Expression of extracellular matrix genes in relation to myogenesis and neoplastic transformation.

Fibronectin and alpha 1(I) and alpha 2(I) collagen proteins and RNAs are highly expressed during the growth phase of the non-transformed L6 alpha 1 rat myoblasts. When L6 alpha 1 cells from myotubes following transfer to low serum medium, the levels of fibronectin RNA decrease 8-fold, those of both alpha 2(I) transcripts decrease only 2-fold, while those of both alpha 1(I) transcripts remain stable. The L6 alpha 1 cell-derived non-differentiable low-malignant M4 cell and high-malignant RMS4 cell display only one size of alpha 1(I) and alpha 2(I) transcripts. Compared with L6 alpha 1 myoblasts, the levels of fibronectin and alpha 1(I) RNAs are reduced by factors of 4-5 and 9-10 respectively in both M4 and RMS4 and those of alpha 2(I) RNAs by factors of 10-11 and 20-22 in M4 and RMS4, respectively. Transcription rates are similarly decreased for fibronectin RNA, but are decreased less for collagen RNAs.