ANALYSIS OF THE PRIMARY STRUCTURE OF INSULIN-LIKE GROWTH-FACTOR BINDING PROTEIN-3 CDNA FROM WERNER SYNDROME FIBROBLASTS

The mRNA encoding insulin-like growth factor binding protein-3 (IGFBP-3) is equally overexpressed in late-passage (old) normal human diploid fibroblasts (HDF) and in HDF derived from individuals with the premature aging disorder Werner syndrome (WS), relative to early-passage (young) normal HDF. However, the accumulation of IGFBP-3 protein in medium conditioned by WS cells is substantially less than in medium of old cells. In an attempt to understand this disparity between mRNA levels and protein output, we determined the nucleotide sequence of IGFBP-3 cDNA isolated from a WS cDNA library derived from mRNA of WS HDF, and compared it to three published normal IGFBP-3 DNA sequences. In the open reading frame, our results differed from one of the three sequences by a glycine substitution for alanine at residue 32. Minor differences in the 3'-untranslated region between the WS cDNA sequence and all three of the normal DNA sequences were also detected as 12 individual base substitutions and one adenine insertion. Thus, dampened accumulation of IGFBP-3 in medium conditioned by WS cells is not due to significant alterations in the sequence of the cognate mRNA.