Characterization of the cck-b/gastrin-like receptor in human colon
cancer.
Smith, Jill P., Elizabeth A. Stock, Michael G. Wotring, Patricia J.
McLaughlin, Ian S. Zagon.
Departments of Medicine and Neuroscience and Anatomy, The Milton S.
Hershey Medical Center, The Pennsylvania State University, Hershey,
Pennsylvania
APStracts 3:0093R, 1996.
The gastrointestinal peptide, gastrin, tonically stimulates growth of
human colon cancer cells in vivo and in vitro, and does so in a
receptor-mediated fashion. This study defined the nature of gastrin
binding in human colon cancer using [3H]L-365,260, a specific CCK
-B/gastrin antagonist found to block gastrin's effects on growth.
Following elucidation of optimal binding conditions (e.g., pH, time,
and temperature) in log phase HT-29 human colon cancer cells,
specific and saturable binding with a Kd of 4.8 +/- 0.7 nM and a Bmax
of 320 +/- 120 fmol/mg protein, and consistent with a single binding
site, was recorded. Binding was localized to the membrane fraction.
Exposure to gastrin or receptor antagonist decreased and increased,
respectively, the Bmax. Competition experiments indicated that L
-365,260 was 25- and 200-fold more effective at displacing
radiolabeled L-365,260 than gastrin and CCK, respectively. In
contrast to log phase cells, the Bmax was decreased by 67% to 76% in
confluent and post-confluent cultures. Binding activity was observed
in other cell lines examined, as well as in xenografts and colon
cancers obtained at surgery. Binding in normal human colonic mucosa
was 10-fold less than in colon cancer. These results provide the
first comprehensive identification and characterization of a CCK
-B/gastrin-like receptor in human colon cancer.
Received 18 December 1995; accepted in final form 1 March 1996.
APS Manuscript Number R802-5.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 20 March 96