Vol. 179, No. 3, 1991 September 30, 1991 BIOCHEMICAL AND BIOPHYSICAL RESEARCH COMMUNICATIONS Pages 1455-1463 ISOLATION AND EXPRESSION OF A GUANYLATE CYCLASE- COUPLED HEAT STABLE ENTEROTOXIN RECEPTOR cDNA FROM A HUMAN COLONIC CELL LINE Sujay Singh*, Gita Singh, Jiirg-Martin Heim, and Rupert Gerzer Labor ffir Klinische Pharmakologie, Medizinische Klinik, Klinikum Innenstadt der Universitgt, Ziemssenstrasse 1, D-8000 Mfinchen 2, Germany Received August 8, 1991 Heat stable enterotoxins (STs) are low molecular-weight peptides secreted by enterotoxigenic bacteria. One type of these enterotoxins (STa) induces intestinal secretion leading to acute diarrhea by binding to a membrane form of guanylate c clase. We have isolated a cDNA from a human colonic cell line, T84, enco cling for a guanylate cyclase-coupled enterotoxin receptor (STaR). The predicted amino acid sequence of the human STa receptor is 81 % identical with the tor (GC-C) from rat intestine. COS-7 P reviously cloned enterotoxin rece ce 1s transiently transfected with R t e cloned cDNA expressed specific concentration-dependent response to STa as measured by cyclic GMP accumulation and is about 20 times more sensitive to the stimulation by STa than has been shown for CC-C. 0 1991 Academic Press, Inc. Guanylate cyclase belongs to a diverse family of receptors that exert their biological effects through the second messenger cyclic GMP (cGMP). Three different membrane forms of guanylate cyclase (GC) have been identified from various mammalian tissues. Two of them act as a receptor for natriuretic peptides and have been designated as ANP-A and ANP-B receptors in human ( 1, 21, GC-A and GC-B in rat (3, 4). and GC-A in mouse (5). In the mammalian intestine, a number of enteropathogens stimulate fluid secretion by increasing intracellular concentration of either CAMP or cGMP. The enterotoxigenic bacteria, Escherichia coli and Yersinia entero- colitica produce heat stable peptide- enterotoxins (STa) (6, 7). The pharma- cological effects of STa are displayed by its binding to specific cell surface receptors located on the brush border of small intestinal enterocytes (8 - 11). This stimulates the guanylate cyclase-cGMP system, raises the level of cGMP and results in impaired sodium chloride absorption and net chloride secretion (9 - 14). This increase in cyclic GMP levels leads to fluid secretion and causes watery diarrhea in man and various domestic animals (12). *To whom correspondence should be addressed. 0006-291X/91 $1.50 CoDright 0 1991 by Academic Press, Inc. 1455 Ail rights of reproduction in any form reserved.