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Identification and characterization of zeta-opioid receptor in human colon cancer
S D Hytrek1, J P Smith, T J McGarrity
1Department of Comparative Medicine, Pennsylvania State University College of Medicine, Hershey 17033, USA.
Abstract:
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.
Insights
Opioid growth factor (OGF) inhibits human colon cancer growth. The OGF receptor, identified as the zeta-opioid receptor, is located in the cell nucleus and mediates this effect.
Area of Science:
- Oncology
- Neuroscience
- Pharmacology
Background:
- Opioid growth factor (OGF), also known as [Met5]enkephalin, is recognized for its role in inhibiting human colon cancer cell proliferation.
- The precise mechanism and receptor mediating OGF's growth-regulatory effects in colon cancer require detailed characterization.
Purpose of the Study:
- To identify and characterize the specific receptor responsible for mediating the anti-proliferative effects of OGF in human colon cancer.
- To determine the binding characteristics, localization, and pharmacological profile of the OGF receptor in colon cancer cells.
Main Methods:
- Ligand binding assays using radiolabeled [Met5]enkephalin ([3H][Met5]enkephalin) on HT-29 human colon cancer cells.
- Scatchard analysis to determine binding affinity and capacity.
- Subcellular fractionation to ascertain receptor location.
- Competition binding experiments to identify the most effective displacing ligand.
Main Results:
- Specific and saturable binding of [3H][Met5]enkephalin was observed in HT-29 colon cancer tissue.
- Scatchard analysis indicated a single binding site with a binding affinity of 15.4 +/- 2.0 nM and capacity of 364.8 +/- 25.7 fmol/mg protein.
- Binding was predominantly localized to the nuclear fraction, and [Met5]enkephalin was the most potent displacer, consistent with the zeta-opioid receptor.
Conclusions:
- The OGF receptor in human colon cancer exhibits characteristics consistent with the zeta-opioid receptor.
- This receptor is located in the nuclear fraction and mediates the growth-inhibitory effects of OGF.
- Findings support the potential therapeutic role of OGF in colon cancer treatment.