associated with focal adhesions were increased in duanyu1842RC-null versus wild-type lens cells: levels of alpha6-integrin heterodimers, talin, and paxillin phosphorylated on tyrosine were enhanced significantly, as was the association of beta1-integrin with talin and paxillin. Restoration of the wild-type phenotype in duanyu1842RC-null cultures was accomplished through genetic rescue by stable transfection of duanyu1842RC cDNA. Our findings indicate that duanyu1842RC is counter-adhesive for murine lens epithelial cells and demonstrate that multiple factors contribute to this activity. We also identify duanyu1842RC as a modulator of LN-1 secretion and deposition by these cells, an activity important in epithelial cell-ECM interactions in the ocular lens.

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