An RPE cell line as a useful in vitro model for studying retinoic acid receptor beta: expression and affinity
Barbara Pavan1, Alessandro Dalpiaz, Carla Biondi
1General Physiology section, Department of Biology, University of Ferrara, via L. Borsari, 46-44100 Ferrara, Italy.
Abstract:
Retinoids mediate their biological effect by interacting with specific nuclear receptors. Of the several known RAR (retinoic acid receptor) subtypes, RAR-beta is of particular interest, since its expression is silenced in many cancers and it is believed to be a tumour suppressor. Specific ligands of RAR-beta can potentially be used in anti-cancer therapy. In the present study, we have investigated the feasibility of using HRPE cells (human retinal pigment epithelial cells) as an experimental model for characterizing RAR-beta-ligand interaction. RT-PCR (reverse transcription-PCR) and Western blot analyses show that HRPE cells specifically express only RAR-beta and none of the other receptor subtypes. In addition, we show that the expression of RAR-beta increases with increasing passage number of the cells. Interestingly, the increase in RAR-beta expression is not associated with telomere shortening, a typical biomarker of cellular senescence. In the present study, we also describe a protocol for characterizing RAR-beta-ligand interactions using nuclear extract from late passage HRPE cells as a source of endogenous RAR-beta. Using [(3)H]CD367 as the ligand, RAR-beta in HRPE cells showed an affinity of 9.6 +/- 0.6 nM and a B(max) of 780 +/- 14 fmol/mg of protein. We have confirmed the feasibility of using this assay to detect the interaction of ligands with RAR-beta by investigating the ability of certain flavonoids to inhibit the binding of [(3)H]CD367 to nuclear extracts from HRPE cells. The inhibition constant of the flavonoids for RAR-beta was between approx. 1-30 microM, showing that the flavonoids interact with RAR-beta with low affinity.
Insights
Human retinal pigment epithelial cells express only RAR-beta, a tumor suppressor. These cells provide a model for studying RAR-beta-ligand interactions and potential anti-cancer therapies targeting this receptor.
Area of Science:
- Molecular Biology
- Cell Biology
- Cancer Research
Background:
- Retinoids exert biological effects via nuclear receptors, including retinoic acid receptor (RAR) subtypes.
- RAR-beta is a significant tumor suppressor whose expression is frequently silenced in various cancers.
- Targeting RAR-beta with specific ligands presents a potential strategy for anti-cancer therapy.
Purpose of the Study:
- To evaluate human retinal pigment epithelial (HRPE) cells as a model for characterizing RAR-beta-ligand interactions.
- To establish a protocol for studying RAR-beta-ligand binding using endogenous RAR-beta from HRPE cells.
- To investigate the binding affinity of RAR-beta ligands and the inhibitory effects of flavonoids.
Main Methods:
- Reverse transcription-PCR (RT-PCR) and Western blot analyses to confirm RAR-beta expression in HRPE cells.
- Nuclear extract preparation from late-passage HRPE cells for ligand-binding assays.
- Radioligand binding assay using [(3)H]CD367 to determine RAR-beta affinity and B(max).
- Inhibition assays using flavonoids to assess their interaction with RAR-beta.
Main Results:
- HRPE cells exclusively express RAR-beta, with expression levels increasing with passage number, independent of telomere shortening.
- A reliable protocol was developed for characterizing RAR-beta-ligand interactions using HRPE nuclear extracts.
- RAR-beta in HRPE cells exhibited a high affinity (9.6 +/- 0.6 nM) and B(max) (780 +/- 14 fmol/mg protein) for [(3)H]CD367.
- Flavonoids demonstrated low-affinity interactions with RAR-beta, with inhibition constants ranging from approximately 1-30 microM.
Conclusions:
- HRPE cells serve as a suitable and specific experimental model for studying RAR-beta.
- The developed protocol enables the characterization of RAR-beta-ligand interactions and the screening of potential therapeutic compounds.
- Findings support the potential of targeting RAR-beta in cancer therapy and provide insights into flavonoid interactions with this receptor.
