Growth inhibitory and stimulatory effects of retinoic acid on murine 3T3 cells

Chronicle of a discovery: the retinoic acid receptor

The landmark 1987 discovery of the retinoic acid receptor (RAR) came as a surprise, uncovering a genomic kinship between the fields of vitamin A biology and steroid receptors. This stunning breakthrough triggered a cascade of studies to deconstruct the roles played by the RAR and its natural and synthetic ligands in embryonic development, skin, growth, physiology, vision, and disease as well as providing a template to elucidate the molecular mechanisms by which nuclear receptors regulate gene expression. In this review, written from historic and personal perspectives, we highlight the milestones that led to the discovery of the RAR and the subsequent studies that enriched our knowledge of the molecular mechanisms by which a low-abundant dietary compound could be so essential to the generation and maintenance of life itself.

Impact of aldo-keto reductase family 1 member B10 on the risk of hepatitis C virus-related hepatocellular carcinoma

BACKGROUND AND AIM

Aldo-keto reductase family 1 member B10 (AKR1B10), a cancer-related oxidoreductase, was recently reported to be upregulated in some chronic liver diseases. However, its relevance in hepatocellular carcinoma (HCC) development is not fully assessed, especially in patients with chronic hepatitis C virus (HCV) infection.

METHODS

Aldo-keto reductase family 1 member B10 expression in the liver of 550 patients with chronic HCV infection was immunohistochemically assessed and quantified. A multivariate Cox model was used to estimate the hazard ratios (HRs) of AKR1B10 expression for HCC development, and the cumulative incidence of HCC was evaluated using the Kaplan-Meier method.

RESULTS

Aldo-keto reductase family 1 member B10 expression in the patients ranged from 0% to 80%. During the median follow-up of 3.2 years, 43 of 550 patients developed HCC. Multivariate analysis demonstrated that high AKR1B10 expression (≥6%) was an independent risk factor for HCC (HR, 6.43; 95% confidence interval, 2.90-14.25; P < 0.001). The 5-year cumulative incidences of HCC were 22.8% and 2.2% in patients with high and low AKR1B10 expression, respectively (P < 0.001). In subgroup analyses, the effects of high AKR1B10 expression on HCC development risk were significant over strata. In particular, HRs attributed to high AKR1B10 expression were significant in the subgroups that had been considered at a lower risk of HCC, such as in patients with younger age and mild hepatic fibrosis or those who achieved sustained virological response after interferon therapy.

CONCLUSION

Various degrees of AKR1B10 upregulation in the liver were observed in patients with chronic HCV infection, and high AKR1B10 expression could be a novel predictor of HCC.

Expression of aldo-keto reductase family 1 member b10 in the early stages of human hepatocarcinogenesis

Aldo-keto reductase family 1, member B10 (AKR1B10), a cancer-related oxidoreductase, is expressed in well-differentiated hepatocellular carcinomas (HCCs). However, AKR1B10 levels are minimal in normal liver tissues (NLs), similar to the 70-kilodalton heat shock protein (HSP70) and glypican-3. Moreover, the role of AKR1B10 in chronic hepatitis or cirrhosis, which are considered preneoplastic conditions for HCC, has not been fully elucidated. The aim of this study was to evaluate the expression of AKR1B10, HSP70, and glypican-3 in 61 HCC tissue samples compared to corresponding non-tumorous liver tissues (NTs), comprising 42 chronic hepatitis and 19 cirrhosis cases to clarify the significance of molecular changes at the preneoplastic stages of HCC. Immunohistochemical analysis demonstrated that the median expression levels of AKR1B10 were higher in HCCs than in NTs (p < 0.001) and higher in NTs than NLs (p < 0.001) with 54.8%, 2.1%, and 0.3% expression in HCCs, NTs, and NLs, respectively. HSP70 and glypican-3 were expressed in HCCs, but minimally in NTs and NLs with no significant difference between expression in NTs and NLs. Furthermore, a multivariate analysis identified an association between hepatic steatosis and AKR1B10 expression in NTs (p = 0.020). Of the three protein expressed in well-differentiated HCCs, only AKR1B10 was upregulated in preneoplastic conditions, and a steatosis-related factor might influence its expression.

Up-regulated aldo-keto reductase family 1 member B10 in chronic hepatitis C: association with serum alpha-fetoprotein and hepatocellular carcinoma

BACKGROUND

Elevated serum alpha-fetoprotein (AFP) is not only a diagnostic marker for hepatocellular carcinoma (HCC), but is also a risk factor for HCC in chronic hepatitis C patients who do not have HCC.

AIM

The aim was to analyse the hepatic gene expression signature in chronic hepatitis C patients with elevated AFP, who were at high risk for HCC.

METHODS

Liver tissue samples from 48 chronic hepatitis C patients were stratified by their serum AFP levels and analysed for gene expression profiles. The association between aldo-keto reductase family 1 member B10 (AKR1B10) expression and serum AFP was confirmed by quantitative real-time reverse transcription polymerase chain reaction (qRT-PCR) and immunohistochemical analyses. A matched case-control study was performed to evaluate the risk of AKR1B10 expression for HCC development.

RESULTS

Distinct hepatic gene expression patterns were demonstrated in patients with elevated AFP (≥10 ng/mL) and normal AFP (<10 ng/mL). Of the 627 differently expressed genes, the most abundantly expressed gene in patients with elevated AFP was AKR1B10 (fold change, 26.2; P < 0.001), which was originally isolated as an overexpressed gene in human HCC. The qRT-PCR and immunohistochemical studies confirmed a proportional correlation between AKR1B10 expression and serum AFP. A matched case-control study identified that AKR1B10 up-regulation (>6%) was an independent risk factor for HCC development (hazard ratio, 21.4; P = 0.001).

CONCLUSION

AKR1B10 was up-regulated in association with serum AFP, and was an independent risk factor for HCC in chronic hepatitis C patients, suggesting its possible involvement at a very early stage of hepatocarcinogenesis.

Epigenetic regulatory mechanisms distinguish retinoic acid-mediated transcriptional responses in stem cells and fibroblasts

Retinoic acid (RA), a vitamin A metabolite, regulates transcription by binding to RA receptor (RAR) and retinoid X receptor (RXR) heterodimers. This transcriptional response is determined by receptor interactions with transcriptional regulators and chromatin modifying proteins. We compared transcriptional responses of three RA target genes (Hoxa1, Cyp26a1, RARbeta(2)) in primary embryo fibroblasts (mouse embryonic fibroblasts), immortalized fibroblasts (Balb/c3T3), and F9 teratocarcinoma stem cells. Hoxa1 and Cyp26a1 transcripts are not expressed, but RARbeta(2) transcripts are induced by RA in mouse embryonic fibroblasts and Balb/c3T3 cells. Retinoid receptors (RARgamma, RXRalpha), coactivators (pCIP (NCOA3, SRC3)), and p300 and RNA polymerase II are recruited only to the RARbeta(2) RA response element (RARE) in Balb/c3T3, whereas these proteins are recruited to RAREs of all three genes by RA in F9 cells. In F9, RA reduces polycomb (PcG) protein Suz12 and the associated H3K27me3 repressive epigenetic modification at the RAREs of all three genes. In contrast, in Balb/c3T3 cells cultured in the +/-RA, Suz12 is not associated with the Hoxa1, RARbeta(2), and Cyp26a1 RAREs, whereas slow levels of the H3K27me3 mark are seen at these RAREs. Thus, Suz12 is not required for gene repression in the absence of RA. Even though the Hoxa1 RARE and proximal promoter show high levels of H3K9,K14 acetylation in Balb/c3T3, the Hoxa1 gene is not transcriptionally activated by RA. In Balb/c3T3, CpG islands are methylated in the Cyp26a1 promoter region but not in the Hoxa1 promoter or in these promoters in F9 cells. We have delineated the complex mechanisms that control RA-mediated transcription in fibroblasts versus stem cells.

In vitro effects of retinoids on the proliferation and differentiation features of Epstein-Barr virus-immortalized B lymphocytes

Retinoids have been shown to be effective in the chemoprevention and treatment of certain human malignancies. In this review, we will summarize our recent results concerning the effects of retinoids on the proliferation and differentiation of Epstein-Barr virus (EBV)-immortalized lymphoblastoid B-cell lines (LCLs), an in vitro model of EBV-related lymphoproliferative disorders arising in immunosuppressed hosts. Retinoids proved to be powerful inhibitors of the proliferation of EBV-infected LCLs in vitro, with 13-cis-retinoic acid (RA), all-trans-RA, and 9-cis-RA being the most effective compounds. Of note, retinoid-induced growth arrest in vitro appears irreversible at drug concentrations (10(-6) mol/L) which may be reached in man after oral systemic therapy. The antiproliferative activity exerted by retinoids on LCLs is a generalized phenomenon usually associated with a progressive accumulation in G0/G1 phases of treated cells. The strong upregulation of p27Kip1 invariably observed in cells exposed to retinoids may contribute to the decreased number of cycling cells, probably by inhibiting the transition from the G1 to S phase. Moreover, we obtained evidence indicating that the antiproliferative effects of retinoids are not dependent on the induction of terminal differentiation of EBV-immortalized B lymphocytes. In fact, the modifications induced by retinoids relative to LCL morphology, phenotype (downregulation of CD19, HLA-DR, and s-Ig, and upregulation of CD38 and c-Ig), and IgM production were highly variable among the lines tested and often only slightly relevant. Finally, the antiproliferative activity exerted by retinoids on LCLs is not mediated by a direct modulation of viral latent antigens, since EBNA-2 and LMP- downregulation was a late event detected only in some cell lines. These results indicate that retinoids may be useful in the medical treatment of EBV-related lymphoproliferative disorders of immunosuppressed patients, particularly in the earlier phases of these diseases.

Modulation of growth and proliferation in squamous cell carcinoma by retinoic acid: a rationale for combination therapy with chemotherapeutic agents

We have previously shown that beta-all trans retinoic acid (RA) inhibits macrocellular growth of a multicellular tumor spheroid model for squamous carcinoma, as measured by spheroid size, but allows for continuing DNA synthesis and cell cycle progression, the two being reconciled by a cell death effect. DNA synthesis in the presence of growth inhibition suggested a rationale for examining combination chemotherapy with RA-inhibited cells. To this aim, we have extended this observation to a series of 8 squamous carcinoma cell lines. Cells were treated with 1 microM RA for 7 days and cell growth parameters monitored. Although growth inhibition ranged from 0% (A431) to approx. 80% (MDA 886Ln), [3H]-thymidine incorporation (cpm/microgram protein) and percent S-phase (by flow cytometry) in 7-day RA-treated cells was equal or higher than in their control vehicle-treated cells in 7/8 SCC cell lines. Thus RA-induced growth inhibition is not just cytostasis. Combination therapy was examined with MDA 886Ln, MDA 686Ln, 1483 and A431 cells pre-treated for 7 days with 1 microM RA followed by cisplatin or 5-fluorouracil treatment. An increased effectiveness for the combination was shown using 5-day tetrazolium dye (MTT) growth assays when cells were growth-inhibited by RA. Computerized analysis of data using median-effect and isobologram techniques indicated that the interaction of RA with these chemotherapeutic agents was synergistic. With squamous carcinoma, RA treatment inhibits growth while allowing for continuing DNA synthesis, and these RA-treated, growth-inhibited cells exhibit increased sensitivity to chemotherapeutic agents.

Human dermal fibroblasts modulate the effects of retinoids on epidermal growth

We report the pharmacologic effects of retinoids in a human skin-equivalent model. This sophisticated culture system is composed, as in vivo, of a dermis and epidermis, and provides a unique in vitro system for studying dermal-epidermal interactions and thus, whether normal dermal fibroblasts influence the effects of retinoids on epidermal growth. Epidermalization was initiated on collagen substrates in which fibroblasts were either viable or lysed by osmotic shock. Retinoic acid, isotretinoin, and acitretin at 10(-6) M or 10(-7) M were added to the cultures just after epidermalization, then every two days. Epidermal growth was determined after 2 weeks in terms of the surface area, DNA content, and tritiated thymidine incorporation during the last 24 h of culture. In the absence of viable fibroblasts, retinoic acid and isotretinoin increased epidermal growth, whereas etretin inhibited it. In contrast, in the presence of viable fibroblasts, retinoic acid and isotretinoin inhibited epidermal growth, whereas etretin had no effect. Thus, retinoic acid and isotretinoin had a similar effect on keratinocyte proliferation that contrasted with that of etretin. Taken as a whole, these results show that fibroblasts, present within a collagen substrate, can modulate the pharmacologic effects of retinoids on epidermal growth.

Effects of beta-all-trans retinoic acid on growth, proliferation, and cell death in a multicellular tumor spheroid model for squamous carcinomas

The growth of multicellular tumor spheroids, MTSs, from squamous carcinoma line MDA 886Ln was inhibited by beta-all-trans retinoic acid (RA). Inhibition occurred within 3 to 5 days of treatment, and MTS size then remained static for up to 2 weeks. Although their growth stopped, 10-day-treated MTSs incorporated [3H]thymidine into trichloroacetic acid-precipitable material, and the [3H]thymidine labeling index, determined by autoradiography, was equivalent between control and RA-treated MTSs. Bivariate flow cytometric analysis of bromodeoxyuridine-labeled MTSs showed equivalent S phase progression of labeled cells over an 8-hour chase. MTS growth stasis was not related to RA-induced cell cycle effects. Monitoring of MTSs for cell sloughing showed no significant cell shedding that could account for stasis. Quantitation of cell number and DNA content per MTS showed an RA-induced decrease. This was confirmed by histological analysis, which demonstrated the temporal appearance of acellular areas. MTS growth statis is thus related to an RA-induced cell loss in this MTS model for squamous carcinomas.

Control of the adipogenic differentiation of 3T3-F442A cells by retinoic acid, dexamethasone, and insulin: a topographic analysis

Differentiation of 3T3-F442A adipocytes, monitored by accumulation of neutral lipid and by using the sensitive marker glycerophosphate dehydrogenase, is inhibited by incubation of confluent 3T3-F442A fibroblasts in medium containing retinoic acid or dexamethasone. When added together, dexamethasone (0.25 microM) potentiates about 50-fold the inhibitory effect of retinoic acid (10 microM). Insulin cannot counteract the retinoic acid blockade; however, it can overcome the inhibition of differentiation elicited by dexamethasone. These differential effects of insulin are used for characterizing the adipose conversion cycle. We describe cell culture conditions where terminal differentiation of 3T3-F442A preadipocytes is achieved by low, physiological levels of insulin. They include the switch from a high-serum medium containing isobutyl methyl xanthine and dexamethasone to a serum-free, hormone-supplemented medium. The data reported establish the existence of two successive states for commitment to adipogenic differentiation: a first commitment point (CA) to differentiation which requires serum adipogenic factors, and a second commitment point (CH) controlled by lipogenic hormones, namely insulin, after which terminal maturation can resume. We demonstrate that retinoic acid can prevent and interrupt differentiation by blocking the cells within the early differentiation phase.

Retinoic acid alters subcellular compartmentalization of ATP pools in 3T3 cells but not in HeLa cells

Retinoic acid (RA; beta-all-trans) inhibits the proliferation of both murine 3T3 cells and human HeLa cells. Flow cytometric analyses of exponentially growing cultures show that 3T3 cells are inhibited during the S phase of their cell cycle, while HeLa cells show only a small increase in G1 phase cells. RA (10 microM) causes a 50% increase in total cellular adenosine triphosphate (ATP) pools of 3T3 cells, but not of HeLa cells. We have previously demonstrated that the effects of RA on cellular ATP pools of 3T3 cells are directly related to its inhibition of cellular growth, and now report data which provide a biochemical basis for this process. Established procedures were utilized to investigate the effects of RA on the functional compartmentalization of the nuclear ATP pool which serves as a precursor for RNA synthesis in these cells, and which is shown to be a small pool in comparison with cytoplasmic ATP pools. Expansion of total cellular ATP pools by 1 mM of exogenously supplied unlabeled adenosine is ineffective in reducing the subsequent incorporation of [3H]adenosine into RNA of 3T3 cells. Similar treatment of HeLa cells yields a modest reduction in the incorporation of [3H]adenosine into RNA. RA treatment of HeLa cells does not affect the preferential uptake of exogenous [3H] adenosine into the immediate precursor ATP pool for RNA synthesis. RA treatment of 3T3 cells markedly reduces the incorporation of [3H] adenosine into RNA, indicating a lesser degree of functional compartmentalization of the nuclear ATP pool. Similar conclusions are drawn from correlations of the specific radioactivities of total cellular [3H] ATP pools and the levels of incorporation of radioactive label into cellular RNA. In addition, pulse-chase experiments show that RA-treated 3T3 cells continue to incorporate radioactive label from pools prelabeled with [3H]adenosine despite the presence of a large excess of unlabeled adenosine in the chase medium. Control 3T3 and both control and RA-treated HeLa cells cease to incorporate label immediately upon the start of the chase, suggesting that the functional precursor ATP pool for RNA synthesis is small and readily diluted. These data suggest that RA decreases the degree of functional compartmentalization for 3T3, but not HeLa cell ATP pools, and provides a probable mechanism for expansion of nuclear ATP pools of 3T3 cells. The expanded nuclear ATP pools may provide the biochemical mechanism for the inhibition of DNA synthesis during the S phase of the 3T3 cell cycle.

Retinoic acid restores shape-dependent growth control in neoplastic cells cultured on poly(2-hydroxyethyl methacrylate)-coated substrate

The ability of retinoic acid to modulate cell-shape-dependent growth of untransformed (human skin fibroblasts and mouse embryo Swiss 3T3 fibroblasts) and neoplastic cells (human cervical carcinoma HeLa-S3, osteosarcoma Hs791, and murine melanomas B16-F1, S91-C2 and S91-C154) was examined. The cells were plated on tissue culture dishes coated with increasing concentrations of poly(2-hydroxyethyl methacrylate), poly(HEMA) which cause a gradual decrease in substrate adhesiveness. Untreated cells as well as cells pretreated with 10 microM retinoic acid for 4 days displayed a similar graded series of cell shapes between flat and spherical on these modified substrata, with the exception of HeLa-S3 cells which were rounded and loosely attached even on uncoated plastic dishes. A marked cell-shape-dependent decrease in DNA synthesis was observed in untransformed human skin fibroblasts, Swiss 3T3 fibroblasts and neoplastic human Hs791 cells 20 h following plating of untreated cells on poly(HEMA)-coated substrates of decreasing adhesiveness. Conversely, in B16-F1, HeLa-S3 and S91-C154 cells DNA synthesis was only slightly affected by changes in cell shape. Pretreatment with retinoic acid rendered DNA synthesis in Swiss 3T3, Hs791, B16-F1 and S91-C2 cells much more sensitive to changes in cell shape. In contrast, retinoic acid exerted only marginal effects on the sensitivity of DNA synthesis to changes in cell shape in untransformed human skin fibroblasts, in HeLa-S3 cells and in the retinoic-acid-resistant S91-C154 cells. The results suggest that retinoic acid can restore in certain tumor cells the tight coupling between cell shape and DNA synthesis that exists in untransformed cells.

Stimulation of cell proliferation by vitamin A derivatives on murine sarcoma virus-transformed mouse cells in serum-free culture

The effect of retinoids (Rds) on cell proliferation was studied in serum-free culture condition, using non-transformed and transformed derivatives of BALB 3T3. Cell proliferation of an SV40-transformed line was inhibited significantly by Rd treatment. However, proliferation of two cell lines that were transformed by a Kirsten and Moloney strain of murine sarcoma virus (MSV) and produced growth factor into culture medium, was remarkably stimulated by Rds. Addition of serum masked both the inhibitory and stimulatory effects of Rds.

Retinoic acid-promoted expansion of total cellular ATP pools in 3T3 cells can mediate its stimulatory and growth inhibitory effects

Exposure of Swiss 3T3 cells to micromolar quantities of beta-all-trans-retinoic acid (RA) results in either inhibition of growth or stimulation of cellular responsiveness to mitogens, depending on the length of treatment. Inhibition of growth is produced by treatment of the cells with RA for at least 48 hours. The total cellular pools of adenosine 5'-triphosphate (ATP) are markedly increased after 48-hour RA treatment and dose dependence studies show a correlation between the expanded ATP pools and the inhibitor effects. The expansion of total cellular ATP pools by retinoic acid occurs throughout the cell cycle and parallels the cell cycle-dependent fluctuations in total cellular ATP pools of untreated cells. Studies of [3H]thymidine incorporation and labeling indices in intact cells and [3H]dTTP incorporation and labeling indices in isolated nuclei of RA-treated and control cultures suggest that cellular acid-soluble nucleotide pools mediate the inhibition of DNA replication in the 48-hour-RA-treated cells. The stimulatory activity of RA for mitogenic responsiveness is demonstrated by treatment of G0/G1-arrested 3T3 cells with micromolar levels of RA for a maximum of 18 hours resulting in the potentiation of phorbol myristate acetate (PMA)-stimulated transition into S phase of the cell cycle. Marked increases in total cellular ATP and UTP pools are produced by 18-hour treatment of G0/G1-arrested cells with RA, before their exposure to PMA.