Human colorectal cancers express a constitutively active cholecystokinin-B/gastrin receptor that stimulates cell growth.
Although ectopic expression of the cholecystokinin B/gastrin receptor (CCK-BR) is widely reported in human colorectal cancers, its role in mediating the proliferative effects of gastrin1-17 (G-17) on these cancers is unknown. Here we report the isolation of a novel splice variant of CCK-BR that exhibits constitutive (ligand-independent) activation of pathways regulating intracellular free Ca(2+) ([Ca(2+)](i)) and cell growth. The splice variant (designated CCK-BRi4sv for intron 4-containing splice variant) is expressed in colorectal cancers but not in normal colonic mucosa adjacent to the cancer. Balb3T3 cells expressing CCK-BRi4sv exhibited spontaneous, ligand-independent, oscillatory increases in [Ca(2+)](i), whereas cells expressing wild-type CCK-BR did not. Primary cultures of cells isolated from resected colorectal cancers also exhibited a similar pattern of spontaneous [Ca(2+)](i) oscillations. For both Balb3T3 and primary tumor cells, application of G-17 (10 and 200 nm, respectively) caused an increase in [Ca(2+)](i). Selective CCK-BR antagonists blocked the G-17-stimulated Ca(2+) responses but not the spontaneous [Ca(2+)](i) oscillations. Cells expressing CCK-BRi4sv exhibited an increased growth rate ( approximately 2.5-fold), in the absence of G-17, compared with cells expressing wild-type CCK-BR. The selective pattern of expression, constitutive activity, and trophic action associated with CCK-BRi4sv suggest that this variant may regulate colorectal cancer cell proliferation though a gastrin-independent mechanism.
Hellmich
M R
MR
Departments of Surgery, Physiology and Biophysics, and Internal Medicine, the University of Texas Medical Branch, Galveston, Texas 77555, USA. mhellmic@utmb.edu
Rui
X L
XL
Hellmich
H L
HL
Fleming
R Y
RY
Evers
B M
BM
Townsend
C M
CM
D016475:3T3 Cells; D017398:Alternative Splicing / Q000235:genetics; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001667:Binding, Competitive; D002118:Calcium / Q000378:metabolism; D020013:Calcium Signaling / Q000187:drug effects; D002455:Cell Division / Q000187:drug effects; D003001:Cloning, Molecular; D015179:Colorectal Neoplasms / Q000235:genetics* / Q000378:metabolism / Q000473:pathology*; D005260:Female; D005755:Gastrins / Q000037:antagonists & inhibitors / Q000494:pharmacology; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D007438:Introns / Q000235:genetics; D008297:Male; D051379:Mice; D008969:Molecular Sequence Data; D009367:Neoplasm Staging; D043887:Receptor, Cholecystokinin B; D011949:Receptors, Cholecystokinin / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D014407:Tumor Cells, Cultured
D005755:Gastrins; D043887:Receptor, Cholecystokinin B; D011949:Receptors, Cholecystokinin; C013550:gastrin 17; D002118:Calcium