Coactivator MYST1 regulates nuclear factor-κB and androgen receptor functions during proliferation of prostate cancer cells

In prostate cancer (PCa), the functional synergy between androgen receptor (AR) and nuclear factor-κ B (NF-κB) escalates the resistance to therapeutic regimens and promotes aggressive tumor growth. Although the underlying mechanisms are less clear, gene regulatory abilities of coactivators can bridge the transcription functions of AR and NF-κB. The present study shows that MYST1 (MOZ, YBF2 and SAS2, and TIP60 protein 1) costimulates AR and NF-κB functions in PCa cells. We demonstrate that activation of NF-κB promotes deacetylation of MYST1 by sirtuin 1. Further, the mutually exclusive interactions of MYST1 with sirtuin 1 vs AR regulate the acetylation of lysine 16 on histone H4. Notably, in AR-lacking PC3 cells and in AR-depleted LNCaP cells, diminution of MYST1 activates the cleavage of poly(ADP-ribose) polymerase and caspase 3 that leads to apoptosis. In contrast, in AR-transformed PC3 cells (PC3-AR), depletion of MYST1 induces cyclin-dependent kinase (CDK) N1A/p21, which results in G2M arrest. Concomitantly, the levels of phospho-retinoblastoma, E2F1, CDK4, and CDK6 are reduced. Finally, the expression of tumor protein D52 (TPD52) was unequivocally affected in PC3, PC3-AR, and LNCaP cells. Taken together, the results of this study reveal that the functional interactions of MYST1 with AR and NF-κB are critical for PCa progression.

KLF6-SV1 drives breast cancer metastasis and is associated with poor survival

Metastasis is the major cause of cancer mortality. A more thorough understanding of the mechanisms driving this complex multistep process will aid in the identification and characterization of therapeutically targetable genetic drivers of disease progression. We demonstrate that KLF6-SV1, an oncogenic splice variant of the KLF6 tumor suppressor gene, is associated with increased metastatic potential and poor survival in a cohort of 671 lymph node-negative breast cancer patients. KLF6-SV1 overexpression in mammary epithelial cell lines resulted in an epithelial-to-mesenchymal-like transition and drove aggressive multiorgan metastatic disease in multiple in vivo models. Additionally, KLF6-SV1 loss-of-function studies demonstrated reversion to an epithelial and less invasive phenotype. Combined, these findings implicate KLF6-SV1 as a key driver of breast cancer metastasis that distinguishes between indolent and lethal early-stage disease and provides a potential therapeutic target for invasive breast cancer.

Primary aldosteronism: emerging trends

Primary aldosteronism (PA) is the most common etiology of endocrine hypertension (HTN), and recent prevalence studies suggest that it may be under-diagnosed. Indications for screening have been expanded with recognition that many patients with PA do not have hypokalemia and that the disease may be familial. The aldosterone:renin ratio (ARR) is the preferred screening test for PA. The ARR can be interpreted in patients on most anti-hypertensive agents, and can be used to guide medical therapy of HTN even in patients without PA. Once PA is confirmed, adrenal venous sampling (AVS) should be performed to determine if PA is due to bilateral disease or a unilateral adenoma, if surgery is being considered. Targeted medical or surgical therapy improves patient outcomes.

Androgens up-regulate transcription of the Notch inhibitor Numb in C2C12 myoblasts via Wnt/β-catenin signaling to T cell factor elements in the Numb promoter

Androgen signaling via the androgen receptor is a key pathway that contributes to development, cell fate decisions, and differentiation, including that of myogenic progenitors. Androgens and synthetic steroids have well established anabolic actions on skeletal muscle. Wnt and Notch signaling pathways are also essential to myogenic cell fate decisions during development and tissue repair. However, the interactions among these pathways are largely unknown. Androgenic regulation of Wnt signaling has been reported. Nandrolone, an anabolic steroid, has been shown to inhibit Notch signaling and up-regulate Numb, a Notch inhibitor. To elucidate the mechanisms of interaction between nandrolone and Wnt/Notch signaling, we investigated the effects of nandrolone on Numb expression and Wnt signaling and determined the roles of Wnt signaling in nandrolone-induced Numb expression in C2C12 myoblasts. Nandrolone increased Numb mRNA and protein levels and T cell factor (Tcf) transcriptional activity via inhibition of glycogen synthase kinase 3β. Up-regulation of Numb expression by nandrolone was blocked by the Wnt inhibitors, sFRP1 and DKK1, whereas Wnt3a increased Numb mRNA and protein expression. In addition, we observed that the proximal promoter of the Numb gene had functional Tcf binding elements to which β-catenin was recruited in a manner enhanced by both nandrolone and Wnt3a. Moreover, site-directed mutagenesis indicated that the Tcf binding sites in the Numb promoter are required for the nandrolone-induced Numb transcriptional activation in this cell line. These results reveal a novel molecular mechanism underlying up-regulation of Numb transcription with a critical role for increased canonical Wnt signaling. In addition, the data identify Numb as a novel target gene of the Wnt signaling pathway by which Wnts would be able to inhibit Notch signaling.

ACTH-producing remnants following apoplexy of an ACTH-secreting pituitary macroadenoma

Describe a case of apoplexy of an ACTH-producing pituitary adenoma which resulted not only in an empty sella with concurrent hypothyroidism, hypoprolactinemia, and hypogonadism but persistent hypercortisolemia from two distinct extrasellar remnants of the original adenoma. Review the literature to identify other similar cases. The patient's medical history, physical exam, lab data, imaging exams and histopathological results were analyzed and compiled into a case report, and an extensive review of the literature was performed. Endocrinological data revealed hypercortisolism and an elevated ACTH with an otherwise suppressed pituitary axis. A pituitary MRI showed a macroadenoma in the left cavernous sinus in addition to an empty sella. An octreotide scan revealed lesions in the left sella turcica and the right sphenoid sinus. Tissue samples of both lesions stained positive for ACTH and negative for GH, prolactin, FSH, LH, and TSH. The lesions were surgically removed, and the patient treated with radiation and ketoconazole. This resulted in a significant decrease in ACTH and cortisol as well as a marked improvement in blood glucose control. The review of literature revealed the absence of any similar cases in the past. The patient presented with apoplexy of an ACTH-secreting pituitary macroadenoma with two hormonally active extrasellar remnants. Several cases in the literature describe recurrence of Cushing's disease following infarction of ACTH-secreting adenomas. This is the first documented case of infarction of an ACTH-producing adenoma resulting in two distinct ACTH-producing remnants without recurrence of the original adenoma.

Adrenal cortical carcinoma with late pulmonary metastases causing clinicical Cushing's syndrome: case report with immunohistochemical analysis of steriodogenic enzyme production

OBJECTIVE

To present a case of pulmonary metastases from adrenocortical carcinomas (ACC) that were secreting fully-functional cortisol resulting in clinical Cushing's syndrome and to compare the steroidogenic enzyme expression in the primary tumor and lung.

METHODS

We analyzed and summarized the patient's medical history, physical examination results, laboratory data, imaging studies, and histopathologic results. The original tumor and the pulmonary metastases were then immunohistochemically evaluated for steroidogenic enzymes.

RESULTS

Initial endocrinological workup revealed hyperandrogenism and adrenocorticotropic hormone (ACTH) independent Cushing's due to a 4 cm left adrenal mass. The patient was initially diagnosed with an adrenal adenoma. Four years later, the patient developed recurrent Cushing's syndrome. Repeat magnetic resonance imaging (MRI) showed no adrenal masses; however, chest computed tomography (CT) showed multiple bilateral lung nodules and biopsy revealed metastases of adrenal origin. Upon immunohistochemical analysis, side chain cleavage, 17α hydroxylase, 3β hydroxysteroid dehydrogenase, and 21 hydroxylase immunoreactivity were detected in both the original and pulmonary metastatic lesions with patterns of disorganized steroidogenesis. Dehydroepiandrosterone-sulfotransferase (DHEA-ST) immunoreactivity was detected in the original tumor but not in the lung metastases.

CONCLUSION

This case demonstrates some interesting features of ACC that pose challenges to its management, including the difficulties in establishing the pathologic diagnosis, the potential for fully functional steroidogenesis even in late metastases, and the plasticity of steroidogenic potential in tumor cells.

Nandrolone, an anabolic steroid, stabilizes Numb protein through inhibition of mdm2 in C2C12 myoblasts

Nandrolone, an anabolic steroid, slows denervation atrophy of rat muscle, prevents denervation-induced nuclear accumulation of intracellular domain of the Notch receptor, and elevates expression of Numb. Numb acts as an inhibitor of Notch signaling and promotes myogenic differentiation of satellite cells. Turnover of Numb is regulated by mdm2, an E3 ubiquitin ligase. With these considerations in mind, we investigated the effects of nandrolone on the expression of Numb and mdm2 proteins and determined the effect of mdm2 on nandrolone-induced alterations in Numb protein in C2C12 myoblasts. When C2C12 cells were cultured in a medium favoring differentiation (Dulbecco modified Eagle medium containing 2% horse serum), nandrolone up-regulated Numb protein levels in a time-dependent manner and prolonged Numb protein half-life from 10 to 18 hours. In contrast, nandrolone reduced the expression of mdm2 protein. To determine whether the decreased mdm2 expression induced by nandrolone was responsible for the increased levels and prolonged half-life of Numb protein in this cell line, mdm2-small interfering RNA (siRNA) was employed to inhibit mdm2 expression. Compared to cells transfected with scrambled siRNA (negative control), transfection with mdm2-siRNA increased basal Numb protein expression but abolished the further increase in Numb protein levels by nandrolone. In addition, transfection of mdm2-siRNA mimicked the effect of nandrolone to prolong the half-life of Numb protein. Moreover, when C2C12 cells were forced to overexpress mdm2, there was a significant decline in the expression of both basal and inducible Numb protein. Our data suggest that nandrolone, by a novel mechanism for this agent in a muscle cell type, increases Numb protein levels in C2C12 myoblasts by stabilizing Numb protein against degradation, at least in part, via suppression of mdm2 expression.

Androgen deprivation therapy as primary treatment for prostate cancer

CONTEXT

Hormonal therapy has been the mainstay of treatment for advanced prostate cancer for over 70 yr. The timing and extent of androgen ablative therapy for earlier stage disease remains controversial. In addition, recent studies demonstrate that so-called "castration-resistant" tumors are still dependent on androgen receptor signaling.

PATIENT AND METHODS

A 66-yr-old man presented with clinical stage T1C N+ M0 prostate cancer and received primary androgen deprivation therapy. Over the course of the next 17 yr, he was treated with various forms of androgen deprivation therapy, including two newer agents, abiraterone acetate and MDV 3100. A review of the literature was conducted to identify indications, controversies, and new developments regarding hormonal therapy for prostate cancer.

CONCLUSIONS

Androgen deprivation therapy remains the treatment of choice for metastatic prostate cancer; however, it is not without its adverse effects, and most men with advanced disease eventually develop castration resistance. Newer compounds that more specifically and effectively target androgen and androgen receptor signaling in prostate cancer cells may provide more long-lasting remissions in advanced disease.

Prostatic acid phosphatase is expressed in human prostate cancer bone metastases and promotes osteoblast differentiation

Prostate cancer (PCa) bone metastases are a major cause of morbidity and mortality. There are no effective therapies for PCa bone metastases that prolong survival. Prostatic acid phosphatase (PAP) is a secretory protein expressed by PCa cells. We demonstrate that PAP is strongly expressed in PCa bone metastases in 7/7 patients, while prostate-specific antigen (PSA) is only weakly expressed. The human PCa cell line VCaP secretes PAP and induces an osteoblastic reaction in bone similar to that seen in human PCa bone metastases. Coculture of MC3T3 mouse preosteoblast cells with VCaP cells induces MC3T3 cell growth and differentiation as measured by alkaline phosphatase secretion, and this effect is inhibited by addition of the PAP-inhibitor, l-tartrate. Taken together, these data indicate that PAP is expressed in PCa bone metastases and may play a causal role in the osteoblastic phase of the disease.

Nandrolone reduces activation of Notch signaling in denervated muscle associated with increased Numb expression

Nandrolone, an anabolic steroid, slows denervation-atrophy in rat muscle. The molecular mechanisms responsible for this effect are not well understood. Androgens and anabolic steroids activate Notch signaling in animal models of aging and thereby mitigate sarcopenia. To explore the molecular mechanisms by which nandrolone prevents denervation-atrophy, we investigated the effects of nandrolone on Notch signaling in denervated rat gastrocnemius muscle. Denervation significantly increased Notch activity reflected by elevated levels of nuclear Notch intracellular domain (NICD) and expression of Hey1 (a Notch target gene). Activation was greatest at 7 and 35 days after denervation but remained present at 56 days after denervation. Activation of Notch in denervated muscle was prevented by nandrolone associated with upregulated expression of Numb mRNA and protein. These data demonstrate that denervation activates Notch signaling, and that nandrolone abrogates this response associated with increased expression of Numb, suggesting a potential mechanism by which nandrolone reduces denervation-atrophy.

Androgens and prostate cancer bone metastases: effects on both the seed and the soil

Androgens are essential for normal prostate development and are necessary, but not sufficient, for the development of prostate cancer (PCa). Androgen deprivation therapy has long been the mainstay of treatment for PCa bone metastases, providing palliation of symptoms in the majority of patients, followed by relapse and progression. The majority of published preclinical studies demonstrate a stimulatory effect of androgens and androgen receptor signaling on the multistep process of PCa bone metastases, including androgenic promotion of local PCa growth, angiogenesis, invasion, bone targeting, stimulation of PCa growth factors that enhance osteoclastogenesis, and enhancement of Wnt signaling in osteoblasts.

Abstract LB-375: Development of new compounds specifically targeting prostate cancer bone metastases

Introduction: Bone metastases are a major cause of morbidity for men with prostate cancer (PCa). Although PCa cells produce osteoblastic metastases, there is an initial and ongoing osteoclast (OC)-mediated osteolytic phase that is essential for PCa bone metastases. OC-mediated bone resorption is dependent upon OC secretion of bone acid phosphatase. PCa cells in bone secrete high levels of prostatic acid phosphatase (PAP) which differs from BAP in that PAP enzymatic activity is inhibited by tartrate and glyceric acid, whereas BAP is tartrate-resistant.

Hypothesis: PAP secreted by human PCa cells in bone acts similarly to OC-derived bone acid phosphatase to degrade bone matrix and enhance PCa bone-targeting and growth in bone. We developed new compounds consisting of glyceric acid or tartrate (known PAP inhibitors) conjugated to a bisphosphonate to inhibit PCa bone metastases.

Methods: PCa bone metastases derived from 7 patients were immunostained for androgen receptor (AR), prostate specific antigen (PSA) and PAP expression. The VCaP human PCa cell line derived from a vertebral metastases was inoculated intratibially into SCID mice (n=8) and bone lesions immunostained for AR, PSA, and PAP. Co-cultures of MC3T3 osteoblasts and VCaP cells were treated with tartrate and the effects on cell number, PAP and bone alkaline phosphatase (ALP) secretion measured by ELISA. Glyceric Acid and Tartaric acid were then conjugated with alendronate and the effects of these new conjugates on PAP enzymatic activity were compared to alendronate alone and tartrate alone.

Results: Human PCa bone lesions (7/7) had strongly positive expression of PAP, with little AR or PSA expression. 8/8 SCID mice inoculated with VCaP cells intratibially developed osteoblastic VCaP lesions and these similarly had high PAP expression and no PSA expression. Tartrate addition to co-cultures of VCaP and MC3T3 osteoblasts reduced MC3T3 cell numbers and ALP secretion. In vitro testing of the conjugates revealed that the glyceric acid-alendronate conjugate inhibited PAP enzymatic activity but the tartrate-alendronate conjugate and alendronate alone had no significant inhibitory activity.

Discussion: We have evidence that PAP secretion by PCa cells enhances their bone metastatic ability. We have developed new bone-targeting agents that consist of alendronate conjugated to PAP-inhibitory small molecules for further development as oral agents to prevent and treat PCa bone metastases.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr LB-375.

Prostaglandin E2 modulates components of the Wnt signaling system in bone and prostate cancer cells

Both Wnt signaling and prostaglandin E(2) (PGE(2)) play pivotal roles in bone development, remodeling, osteoporosis and prostate cancer (PCa) bone metastases. We investigated the effects of PGE(2) on Wnt signaling in osteoblast-lineage cells and Wnt-inhibitor expression in PCa cells. We demonstrate that low dose PGE(2) (0.1 microM) promotes Wnt signaling while higher doses of PGE(2) (1.0-10 microM) inhibit these same parameters in osteoblast-lineage cells. The differential effects of low vs high-dose PGE(2) on pre-osteoblasts may be attributed to dose-dependent modulation of prostaglandin receptor (EP) subtype expression; with lower doses increasing the expression the cAMP-stimulatory EP4 receptor subtype and higher doses increasing the expression of the cAMP-inhibitory EP3 receptor subtype. Moreover, we demonstrate that high expression levels of COX-2 and PGE(2) promote the secretion of Wnt inhibitors from prostate cancer cells. These data demonstrate that there are dose-dependent effects of PGE(2) on Wnt activation in osteoblast-lineage cells and Wnt-inhibitor expression in PCa cells which may have clinical implications in the management.

Ribosome-inactivating proteins isolated from dietary bitter melon induce apoptosis and inhibit histone deacetylase-1 selectively in premalignant and malignant prostate cancer cells

Epidemiologic evidence suggests that a diet rich in fruits and vegetables is associated with a reduced risk of prostate cancer (PCa) development. Although several dietary compounds have been tested in preclinical PCa prevention models, no agents have been identified that either prevent the progression of premalignant lesions or treat advanced disease. Momordica charantia, known as bitter melon in English, is a plant that grows in tropical areas worldwide and is both eaten as a vegetable and used for medicinal purposes. We have isolated a protein, designated as MCP30, from bitter melon seeds. The purified fraction was verified by SDS-PAGE and mass spectrometry to contain only 2 highly related single chain Type I ribosome-inactivating proteins (RIPs), alpha-momorcharin and beta-momorcharin. MCP30 induces apoptosis in PIN and PCa cell lines in vitro and suppresses PC-3 growth in vivo with no effect on normal prostate cells. Mechanistically, MCP30 inhibits histone deacetylase-1 (HDAC-1) activity and promotes histone-3 and -4 protein acetylation. Treatment with MCP30 induces PTEN expression in a prostatic intraepithelial neoplasia (PIN) and PCa cell lines resulting in inhibition of Akt phosphorylation. In addition, MCP30 inhibits Wnt signaling activity through reduction of nuclear accumulation of beta-catenin and decreased levels of c-Myc and Cyclin-D1. Our data indicate that MCP30 selectively induces PIN and PCa apoptosis and inhibits HDAC-1 activity. These results suggest that Type I RIPs derived from plants are HDAC inhibitors that can be utilized in the prevention and treatment of prostate cancer.

Androgenic regulation of hedgehog signaling pathway components in prostate cancer cells

Hedgehog signaling is thought to play a role in several human cancers including prostate cancer. Although prostate cancer cells express many of the gene products involved in hedgehog signaling, these cells are refractory to the canonical signaling effects of exogenous hedgehog ligands or to activated Smoothened, the hedgehog-regulated mediator of Gli transcriptional activation. Here, we show that the expression of hedgehog ligands and some hedgehog target genes are regulated by androgen in the human prostate cancer cell line, LNCaP and its more metastatic variants (C4-2 and C4-2B). Androgen (R1881) strongly suppressed the expression of hedgehog ligands in these cells and their prolonged maintenance in androgen-deficient medium upregulated Sonic and Indian hedgehog mRNA and protein levels by up to 30,000-fold. Hedgehogs were released into the conditioned medium of androgen-deprived LNCaP cells and this medium was able to increase hedgehog target gene expression in hedgehog-responsive mouse fibroblasts (MC3T3-E1). Moreover, this activity was accompanied by increased expression of Gli target genes, Patched 1 and Gli2, in LNCaP that could be suppressed by cyclopamine, indicating that chronic androgen-deprivation also re-awakens the autocrine responsiveness of the cancer cells to hedgehog. In contrast to the suppressive effects of R1881 on hedgehog ligand and Gli2 expression, we found that Gli1 expression in LNCaP cells was induced by R1881. Given the ability of androgen to modulate the expression and release of hedgehog ligands and the activity of the autocrine hedgehog signaling pathway in these prostate cancer cells, our results imply that chronic androgen deprivation therapy (ADT) for prostate cancer might create a hedgehog signaling environment in the region of the tumor that could ultimately impact on the long term effectiveness of this treatment. This consideration supports the idea of clinically testing hedgehog-blocking drugs in conjunction with ADT in patients with advanced prostate cancer.

Androgens promote preosteoblast differentiation via activation of the canonical Wnt signaling pathway

Although androgens stimulate bone formation the precise events underlying these effects have not been elucidated. Wnt signaling plays a central role in osteoblast development and bone formation. We demonstrated that dihydrotestosterone (DHT) significantly stimulates MC3T3 preosteoblast differentiation with no effect on cell growth. This effect of DHT was accompanied by increased Wnt signaling in the same cells. Moreover, the stimulatory effects of DHT on preosteoblast differentiation were inhibited by overexpression of soluble frizzed-related protein (sFRP), a naturally occurring Wnt antagonist. These results suggest that androgens promote preosteoblastic differentiation via effects on the canonical Wnt signaling pathway.

Concomitant Secretion of Glucocorticoid, Androgens, and Mineralocorticoid by an Adrenocortical Carcinoma: Case Report and Review of Literature

OBJECTIVE

To present a case of concomitant secretion of cortisol, androgens, and 11-deoxycorticosterone (DOC) by an adrenocortical carcinoma and review the literature in an attempt to identify similar cases.

METHODS

The patient's medical history, physical examination, laboratory data, computed tomographic scan, and histopathologic results were analyzed and summarized in a case report, and an extensive review of the literature was performed.

RESULTS

Endocrinologic data showed excess cortisol production, substantially elevated testosterone and androstenedione levels, and profoundly increased DOC in the setting of suppressed aldosterone. An abdominal computed tomographic scan showed a left adrenal tumor. A left adrenalectomy was performed, and the histopathologic diagnosis was stage II adrenocortical carcinoma. The review of the pertinent literature revealed the absence of any identical cases in the past.

CONCLUSION

Our patient presented with a rare case of cosecretion of cortisol, testosterone, androstenedione, and DOC by an adrenocortical carcinoma, resulting in a clinical picture consistent with Cushing's syndrome, hyperandrogenism, and primary hypermineralocorticoidism. We recommend the routine performance of a DOC assay in the setting of mineralocorticoid excess in association with low plasma aldosterone levels.

Androgen-Induced Wnt Signaling in Preosteoblasts Promotes the Growth of MDA-PCa-2b Human Prostate Cancer Cells

The high morbidity and mortality associated with prostate cancer (PCa) result from its tendency to metastasize to bone where it produces predominantly osteoblastic lesions. The Wnt signaling pathway plays an important role in embryogenesis, tumorigenesis, osteoblast development, and bone formation. Androgen signaling via the androgen receptor (AR) is critical in both PCa and bone cell growth. We examined the effects of androgens on cell growth and Wnt signaling in the AR-positive MDA-PCa-2b cell line and MC3T3 preosteoblasts, grown alone and in coculture. We show that the potent androgen dihydrotestosterone increases AR expression and transcriptional activity only in the preosteoblasts. Although dihydrotestosterone induced an 80% increase in PCa cell growth when the cells were grown alone, dihydrotestosterone had a more significant effect on MDA-PCa-2b cell proliferation (3.2-fold increase) when the PCa cells were cocultured with preosteoblasts. Dihydrotestosterone addition to preosteoblasts promoted Wnt-dependent transcriptional reporter activity associated with GSK3beta(S-9) phosphorylation and accumulation of nuclear beta-catenin as well as elevated Runx2 expression. In addition, the increased proliferation of PCa cells in coculture with MC3T3 cells in response to dihydrotestosterone was abrogated by the addition of either exogenous DKK-1 or sFRP-1 protein, two naturally occurring Wnt antagonists. Finally, we show that the paracrine growth-promoting effect of androgens is limited to MDA-PCa-2b cells. These data imply that Wnt signaling is involved in the androgen-regulated crosstalk between preosteoblasts and PCa cells and suggest that androgens may stimulate growth of some prostate tumor cells indirectly, via up-regulation of Wnt signaling in bone cells.

Interactive Effect of Interleukin-6 and Prostaglandin E2 on Osteoclastogenesis via the OPG/RANKL/RANK System

The OPG/RANKL/RANK system regulates osteoclastogenesis. Both cyclooxygenase-2 (COX-2)/prostaglandin E2 (PGE2) and interleukin-6 (IL-6) are reported to induce osteoclast differentiation. The mechanisms underlying these signaling pathways on the OPG/RANKL/RANK system are not fully understood. We herein demonstrate that COX-2 and PGE2 stimulated osteoclastogenesis through inhibition of OPG secretion, stimulation of RANKL production by osteoblasts, and upregulation of RANK expression in osteoclasts. PGE2 also stimulated IL-6 production, and IL-6, in turn, increased PGE2 secretion, COX-2, and EP4/EP2 expression in bone cells. These findings provide evidence of interactive effect of PGE2 and IL-6 signaling pathways in osteoclastogenesis via effect on the OPG/RANKL/RANK system.

Sex steroids have differential effects on growth and gene expression in primary human prostatic epithelial cell cultures derived from the peripheral versus transition zones

The majority of human prostate cancers arise from the peripheral zone (PZ). Prostate epithelial stem cells have been localized to the basal epithelial cell compartment. In addition, basal cells have been shown to maintain luminal epithelial cell differentiation and may mediate signals between the stromal and luminal cell compartments. Therefore, the study of adult prostate basal cells derived from different prostate zones may give insights into the mechanisms underlying normal and abnormal prostate growth. We herein compare the basal and sex steroid-stimulated expression and activity of several genes/proteins that are known to be critical in prostate cancer development in primary cultures of basal cells derived from the transition zone (TZ) and PZ of prostatectomy specimens. Our results demonstrate that prostate basal cells derived from the PZ versus TZ are more viable in culture, particularly in response to sex steroid addition. PZ cells exhibit higher telomerase activity and increased expression levels of androgen receptor, the anti-apoptotic protein bcl-2, and the dominant-negative splice variant of Kruppel-like Factor 6. PZ cells have lower basal expression levels of estrogen receptor-beta, the pro-apoptotic protein Bax, and cell-cycle inhibitor proteins (p53, p21(waf1/Cip1)). Finally, we demonstrate divergent responses to sex hormones in the two basal cell populations. The gene expression pattern in the PZ cells may partially explain the predominance of prostate cancer development in this region.

Cross-talk between the interleukin-6 and prostaglandin E(2) signaling systems results in enhancement of osteoclastogenesis through effects on the osteoprotegerin/receptor activator of nuclear factor-{kappa}B (RANK) ligand/RANK system

The osteoprotegerin (OPG)/receptor activator of nuclear factor-kappaB ligand (RANKL)/receptor activator of nuclear factor-kappaB (RANK) system is the dominant and final mediator of osteoclastogenesis. Abnormalities of this system have been implicated in the pathogenesis of many skeletal diseases. Cyclooxygenase (COX)-2 and prostaglandin (PG)E(2), a major eicosanoid product of the COX-2-catalyzed pathway, play key roles in normal bone tissue remodeling. PGE(2) exerts its actions by binding and activating the E series of prostaglandin (EP) receptor. Activation of EP(2) and EP(4) receptors is associated with PGE(2)-induced osteoclast differentiation. IL-6, a major proinflammatory cytokine, has also been reported to induce osteoclast differentiation. Although interactions between the COX-2/PGE(2) and IL-6 systems have been described in bone cells, the mechanisms underlying these cooperative signaling pathways and the possible involvement of the OPG/RANKL/RANK system have not been fully elucidated. We demonstrate that COX-2, PGE(2), and IL-6 stimulate osteoblast growth and osteoclast differentiation. Effects on osteoclast differentiation, particularly with IL-6, were most marked when osteoclast precursor cells were grown in coculture with osteoblasts, indicating a possible role of the RANK/RANKL/OPG system. COX-2 and PGE(2) stimulated osteoclastogenesis through inhibition of OPG secretion, stimulation of RANKL production by osteoblasts, and up-regulation of RANK expression in osteoclasts. PGE(2) stimulated IL-6 secretion by bone cells, whereas COX-2 inhibitors decreased this same parameter. IL-6, in turn, increased PGE(2) secretion, COX-2, and EP receptor subtype expression in bone cells. Finally, IL-6 was the mediator of PGE(2)-induced suppression of OPG production by osteoblasts. These findings provide evidence for cross-talk between the PGE(2) and IL-6 signaling enhance osteoclast differentiation via effects on the OPG/RANKL/RANK system in bone cells.

Cyclooxygenase-2 suppresses hypoxia-induced apoptosis via a combination of direct and indirect inhibition of p53 activity in a human prostate cancer cell line

Although p53-inactivating mutations have been described in the majority of human cancers, their role in prostate cancer is controversial as mutations are uncommon, particularly in early lesions. p53 is activated by hypoxia and other stressors and is primarily regulated by the Mdm2 protein. Cyclooxygenase (COX)-2, an inducible enzyme that catalyzes the conversion of arachidonic acid to prostaglandins and other eicosanoids, is also induced by hypoxia. COX-2 and resultant prostaglandins increase tumor cell proliferation, resistance to apoptosis, and angiogenesis. Previous reports indicate a complex, reciprocal relationship between p53 and COX-2. To elucidate the effects of COX-2 on p53 in response to hypoxia, we transfected the COX-2 gene into the p53-positive, COX-2-negative MDA-PCa-2b human prostate cancer cell line. The expression of functional p53 and Mdm2 was compared in COX-2+ versus COX-2- cells under normoxic and hypoxic conditions. Our results demonstrated that hypoxia increases both COX-2 protein levels and p53 transcriptional activity in these cells. Forced expression of COX-2 increased tumor cell viability and decreased apoptosis in response to hypoxia. COX-2+ cells had increased Mdm2 phosphorylation in either normoxic or hypoxic conditions. Overexpression of COX-2 abrogated hypoxia-induced p53 phosphorylation and promoted the binding of p53 to Mdm2 protein in hypoxic cells. In addition, COX-2-expressing cells exhibited decreased hypoxia-induced nuclear accumulation of p53 protein. Finally, forced expression of COX-2 suppressed both basal and hypoxia-induced p53 transcriptional activity, and this effect was mimicked by the addition of PGE2 to wild-type cells. These results demonstrated a role for COX-2 in the suppression of hypoxia-induced p53 activity via both direct effects and indirect modulation of Mdm2 activity. These data imply that COX-2-positive prostate cancer cells can have impaired p53 function even in the presence of wild-type p53 and that p53 activity can be restored in these cells via inhibition of COX-2 activity.