Altered regulation of platelet‐derived growth factor A‐chain and c‐fos gene expression in senescent progeria fibroblasts

Abstract

The study of human genetic disorders known as premature aging syndromes may provide insight into the mechanisms of cellular senescence. These diseases are clinically characterized by the premature onset and accelerated progression of numerous features normally associated with human aging. Previous studies have indicated that fibroblasts derived from premature aging syndrome patients have in vitro growth properties similar to senescent fibroblasts from normal individuals. As an initial approach to determine whether gene expression is altered in premature aging syndrome fibroblasts, RNA was prepared from various cell strains and used for gel blot hybridization experiments. Although normal fibroblasts only express platelet-derived growth factor (PDGF) A-chain mRNA for a brief period following mitogenic stimulation, one strain of Hutchinson-Gilford (progeria) syndrome fibroblasts, AG3513, constitutively expresses PDGF A-chain mRNA and PDGF-AA homodimers. The PDGF A-chain gene does not appear to be amplified or rearranged in these fibroblasts. AG3513 progeria fibroblasts have properties characteristic of senescent cells, including an altered morphology and a diminished mitogenic response to growth promoters. The diminished response of AG3513 progeria fibroblasts to PDGF stimulation was examined in some detail. Studies using 125I-PDGF-BB, which binds with high affinity to both A- and B-type PDGF receptors, indicate that normal and AG3513 progeria fibroblasts have a similar number of PDGF receptors. Although receptor autophosphorylation occurs normally in PDGF-stimulated AG3513 progeria fibroblasts, c-fos mRNA induction does not. The senescent phenotype of AG3513 fibroblasts is probably unrelated to their constitutive PDGF A-chain gene expression; further studies are necessary in order to directly address this issue. Also, additional analysis of this progeria fibroblast strain may provide information on the control of mitogen-inducible gene expression in normal cells.

Transcription factor activity during cellular aging of human diploid fibroblasts

“…This reduction is primarily due to decreased transcription of the c-fos gene as previously reported for different fibroblast lines (Seshadri and Campisi 1990;Winkles et al 1990), but is likely due also to altered modification of Fos within aged fibroblasts, since although old fibroblasts express Fos protein, none of this protein is detectable in a form capable of binding a consensus AP-1 site (Fig. 6).…”

“…These include c-fos (Holt et al 1986;Nishikura and Murray 1987;Riabowol et al 1988;Kovary and Bravo 1991), c-HRas (Mulcahy et al 1985), c-myc (Armelin et al 1984;Heikkila et al 1987;Holt et al 1988), and c-raf-1 (Kolch et al 1991). However, expression of these genes is not appreciably changed in senescent cells (Rittling et al 1986), with the exception of c-fos (Seshadri and Campisi 1990;Winkles et al 1990;Riabowol et al 1992). Previous work has suggested that senescent cells are unable to pass through the GI phase of the cell cycle (Macieira-Coelho and Taboury 1982;Cristofalo et al 1989).…”

Polo-like Kinase 3 Functions as a Tumor Suppressor and Is a Negative Regulator of Hypoxia-Inducible Factor-1α under Hypoxic Conditions

“…PCR was performed for 35 cycles using the following conditions: denaturing at 94jC for 30 s, annealing at 66jC for 30 s, and extension at 72jC for 30 s. For Southern blotting, genomic DNA was isolated as described above and then digested with EcoRI and SalI. Hybridization analysis was conducted as described (16). Targeted ES clones were injected into C57BL/6 blastocysts to generate chimeras.…”

Loss of serum response element-binding activity and hyperphosphorylation of serum response factor during cellular aging.

“…For the majority of cellular genes examined, changes in expression have been found to be minimal. For example, the expression of genes encoding actin, ornithine decarboxylase, c-Myc, pl05Rb, and Jun, among others (34,35,39,46,47,56), decreases by s50% as cells become senescent. In contrast, considerable changes in expression levels have been observed for a subset of growth-related genes such as those encoding insulin-like growth factor (IGF)-binding protein 3, cyclin D1, cdc2, cdk2, cyclin A, the A chain of platelet-derived growth factor, cyclin B, and Fos (2,10,23,31,34,38,48,(54)(55)(56).…”