Loss of type I procollagen gene expression in SV40-transformed human fibroblasts is accompanied by hypermethylation of these genes

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Abstract
Transformation of human lung fibroblasts (WI-38) by Simian Virus 40 (SV40) resulted in a decline of 25–30% in the amount of secreted collagen. The collagen produced by the transformed fibroblasts contained no type I collagen (i.e. α1(I) and α2 chains), which was the major collagen component produced by untransformed fibroblasts. Measurement of the procollagen mRNA levels by dot hybridization with nick-translated procollagen-cDNA clones showed that the absence of type I collagen was due to the absence of α1(I) and α2 procollagen mRNAs. This result was confirmed by hybridization of cDNA to total RNA with southern blots of the procollagen clones. To clarify the mechanism by which type I procollagen gene transcription is abolished in transformed cells, the methylation patterns of the α1(I) and α2 procollagen genes in normal and SV40-transformed fibroblasts were compared, using the chicken α1(I) and α2 procol-lagen-cDNA clones as probes. Methylated sites were detected by means of the restriction endonuclease isoschizomers Hpall and Mspl. Methylation of the procollagen α1(I) and α2 genes was increased in the SV40-transformed fibroblasts, concurrently with the loss of type I collagen synthesis. DNA methylation may thus contribute to altered regulation of gene expression upon cell transformation.