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Characterization of zeta (zeta): a new opioid receptor involved in growth
I S Zagon1, S R Goodman, P J McLaughlin
1Department of Anatomy, M.S. Hershey Medical Center, Pennsylvania State University, Hershey, PA 17033.
Abstract:
Endogenous opioid systems (i.e., opioids and opioid receptors) are known to play a role in neural cancer. Using [3H]-[Met5]enkephalin, a potent ligand involved in growth, specific and saturable binding was detected in homogenates of S20Y neuroblastoma transplanted into A/Jax mice; the data fit a single binding site. Scatchard analysis yielded a Kd of 0.49 nM and a binding capacity of 5.32 fmol/mg protein. Binding was dependent on protein concentration, time, temperature, and pH, and was sensitive to Na+ and guanine nucleotides. Optimal binding required protease inhibitors, and pretreatment of the tumor homogenates with trypsin markedly reduced [3H]-[Met5]enkephalin binding, suggesting that the binding site was proteinaceous in character. Displacement experiments indicated that [Met5]enkephalin was the most potent displacer of [3H]-[Met5]enkephalin; other ligands selective for mu, delta, kappa, epsilon, and sigma were not highly competitive. Given the functional significance of [Met5]enkephalin as a potent regulator of normal and abnormal growth, and that the receptor recognized by [Met5]enkephalin does not resemble any previously described, the present study has demonstrated the presence of a new opioid receptor termed zeta (zeta) (from the Greek 'Zoe', life) related to the proliferation of cells and tissues.
Insights
Researchers discovered a novel opioid receptor, termed zeta (ζ), in neuroblastoma cells. This receptor binds [Met5]enkephalin and is linked to cell proliferation, suggesting a new target for neural cancer therapies.
Area of Science:
- Neuroscience
- Molecular Biology
- Oncology
Background:
- Endogenous opioid systems, including opioids and opioid receptors, are implicated in neural cancer development.
- The specific role of opioid ligands in neuroblastoma proliferation requires further elucidation.
Purpose of the Study:
- To investigate the presence and characteristics of opioid receptors in S20Y neuroblastoma.
- To identify potential novel targets for neural cancer treatment.
Main Methods:
- Utilized [3H]-[Met5]enkephalin, a potent growth-related ligand, for binding assays in S20Y neuroblastoma homogenates.
- Performed Scatchard analysis to determine binding kinetics (Kd and binding capacity).
- Conducted displacement experiments with various opioid ligands to characterize the receptor's selectivity.
Main Results:
- Specific and saturable binding of [3H]-[Met5]enkephalin was detected, fitting a single binding site model.
- Scatchard analysis revealed a Kd of 0.49 nM and a binding capacity of 5.32 fmol/mg protein.
- [Met5]enkephalin was the most potent displacer, while other opioid receptor ligands showed low competitive binding, indicating a novel receptor.
Conclusions:
- Demonstrated the presence of a previously undescribed opioid receptor, designated zeta (ζ), in S20Y neuroblastoma.
- The zeta receptor is proteinaceous, sensitive to Na+ and guanine nucleotides, and preferentially binds [Met5]enkephalin.
- This novel receptor's association with cell proliferation suggests its potential as a therapeutic target in neural cancers.