Activation of MAPK/ERK signaling by Burkholderia pseudomallei cycle inhibiting factor (Cif).
Cycle inhibiting factors (Cifs) are virulence proteins secreted by the type III secretion system of some Gram-negative pathogenic bacteria including Burkholderia pseudomallei. Cif is known to function to deamidate Nedd8, leading to inhibition of Cullin E3 ubiquitin ligases (CRL) and consequently induction of cell cycle arrest. Here we show that Cif can function as a potent activator of MAPK/ERK signaling without significant activation of other signaling pathways downstream of receptor tyrosine kinases. Importantly, we found that the ability of Cif to activate ERK is dependent on its deamidase activity, but independent of Cullin E3 ligase inhibition. This suggests that apart from Nedd8, other cellular targets of Cif-dependent deamidation exist. We provide evidence that the mechanism involved in Cif-mediated ERK activation is dependent on recruitment of the Grb2-SOS1 complex to the plasma membrane. Further investigation revealed that Cif appears to modify the phosphorylation status of SOS1 in a region containing the CDC25-H and proline-rich domains. It is known that prolonged Cullin E3 ligase inhibition leads to cellular apoptosis. Therefore, we hypothesize that ERK activation is an important mechanism to counter the pro-apoptotic effects of Cif. Indeed, we show that Cif dependent ERK activation promotes phosphorylation of the proapoptotic protein Bim, thereby potentially conferring a pro-survival signal. In summary, we identified a novel deamidation-dependent mechanism of action of the B. pseudomallei virulence factor Cif/CHBP to activate MAPK/ERK signaling. Our study demonstrates that bacterial proteins such as Cif can serve as useful molecular tools to uncover novel aspects of mammalian signaling pathways.
Department of Biochemistry, Yong Loo Lin School of Medicine, National University of Singapore, Singapore.
Mei Ying
MY
Ng
Department of Biochemistry, Yong Loo Lin School of Medicine, National University of Singapore, Singapore.|Program in Cancer and Stem Cell Biology, Duke-NUS Graduate Medical School, Singapore, Singapore.
Mei
M
Wang
Program in Cancer and Stem Cell Biology, Duke-NUS Graduate Medical School, Singapore, Singapore.
Patrick J
PJ
Casey
Department of Biochemistry, Yong Loo Lin School of Medicine, National University of Singapore, Singapore.
Yunn-Hwen
YH
Gan
Department of Biochemistry, Yong Loo Lin School of Medicine, National University of Singapore, Singapore.
Thilo
T
Hagen
D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D000072224:Bcl-2-Like Protein 11 / Q000378:metabolism; D016957:Burkholderia pseudomallei / Q000235:genetics / Q000378:metabolism* / Q000472:pathogenicity*; D002460:Cell Line; D004789:Enzyme Activation; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D015870:Gene Expression; D006801:Humans; D020935:MAP Kinase Signaling System; D008554:Melioidosis / Q000378:metabolism* / Q000382:microbiology*; D010766:Phosphorylation; D054730:Protein Interaction Domains and Motifs; D020837:SOS1 Protein / Q000378:metabolism; D037521:Virulence Factors / Q000235:genetics / Q000378:metabolism*; D020687:cdc25 Phosphatases / Q000737:chemistry / Q000378:metabolism
D001426:Bacterial Proteins; D000072224:Bcl-2-Like Protein 11; D020837:SOS1 Protein; D037521:Virulence Factors; D048049:Extracellular Signal-Regulated MAP Kinases; D020687:cdc25 Phosphatases