Cyclin D1 proteolysis: a retinoid chemoprevention signal in normal, immortalized, and transformed human bronchial epithelial cells

All-Trans-Retinoic Acid Stimulates Overexpression of Tumor Protein D52 (TPD52, Isoform 3) and Neuronal Differentiation of IMR-32 Cells

Tumor protein D52 (TPD52), a proto-oncogene is overexpressed in a variety of epithelial carcinomas and plays an important role in cell proliferation, migration, and cell death. In the present study we found that the treatment of IMR-32 neuroblastoma (NB) cells with retinoic acid (RA) stimulates an increase in expression of TPD52. TPD52 expression is detectable after 72 h, can be maintained till differentiation of NB cells suggesting that TPD52 is involved in differentiation. Here, we demonstrate that TPD52 is essential for RA to promote differentiation of NB cells. Our results show that exogenous expression of EGFP-TPD52 in IMR-32 cells resulted cell differentiation even without RA. RA by itself and with overexpression of TPD52 can increase the ability of NB cells differentiation. Interestingly, transfection of IMR-32 cells with a specific small hairpin RNA for efficient knockdown of TPD52 attenuated RA induced NB cells differentiation. Transcriptional and translational level expression of neurotropic (BDNF, NGF, Nestin) and differentiation (β III tubulin, NSE, TH) factors in NB cells with altered TPD52 expression and/or RA treatment confirmed essential function of TPD52 in cellular differentiation. Furthermore, we show that TPD52 protects cells from apoptosis and arrest cell proliferation by varying expression of p27Kip1, activation of Akt and ERK1/2 thus promoting cell differentiation. Additionally, inhibition of STAT3 activation by its specific inhibitor arrested NB cells differentiation by EGFP-TPD52 overexpression with or without RA. Taken together, our data reveal that TPD52 act through activation of JAK/STAT signaling pathway to undertake NB cells differentiation induced by RA. J. Cell. Biochem. 118: 4358-4369, 2017. © 2017 Wiley Periodicals, Inc.

RARβ2 hypermethylation is associated with poor recurrence-free survival in never-smokers with adenocarcinoma of the lung

Background

This study was aimed at investigating if the effect of RARβ2 hypermethylation on recurrence-free survival (RFS) in non-small cell lung cancer (NSCLC) depends on one’s smoking status and specific interacting proteins.

Results

We retrospectively analyzed the expressions of five proteins using immunohistochemistry in archival formalin-fixed and paraffin-embedded tissues from 578 NSCLC patients who had undergone surgical resection from 1994 through 2004. Promoter methylation of RARβ2 was assessed by bisulfite pyrosequencing. Recurrence was found in 268 (46%) of 578 NSCLCs with a median follow-up period of 4.8 years. Overexpression of β-catenin, c-MET, cyclin D1, and EGFR occurred in 55%, 72%, 51%, and 41% of the patients, respectively. E-cadherin expression was negative in 62% of the patients, and RARβ2 hypermethylation was found in 37%. The abnormal expression of c-MET (P = 0.002) and EGFR (P = 0.001) was found to be highly prevalent in never-smokers. RARβ2 hypermethylation was significantly associated with poor recurrence-free survival (RFS) in 128 never-smokers with adenocarcinoma (P = 0.01) For parsimonious model building, the five proteins were clustered into three groups (β-catenin and E-cadherin; c-MET; cyclin D1 and EGFR) by an unsupervised hierarchical clustering and were included in a multivariate analysis. Cox proportional hazard analysis showed that RARβ2 hypermethylation was significantly associated with poor RFS in 128 never-smokers with adenocarcinoma (adjusted hazard ratio [HR] = 2.19, 95% confidence interval [CI] = 1.28 to 3.47; P = 0.009), after adjusting for interacting proteins.

Conclusions

The present study suggests that RARβ2 hypermethylation may be an independent prognostic factor of RFS in never-smokers with adenocarcinoma of the lung.

Phase I and pharmacokinetic study of bexarotene in combination with gefitinib in the third-line treatment of non-small-cell lung cancer: brief report

Gefitinib (an epidermal growth factor receptor tyrosine kinase inhibitor) and bexarotene (a rexinoid) affect similar oncogenic pathways and are both metabolized through cytochrome P450 CYP3A4. We studied the combination of bexarotene and gefitinib in the third-line treatment of advanced non-small-cell lung cancer to examine pharmacokinetic interactions and establish the maximum tolerated dose. This was a single-institution, nonrandomized, open-label, phase I clinical trial with a standard 3+3 dose escalation. Three patients were enrolled at each dose level on the basis of pharmacokinetic analysis with dose level 1 including gefitinib (Iressa) 250 mg oral daily and bexarotene (Targretin) 400 mg/m oral daily and dose level +1 including gefitinib 500 mg oral daily and bexarotene 400 mg/m oral daily. Patients received gefitinib alone for 2 weeks to allow for steady state and thereafter, bexarotene was added. In dose level 1, two of three patients had undetectable gefitinib levels at day 15 for unknown reasons. However, the peak levels on day 29 for all three patients receiving 250 mg of gefitinib with bexarotene are lower than published peak levels. Among the three patients in dose level +1, ∼40% lower gefitinib plasma concentrations were noted on day 29 compared with day 15 along with a mean 44% reduction in area under the plasma concentration-time curve from 0 to 24 h (AUC0-24). Bexarotene appears to lower the C max and AUC0-24 of gefitinib through cytochrome P450 CYP3A4. Our results have pharmacokinetic implications for ongoing trials that combine bexarotene with other small molecules in the era of personalized cancer therapy.

Chemoprevention of lung cancer: concepts and strategies

Lung cancer develops in a stepwise fashion, with an accumulation of molecular alterations progressing through preinvasive steps to invasive disease. This progression could be arrested or reversed through pharmacologic treatments, which are known as cancer chemoprevention. Preclinical and clinical findings relating to different classes of candidate chemopreventive agents provide support for this strategy as an active and promising approach for controlling this disease.

Comparing histone deacetylase inhibitor responses in genetically engineered mouse lung cancer models and a window of opportunity trial in patients with lung cancer

Histone deacetylase inhibitor (HDACi; vorinostat) responses were studied in murine and human lung cancer cell lines and genetically engineered mouse lung cancer models. Findings were compared with a window of opportunity trial in aerodigestive tract cancers. In human (HOP62, H522, and H23) and murine transgenic (ED-1, ED-2, LKR-13, and 393P, driven, respectively, by cyclin E, degradation-resistant cyclin E, KRAS, or KRAS/p53) lung cancer cell lines, vorinostat reduced growth, cyclin D1, and cyclin E levels, but induced p27, histone acetylation, and apoptosis. Other biomarkers also changed. Findings from transgenic murine lung cancer models were integrated with those from a window of opportunity trial that measured vorinostat pharmacodynamic responses in pre- versus posttreatment tumor biopsies. Vorinostat repressed cyclin D1 and cyclin E expression in murine transgenic lung cancers and significantly reduced lung cancers in syngeneic mice. Vorinostat also reduced cyclin D1 and cyclin E expression, but increased p27 levels in post- versus pretreatment human lung cancer biopsies. Notably, necrotic and inflammatory responses appeared in posttreatment biopsies. These depended on intratumoral HDACi levels. Therefore, HDACi treatments of murine genetically engineered lung cancer models exert similar responses (growth inhibition and changes in gene expression) as observed in lung cancer cell lines. Moreover, enhanced pharmacodynamic responses occurred in the window of opportunity trial, providing additional markers of response that can be evaluated in subsequent HDACi trials. Thus, combining murine and human HDACi trials is a strategy to translate preclinical HDACi treatment outcomes into the clinic. This study uncovered clinically tractable mechanisms to engage in future HDACi trials.

Repression of exogenous gene expression by the retinoic acid target gene G0S2

The G0/G1 switch gene 2 (G0S2) is rapidly induced by all-trans-retinoic acid (RA)-treatment of acute promyelocytic leukemia (APL) and other cells. G0S2 regulates lipolysis via inhibition of adipose triglyceride lipase (ATGL). This study found that retinoic acid receptor (RAR), but not retinoid X receptor (RXR) agonists induced G0S2 expression in APL cells. Novel G0S2 functions were uncovered that included repression of exogenous gene expression and transcriptional activity. Transient G0S2 transfection repressed the activities of multiple reporter constructs (including the retinoid-regulated species RARβ, UBE1L and G0S2); this occurred in diverse cell contexts. This inhibition was antagonized by siRNA-mediated G0S2 knockdown. To determine the inhibitory effects were not due to transient G0S2 expression, G0S2 was stably overex-pressed in cells without appreciable basal G0S2 expression. As expected, this repressed transcriptional activities. Intriguingly, transfection of G0S2 did not affect endogenous RARβ, UBE1L or G0S2 expression. Hence, only exogenously expressed genes were affected by G0S2. The domain responsible for this repression was localized to the G0S2 hydrophobic domain (HD). This was the same region responsible for the ability of G0S2 to inhibit ATGL activity. Whether an interaction with ATGL accounted for this new G0S2 activity was studied. Mimicking the inhibition of ATGL by oleic acid treatment that increased lipid droplet size or ATGL siRNA knockdown did not recapitulate G0S2 repressive effects. Engineered gain of ATGL expression did not rescue G0S2 transcriptional repression either. Thus, transcriptional repression by G0S2 did not depend on the ability of G0S2 to inhibit ATGL. Subcellular localization studies revealed that endogenous and exogenously-expressed G0S2 proteins were localized to the cytoplasm, particularly in the perinuclear region. Expression of a mutant G0S2 species that lacked the HD domain altered cytosolic G0S2 localization. This linked G0S2 subcellular localization to G0S2 transcriptional repression. The potential mechanisms responsible for this G0S2 repression are examined.

Evidence for the ubiquitin protease UBP43 as an antineoplastic target

New pharmacologic targets are needed for lung cancer. One candidate pathway to target is composed of the E1-like ubiquitin-activating enzyme (UBE1L) that associates with interferon-stimulated gene 15 (ISG15), which complexes with and destabilizes cyclin D1. Ubiquitin protease 43 (UBP43/USP18) removes ISG15 from conjugated proteins. This study reports that gain of UBP43 stabilized cyclin D1, but not other D-type cyclins or cyclin E. This depended on UBP43 enzymatic activity; an enzymatically inactive UBP43 did not affect cyclin D1 stability. As expected, small interfering RNAs that reduced UBP43 expression also decreased cyclin D1 levels and increased apoptosis in a panel of lung cancer cell lines. Forced cyclin D1 expression rescued UBP43 apoptotic effects, which highlighted the importance of cyclin D1 in conferring this. Short hairpin RNA-mediated reduction of UBP43 significantly increased apoptosis and reduced murine lung cancer growth in vitro and in vivo after transplantation of these cells into syngeneic mice. These cells also exhibited increased response to all-trans-retinoic acid, interferon, or cisplatin treatments. Notably, gain of UBP43 expression antagonized these effects. Normal-malignant human lung tissue arrays were examined independently for UBP43, cyclin D1, and cyclin E immunohistochemical expression. UBP43 was significantly (P < 0.01) increased in the malignant versus normal lung. A direct relationship was found between UBP43 and cyclin D1 (but not cyclin E) expression. Differential UBP43 expression was independently detected in a normal-malignant tissue array with diverse human cancers. Taken together, these findings uncovered UBP43 as a previously unrecognized antineoplastic target.

Bexarotene plus erlotinib suppress lung carcinogenesis independent of KRAS mutations in two clinical trials and transgenic models

The rexinoid bexarotene represses cyclin D1 by causing its proteasomal degradation. The epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor (TKI) erlotinib represses cyclin D1 via different mechanisms. We conducted a preclinical study and 2 clinical/translational trials (a window-of-opportunity and phase II) of bexarotene plus erlotinib. The combination repressed growth and cyclin D1 expression in cyclin-E- and KRAS/p53-driven transgenic lung cancer cells. The window-of-opportunity trial in early-stage non-small-cell lung cancer (NSCLC) patients (10 evaluable), including cases with KRAS mutations, repressed cyclin D1 (in tumor biopsies and buccal swabs) and induced necrosis and inflammatory responses. The phase II trial in heavily pretreated, advanced NSCLC patients (40 evaluable; a median of two prior relapses per patient (range, 0-5); 21% with prior EGFR-inhibitor therapy) produced three major clinical responses in patients with prolonged progression-free survival (583-, 665-, and 1,460-plus days). Median overall survival was 22 weeks. Hypertriglyceridemia was associated with an increased median overall survival (P = 0.001). Early PET (positron emission tomographic) response did not reliably predict clinical response. The combination was generally well tolerated, with toxicities similar to those of the single agents. In conclusion, bexarotene plus erlotinib was active in KRAS-driven lung cancer cells, was biologically active in early-stage mutant KRAS NSCLC, and was clinically active in advanced, chemotherapy-refractory mutant KRAS tumors in this study and previous trials. Additional lung cancer therapy or prevention trials with this oral regimen are warranted.

All-trans retinoic acid induces cellular senescence via upregulation of p16, p21, and p27

We here present a new anti-tumor mechanism of all-trans retinoic acid (ATRA). ATRA induced several biomarkers of cellular senescence including irreversible G1 arrest, morphological changes, senescence-associated β-galactosidase, and heterochromatin foci in HepG2 cells. ATRA also upregulated levels of p16, p21, and p27 which lead to activation of Rb and subsequent inactivation of E2F1. These effects were abolished by the RNA interference-mediated silencing of p16, p21, and p27. Moreover, ATRA failed to induce cellular senescence in Huh7 and HCT116, in which p16, p21, and p27 were not upregulated by ATRA, confirming that ATRA induces cellular senescence via upregulation of p16, p21, and p27.

Global assessment of genetic variation influencing response to retinoid chemoprevention in head and neck cancer patients

Head and neck squamous cell carcinoma (HNSCC) patients are at an increased risk of developing a second primary tumor (SPT) or recurrence following curative treatment. 13-cis-retinoic acid (13-cRA) has been tested in chemoprevention clinical trials, but the results have been inconclusive. We genotyped 9,465 single nucleotide polymorphisms (SNP) in 450 patients from the Retinoid Head and Neck Second Primary Trial. SNPs were analyzed for associations with SPT/recurrence in patients receiving placebo to identify prognosis markers and further analyzed for effects of 13-cRA in patients with these prognostic loci. Thirteen loci identified a majority subgroup of patients at a high risk of SPT/recurrence and in whom 13-cRA was protective. Patients carrying the common genotype of rs3118570 in the retinoid X receptor (RXRA) were at a 3.33-fold increased risk (95% CI, 1.67-6.67) and represented more than 70% of the study population. This locus also identified individuals who received benefit from chemoprevention with a 38% reduced risk (95% CI, 0.43-0.90). Analyses of cumulative effect and potential gene-gene interactions also implicated CDC25C:rs6596428 and JAK2:rs1887427 as 2 other genetic loci with major roles in prognosis and 13-cRA response. Patients with all 3 common genotypes had a 76% reduction in SPT/recurrence (95% CI, 0.093-0.64) following 13-cRA chemoprevention. Carriers of these common genotypes constituted a substantial percentage of the study population, indicating that a pharmacogenetic approach could help select patients for 13-cRA chemoprevention. The lack of any alternatives for reducing risk in these patients highlights the need for future clinical trials to prospectively validate our findings.

Prevention of bronchial hyperplasia by EGFR pathway inhibitors in an organotypic culture model

Lung cancer is the leading cause of cancer-related mortality worldwide. Early detection or prevention strategies are urgently needed to increase survival. Hyperplasia is the first morphologic change that occurs in the bronchial epithelium during lung cancer development, followed by squamous metaplasia, dysplasia, carcinoma in situ, and invasive tumor. This study was designed to determine the molecular mechanisms that control bronchial epithelium hyperplasia. Using primary normal human tracheobronchial epithelial (NHTBE) cells cultured by using the 3-dimensional (3D) organotypic method, we found that the epidermal growth factor receptor (EGFR) ligands, EGF, TGF-α, and amphiregulin induced hyperplasia, as determined by cell proliferation and multilayered epithelium formation. We also found that EGF induced increased cyclin D1 expression, which plays a critical role in bronchial hyperplasia; this overexpression was mediated by activating the mitogen-activated protein kinase pathway but not the phosphoinositide 3-kinase/Akt signaling pathway. Erlotinib, an EGFR tyrosine kinase inhibitor, and U0126, a MAP/ERK kinase (MEK) inhibitor, completely inhibited EGF-induced hyperplasia. Furthermore, a promoter analysis revealed that the activator protein-1 transcription factor regulates EGF-induced cyclin D1 overexpression. Activator protein-1 depletion by using siRNA targeting its c-Jun component completely abrogated EGF-induced cyclin D1 expression. In conclusion, we showed that bronchial hyperplasia can be modeled in vitro by using primary NHTBE cells maintained in a 3D organotypic culture. EGFR and MEK inhibitors completely blocked EGF-induced bronchial hyperplasia, suggesting that they have a chemopreventive role.

The natural tumor suppressor protein maspin and potential application in non small cell lung cancer

The grim prognosis of lung cancer, that has an overall 10-15% survival at 5 years, remains in the US the leading cause of cancer mortality, provides a compelling rationale for studying the molecular basis of this malignancy. Surmising the common, general association with smoking, lung cancers differ at the microscopic, anatomical, epidemiological and clinical level and harbor complex genetic and epigenetic alterations. Currently, lung cancer is divided into small cell lung carcinoma (SCLC) and non small cell lung carcinoma (NSCLC) for the purpose of clinical management. (NSCLC) constitutes 80-85% of lung cancers and is further divided into histological subtypes such as adenocarcinoma, squamous cell carcinoma, and large cell carcinoma, etc. The ultimate goal for lung cancer research is to develop a strategy to block the tumor progression and improve the prognosis of lung cancer. This goal can realistically be achieved only when the biological complexity of this disease is taken into account. To this end, identification and understanding of molecular markers that are mechanistically involved in tumor progression is needed. Our recent studies suggest histological subtype-dependent distinct correlations between the expression and/or subcellular localization of tumor suppressive maspin with the progression and prognosis of NSCLC. Maspin is an epithelial specific member of the serine protease inhibitor (serpin) superfamily but recently identified as an endogenous inhibitor of histone deacetylase 1 (HDAC1). This novel biochemical activity coincides with a consensus emerged recently from the evidence that nuclear maspin confers better differentiated epithelial phenotypes, decreased tumor angiogenesis, increased tumor sensitivity to drug-induced apoptosis, and a more favorable prognosis. In the current review, we discuss the evidence that maspin may be a marker that stratifies the progression and prognosis of different subtypes of NSCLC.

UBE1L causes lung cancer growth suppression by targeting cyclin D1

UBE1L is the E1-like ubiquitin-activating enzyme for the IFN-stimulated gene, 15-kDa protein (ISG15). The UBE1L-ISG15 pathway was proposed previously to target lung carcinogenesis by inhibiting cyclin D1 expression. This study extends prior work by reporting that UBE1L promotes a complex between ISG15 and cyclin D1 and inhibited cyclin D1 but not other G1 cyclins. Transfection of the UBE1L-ISG15 deconjugase, ubiquitin-specific protein 18 (UBP43), antagonized UBE1L-dependent inhibition of cyclin D1 and ISG15-cyclin D1 conjugation. A lysine-less cyclin D1 species was resistant to these effects. UBE1L transfection reduced cyclin D1 protein but not mRNA expression. Cycloheximide treatment augmented this cyclin D1 protein instability. UBE1L knockdown increased cyclin D1 protein. UBE1L was independently retrovirally transduced into human bronchial epithelial and lung cancer cells. This reduced cyclin D1 expression and clonal cell growth. Treatment with the retinoid X receptor agonist bexarotene induced UBE1L and reduced cyclin D1 immunoblot expression. A proof-of-principle bexarotene clinical trial was independently examined for UBE1L, ISG15, cyclin D1, and Ki-67 immunohistochemical expression profiles in pretreatment versus post-treatment tumor biopsies. Increased UBE1L with reduced cyclin D1 and Ki-67 expression occurred in human lung cancer when a therapeutic bexarotene intratumoral level was achieved. Thus, a mechanism for UBE1L-mediated growth suppression was found by UBE1L-ISG15 preferentially inhibiting cyclin D1. Molecular therapeutic implications are discussed.

Cyclin degradation for cancer therapy and chemoprevention

Cancer is characterized by uncontrolled cell division resulting from multiple mutagenic events. Cancer chemoprevention strategies aim to inhibit or reverse these events using natural or synthetic pharmacologic agents. Ideally, this restores normal growth control mechanisms. Diverse classes of compounds have been identified with chemopreventive activity. What unites many of them is an ability to inhibit the cell cycle by specifically modulating key components. This delays division long enough for cells to respond to mutagenic damage. In some cases, damage is repaired and in others cellular damage is sufficient to trigger apoptosis. It is now known that pathways responsible for targeting G1 cyclins for proteasomal degradation can be engaged pharmacologically. Emergence of induced cyclin degradation as a target for cancer therapy and chemoprevention in pre-clinical models is discussed in this article. Evidence for cyclin D1 as a molecular pharmacologic target and biological marker for clinical response is based on experience of proof of principle trials.

Prognostic significance of cyclin D1 and p16 in patients with intermediate-risk head and neck squamous cell carcinoma treated with docetaxel and concurrent radiotherapy

BACKGROUND

The current study aimed to evaluate the significance of the cell-cycle-control proteins cyclin D1 and p16 as prognostic markers in head and neck squamous cell carcinoma (HNSCC) patients treated with docetaxel and radiotherapy.

METHODS

Cyclin D1 and/or p16 protein expression was retrospectively evaluated by immunohistochemistry in 53 patients with stage T1-3N0-2M0 (except T1N0 glottis) HNSCC who were treated with 10 mg/m(2)/week docetaxel 4 to 6 times and received concurrent chemoradiotherapy.

RESULTS

Kaplan-Meier univariate analysis revealed that patients with cyclin D1-positive tumors or p16-negative tumors had a worse prognosis compared with those with cyclin D1-negative tumors or p16-positive tumors (p = .0004 and p = .025, respectively). The prognostic significance of cyclin D1 expression, not p16 expression, was confirmed using a proportional hazard regression model.

CONCLUSIONS

An assessment of cyclin D1 and p16 levels might be of clinical use in defining subgroups of patients with poor prognosis.

Viral defense, carcinogenesis and ISG15: novel roles for an old ISG

Recent studies have established that type I interferon modulates expression of large number of cellular genes. While the proteins encoded by some of these genes have a direct antiviral activity, the functions of the majority of the others have not yet been determined. One of the first identified IFN stimulated gene, encodes ubiquitin like protein ISG15 that is also expressed in response to different stress stimuli. Although it was shown that ISG15 functions as protein modifier, it has been only recently that the targets of ISG15 conjugation were identified. Recent studies have also revealed mechanism of ISG15 conjugation and its interaction with the ubiquitin conjugation pathway. This review is focused on the possible role of ISG15 in the antiviral response, regulation of cell growth and carcinogenesis.

Diverse actions of retinoid receptors in cancer prevention and treatment

Retinoids (retinol [vitamin A] and its biologically active metabolites) are essential signaling molecules that control various developmental pathways and influence the proliferation and differentiation of a variety of cell types. The physiological actions of retinoids are mediated primarily by the retinoic acid receptors alpha, beta, and gamma (RARs) and rexinoid receptors alpha, beta, and gamma. Although mutations in RARalpha, via the PML-RARalpha fusion proteins, result in acute promyelocytic leukemia, RARs have generally not been reported to be mutated or part of fusion proteins in carcinomas. However, the retinoid signaling pathway is often compromised in carcinomas. Altered retinol metabolism, including low levels of lecithin:retinol acyl trasferase and retinaldehyde dehydrogenase 2, and higher levels of CYP26A1, has been observed in various tumors. RARbeta(2) expression is also reduced or is absent in many types of cancer. A greater understanding of the molecular mechanisms by which retinoids induce cell differentiation, and in particular stem cell differentiation, is required in order to solve the issue of retinoid resistance in tumors, and thereby to utilize RA and synthetic retinoids more effectively in combination therapies for human cancer.

Uncovering novel targets for cancer chemoprevention

Tobacco carcinogen treatment of immortalized human bronchial epithelial (HBE) cells has uncovered novel targets for cancer chemoprevention. Experiments were conducted with HBE cells and independent treatments with tobacco carcinogens along with the chemopreventive agent all-trans-retinoic acid (RA). That work highlighted D-type and E-type cyclins as novel molecular pharmacologic targets of several chemopreventive agents. G1 cyclins are often aberrantly expressed in bronchial preneoplasia and lung cancers. This implicated these species as targets for clinical cancer chemoprevention. Retinoid regulation mechanisms of D-type cyclins in lung cancer chemoprevention have been comprehensively explored. Retinoid chemoprevention has been mechanistically linked to proteasomal degradation of cyclin D1 and cyclin D3. Threonine 286 mutation stabilized cyclin D1, implicating phosphorylation in this retinoid chemoprevention. Studies with a phospho-specific anti-cyclin D1 antibody confirmed this hypothesis. Glycogen synthase kinase (GSK) inhibitors established a role for this kinase in the retinoid regulation of cyclin D1, but not cyclin D3. Involvement of D-type cyclins in this chemoprevention was shown using small interfering RNAs (siRNAs). Gene profiling experiments highlighted the E1-like ubiquitin-activating enzyme (UBE1L) in the retinoid regulation of cyclin D1. Proof of principle trials have translated these studies into the clinic and established that chemopreventive agents can target D-type cyclins. These findings have been built upon with a targeted combination regimen that cooperatively affects D-type cyclins. Taken together, these preclinical and clinical findings strongly implicate these cyclins as novel molecular pharmacological targets for cancer chemoprevention.

The regulation of cyclin D1 degradation: roles in cancer development and the potential for therapeutic invention

Cyclin D1 is an important regulator of cell cycle progression and can function as a transcriptionl co-regulator. The overexpression of cyclin D1 has been linked to the development and progression of cancer. Deregulated cyclin D1 degradation appears to be responsible for the increased levels of cyclin D1 in several cancers. Recent findings have identified novel mechanisms involved in the regulation of cyclin D1 stability. A number of therapeutic agents have been shown to induce cyclin D1 degradation. The therapeutic ablation of cyclin D1 may be useful for the prevention and treatment of cancer. In this review, current knowledge on the regulation of cyclin D1 degradation is discussed. Novel insights into cyclin D1 degradation are also discussed in the context of ablative therapy. A number of unresolved questions regarding the regulation of cellular cyclin D1 levels are also addressed.

A Proof-of-Principle Clinical Trial of Bexarotene in Patients with Non–Small Cell Lung Cancer

PURPOSE

Bexarotene is a rexinoid (selective retinoid X receptor agonist) that affects proliferation, differentiation, and apoptosis in preclinical studies. The relationship between bexarotene levels and biomarker changes in tumor tissues has not been previously studied.

EXPERIMENTAL DESIGN

BEAS-2B human bronchial epithelial (HBE) cells, retinoid-resistant BEAS-2B-R1 cells, A427, H226, and H358 lung cancer cells were treated with bexarotene. Proliferation and biomarker expression were assessed. In a proof-of-principle clinical trial, bexarotene tumor tissue levels and intratumoral pharmacodynamic effects were assessed in patients with stages I to II non-small cell lung cancer. Bexarotene (300 mg/m(2)/day) was administered p.o. for 7 to 9 days before resection.

RESULTS

Bexarotene-induced dosage-dependent repression of growth, cyclin D1, cyclin D3, total epidermal growth factor receptor (EGFR), and phospho-EGFR expression in BEAS-2B, BEAS-2B-R1, A427, and H358, but not H226 cells. Twelve patients were enrolled, and 10 were evaluable. Bexarotene treatment was well tolerated. There was nonlinear correlation between plasma and tumor bexarotene concentrations (r(2) = 0.77). Biomarker changes in tumors were observed: repression of cyclin D1, total EGFR and proliferation in one case; repression of cyclin D3, total and phospho-EGFR in another. The cases with multiple biomarker changes had high tumor bexarotene (107-159 ng/g). A single biomarker change was detected in one case with low tumor bexarotene.

CONCLUSION

Bexarotene represses proliferation and biomarker expression in responsive, but not resistant HBE and lung cancer cells. Similar biomarker changes occur in lung tumors when therapeutic intratumoral bexarotene levels are achieved. This proof-of-principle trial approach is useful to uncover pharmacodynamic mechanisms in vivo and relate these to intratumoral pharmacokinetic effects.

Antiestrogenic activity of vitamin A in in vivo uterotrophic assay

All-trans-retinoic acid (ATRA), the primary active metabolite of vitamin A, was examined for its antiestrogenic activity in rats using an in vivo uterotrophic assay. All rats were ovariectomized 2 weeks prior to receiving 5 mg/kg/day ATRA or 0.3 micro g/kg/day ethynyl estradiol (EE) subcutaneously once a day for 3 consecutive days. Rats were sacrificed 1, 3, 6, 12 or 24 h after the last treatment. EE increased uterine weight and the coinjection of ATRA with EE significantly suppressed this effect 3 and 24 h after treatment. mRNA expression was examined during this 24-h period and the mRNA expression levels of estrogen receptor alpha (ER alpha), retinoic acid receptor beta (RAR beta), retinoid X receptor gamma (RXR gamma) and cellular retinol-binding protein I (CRBP I) were found to have significantly increased in the ATRA+EE group compared with those in the EE group. This is the first report on the antiestrogenic activity of ATRA determined using an in vivo adult rat uterotrophic assay. The up-regulation of RAR or RXR mRNA expression level was probably responsible for the antiestrogenic activity of ATRA.

Progress in chemoprevention drug development: the promise of molecular biomarkers for prevention of intraepithelial neoplasia and cancer--a plan to move forward

This article reviews progress in chemopreventive drug development, especially data and concepts that are new since the 2002 AACR report on treatment and prevention of intraepithelial neoplasia. Molecular biomarker expressions involved in mechanisms of carcinogenesis and genetic progression models of intraepithelial neoplasia are discussed and analyzed for how they can inform mechanism-based, molecularly targeted drug development as well as risk stratification, cohort selection, and end-point selection for clinical trials. We outline the concept of augmenting the risk, mechanistic, and disease data from histopathologic intraepithelial neoplasia assessments with molecular biomarker data. Updates of work in 10 clinical target organ sites include new data on molecular progression, significant completed trials, new agents of interest, and promising directions for future clinical studies. This overview concludes with strategies for accelerating chemopreventive drug development, such as integrating the best science into chemopreventive strategies and regulatory policy, providing incentives for industry to accelerate preventive drugs, fostering multisector cooperation in sharing clinical samples and data, and creating public-private partnerships to foster new regulatory policies and public education.

Lycopene inhibition of IGF-induced cancer cell growth depends on the level of cyclin D1

BACKGROUND

Insulin-like growth factors (IGFs) play an important role in normal and cancerous cell proliferation. Moreover, in recent studies IGF-I has been implicated as a major cancer risk factor. The tomato carotenoid lycopene and all-trans retinoic acid (atRA) have been shown to inhibit growth factor-induced proliferation of different types of cancer cells. This action is associated with inhibition of cell cycle progression in G0/G1 phase. Cyclin D1 acts as a growth factor sensor in G1 phase and is overexpressed in many breast cancer tumors. We have previously demonstrated that slowdown of serum-stimulated cell cycle progression from G1 to S phase by lycopene correlates with reduction in cyclin D1 levels, suggesting that the expression of this protein is a main target for lycopene's action.

AIM OF THE STUDY

To determine whether the reported reduction in cyclin D1 level is the key mechanism for lycopene and atRA inhibitory action on IGF-I-induced cell cycle progression.

RESULTS

Human breast (MCF-7) and endometrial (ECC-1) cancer cells were synchronized in G0/G1 phase by serum deprivation followed by stimulation with IGF-I. Cell treatment with lycopene and atRA inhibited IGF-I-stimulated cell cycle progression from G1 to S phase and decreased retinoblastoma protein (pRb) phosphorylation. These events were associated with a reduction in cyclin D1 and p21(CIP1/WAF1) level, but not that of p27(KIP1). To test the hypothesis that the decrease in cyclin D1 has a major role in the inhibitory effects of lycopene and atRA, we examined the ability of these two agents to suppress cell cycle progression in MCF-7.7D1.13 cells which are capable of expressing cyclin D1 under the control of the Zn-inducible metallothionein promoter. Our results showed that ectopic expression of cyclin D1 can overcome cell cycle inhibition caused by lycopene and atRA.

CONCLUSIONS

Our findings suggest that attenuation of cyclin Dl levels by lycopene and atRA is an important mechanism for the reduction of the mitogenic action of IGF-I.

Bexarotene and erlotinib for aerodigestive tract cancer

PURPOSE

The epidermal growth factor receptor (EGFR) and cyclin D1 are overexpressed in lung carcinogenesis. The rexinoid, bexarotene, represses cyclin D1 and EGFR expression in vitro. It was hypothesized that combining bexarotene with the EGFR inhibitor, erlotinib, would augment clinical activity.

PATIENTS AND METHODS

In vitro studies and a phase I clinical trial were performed. Twenty-four patients with advanced aerodigestive tract cancers were enrolled; 79% had non-small-cell lung cancer (NSCLC). The primary objective was to determine the maximum-tolerated dose. Clinical activity was a secondary objective.

RESULTS

Combining erlotinib with bexarotene enhanced growth suppression in vitro compared with each single-agent treatment. This cooperatively repressed cyclin D1 expression. Clinically, the most frequent toxicities were mild hypertriglyceridemia and skin rash. Two serious treatment-related adverse events occurred (creatine phosphokinase elevation attributed to antilipid therapy and a case of generalized pain). Five objective responses (four partial and one minor) were observed in NSCLC patients. Responses were observed in males and smokers. EGFR sequence analyses did not reveal activating mutations in tumors from assessable responding patients. Median time to progression was 2.0 months; overall survival time was 14.1 months; and 1-year survival rate was 73.8%.

CONCLUSION

The recommended phase II doses are erlotinib 150 mg/d and bexarotene 400 mg/m2/d orally. These agents can be administered in combination at the recommended single-agent doses without added toxicity. Overall survival and clinical features of responding patients differ from prior reports of single-agent erlotinib treatment. These findings are encouraging and warrant further investigation of this regimen.

Retinol inhibits the growth of all-trans-retinoic acid-sensitive and all-trans-retinoic acid-resistant colon cancer cells through a retinoic acid receptor-independent mechanism

Retinol (vitamin A) is thought to exert its effects through the actions of its metabolite, all-trans-retinoic acid (ATRA), on gene transcription mediated by retinoic acid receptors (RAR) and retinoic acid response elements (RARE). However, retinoic acid resistance limits the chemotherapeutic potential of ATRA. We examined the ability of retinol to inhibit the growth of ATRA-sensitive (HCT-15) and ATRA-resistant (HCT-116, SW620, and WiDR) human colon cancer cell lines. Retinol inhibited cell growth in a dose-responsive manner. Retinol was not metabolized to ATRA or any bioactive retinoid in two of the cell lines examined. HCT-116 and WiDR cells converted a small amount of retinol to ATRA; however, this amount of ATRA was unable to inhibit cell growth. To show that retinol was not inducing RARE-mediated transcription, each cell line was transfected with pRARE-chloramphenicol acetyltransferase (CAT) and treated with ATRA and retinol. Although treatment with ATRA increased CAT activity 5-fold in ATRA-sensitive cells, retinol treatment did not increase CAT activity in any cell line examined. To show that growth inhibition due to retinol was ATRA, RAR, and RARE independent, a pan-RAR antagonist was used to block RAR signaling. Retinol-induced growth inhibition was not alleviated by the RAR antagonist in any cell line, but the antagonist alleviated ATRA-induced growth inhibition of HCT-15 cells. Retinol did not induce apoptosis, differentiation or necrosis, but affected cell cycle progression. Our data show that retinol acts through a novel, RAR-independent mechanism to inhibit colon cancer cell growth.

A Novel Retinoic Acid Receptor β Isoform and Retinoid Resistance in Lung Carcinogenesis

BACKGROUND

We previously reported that all-trans-retinoic acid (RA) treatment can prevent in vitro transformation of immortalized human bronchial epithelial (HBE) cells.

METHODS

To determine whether methylation inhibits RARbeta expression in HBE cells, we used sodium bisulfite sequencing to compare RARbeta P2 promoter methylation patterns in RA-sensitive (BEAS-2B) and RA-resistant (BEAS-2B-R1) HBE cells. Immunoblotting was used to assess induction of the RARbeta, placental transforming growth factor beta (PTGF-beta), Fos-related antigen 1 (Fra-1), and transglutaminase II (TGase II) proteins by RA following treatment with azacitidine, a DNA demethylating agent. The expression, transcriptional activity, and growth suppressive activity of RARbeta1', a novel RAR isoform, were evaluated in lung cancer cells transfected with RARbeta1', and expression was also studied in paired normal lung tissues and lung tumors. All statistical tests were two-sided.

RESULTS

Hypermethylation was observed in the 3' region of the RARbeta P2 promoter of BEAS-2B-R1 but not BEAS-2B cells. Azacitidine treatment of BEAS-2B-R1 cells restored RA-inducible RARbeta2 and PTGF-beta expression but not that of RARbeta1', Fra-1, or TGase II. RARbeta1' expression was repressed in RA-resistant BEAS-2B-R1 cells and in lung cancers, compared with adjacent normal lung tissues. BEAS-2B-R1 cells transiently transfected with RARbeta1' had increased RA-dependent activation of a retinoic acid receptor element (RARE)-containing reporter plasmid compared with vector control (mean = 3.2, 95% confidence interval [CI] = 3.1 to 3.3 versus mean = 1.4, 95% CI = 1.3 to 1.5; P<.001). In H358 lung cancer cells transiently transfected with RARbeta1', RA treatment restored target gene expression compared with that in vector-transfected cells and suppressed cell growth compared with that in untreated cells (4 microM; treated mean = 0.49 versus untreated mean = 1.0, difference = 0.51, 95% CI = 0.35 to 0.67, P = .003; 8 microM: treated mean = 0.50 versus untreated mean = 1.0, difference = 0.50, 95% CI = 0.26 to 0.74, P = .015).

CONCLUSION

Restoration of RARbeta1' expression may overcome retinoid resistance in lung carcinogenesis.

Macrocephaly and the control of brain growth in autistic disorders

Autism is a childhood-onset neuropsychiatric disorder characterized by marked impairments in social interactions and communication, with restricted stereotypic and repetitive patterns of behavior, interests, and activities. Genetic epidemiology studies indicate that a strong genetic component exists to this disease, but these same studies also implicate significant environmental influence. The disorder also displays symptomatologic heterogeneity, with broad individual differences and severity on a graded continuum. In the search for phenotypes to resolve heterogeneity and better grasp autism's underlying biology, investigators have noted a statistical overrepresentation of macrocephaly, an indicator of enlarged brain volume. This feature is one of the most widely replicated biological findings in autism. What then does brain enlargement signify? One hypothesis invoked for the origin of macrocephaly is a reduction in neuronal pruning and consolidation of synapses during development resulting in an overabundance of neurites. An increase in generation of cells is an additional mechanism for macrocephaly, though it is less frequently discussed in the literature. Here, we review neurodevelopmental mechanisms regulating brain growth and highlight one underconsidered potential causal mechanism for autism and macrocephaly--an increase in neurogenesis and/or gliogenesis. We review factors known to control these processes with an emphasis on nuclear receptor activation as one signaling control that may be abnormal and contribute to increased brain volume in autistic disorders.

Retinoid Targeting of Different D-Type Cyclins through Distinct Chemopreventive Mechanisms

D-type cyclins (cyclins D1, D2, and D3) promote G1-S progression and are aberrantly expressed in cancer. We reported previously that all-trans-retinoic acid chemo-prevented carcinogenic transformation of human bronchial epithelial (HBE) cells through proteasomal degradation of cyclin D1. Retinoic acid is shown here to activate distinct mechanisms to regulate different D-type cyclins in HBE cells. Retinoic acid increased cyclin D2, decreased cyclin D3 and had no effect on cyclin D1 mRNA expression. Retinoic acid decreased cyclin D1 and cyclin D3 protein expression. Repression of cyclin D3 protein preceded that of cyclin D3 mRNA. Proteasomal inhibition prevented the early cyclin D3 degradation by retinoic acid. Threonine 286 (T286) mutation of cyclin D1 stabilized cyclin D1, but a homologous mutation of cyclin D3 affecting threonine 283 did not affect cyclin D3 stability, despite retinoic acid treatment. Lithium chloride and SB216763, both glycogen synthase kinase 3 (GSK3) inhibitors, inhibited retinoic acid repression of cyclin D1, but not cyclin D3 proteins. Notably, phospho-T286 cyclin D1 expression was inhibited by lithium chloride, implicating GSK3 in these effects. Expression of cyclin D1 and cyclin D3 was deregulated in retinoic acid-resistant HBE cells, directly implicating these species in retinoic acid response. D-type cyclins were independently targeted using small interfering RNAs. Repression of each D-type cyclin suppressed HBE growth. Repression of all D-type cyclins cooperatively suppressed HBE growth. Thus, retinoic acid repressed cyclin D1 and cyclin D3 through distinct mechanisms. GSK3 plays a key role in retinoid regulation of cyclin D1. Taken together, these findings highlight these cyclins as molecular pharmacologic targets for cancer chemoprevention.

Retinoic acid stabilizes p27Kip1 in EBV-immortalized lymphoblastoid B cell lines through enhanced proteasome-dependent degradation of the p45Skp2 and Cks1 proteins

Retinoic acid (RA) arrests the growth of EBV-immortalized lymphoblastoid B cell lines (LCLs) by upregulating the cyclin-dependent kinase inhibitor p27Kip1. Here, we show that in LCLs, RA inhibits ubiquitination and proteasome-dependent degradation of p27Kip1, a phenomenon that is associated with downregulation of Thr187 phosphorylation of the protein, whereas the phosphorylation on Ser10 is unaffected. Furthermore, we demonstrate that RA downregulates the expression of the p45Skp2 and Cks1 proteins, two essential components of the SCF(Skp2) ubiquitin ligase complex that target p27Kip1 for degradation. Downregulation of p45Skp2)and Cks1 occurs before the onset of growth arrest and is due to enhanced proteasome-mediated proteolysis of these proteins. Moreover, overexpression of p45Skp2 in DG75 cells prevents p27Kip1 protein accumulation and promotes resistance to the antiproliferative effects of RA. Treatment with Leptomycin B (LMB) blocked the translocation of p27Kip1 to the cytoplasm and prevented its degradation, indicating that CRM1-dependent nuclear export is required for p27Kip1 degradation. The shuttle protein p38Jab1, however, does not accumulate in the nucleus upon LMB treatment, nor does it interact with p27Kip1. Conversely, p45Skp2 is associated with p27Kip1 both in the nucleus and in the cytoplasm, accumulating within the nuclei after exposure to LMB and co-localizing with the exportin CRM1, suggesting a possible involvement of p45Skp2 in CRM1-dependent nuclear export of p27Kip1. These results indicate that downregulation of p45Skp2 is a key element underlying RA-induced p27Kip1 stabilization in B cells, resulting in an impaired targeting of the protein to the ubiquitin-proteasome pathway and probably contributing to the nuclear accumulation of p27Kip1.

Retinoic Acid Inhibits the Proliferative Response Induced by CD40 Activation and Interleukin-4 in Mantle Cell Lymphoma

Mantle cell lymphoma (MCL) is an aggressive B-cell non-Hodgkin's lymphoma with poor response to therapy and unfavorable prognosis. Here, we show that retinoic acid (RA) isomers significantly inhibit the proliferation of both primary MCL cultures (n = 7) and established cell lines (Granta 519 and SP-53) as shown by [3H]thymidine uptake and carboxyfluorescein diacetate succinimidyl ester labeling coupled with cyclin D1 staining. RA induces cell accumulation in G0-G1 together with a marked up-regulation of p27Kip1 by inhibiting ubiquitination and proteasome-dependent degradation of the protein. The p21Cip1 inhibitor was also up-regulated by RA in Granta 519 cells, whereas the expression of cyclin D1 is unaffected. Most of RA-induced p27Kip1 was bound to cyclin D1/cyclin-dependent kinase 4 complexes, probably contributing to the decreased cyclin-dependent kinase 4 kinase activity and pRb hypophosphorylation observed in RA-treated cells. Experiments with receptor-selective ligands indicate that RA receptor α cooperates with retinoid X receptors in mediating RA-dependent MCL cell growth inhibition. Notably, RA isomers, and particularly 9-cis-RA, also inhibited the growth-promoting effect induced in primary MCL cells by CD40 activation alone or in combination with interleukin-4. Immunohistochemical analysis showed that significant numbers of CD40L-expressing lymphoid cells are present in lymph node biopsies of MCL patients. These results therefore further strengthen the possibility that triggering of CD40 by infiltrating CD40L+ cells may continuously promote the growth of MCL cells in vivo. On these grounds, our findings that RA inhibits basal MCL proliferation as well as MCL growth-promoting effects exerted by microenvironmental factors make these compounds highly attractive in terms of potential clinical efficacy in this setting.

Isotretinoin therapy induces DNA oxidative damage

Background: Isotretinoin (Iso) is currently indicated for the treatment of cystic acne (CA) and is related to marked teratogenicity.

Aim: The aim of the study was to evaluate the relationship between total antioxidant status (TAS) and a serum marker of DNA oxidative damage, 8-hydroxy-2-desoxyguanosine (8-OHdG), in patients on Iso treatment.

Patients and methods: Patients with CA (n=18) were evaluated before and 45days after Iso (0.5mg/kg per day) treatment and non-diseased controls (n=22) were tested only once. Plasma TAS levels and 8-OHdG were measured spectrophotometrically and with an immunoassay, respectively. Liver biochemical parameters and muscle enzymes were measured on a blood chemistry analyzer.

Results: TAS levels were significantly (p<0.0001) lower in patients before treatment (921±124μmol/L) compared with those after treatment (1335±93μmol/L) and in controls (1536±126μmol/L). In contrast, 8-OHdG serum levels were two-fold higher in patients after treatment (0.21±0.03ng/mL) than before treatment (0.11±0.02ng/mL) and three-fold higher than in controls (0.07±0.01ng/mL; p<0.0001). Negative correlations were found between TAS and 8-OHdG (r=−0.754, p<0.0001) in patients before therapy and positive correlations were found between creatine kinase (CK) and 8-OHdG (r=0.488, p<0.001) and liver enzymes after Iso treatment.

Conclusions: High serum levels of 8-OHdG in patients on Iso therapy may be due to a direct effect of Iso on liver, muscle and skin epidermal cells. Regular evaluation of 8-OHdG in sera of patients, especially of women of reproductive age, on Iso treatment could be a sensitive follow-up biomarker of DNA oxidation.

Nonclassical Retinoids and Lung Carcinogenesis

The retinoids are natural and synthetic derivatives of vitamin A. These cancer therapeutic and chemopreventive agents exert antiproliferative, differentiation-inducing, proapoptotic, and other biologic effects. The retinoids act through nuclear retinoid receptors to activate target genes that signal biologic effects. Agents that specifically activate the nuclear retinoid X receptors (RXRs) are known as rexinoids. Rexinoid growth suppression of human bronchial epithelial cells was linked to triggering of G1 cell cycle arrest, concomitant growth suppression, and a decrease in expression of G1 cyclins through activation of a proteasome-dependent degradation pathway. Clinical studies have demonstrated prolonged survival of subsets of patients with non-small-cell lung cancer (NSCLC) treated with rexinoids as single agents or as part of combination regimens. The critical role of RXR in downstream signaling makes rexinoids especially attractive agents to consider in combination therapy. There is encouraging evidence for therapeutic benefit of combination regimens of rexinoids with other targeted agents, such as epidermal growth factor receptor inhibitors, and with chemotherapy. Results from randomized phase III clinical trials in NSCLC will ultimately determine the impact for rexinoid-based therapy or chemoprevention for lung cancer.

Signal transduction pathways as novel therapy targets in lung cancer

Cytotoxic therapy for lung-cancer patients has only moderately improved during the last decades. Simultaneously, efforts of intensive research to increase our understanding of the molecular basis of lung cancer have been undertaken. The cancer cell has been characterised by several genetic changes that lead to altered cellular functions. In addition, multiple factors of the cancer-cell environment further affect the tumour cell via various receptors and subsequent signaling pathways. The increased knowledge of cellular signaling offers the opportunity to develop novel substances that target specific pathway molecules. In the current review, some of the most essential receptors and signaling pathways involved in lung cancer will be described. In conjunction, examples of novel target-specific agents that have already found their way into clinical trials will be discussed.

Specific chemopreventive agents trigger proteasomal degradation of G1 cyclins: implications for combination therapy

PURPOSE

There is a need to identify cancer chemoprevention mechanisms. We reported previously that all-trans-retinoic acid (RA) prevented carcinogenic transformation of BEAS-2B immortalized human bronchial epithelial cells by causing G(1) arrest, permitting repair of genomic DNA damage. G(1) arrest was triggered by cyclin D1 proteolysis via ubiquitin-dependent degradation. This study investigated which chemopreventive agents activated this degradation program and whether cyclin E was also degraded.

EXPERIMENTAL DESIGN

This study examined whether: (a) cyclin E protein was affected by RA treatment; (b) cyclin degradation occurred in derived BEAS-2B-R1 cells that were partially resistant to RA; and (c) other candidate chemopreventive agents caused cyclin degradation.

RESULTS

RA treatment triggered degradation of cyclin E protein, and ALLN, a proteasomal inhibitor, inhibited this degradation. Induction of the retinoic acid receptor beta, growth suppression, and cyclin degradation were each inhibited in BEAS-2B-R1 cells. Transfection experiments in BEAS-2B cells indicated that RA treatment repressed expression of wild-type cyclin D1 and cyclin E, but ALLN inhibited this degradation. Mutation of threonine 286 stabilized transfected cyclin D1, and mutations of threonines 62 and 380 stabilized transfected cyclin E, despite RA treatment. Specific chemopreventive agents triggered cyclin degradation. Nonclassical retinoids (fenretinide and retinoid X receptor agonists) and a synthetic triterpenoid (2-cyano-3,12-dioxooleana-1,9-dien-28-oic acid) each suppressed BEAS-2B growth and activated this degradation program. However, a vitamin D3 analog (RO-24-5531), a cyclooxygenase inhibitor (indomethacin), and a peroxisome proliferator-activated receptor gamma agonist (rosiglitazone) each suppressed BEAS-2B growth, but did not cause cyclin degradation. BEAS-2B-R1 cells remained responsive to nonclassical retinoids and to 2-cyano-3,12-dioxooleana-1,9-dien-28-oic acid.

CONCLUSIONS

Specific chemopreventive agents activate cyclin proteolysis. Yet, broad resistance did not occur after acquired resistance to a single agent. This provides a therapeutic rationale for combination chemoprevention with agents activating non-cross-resistant pathways.

Microarray analyses uncover UBE1L as a candidate target gene for lung cancer chemoprevention

Retinoids, natural and synthetic derivatives of vitamin A, are active in cancer therapy and chemoprevention. We reported previously that all-trans-retinoic acid (RA) treatment prevented carcinogen-induced transformation of immortalized human bronchial epithelial (HBE) cells. To identify cancer chemopreventive mechanisms, immortalized (BEAS-2B), carcinogen-transformed (BEAS-2B(NNK)), and RA-chemoprevented (BEAS-2B(NNK/RA)) HBE cells were used to conduct microarray analyses independently. Species increased in chemoprevented as compared with immortalized HBE cells (group I) and those augmented in chemoprevented as compared with transformed HBE cells (group II) included known RA-target genes as well as previously unrecognized RA-target genes in HBE cells. Unexpectedly, both groups were also enriched for interferon-stimulated genes. One interferon-stimulated gene of particular interest was UBE1L, the ubiquitin-activating enzyme E1-like protein. UBE1L expression was also induced after prolonged RA-treatment of immortalized HBE cells. UBE1L mRNA was shown previously as repressed in certain lung cancer cell lines, directly implicating UBE1L in lung carcinogenesis. Notably, UBE1L immunoblot expression was reduced in a subset of malignant as compared with adjacent normal lung tissues that were examined. Immunohistochemical analyses were performed using a new assay developed to detect this species using rabbit polyclonal anti-UBE1L antibodies independently raised against the amino- or carboxyl-termini of UBE1L. Studies done on paraffin-embedded and fixed tissues revealed abundant UBE1L, but low levels of cyclin D1 expression in the normal human bronchial epithelium, indicating an inverse relationship existed between these species. To study this further, cotransfection into HBE cells of wild-type or mutant UBE1L species was accomplished. In a dose-dependent manner, wild-type but not mutant UBE1L species repressed cyclin D1 expression. This implicated UBE1L in a retinoid chemoprevention mechanism involving cyclin D1 repression described previously. Taken together, these findings directly implicate UBE1L as a candidate-pharmacologic target for lung cancer chemoprevention. These findings also provide a mechanistic basis for the tumor suppressive effects of UBE1L through cyclin D1 repression.

Epidermal Growth Factor Receptor Tyrosine Kinase Inhibition Represses Cyclin D1 in Aerodigestive Tract Cancers

PURPOSE

Epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs) are active in cancer therapy. Mechanisms engaged during these clinical responses need to be determined. We reported previously that epidermal growth factor stimulation markedly increased cyclin D1 protein expression in human bronchial epithelial (HBE) cells, and this was opposed by chemoprevention with all-trans-retinoic acid. The current study sought to determine whether the EGFR TKI erlotinib repressed cyclin D1 protein expression in immortalized HBE cells, lung cancer cell lines, and clinical aerodigestive tract cancers.

EXPERIMENTAL DESIGN

The BEAS-2B immortalized HBE cell line was exposed to varying concentrations of erlotinib, and effects on proliferation, cell cycle distribution, G1 cyclin expression, and cyclin D1 reporter activity were measured. Non-small-cell lung cancer cell lines were also evaluated for changes in proliferation and cyclin protein expression after erlotinib treatments. A proof of principle clinical trial was conducted. During this study, patients underwent a 9-day course of erlotinib treatment. Pretreatment and posttreatment tumor biopsies were obtained, and changes in candidate biomarkers were determined by immunostaining. Plasma pharmacokinetics and tumor tissue erlotinib concentrations were measured.

RESULTS

Erlotinib, at clinically achievable dosages, repressed BEAS-2B cell growth, triggered G1 arrest, and preferentially reduced cyclin D1 protein expression and transcriptional activation. Erlotinib also preferentially repressed proliferation and cyclin D1 protein expression in responsive, but not resistant, non-small-cell lung cancer cell lines. This occurred in the presence of wild-type EGFR sequence at exons 18, 19, and 21. Five patients were enrolled onto an erlotinib proof of principle clinical trial, and four cases were evaluable. Pharmacokinetic studies established therapeutic erlotinib plasma levels in all patients, but tissue levels exceeding 2 micromol/L were detected in only two cases. Notably, these cases had pathological evidence of response (necrosis) in posttreatment biopsies as compared with pretreatment biopsies. In these cases, marked repression of cyclin D1 and the proliferation marker Ki-67 was detected by immunohistochemical assays. Cases without pathological response to erlotinib did not exhibit changes in cyclin D1 or Ki-67 immunohistochemical expression and had much lower erlotinib tissue levels than did responding cases.

CONCLUSIONS

Taken together, these in vitro and in vivo findings provide direct evidence for repression of cyclin D1 protein as a surrogate marker of response in aerodigestive tract cancers to erlotinib treatment. These findings also provide a rationale for combining an EGFR TKI with an agent that would cooperatively repress cyclin D1 expression in clinical trials for aerodigestive tract cancer therapy or chemoprevention.

Nutrient regulation of cell cycle progression

Cell replication is tightly controlled in normal tissues and aberrant during disease progression, such as in tumorigenesis. The replication of cells can be divided into four distinct phases: Gap 1 (G1), synthesis (S), gap 2 (G2), and mitosis (M). The progression from one phase to the next is intricately regulated and has many "checkpoints" that take into account cellular status and environmental cues. Among the modulators of cell cycle progression are specific nutrients, which function as energy sources or regulate the production and/or function of proteins needed to advance cells through a replicative cycle. In this review, we focus on the roles of specific nutrients (vitamin A, vitamin D, iron, folic acid, vitamin B12, zinc, and glucose) in the control of cell cycle progression and discuss how insights into the mechanisms by which these nutrients modulate this process can be and have been used to control aberrant cell growth in the treatment of prevalent pathologies.

Retinoic acid mediates degradation of IRS-1 by the ubiquitin–proteasome pathway, via a PKC-dependant mechanism

Insulin receptor substrate-1 (IRS-1) mediates signaling from the insulin-like growth factor type-I receptor. We found that all-trans retinoic acid (RA) decreases IRS-1 protein levels in MCF-7, T47-D, and ZR75.1 breast cancer cells, which are growth arrested by RA, but not in the RA-resistant MDA-MB-231 and MDA-MB-468 cells. Based on prior reports of ubiquitin-mediated degradation of IRS-1, we investigated the ubiquitination of IRS-1 in RA-treated breast cancer cells. Two proteasome inhibitors, MG-132 and lactacystin, blocked the RA-mediated degradation of IRS-1, and RA increased ubiquitination of IRS-1 in the RA-sensitive breast cancer cells. In addition, we found that RA increases serine phosphorylation of IRS-1. To elucidate the signaling pathway responsible for this phosphorylation event, pharmacologic inhibitors were used. Two PKC inhibitors, but not a MAPK inhibitor, blocked the RA-induced degradation and serine phosphorylation of IRS-1. We demonstrate that RA activates PKC-delta in the sensitive, but not in the resistant cells, with a time course that is consistent with the RA-induced decrease of IRS-1. We also show that: (1) RA-activated PKC-delta phosphorylates IRS-1 in vitro, (2) PKC-delta and IRS-1 interact in RA-treated cells, and (3) mutation of three PKC-delta serine sites in IRS-1 to alanines results in no RA-induced in vitro phosphorylation of IRS-1. Together, these results indicate that RA regulates IRS-1 levels by the ubiquitin-proteasome pathway, involving a PKC-sensitive mechanism.

Increased osteonectin expression is associated with malignant transformation and tumor associated fibrosis in the lung

Chemical transformation of the SV-40 immortalized bronchial epithelial cell line BEAS2-B induces alterations in molecules involved in cell cycle control, including up-regulation of EGFR and cyclin E [Oncogene 13 (1996) 1983; Clin Cancer Res 8 (2002) 54]. The finding that these changes also occur in vivo, in both pre-invasive and invasive lung cancer [Cancer Res 55 (1995) 1365; Cancer Res 59 (1999) 2470], proves this to be a suitable model to study lung carcinogenesis. The current study tested the hypothesis that chemical treatment of BEAS2-B with Cigarette Smoke Condensate (CSC) may affect levels of gene products involved in cell adhesion and tissue remodeling. To this end, we studied the extent of changes in osteonectin (ON) protein levels induced in BEAS 2 B-cells by CSC treatment and its timing to changes occurring in the anchorage independent cloning efficiency. ON, a multimodular protein component of the extra-cellular matrix, has been implicated in tissue remodeling occurring in neoplastic and non-neoplastic conditions, but its role in lung carcinogenesis is incompletely characterized. To validate the in vitro findings, as in our previous reports, we studied resected lung tissue, to assess whether ON expression in neoplastic lung tissue differs from normal, and to determine its cellular localization. We found that CSC treatment of BEAS2-B cells results in a 7-16-fold increase in ON protein levels, that is associated with increased colony forming efficiency. ON is absent in normal lung; in contrast it is present in the majority (39/52) of non-small cell lung cancer (NSCLC). Here, its expression is restricted to peritumoral fibroblasts in squamous cell carcinoma and adenocarcinoma. In contrast, it is localized to tumor cells in pulmonary sarcomatoid carcinoma (8/10). Thus, up-regulated ON is linked in vitro to cell transformation and in vivo, it is frequently expressed in tumor-associated fibrosis, compatible with its proposed role in tissue remodelling. Increased ON expression by tumor cells appears to represent a marker of sarcomatoid NSCLC.

Promoter methylation of retinoic acid receptor beta 2 and the development of second primary lung cancers in non-small-cell lung cancer

PURPOSE

To investigate whether the promoter hypermethylation of retinoic acid receptor beta 2 (RARbeta2) is associated with the development of second primary lung cancers (SPLCs) differentially according to smoking status in primary non-small-cell lung cancer (NSCLC).

PATIENTS AND METHODS

We retrospectively analyzed the relationship between RARbeta2 methylation and the SPLC development in a total of 342 NSCLCs. The methylation status of RARbeta2 was determined by using methylation-specific polymerase chain reaction. The difference in the time to SPLC development was analyzed by using the log-rank test and the Cox proportional hazards model. The median follow-up was 4.1 years.

RESULTS

SPLCs developed in 19 (5.6%) of the 342 NSCLCs, and overall incidence rate of SPLC development was 1.54 per 100 patient-years. SPLCs did not occur in 39 patients who had not smoked. After controlling for possible confounding factors, the hazard of failure for former smokers with RARbeta2 hypermethylation was about 2.87 (95% CI, 0.92 to 13.64; P =.08) times higher compared to those without RARbeta2 methylation. However, for current smokers, hypermethylation of the RARbeta2 was found to have a protective effect against the SPLC development (hazard ratio = 0.23; 95% CI, 0.11 to 0.87; P =.03).

CONCLUSION

Hypermethylation of RARbeta2 promoter had a differential effect on the development of SPLCs in NSCLC, and this was dependent on smoking status. Our study suggests that a combination of retinoids and/or a demethylating agent may be effective in the prevention of SPLCs in never-smokers and former smokers with NSCLC.

RARgamma acts as a tumor suppressor in mouse keratinocytes

All-trans retinoic acid (RA), the principle biologically active form of vitamin A, is essential for many developmental process as well as homeostasis in the adult. Many lines of evidence also suggest that RA, acting through the RA receptors (RARs), can also suppress growth of tumors of diverse origin. To assess directly the role of the RARs in a model of epidermal tumorigenesis, we investigated the incidence of tumor formation using keratinocytes lacking specific RAR types. Our data suggest that loss of RARgamma, but not RARalpha, predisposed keratinocytes to v-Ha-Ras-induced squamous cell carcinoma. We also found that ablation of RARgamma, but not RARalpha, abolished RA-induced cell cycle arrest and apoptosis in these keratinocytes. Reconstitution of receptor expression into RAR-null cells restored sensitivity to RA, and reversed the tumorigenic potential of receptor-deficient keratinocytes. These data strongly support a tumor suppressor effect for the RARs, in particular endogenous RARgamma, in murine keratinocytes.

Paradoxical age-related cell cycle quickening of human CD4+ lymphocytes: a role for cyclin D1 and calpain

Precise determination of cell cycle length and G(0)-->G(1) transition time of CD4(+) lymphocytes in relation to age was never done before. We show that the cell cycle of healthy elderly donors' CD4(+) cells is significantly shorter, while time to the first division (G(0)-->G(1)) extended compared to cells of young people. The G(0)-->G(1) time inversely correlates with cycle length and the number of CD28 molecules. Quickening of elderly CD4(+) cell divisions depends on overexpression of cyclin D1, possibly related to lowered proteolytic degradation by calpain. Apoptosis eliminates most of responding cells after only one or two divisions, especially in older donors.

Acyclic retinoid activates retinoic acid receptor β and induces transcriptional activation of p21CIP1 in HepG2 human hepatoma cells

Acyclic retinoid (ACR), a novel synthetic retinoid, has recently been demonstrated by us to inhibit the in vitro growth of human hepatoma cells, and this effect was associated with decreased expression of cell cycle-related molecules. These results, taken together with previous in vitro and clinical studies with ACR, suggest that this agent may be useful in the chemoprevention and therapy of hepatoma and possibly other human malignancies. In the present study, we further examined the molecular effects of ACR on the HepG2 human hepatoma cell line, focusing on the expression of nuclear retinoid receptors and the cell cycle inhibitor protein p21CIP1. Reverse transcription-PCR assays and Western blot analyses indicated that these cells express retinoic acid receptors (RARs) α, β, and γ, retinoid X receptors (RXRs) α and β, and peroxisome proliferator-activated receptors (PPAR) γ mRNA. Treatment with ACR caused a rapid induction within 3 h of RARβ mRNA and the related protein, but there was no significant change in the levels of the mRNA or proteins for RARs α and γ, RXRs α and β, and PPARγ. There was also a rapid increase in p21CIP1 mRNA and protein in HepG2 cells treated with ACR, and this induction occurred via a p53-independent mechanism. In transient transfection reporter assays, we cotransfected the retinoic acid response element-chloramphenicol acetyltransferase (CAT) reporter gene into HepG2 cells together with a RARβ expression vector. RARβ expression markedly stimulated CAT activity (up to about 4-fold) after the addition of ACR. However, CAT activity in the presence of ACR was only about 2-fold higher than that in the absence of ACR, when cells were cotransfected with RARs α and γ or RXRα. These findings suggest that the growth inhibitory effects of ACR are mediated at least in part through RARβ and that both RARβ and p21CIP1 play critical roles in the molecular mechanisms of growth inhibition induced by ACR.

Retinoic acid causes cell growth arrest and an increase in p27 in F9 wild type but not in F9 retinoic acid receptor β2 knockout cells

We have previously shown that an F9 teratocarcinoma retinoic acid receptor beta(2) (RARbeta(2)) knockout cell line exhibits no growth arrest in response to all-trans-retinoic acid (RA), whereas F9 wild type (Wt), F9 RARalpha(-/-), and F9 RARgamma(-/-) cell lines do growth arrest in response to RA. To examine the role of RARbeta(2) in growth inhibition, we analyzed the cell cycle regulatory proteins affected by RA in F9 Wt and F9 RARbeta(2)(-/-) cells. Flow microfluorimetry analyses revealed that RA treatment of F9 Wt cells greatly increased the percentage of cells in the G1/G0 phase of the cell cycle. In contrast, RA did not alter the cell cycle distribution profile of RARbeta(2)(-/-) cells. In F9 Wt cells, cyclin D1, D3, and cyclin E protein levels decreased, while cyclin D2 and p27 levels increased after RA treatment. Compared to the F9 Wt cells, the F9 RARbeta(2)(-/-) cells exhibited lower levels of cyclins D1, D2, D3, and E in the absence of RA, but did not exhibit further changes in the levels of these cell cycle regulators after RA addition. Since RA significantly increased the level of p27 protein (approximately 24-fold) in F9 Wt as compared to the F9 RARbeta(2)(-/-) cells, we chose to study p27 in greater detail. The p27 mRNA level and the rate of p27 protein synthesis were increased in RA-treated F9 Wt cells, but not in F9 RARbeta(2)(-/-) cells. Moreover, RA increased the half-life of p27 protein in F9 Wt cells. Reduced expression of RARbeta(2) is associated with the process of carcinogenesis and RARbeta(2) can mediate the growth arrest induced by RA in a variety of cancer cells. Using both genetic and molecular approaches, we have identified some of the molecular mechanisms, such as the large elevation of p27, through which RARbeta(2) mediates these growth inhibitory effects of RA in F9 cells.

Cyclin D1 as a target for chemoprevention

Lung cancer is the leading cause of cancer mortality. Chemoprevention is an attractive strategy to combat this major public health problem. Pre-clinical and clinical studies have identified diverse candidate chemopreventive agents that affect cellular proliferation, differentiation, apoptosis and tumor angiogenesis, among other pathways. These pharmacological agents are undergoing testing through use of pre-clinical models and clinical trials. These studies have uncovered cyclin D1 as a chemoprevention target and a surrogate marker of chemopreventive response in the lung. Chemoprevention of tobacco-carcinogen transformed human bronchial epithelial (HBE) cells appears to be due at least partly to degradation of cyclin D1. These studies of cultured HBE cells were extended to the in vivo setting by examination of preneoplastic bronchial lesions that established the frequent aberrant expression of cyclin D1 in lung carcinogenesis. Certain retinoids, natural and synthetic derivatives of vitamin A, repress cyclin D1, but activation of the epidermal growth factor receptor (EGFR) induces cyclin D1. Retinoids and specific chemopreventive agents can activate the proteasome-dependent degradation of cyclin D1 and also repress EGFR expression, thereby reducing cyclin D1 levels. These actions oppose the mitogenic effects of cyclin D1. This is hypothesized to trigger G1 arrest and thereby permit repair of carcinogenic damage of genomic DNA. These and other pre-clinical and clinical studies that will be reviewed here indicate that cyclin D1 and perhaps other cyclins are attractive pharmacological targets for lung cancer chemoprevention.

Microarray analysis uncovers retinoid targets in human bronchial epithelial cells

Retinoids, the natural and synthetic derivatives of vitamin A, have a role in cancer treatment and prevention. There is a need to reveal mechanisms that account for retinoid response or resistance. This study identified candidate all-trans-retinoic acid (RA) target genes linked to growth suppression in BEAS-2B human bronchial epithelial cells. Microarray analyses were performed using Affymetrix arrays. A total of 11 RA-induced species were validated by reverse transcription polymerase chain reaction (RT-PCR), Western or Northern analyses. Three of these species were novel candidate RA-target genes in human bronchial epithelial cells. These included: placental bone morphogenetic protein (PLAB), polyamine oxidase isoform 1 (PAOh1) and E74-like factor 3 (ELF3). Expression patterns were studied in RA-resistant BEAS-2B-R1 cells. In BEAS-2B-R1 cells, RA dysregulated the expression of the putative lymphocyte G0/G1 switch gene (G0S2), heme oxygenase 1 (HMOX1), tumor necrosis factor-alpha-induced protein 2 (TNFAIP2), inhibitor of DNA binding 1(Id1), fos-like antigen 1 (FOSL1), transglutaminase 2 (TGM2), asparagine synthetase (ASNS), PLAB, PAOh1 and ELF3, while prominent induction of insulin-like growth-factor-binding protein 6 (IGFBP6) still occurred. In summary, this study identified 11 candidate RA-target genes in human bronchial epithelial cells including three novel species. Expression studies in BEAS-2B-R1 cells indicated that several were directly implicated in RA signaling, since their aberrant expression was linked to RA resistance of human bronchial epithelial cells.

Lung cancer prevention: the guidelines

Lung carcinogenesis is a chronic and multi-step process resulting in malignant lung tumors. This progression from normal to neoplastic pulmonary cells or tissues could be arrested or reversed through pharmacologic treatments, which are known as cancer chemoprevention. These therapeutic interventions should reduce or avoid the clinical consequences of lung cancer by treating early neoplastic lesions before the development of clinically evident signs or symptoms of malignancy. Preclinical, clinical, and epidemiologic findings relating to different classes of candidate chemopreventive agents provide strong support for lung cancer prevention as an attractive therapeutic strategy. Smoking prevention and smoking cessation represent an essential approach to reduce the societal impact of tobacco carcinogenesis. However, even if all the goals of the national antismoking efforts were met, there still would be a large population of former smokers who would be at increased risk for lung cancers. Lung cancer also can occur in those persons who never have smoked. This article focuses on what is now known about pharmacologic strategies for lung cancer prevention. Randomized clinical trials using beta-carotene, retinol, isotretinoin or N-acetyl-cysteine did not show benefit for primary and tertiary lung cancer prevention. There is also evidence that the use of beta-carotene and isotretinoin for lung cancer chemoprevention in high-risk individuals may increase the risk for lung cancer, especially in individuals who continue to smoke. There is a need for relevant in vitro models to identify pathways that activate chemopreventive effects in the lung. An improved understanding of cancer prevention mechanisms should aid in the design of clinical trials and in the validation of candidate chemopreventive targets as well as the discovery of new targets. Until such studies are completed, no agent or combination of agents should be used for lung cancer prevention outside of a clinical trial.

Reduced cyclin D1 ubiquitination in UVB-induced murine squamous cell carcinomas

Ubiquitination of cyclin D1 signals for its proteosomal degradation. To assess the possibility that reduced cyclin D1 proteolysis is a putative mechanism for its accumulation during UVB-induced skin tumorigenesis, ubiquitination activity of cyclin D1 was assessed in UVB-induced murine SCCs. Cyclin D1 was rapidly ubiquitinated by control skin extract, whereas ubiquitination of cyclin D1 was significantly reduced in SCCs. Mutant cyclin D1, in which residues important for GSK3beta-mediated degradation of cyclin D1 are altered to non-phosphorylatable alanine, was not ubiquitinated. We also observed phosphorylation-dependent inactivation of GSK3beta in SCCs. Our results indicate reduced ubiquitination of cyclin D1 in UVB-induced murine SCCs and suggest that inactivation of GSK3beta-dependent cyclin D1 degradation pathway contributes to the accumulation of cyclin D1 in UVB-induced murine SCCs.

Cyclin D1-dependent regulation of B-myb activity in early stages of neuroblastoma differentiation

Levels of the transcription factor B-myb must be down-regulated to allow terminal differentiation of neuroectodermal cells and yet its constitutive expression induces early markers of neural differentiation. Thus, we investigated potential mechanisms of enhanced B-myb activity in early stages of neural differentiation. We report here that B-myb expression does not decrease, cyclin A and Sp1 levels remain constant while p21 levels increase continuously upon retinoic acid-induced differentiation of the LAN-5 neuroblastoma cell line. In contrast, cyclin D1 expression is down-regulated at the onset of the differentiative process by protein destabilization. Luciferase assays of promoter activity indicate that B-myb-dependent transactivation is enhanced in LAN-5 cells treated with retinoic acid (RA) for 24 h. The enhancement is independent from cyclin A but is suppressed by a degradation-resistant mutant form of cyclin D1. The importance of cyclin D1 in controlling B-myb activity is further suggested by co-immunoprecipitation experiments, showing that the amount of cyclin D1 co-immunoprecipitated with B-myb decreased after RA treatment. Thus, B-myb may play an active role in the early stages of differentiation when its transactivation activity is enhanced as a consequence of cyclin D1 down-modulation.