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Abstract
In a previous report, collagen synthesis did not correlate with steady-state collagen RNA levels; substantial amounts of type I collagen RNAs in endothelial cells were not translated into the respective protein. The current investigation was extended to study the level of the control mechanism in collagen gene expression in normal corneal endothelial cells or those modulated by corneal endothelium modulation factor released by polymorphonuclear leukocytes. Northern-blot analysis using cloned rabbit types I and IV cDNA probes (same species as RNA sources) demonstrated specific mRNA transcripts for collagen types I and IV in the endothelial cells, although the steady-state level of these mRNAs in modulated endothelial cells was low. The turnover rate of collagen RNAs was determined; normal cells contain very stable alpha 2(I) and alpha 2(IV) mRNAs whose half-lives exceed 24 hr. The same messages decayed rapidly in the modulated cells, where they had an apparent half-life of approximately 8 hr. Using nuclear run-off transcription, the rate of transcription in normal cells was found to be slightly lower than that in modulated cells. When the relative rate of collagen gene transcription was compared, that of alpha 2(I) was the lowest and of alpha 2(IV), the highest in both cells. The relative transcriptional rates of individual collagen chains did not account for the steady-state levels, suggesting that transcriptional regulation in corneal endothelial cells was less than was translational regulation. On the other hand, during early stages of corneal endothelial cell modulation induced by factors released by polymorphonuclear leukocytes there was a differential effect on both transcriptional rate and the steady-state level of collagen RNAs.(ABSTRACT TRUNCATED AT 250 WORDS)