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© The Rockefeller University Press, 0021-9525/2002/10/200-a $5.00
The Journal of Cell Biology, Volume 159, Number 2, 200-a-201

Little PIP, little PIP, let me in

PIP2 (green) is eliminated by bacteria (pink) that express SigD (right). Grinstein/Macmillan

In one simple hydrolysis step, bacteria make the plasma membrane squishy enough to ease invasion, according to new results from two groups.

The groups studied different pathogens, but both came to similar conclusions. Both bacteria, Shigella and Salmonella, inject several invasion-promoting proteins into the host, including a protein with similarity to a mammalian inositol phosphatase. Mauricio Terebiznik, Sergio Grinstein (Hospital for Sick Children, Toronto, ON), and colleagues watched how phosphoinositides were affected during Salmonella infection. They found that one PIP₂ species, PtdIns(4,5)P₂, was depleted from the base of membrane ruffles that formed where bacteria were pushing to get in, thanks to the phosphatase activity of the SigD effector protein. Like SigD, the Shigella effector IpgD studied by Kirsten Nieburh (Institut Pasteur, Paris, France), Bernard Payrastre (INSERM, Toulouse, France), and colleagues also removed PIP₂ from target cells; in this case, the product was identified as PtdIns(5)P.

The result in both cases was a softer plasma membrane. Expression of either phosphatase in mammalian cells caused membrane blebbing and relaxed attachment between the actin cytoskeleton and the membrane. Vesicles were released from the membrane into the SigD-expressing cells. The loosened membrane sped up bacterial invasion—Salmonella mutants lacking SigD were slower to gain entry.

Although PtdIns(5)P may affect membrane-cytoskeleton interactions, both groups imagine that the loss of PIP₂ is at the heart of it all. "Actin cross-linkers are bound by PIP₂," says Grinstein. "Bacteria have taken advantage of this. By chewing away PIP₂, they weaken the interaction." The weakening of the plasma membrane environment may assist the fission of vesicles from the membrane. It remains to be seen whether phosphatase conversion of PIP₂ into PtdIns(5)P is a general mechanism to control membrane properties during other processes, such as motility or endocytosis.

References:

Niebuhr, K., et al. 2002. EMBO J. 21:5069–5078.[CrossRef][Medline]

Terebiznik, M., et al. 2002. Nat. Cell Biol. 4:766–773.[CrossRef][Medline]

Nicole LeBrasseur

lebrasn{at}rockefeller.edu

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This Article Full Text (PDF, 315K) PPT slides of all figures Alert me when this article is cited Services Email this article Similar articles in this journal Alert me to new content in the JCB Download to citation manager Citing Articles Citing Articles via CrossRef Citing Articles via Google Scholar Google Scholar Articles by LeBrasseur, N. Search for Related Content PubMed Articles by LeBrasseur, N. Social Bookmarking                            What's this?