Collagen protects EGFP-S188/190A from degradation. A) NBT-II cells transfected with EGFP-paxillin or EGFP-S188/190A were plated on glass cover-slips for 18 h prior to fixation. The localization of the fusion proteins was observed by EGFP-fluorescence microscopy. B) NBT-II cells expressing wild type or mutant paxillin were pulse-chased on plastic or collagen-coated dishes for the indicated times. Cell lysates were immunoprecipitated with paxillin antibody prior to SDS-PAGE followed by autoradiography (left panels). The upper arrowhead points to EGFP-paxillin proteins bands and the lower arrowhead to endogenous paxillin bands. By densitometric analyses, mean exogenous 35S-paxillin levels were calculated relatively to the density of the paxillin band in the control lane. Means and SEM from 3 independent experiments were then calculated. The Student's t test was used to evaluate the data (right panels). *, p < 0.05.