An RPE cell line as a useful in vitro model for studying retinoic acid receptor beta: expression and affinity

Synergistic effect of co-treatment with all-trans retinoic acid and 9-cis retinoic acid on human lung cancer cell line at molecular level

The major challenge in treating cancers with ATRA is the limited availability inside the cell and resistance developed in prolonged treatment. We made an attempt for co-treatment of human NSCLC cell lines (A549) with ATRA and its isomeric precursor (9cisRA). In this study, the growth inhibitory effect of ATRA, 9cisRA and combination of both were tested in A549 cells by MTT and Trypan blue assays. As the effects of retinoid are mediated through their receptors, their gene expression levels were analyzed by RT-PCR. The target gene receptor, RAR-β protein expression, was analyzed by immunocytochemistry. The cancer cell (A549) growth inhibitory effect was significantly (p ≤ 0.001) enhanced in combination treatment when compared with the result of individual treatments. The mRNA expression levels of both RAR-β and RXR-β were found to be increased in co-treatment (band density of 0.75 and 0.806, respectively) when compared with 9cisRA treatment (0.25 and 0.112) and ATRA treatment (0.01 and 0.081). A concomitant enhancement in the target RAR-β protein expression was observed in co-treated cells when compared with individual treatments. We thus conclude that the co-treatment had increased the availability of ATRA, by isomerization of the 9cisRA which then resulted in an increased expression of both RAR-β and RXR-β receptors and the target protein RAR-β which in turn inhibited lung cancer cell growth. Our study results have explored the mechanism of synergistic effect of co-treatment with ATRA and 9cisRA and further preclinical studies are necessary to validate the application of co-treatment of retinoid in clinical use.

Inhibitory effects of fenretinide metabolites N-[4-methoxyphenyl]retinamide (MPR) and 4-oxo-N-(4-hydroxyphenyl)retinamide (3-keto-HPR) on fenretinide molecular targets β-carotene oxygenase 1, stearoyl-CoA desaturase 1 and dihydroceramide Δ4-desaturase 1

The therapeutic capacity of fenretinide (N-[4-hydroxyphenyl] retinamide; 4-HPR) has been demonstrated for several conditions, including cancer, obesity, diabetes, and ocular disease. Yet, the mechanisms of action for its pleiotropic effects are still undefined. We hypothesized that investigation of two of the major physiological metabolites of fenretinide, N-[4-methoxyphenyl]retinamide (MPR) and 4-oxo-N-(4-hydroxyphenyl)retinamide (3-keto-HPR), might begin to resolve the multifaceted effects of this synthetic retinoid. We analyzed the effects of fenretinide, MPR, 3-keto-HPR, and the non-retinoid RBP4 ligand A1120, on the activity of known targets of fenretinide, stearoyl-CoA desaturase 1 (SCD1) and dihydroceramide Δ4-desaturase 1 (DES1) in ARPE-19 cells, and purified recombinant mouse beta-carotene oxygenase 1 (BCO1) in vitro. Lipids and retinoids were extracted and quantified by liquid chromatography-mass spectrometry and reversed phase HPLC, respectively. The data demonstrate that while fenretinide is an inhibitor of the activities of these three enzymes, that 3-keto-HPR is a more potent inhibitor of all three enzymes, potentially mediating most of the in vivo beneficial effects of fenretinide. However, while MPR does not affect SCD1 and DES1 activity, it is a potent specific inhibitor of BCO1. We conclude that a deeper understanding of the mechanisms of action of fenretinide and its metabolites provides new avenues for therapeutic specificity. For example, administration of 3-keto-HPR instead of fenretinide may be preferential if inhibition of SCD1 or DES1 activity is the goal (cancer), while MPR may be better for BCO1 modulation (carotenoid metabolism). Continued investigation of fenretinide metabolites in the context of fenretinide’s various therapeutic uses will begin to resolve the pleotropic nature of this compound.

Sensitivity of staurosporine-induced differentiated RGC-5 cells to homocysteine

PURPOSE

Homocysteine is implicated in ganglion cell death associated with glaucoma. To understand mechanisms of homocysteine-induced cell death, we analyzed the sensitivity of the RGC-5 cell line, differentiated using staurosporine, to physiologically-relevant levels of the excitotoxic amino acid homocysteine.

METHODS

RGC-5 cells were differentiated 24 hr using 316 nM staurosporine and tested for expression of Thy 1.2 via immunodetection, RT-PCR, and immunoblotting. The sensitivity of staurosporine-differentiated RGC-5 cells to physiological levels of homocysteine (50, 100, 250 microM) and to high levels of homocysteine (1 mM), glutamate (1 mM), and oxidative stress (25 microM:10 mU/ml xanthine:xanthine oxidase) was assessed by TUNEL assay and by immunodetection of cleaved caspase-3. The sensitivity of undifferentiated RGC-5 cells to high (1, 5, and 10 mM) homocysteine was also examined.

RESULTS

Undifferentiated RGC-5 cells express Thy 1.2 mRNA and protein. Staurosporine-differentiated RGC-5 cells extend neurite processes and express Thy 1.2 after 24 hr differentiation; they express NF-L after 1 and 3 days differentiation. Treatment of staurosporine -differentiated RGC-5 cells with 50, 100, or 250 microM homocysteine did not alter neurite processes nor induce cell death (detected by TUNEL and active caspase-3) to a level greater than that observed in the control (non-homocysteine-treated, staurosporine-differentiated) cells. The 1 mM dosage of homocysteine in staurosporine-differentiated RGC-5 cells also did not induce cell death above control levels, although 18 hr treatment of non-differentiated RGC-5 cells with 5 mM homocysteine decreased survival by 50%.

CONCLUSIONS

RGC-5 cells differentiated for 24 hr with 316 nM staurosporine project robust neurite processes and are positive for ganglion cell markers consistent with a more neuronal phenotype than non-staurosporine-differentiated RGC-5 cells. However, concentrations of homocysteine known to induce ganglion cell death in vivo and in primary ganglion cells are not sufficient to induce death of RGC-5 cells, even when they are differentiated with staurosporine.