Expression of the NF-κB target gene IEX-1 (p22/PRG1) does not prevent cell death but instead triggers apoptosis in Hela cells

Abstract

P22PRG1/IEX-1 is a putative NF-kappaB target gene implicated in the regulation of cellular viability. Here, we show that in HeLa cells TNFalpha induces expression of p22PRG1/IEX-1 in an NF-kappaB dependent fashion. Blockade of NF-kappaB activation by various NF-kappaB inhibitors abolished TNFalpha-induced p22PRG1/IEX-1 expression and increased the sensitivity to apoptosis induced by TNFalpha, an activating Fas-antibody or the anti-cancer drug etoposide. Surprisingly, ectopic expression of p22PRG1/IEX-1 in HeLa cells transfected with an inducible p22PRG1/IEX-1-expression vector augments the susceptibility to apoptosis initiated by death-receptor ligands or by etoposide. In addition, p22PRG1/IEX-1 expressing HeLa cells exhibit an accelerated progression through the cell cycle. Transfection of an antisense hammerhead ribozyme targeted to p22PRG1/IEX-1 reduced the speed in cell cycle progression and decreased the apoptotic response to death ligands. Our data demonstrate that p22PRG1/IEX-1 is specifically induced during NF-kappaB activation, but this seems not to be related to the anti-apoptotic actions of NF-kappaB. Instead, NF-kappaB dependent recruitment of p22PRG1/IEX-1 might be related to a modulation in the cell cycle, and hereby, p22PRG1/IEX-1 may accelerate cell growth on the one hand, but may trigger apoptosis on the other. Oncogene (2001) 20, 69 - 76.

Immediate early gene X-1 interacts with proteins that modulate apoptosis

“…IEX-1 enhances apoptosis in some cells, whereas in other cell systems, IEX-1 protects against apoptosis [7,8,[11][12][13]19,22,23]. Our findings show that IEX-1 may function in the control of apoptosis by directly binding to a variety of proteins associated with either the enhancement or inhibition of apoptosis and that differential binding and activation may provide an explanation for the varied effects of this protein in different cells.…”

“…The human immediate early gene X-1 (IEX-1, also known as Dif2, and murine orthologs gly96 and PRG1) plays a role in the control of apoptosis and cellular growth [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. The gene (gly96) was initially identified in mouse fibroblasts as a serum-regulated, glycosylated, immediate early gene [1].…”

“…Increased expression of IEX-1 is associated with an increase in the growth rate of keratinocytes and HeLa cells, and disruption of IEX-1 gene expression in HeLa cells and 293 cells is associated with a decrease in cellular proliferation [3,7,8,21]. IEX-1 has been shown to be induced in cardiomyocytes and vascular smooth muscle cells by mechanical stretch, and overexpression of IEX-1 in vascular smooth muscle cells protects against stretch-induced hypertrophy [9,15] IEX-1 is regulated by a variety of factors.…”

“…The messenger RNA of a similar gene (p22/PRG1) is induced in rat pancreatic cells by pituitary adenylate cyclase activating peptide (PACAP) [20]. The human ortholog of gly96 and PRG1, IEX-1, was identified as an X-radiation induced in fibroblasts by Kondratyev et al [2], and as a UV-radiation and 1α, 25-dihydroxyvitamin D 3 -regulated gene in human keratinocytes [3,4].Increased expression of IEX-1 is associated with an increase in the growth rate of keratinocytes and HeLa cells, and disruption of IEX-1 gene expression in HeLa cells and 293 cells is associated with a decrease in cellular proliferation [3,7,8,21]. IEX-1 has been shown to be induced in cardiomyocytes and vascular smooth muscle cells by mechanical stretch, and overexpression of IEX-1 in vascular smooth muscle cells protects against stretch-induced hypertrophy [9,15] IEX-1 is regulated by a variety of factors.…”

“…For example, in keratinocytes [22], HeLa cells [7], hepatocyte (Hc) [19], and 293 cells [8], IEX-1 increases the rate of apoptosis. With respect to the induction of apoptosis, the effect of IEX-1 can be explained partially by its inhibitory effect on survival signals.…”