RTP801 is a newly discovered stress response gene that is induced by hypoxia and other cell stress signals. Here, we investigated the mechanism by which a DNA damaging agent, methyl methanesulfonate (MMS), induces RTP801 transcription. In HaCaT human keratinocytes, MMS was able to induce a rapid increase in the mRNA level of RTP801. Correspondingly, MMS treatment was capable of stimulating a 2.5 kb RTP801 promoter. Deletion studies with the promoter demonstrated a critical region between -1057 and -981 bp of the promoter that is responsive to MMS treatment. Point mutations of the consensus Elk-1 and C/EBP sites within this region were able to abrogate the stimulatory effect of MMS, indicating that Elk-1 and C/EBP are both involved in the transcriptional regulation of the RTP801 gene by MMS. Furthermore, a gel mobility shift assay revealed that MMS was able to initiate rapid formation of a protein complex that bound the C/EBP site of the promoter. In addition, an anti-C/EBPbetaantibody was capable of further shifting the bound protein complex. Therefore, these studies indicate that RTP801 is a transcriptional target of MMS in human keratinocytes and that C/EBP is implicated in transcriptional control of the gene.