Androgen Regulation of Stage-Dependent Cyclin D2 Expression in Sertoli Cells Suggests a Role in Modulating Androgen Action on Spermatogenesis1

Regulation of spermatogenesis involves stage-dependent androgen action on Sertoli cells, but the pathways involved are unclear. We assessed if cyclin D2 could play a role. In rats, Sertoli cell nuclear, stage-dependent immunoexpression of cyclin D2 switched on after Day 10 and persisted through Day 35, but disappeared by adulthood. However, ethane dimethane sulfonate (EDS)-induced testosterone withdrawal in adult rats for 6 days induced stage-dependent cyclin D2 immunoexpression in Sertoli cells, with highest expression at stages IX-XII and nondetectable at stages VI-VIII (opposite that for androgen receptor [AR] immunoexpression). In EDS-treated rats, a single injection of testosterone but not of estrogen reversed this change in 4 h, and testosterone administration from the time of EDS treatment prevented expression of cyclin D2 in Sertoli cells. The EDS-induced changes in cyclin D2 immunoexpression were matched by changes in expression of Ccnd2 (cyclin D2) mRNA in isolated stage-dissected tubules. Treatment of adult rats with flutamide induced stage-dependent cyclin D2 immunoexpression in Sertoli cells within 18 h, and confocal microscopy revealed that immunoexpression of AR and cyclin D2 were mutually exclusive within individual seminiferous tubules in these animals. Sertoli cell-selective ablation of the AR in mice using Cre/loxP technology also resulted in stage-dependent Sertoli cell cyclin D2 immunoexpression. Downstream from cyclin D2 action is retinoblastoma 1 (RB1), a tumor suppressor protein, immunoexpression of which paralleled stage-dependent AR expression in Sertoli cells; RB1 stage specificity disappeared after EDS treatment. These results point to a non-cell cycle role for cyclin D2 and RB1 in mature Sertoli cells in the stage-dependent mechanisms regulated by AR expression and androgen action.

Genetic classification of benign and malignant thyroid follicular neoplasia based on a three-gene combination

Thyroid carcinoma is a common endocrine cancer with a favorable prognosis if subjected to timely treatment. However, the clinical identification of follicular thyroid carcinoma (FTC) among patients with benign thyroid nodules is still a challenge. Preoperative fine needle aspiration-based cytology cannot always differentiate follicular carcinomas from benign follicular neoplasias. Because current methods fail to improve preoperative diagnosis of thyroid nodules, new molecular-based diagnoses should be explored. We conducted a microarray-based study to reveal the genetic profiles unique to FTC and follicular adenomas (FAs), to identify the most parsimonious number of genes that could accurately differentiate between benign and malignant follicular thyroid neoplasia. We confirmed our data by quantitative RT-PCR and immunohistochemistry in two independent validation sets with a total of 114 samples. We were able to identify three genes, cyclin D2 (CCND2), protein convertase 2 (PCSK2), and prostate differentiation factor (PLAB), that allow the accurate molecular classification of FTC and FA. Two independent validation sets revealed that the combination of these three genes could differentiate FTC from FA with a sensitivity of 100%, specificity of 94.7%, and accuracy of 96.7%. In addition, our model allowed the identification of follicular variants of papillary thyroid carcinoma with an accuracy of 85.7%. Three-gene profiling of thyroid nodules can accurately predict the diagnosis of FTC and FA with high sensitivity and specificity, thus identifying promising targets for further investigation to ultimately improve preoperative diagnosis.

Cyclin D and cisplatin cytotoxicity in primary neuroblastoma cell lines

Cyclin D1 is a key cell cycle regulator protein with demonstrated oncogenenic activity in a variety of malignancies. Overexpression of Cyclin D1 protein has been observed in many types of tumors. We hypothesized that Cyclin D1 might be an important determinant of the sensitivity of neuroblastomas to cisplatin. Cyclin D1, D2 and D3, and Cdk4, Cdk6 and Rb protein, and Cyclin D1 mRNA expression were measured in primary patient-derived neuroblastoma cell lines. Cell cycle distribution was examined using flow cytometry. A modified MTT assay was used to determine the sensitivity of the cell lines to cisplatin. All 14 cell lines expressed Cyclin D1 protein to a variable extent (0.22-1.47 normalized to actin protein expression). All cell lines expressed Cyclin D2 and D3. There was no relationship between expression of Cyclin D1 and expression of Cyclin D2 or D3 (p>0.05 and R2<0.2 for both). All cell lines expressed Cdk4 and Cdk6 protein. In addition, Rb and two related proteins, p105 and p130, were detected in all the cell lines. The mean cisplatin IC50 was 19.2 microM (range 0.6-40 microM). We conclude that there was no correlation between the amount of Cyclin D1 expressed and the cisplatin IC50. Our results do not support the hypothesis that Cyclin D1 expression is significantly related to cisplatin resistance.

Involvement of kv1 potassium channels in spreading acidification and depression in the cerebellar cortex

Spreading acidification and depression (SAD) is a form of propagated activity in the cerebellar cortex characterized by acidification and a transient depression in excitability. This study investigated the role of Kv1 potassium channels in SAD using neutral red, flavoprotein autofluorescence, and voltage-sensitive dye optical imaging in the mouse cerebellar cortex, in vivo. The probability of evoking SAD was greatly increased by blocking Kv1.1 as well as Kv1.2 potassium channels by their specific blockers dendrotoxin K (DTX-K) and tityustoxin (TsTX), respectively. DTX-K not only greatly lowered the threshold for evoking SAD but also resulted in multiple cycles of spread and spontaneous SAD. The occurrence of spontaneous SAD originating from spontaneous parallel fiber-like beams of activity suggests that blocking Kv1 channels increased parallel fiber excitability. This was confirmed by the generation of parallel fiber-like beams with the microinjection of glutamate into the upper molecular layer in the presence of DTX-K. The dramatic effects of DTX-K suggest a possible connection between SAD and episodic ataxia type 1 (EA1), a Kv1.1 potassium channelopathy. The threshold for evoking SAD was significantly lowered in the Kv1.1 heterozygous knockout mouse compared with wild-type littermates. Carbamazepine and acetazolamide, both effective in the treatment of EA1, significantly decreased the likelihood of evoking SAD. Blocking GABAergic neurotransmission did not alter the effectiveness of DTX-K. The cyclin D2 null mouse, which lacks cerebellar stellate cells, also exhibited SAD. Therefore blocking Kv1 potassium channels establishes the conditions needed to generate SAD. Furthermore, the results are consistent with the hypothesis that SAD may underlie the transient attacks of ataxia characterizing EA1.

CD38 signaling regulates B lymphocyte activation via a phospholipase C (PLC)-gamma 2-independent, protein kinase C, phosphatidylcholine-PLC, and phospholipase D-dependent signaling cascade

The CD38 cell surface receptor is a potent activator for splenic, B lymphocytes. The molecular mechanisms regulating this response, however, remain incompletely characterized. Activation of the nonreceptor tyrosine kinase, Btk, is essential for CD38 downstream signaling function. The major Btk-dependent substrate in B cells, phospholipase C-gamma2 (PLC-gamma2), functions to generate the key secondary messengers, inositol-1,4,5 trisphosphate and diacylglycerol. Surprisingly, CD38 ligation results in no detectable increase in phosphoinositide metabolism and only a minimal increase in cytosolic calcium. We hypothesized that Btk functioned independently of PLC-gamma2 in the CD38 signaling pathway. Accordingly, we demonstrate that CD38 cross-linking does not result in the functional phosphorylation of PLC-gamma2 nor an increase in inositol-1,4,5 trisphosphate production. Furthermore, splenic B cells exhibit a normal CD38-mediated, proliferative response in the presence of the phosphoinositide-PLC inhibitor, U73122. Conversely, protein kinase C (PKC) beta-deficient mice, or PKC inhibitors, indicated the requirement for diacylglycerol-dependent PKC isoforms in this pathway. Loss of PKC activity blocked CD38-dependent, B cell proliferation, NF-kappaB activation, and subsequent expression of cyclin-D2. These results suggested that an alternate diacylglycerol-producing phospholipase must participate in CD38 signaling. Consistent with this idea, CD38 increased the enzymatic activity of the phosphatidylcholine (PC)-metabolizing enzymes, PC-PLC and phospholipase D. The PC-PLC inhibitor, D609, completely blocked CD38-dependent B cell proliferation, IkappaB-alpha degradation, and cyclin-D2 expression. Analysis of Btk mutant B cells demonstrated a partial requirement for Btk in the activation of both enzymes. Taken together, these data demonstrate that CD38 initiates a novel signaling cascade leading to Btk-, PC-PLC-, and phospholipase D-dependent, PLC-gamma2-independent, B lymphocyte activation.

Bone marrow mesenchymal stem cells induce division arrest anergy of activated T cells

It has been shown that mesenchymal stem cells (MSCs) induce T cells to become unresponsive. We characterized the phenotype of these T cells by dissecting the effect of MSCs on T-cell activation, proliferation, and effector function. For this purpose, an in vitro murine model was used in which T-cell responses were generated against the male HY minor histocompatibility antigen. In the presence of MSCs, the expression of early activation markers CD25 and CD69 was unaffected but interferon-γ (IFN-γ) production was reduced. The inhibitory effect of MSCs was directed mainly at the level of cell proliferation. Analysis of the cell cycle showed that T cells, stimulated in the presence of MSCs, were arrested at the G1 phase. At the molecular level, cyclin D2 expression was profoundly inhibited, whereas p27kip1 was up-regulated. When MSCs were removed from the cultures and restimulated with the cognate peptide, T cells produced IFN-γ but failed to proliferate. The addition of exogenous interleukin-2 (IL-2) did not restore proliferation. MSCs did not preferentially target any T-cell subset, and the inhibition was also extended to B cells. MSC-mediated inhibition induces an unresponsive T-cell profile that is fully consistent with that observed in division arrest anergy.

Temporal expression changes during differentiation of neural stem cells derived from mouse embryonic stem cell

Temporal analysis in gene expression during differentiation of neural stem cells (NSCs) was performed by using in-house microarrays composed of 10,368 genes. The changes in mRNA level were measured during differentiation day 1, 2, 3, 6, 12, and 15. Out of 10,368 genes analyzed, 259 genes were up-regulated or down-regulated by 2-fold or more at least at one time-point during differentiation, and were classified into six clusters based on their expression patterns by K-means clustering. Clusters characterized by gradual increase have large numbers of genes involved in transport and cell adhesion; those which showed gradual decrease have much of genes in nucleic acid metabolism, cell cycle, transcription factor, and RNA processing. In situ hybridization (ISH) validated microarray data and it also showed that Fox M1, cyclin D2, and CDK4 were highly expressed in CNS germinal zones and ectonucleotide pyrophosphatase/phosphodiesterase 2 (Enpp2) was highly expressed in choroid plexus where stem/progenitor cells are possibly located. Together, this clustering analysis of expression patterns of functionally classified genes may give insight into understanding of CNS development and mechanisms of NSCs proliferation and differentiation.

Genetic replacement of cyclin D1 function in mouse development by cyclin D2

D cyclins (D1, D2, and D3) are components of the core cell cycle machinery in mammalian cells. It is unclear whether each of the D cyclins performs unique, tissue-specific functions or the three proteins have virtually identical functions and differ mainly in their pattern of expression. We previously generated mice lacking cyclin D1, and we observed that these animals displayed hypoplastic retinas and underdeveloped mammary glands and a presented developmental neurological abnormality. We now asked whether the specific requirement for cyclin D1 in these tissues reflected a unique pattern of D cyclin expression or the presence of specialized functions for cyclin D1 in cyclin D1-dependent compartments. We generated a knock-in strain of mice expressing cyclin D2 in place of D1. Cyclin D2 was able to drive nearly normal development of retinas and mammary glands, and it partially replaced cyclin D1's function in neurological development. We conclude that the differences between these two D cyclins lie mostly in the tissue-specific pattern of their expression. However, we propose that subtle differences between the two D cyclins do exist and they may allow D cyclins to function in a highly optimized fashion. We reason that the acquisition of multiple D cyclins may allow mammalian cells to drive optimal proliferation of a diverse array of cell types.

Microvesicles derived from activated platelets induce metastasis and angiogenesis in lung cancer

The role of platelets in tumor progression and metastasis has been recognized but the mechanism of their action remains unclear. Five human lung cancer cell lines (A549, CRL 2066, CRL 2062, HTB 183, HTB 177) and a murine Lewis lung carcinoma (LCC) cell line (for an in vivo model of metastasis) were used to investigate how platelet-derived microvesicles (PMV), which are circular fragments shed from the surface membranes of activated platelets, and exosomes released from platelet alpha-granules, could contribute to metastatic spread. We found that PMV transferred the platelet-derived integrin CD41 to most of the lung cancer cell lines tested and stimulated the phosphorylation of mitogen-activated protein kinase p42/44 and serine/threonine kinase as well as the expression of membrane type 1-matrix metalloproteinase (MT1-MMP). PMV chemoattracted 4 of the 5 cell lines, with the highly metastatic A549 cells exhibiting the strongest response. In A549 cells, PMV were shown to stimulate proliferation, upregulate cyclin D2 expression and increase trans-Matrigel chemoinvasion. Furthermore, in these cells, PMV stimulated mRNA expression for angiogenic factors such as MMP-9, vascular endothelial growth factor, interleukin-8 and hepatocyte growth factor, as well as adhesion to fibrinogen and human umbilical vein endothelial cells. Intravenous injection of murine PMV-covered LLC cells into syngeneic mice resulted in significantly more metastatic foci in their lungs and LLC cells in bone marrow than in control animals injected with LCC cells not covered with PMV. Based on these findings, we suggest that PMV play an important role in tumor progression/metastasis and angiogenesis in lung cancer.

Multiple functions of D-type cyclins can antagonize pRb-mediated suppression of proliferation

The most well understood function of the D-type cyclins is to activate the G(1) kinases, cdk4 and cdk6, and target the retinoblastoma gene product (pRb) for phosphorylation and inactivation. pRb can suppress S phase entry, cause a transient G(1) arrest following DNA damage, and is critical in establishing terminal cell cycle withdrawal in cells exposed to differentiation or senescence-inducing signals. Each of these functions of pRb can be demonstrated in cultured cells derived from human tumors that have suffered RB1 gene inactivation. In such in vitro assays, coexpression of D type cyclins has been shown to inhibit the function of pRb, likely reflecting an oncogenic role of cyclin D1 in vivo. Two regions of cyclin D, the LxCxE pRb-binding motif, and the cyclin box, are thought to be critical for the proper function of cyclin D. Here we show that the LxCxE motif is dispensable in cyclin D1 for all functions tested, but is required by cyclin D2. This observation suggests that there is a functional difference between cyclins D1 and D2 in pRb regulation, and argues against complete functional redundancy of these D cyclins. In addition, the ability of cyclins D1 and D2 to activate cdk partners is required for induction of pRb phosphorylation and S phase entry. However, mutant forms of cyclins D1 and D2 that are incapable of activating kinase partners were still able to prevent pRb-induced senescence. Thus, D cyclins have both kinase-dependent and kinase-independent mechanisms of interfering with proliferation arrest and senescence.

Increased cyclin E expression may obviate the role of cyclin D1 during brain development in cyclin D1 knockout mice

Cyclins D and E play critical roles during the G1 phase of mammalian cell division. Cyclin D1 expression is high and expected to play an important role during mouse brain development. However, in the present study, we found no difference in CNS morphology between cyclin D1 knockout (KO) and control wild-type mice at the ages of 1, 4 and 12 months. Analysis of protein expression in embryonic brains revealed that cyclin E is obviously increased in cyclin D1 KO mice at 13.5 days post coitum. At the same age a high level of cyclin D1 expression is detected in the embryonic brain of wild-type mice. The data indicate that enhanced cyclin E protein expression in cyclin D1 KO mice may obviate the role of cyclin D1 and contribute to the normal brain development of cyclin D1 KO mice.

Early genetic events provide the basis for a clinical classification of multiple myeloma

Multiple myeloma is a tumor of somatically mutated, isotype-switched plasma cells that accumulate in the bone marrow leading to bone destruction and bone marrow failure. The germinal center processes of somatic hypermutation and switch recombination are implicated in the development of recurrent immunoglobulin gene translocations in 40% of patients. These affect five loci: 11q13, 6p21, 4p16, 16q23 and 20q11, leading to dysregulation of CCND1, CCND2, FGFR3/MMSET, c-MAF and MAFB respectively. The remaining 60% of patients can be divided into four groups based on their expression of CCND1 and CCND2. The largest group (40%) ectopically express CCND1 bi-allelically and have hyperdiploidy with multiple trisomies of chromosomes 3, 5, 7, 9, 11, 15, 19 and 21. The translocation and cyclin D (TC) groups identify patients with different genetics, biology, clinical features, prognosis and response to therapy.

Promoter hypermethylation in benign breast epithelium in relation to predicted breast cancer risk

INTRODUCTION

The tumor suppressor genes RASSF1A, APC, H-cadherin, RARbeta2, and cyclin D2 are methylated more frequently in breast cancer than in adjacent benign tissue. However, it is unclear whether promoter methylation of tumor suppressor genes in benign breast tissue is associated with an increased risk for breast cancer.

METHODS

Promoter hypermethylation was measured in benign and malignant breast samples obtained by fine needle aspiration biopsy from 27 breast cancer patients and 55 unaffected women whose risk of breast cancer had been defined using the Gail, Claus, and BRCAPRO models.

RESULTS

Cyclin D2 methylation occurred in 57% of tumor samples but not in corresponding benign breast samples and in only one sample from an unaffected patient (P < 0.0001). RARbeta2 methylation occurred in 32% of benign breast samples from cancer patients but only 9% of similar samples from unaffected women (P = 0.002). Promoter methylation of RASSF1A and APC occurred more frequently (70% and 56%, respectively) in unaffected women at high-risk for breast cancer as defined by the Gail model than in low/intermediate risk women (29% and 20%, P = 0.04 and P = 0.03). Of the Gail model risk factors, only number of prior breast biopsies was highly correlated with APC and RASSF1A methylation (P = 0.0001 and 0.02, respectively).

CONCLUSIONS

Since cyclin D2 promoter methylation occurs almost exclusively in tumors, it may be possible to exploit it for the early detection of breast cancer. Promoter methylation of APC, RARbeta2, and RASSF1A in benign breast epithelium is associated with epidemiologic markers of increased breast cancer risk.

High-density growth arrest in Ras-transformed cells: low Cdk kinase activities in spite of absence of p27(Kip) Cdk-complexes

The ras oncogene transforms immortalized, contact-inhibited non-malignant murine fibroblasts into cells that are focus forming, exhibit increased saturation density, and are malignant in suitable hosts. Here, we examined changes in cell cycle control complexes as normal and Ras-transformed cells ceased to grow exponentially, to reveal the molecular basis for Ras-dependent focus formation. As normal cells entered density-dependent arrest, cyclin D1 decreased while cyclin D2 was induced and replaced D1 in Cdk4 complexes. Concomitantly, p27(Kip1) levels rose and the inhibitor accumulated in both Cdk4 and Cdk2 complexes, as these kinases were inactivated. Ras-transformed cells failed to arrest at normal saturation density and showed no significant alterations in cell control complexes at this point. Yet, at an elevated density the Ras-transformed cells ceased to proliferate and entered a quiescent-like state with low Cdk4 and Cdk2 activity. Surprisingly, this delayed arrest was molecularly distinct from contact inhibition of normal cells, as it occurred in the absence of p27(Kip1) induction and cyclin D1 levels remained high. This demonstrates that although oncogenic Ras efficiently disabled the normal response to contact inhibition, a separate back-up mechanism enforced cell cycle arrest at higher cell density.

Induction of cyclin D2 in rat granulosa cells requires FSH-dependent relief from FOXO1 repression coupled with positive signals from Smad

Ovarian follicles undergo exponential growth in response to follicle-stimulating hormone (FSH), largely as a result of the proliferation of granulosa cells (GCs). In vitro under serum-free conditions, rat GCs differentiate in response to FSH but do not proliferate unless activin is also present. In the presence of FSH plus activin, GCs exhibit enhanced expression of cyclin D2 as well as inhibin-alpha, aromatase, steroidogenic factor-1 (SF-1), cholesterol side chain (SCC), and epiregulin. In this report we sought to identify the signaling pathways by which FSH and activin promote GC proliferation and differentiation. Our results show that these responses are associated with prolonged Akt phosphorylation relative to time-matched controls and are dependent on phosphatidylinositol 3-kinase (PI 3-kinase) and Smad2/3 signaling, based on the ability of the PI 3-kinase inhibitor LY294002 or infection with adenoviral dominant negative Smad3 (DN-Smad3) mutant to attenuate induction of cyclin D2, inhibin-alpha, aromatase, SCC, SF-1, and epiregulin. The DN-Smad3 mutant also abolished prolonged Akt phosphorylation stimulated by FSH plus activin 24 h post-treatment. Infection with the adenoviral constitutively active forkhead box-containing protein, O subfamily (FOXO)1 mutant suppressed induction of cyclin D2, aromatase, inhibin-alpha, SF-1, and epiregulin. Transient transfections of GCs with constitutively active FOXO1 mutant also suppressed cyclin D2, inhibin-alpha, and epiregulin promoter-reporter activities. Chromatin immunoprecipitation results demonstrate in vivo the association of FOXO1 with the cyclin D2 promoter in untreated GCs and release of FOXO1 from the cyclin D2 promoter upon addition of FSH plus activin. These results suggest that proliferation and differentiation of GCs in response to FSH plus activin requires both removal of FOXO1-dependent repression and positive signaling from Smad2/3.

Cyclin D2 induces proliferation of cardiac myocytes and represses hypertrophy

The myocytes of the adult mammalian heart are considered unable to divide. Instead, mitogens induce cardiomyocyte hypertrophy. We have investigated the effect of adenoviral overexpression of cyclin D2 on myocyte proliferation and morphology. Cardiomyocytes in culture were identified by established markers. Cyclin D2 induced DNA synthesis and proliferation of cardiomyocytes and impaired hypertrophy induced by angiotensin II and serum. At the molecular level, cyclin D2 activated CDK4/6 and lead to pRB phosphorylation and downregulation of the cell cycle inhibitors p21Waf1/Cip1 and p27Kip1. Expression of the CDK4/6 inhibitor p16 inhibited proliferation and cyclin D2 overexpressing myocytes became hypertrophic under such conditions. Inhibition of hypertrophy by cyclin D2 correlated with downregulation of p27Kip1. These data show that hypertrophy and proliferation are highly related processes and suggest that cardiomyocyte hypertrophy is due to low amounts of cell cycle activators unable to overcome the block imposed by cell cycle inhibitors. Cell cycle entry upon hypertrophy may be converted to cell division by increased expression of activators such as cyclin D2.

Homeostatic cell-cycle control by BLyS: Induction of cell-cycle entry but not G1/S transition in opposition to p18INK4c and p27Kip1

Cell-cycle entry is critical for homeostatic control in physiologic response of higher organisms but is not well understood. The antibody response begins with induction of naive mature B cells, which are naturally arrested in G(0)/G(1) phase of the cell cycle, to enter the cell cycle in response to antigen and cytokine. BLyS (BAFF), a cytokine essential for mature B cell development and survival, is thought to act mainly by attenuation of apoptosis. Here, we show that BLyS alone induces cell-cycle entry and early G(1) cell-cycle progression, but not S-phase entry, in opposition to the cyclin-dependent kinase inhibitors p18(INK4c). Independent of its survival function, BLyS enhances the synthesis of cyclin D2, in part through activation of NF-kappaB, as well as CDK4 and retinoblastoma protein phosphorylation. By convergent activation of the same cell-cycle regulators in opposition to p18(INK4c), B cell receptor signaling induces cell-cycle entry and G(1) progression in synergy with BLyS, but also DNA replication. The failure of BLyS to induce S-phase cell-cycle entry lies in its inability to increase cyclin E and reduce p27(Kip1) expression. Antagonistic cell-cycle regulation by BLyS and p18(INK4c) is functionally linked to apoptotic control and conserved from B cell activation in vitro to antibody response in vivo, further indicating a physiologic role in homeostasis.

FoxO3a and BCR-ABL regulate cyclin D2 transcription through a STAT5/BCL6-dependent mechanism

Cell cycle arrest by FoxO transcription factors involves transcriptional repression of cyclin D, although the exact mechanism remains unclear. In this study, we used the BCR-ABL-expressing cell line BV173 as a model system to investigate the mechanisms whereby FoxO3a regulates cyclin D2 expression. Inhibition of BCR-ABL by STI571 results in down-regulation of cyclin D2 expression, activation of FoxO3a activity, and up-regulation of BCL6 expression. Using reporter gene assays, we demonstrate that STI571, FoxO3a, and BCL6 can repress cyclin D2 transcription through a STAT5/BCL6 site located within the cyclin D2 promoter. We propose that BCR-ABL inhibition leads to FoxO3a activation, which in turn induces the expression of BCL6, culminating in the repression of cyclin D2 transcription through this STAT5/BCL6 site. This process was verified by mobility shift and chromatin immunoprecipitation analyses. We find that conditional activation of FoxO3a leads to accumulation of BCL6 and down-regulation of cyclin D2 at protein and mRNA levels. Furthermore, silencing of FoxO3a and BCL6 in BCR-ABL-expressing cells abolishes STI571-mediated effects on cyclin D2. This report establishes the signaling events whereby BCR-ABL signals are relayed to cyclin D2 to mediate cell cycle progression and defines a potential mechanism by which FoxO proteins regulate cyclin D2 expression.

The critical role of cyclin D2 in adult neurogenesis

Adult neurogenesis (i.e., proliferation and differentiation of neuronal precursors in the adult brain) is responsible for adding new neurons in the dentate gyrus of the hippocampus and in the olfactory bulb. We describe herein that adult mice mutated in the cell cycle regulatory gene Ccnd2, encoding cyclin D2, lack newly born neurons in both of these brain structures. In contrast, genetic ablation of cyclin D1 does not affect adult neurogenesis. Furthermore, we show that cyclin D2 is the only D-type cyclin (out of D1, D2, and D3) expressed in dividing cells derived from neuronal precursors present in the adult hippocampus. In contrast, all three cyclin D mRNAs are present in the cultures derived from 5-day-old hippocampi, when developmental neurogenesis in the dentate gyrus takes place. Thus, our results reveal the existence of molecular mechanisms discriminating adult versus developmental neurogeneses.

Targeted expression of cyclin D2 results in cardiomyocyte DNA synthesis and infarct regression in transgenic mice

Restriction point transit and commitment to a new round of cell division is regulated by the activity of cyclin-dependent kinase 4 and its obligate activating partners, the D-type cyclins. In this study, we examined the ability of D-type cyclins to promote cardiomyocyte cell cycle activity. Adult transgenic mice expressing cyclin D1, D2, or D3 under the regulation of the alpha cardiac myosin heavy chain promoter exhibited high rates of cardiomyocyte DNA synthesis under baseline conditions. Cardiac injury in mice expressing cyclin D1 or D3 resulted in cytoplasmic cyclin D accumulation, with a concomitant reduction in the level of cardiomyocyte DNA synthesis. In contrast, cardiac injury in mice expressing cyclin D2 did not alter subcellular cyclin localization. Consequently, cardiomyocyte cell cycle activity persisted in injured hearts expressing cyclin D2, ultimately resulting in infarct regression. These data suggested that modulation of D-type cyclins could be exploited to promote regenerative growth in injured hearts.

CpG methylation of the FHIT, FANCF, cyclin-D2, BRCA2 and RUNX3 genes in Granulosa cell tumors (GCTs) of ovarian origin

Background

Granulosa cell tumors (GCTs) are relatively rare and are subtypes of the sex-cord stromal neoplasms. Methylation induced silencing in the promoters of genes such as tumor suppressor genes, DNA repair genes and pro-apoptotic genes is recognised as a critical factor in cancer development.

Methods

We examined the role of promoter hypermethylation, an epigenetic alteration that is associated with the silencing tumor suppressor genes in human cancer, by studying 5 gene promoters in 25 GCTs cases by methylation specific PCR and RT-PCR. In addition, the compatible tissues (normal tissues distant from lesion) from three non-astrocytoma patients were also included as the control.

Results

Frequencies of methylation in GCTs were 7/25 (28 % for FHIT), 6/25 (24% for FNACF), 3/25 (12% for Cyclin D2), 1/25 (4% for BRCA2) and 14/25 (56%) in RUNX3 genes. Correlation of promoter methylation with clinical characteristics and other genetic changes revealed that overall promoter methylation was higher in more advanced stage of the disease. Promoter methylation was associated with gene silencing in GCT cell lines. Treatment with methylation or histone deacetylation-inhibiting agents resulted in profound reactivation of gene expression.

Conclusions

These results may have implications in better understanding the underlying epigenetic mechanisms in GCT development, provide prognostic indicators, and identify important gene targets for treatment.

External imaging of CCND1 cancer gene activity in experimental human breast cancer xenografts with 99mTc-peptide-peptide nucleic acid-peptide chimeras

Detection of a new or recurrent breast cancer lesion relies on physical examination and imaging studies, primarily mammography, followed by histopathologic evaluation of biopsy tissue for morphologic confirmation. Approximately 66%-85% of detected lesions are not malignant. Therefore, biopsies are unnecessary for at least two thirds of patients. Human estrogen receptor-positive breast cancer cells typically display an elevated level of cyclin D1 protein because of the overexpression of CCND1 messenger RNA (mRNA) and an elevated level of insulin-like growth factor 1 (IGF1) receptor (IGF1R) because of the overexpression of IGF1R mRNA. We hypothesized that scintigraphic detection of CCND1 peptide nucleic acid (PNA) hybridization probes with a (99m)Tc-chelating peptide on the N terminus and an IGF1 peptide loop on the C terminus could detect CCND1 mRNA in human MCF7 breast cancer xenografts in nude mice from outside the body.

METHODS

We prepared the CCND1 probes as well as mismatched controls by solid-phase synthesis. We used fluorescence microscopy to detect the cellular uptake of fluoresceinyl probes and quantitative reverse transcription-polymerase chain reaction to detect the hybridization of probes to mRNA. We imaged (99m)Tc-probes in MCF7 xenografts scintigraphically and measured distribution by scintillation counting of dissected tissues.

RESULTS

IGF1R-overexpressing MCF7 cells internalized the fluorescein-chelator-CCND1 PNA-IGF1 peptide but not the mismatched control peptide. The chelator-CCND1 PNA-IGF1 peptide but not the control peptide lowered the level of cyclin D1 protein in IGF1R-overexpressing MCF7 xenografts in nude mice after intratumoral injection. IGF1R-overexpressing MCF7 xenografts in nude mice were visualized at 4, 12, and 24 h after tail vein administration of the (99m)Tc-CCND1 antisense probe but not the control probe. (99m)Tc-chimeras were distributed normally in the kidneys, liver, tumors, and other tissues.

CONCLUSION

Cancer gene activity can be detected from outside the body by probing with radionuclide-chelator-PNA-peptide chimeras.

The mood stabilizer valproic acid stimulates GABA neurogenesis from rat forebrain stem cells

Valproate, an anticonvulsant drug used to treat bipolar disorder, was studied for its ability to promote neurogenesis from embryonic rat cortical or striatal primordial stem cells. Six days of valproate exposure increased by up to fivefold the number and percentage of tubulin beta III-immunopositive neurons, increased neurite outgrowth, and decreased by fivefold the number of astrocytes without changing the number of cells. Valproate also promoted neuronal differentiation in human fetal forebrain stem cell cultures. The neurogenic effects of valproate on rat stem cells exceeded those obtained with the neurotrophins brain-derived growth factor (BDNF) or NT-3, and slightly exceeded the effects obtained with another mood stabilizer, lithium. No effect was observed with carbamazepine. Most of the newly formed neurons were GABAergic, as shown by 10-fold increases in neurons that immunostained for GABA and the GABA-synthesizing enzyme GAD65/67. Double immunostaining for bromodeoxyuridine and tubulin beta III showed that valproate increased by four- to fivefold the proliferation of neuronal progenitors derived from rat stem cells and increased cyclin D2 expression. Valproate also regulated the expression of survival genes, Bad and Bcl-2, at different times of treatment. The expression of prostaglandin E synthase, analyzed by quantitative RT-PCR, was increased by ninefold as early as 6 h into treatment by valproate. The enhancement of GABAergic neuron numbers, neurite outgrowth, and phenotypic expression via increases in the neuronal differentiation of neural stem cell may contribute to the therapeutic effects of valproate in the treatment of bipolar disorder.

Beta cell replication is the primary mechanism for maintaining postnatal beta cell mass

The endocrine pancreas undergoes major remodeling during neonatal development when replication of differentiated beta cells is the major mechanism by which beta cell mass is regulated. The molecular mechanisms that govern the replication of terminally differentiated beta cells are unclear. We show that during neonatal development, cyclin D2 expression in the endocrine pancreas coincides with the replication of endocrine cells and a massive increase in islet mass. Using cyclin D2-/- mice, we demonstrate that cyclin D2 is required for the replication of endocrine cells but is expendable for exocrine and ductal cell replication. As a result, 14-day-old cyclin D2-/- mice display dramatically smaller islets and a 4-fold reduction in beta cell mass in comparison to their WT littermates. Consistent with these morphological findings, the cyclin D2-/- mice are glucose intolerant. These results suggest that cyclin D2 plays a key role in regulating the transition of beta cells from quiescence to replication and may provide a target for the development of therapeutic strategies to induce expansion and/or regeneration of beta cells.

Methoxychlor Induces Proliferation of the Mouse Ovarian Surface Epithelium

While the pesticide methoxychlor (MXC) has a variety of adverse effects on the female reproductive system, the effects of MXC on the ovarian surface epithelium (OSE) are unknown. Thus, this study tested the hypothesis that MXC alters the growth of the OSE. Mouse OSE cells were isolated by enzymatic digestion and cultured with vehicle, 3 microM of MXC, or 3 microM of 2,2-bis[p-hydroxyphenyl]-1,1,1,-trichloroethane (HPTE) for 14 days. After culture, proliferation and apoptosis were assessed by measurement of cell density, immunohistochemistry, and real-time polymerase chain reaction. Cell density was 66% greater for MXC-treated cells and 95% greater for HPTE-treated cells than controls (p < or = 0.05). The estrogen receptor blocker ICI 182,780 abolished MXC- and HPTE-induced increases in cell density. Proliferating cell nuclear antigen (PCNA) staining was positive in only 22 +/- 2.3% of controls, compared to 35 +/- 2.4% of MXC-treated cells and 40 +/- 2.4% of HPTE-treated cells (p < or = 0.05). The cell cycle regulators, cyclinD2 and cdk4, were significantly increased in MXC- and HPTE-treated cells compared to controls. The ApopTag assay demonstrated apoptotic cells in 4.8 +/- 0.45% of controls, 2.2 +/- 0.56% of MXC-treated cells, and 2.1 +/- 0.33% of HPTE-treated cells (p < or = 0.005). Expression of bcl-2 was significantly increased in MXC- and HPTE-treated cells, while bax was decreased in MXC- and HPTE-treated cells compared to controls. Collectively, these data indicate that MXC and HPTE stimulate OSE cell growth by increasing proliferation and inhibiting apoptosis. Further, since ICI 182,780 blocked MXC- and HPTE-induced OSE growth, these data suggest that the effects of MXC and HPTE on the OSE are mediated by estrogen receptors.