Nuclear and cytoplasmic alpha 1 (I) collagen mRNA-binding proteins.

We have recently identified a cytoplasmic protein, alpha 1-RBF67, that specifically interacts with the conserved 3'-untranslated region of the alpha 1 (I) collagen gene. The binding activity was decreased in extracts from dexamethasone treated cells, which correlates with the known accelerated turnover of the COL1A1 RNA [Määttä, A. and Penttinen, R.P.K. (1993) Biochem. J. 295, 691-698]. Now we report that a very similar protein is present in nuclear extracts of NIH 3T3, human fibroblast and HeLa cells, which suggests that determination of cytoplasmic mRNA stability is not the sole function of the alpha 1-RBF67 activity. The binding to the RNA probe can be inhibited by annealing a DNA oligonucleotide or using excess of cold specific competitors. In UV-cross linking assays the nuclear protein has the same molecular weight (67 kDa) as the cytoplasmic one and the RNA-bound peptides generated by CNBr or V8 protease cleavage from both the cytoplasmic and the nuclear protein were identical. This protein was the only one of several nuclear collagen mRNA 3'-UTR binding proteins that was present in both nuclear and cytoplasmic extracts. In fibroblasts heparin-resistant nuclear RNA binding proteins had molecular weights of 45, 67 (alpha 1-RBF67), and 71 kDa. HeLa-cells contained an additional protein of 51 kDa and several non-specific RNA-binding proteins. The binding activity is modified by changes in the redox state, which implicates that in the nucleus the binding affinities of alpha 1(I) collagen RNA-binding protein and AP-1, a redox sensitive nuclear factor, that is important in the transcription of alpha 1(I) collagen gene, can be regulated simultaneously to the same direction.