Molecular mechanisms of enhanced renal cell division in protection against S-1,2-dichlorovinyl-L-cysteine-induced acute renal failure and death. Am J Physiol Renal Physiol 000 - 000, 2005. Sustained activation of ERK 1/2 by a low dose (15 mg/kg, ip) of S-1, 2-dichlorovinyl-L-cysteine (DCVC) 72 h before administration of a lethal dose of DCVC (75 mg/kg, ip) enhances renal cell division and protects mice against acute renal failure and death (autoprotection). Objective of this study was to determine correlation among extent of S-phase DNA synthesis, activation of transcription factors, expression of G₁/S cyclins, cyclin dependent kinases (CDKs), and CDK inhibitors (CKIs) downstream of ERK 1/2 following DCVC-induced ARF in autoprotection. Administration of the lethal dose alone caused a general downregulation or an unsustainable increase, in transcriptional and post-transcriptional events thereby preventing G₁-S transition of renal cell cycle. Phosphorylation of IB was inhibited resulting in limited nuclear translocation of NFB. However, cyclin D1 expression was high probably due to transcriptional cooperation of AP-1. Cyclin D1/cyclin dependent kinase 4 (cdk4)-cdk6 system mediated phosphorylation of retinoblastoma protein was downregulated due to overexpression of p16 at 24 h after exposure to the lethal dose alone. Inhibition of S-phase stimulation was confirmed by proliferating cell nuclear antigen assay (PCNA). This inhibitory response was prevented if the lethal dose was administered 72 h after the low priming dose of DCVC due to promitogenic effect of the low dose. NFB-DNA binding is not limited if mice were pretreated with the priming dose. Cyclin D1/cdk4-cdk6 expression stimulated by the priming dose of DCVC was unaltered even after the lethal dose in the autoprotected group, explaining higher phosphorylated-pRB (P-pRB) and S-phase stimulation found in this group. These results were corroborated with PCNA immunohistochemistry. These findings suggest that the priming dose relieves the block on compensatory tissue repair by upregulation of promitogenic mechanisms, normally blocked by the high dose when administered without the prior priming dose.