Intracellular calcium release and protein kinase C activation stimulate sonic hedgehog gene expression during gastric acid secretion.
OBJECTIVE
Hypochlorhydria during Helicobacter pylori infection inhibits gastric Sonic Hedgehog (Shh) expression. We investigated whether acid-secretory mechanisms regulate Shh gene expression through intracellular calcium (Ca2(+)(i))-dependent protein kinase C (PKC) or cyclic adenosine monophosphate (cAMP)-dependent protein kinase A (PKA) activation.


METHODS
We blocked Hedgehog signaling by transgenically overexpressing a secreted form of the Hedgehog interacting protein-1, a natural inhibitor of hedgehog ligands, which induced hypochlorhydria. Gadolinium, ethylene glycol-bis(β-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) + 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA), PKC-overexpressing adenoviruses, and PKC inhibitors were used to modulate Ca(2+)(i)-release, PKC activity, and Shh gene expression in primary gastric cell, organ, and AGS cell line cultures. PKA hyperactivity was induced in the H(+)/K(+)-β-cholera-toxin-overexpressing mice.


RESULTS
Mice that expressed secreted hedgehog-interacting protein-1 had lower levels of gastric acid (hypochlorhydria), reduced production of somatostatin, and increased gastrin gene expression. Hypochlorhydria in these mice repressed Shh gene expression, similar to the levels obtained with omeprazole treatment of wild-type mice. However, Shh expression also was repressed in the hyperchlorhydric H(+)/K(+)-β-cholera-toxin model with increased cAMP, suggesting that the regulation of Shh was not solely acid-dependent, but pertained to specific acid-stimulatory signaling pathways. Based on previous reports that Ca(2+)(i) release also stimulates acid secretion in parietal cells, we showed that gadolinium-, thapsigargin-, and carbachol-mediated release of Ca(2+)(i) induced Shh expression. Ca(2+)-chelation with BAPTA + EGTA reduced Shh expression. Overexpression of PKC-α, -β, and -δ (but not PKC-ϵ) induced an Shh gene expression. In addition, phorbol esters induced a Shh-regulated reporter gene.


CONCLUSIONS
Secretagogues that stimulate gastric acid secretion induce Shh gene expression through increased Ca(2+)(i)-release and PKC activation. Shh might be the ligand transducing changes in gastric acidity to the regulation of G-cell secretion of gastrin.
El-Zaatari
Mohamad
M
Department of Internal Medicine-Gastroenterology, University of Michigan, Ann Arbor, Michigan, USA.
Zavros
Yana
Y
Tessier
Art
A
Waghray
Meghna
M
Lentz
Steve
S
Gumucio
Deborah
D
Todisco
Andrea
A
Merchant
Juanita L
JL
D000126:Achlorhydria / Q000378:metabolism* / Q000503:physiopathology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D005744:Gastric Acid / Q000378:metabolism*; D005755:Gastrins / Q000235:genetics / Q000378:metabolism; D005786:Gene Expression Regulation / Q000502:physiology; D017506:H(+)-K(+)-Exchanging ATPase / Q000378:metabolism; D053823:Hedgehog Proteins / Q000235:genetics* / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D011493:Protein Kinase C / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology
D002352:Carrier Proteins; D005755:Gastrins; D053823:Hedgehog Proteins; C498447:Hhip protein, mouse; D008562:Membrane Glycoproteins; C465570:Shh protein, mouse; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; D017506:H(+)-K(+)-Exchanging ATPase; D002118:Calcium
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