Epidermal growth factor receptor expression in a retinoic acid-treated human melanoma cell line

Vitamins and Melanoma

A tremendous amount of information was published over the past decades in relation to the role of vitamins in various neoplastic diseases. In particular, several studies showed an inverse relationship between selected vitamins intake and cancer risk. In this review we will focus on the role played by vitamins in melanoma with particular regard to vitamin A, D, K, E and C. Given that vitamin supplementation is easy, convenient, and readily accepted by patients, in the future the use of vitamins in chemoprevention and therapy of melanoma could be encouraged if supported by pre-clinical and clinical evidence.

Retinoic acid and cancer treatment

Retinoic acid which belongs to the retinoid class of chemical compounds is an important metabolite of vitamin A in diets. It is currently understood that retinoic acid plays important roles in cell development and differentiation as well as cancer treatment. Lung, prostate, breast, ovarian, bladder, oral, and skin cancers have been demonstrated to be suppressed by retinoic acid. Our results also show that low doses and high doses of retinoic acid may respectively cause cell cycle arrest and apoptosis of cancer cells. Also, the common cell cycle inhibiting protein, p27, and the new cell cycle regulator, Cdk5, are involved in retinoic acid’s effects. These results provide new evidence indicating that the molecular mechanisms of/in retinoic acid may control cancer cells’ fates. Since high doses of retinoic acid may lead to cytotoxicity, it is probably best utilized as a potential supplement in one’s daily diet to prevent or suppress cancer progression. In this review, we have collected numerous references demonstrating the findings of retinoic acid in melanoma, hepatoma, lung cancer, breast cancer, and prostate cancer. We hope these observations will shed light on the future investigation of retinoic acid in cancer prevention and therapy.

The proliferative effects of retinoic acid on primary cultures of adult rat type II pneumocytes depend upon cell density

Retinoic acid (RA) is important for maintaining integrity of alveolar epithelial cells, but the mechanism has not been defined. We cultured type II pneumocytes at confluent, high cell density (10(4) cells/mm(2)) and found that RA (10(-6) M) inhibited thymidine incorporation to 60% of control, despite a dose-dependent increase in epidermal growth factor receptor (EGFR) levels. However, at lower, subconfluent density (10(2) cells/mm(2)), RA stimulated thymidine incorporation to 280% of control. EGF increased thymidine incorporation at concentrations as low as 0.1 ng/mL, but no further increase was observed at higher concentrations up to 100 ng/mL. In subconfluent cells co-treated with EGF (100 ng/mL) and increasing concentrations of RA (10(-8) M-10(-5) M RA), thymidine incorporation was significantly greater at all concentrations than RA alone, with greatest increases observed at 10(-7) (422% of control) and 10(-6) (470% of control) M RA. In summary, the effects of RA on thymidine incorporation are sensitive to changes in cell density. RA inhibits thymidine incorporation at high cell density and stimulates thymidine incorporation at low density. RA increases EGFRs in cultured type II pneumocytes, and EGF stimulates thymidine incorporation independent of the cultured cell density. These data may help to explain how RA mediates lung repair in vivo.

Pretreatment with vitamin A inhibits transforming growth factor alpha stimulation of human mammary carcinoma cells

Vitamin A or retinol is an important agent in the normal differentiation and growth of cells. Retinol is an effective inhibitor of the growth of many transformed cells in vitro and in vivo but its mechanism of action is unclear. Transforming growth factor alpha (TGF alpha) is a known mitogen. We examined the effect of retinol treatment on TGF alpha stimulation of two human mammary carcinoma cell lines, one which is growth inhibited by retinol and one which is not. Pretreatment of both cell lines for 48 hours with retinol resulted in inhibition of TGF alpha stimulation of growth. In the T47D cell line the mechanism was not related to an effect on the cellular content of TGF alpha, epidermal growth factor (EGF) receptor protein, EGF receptor mRNA, or on the binding of TGF alpha to the EGF receptor. However, TGF alpha-induced stimulation of the EGF receptor substrate, phospholipase C-gamma 1, was abrogated in the T47D cell line with retinol pretreatment. In the MDA-MB-468 cell line, pretreatment with retinol resulted in a decrease in tyrosine phosphorylation of the EGF receptor. These results suggest that pretreatment with retinol decreases cellular proliferation seen with TGF alpha treatment by altering phospholipase C-gamma 1 response and/or EGF receptor tyrosine kinase activity. Alteration of phospholipase C-gamma 1 activity does not appear to be responsible for the inhibition of cell growth seen in the absence of TGF alpha stimulation.

The effects of retinoic acid on the expression of alpha-fetoprotein and albumin genes in rat hepatoma cell lines

Many transcriptional regulators can stimulate or repress gene expression depending on the cellular or genetic contexts. Thus dexamethasone increases the amount of alpha-fetoprotein mRNA in Morris rat hepatoma derived cell line McA-RH 8994 cells, but decreases it in McA-RH 7777 cells. In the present study, we demonstrated that retinoic acid, whose receptors belong to the steroid/thyroid hormone receptor gene family, also enhanced the expression of alpha-fetoprotein and albumin gene in McA-RH 8994 cells, but had no effect on alpha-fetoprotein gene expression in McA-RH 7777 cells. In contrast to the effect of dexamethasone on the alpha-fetoprotein gene expression, which requires ongoing protein synthesis, cycloheximide, a protein synthesis inhibitor, enhanced the effect of retinoic acid. Actinomycin D inhibited the retinoic acid mediated increase in alpha-fetoprotein and albumin mRNA expression. Since the McA-RH 8994 cells did not express retinoic acid receptor beta mRNA, the observed regulatory effects of retinoic acid on alpha-fetoprotein and albumin gene expression were not mediated through retinoic acid receptor beta. We also conclude that the regulation was at the level of transcription and that retinoic acid and dexamethasone probably regulate the expression of liver specific genes through different mechanisms.