The cDNA for a membrane-associated cGMP-dependent protein kinase (cGK II) was cloned from rat intestine using reverse trnscriptase PCR and oligonucleotide primers encoding two conserved motifs of known cGMPdependent protein kinases and subsequently by screening a rat intestine cDNA library. A full-length clone encodes a protein of 761 amino acids with an estimated size of 87 kDa. Sequences of eight peptides from purified pig intestinal mucosa cGK II were found in the derived amino acid sequence of this done, identifying it as rat intestinal cGK II. Phylogenetic analysis showed that rat intestinal cGK II is less related to mammalian cGK I than to the Drosophila DG1 gene product and most closely related to a recently cloned mouse brain CGKH isoform. Like several other cGK sequences, that of cGK II contained a leucine/isoleucine heptad repeat motif that has been implicated in dimer formation in cGK I. Expression of cGK II cDNA in HEK 293 cells followed by subcellular fractionation revealed cGK H loalization in the cell particulate fraction, consistent with the membrane association of endogenous rat cGK II. On Northern blots, the major cGK H poly(A) RNA form was 4.8 kb, with minor forms of6.2 and 3.1 kb. The cGK H RNA was highly expressed in rat intestinal mucosa and was 20 times less abundant in rat brain and kidney. The localization of endogenous cGK II RNA in rat small intestine was shown by in situ hybridization to be in villous epithelial cells and to some extent in crypt cells.

IntroductionCertain pathogenic bacteria produce a family of heat stable enterotoxins (STa) which activate intestinal guanylyl cyclases, increase cGMP, and elicit life-threatening secretory diarrhea.

1 The modulation of the guanosine 3':5'-cyclic monophosphate (cyclic GMP)-and adenosine 3':5'-cyclic monophosphate (cyclic AMP)-dependent protein kinase activities by the diastereomers of 8-bromoflphenyl-1,N2-ethenoguanosine 3',5'-cyclic monophosphorothioate, ((Rp)-and (Sp)-8-bromo-PET-cyclic GMPS) was investigated by use of purified protein kinases. In addition, the effects of (Rp)-8-bromo-PET-cyclic GMPS on protein phosphorylation in intact human platelets and on [3H]-noradrenaline release and neurogenic vasoconstriction in electrical field stimulated rat tail arteries were also studied. 6 The NO donor, 3-morpholinosydnonimine (SIN-1) relaxed rat tail arteries precontracted with phenylephrine (1 gM). The SIN-1 concentration-relaxation curve was shifted in a parallel manner to the right by (Rp)-8-bromo-PET-cyclic GMPS, suggesting that the relaxation was mediated by a cyclic GMP/ PKG-dependent mechanism. 7 The [3H]-noradrenaline release-enhancing effect and stimulation-induced decrease in vasoconstriction of forskolin were unaffected by (Rp)-8-bromo-PET-cyclic GMPS. Moreover, the forskolin concentrationrelaxation curve was not changed in the presence of the PKG inhibitor, suggesting a high selectivity in intact cells for PKG-over PKA-mediated effects.8 The results obtained indicate that (Rp)-8-bromo-PET-cyclic GMPS presently is the most potent and selective inhibitor of PKG and is helpful in distinguishing between cyclic GMP and cyclic AMP messenger pathways activation. Therefore, this phosphorothioate stereomer may be a useful tool for studying the role of cyclic GMP in vitro.

AbstractcGMP-based regulatory systems are vital for counteracting the renin-angiotensin system (RAS) which promotes volume expansion and high blood pressure. Natriuretic peptides and nitric oxide acting through their second messenger cGMP normally increase natriuresis and diuresis, and regulate renin release; however, the severe pathological state of cardiac heart failure is characterized by elevated levels of atrial natriuretic peptide that are no longer able to effectively oppose exaggerated RAS effects. There is presently limited information on the intracellular effectors of cGMP actions in the kidney. Recently we reported the cloning of the cDNA for type II cGMP-dependent protein kinase (cGK II), which is highly enriched in intestinal mucosa but was also detected for the first time in kidney. In the present study, cGK II was localized to juxtaglomerular (JG) cells, the ascending thin limb (ATL), and to a lesser extent the brush border of proximal tubules. An activator of renin gene expression, the angiotensin II type I receptor inhibitor, losartan, increased cGK II mRNA and protein three to fourfold in JG cells. In other experiments, water deprivation increased cGK II mRNA and protein three to fourfold in the inner medulla where both cGK II, and a kidney specific Cl

Detailed studies of differences in distinct cGMP kinase isoforms are highly dependent on expression of large amounts of these enzyme isoforms that are not easily purified by conventional methods. Here cGMP-dependent protein kinases, the type Ifl soluble form from human placenta, and the type II membrane-associated form from rat intestine, were each expressed in a baculovirus/Sf9 cell system and purified in milligram amounts by affinity chromatography. The expressed recombinant proteins displayed characteristics like those of their native counterparts, cGK Ifl was expressed as a 76 kDa protein predominantly found in the cytosol fraction, whereas cGK II was expressed as an 86 kDa protein predominantly associated with the membrane fraction. The apparent K a and Vmx of eGMP for activation of cGK lfl were 0.5 pM and 3.4 Ixmoffmin/mg, and for eGK II were 0.04/*M and 1.8/,mol/min/mg.