Expression of CCKB/gastrin receptor isoforms in gastro-intestinal tumour cells.
Anti-serum raised against the human cholecystokinin B (CCKB)/gastrin receptor was used in Western blotting to differentiate the cellular locations of receptor isoforms expressed by human gastro-intestinal (GI) tumour cell lines. Using anti-serum directed against the amino-terminal extracellular tail of the CCKB/gastrin receptor, 8/9 cell lines were shown to express immunoreactive proteins of either m.w. 70 or 40 kDa, or both. Both isoforms were found to be associated with intracellular, non-nuclear membranes, whereas only the 70 kDa protein was expressed in the plasma membrane. Receptor expression was related to gastrin production and secretion. Both progastrin and glycine-extended gastrin-17 were produced and secreted by the tumour cell lines; however, carboxy amidated gastrin was not detected by radioimmunoassay. A CCKB/gastrin receptor transfectant NIH3T3 cell line did not produce detectable gastrin and showed exclusive expression of the 70 kDa receptor on the plasma membrane. One cell line had <50 pg/ml cell-associated progastrin and no detectable receptor form. Cell lines expressing 50-150 pg/ml had both 40 and 70 kDa receptor forms. Those expressing >150 pg/ml progastrin had only the 40 kDa isoform, which was shown to be exclusively expressed on intracellular, non-nuclear membranes, in one of the cell lines. Of the 4 cell lines exclusively expressing the lower m.w. receptor, 3 had gastrin present within the cell, which was not secreted. Thus, if cell-associated gastrin induces a proliferative effect, it may be by an intracrine pathway. Our study has identified the presence of CCKB/gastrin receptor isoforms in different cellular locations and may help toward understanding the complex autocrine and intracrine pathways mediated by gastrin peptides.
Watson
S A
SA
Department of Surgery, University of Nottingham, UK. sue.watson@nottingham.ac.uk
Clarke
P A
PA
Smith
A M
AM
Varro
A
A
Michaeli
D
D
Grimes
S
S
Caplin
M
M
Hardcastle
J D
JD
D016475:3T3 Cells / Q000737:chemistry; D000818:Animals; D015153:Blotting, Western; D005770:Gastrointestinal Neoplasms / Q000737:chemistry*; D006801:Humans; D051379:Mice; D008970:Molecular Weight; D009363:Neoplasm Proteins / Q000032:analysis* / Q000235:genetics; D011949:Receptors, Cholecystokinin / Q000032:analysis* / Q000235:genetics; D014162:Transfection
D009363:Neoplasm Proteins; D011949:Receptors, Cholecystokinin