CHARACTERIZATION OF IGFBP-3, PAI-1 AND SPARC MESSENGER-RNA EXPRESSIONIN SENESCENT FIBROBLASTS

The RNA species encoded by IGFBP-3 (insulin-like growth factor binding protein-3), PAI-1 (plasminogen activator inhibitor-1) and SPARC (secr eted protein-acidic and rich in cysteine; a.k.a. osteonectin) are over expressed in senescent human diploid fibroblasts (HDF). Their extracel lular products have the ability to modulate cell growth in culture and have been shown to have inhibitory effects on DNA synthesis and/or ce ll growth. This overproduction may contribute to a number of features of aging, including osteoporosis, atherosclerosis and diabetes mellitu s type II. Based on analysis of steady-state mRNA levels; which showed similar patterns for all three along with overexpression in senescent cells, we further investigated their transcription rates and stabilit y to determine reasons for their overexpression and to determine if co ordinate gene regulation was involved. Characterization of the rates o f transcription and the levels of message stability of these genes in early passage (young) versus late passage (old) HDF revealed that IGFB P-3, PAI-1 and SPARC are coordinately overexpressed but not regulated by a unique or simple mechanism encompassing all three transcripts. On ly PAI-1 shows an increase in the rate of transcription, while all thr ee show evidence that their overexpression is due to an increase in th e stability of RNA. Thus, the overexpression of these genes in senesce nt fibroblasts involves interactions not only at the transcriptional l evel but also with protein factors involved in determining the stabili ty and the degradation of RNA. (C) 1996 Elsevier Science Ireland Ltd.