INDUCTION OF HEAT-STABLE ENTEROTOXIN RECEPTOR ACTIVITY BY A HUMAN ALUREPEAT

The heat-stable enterotoxins (ST) elaborated by enterotoxigenic Escher ichia coli are a family of small cysteine-rich peptides that bind to s pecific epithelial receptors in the mammalian intestine, causing a sec retory diarrhea. The expression of ST receptors is tightly regulated; they are found primarily in intestine, and their expression is develop mentally modulated. One receptor for ST has been cloned, and its cDNA encodes a similar to 120-kDa particulate guanylyl cyclase (guanylyl cy clase-C). Recent studies suggest that there are additional ST receptor s that are not homologous to guanylyl cyclase-C. We used an expression cloning strategy to identify intestinal mRNAs that lead to expression of ST receptor activity in transfected cells. Using an ST-specific af finity panning system, we identified a novel 1891-base pair cDNA that does not encode a receptor protein, but instead, consists primarily of untranslated sequence. This cDNA induced receptor activity in both CO S and 293 embryonic kidney cells. Northern analysis of the T84 human i ntestinal cell line, from which this cDNA was cloned, suggests that it is part of a 7.8 kilobase mRNA transcript. This transcript was also i dentified in human small intestine and colon, as well. as in several e xtraintestinal tissues. Functional analysis of subcloned fragments rev eals that ST binding activity is induced by a 457-base pair human Alu repetitive sequence within the cDNA and that the phenoytpe is independ ent of orientation. These findings suggest that a human Alu element in duces expression of a unique ST receptor by a transacting mechanism. A n unrelated Alu-rich genomic clone did not confer ST binding, suggesti ng that there may be structural and functional specificity within indi vidual Alu sequences.