SENESCENT WI-38 FIBROBLASTS OVEREXPRESS LPC-1, A PUTATIVE TRANSMEMBRANE SHOCK PROTEIN

We have recently reported the isolation of cDNAs for a number of genes that are differentially expressed between nonproliferating early (you ng) and late (senescent) population doubling level (PDL) WI-38 human, fetal lung-derived, fibroblast-like cells. We now demonstrate that one of these isolates, LPC-1 (Late PDL cDNA-1), derives from an approxima tely 2.9-kb mRNA species that is expressed at a two- to fivefold highe r level in serum-starved, confluent, senescent versus similarly treate d young WI-38 cells. Nucleotide sequence analysis of this cDNA confirm s its identity with that of a cDNA encoding a marker (p63) for the rou gh endoplasmic recticulum and a related swine hepatic cardiogenic shoc k protein. We show that LPC-1 expression in early PDL WI-38 cells is s trictly cell cycle-regulated and its expression peaks 9-12 h after ser um stimulation of G(0) cultures. The steady state levels of LPC-1 tran script in early PDL cells preceeding and following its peak expression are low, reflecting basal levels seen in G(0) upon removal of serum, Late PDL cells, however, seem to have lost this tight cell cycle regul ation seen in early PDL cells and inappropriately express high levels of the transcript after serum stimulation. Specific antiserum detects a protein of approximately 63 kDa by Western analysis and elicits inte nse cytoplasmic staining of senescent fibroblasts by immunohistochemis try. Related genomic sequences are found in all mammalian species exam ined as well as in the chicken. These findings are consistent with the hypothesis that senescent WI-38 cells exhibit a state of growth arres t fundamentally distinct from that of quiescent (G(0)) young cells. (C ) 1998 Academic Press.