Post-Transcriptional Regulation of Virulence Genes by GlmY and GlmZ in Enterohemorrhagic E. Coli
Gruber, Charley C.
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Enterohemorrhagic E. coli O157:H7 (EHEC) is a major cause of foodborne illness and hemolytic uremic syndrome (HUS) throughout the world. One of the major virulence factors in this pathogen is a type III secretion system (T3SS) encoded by the locus of enterocyte effacement (LEE). EHEC uses this proteinaceous needle to inject effector proteins into host cells to hijack various host cellular processes, as well as the translocation and insertion of the translocated intimin receptor (Tir) into the host cell membrane. The bacterial adhesin intimin then binds to Tir, allowing EHEC to tightly adhere to the host cell’s membrane (109). Tir also indirectly recruits another bacterial effector EspFu, which induces actin polymerization. This causes the formation of the characteristic pedestal that cups the bacterial cell. This process from the assembly of the needle apparatus to the formation of the pedestal must be tightly regulated both transcriptionally and post-transcriptionally. The two two-component systems QseEF and QseBC have been previously shown to regulate various virulence genes. We established that these systems both regulate the transcription of the small RNA (sRNA) glmY. GlmY is known to stabilize another sRNA, GlmZ, which activates the translation of glucosamine synthetase (GlmS) (72). Here we show that GlmY and GlmZ are also important players in the post-transcriptional regulation of virulence genes in EHEC. The transcription factor QseF is required for the expression of EspFu and thus pedestal formation. This defect can be complemented by overexpression of either GlmY or GlmZ and is not at the transcriptional level. Instead, the expression of espFu requires a processing event that is QseF dependent. We have shown that GlmZ also post-transcriptionally regulates two of the operons of the LEE, LEE4 and LEE5. Both of these operons are transcribed from a single promoter, but there is a processing event that separates the first gene of the operon from the rest that requires the endoribonuclease RNase E. Overexpression of either sRNA results in the downregulation of the latter fragment of both the LEE4 and LEE5 operons. In the case of LEE4, this is through direct binding of GlmZ to a region within the LEE4 mRNA. We also investigated the global role of GlmY and GlmZ in EHEC through microarrays and RNA sequencing of the knockout strains. Aside from the LEE, GlmZ also regulates curli which are used to facilitate bacteria attachment to host cells. These data show that GlmZ has been co-opted into being an important regulator of virulence genes in EHEC.