CDK-independent activation of estrogen receptor by cyclin D1

Association among the expression of β-catenin, cyclin D1 and estrogen receptor-β in human breast cancer

β-catenin, cyclin D1 and estrogen receptor (ER)-β are closely associated with the pathogenesis of breast cancer. In the present study, tissue samples were collected from 226 patients with breast cancer. Subsequently, immunohistochemical analysis was performed to detect the expression of β-catenin, cyclin D1 and ER-β, and the Kaplan-Meier method was used for survival analysis. The abnormal expression rate of β-catenin was 75.2%, while the cyclin D1 positive expression rate was 77.0% and the ER-β positive expression rate was 43.4%. In the tissue samples exhibiting abnormal expression of β-catenin, the positive expression rate of cyclin D1 (85.9%) was significantly higher compared with the samples that expressed β-catenin normally (50.0%). Furthermore, the positive expression rate of ER-β (35.7%) in the β-catenin normal expression tissues was significantly lower compared with that in the β-catenin abnormal expression tissues (45.9%). In the tissues with positive cyclin D1 expression, the positive expression rate of ER-β (48.4%) was significantly higher compared with the cyclin D1 negative expression samples (26.9%). In addition, patients with normal expression of β-catenin and positive expression of cyclin D1 exhibited longer tumor-free survival times. Therefore, an association exists among the abnormal expression of β-catenin and the positive expression of cyclin D1 and ER-β, which may contribute to the development of breast cancer.

Molecular Pathways: Targeting the Cyclin D-CDK4/6 Axis for Cancer Treatment

Cancer cells bypass normal controls over mitotic cell-cycle progression to achieve a deregulated state of proliferation. The retinoblastoma tumor suppressor protein (pRb) governs a key cell-cycle checkpoint that normally prevents G1-phase cells from entering S-phase in the absence of appropriate mitogenic signals. Cancer cells frequently overcome pRb-dependent growth suppression via constitutive phosphorylation and inactivation of pRb function by cyclin-dependent kinase (CDK) 4 or CDK6 partnered with D-type cyclins. Three selective CDK4/6 inhibitors, palbociclib (Ibrance; Pfizer), ribociclib (Novartis), and abemaciclib (Lilly), are in various stages of development in a variety of pRb-positive tumor types, including breast cancer, melanoma, liposarcoma, and non-small cell lung cancer. The emerging, positive clinical data obtained to date finally validate the two decades-old hypothesis that the cyclin D-CDK4/6 pathway is a rational target for cancer therapy.

Molecular aspects of bovine cystic ovarian disease pathogenesis

Cystic ovarian disease (COD) is one of the main causes of reproductive failure in cattle and causes severe economic loss to the dairy farm industry because it increases both days open in the post partum period and replacement rates due to infertility. This disease is the consequence of the failure of a mature follicle to ovulate at the time of ovulation in the estrous cycle. This review examines the evidence for the role of altered steroid and gonadotropin signaling systems and the proliferation/apoptosis balance in the ovary with cystic structures. This evidence suggests that changes in the expression of ovarian molecular components associated with these cellular mechanisms could play a fundamental role in the pathogenesis of COD. The evidence also shows that gonadotropin receptor expression in bovine cystic follicles is altered, which suggests that changes in the signaling system of gonadotropins could play a fundamental role in the pathogenesis of conditions characterized by altered ovulation, such as COD. Ovaries from animals with COD exhibit a disrupted steroid receptor pattern with modifications in the expression of coregulatory proteins. These changes in the pathways of endocrine action would trigger the changes in proliferation and apoptosis underlying the aberrant persistence of follicular cysts.

Free Spanish abstract: A Spanish translation of this abstract is freely available at http://www.reproduction-online.org/content/149/6/R251/suppl/DC1.

Minireview: Tipping the balance: ligand-independent activation of steroid receptors

Steroid receptors are prototypical ligand-dependent transcription factors and a textbook example for allosteric regulation. According to this canonical model, binding of cognate steroid is an absolute requirement for transcriptional activation. Remarkably, the simple one ligand-one receptor model could not be farther from the truth. Steroid receptors, notably the sex steroid receptors, can receive multiple inputs. Activation of steroid receptors by other signals, working through their own signaling pathways, in the absence of the cognate steroids, represents the most extreme form of signaling cross talk. Compared with cognate steroids, ligand-independent activation pathways produce similar but not identical outputs. Here we review the phenomena and discuss what is known about the underlying molecular mechanisms and the biological significance. We hypothesize that steroid receptors may have evolved to be trigger happy. In addition to their cognate steroids, many posttranslational modifications and interactors, modulated by other signals, may be able to tip the balance.

GCNF-dependent activation of cyclin D1 expression via repression of Mir302a during ESC differentiation

Cyclin D1 plays an important role in the regulation of cellular proliferation and its expression is activated during gastrulation in the mouse; however, it remains unknown how cyclin D1 expression is regulated during early embryonic development. Here, we define the role of germ cell nuclear factor (GCNF) in the activation of cyclin D1 expression during embryonic stem cell (ESC) differentiation as a model of early development. During our study of GCNF knockout (GCNF(-) (/) (-) ) ESC, we discovered that loss of GCNF leads to the repression of cyclin D1 activation during ESC differentiation. This was determined to be an indirect effect of deregulation Mir302a, which is a cyclin D1 suppressor via binding to the 3'UTR of cyclin D1 mRNA. Moreover, we showed that Mir302 is a target gene of GCNF that inhibits Mir302 expression by binding to a DR0 element within its promoter. Inhibition of Mir302a using Mir302 inhibitor during differentiation of GCNF(-) (/) (-) ESCs restored cyclin D1 expression. Similarly over-expression of GCNF during differentiation of GCNF(-) (/) (-) ESCs rescued the inhibition of Mir302a expression and the activation of cyclin D1. These results reveal that GCNF plays a key role in regulating activation of cyclin D1 expression via inhibition of Mir302a.

Humanization of the mouse mammary gland by replacement of the luminal layer with genetically engineered preneoplastic human cells

Introduction

The cell of origin for estrogen receptor α (ERα) positive breast cancer is probably a luminal stem cell in the terminal duct lobular units. To model these cells we have used the murine myoepithelial layer in the mouse mammary ducts as a scaffold upon which to build a human luminal layer. To prevent squamous metaplasia, a common artifact in genetically engineered breast cancer models, we sought to limit activation of the epidermal growth factor receptor (EGFR) during in vitro cell culture before grafting the cells.

Methods

Human reduction mammoplasty cells were grown in vitro in WIT medium. Epidermal growth factor (EGF) in the medium was replaced with amphiregulin and neuregulin to decrease activation of EGFR and increase activation of EGFR homologs 3 and 4 (ERBB3 and ERBB4). Lentiviral vectors were used to express oncogenic transgenes and fluorescent proteins. Human mammary epithelial cells were mixed with irradiated mouse fibroblasts and matrigel, then injected through the nipple into the mammary ducts of immunodeficient mice. Engrafted cells were visualized by stereomicroscopy for fluorescent proteins and characterized by histology and immunohistochemistry.

Results

Growth of normal mammary epithelial cells in conditions favoring ERBB3/4 signaling prevented squamous metaplasia in vitro. Normal human cells were quickly lost after intraductal injection but cells infected with lentiviruses expressing CCND1, MYC, TERT, BMI1 and a short hairpin RNA targeting TP53 were able to engraft and progressively replace the luminal layer in the mouse mammary ducts, resulting in the formation of an extensive network of humanized ducts. Despite expressing multiple oncogenes, the human cells formed a morphologically normal luminal layer. Expression of a single additional oncogene, PIK3CA-H1047R, converted the cells into invasive cancer cells. The resulting tumors were ERα+, Ki67+ luminal B adenocarcinomas that were resistant to treatment with fulvestrant.

Conclusions

Injection of preneoplastic human mammary epithelial cells into the mammary ducts of immunodeficient mice leads to replacement of the murine luminal layer with morphologically normal human cells. Genetic manipulation of the injected cells makes it possible to study defined steps in the transformation of human mammary epithelial cells in a more physiological environment than has hitherto been possible.

Electronic supplementary material

The online version of this article (doi:10.1186/s13058-014-0504-9) contains supplementary material, which is available to authorized users.

Cooperation of DLC1 and CDK6 affects breast cancer clinical outcome

Low DLC1 expression is found to frequently co-occur with aberrant expression of cell cycle genes including CDK6 in human lung and colon cancer. Here, we explore the influence of the synergistic effect of DLC1 and CDK6 on human breast cancer survival at the genetic, transcriptional, and translational levels. We found that high DLC1 and low CDK6 expression are associated with good prognosis. The DLC1 intronic SNP rs561681 is found to fit a recessive model, complying with the tumor suppressive role of DLC1. The heterozygote of the DLC1 SNP is found to increase the hazard when the CDK6 intronic SNP rs3731343 is rare homozygous, and it becomes protective when rs3731343 is common homozygous. We propose that DLC1 expression is the lowest in patients harboring the rare homozygote of rs561681 and functional DLC1 is the lowest when rs561681 is heterozygous and rs3731343 is rare homozygous. We are the first to report such synergistic effects of DLC1 and CDK6 on breast cancer survival at the transcriptional level, the overdominant model fitted by the SNP pair, and the dominant negative effect at the translational level. These findings link the germline genetic polymorphisms and synergistic effect of DLC1 and CDK6 with breast cancer progression, which provide the basis for experimentally elucidating the mechanisms driving differential tumor progression and avail in tailoring the clinical treatments for such patients based on their genetic susceptibility.

Cyclin D1 represses gluconeogenesis via inhibition of the transcriptional coactivator PGC1α

Hepatic gluconeogenesis is crucial to maintain normal blood glucose during periods of nutrient deprivation. Gluconeogenesis is controlled at multiple levels by a variety of signal transduction and transcriptional pathways. However, dysregulation of these pathways leads to hyperglycemia and type 2 diabetes. While the effects of various signaling pathways on gluconeogenesis are well established, the downstream signaling events repressing gluconeogenic gene expression are not as well understood. The cell-cycle regulator cyclin D1 is expressed in the liver, despite the liver being a quiescent tissue. The most well-studied function of cyclin D1 is activation of cyclin-dependent kinase 4 (CDK4), promoting progression of the cell cycle. We show here a novel role for cyclin D1 as a regulator of gluconeogenic and oxidative phosphorylation (OxPhos) gene expression. In mice, fasting decreases liver cyclin D1 expression, while refeeding induces cyclin D1 expression. Inhibition of CDK4 enhances the gluconeogenic gene expression, whereas cyclin D1-mediated activation of CDK4 represses the gluconeogenic gene-expression program in vitro and in vivo. Importantly, we show that cyclin D1 represses gluconeogenesis and OxPhos in part via inhibition of peroxisome proliferator-activated receptor γ coactivator-1α (PGC1α) activity in a CDK4-dependent manner. Indeed, we demonstrate that PGC1α is novel cyclin D1/CDK4 substrate. These studies reveal a novel role for cyclin D1 on metabolism via PGC1α and reveal a potential link between cell-cycle regulation and metabolic control of glucose homeostasis.

Cyclin A2 and its associated kinase activity are required for optimal induction of progesterone receptor target genes in breast cancer cells

A role for the cell cycle protein cyclin A2 in regulating progesterone receptor (PR) activity is emerging. This study investigates the role of cyclin A2 in regulating endogenous PR activity in T47D breast cancer cells by depleting cyclin A2 expression and measuring PR target genes using q-RT-PCR. Targets examined included genes induced by the PR-B isoform more strongly than PR-A (SGK1, FKBP5), a gene induced predominantly by PR-A (HEF1), genes induced via PR tethering to other transcription factors (p21, p27), a gene induced in part via extra-nuclear PR signaling mechanisms (cyclin D1) and PR-repressed genes (DST, IL1R1). Progestin induction of target genes was reduced following cyclin A2 depletion. However, cyclin A2 depletion did not diminish progestin target gene repression. Furthermore, inhibition of the associated Cdk2 kinase activity of cyclin A2 also reduced progestin induction of target genes, while Cdk2 enhanced the interaction between PR and cyclin A2. These results demonstrate that cyclin A2 and its associated kinase activity are important for progestin-induced activation of endogenous PR target genes in breast cancer cells.

Palbociclib: an evidence-based review of its potential in the treatment of breast cancer

Cellular proliferation, growth, and division following DNA (deoxyribonucleic acid) damage are tightly controlled by the cell-cycle regulatory machinery. This machinery includes cyclin-dependent kinases (CDKs) which complex with their cyclin partners, allowing the cell cycle to progress. The cell-cycle regulatory process plays a critical role in oncogenesis and in the development of therapeutic resistance; it is frequently disrupted in breast cancer, providing a rational target for therapeutic development. Palbociclib is a potent and selective inhibitor of CDK4 and -6 with significant activity in breast cancer models. Furthermore, it has been shown to significantly prolong progression-free survival when combined with letrozole in the management of estrogen receptor-positive metastatic breast cancer. In this article we review the cell cycle and its regulatory processes, their role in breast cancer, and the rationale for CDK inhibition in this disease. We describe the preclinical and clinical data relating to the activity of palbociclib in breast cancer and the plans for the future development of this agent.

Mechanisms associated with resistance to tamoxifen in estrogen receptor-positive breast cancer (review)

Anti-estrogens such as tamoxifen are widely used in the clinic to treat estrogen receptor-positive breast tumors. Patients with estrogen receptor-positive breast cancer initially respond to treatment with anti-hormonal agents such as tamoxifen, but remissions are often followed by the acquisition of resistance and, ultimately, disease relapse. The development of a rationale for the effective treatment of tamoxifen-resistant breast cancer requires an understanding of the complex signal transduction mechanisms. In the present study, we explored some mechanisms associated with resistance to tamoxifen, such as pharmacologic mechanisms, loss or modification in estrogen receptor expression, alterations in co-regulatory proteins and the regulation of the different signaling pathways that participate in different cellular processes such as survival, proliferation, stress, cell cycle, inhibition of apoptosis regulated by the Bcl-2 family, autophagy, altered expression of microRNA, and signaling pathways that regulate the epithelial-mesenchymal transition in the tumor microenvironment. Delineation of the molecular mechanisms underlying the development of resistance may aid in the development of treatment strategies to enhance response and compromise resistance.

Chemopreventive and therapeutic activity of dietary blueberry against estrogen-mediated breast cancer

Berries are gaining increasing importance lately for their chemopreventive and therapeutic potential against several cancers. In earlier studies, a blueberry-supplemented diet has shown protection against 17β-estradiol (E2)-mediated mammary tumorigenesis. This study tested both preventive and therapeutic activities of diet supplemented with whole blueberry powder (50:50 blend of Tifblue and Rubel). Animals received 5% blueberry diet, either 2 weeks prior to or 12 weeks after E2 treatment in preventive and therapeutic groups, respectively. Both interventions delayed the tumor latency for palpable mammary tumors by 28 and 37 days, respectively. Tumor volume and multiplicity were also reduced significantly in both modes. The effect on mammary tumorigenesis was largely due to down-regulation of CYP 1A1 and ER-α gene expression and also favorable modulation of microRNA (miR-18a and miR-34c) levels. These data suggest that the blueberry blend tested is effective in inhibiting E2-mediated mammary tumorigenesis in both preventive and therapeutic modes.

The other side of the coin: the tumor-suppressive aspect of oncogenes and the oncogenic aspect of tumor-suppressive genes, such as those along the CCND-CDK4/6-RB axis

Although cancer-regulatory genes are dichotomized to oncogenes and tumor-suppressor gene s, in reality they can be oncogenic in one situation but tumor-suppressive in another. This dual-function nature, which sometimes hampers our understanding of tumor biology, has several manifestations: (1) Most canonically defined genes have multiple mRNAs, regulatory RNAs, protein isoforms, and posttranslational modifications; (2) Genes may interact at different levels, such as by forming chimeric RNAs or by forming different protein complexes; (3) Increased levels of tumor-suppressive genes in normal cells drive proliferation of cancer progenitor cells in the same organ or tissue by imposing compensatory proliferation pressure, which presents the dual-function nature as a cell-cell interaction. All these manifestations of dual functions can find examples in the genes along the CCND-CDK4/6-RB axis. The dual-function nature also underlies the heterogeneity of cancer cells. Gene-targeting chemotherapies, including that targets CDK4, are effective to some cancer cells but in the meantime may promote growth or progression of some others in the same patient. Redefining "gene" by considering each mRNA, regulatory RNA, protein isoform, and posttranslational modification from the same genomic locus as a "gene" may help in better understanding tumor biology and better selecting targets for different sub-populations of cancer cells in individual patients for personalized therapy.

Transcription Factor STAT3 as a Novel Molecular Target for Cancer Prevention

Signal Transducers and Activators of Transcription (STATs) are a family of transcription factors that regulate cell proliferation, differentiation, apoptosis, immune and inflammatory responses, and angiogenesis. Cumulative evidence has established that STAT3 has a critical role in the development of multiple cancer types. Because it is constitutively activated during disease progression and metastasis in a variety of cancers, STAT3 has promise as a drug target for cancer therapeutics. Recently, STAT3 was found to have an important role in maintaining cancer stem cells in vitro and in mouse tumor models, suggesting STAT3 is integrally involved in tumor initiation, progression and maintenance. STAT3 has been traditionally considered as nontargetable or undruggable, and the lag in developing effective STAT3 inhibitors contributes to the current lack of FDA-approved STAT3 inhibitors. Recent advances in cancer biology and drug discovery efforts have shed light on targeting STAT3 globally and/or specifically for cancer therapy. In this review, we summarize current literature and discuss the potential importance of STAT3 as a novel target for cancer prevention and of STAT3 inhibitors as effective chemopreventive agents.

Protein arginine methyltransferase 6 enhances ligand-dependent and -independent activity of estrogen receptor α via distinct mechanisms

Recent studies reported that protein arginine methyltransferase 6 (PRMT6) enhances estrogen-induced activity of estrogen receptor α (ERα) and dysfunction of PRMT6 is associated with overall better survival for ERα-positive breast cancer patients. However, it is unclear how PRMT6 promotes ERα activity. Here we report that PRMT6 specifically interacts with ERα at its ligand-binding domain. PRMT6 also methylates ERα both in vitro and in vivo. In addition to enhancing estrogen-induced ERα activity, PRMT6 over-expression up-regulates estrogen-independent activity of ERα and PRMT6 gene silencing in MCF7 cells inhibits ligand-independent ERα activation. More interestingly, the effect of PRMT6 on the ligand-independent ERα activity does not require its methyltransferase activity. Instead, PRMT6 competes with Hsp90 for ERα binding: PRMT6 and Hsp90 bindings to ERα are mutually exclusive and PRMT6 over-expression reduces ERα interaction with Hsp90. In conclusion, PRMT6 requires its methyltransferase activity to enhance ERα's ligand-induced activity, but its effect on ligand-independent activity is likely mediated through competing with Hsp90 for binding to the C-terminal domain of ERα. PRMT6-ERα interaction would prevent ERα-Hsp90 association. Since Hsp90 and associated chaperones serve to maintain ERα conformation for ligand-binding yet functionally inactive, inhibition of ERα-Hsp90 interaction would relieve ERα from the constraint of chaperone complex.

Longer survival in patients with breast cancer with cyclin d1 over-expression after tumor recurrence: longer, but occupied with disease

Purpose

The effect of cyclin D1 overexpression on breast cancer outcomes and prognosis is controversial, even though amplification of the cyclin D1 gene, CCND1, has been shown to be associated with early relapse and poor prognosis. In this study, we examined the relationship between cyclin D1 overexpression and disease-specific survival (DSS). We also analyzed survival in patients who experienced recurrence.

Methods

We retrospectively analyzed data from patients diagnosed with ductal carcinoma between April 2005 and December 2010. We examined clinicopathologic factors associated with cyclin D1 overexpression and analyzed the influence of cyclin D1 on recurrence-free survival and DSS.

Results

We identified 236 patients diagnosed with primary breast cancer who completed all phases of their primary treatment. Cyclin D1 overexpression was significantly associated with longer DSS (5-year DSS, 89.9% in patients without cyclin D1 overexpression vs. 98.9% in patients with cyclin D1 overexpression; p=0.008). Multivariate analysis also found that patients with cyclin D1 overexpressing tumors had significantly longer disease-specific survival than patients whose tumors did not overexpress cyclin D1, with a hazard ratio for disease-specific mortality of 7.97 (1.17-54.22, p=0.034). However, in the group of patients who experienced recurrence, cyclin D1 overexpression was not significantly associated with recurrence-free survival. Cyclin D1 overexpression was significantly associated with increased survival after disease recurrence, indicating that cyclin D1 overexpression might be indicative of more indolent disease progression after metastasis.

Conclusion

Cyclin D1 overexpression is associated with longer DSS, but not recurrence-free survival, in patients with breast cancer. Longer postrecurrence survival could explain the apparent inconsistency between DSS and recurrence-free survival. Patients with cyclin D1-overexpressing tumors survive longer, but with metastatic disease after recurrence. This information should spark the urgent development of tailored therapies to cure these patients.

Identifying gastric cancer related genes using the shortest path algorithm and protein-protein interaction network

Gastric cancer, as one of the leading causes of cancer related deaths worldwide, causes about 800,000 deaths per year. Up to now, the mechanism underlying this disease is still not totally uncovered. Identification of related genes of this disease is an important step which can help to understand the mechanism underlying this disease, thereby designing effective treatments. In this study, some novel gastric cancer related genes were discovered based on the knowledge of known gastric cancer related ones. These genes were searched by applying the shortest path algorithm in protein-protein interaction network. The analysis results suggest that some of them are indeed involved in the biological process of gastric cancer, which indicates that they are the actual gastric cancer related genes with high probability. It is hopeful that the findings in this study may help promote the study of this disease and the methods can provide new insights to study various diseases.

Prognostic and predictive value of copy number alterations in invasive breast cancer as determined by multiplex ligation-dependent probe amplification

BACKGROUND

Breast cancer is a leading cause of morbidity and mortality in women worldwide. About 70 % of breast cancers are estrogen receptor (ER) positive. Blocking estrogen action by tamoxifen has been the treatment of choice in ER positive breast cancers for more than 30 years. In the past, several studies have revealed associations between gene copy number alterations and responsiveness to tamoxifen therapy, but so far no single gene copy number alteration could completely explain the response variation observed between individual breast cancer patients. Here, we set out to perform a simultaneous analysis of copy number alterations of several genes involved in the prognosis and response to therapy by multiplex ligation-dependent probe amplification (MLPA).

METHODS

A case-control study was designed encompassing 170 non-metastatic ER positive breast cancer patients (case group = 85, control group = 85). All patients in the control group had received standard adjuvant tamoxifen treatment for 5 years without any evidence of recurrence. Patients in the case group had experienced early recurrences while receiving tamoxifen treatment. 76 % of the patients of the case group and 73 % of the patients of the control group had received anthracycline-based adjuvant chemotherapy. Gene copy number alterations detected by MLPA in both groups were compared.

RESULTS

Amplification of CCND1 (OR = 3.13; 95 % CI = 1.35 to 7.26; p = 0.006) and TOP2A (OR = 3.05; 95 % CI = 1.13 to 8.24; p = 0.022) were significantly more prevalent in the case group, compared to the control group. In a multivariate analysis CCND1 (p = 0.01) and TOP2A (p = 0.041) amplifications remained significant predictors of recurrence.

CONCLUSIONS

Our results indicate that CCND1 amplification may serve as a useful biomarker for hormone responsiveness, and that TOP2A amplification may serve as a useful prognostic biomarker.

Progesterone receptor-cyclin D1 complexes induce cell cycle-dependent transcriptional programs in breast cancer cells

The progesterone receptor (PR) and its coactivators are direct targets of activated cyclin-dependent kinases (CDKs) in response to peptide growth factors, progesterone, and deregulation of cell cycle inhibitors. Herein, using the T47D breast cancer model, we probed mechanisms of cell cycle-dependent PR action. In the absence of exogenous progestin, the PR is specifically phosphorylated during the G2/M phase. Accordingly, numerous PR target genes are cell cycle regulated, including HSPB8, a heat-shock protein whose high expression is associated with tamoxifen resistance. Progestin-induced HSPB8 expression required cyclin D1 and was insensitive to antiestrogens but blocked by antiprogestins or inhibition of specificity factor 1 (SP1). HSPB8 expression increased with or without ligand when cells were G2/M synchronized or contained high levels of cyclin D1. Knockdown of PRs abrogated ligand-independent HSPB8 expression in synchronized cells. Notably, PRs and cyclin D1 copurified in whole-cell lysates of transiently transfected COS-1 cells and in PR-positive T47D breast cancer cells expressing endogenous cyclin D1. PRs, cyclin D1, and SP1 were recruited to the HSPB8 promoter in progestin-treated T47D breast cancer cells. Mutation of PR Ser345 to Ala (S345A) or inhibition of CDK2 activity using roscovitine disrupted PR/cyclin D1 interactions with DNA and blocked HSPB8 mRNA expression. Interaction of phosphorylated PRs with SP1 and cyclin D1 provides a mechanism for targeting transcriptionally active PRs to selected gene promoters relevant to breast cancer progression. Understanding the functional linkage between PRs and cell cycle regulatory proteins will provide keys to targeting novel PR/cyclin D1 cross talk in both hormone-responsive disease and HSPB8-high refractory disease with high HSPB8 expression.

Palbociclib (PD 0332991) : targeting the cell cycle machinery in breast cancer

INTRODUCTION

The cyclin D-cyclin-dependent kinases 4 and 6 (CDK4/6)-retinoblastoma (Rb) pathway, governing the cell cycle restriction point, is frequently altered in breast cancer and is a potentially relevant target for anticancer therapy. Palbociclib (PD 0332991) , a potent and selective inhibitor of CDK4 and CDK6, inhibits proliferation of several Rb-positive cancer cell lines and xenograft models.

AREAS COVERED

The basic features and abnormalities of the cell cycle in breast cancer are described, along with their involvement in estrogen signaling and endocrine resistance. The pharmacological features of palbociclib, its activity in preclinical models of breast cancer and the potential determinants of response are then illustrated, and its clinical development in breast cancer described. A literature search on the topic was conducted through PubMed and the proceedings of the main cancer congresses of recent years.

EXPERT OPINION

The combination of palbociclib with endocrine agents is a very promising treatment and Phase III clinical trials are ongoing to confirm its efficacy. Further, potentially useful combinations are those with drugs targeting mitogenic signaling pathways, such as HER2- and PI3K-inhibitors. Combination with chemotherapy seems more problematic, as antagonism has been reported in preclinical models. The identification of predictive factors, already explored in preclinical studies, must be further refined and validated in clinical trials.

Altered methylation and expression of ER-associated degradation factors in long-term alcohol and constitutive ER stress-induced murine hepatic tumors

Mortality from liver cancer in humans is increasingly attributable to heavy or long-term alcohol consumption. The mechanisms by which alcohol exerts its carcinogenic effect are not well understood. In this study, the role of alcohol-induced endoplasmic reticulum (ER) stress response in liver cancer development was investigated using an animal model with a liver knockout (KO) of the chaperone BiP and under constitutive hepatic ER stress. Long-term alcohol and high fat diet feeding resulted in higher levels of serum alanine aminotransferase, impaired ER stress response, and higher incidence of liver tumor in older (aged 16 months) KO females than in either middle-aged (6 months) KOs or older (aged 16 months) wild type females. In the older KO females, stronger effects of the alcohol on methylation of CpG islands at promoter regions of genes involved in the ER-associated degradation (ERAD) were also detected. Altered expression of ERAD factors including derlin 3, Creld2 (cysteine-rich with epidermal growth factor-like domains 2), Herpud1 (homocysteine-inducible, endoplasmic reticulum stress-inducible, ubiquitin-like domain member), Wfs1 (Wolfram syndrome gene), and Yod1 (deubiquitinating enzyme 1) was co-present with decreased proteasome activities, increased estrogen receptor α variant (ERα36), and enhanced phosphorylations of ERK1/2 (extracellular signal-regulated protein kinases 1 and 2) and STAT3 (the signal transducers and activators of transcription) in the older KO female fed alcohol. Our results suggest that long-term alcohol consumption and aging may promote liver tumorigenesis in females through interfering with DNA methylation and expression of genes involved in the ERAD.

New roles of cyclin D1

Cyclins encode regulatory subunits of holoenzymes that phosphorylate a variety of cellular substrates. Although the classic role of cyclins in cell cycle progression and tumorigenesis has been well characterized, new functions have been identified, including the induction of cellular migration and invasion, enhancement of angiogenesis, inhibition of mitochondrial metabolism, regulation of transcription factor signaling via a DNA-bound form, the induction of chromosomal instability, enhancement of DNA damage sensing and DNA damage repair, and feedback governing expression of the noncoding genome. This review describes the mechanisms of these new functions of cyclin D1.

Monoallelic loss of tumor suppressor GRIM-19 promotes tumorigenesis in mice

Gene-associated with retinoid-interferon induced mortality-19 (GRIM-19), a STAT3-inhibitory protein, was isolated as a growth-suppressive gene product using a genome-wide expression knockdown screen. We and others have shown a loss of expression and occurrence of mutations in the GRIM-19 gene in a variety of primary human cancers, indicating its potential role as tumor suppressor. To help investigate its role in tumor development in vivo, we generated a genetically modified mouse in which Grim-19 can be conditionally inactivated. Deletion of Grim-19 in the skin significantly increased the susceptibility of mice to chemical carcinogenesis, resulting in development of squamous cell carcinomas. These tumors had high Stat3 activity and an increased expression of Stat3-responsive genes. Loss of Grim-19 also caused mitochondrial electron transport dysfunction resulting from failure to assemble electron transport chain complexes and altered the expression of several cellular genes involved in glycolysis. Surprisingly, the deletion of a single copy of the Grim-19 gene was sufficient to promote carcinogenesis and formation of invasive squamous cell carcinomas. These observations highlight the critical role of GRIM-19 as a tumor suppressor.

Female-specific rectal carcinogenesis in cyclin D1b transgenic mice

Human cyclin D1 generates two major isoforms via alternative splicing: cyclin D1a and cyclin D1b. Cyclin D1b is hardly expressed in normal tissues but is frequently expressed in certain types of cancer tissues. To clarify the oncogenic potential of cyclin D1b variant, we developed cyclin D1b transgenic (Tg) mice and analyzed their phenotypes. We detected rectal tumors in 63% (15/24) of the female Tg mice. All rectal tumors had the histological characteristics similar to human sessile serrated adenoma/polyps (SSA/Ps). Adenocarcinomas were also found in 53% (8/15) of the rectal tumors, suggesting that these adenocarcinomas originated from the SSA/P-like lesions. No rectal tumors were found in the ovariectomized female cyclin D1b Tg mice (0/10), indicating that ovarian hormones played a critical role in rectal carcinogenesis in these Tg mice. Both phosphorylation of Erk, without activating MEK, and expression of estrogen receptor β were elevated in the rectal tumors of female cyclin D1b Tg mice compared with normal rectums of female wild-type mice. In addition, we established a cell line, D1bTgRT, derived from a rectal cancer of female Tg mouse. Small interfering RNA-induced cyclin D1b knockdown in this cell line suppressed Erk phosphorylation, anchorage-independent growth, cell invasiveness and tumorigenicity in nude mice. In humans, expression of cyclin D1b messenger RNA was detected in 17% (1/6) of colorectal cancer cell lines and 9.7% (3/31) of colorectal cancer tissues. Taken together, these results indicate that cyclin D1b expression contributes to the female- specific rectal carcinogenesis in mouse model.

Cooperation between Dmp1 loss and cyclin D1 overexpression in breast cancer

Cyclin D1 is a component of the core cell-cycle machinery and is frequently overexpressed in breast cancer. It physically interacts with the tumor suppressor Dmp1 that attenuates the oncogenic signals from Ras and HER2 by inducing Arf/p53-dependent cell-cycle arrest. Currently, the biological significance of Dmp1-cyclin D1 interplay in breast cancer has not been determined. Here, we show that cyclin D1 bound to Dmp1 to activate both Arf and Ink4a promoters and, consequently, induced apoptosis or G2/M cell-cycle delay in normal cells to protect them from neoplastic transformation. The cyclin D1-induced Ink4a/Arf gene expression was dependent on Dmp1 because the induction was not detected in Dmp1-deficient or DMP1-depleted cells. Arf/Ink4a expression was increased in pre-malignant mammary glands from Dmp1(+/+);MMTV-cyclin D1 and Dmp1(+/+);MMTV-D1T286A mice but significantly down-regulated in those from Dmp1-deficient mice. Selective Dmp1 deletion was found in 21% of the MMTV-D1 and D1T286A mammary carcinomas, and the Dmp1 heterozygous status significantly accelerated mouse mammary tumorigenesis with reduced apoptosis and increased metastasis. Overall, our study reveals a pivotal role of combined Dmp1 loss and cyclin D1 overexpression in breast cancer.

Cyclin D1 promotes cell cycle progression through enhancing NDR1/2 kinase activity independent of cyclin-dependent kinase 4

Cyclin/cyclin-dependent kinases (Cdks) are critical protein kinases in regulating cell cycle progression. Among them, cyclin D1/Cdk4 exerts its function mainly in the G1 phase. By using the tandem affinity purification tag approach, we identified a set of proteins interacting with Cdk4, including NDR1/2. Interestingly, confirming the interactions between NDR1/2 and cyclin D1/Cdk4, we observed that NDR1/2 interacted with cyclin D1 independent of Cdk4, but NDR1/2 and cyclin D1/Cdk4 did not phosphorylate each other. In addition, we found that NDR1/2 did not affect the kinase activity of cyclin D1/Cdk4 upon phosphorylation of GST-Rb. However, cyclin D1 but not Cdk4 promoted the kinase activity of NDR1/2. We also demonstrated that cyclin D1 K112E, which could not bind Cdk4, enhanced the kinase activity of NDR1/2. To test whether cyclin D1 promotes G1/S transition though enhancing NDR1/2 kinase activity, we performed flow cytometry analysis using cyclin D1 and cyclin D1 K112E Tet-On inducible cell lines. The data show that both cyclin D1 and cyclin D1 K112E promoted G1/S transition. Importantly, knockdown of NDR1/2 almost completely abolished the function of cyclin D1 K112E in promoting G1/S transition. Consistently, we found that the protein level of p21 was reduced in cells overexpressing cyclin D1 K112E but not when NDR1/2 was knocked down. Taken together, these results reveal a novel function of cyclin D1 in promoting cell cycle progression by enhancing NDR kinase activity independent of Cdk4.

Cyclin D1 determines estrogen signaling in the mammary gland in vivo

The CCND1 gene, which is frequently overexpressed in cancers, encodes the regulatory subunit of a holoenzyme that phosphorylates the retinoblastoma protein. Although it is known that cyclin D1 regulates estrogen receptor (ER)α transactivation using heterologous reporter systems, the in vivo biological significance of cyclin D1 to estrogen-dependent signaling, and the molecular mechanisms by which cyclin D1 is involved, are yet to be elucidated. Herein, genome-wide expression profiling conducted of 17β-estradiol-treated castrated virgin mice deleted of the Ccnd1 gene demonstrated that cyclin D1 determines estrogen-dependent gene expression for 88% of estrogen-responsive genes in vivo. In addition, expression profiling of 17β-estradiol-stimulated cyclin D1 small interfering RNA treated MCF7 cells shows cyclin D1 is required for estrogen-mediated gene expression in vitro. Genome-wide chromatin immunoprecipitation-Seq analysis revealed a cyclin D1-DNA bound form associated with genes that were regulated by estrogen in a cyclin D1-dependent manner. The cyclin D1-dependent estrogen signaling pathways identified in vivo were highly enriched for extracellular membrane-associated growth factor receptors (epidermal growth factor receptor, ErbB3, and EphB3) and their ligands (amphiregulin, encoded by AREG gene), and matrix metalloproteinase. The AREG protein, a pivotal ligand for epidermal growth factor receptors to promote cellular proliferation, was induced by cyclin D1 via the AREG promoter. Chromatin immunoprecipitation analysis demonstrated the recruitment of cyclin D1 to the breast cancer 1 (Brca1)/ERα binding site of the Areg gene. Cyclin D1 genetic deletion demonstrated the in vivo requirement for cyclin D1 in assembling the estrogen-dependent amplified in breast cancer 1-associated multiprotein complex. The current studies define a requirement for cyclin D1 in estrogen-dependent signaling modules governing growth factor receptor and ligand expression in vivo and reveal a noncanonical function of cyclin D1 at ERα target gene promoters. Cyclin D1 mediates the convergence of ERα and growth factor signaling at a common cis-element of growth factor genes.

Biomarkers for the clinical management of breast cancer: international perspective

The higher incidence of breast cancer in developed countries has been tempered by reductions in mortality, largely attributable to mammographic screening programmes and advances in adjuvant therapy. Optimal systemic management requires consideration of clinical, pathological and biological parameters. Oestrogen receptor alpha (ERα), progesterone receptor (PgR) and human epidermal growth factor receptor 2 (HER2) are established biomarkers evaluated at diagnosis, which identify cardinal subtypes of breast cancer. Their prognostic and predictive utility effectively guides systemic treatment with endocrine, anti-HER2 and chemotherapy. Hence, accurate and reliable determination remains of paramount importance. However, the goals of personalized medicine and targeted therapies demand further information regarding residual risk and potential benefit of additional treatments in specific circumstances. The need for biomarkers which are fit for purpose, and the demands placed upon them, is therefore expected to increase. Technological advances, in particular high-throughput global gene expression profiling, have generated multi-gene signatures providing further prognostic and predictive information. The rational integration of routinely evaluated clinico-pathological parameters with key indicators of biological activity, such as proliferation markers, also provides a ready opportunity to improve the information available to guide systemic therapy decisions. The additional value of such information and its proper place in patient management is currently under evaluation in prospective clinical trials. Expanding the utility of biomarkers to lower resource settings requires an emphasis on cost effectiveness, quality assurance and possible international variations in tumor biology; the potential for improved clinical outcomes should be justified against logistical and economic considerations.

Cyclins and cell cycle control in cancer and disease

Cyclin D1 overexpression is found in more than 50% of human breast cancers and causes mammary cancer in transgenic mice. Dysregulation of cyclin D1 gene expression or function contributes to the loss of normal cell cycle control during tumorigenesis. Recent studies have demonstrated that cyclin D1 conducts additional specific functions to regulate gene expression in the context of local chromatin, promote cellular migration, and promote chromosomal instability. It is anticipated that these additional functions contribute to the pathology associated with dysregulated cyclin D1 abundance. This article discusses evidence that examines the functional roles that cyclin D1 may play in cancer with an emphasis on other cyclin family members that also may contribute to cancer and disease in a similar fashion.

Association of cyclin D and estrogen receptor α36 with hepatocellular adenomas of female mice under chronic endoplasmic reticulum stress

BACKGROUND AND AIMS

Hepatocellular adenomas (HCAs) are benign tumors that can lead to medical complications. Chronic inflammation and mutations in β-catenin, hepatocyte nuclear factor 1α, or glycoprotein 130 are potential causes for human HCA. However, additional causes may exist due to heterogeneity of HCA. We investigated whether HCA are caused by endoplasmic reticulum (ER) stress.

METHODS

Mice with a liver-specific deletion of the major chaperone BiP (LGKO) were used. Liver tumor occurrence was examined in LGKO with or without feeding of a high-fat diet (HFD) and characterized with immunohistochemistry with molecular markers of proliferation/malignancy. Molecular changes were analyzed with immunoblotting.

RESULTS

Spontaneous monoclonal liver tumors were observed in 34% of LGKO females with constitutive hepatic ER stress. Lack of portal tracks or central veins, dilated sinusoidal spaces, hemorrhagic areas, active proliferation, and lipid deposits were observed in the liver tumors. HFD feeding induced multiclonal liver tumors in 83% of the LGKO females versus 0 in wild-type females. Hepatocytes reactive to antiglypican 3 antibodies were detected in the HFD-induced, but not spontaneous, tumors. In the liver tumors, inhibition of cyclin D and increase of the 36 kD estrogen receptor variant (estrogen receptor α36), active transcription activator 4/6, glycogen synthase kinase 3β, and extracellular signal-regulated protein kinases 1 and 2 were detected, whereas no change of hepatocyte nuclear factor 1α, β-catenin, p-53, androgen receptor α, or estrogen receptor α was detected. HFD activated Janus kinase and signal transducers and activators of transcription 3.

CONCLUSIONS

Our evidence supports a novel link of HCA with ER stress and altered expression of cyclin D and estrogen receptor α36. Additional stress such as HFD may promote malignant transformation of HCA through the Janus kinase-signal transducers and activators of transcription pathway.

Role of cyclins in controlling progression of mammalian spermatogenesis

Cyclins are key regulators of the mammalian cell cycle, functioning primarily in concert with their catalytic partners, the cyclin-dependent kinases (Cdks). While their function during mitosis in somatic cells has been extensively documented, their function during both mitosis and meiosis in the germ line is poorly understood. From the perspective of cell cycle regulation there are several aspects of mammalian spermatogenesis that suggest unique modes of regulation and hence, possible unique functions for the cyclins. This review will summarize our current understanding of cyclin expression and function in the male germ line, with particular focus on the A and E type cyclins in the mouse model. While the focus is on mammalian spermatogenesis, we note contrasts with similar functions in the female germ line when relevant and also draw upon observations in other model systems to provide further insight.

Sexual dimorphism of STGC3 tumor suppressor function in nasopharyngeal carcinoma CNE2 cells

STGC3 is a potential tumor suppressor in nasopharyngeal carcinoma. We previously found that CNE2 cells that re-expressed STGC3 formed smaller tumors in female mice than in male mice. Here, we investigated the sexual dimorphism of STGC3 as a tumor-suppressor in female and male nude mice injected subcutaneously with pcDNA3.1(+)-STGC3/CNE2 cells. ER-α was positively expressed in vitro in the CNE2 cells. The pcDNA3.1(+)-STGC3/CNE2 cell growth rate decreased after treatment with β-estradiol in vitro. There were significant differences in tumor size or mass between pcDNA3.1(+)-STGC3/CNE2 and control cases (P < 0.05), but there were significant differences in tumor size between female and male nude mice in the STGC3 transfection groups, and the pcDNA3.1(+)-STGC3/CNE2 tumor growth rate in the female nude mice was the lowest in all cases (P < 0.05). There were no significant differences between female and male nude mice in control groups. Furthermore, a greater number of cells were blocked in the G(0)/G(1) phase in pcDNA3.1(+)-STGC3/ CNE2 tumor xenografts in the female mice. Protemic analysis found 9 differentially expressed proteins in the pcDNA3.1-STGC3/CNE2 xenograft tissues in females and males. A heat shock 70 protein 8 isoform 2 variant was identified as a down-regulated protein associated with cell cycle control and its downstream factor cyclin D1 was also decreased in STGC3-repressed xenografts in female mice. The data above suggest that STGC3 and its associated proteins play an important role in nasopharyngeal carcinoma gender differences.

Cyclin D1 in invasive breast carcinoma: favourable prognostic significance in unselected patients and within subgroups with an aggressive phenotype

AIMS

  To study the clinicopathological and prognostic value of cyclin D1 overexpression in patients with breast carcinoma.

METHODS AND RESULTS

  Immunohistochemistry was performed on paraffin-embedded tissue specimens from 290 invasive breast carcinomas to detect the proteins cyclin D1, oestrogen receptor (ER), progesterone receptor (PR), p53, c-erbB2, and topoisomerase IIα (topoIIα). Cyclin D1 staining was quantified using a computerized image analysis method. Cyclin D1 overexpression characterized smaller, ER-positive and PR-positive tumours (P = 0.017, P < 0.0001, and P < 0.0001, respectively), of a lower histological and nuclear grade (P = 0.011 and P < 0.0001, respectively), and with reduced expression of topoIIα (P = 0.001) and p53 (P < 0.001). Cyclin D1 was found to have an independent favourable impact on the overall survival of both the unselected cohort of patients (P = 0.011) and of patients with ER-negative and lymph node-positive tumours (P = 0.034 and P = 0.015, respectively). In triple-negative tumours, cyclin D1 overexpression was found to have independent favourable impacts on both overall and relapse-free survival (P = 0.002 for both).

CONCLUSIONS

  This is the first immunohistochemical study to dissociate the advantageous prognostic effect of cyclin D1 overexpression from its association with ER expression, and to provide evidence that cyclin D1 overexpression may be a marker of prolonged survival in patient subgroups with aggressive phenotypes.

Splice isoforms as therapeutic targets for colorectal cancer

Alternative pre-mRNA splicing allows exons of pre-mRNA to be spliced in different arrangements to produce functionally distinct mRNAs. More than 95% of human genes encode splice isoforms, some of which exert antagonistic functions. Recent studies revealed that alterations of the splicing machinery can cause the development of neoplasms, and understanding the splicing machinery is crucial for developing novel therapeutic strategies for malignancies. Colorectal cancer patients need novel strategies not only to enhance the efficacy of the currently available agents but also to utilize newly identified therapeutic targets. This review summarizes the current knowledge about the splice isoforms of VEGFA, UGT1A, PXR, cyclin D1, BIRC5 (survivin), DPD, K-RAS, SOX9, SLC39A14 and other genes, which may be possible therapeutic targets for colorectal cancer. Among them, the VEGFA splice isoforms are classified into VEGFAxxx and VEGFAxxxb, which have proangiogenic and antiangiogenic properties, respectively; UGT1A is alternatively spliced into UGT1A1 and other isoforms, which are regulated by pregnane X receptor isoforms and undergo further splicing modifications. Recently, the splicing machinery has been extensively investigated and novel discoveries in this research field are being reported at a rapid pace. The information contained in this review also provides suggestions for how therapeutic strategies targeting alternative splicing can be further developed.

Thyroid Hormone Analogue Stimulates Keratinocyte Proliferation but Inhibits Cell Differentiation in Epidermis

Gross clinical manifestations of thyroid hormone (TH) imbalance are often first seen in the skin where TH plays an integral role in sustaining natural function. Although mounting evidence suggests that TH plays an important role in epidermal proliferation and wound healing, the physiologic role of thyroid hormone in skin is not well understood. In the current study, we investigated the effect of a natural thyroid hormone analogue-3, 3', 5-triiodo-thyroacetic acid (TRIAC) on regulating proliferation and differentiation and its possible molecular mechanism in normal human epidermal keratinocytes and C57BL/6 mice. We determined that TRIAC could stimulate epidermal thickening in mice and promote human keratinocyte proliferation by activating Cyclin D1 expression and promoting entrance into S phase. Moreover, TRIAC might inhibit cell differentiation through repressing the expression of Casein Kinase 1 (CK1), which is a key regulatory protein involved in the control of cell differentiation. Taken together, our data explored the physiologic effect of TRIAC on skin and the possible molecular mechanism of TRIAC, which might be an interesting compound for the treatment of hyperkeratotic skin disorders.

CyclinD1 protein plays different roles in modulating chemoresponses in MCF7 and MDA-MB231 cells

Background:

CyclinD1 is an essential sensor and activator of cell cycle initiation and progression; overexpression of cyclinD1 is linked to various human cancers, including breast cancer. The elevated cyclinD1 in some types of cancers is believed to be associated with tumor progression and response to systemic treatments.

Aims:

In this study, we anticipate to address the questions in human breast cancer; the function of cyclinD1 in mediating chemoresponses; and the signaling pathway cooperating with cyclinD1 to interfere with the drug functions.

Materials and Methods:

Using the cell clones, concurrent ectopic expression of the wild-type or K112E-mutated human cyclinD1 protein in the MCF7 and MDA-MB231 (MB231) breast cancer cells to study the function of cyclinD1 in responses to the chemotherapeutic treatments. Three drugs, cisplatin (CDDP), 5-fluorouracil (5-FU), and Gemzar were used in this study; the 3-(4,5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) assay, cell cycle and cell death analysis, clonogenic survival assay, acridine orange (AO)/ethidium bromide (EB) staining, and Western blot assay were conducted to evaluate the drugs’ effects in the cell clones.

Results:

The cell clones expressing the D1 protein in MCF7 and MB231 cells result in distinct effects on the responses to chemotherapeutic treatments. Particularly with Gemzar, ectopic expression of cyclinD1 protein in MCF7 cells results in a potentiated effect, which is CDK4 kinase activity dependent, whereas in MB231 cells, an opposite effect was observed. Moreover, our results suggested that the distinct chemosensitivities among those cell clones were not resulted from accelerated cell cycle, cell proliferation driven by the cyclinD1CDK4/6-Rb-E2F signaling chain, rather, they were results of the cell cycle-independent functions led by cyclinD1 alone or in complex with CDK4.

Conclusions:

Our results suggest that the functions of cyclinD1 protein in modulating chemoresponses in the MCF7 and MB231 cells are independent to its function as cell cycle initiator through activation of CDK4/6. Furthermore, the signals modulated by cyclinD1 upon treatment are determined by the drug and the cellular network.

Proyl isomerase Pin1 facilitates ubiquitin-mediated degradation of cyclin-dependent kinase 10 to induce tamoxifen resistance in breast cancer cells

Endocrine therapies that inhibit estrogen receptor (ER)-α signaling are the most common and effective treatment for ER-α-positive breast cancer. However, the use of these agents is limited by the frequent development of resistance. The aim of this study was to elucidate the mechanisms by which downregulation of CDK10 expression confers resistance to tamoxifen in breast cancer. Here, we show that peptidyl-prolyl isomerase Pin1 downregulates CDK10 protein as a result of its interaction with and ubiquitination of CDK10, thereby affecting CDK10-dependent Raf-1 phosphorylation (S338). Pin1(-/-) mouse embryonic fibroblasts (MEFs) show higher CDK10 expression than Pin1(+/+) MEFs, whereas CDK10 protein was downregulated in the rescued Pin1(-/-) MEFs after reexpression of Pin1. Pin1 silencing in SKBR-3 and MCF7 cells increased the CDK10 expression. In human tamoxifen-resistant breast cancer and tamoxifen-resistant MCF7 cells, immunohistochemical staining and immunoblotting analysis shows an inverse correlation between the expression of CDK10 and the degree of tamoxifen resistance. There was also a positive correlation between the high level of P-Raf-1 (Ser338) and Pin1 in human tamoxifen-resistant breast cancer and tamoxifen-resistant MCF7 (TAMR-MCF7) cells. Importantly, 4-OH tamoxifen (4-OHT), when used in combination with overexpressed CDK10 or Raf-1 inhibitor, increased cleaved PARP and DNA fragmentation to inhibit cologenic growth of MCF7 cells and Tamoxifen-resistant MCF7 cells, respectively. On the basis of these findings, we suggest that the Pin1-mediated CDK10 ubiquitination is a major regulator of tamoxifen-resistant breast cancer cell growth and survival.

Caspase-2-Based Regulation of the Androgen Receptor and Cell Cycle in the Prostate Cancer Cell Line LNCaP

Caspase-2 can induce apoptosis in response to extrinsic and intrinsic signals. Unlike other caspases, this protein is not expressed solely in nonnuclear compartments; a subpopulation is constitutively localized in the nucleus. As one of the most evolutionarily conserved caspases, caspase-2 may have roles in multiple cellular processes. However, its contribution to nonapoptotic processes remains a mystery. In this study, we show that caspase-2 activity is important for proliferation by cells of the androgen-dependent prostate cancer cell line LNCaP. LNCaP cells expressing either a dominant-negative (dn) form of caspase or an siRNA against caspase-2 had lower androgen receptor (AR)-dependent proliferative responses than control cells, and application of the siRNA resulted in downregulation of the expression of both AR-dependent prostate-specific antigen (PSA) and AR-dependent reporter luciferase. Also, caspase-2 formed complexes with the cell cycle regulatory proteins cyclin D3, CDK4, and p21/Cip1, and caspase-2 regulated AR transactivation by inhibiting the repressive function of cyclin D3. Taken together, these results reveal, for the first time, that caspase-2 is involved in cell cycle promotion and AR activation. Given that prostate cancer cells depend on AR activity in order to survive, the fact that our data indicate that caspase-2 positively regulates AR activity suggests that caspase-2 has potential as a target in the treatment of prostate cancer.

p14ARF post-transcriptional regulation of nuclear cyclin D1 in MCF-7 breast cancer cells: discrimination between a good and bad prognosis?

As part of a cell’s inherent protection against carcinogenesis, p14ARF is upregulated in response to hyperproliferative signalling to induce cell cycle arrest. This property makes p14ARF a leading candidate for cancer therapy. This study explores the consequences of reactivating p14ARF in breast cancer and the potential of targeting p14ARF in breast cancer treatment. Our results show that activation of the p14ARF-p53-p21-Rb pathway in the estrogen sensitive MCF-7 breast cancer cells induces many hallmarks of senescence including a large flat cell morphology, multinucleation, senescence-associated-β-gal staining, and rapid G1 and G2/M phase cell cycle arrest. P14ARF also induces the expression of the proto-oncogene cyclin D1, which is most often associated with a transition from G1-S phase and is highly expressed in breast cancers with poor clinical prognosis. In this study, siRNA knockdown of cyclin D1, p21 and p53 show p21 plays a pivotal role in the maintenance of high cyclin D1 expression, cell cycle and growth arrest post-p14ARF induction. High p53 and p14ARF expression and low p21/cyclin D1 did not cause cell-cycle arrest. Knockdown of cyclin D1 stops proliferation but does not reverse senescence-associated cell growth. Furthermore, cyclin D1 accumulation in the nucleus post-p14ARF activation correlated with a rapid loss of nucleolar Ki-67 protein and inhibition of DNA synthesis. Latent effects of the p14ARF-induced cellular processes resulting from high nuclear cyclin D1 accumulation included a redistribution of Ki-67 into the nucleoli, aberrant nuclear growth (multinucleation), and cell proliferation. Lastly, downregulation of cyclin D1 through inhibition of ER abrogated latent recurrence. The mediation of these latent effects by continuous expression of p14ARF further suggests a novel mechanism whereby dysregulation of cyclin D1 could have a double-edged effect. Our results suggest that p14ARF induced-senescence is related to late-onset breast cancer in estrogen responsive breast cancers and/or the recurrence of more aggressive breast cancer post-therapy.

Expression and clinical significance of Wnt players and survivin in pituitary tumours

Deregulation of the Wnt pathway has been implicated in oncogenesis of numerous tissues including the pituitary gland. Immunohistochemical localization and quantification of β-catenin, Cyclin D1, c-MYC and Survivin expression in 47 pituitary adenomas (35 non-functioning, seven GH-secreting, three prolactinomas, two ACTH-secreting tumour) and six normal controls was undertaken in this study and correlation of protein expression to patient and tumour characteristics analysed. β-catenin was strictly membrane-bound with no difference observed between normal and tumour tissue. In contrast, Cyclin D1 and c-MYC localization was nuclear and significantly higher in tumour versus normal tissue (p < 0.05). c-MYC expression correlated negatively with age at diagnosis (p = 0.006, R = -0.395) while Cyclin D1 expression correlated positively with age (p = 0.036, R = 0.306) and was higher in males than in females (p = 0.036). c-MYC expression was significantly lower in patients with functional tumours requiring octreotide treatment and in patients with non-functioning tumours suffering from hypopituitarism. Survivin expression was extremely low in tumours and absent in normal controls. Involvement of the canonical Wnt pathway appears to be minimal, given the segregation of β-catenin to the membrane. Our data suggest that c-MYC may have an important role in early pituitary tumorigenesis while Cyclin D1 is likely to promote tumour growth at a later stage. We also report a novel gender difference in Cyclin D1 expression, the biological significance of which merits further analysis. The reported reduction of c-MYC in functional tumours subsequently treated with octreotide further supports a role of c-MYC in early tumorigenesis and not in recurrence. The decrease in c-MYC in patients with hypopituitarism provides the first in vivo evidence for hormonal regulation of c-MYC expression.

Prolactin promotes mammary pathogenesis independently from cyclin D1

Epidemiological and experimental studies have revealed an important role for prolactin (PRL) in breast cancer. Cyclin D1 is a major downstream target of PRL in lobuloalveolar development during pregnancy and is amplified and/or overexpressed in many breast carcinomas. To examine the importance of cyclin D1 in PRL-induced pathogenesis, we generated transgenic mice (NRL-PRL) that overexpress PRL in mammary epithelial cells, with wild-type, heterozygous, or genetically ablated cyclin D1 in the FVB/N genetic background. Although loss of one cyclin D1 allele did not affect PRL-induced mammary lesions in nonparous females, the complete absence of cyclin D1 (D1(-/-)) markedly decreased tumor incidence. Nevertheless, NRL-PRL/D1(-/-) females developed significantly more preneoplastic lesions (eg, epithelial hyperplasias and mammary intraepithelial neoplasias) than D1(-/-) females. Moreover, although lack of cyclin D1 reduced proliferation of morphologically normal mammary epithelium, transgenic PRL restored it to rates of wild-type females. PRL posttranscriptionally increased nuclear cyclin D3 protein in D1(-/-) luminal cells, indicating one compensatory mechanism. Consistently, pregnancy induced extensive lobuloalveolar growth in the absence of cyclin D1. However, transcripts for milk proteins were reduced, and pups failed to survive, suggesting that mammary differentiation was inadequate. Together, these results indicate that cyclin D1 is an important, but not essential, mediator of PRL-induced mammary proliferation and pathology in FVB/N mice and is critical for differentiation and lactation.

Endometrial tumorigenesis in Pten(+/-) mice is independent of coexistence of estrogen and estrogen receptor α

Numerous studies support the role for mutations in the phosphatase and tensin homologue (PTEN) tumor suppressor gene and unopposed estrogen stimulation in the pathogenesis of uterine endometrioid carcinoma. However, the relation between PTEN signaling and estrogen/estrogen receptor in endometrial tumorigenesis remains unresolved. We used genetically engineered mice as a model to address this relation. Mice with a single deleted Pten allele (Pten(+/-)) spontaneously develop complex atypical hyperplasia and ~20% develop endometrial cancer. To determine the effect of removing endogenous estrogen, we performed oophorectomies on Pten(+/-) mice. Although there was a reduction in the number and severity of hyperplastic lesions, the endometrial phenotype persisted, suggesting that Pten mutation, independent of estrogen, can initiate the development of complex atypical hyperplasia. To recapitulate the situation in women with unopposed estrogen, we implanted 17β-estradiol pellets in adult female Pten heterozygous mice, resulting in increased carcinoma incidence. Because studies have shown that estrogen largely acts on the endometrium via estrogen receptor ERα, we generated Pten(+/-)ERα(-/-) mice. Strikingly, 88.9% of Pten(+/-)ERα(-/-) mice developed endometrial hyperplasia/carcinoma. Furthermore, Pten(+/-)ERα(-/-) mice showed a higher incidence of in situ and invasive carcinoma, suggesting that endometrial tumorigenesis can progress in the absence of ERα. Thus, the relation between Pten alterations and estrogen signaling in the development of endometrial carcinoma is complex; the results presented herein have important implications for the treatment of endometrial hyperplasia and carcinoma in women.