PrfA, the transcriptional activator of virulence genes, is upregulated during interaction of Listeria monocytogenes with mammalian cells and in eukaryotic cell extracts

Most virulence genes of Listeria monocytogenes are activated by the transcr iptional regulator PrfA. Previous studies have shown that environmental par ameters, such as temperature, pH, stress conditions and medium composition, affect the expression of PrfA and PrfA-dependent proteins. In this report, we demonstrate a threefold increase in PrfA protein synthesis during infec tion of mammalian cells, which correlates with the increased activity of th e plcA promoter, the major prfA promoter. Increased PrfA synthesis begins w hen L. monocytogenes adheres to host cells. In addition, we show that the o bserved induction of PrfA during the interaction of L. monocytogenes with m ammalian cells can be reproduced in vitro using total cell extracts. Our da ta suggest a role for host proteinase K-sensitive protein(s) in PrfA upregu lation.