Proliferative signaling by store-operated calcium channels opposes colon cancer cell cytostasis induced by bacterial enterotoxins.
Guanylyl cyclase C and accumulation of cGMP induced by bacterial heat-stable enterotoxins (STs) promote colon cancer cell cytostasis, serving as a tumor suppressor in intestine. Conversely, capacitative calcium entry through store-operated calcium channels (SOCs) is a key signaling mechanism that promotes colon cancer cell proliferation. The present study revealed that proliferative signaling by capacitative calcium entry through SOCs opposes and is reciprocally coupled to cytostasis mediated by guanylyl cyclase C in T84 human colon carcinoma cells. Elimination of capacitative calcium entry employing 2-aminoethoxydiphenylborate (2-APB), a selective inhibitor of SOCs, potentiated cytostasis induced by ST. Opposition of ST-induced cytostasis by capacitative calcium entry reflects reciprocal inhibition of guanylyl cyclase C signaling. Calcium entry through SOCs induced by the calcium-ATPase inhibitor thapsigargin or the receptor agonists UTP or carbachol inhibited guanylyl cyclase C-dependent cGMP accumulation. This effect was mimicked by the calcium ionophore ionomycin and blocked by 2-APB and intracellular 1,2-bis(o-amino-5,5'-dibromophenoxy)ethane-N,N,N',N'-tetraacetic acid-acetoxymethyl ester (BAPTA-AM), a chelator of calcium. Moreover, regulation by capacitative calcium entry reflected ligand-dependent sensitization of guanylyl cyclase C to inhibition by that cation. Although basal catalytic activity was refractory, ST-stimulated guanylyl cyclase C was inhibited by calcium, which antagonized binding of magnesium to allosteric sites required for receptor-effector coupling. These observations demonstrate that reciprocal regulation of guanylyl cyclase C signaling by capacitative calcium entry through SOCs represents one limb of a coordinated mechanism balancing colon cancer cell proliferation and cytostasis. They suggest that combining guanylyl cyclase C agonists and SOC inhibitors offers a novel paradigm for cGMP-directed therapy and prevention for colorectal tumors.
Kazerounian
Shiva
S
Division of Clinical Pharmacology, Department of Medicine, Thomas Jefferson University, Philadelphia, PA 19107, USA.
Pitari
Giovanni M
GM
Shah
Fawad J
FJ
Frick
Glen S
GS
Madesh
Muniswamy
M
Ruiz-Stewart
Inez
I
Schulz
Stephanie
S
Hajnóczky
Gyorgy
G
Waldman
Scott A
SA
D001427:Bacterial Toxins / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000502:physiology*; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D003110:Colonic Neoplasms / Q000188:drug therapy / Q000473:pathology*; D006152:Cyclic GMP / Q000502:physiology; D004768:Enterotoxins / Q000494:pharmacology*; D029968:Escherichia coli Proteins; D006162:Guanylate Cyclase / Q000502:physiology; D006801:Humans; D015398:Signal Transduction
D001427:Bacterial Toxins; D015220:Calcium Channels; D004768:Enterotoxins; D029968:Escherichia coli Proteins; C034151:heat stable toxin (E coli); D006162:Guanylate Cyclase; D006152:Cyclic GMP; D002118:Calcium