Cloning from a mouse osteoblastic cell line of a set of transforming‐growth‐factor‐β1‐regulated genes, one of which seems to encode a follistatin‐related polypeptide

Transforming growth factor(TGF)β1 is a potent inhibitor of growth in mouse osteoblastic MC3T3‐E1 cells. To isolate genes that are induced by TGFβ1, the differential screening method was adopted using a cDNA library constructed from cells treated with TGFβ1 for 4 h. Six independent cDNA clones were isolated (TGFβ‐stimulated clone, TSC‐5, TSC‐36, TSC‐115, TSC‐128, TSC‐160 and TSC‐161), the expression of which was increased by TGFβ1‐treatment with maximal expression at 6–10 h. The steady‐state levels of TSC‐36, TSC‐128 and TSC‐160 increased almost tenfold, whereas those of TSC‐5, TSC‐115 and TSC‐161 were elevated at most threefold. From partial nucleotide sequences, TSC‐160 was found to be identical to rrg ( ras ‐recision gene, lysyl oxydase), and TSC‐115 had 80% similarity with tropomyosin cDNA, whereas other genes seemed novel. Expression of TSC‐36 and TSC‐160 was dramatically decreased in v‐Ki‐ ras ‐transformed MC3T3 cells or in transformed NIH 3T3 cells (DT), and was recovered to normal levels in a flat revertant (C11). A nearly full‐length copy of TSC‐36 cDNA was isolated, and an open reading frame indicated that it encodes a protein of 35 kDa. An antiserum was raised against the C‐terminal peptide predicted from the nucleotide sequence, and a polypeptide with an approximate molecular mass of 38 kDa was detected in cultured medium of MC3T3‐E1 cells. The amino acid sequence of TSC‐36 protein was found to have some similarity with follistatin, an activin‐binding protein, and a limited similarity with the secreted protein rich in cysteine (SPARC).