AJP - Regulatory, Integrative and Comparative Physiology, Vol 271, Issue 1 115-R121, Copyright © 1996 by American Physiological Society
Identification and characterization of zeta-opioid receptor in human colon cancer
S. D. Hytrek, J. P. Smith, T. J. McGarrity, P. J. McLaughlin, C. M. Lang and I. S. Zagon
Department of Comparative Medicine, Pennsylvania State University College of Medicine, Hershey 17033, USA.
Opioid growth factor (OGF, [Met5]enkephalin) inhibits the growth of human
colon cancer in nude mice in a receptor-mediated fashion. Ligand binding
assays using HT-29 human colon cancer tissue and [3H][Met5]enkephalin were
performed to characterize the receptor responsible for the
growth-regulatory effects of OGF in colon cancer. Specific and saturable
binding was detected, and Scatchard analysis revealed that the data were
consistent for a single binding site with a binding affinity of 15.4 +/-
2.0 nM and a binding capacity of 364.8 +/- 25.7 fmol/mg protein.
Subcellular fractionation studies revealed that binding was restricted to
the nuclear fraction. Competition experiments showed that cold
[Met5]enkephalin was the most effective ligand at displacing
[3H][Met5]enkephalin. Binding to radiolabeled [Met5]enkephalin also was
detected in colon cancers obtained from surgical resections. The function,
pharmacological and biochemical characteristics, distribution, and
subcellular location of this OGF receptor in human colon cancer are
consistent with the zeta-opioid receptor.
