Absence of SPARC in lens epithelial cells results in altered adhesion and extracellular matrix production in vitro.
The matricellular protein SPARC (also known as osteonectin and BM-40) is expressed abundantly in lens epithelium. That SPARC-null mice exhibit early cataractogenesis, indicates a role for SPARC in the maintenance of lens transparency. Comparison of cultured wild-type and SPARC-null lens epithelial cells revealed significant changes in adhesion to different substrates. SPARC-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 SPARC, there was increased deposition of the ECM protein laminin-1 (LN-1). Proteins associated with focal adhesions were increased in SPARC-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 SPARC-null cultures was accomplished through genetic rescue by stable transfection of SPARC cDNA. Our findings indicate that SPARC is counter-adhesive for murine lens epithelial cells and demonstrate that multiple factors contribute to this activity. We also identify SPARC as a modulator of LN-1 secretion and deposition by these cells, an activity important in epithelial cell-ECM interactions in the ocular lens.
Weaver
Matt S
MS
Hope Heart Program, Benaroya Research Institute at Virginia Mason, Seattle, Washington 98101-2795, USA.
Sage
E Helene
EH
Yan
Qi
Q
D000818:Animals; D002448:Cell Adhesion; D002478:Cells, Cultured; D004847:Epithelial Cells / Q000378:metabolism; D005109:Extracellular Matrix / Q000378:metabolism / Q000502:physiology; D016326:Extracellular Matrix Proteins / Q000378:metabolism* / Q000502:physiology; D016023:Integrins / Q000378:metabolism / Q000502:physiology; D007908:Lens, Crystalline / Q000166:cytology / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D015676:Osteonectin / Q000235:genetics* / Q000378:metabolism; D015398:Signal Transduction
D016326:Extracellular Matrix Proteins; D016023:Integrins; D015676:Osteonectin