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R Lotan

Publications and source records attributed to R Lotan.

At least 19 recordsLinked to original sources
PubMed2006

N-(4-hydroxyphenyl)retinamide-induced apoptosis triggered by reactive oxygen species is mediated by activation of MAPKs in head and neck squamous carcinoma cells.

N-(4-hydroxyphenyl)retinamide (4HPR), a synthetic retinoid effective in cancer chemoprevention and therapy, is thought to act via apoptosis induction resulting from increased reactive oxygen species (ROS) generation. As ROS can activate MAP kinases and protein kinase C (PKC), we examined the role of such enzymes in 4HPR-induced apoptosis in HNSCC UMSCC22B cells. 4HPR increased ROS level within 1 h and induced activation of caspase 3 and PARP cleavage within 24 h. Activation of MKK3/6 and MKK4, JNK, p38 and ERK was detected between 6 and 12 h, increased up to 24 h and preceded apoptosis. 4HPR-induced activation of these kinases was abrogated by the antioxidants BHA and vitamin C. SP600125, a JNK inhibitor, suppressed 4HPR-induced c-Jun phosphorylation, cytochrome c release from mitochondria and apoptosis. Suppression of JNK1 and JNK2 using siRNA decreased, whereas overexpression of wild type-JNK1 enhanced 4HPR-induced apoptosis. PD169316, a p38, inhibitor suppressed phosphorylation of Hsp27 and apoptosis. PD98059, an MEK1/2 inhibitor, also suppressed ERK1/2 activation and apoptosis induced by 4HPR. Likewise, PKC inhibitor GF109203X suppressed ERK and p38 phosphorylation and PARP cleavage. These data indicate that 4HPR-induced apoptosis is triggered by ROS increase, leading to the activation of the mitogen-activated protein serine/threonine kinases JNK, p38, PKC and ERK, and subsequent apoptosis.

Anticarcinogenic Agents↗
PubMed2006

Mechanisms of fenretinide-induced apoptosis.

Fenretinide, a synthetic retinoid, has emerged as a promising anticancer agent based on numerous in vitro and animal studies, as well as chemoprevention clinical trials. In vitro observations suggest that the anticancer activity of fenretinide may arise from its ability to induce apoptosis in tumor cells. Diverse signaling molecules including reactive oxygen species, ceramide, and ganglioside GD3 can mediate apoptosis induction by fenretinide in transformed, premalignant, and malignant cells. In many cell types, these signaling intermediates appear to be induced by mechanisms that are independent of retinoic acid receptor activation, and ultimately initiate the intrinsic or mitochondrial-mediated pathway of cell elimination. Numerous investigations conducted during the past 10 years have discovered a great deal about the apoptogenic activity of fenretinide. In this review we explore the mechanisms associated with fenretinide-induced apoptosis and highlight certain mechanistic underpinnings of fenretinide-induced cell death that remain poorly understood and thus warrant further characterization.

Animals↗
PubMed2005

Global detection of molecular changes reveals concurrent alteration of several biological pathways in nonsmall cell lung cancer cells.

To identify the molecular changes that occur in non-small cell lung carcinoma (NSCLC), we compared the gene expression profile of the NCI-H292 (H292) NSCLC cell line with that of normal human tracheobronchial epithelial (NHTBE) cells. The NHTBE cells were grown in a three-dimensional organotypic culture system that permits maintenance of the normal pseudostratified mucociliary phenotype characteristic of bronchial epithelium in vivo. Microarray analysis using the Affymetrix oligonucleotide chip U95Av2 revealed that 1,683 genes showed a >1.5-fold change in expression in the H292 cell line relative to the NHTBE cells. Specifically, 418 genes were downregulated and 1,265 were upregulated in the H292 cells. The expression data for selected genes were validated in several different NSCLC cell lines using quantitative real-time PCR and Western analysis. Further analysis of the differentially expressed genes indicated that WNT responses, apoptosis, cell cycle regulation and cell proliferation were significantly altered in the H292 cells. Functional analysis using fluorescence-activated cell sorting confirmed concurrent changes in the activity of these pathways in the H292 line. These findings show that (1) NSCLC cells display deregulation of the WNT, apoptosis, proliferation and cell cycle pathways, as has been found in many other types of cancer cells, and (2) that organotypically cultured NHTBE cells can be used as a reference to identify genes and pathways that are differentially expressed in tumor cells derived from bronchogenic epithelium.

Apoptosis↗
PubMed2005

ICAM-5 (telencephalin) gene expression in head and neck squamous carcinoma tumorigenesis and perineural invasion!

ICAM-5 (telencephalin) is an intercellular adhesion molecule reported to be expressed only in the somatodendritic membrane of telencephalic neurons. We recently identified high ICAM-5 expression in a cDNA array study of head and neck neoplasms with a propensity for perineural invasion. To determine the association of this gene in tumorigenesis and perineural invasion, we analyzed the expression and functional status of ICAM-5 mRNA transcripts in 30 different human cancer cell lines and 25 head and neck squamous carcinoma specimens by reverse-transcriptase polymerase chain reaction (cell lines and specimens) and in vitro functional assays (cell lines). ICAM-5 transcripts were detected in 28 (93%) of 30 cell lines derived from primary head and neck, colon, thyroid, cervical, pancreatic, skin, and adenoid cystic carcinomas. In cell lines, small interfering RNA blocked ICAM-5 expression and inhibited cell proliferation. Treatment with the phosphatidylinositol 3'-kinase (PBK) inhibitor LY294002 resulted in ICAM-5 down-regulation. In tissue specimens, none of the 25 histologically normal oral mucosal specimens had detectable ICAM-5 level, whereas 16 (64%) of the 25 matched primary squamous carcinomas showed expression. Carcinoma specimens high ICAM-5 expression had a high incidence of perineural invasion. Our study indicates that ICAM-5 may play a role in tumorigenesis and perineural invasion, most likely through the P13K/Akt-signaling pathway.

Adult↗
PubMed2004

Apoptosis induction by the natural product cancer chemopreventive agent deguelin is mediated through the inhibition of mitochondrial bioenergetics.

Deguelin exhibits chemopreventive properties in animal carcinogenesis models. The mechanism underpinning the chemopreventive effects of deguelin has not been fully elucidated. However, it has been suggested that this agent reduces ornithine decarboxylase activity, and perhaps the activity of other signaling intermediates associated with tumorigenesis, by inhibiting mitochondrial bioenergetics. We sought to determine if deguelin could trigger apoptosis by inhibiting mitochondrial bioenergetics. Therefore, we compared and contrasted the effects of deguelin on cells from two human cutaneous squamous cell carcinoma cell lines (parental cells) and their respiration-deficient clones lacking mitochondrial DNA (rho0). While deguelin promoted marked apoptosis in the parental cells in a dose- and time-dependent manner, it failed to do so in the rho0 clones. Furthermore, short-term exposure to deguelin diminished oxygen consumption by the parental cells and promoted mitochondrial permeability transition as evidenced by the dissipation of mitochondrial inner transmembrane potential, reactive oxygen species production, cardiolipin peroxidation, caspase activation, and mitochondrial swelling. Mitochondrial permeability transition was not observed in the rho0 clones exposed to deguelin. These results demonstrate that deguelin induces apoptosis in skin cancer cells by inhibiting mitochondrial bioenergetics and provide a novel mechanism for the putative anticancer activity of this agent.

Apoptosis↗
PubMed2004

Involvement of c-Fos in fenretinide-induced apoptosis in human ovarian carcinoma cells.

Fenretinide (HPR), a synthetic retinoid that exhibits lower toxicity than other retinoids, has shown preventive and therapeutic activity against ovarian tumors. Although the growth inhibitory effects of HPR have been ascribed to its ability to induce apoptosis, little is known about the molecular mechanisms involved. Since the proto-oncogene c-Fos has been implicated in apoptosis induction, we analyzed its role in mediating HPR response in a human ovarian carcinoma cell line (A2780) sensitive to HPR apoptotic effect. In these cells, HPR treatment caused induction of c-Fos expression, whereas such an effect was not observed in cells made resistant to HPR-induced apoptosis (A2780/HPR). Moreover, in a panel of other human ovarian carcinoma cell lines, c-Fos inducibility and HPR sensitivity were closely associated. Ceramide, which is involved in HPR-induced apoptosis, was also involved in c-Fos induction because its upregulation by HPR was reduced by fumonisin B(1), a ceramide synthase inhibitor. The causal relationship between c-Fos induction and apoptosis was established by the finding of an increased apoptotic rate in cells overexpressing c-Fos. Similarly to that observed for c-Fos expression, HPR treatment increased c-Jun expression in HPR-sensitive but not in HPR-resistant cells, suggesting the involvement of the transcription factor activating protein 1 (AP-1) in HPR-induced apoptosis. In gene reporter experiments, HPR stimulated AP-1 transcriptional activity and potentiated the AP-1 activity induced by 12-tetradecanoylphorbol 13-acetate. Furthermore, inhibition of AP-1 DNA binding, by transfecting A2780 cells with a dominant-negative Fos gene, caused decreased sensitivity to HPR apoptotic effects. Overall, the results indicate that c-Fos plays a role in mediating HPR-induced growth inhibition and apoptosis in ovarian cancer cells and suggest that c-Fos regulates these processes as a member of the AP-1 transcription factor.

Antineoplastic Agents↗
PubMed2001

Mitochondrial respiration is uniquely associated with the prooxidant and apoptotic effects of N-(4-hydroxyphenyl)retinamide.

The synthetic retinoid N-(4-hydroxyphenyl)retinamide (4HPR) is being examined in both chemoprevention and therapy clinical trials. Yet, its mechanism(s) of action is still not fully elucidated. In previous studies, an increase in mitochondrial reactive oxygen species has been proposed as one mechanism through which 4HPR could exert its proapoptotic effects. This study explored whether mitochondrial respiration is required for 4HPR action using human cutaneous squamous cell carcinoma cells and respiration-deficient clones. In parental cells, 4HPR rapidly promoted hydroperoxide production followed by mitochondrial permeability transition, caspase activity, and DNA fragmentation. Short term exposure to 4HPR also inhibited oxygen consumption in parental cells. This activity was reversed by the antioxidant vitamin C indicating the prooxidant effect of 4HPR directly impaired mitochondrial function. In respiration-deficient clones, the proapoptotic qualities of 4HPR were conspicuously diminished illustrating a central role for mitochondrial respiration in 4HPR-induced cell death. In parental cells, various mitochondrial inhibitors were examined to determine potential sites associated with the prooxidant activity of 4HPR. Inhibitors of Complex II as well as center i inhibitors of Complex III enhanced 4HPR-induced hydroperoxide production. Complex I inhibitors, center o inhibitors of Complex III, cyanide, oligomycin A, and coenzyme Q analogues decreased 4HPR-induced hydroperoxide production. The coenzyme Q analogues were very effective in this respect, and they also blocked the enhanced hydroperoxide production obtained when center i inhibitors were combined with 4HPR. These results suggest the prooxidant property of 4HPR is associated with redox metabolism via an enzymatic process occurring at a quinone-binding site in Complex I and/or center o of Complex III.

Apoptosis↗
PubMed2001

Diminished expression of S100A2, a putative tumor suppressor, at early stage of human lung carcinogenesis.

To identify and understand early events in lung carcinogenesis, we used a cDNA array to screen for genes that are expressed differentially in normal human bronchial epithelial (NHBE) cells and a tumorigenic cell line (1170-I) derived from immortalized HBE cells after exposure to cigarette smoke condensate in vivo. Among these genes, we have identified the S100A2 gene, which encodes a nuclear calcium-binding protein, as being down-regulated in the 1170-I cells. Because this gene has been implicated as a tumor suppressor in breast cancer, we examined its potential role as a tumor suppressor in lung carcinogenesis. Levels of S100A2 transcript and protein, which were high in NHBE cells, decreased by up to 50% in immortalized HBE cells (BEAS-2B and 1799) and to low to nearly undetectable levels in transformed (1198) and tumorigenic (1170-I) HBE cells. Furthermore, S100A2 mRNA and protein were undetectable in 8 and expressed at a reduced level in 3 of 11 non-small cell lung cancer (NSCLC) cell lines. Positive immunohistochemical staining of S100A2 was detected in the majority (75-83%) of normal and hyperplastic lung tissues, whereas it was detected in <10% of metaplastic lung tissues, squamous cell carcinoma, and adenocarcinoma. Treatment of 1170-I HBE and NSCLC cells with 5-aza-2'-deoxycytidine resulted in partial restoration of S100A2 expression in seven of eight cell lines. Indeed, CpG methylation was detected in the promoter region of the S100A2 gene. Our results suggest that S100A2 expression is suppressed early during lung carcinogenesis, possibly by hypermethylation of its promoter, and that its loss may be a contributing factor in lung cancer development or a biomarker of early changes in this process.

Animals↗
PubMed2001

Differential effects of chromosome 3p deletion on the expression of the putative tumor suppressor RAR beta and on retinoid resistance in human squamous carcinoma cells.

Retinoids' effects on cell growth and differentiation are mediated by nuclear retinoid receptors, which are ligand-activated transcription enhancing factors. Because the expression of the retinoic acid receptor beta (RARbeta) gene, which is located on chromosome 3p24, is diminished in premalignant and malignant tissues it has been proposed that it acts as a tumor suppressor. To test the hypothesis that RARbeta loss leads to retinoid resistance, we studied several karyotyped head and neck squamous carcinoma (HNSCC) cell lines (UMSCC-17A, -17B, -22A, -22B, and -38) with deletion of one chromosome 3p arm. RARbeta mRNA was neither detected nor induced by retinoic acid in these cells, whereas it was expressed and induced by retinoic acid in two other HNSCC cell lines (1483 and 183) without 3p deletion. Methylation of the RARbeta gene promoter was detected in the 17B and 22B cells that failed to express RARbeta but no methylation was found in 183A cells that did express RARbeta mRNA. Responsiveness of HNSCC cells to several retinoids in assays of growth inhibition and colony formation, was rank ordered as: 22B>1483>38>183>17B. Additionally, retinoid response elements were transactivated in 22B more efficiently than in 17B cells. These results indicate that loss of RARbeta expression does not necessarily lead to loss of growth inhibition by retinoids or to a block of retinoid signaling.

Antineoplastic Agents↗
PubMed2001

Evidence supporting a role for mitochondrial respiration in apoptosis induction by the synthetic retinoid CD437.

Retinoids have been shown to modulate cell proliferation, differentiation, and apoptosis. It is thought that these effects mediate the chemopreventive and therapeutic effects of retinoids. Recently, some synthetic retinoids, including 6-[3-(1-adamantyl)-4-hydroxyphenyl]-2-naphthalene carboxylic acid (CD437), have been found to induce apoptosis even in tumor cell lines that are resistant to all-trans retinoic acid. The proapoptotic activity of CD437 has been attributed to mitochondrial dysfunction via the induction of mitochondrial permeability transition (P. Marchetti et al., Cancer Res. 59: 6257-6266, 1999). The mechanistic aspects pertaining to how CD437 promotes changes in mitochondrial function are unclear. This study investigated the role of mitochondrial respiration in CD437-induced apoptosis. Human cutaneous squamous cell carcinoma COLO 16 cells were chronically exposed to ethidium bromide to inhibit mitochondrial DNA synthesis and produce respiration-deficient clones. These clones were exposed to CD437 (<or=10 microM) for 48 h and exhibited a marked resistance to mitochondrial permeability transition and apoptosis illustrating that mitochondrial respiration was required for these effects.

Antineoplastic Agents↗
PubMed2001

Nonsteroidal anti-inflammatory drugs induce apoptosis in esophageal cancer cells by restoring 15-lipoxygenase-1 expression.

In previous studies, we have found that expression of 15-lipoxygenase-1 (15-LOX-1) and its main product, 13-S-hydroxyoctadecadienoic acid, are decreased in human colorectal cancers and that nonsteroidal anti-inflammatory drugs (NSAIDs) can therapeutically induce 15-LOX-1 expression to trigger apoptosis in human colorectal cancer cells. NSAIDs similarly induce apoptosis in esophageal cancer cells, although the mechanisms of these effects remain to be defined. In the present study, we tested whether 15-LOX-1 is down-regulated in human esophageal cancers using paired normal and tumor human surgical samples and whether NSAIDs can up-regulate 15-LOX-1 to restore apoptosis in esophageal cancer cells. We found that: (a) 15-LOX-1 was down-regulated in human esophageal carcinomas; (b) NSAIDs induced 15-LOX-1 expression during apoptosis in esophageal cancer cells; and (c) 15-LOX-1 inhibition suppressed NSAID-induced apoptosis, which was restored by 13-S-hydroxyoctadecadienoic acid but not by its parent compound, linoleic acid. These findings demonstrate that 15-LOX-1 is down-regulated in human esophageal carcinomas and that NSAIDs induce apoptosis in esophageal cancer cells via up-regulation of 15-LOX-1. They also support the concept that the loss of the proapoptotic role of 15-LOX-1 in epithelial cancers is not limited to human colorectal cancers.

Adenocarcinoma↗
PubMed2001

Decrease in drug accumulation and in tumour aggressiveness marker expression in a fenretinide-induced resistant ovarian tumour cell line.

We investigated whether the efficacy of fenretinide (HPR) against ovarian tumours may be limited by induction of resistance. The human ovarian carcinoma cell line A2780, which is sensitive to a pharmacologically achievable HPR concentration (IC(50)= 1 microM), became 10-fold more resistant after exposure to increasing HPR concentrations. The cells (A2780/HPR) did not show cross-resistance to the synthetic retinoid 6-[3-adamantyl-4-hydroxyphenyl]-2-naphthalene carboxylic acid (CD437) and were not sensitive, similarly to the parent line, to all-trans-retinoic acid, 13-cis-retinoic acid or N-(4-methoxyphenyl)retinamide. A2780/HPR cells showed, compared to parental cells, a 3-fold reduction in colony-forming ability in agar. The development of HPR resistance was associated with a marked increase in retinoic acid receptor beta (RARbeta) mRNA and protein levels, which decreased, together with drug resistance, after drug removal. The expression of cell surface molecules associated with tumour progression including HER-2, laminin receptor and beta1 integrin was markedly reduced. The increase in the levels of reactive oxygen species is not involved in HPR-resistance because it was similar in parental and resistant cells. Conversely differences in pharmacokinetics may account for resistance because, in A2780/HPR cells, intracellular peak drug levels were 2 times lower than in A2780 cells and an as yet unidentified polar metabolite was present. These data suggest that acquired resistance to HPR is associated with changes in marker expression, suggestive of a more differentiated status and may be explained, at least in part, by reduced drug accumulation and increased metabolism.

Antineoplastic Agents↗
PubMed2001

Progressive decreases in nuclear retinoid receptors during skin squamous carcinogenesis.

Retinoids are essential for normal skin growth, differentiation, and apoptosis and are active pharmacologically in the prevention and treatment of skin cancers and other lesions. Retinoid effects are mediated mainly by retinoic acid receptors (RARs) and retinoid X receptors (RXRs), which act as transcription factors to alter gene expression. Using in situ hybridization, we analyzed the expression of RARs and RXRs in normal sun-exposed skin (n = 85), squamous cell carcinoma (SCC; n = 28), and actinic keratosis [AK (a precursor to SCC); n = 38]. The expressions of five receptors (RAR-alpha and -gamma and RXR-alpha, -beta, and -gamma) were moderate to very strong in normal skin, with higher expressions in spinous and granular layers than in the basal layer. RAR-beta expression was weak or absent in normal and lesion samples. All five receptors expressed in the skin were suppressed progressively from normal skin to premalignant skin (AK) to invasive skin SCC. Specific receptor decreases in lesions relative to normal skin ranged from 75% (RXR-beta) to 96% (RAR-alpha) in SCC and from 37% (RAR-gamma) to 68% (RXR-beta) in AK. The degree of suppression of RXR-alpha and RAR-gamma, the two predominant retinoid receptors in skin, was relatively less for RXR-alpha (58% versus 86%; P = 0.015) and relatively greater for RAR-gamma (37% versus 89%; P = 0.0001) between AK and SCC, suggesting that suppression of RXR-alpha may be an earlier event and expression of RAR-gamma may be a later event of multistep squamous skin carcinogenesis. Our results indicate that suppressed expression of retinoid receptors occurs early (in AK) and is associated with progression of squamous skin carcinogenesis to SCC.

Aged↗
PubMed2001

Randomized phase III intergroup trial of isotretinoin to prevent second primary tumors in stage I non-small-cell lung cancer.

BACKGROUND: Promising data have suggested that retinoid chemoprevention may help to control second primary tumors (SPTs), recurrence, and mortality of stage I non-small-cell lung cancer (NSCLC) patients. METHODS: We carried out a National Cancer Institute (NCI) Intergroup phase III trial (NCI #I91-0001) with 1166 patients with pathologic stage I NSCLC (6 weeks to 3 years from definitive resection and no prior radiotherapy or chemotherapy). Patients were randomly assigned to receive a placebo or the retinoid isotretinoin (30 mg/day) for 3 years in a double-blind fashion. Patients were stratified at randomization by tumor stage, histology, and smoking status. The primary endpoint (time to SPT) and the secondary endpoints (times to recurrence and death) were analyzed by log-rank test and the Cox proportional hazards model. All statistical tests were two-sided. RESULTS: After a median follow-up of 3.5 years, there were no statistically significant differences between the placebo and isotretinoin arms with respect to the time to SPTs, recurrences, or mortality. The unadjusted hazard ratio (HR) of isotretinoin versus placebo was 1.08 (95% confidence interval [CI] = 0.78 to 1.49) for SPTs, 0.99 (95% CI = 0.76 to 1.29) for recurrence, and 1.07 (95% CI = 0.84 to 1.35) for mortality. Multivariate analyses showed that the rate of SPTs was not affected by any stratification factor. Rate of recurrence was affected by tumor stage (HR for T(2) versus T(1) = 1.77 [95% CI = 1.35 to 2.31]) and a treatment-by-smoking interaction (HR for treatment-by-current-versus-never-smoking status = 3.11 [95% CI = 1.00 to 9.71]). Mortality was affected by tumor stage (HR for T(2) versus T(1) = 1.39 [95% CI = 1.10 to 1.77]), histology (HR for squamous versus nonsquamous = 1.31 [95% CI = 1.03 to 1.68]), and a treatment-by-smoking interaction (HR for treatment-by-current-versus-never-smoking = 4.39 [95% CI = 1.11 to 17.29]). Mucocutaneous toxicity (P<.001) and noncompliance (40% versus 25% at 3 years) were higher in the isotretinoin arm than in the placebo arm. CONCLUSIONS: Isotretinoin treatment did not improve the overall rates of SPTs, recurrences, or mortality in stage I NSCLC. Secondary multivariate and subset analyses suggested that isotretinoin was harmful in current smokers and beneficial in never smokers.

Adult↗
PubMed2001

Overexpression of BCL2 blocks TNF-related apoptosis-inducing ligand (TRAIL)-induced apoptosis in human lung cancer cells.

The tumor necrosis factor (TNF) related apoptosis-inducing ligand (TRAIL or Apo2L) and its receptors are members of the tumor necrosis factor superfamily. TRAIL triggers apoptosis by binding to its two proapoptotic receptors DR4 and DR5, a process which is negatively regulated by binding of TRAIL to its two decoy receptors TRID and TRUNDD. Here, we show that TRAIL effectively induces apoptosis in H460 human non-small-cell lung carcinoma cells via cleavage of caspases 8, 9, 7, 3, and BID, release of cytochrome c from the mitochondria, and cleavage of poly (ADP-ribose) polymerase (PARP). However, overexpression of Bcl2 blocked TRAIL-induced apoptosis in H460 cells, which correlated with the Bcl2 protein levels. Importantly, the release of cytochrome c and cleavage of caspase 7 triggered by TRAIL were considerably blocked in Bcl2 overexpressing cells as compared to vector control cells. Moreover, inhibition of TRAIL-mediated cytochrome c release and caspase 7 activation by Bcl2 correlated with the inability of PARP to be cleaved and the inability of the Bcl2 transfectants to undergo apoptosis. Thus, these results suggest that Bcl2 can serve an anti-apoptotic function during TRAIL-dependent apoptosis by inhibiting the release of cytochrome c and activation of caspase 7, thereby blocking caspase 7-dependent cleavage of cellular substrates.

Apoptosis↗
PubMed2001

Increased retinoic acid responsiveness in lung carcinoma cells that are nonresponsive despite the presence of endogenous retinoic acid receptor (RAR) beta by expression of exogenous retinoid receptors retinoid X receptor alpha, RAR alpha, and RAR gamma.

Nuclear retinoic acid receptors (RARs) and retinoid X receptors (RXRs) are thought to mediate most of the effects of retinoids on cell growth and differentiation. Despite expressing abundant levels of RAR beta mRNA, lung adenocarcinoma H1792 cells are resistant to the growth-inhibitory effects of all-trans-retinoic acid, suggesting that they have a defect in retinoid signaling. To determine whether transfection of exogenous receptors can restore retinoid responsiveness, we transiently transfected into H1792 cells coexpression vectors containing cDNAs of cell surface antigen CD7 and either RAR alpha, RAR beta, RAR gamma, or RXR alpha. The cells were then treated with retinoids and incubated with 5'-bromo-2'-deoxyuridine. Cells that express exogenous receptor were identified using antibodies against CD7, and cells that synthesized DNA were identified with anti-5'-bromo-2'-deoxyuridine antibodies using secondary antibodies with red and green fluorescence, respectively. RXR alpha and RAR alpha enhanced growth inhibition by all-trans-retinoic acid or 9-cis-retinoic acid, whereas RAR gamma was less effective, and RAR beta was ineffective. The effects of the transfected receptors were associated with antagonism of activator protein 1 (AP-1) activity. Studies with RXR alpha deletion and point mutants indicated that growth suppression is: (a) dependent on intact DNA-binding and ligand-binding regions but not on the NH2-terminal region, which contains a ligand-independent transactivation function; (b) dependent on RXR homodimer formation and transactivation of RXR response element; and (c) associated with AP-1 antagonism. These results demonstrate that transfected receptors can restore responsiveness to retinoids by antagonizing AP-1 in H1792 cells.

Binding Sites↗
PubMed2001

Synthetic retinoid CD437 promotes rapid apoptosis in malignant human epidermal keratinocytes and G1 arrest in their normal counterparts.

Four human cutaneous squamous cell carcinoma (SCC) cell lines and normal human epidermal keratinocyte (NHEK) cells from two donors were examined for sensitivity to the synthetic retinoid 6-[3-(1 -adamantyl)-4-hydroxyphenyl]-2-naph-thalene carboxylic acid (CD437) alone or in combination with other agents. CD437 promoted rapid (within 2 h) apoptosis in SCC cells and G1 arrest in NHEK cells. G1 arrest in NHEK cells was sustained for 48 h while apoptosis occurred in approximately 60% of SCC cell after 24 h. Apoptosis could not be inhibited by nuclear retinoic acid receptor antagonists or cycloheximide, indicating CD437 was functioning in a receptor-independent manner. All-trans retinoic acid not only failed to induce apoptosis in SCC cells even at 20-fold higher concentration relative to the effective concentration of CD437; it also decreased the efficacy of CD437. Because of its differential effects on normal versus malignant keratinocytes, CD437 may be useful for the prevention or treatment of cutaneous SCC.

Antineoplastic Agents↗