Identification of Salmonella SPI-2 secretion system components required for SpvB-mediated cytotoxicity in macrophages and virulence in mice

FEMS Immunol Med Microbiol. 2008 Mar;52(2):194-201. doi: 10.1111/j.1574-695X.2007.00364.x. Epub 2008 Jan 31.

Abstract

The Salmonella SpvB protein possesses ADP-ribosyl transferase activity. SpvB, acting as an intracellular toxin, covalently modifies monomeric actin, leading to loss of F-actin filaments in Salmonella-infected human macrophages. Using defined Salmonella mutants, different functional components of the SPI-2 type three secretion system (TTSS), ssaV, spiC, sseB, sseC, and sseD, were found to be required for SpvB-mediated actin depolymerization in human macrophages. Expression of SpvB protein in Salmonella was not affected by any of the SPI-2 mutants and the effects of these loci were not due to reduced numbers of intracellular bacteria. Interestingly, the major SPI-2 virulence effector, SifA, is not required for SpvB action. Further, caspase-3 activation is an additional marker of cytotoxicity in Salmonella-infected human macrophages. Caspase-3 activity depended on SpvB and SPI-2 TTSS function, but not on SifA. These human macrophage cell culture results were corroborated by virulence studies in mice. Using competitive infection of mice with mixed inocula of single and double mutants, spvBmut1 mutation did not have an effect independent of ssaJ mutation, essential for SPI-2 TTSS function. In contrast, competitive infection studies in mice confirmed that SpvB and SifA have independent virulence effects, as predicted by the macrophage studies.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • ADP Ribose Transferases / metabolism*
  • Actins / metabolism
  • Animals
  • Caspase 3 / metabolism
  • Cells, Cultured
  • Gene Deletion
  • Humans
  • Macrophages / microbiology*
  • Membrane Transport Proteins / genetics
  • Membrane Transport Proteins / metabolism*
  • Mice
  • Mice, Inbred BALB C
  • Mutagenesis, Insertional
  • Protein Transport
  • Salmonella Infections, Animal / microbiology
  • Salmonella enterica / genetics
  • Salmonella enterica / metabolism*
  • Salmonella enterica / pathogenicity*
  • Spleen / microbiology
  • Virulence Factors / metabolism*

Substances

  • Actins
  • Membrane Transport Proteins
  • Virulence Factors
  • ADP Ribose Transferases
  • spvB protein, Salmonella enterica virulence plasmid
  • Caspase 3