Signalling the molecular stress response to nephrotoxic and mutagenic cysteine conjugates: Differential roles for protein synthesis and calcium in the induction ofc-fos andc-myc mRNA in LLC-PK1 cells

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Abstract
Nephrotoxic and mutagenic cysteine conjugates (NCC) are activated by the enzyme cysteine conjugate, β‐lyase, to reactive acylating species which bind covalently to cellular macromolecules. We now show that an early event after treatment of LLC‐PK1 cells with NCC is the induction of mRNA for both c‐fos and c‐myc. Treatment with S‐(1,2‐dichlorovinyl)‐L‐cysteine (DCVC) induced c‐fos (53‐fold) and c‐myc mRNA (20‐fold) and increased transcription about 3‐fold for both genes. Covalent binding was required for induction of both mRNAs. Dithiothreitol partially prevented induction of both c‐fos and c‐myc RNA. Buffering the DCVC‐induced increase in cytosolic free calcium had no effect on c‐fos mRNA but partially blocked c‐myc mRNA induction. Cycloheximide blocked the induction of c‐myc mRNA in the absence of an effect on c‐fos induction. The data suggest that the increase in c‐fos mRNA is a primary response to DCVC toxicity and occurs without a requirement for protein synthesis or an increase in intracellular free calcium. In contrast, c‐myc induction requires protein synthesis, suggesting that the presence of another primary response factor may regulate induction either transcriptionally or posttranscriptionally. The data suggest that different signalling pathways regulate induction of c‐fos and c‐myc mRNA in response to stress caused by reactive acylating species.

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