Retinoic acid downregulates growth, fibronectin and RAR alpha in 3T3 cells: Ha-ras blocks this response and RA metabolism

Vitamin A in health care: Suppression of growth and induction of differentiation in cancer cells by vitamin A and its derivatives and their mechanisms of action

Vitamin A is an important micro-essential nutrient, whose primary dietary source is retinyl esters. In addition, β-carotene (pro-vitamin A) is a precursor of vitamin A contained in green and yellow vegetables that is converted to retinol in the body after ingestion. Retinol is oxidized to produce visual retinal, which is further oxidized to retinoic acid (RA), which is used as a therapeutic agent for patients with promyelocytic leukemia. Thus, the effects of retinal and RA are well known. In this paper, we will introduce (1) vitamin A circulation in the body, (2) the actions and mechanisms of retinal and RA, (3) retinoylation: another RA mechanism not depending on RA receptors, (4) the relationship between cancer and actions of retinol or β-carotene, whose roles in vivo are still unknown, and (5) anti-cancer actions of vitamin A derivatives derived from fenretinide (4-HPR). We propose that vitamin A nutritional management is effective in the prevention of cancer.

Cell nanomechanics and focal adhesions are regulated by retinol and conjugated linoleic acid in a dose-dependent manner

Retinol and conjugated linoleic acid (CLA) have previously been shown to have an important role in gene expression and various cellular processes, including differentiation, proliferation and cell death. In this study we have investigated the effect of retinol and CLA, both individually and in combination, on the intracellular cytoskeleton, focal adhesions (FAs) and the nanomechanical properties of 3T3 fibroblasts. We observed a dose-dependent decrease in the formation of FAs following treatment with either compound, which was directly correlated to an increase in cell height (>30%) and a decrease in the measured Young's modulus (approximately 28%). Furthermore, treatments with both compounds demonstrated an increased effect and led to a reduction of >70% in the average number of FAs per cell and a decrease of >50% in average cell stiffness. These data reveal that retinol and CLA disrupt FA formation, leading to an increase in cell height and a significant decrease in stiffness. These results may broaden our understanding of the interplay between cell nanomechanics and cellular contact with the external microenvironment, and help to shed light on the important role of retinoids and CLA in health and disease.

Isotretinoin ameliorates renal damage in experimental acute renal allograft rejection

BACKGROUND

Retinoic acids, derivatives of vitamin A, act through retinoid receptors that are expressed in renal and immunocompetent cells (B and T cells; monocytes and macrophages). In experimental models of glomerulonephritis and renal interstitial disease, retinoids were shown to reduce both glomerular and tubular damage and inflammation. We therefore examined whether retinoids reduce cellular rejection and renal damage in a model of acute renal allograft rejection.

METHODS

Kidneys of Fisher rats (F344, RT11v1) were orthotopically grafted to Lewis rats (RT11). Animals were killed 7 or 14 days after transplantation. Rats undergoing transplantation were treated with isotretinoin (13 cis-retinoic acid) at a low dose of 2 mg/kg body weight per day (LD isotretinoin) or at a high dose of 20 mg/kg body weight per day (HD isotretinoin) or with vehicle.

RESULTS

At day 14, albuminuria was reduced by approximately 70% (vehicle: 1.1+/-0.2 mg/24 hr vs. LD isotretinoin: 0.32+/-0.1 mg/24 hr; P<0.001). At days 7 and 14 serum creatinine levels were significantly higher in the vehicle-treated group than in the LD and HD isotretinoin-treated rats (P<0.05). Both LD and HD isotretinoin significantly reduced acute vascular injury compared with vehicle-treated rats (score at day 14: LD isotretinoin 20.1+/-5.1 vs. vehicle 57.8+/-9.9, P<0.01), acute glomerular injury (score: LD isotretinoin 6.8+/-1.0 vs. vehicle 10.6+/-0.9 P<0.05), and the number of glomerular monocytes and macrophages and cytotoxic T cells. Isotretinoin also significantly lessened tubulointerstitial damage, tubulointerstitial cell proliferation, and the number of cells infiltrating the tubulointerstitium.

CONCLUSIONS

Isotretinoin significantly ameliorated functional, vascular, glomerular, and tubulointerstitial lesions in acute graft rejection. Although the current study did not definitely eliminate the possibility that isotretinoin only delayed the rejection process, retinoic acid derivatives may provide a new approach in the treatment of acute rejection injury.

Her2/neu induces all-trans retinoic acid (ATRA) resistance in breast cancer cells

We observed that all-trans retinoic acid (ATRA) inhibited the growth of MCF-7 breast cancer cells, but not those transfected with HER2/NEU or its transactivating ligand HEREGULIN. This suggests that Her2/neu causes breast cancer cells to be resistant to the growth inhibitory effects of ATRA. To confirm this observation, MDA-MB-453 and BT-474 cells, which have high levels of Her2/neu and are resistant to ATRA, were incubated with the trastuzumab (Herceptin) antibody so that we could determine whether inhibition of the expression and function of Her2/neu would resensitize these cells to ATRA. Indeed, we found that MDA-MB-453 and BT-474 cells treated with trastuzumab were growth inhibitory by ATRA. We then determined whether Her2/neu uses Grb2 and Akt proteins to induce ATRA resistance. Liposome-incorporated Grb2 antisense oligonucleotides (L-Grb2) and a dominant negative (DN) AKT mutant were used to down-regulate Grb2 expression and inhibit Akt activity, respectively. When incubated with L-Grb2 or transfected with the DN AKT mutant, ATRA-resistant, Her2/neu-overexpressing cells became sensitive to ATRA. Our results indicate that Her2/neu utilizes Grb2 and Akt proteins to induce ATRA resistance in breast cancer cells. ATRA sensitivity was also correlated with RARalpha protein levels since higher RARalpha protein levels were observed in cells in which the Her2/neu pathway was inhibited.

Retinoic acid homeostasis: retinoic acid regulates liver retinol esterification as well as its own catabolic oxidation in liver

Retinol is stored in liver in the form of its esters. The retinol-esterifying enzyme lecithin:retinol acyltransferase (LRAT) catalyzes the conversion of retinol into its storage form. Expression of the LRAT mRNA is induced by retinoic acid (RA), or by dietary vitamin A, and is downregulated upon vitamin A depletion. RA also induces the expression in liver of the mRNA for CYP26, the enzyme that disposes of excess RA by oxidizing RA to 4-oxo-RA. CYP26 is downregulated upon vitamin A depletion.