Developmental expression of the collagen-binding heat-shock protein GP46 and collagen types I and IV in rat tissues

The temporal expression of protein and mRNA encoding the collagen-binding heat-shock glycoprotein, gp46, were determined in the heart, kidney, and lung during early rat postnatal development. The steady-state levels of collagen types I and IV mRNA expression were also examined to determine if gp46 and these collagen types are co-regulated during ontogenesis. Western blot analysis using a monoclonal antibody to gp46 revealed that gp46 levels are developmentally regulated. In heart and kidney, gp46 levels were high on days 3 and 8, reduced significantly on day 25, and low to undetectable on day 69. Protein levels of gp46 in the lung exhibited a similar temporal pattern except on day 3, when very low levels of gp46 were detected. mRNA expression of gp46 during early postnatal development did not correlate with gp46 protein accumulation in these tissues, suggesting a complex pre- and post-translational regulatory scheme. In the heart, protein levels of gp46 correlated well with collagen type I alpha 1(I) mRNA expression but not with collagen type IV alpha 1(IV). In contrast, gp46 protein levels closely paralleled alpha 1(IV) expression in the kidney. Gp46 levels exhibited no apparent correlation with either alpha 1(I) or alpha 1(IV) levels in the lung. These results show that gp46 is developmentally regulated at both the protein and mRNA levels in a tissue specific manner. The relationship between gp46 and collagen alpha 1(I) and alpha 1(IV) chain mRNA expression also has been shown to be tissue specific.