The uptake of labeled vitamin A acid in keratoacanthoma. An electron microscopic radioautography study

The effect of sodium butyrate and retinoic acid on growth and CEA production in a series of human colorectal tumor cell lines representing different states of differentiation

The effect of sodium butyrate and retinoic acid added singly or in combination on substrate-dependent growth, colonization efficiency in soft agar, and carcino-embryonic antigen (CEA) production in three human colorectal carcinoma cell lines differing in their degree of differentiation was studied. All three colon cancer cell lines regardless of their state of differentiation had their growth markedly slowed by sodium butyrate, and to a lesser extent by retinoic acid. When both agents were added together, a small synergistic inhibition of growth was noted in all the cell lines. Butyrate eliminated colony formation in soft agar in all three cell lines, however, retinoic acid only reduced colony formation in the well differentiated cell line DLD-2. Sodium butyrate was able to induce CEA production in the undifferentiated cell (MIP-101) and the moderately differentiated cells (clone D) which were previously negative for this marker. It also enhanced the baseline production of CEA in the well differentiated cells (DLD-2). Retinoic acid did not induce CEA production in clone D or MIP-101 cells, but did enhance the production of CEA in DLD-2 cells. When both retinoic acid and sodium butyrate were added together, CEA production was either additive (DLD-2) or was inhibited (clone D and MIP-101). One explanation of these results is that only well differentiated cells have functional cellular retinoic acid-binding protein (cRABP), and that certain actions of retinoic acid (inhibition of anchorage-dependent growth) are independent of the presence of cRABP.

Effects of vitamins A, C, and E on aflatoxin B1-induced mutagenesis in Salmonella typhimurium TA-98 and TA-100

The effects of retinoids (vitamin A analogs) and vitamins C and E on the aflatoxin B1 (AFB1)-induced mutagenesis in Salmonella typhimurium TA-98 and TA-100 were investigated. The bioassay was performed under conditions that permitted the effects of vitamins on carcinogen metabolism to be assessed separately from effects on the expression of the mutated bacterial cell. Both retinoic acid and retinol inhibited (up to 50%) AFB1-induced mutagenesis in S. typhimurium TA-98, but only retinol inhibited (up to 75%) mutagenesis in TA-100. Retinoic acid inhibition of mutagenesis in S. typhimurium TA-98 was pronounced over a wide concentration range (i.e., 2 X 10(-10) to 2 X 10(-8) M) however, at the higher concentrations (i.e., 2 X 10(-8) to 2 X 10(-6) M range) the predominant effect was the inhibition of the metabolism of AFB1 to its mutagenic metabolites. Vitamin E was more potent in inhibiting the expression of AFB1-induced mutagenesis than vitamin C. However, the major inhibitory effects of vitamin E were related to the metabolism of AFB1, whereas vitamin C was inhibitory at both metabolic and the post-metabolic levels of the AFB1 mutagenesis assay. The results of these investigations suggest that vitamins A, C, or E inhibit both AFB1 metabolism to its mutagenic metabolites as well as the expression of AFB1-induced mutated bacterial cells.

Retinoid binding in normal and neoplastic mammary tissue

The inhibitory effect of dietary supplementation of certain retinoids on mammary carcinogenesis in the rat has been reported from our laboratory. Specific cytosolic retinoic acid binding proteins (cRABP) as well as retinol binding proteins sedimenting as 2S components have been detected in the mammary tissue during normal and neoplastic differentiation. Relatively higher levels of cRABP were observed in the mammary glands from pregnant animals as well as in ovarian hormone independent tumors; whereas in glands obtained from lactating rats and in hormone dependent tumors, lower levels of cRABP were evident. Exogenous treatment of such animals with estradiol-17 beta enhanced the levels of cRABP. The results indicate a possible correlation between endocrine and retinoid function in both normal and neoplastic differentiation of mammary tissue. [3H]retinoic acid-RABP complex, under appropriate conditions, translocates into th nucleus. Unbound [3H]retinoic acid, however, failed to associate with the nuclear sites. Additional studies indicate a possible selective inhibition of ovarian hormones independent tumors by the retinoids.

Antiproliferative effects of retinoids related to the cell cycle-specific inhibition of ornithine decarboxylase

The induction of ornithine decarboxylase (ODC) during G1 phase of the cell cycle appears to be universal and essential for cell cycle progression. This induction has been demonstrated in at least 23 cell types in response to various growth stimuli. Further, specific inhibitors of ODC added to several of these cell lines resulted in inhibition of cell proliferation. The studies of the effects of retinoids to inhibit Chinese hamster ovary (CHO) cell growth indicate that the cells are blocked in G1 of cell cycle, and that there is a concentration-dependent inhibition of ODC induction. Retinoids only inhibit the induction of ODC activity when added in the first 2-3 hr of G1 progression. It is postulated that ODC induction is a requirement for G1 progression and that the antiproliferative properties of retinoids are related to the specific ability to inhibit this expression. Since retinoids do not dramatically alter the rate of protein synthesis, their ability to inhibit ODC may be related to their ability to inhibit messenger RNa synthesis for ODC.

Molecular aspects of control in epidermal differentiation

The mammalian epidermis is organized into layers of structurally different cells--the basal, spinous, granular and cornified layers--which represent steps in the differentiative process that terminates in cornification and desquamation. Investigation of the molecular mechanisms that control this ordered sequence of events provides clues to the etiology of certain epidermal pathologies. DNA synthesis and mitosis are normally restricted to the basal layer. Several substances have been implicated in the mitotic control of epidermal cells, the loss of mitotic activity being the first major step in normal keratinization. Investigations performed in this laboratory indicate that isolated differentiated nuclei can replicate their DNA which they are inhibited from doing in situ. Addition of a high speed supernate from homogenized differentiated cells inhibited this synthetic activity in vitro suggesting the existence of a cytoplasmic inhibitor of DNA synthesis. It is not known whether mitotic inhibition in differentiated epidermal cells is a function of the inhibition of DNA replication. Contrary to previous assumptions, recent experimental evidence clearly indicates that, unlike DNA synthesis, RNA synthesis occurs in differentiated cells. Correlated with this synthetic activity is the observation that a protein rich in histidine is specifically formed in the granular cells. This protein appears to be a component of the keratohyalin granules which fill the cells of the granular layer. Investigations were conducted in this laboratory to determine whether control of the synthesis of this protein occurs at the level of translation or transcription. Translation, in vitro, of mRNA obtained from isolated populations of each epidermal cell type suggested that control of protein synthesis in the differentiating epidermis is transcriptional, i.e. only in the granular cell is there an mRNA for the histidine-rich protein. Transcription, in vitro, of chormatin isolated from the separated cell populations produced RNA with a ratio of cytidine to uracil consistent with the predicted mRNA for this protein thus providing additional support for the hypothesis that epidermal differentiation is controlled at the level of 'gene-readout'.