CADMIUM-INDUCED EXPRESSION OF IMMEDIATE-EARLY GENES IN LLC-PK1 CELLS

To identify molecular mechanisms underlying renal cell damage by cadmi um, the effect of this heavy metal on the level of immediate early gen es (IEGs) transcripts in LLC-PK1 cells was studied. Cadmium chloride ( CdCl2) induced the expression of four IEGs examined, but with differin g time courses. The level of c-fos mRNA peaked at 30 minutes, and then decreased. The levels of c-jun and c-myc transcripts reached a maximu m at one hour, and remained elevated up to four hours. Egr-1 mRNA leve l peaked at one hour, and returned to the control level by three hours . Experiments with cycloheximide and actinomycin D showed, respectivel y, that induction of IEGs by cadmium occurred in a protein synthesis-i ndependent and transcriptional activation-dependent manner. Cadmium in duction of c-fos mRNA was reduced markedly by the intracellular calciu m chelator, bis-(o-aminophenoxy)-ethane-N,N,N:N'-tetraacetic acid tetr a(acetoxymethyl)-ester (BAPTA/AM), and was decreased partially by a pr otein kinase C (PKC) inhibitor, 1-(5-isoquinolinylsulfonyl)-2-methylpi perazine (H-7). These data indicate that IEG induction by cadmium requ ires intracellular calcium mobilization and occurs in part by a PKC-de pendent pathway. Exposure of LLC-PK1 cells to CdCl2 (20 mu M for 1 to 24 hr) resulted loss of cell viability and DNA fragmentation, which wa s indicative of apoptosis.