Sphingosine induction of the hemolytic phospholipase C/sphingomyelinase (PlcH).

Unlabelled: Hemolytic phospholipase C, PlcH, is an important virulence factor for . PlcH preferentially hydrolyzes sphingomyelin and phosphatidylcholine, and this hydrolysis activity drives tissue damage and inflammation and interferes with the oxidative burst of immune cells. Among other contributors, transcription of was previously shown to be induced by phosphate starvation via PhoB and the choline metabolite, glycine betaine, via GbdR. Here, we show that sphingosine can induce transcription and result in secreted PlcH enzyme activity. This induction is dependent on the sphingosine-sensing transcriptional regulator SphR. The SphR induction of occurs from the promoter for the gene upstream of that encodes the neutral ceramidase, CerN, and transcriptional readthrough of the transcription terminator. Evidence for these conclusions came from mutation of the SphR binding site in the promoter, mutation of the terminator, enhancement of termination by adding the terminator, and reverse transcriptase PCR (RT-PCR) showing that the intergenic region between and is made as RNA during sphingosine, but not choline, induction. We also observed that, like glycine betaine induction, sphingosine induction of is under catabolite repression control, which likely explains why such induction was not seen in other studies using sphingosine in rich media. The addition of sphingosine as a novel inducer for PlcH points to the regulation of transcription as a site for the integration of multiple host-derived signals.

Importance: PlcH is a secreted phospholipase C/sphingomyelinase that is important for the virulence of . Here, we show that sphingosine, which presents itself or as a product of sphingomyelinase and ceramidase activity, leads to the induction of plcH transcription. This transcriptional induction occurs from the promoter of the upstream ceramidase gene generating a conditional operon. The transcript on which plcH resides, therefore, is different depending on which host molecule or condition leads to induction, and this may have implications for PlcH post-transcriptional regulation. This work also adds to our understanding of with host-derived sphingolipids.