Role of YopP in Suppression of Tumor Necrosis Factor Alpha Release by Macrophages during Yersinia Infection

Abstract

ABSTRACT The Yersinia plasmid-encoded Yop virulon enables extracellular adhering bacteria to deliver toxic effector proteins inside their target cells. It includes a type III secretion system (Ysc), at least two translocator proteins (YopB, YopD), and a set of intracellular Yop effectors (YopE, YopH, YopO, YopM, and YopP). Infection of macrophages with a wild-type strain leads to low levels of tumor necrosis factor alpha (TNF-α) release compared to infection with plasmid-cured strains, suggesting that the virulence plasmid encodes a factor impairing the normal TNF-α response of infected macrophages. This effect is correlated with the inhibition of the macrophage mitogen-activated protein kinase (MAPK) activities. To identify the Yop protein responsible for the suppression of TNF-α release, we infected J774A.1 and PU5-1.8 macrophages with a battery of knockout Yersinia enterocolitica mutants and we quantified the TNF-α released. Mutants affected in secretion ( yscN ), in translocation ( yopB and yopD ), or in synthesis of all the known Yop effectors ( yopH , yopO , yopP , yopE , and yopM polymutants) were unable to block the TNF-α response of the macrophages. In contrast, single yopE , yopH , yopO , and yopM mutants behaved like the wild-type strain. A yopP mutant elicited elevated TNF-α release, and complementation of the yopP mutant or the yop effector polymutant strain with yopP alone led to a drop in TNF-α release. In addition, YopP was also responsible for the inhibition of the extracellular signal-regulated kinase2 (ERK2) and p38 MAPK activities. These results show that YopP is the Yop effector responsible for the Yersinia -induced suppression of TNF-α release by infected macrophages.