Helicobacter exploits integrin for type IV secretion and kinase activation

Integrins are important mammalian receptors involved in normal cellular functions as well as pathogenesis of chronic inflammation and cancer. We propose that integrins are exploited by the gastric pathogen and type-1 carcinogen Helicobacter pylori for injection of the bacterial oncoprotein cytotoxin-associated gene A (CagA) into gastric epithelial cells. Virulent H. pylori express a type-IV secretion pilus that injects CagA into the host cell; CagA then becomes tyrosine-phosphorylated by Src family kinases. However, the identity of the host cell receptor involved in this process has remained unknown. Here we show that the H. pylori CagL protein is a specialized adhesin that is targeted to the pilus surface, where it binds to and activates integrin alpha5beta1 receptor on gastric epithelial cells through an arginine-glycine-aspartate motif. This interaction triggers CagA delivery into target cells as well as activation of focal adhesion kinase and Src. Our findings provide insights into the role of integrins in H.-pylori-induced pathogenesis. CagL may be exploited as a new molecular tool for our further understanding of integrin signalling.     

An active DNA transposon family in rice

The publication of draft sequences for the two subspecies of Oryza sativa (rice), japonica (cv. Nipponbare) and indica (cv. 93-11), provides a unique opportunity to study the dynamics of transposable elements in this important crop plant. Here we report the use of these sequences in a computational approach to identify the first active DNA transposons from rice and the first active miniature inverted-repeat transposable element (MITE) from any organism. A sequence classified as a Tourist-like MITE of 430 base pairs, called miniature Ping (mPing), was present in about 70 copies in Nipponbare and in about 14 copies in 93-11. These mPing elements, which are all nearly identical, transpose actively in an indica cell-culture line. Database searches identified a family of related transposase-encoding elements (called Pong), which also transpose actively in the same cells. Virtually all new insertions of mPing and Pong elements were into low-copy regions of the rice genome. Since the domestication of rice mPing MITEs have been amplified preferentially in cultivars adapted to environmental extremes-a situation that is reminiscent of the genomic shock theory for transposon activation.