Identification of a negative regulatory cis-element in the enhancer core region of the prostate-specific antigen promoter: implications for intersection of androgen receptor and nuclear factor-kappaB signalling in prostate cancer cells

The Hippo effector YAP1/TEAD1 regulates EPHA3 expression to control cell contact and motility

The EPHA3 protein tyrosine kinase, a member of the ephrin receptor family, regulates cell fate, cell motility, and cell-cell interaction. These cellular events are critical for tissue development, immunological responses, and the processes of tumorigenesis. Earlier studies revealed that signaling via the STK4-encoded MST1 serine-threonine protein kinase, a core component of the Hippo pathway, attenuated EPHA3 expression. Here, we investigated the mechanism by which MST1 regulates EPHA3. Our findings have revealed that the transcriptional regulators YAP1 and TEAD1 are crucial activators of EPHA3 transcription. Silencing YAP1 and TEAD1 suppressed the EPHA3 protein and mRNA levels. In addition, we identified putative TEAD enhancers in the distal EPHA3 promoter, where YAP1 and TEAD1 bind and promote EPHA3 expression. Furthermore, EPHA3 knockout by CRISPR/Cas9 technology reduced cell-cell interaction and cell motility. These findings demonstrate that EPHA3 is transcriptionally regulated by YAP1/TEAD1 of the Hippo pathway, suggesting that it is sensitive to cell contact-dependent interactions.

NOD-like receptors: major players (and targets) in the interface between innate immunity and cancer

Innate immunity comprises several inflammation-related modulatory pathways which receive signals from an array of membrane-bound and cytoplasmic pattern recognition receptors (PRRs). The NLRs (NACHT (NAIP (neuronal apoptosis inhibitor protein), C2TA (MHC class 2 transcription activator), HET-E (incompatibility locus protein from Podospora anserina) and TP1 (telomerase-associated protein) and Leucine-Rich Repeat (LRR) domain containing proteins) relate to a large family of cytosolic innate receptors, involved in detection of intracellular pathogens and endogenous byproducts of tissue injury. These receptors may recognize pathogen-associated molecular patterns (PAMPs) and/or danger-associated molecular patterns (DAMPs), activating host responses against pathogen infection and cellular stress. NLR-driven downstream signals trigger a number of signaling circuitries, which may either initiate the formation of inflammasomes and/or activate nuclear factor κB (NF-κB), stress kinases, interferon response factors (IRFs), inflammatory caspases and autophagy. Disruption of those signals may lead to a number of pro-inflammatory conditions, eventually promoting the onset of human malignancies. In this review, we describe the structures and functions of the most well-defined NLR proteins and highlight their association and biological impact on a diverse number of cancers.

Mapping the STK4/Hippo signaling network in prostate cancer cell

Dysregulation of MST1/STK4, a key kinase component of the Hippo-YAP pathway, is linked to the etiology of many cancers with poor prognosis. However, how STK4 restricts the emergence of aggressive cancer remains elusive. Here, we investigated the effects of STK4, primarily localized in the cytoplasm, lipid raft, and nucleus, on cell growth and gene expression in aggressive prostate cancer. We demonstrated that lipid raft and nuclear STK4 had superior suppressive effects on cell growth in vitro and in vivo compared with cytoplasmic STK4. Using RNA sequencing and bioinformatics analysis, we identified several differentially expressed (DE) genes that responded to ectopic STK4 in all three subcellular compartments. We noted that the number of DE genes observed in lipid raft and nuclear STK4 cells were much greater than cytoplasmic STK4. Our functional annotation clustering showed that these DE genes were commonly associated with oncogenic pathways such as AR, PI3K/AKT, BMP/SMAD, GPCR, WNT, and RAS as well as unique pathways such as JAK/STAT, which emerged only in nuclear STK4 cells. These findings indicate that MST1/STK4/Hippo signaling restricts aggressive tumor cell growth by intersecting with multiple molecular pathways, suggesting that targeting of the STK4/Hippo pathway may have important therapeutic implications for cancer.

Protein kinase C regulates Twist1 expression via NF-κB in prostate cancer

The progression of prostate cancer to metastatic and castration-resistant disease represents a critical step. We previously showed that protein kinase C (PKC) activation followed by Twist1 and androgen receptor (AR) induction played a critical role in castration resistance, but the precise molecular mechanism remains unknown. This study aimed to elucidate the relevant molecular mechanism, focusing on NF-κB transcription factor. We examined the activity of NF-κB after PKC inhibition, and the expression of Twist1 and AR after inhibition of NF-κB in human prostate cancer cells. We also investigated the status of PKC/NF-κB after inhibition of AR signaling in cells resistant to hormonal therapy. As a result, inhibition of PKC signaling using knockdown and small-molecule inhibition of PKC suppressed RelA activity, while blocking NF-κB suppressed Twist1 and AR expression. Conversely, inhibition of AR signaling by androgen depletion and the novel antiandrogen enzalutamide induced PKC and RelA activation, resulting in Twist1/AR induction at the transcript level. Moreover, inhibition of NF-κB signaling prevented enzalutamide-induced Twist1 and AR induction. Finally, NF-κB was activated in both castration-resistant and enzalutamide-resistant cells. In conclusion, NF-κB signaling was responsible for Twist1 upregulation by PKC in response to AR inhibition, resulting in aberrant activation of AR. NF-κB signaling thus appears to play a critical role in promoting both castration resistance and enzalutamide resistance in PKC/Twist1 signaling in prostate cancer.

Involvement of Kallikrein-Related Peptidases in Normal and Pathologic Processes

Human kallikrein-related peptidases (KLKs) are a subgroup of serine proteases that participate in proteolytic pathways and control protein levels in normal physiology as well as in several pathological conditions. Their complex network of stimulatory and inhibitory interactions may induce inflammatory and immune responses and contribute to the neoplastic phenotype through the regulation of several cellular processes, such as proliferation, survival, migration, and invasion. This family of proteases, which includes one of the most useful cancer biomarkers, kallikrein-related peptidase 3 or PSA, also has a protective effect against cancer promoting apoptosis or counteracting angiogenesis and cell proliferation. Therefore, they represent attractive therapeutic targets and may have important applications in clinical oncology. Despite being intensively studied, many gaps in our knowledge on several molecular aspects of KLK functions still exist. This review aims to summarize recent data on their involvement in different processes related to health and disease, in particular those directly or indirectly linked to the neoplastic process.

Neuronal androgen receptor regulates insulin sensitivity via suppression of hypothalamic NF-κB-mediated PTP1B expression

Clinical investigations highlight the increased incidence of metabolic syndrome in prostate cancer (PCa) patients receiving androgen deprivation therapy (ADT). Studies using global androgen receptor (AR) knockout mice demonstrate that AR deficiency results in the development of insulin resistance in males. However, mechanisms by which AR in individual organs coordinately regulates insulin sensitivity remain unexplored. Here we tested the hypothesis that functional AR in the brain contributes to whole-body insulin sensitivity regulation and to the metabolic abnormalities developed in AR-deficient male mice. The mouse model selectively lacking AR in the central nervous system and AR-expressing GT1-7 neuronal cells were established and used to delineate molecular mechanisms in insulin signaling modulated by AR. Neuronal AR deficiency leads to reduced insulin sensitivity in middle-aged mice. Neuronal AR regulates hypothalamic insulin signaling by repressing nuclear factor-κB (NF-κB)-mediated induction of protein-tyrosine phosphatase 1B (PTP1B). Hypothalamic insulin resistance leads to hepatic insulin resistance, lipid accumulation, and visceral obesity. The functional deficiency of AR in the hypothalamus leads to male mice being more susceptible to the effects of high-fat diet consumption on PTP1B expression and NF-κB activation. These findings suggest that in men with PCa undergoing ADT, reduction of AR function in the brain may contribute to insulin resistance and visceral obesity. Pharmacotherapies targeting neuronal AR and NF-κB may be developed to combat the metabolic syndrome in men receiving ADT and in elderly men with age-associated hypogonadism.

Threonine-120 phosphorylation regulated by phosphoinositide-3-kinase/Akt and mammalian target of rapamycin pathway signaling limits the antitumor activity of mammalian sterile 20-like kinase 1

Mst1/Stk4, a hippo-like serine-threonine kinase, is implicated in many cancers, including prostate cancer. However, the mechanisms regulating Mst1 remain obscure. Here, we characterized the effects of phospho-Thr-120 on Mst1 in prostate cancer cells. We demonstrated that phospho-Thr-120 did not alter the nuclear localization or cleavage of Mst1 in a LNCaP or castration-resistant C4-2 prostate tumor cell model, as revealed by a mutagenesis approach. Phospho-Thr-120 appeared to be specific to cancer cells and predominantly localized in the nucleus. In contrast, phospho-Thr-183, a critical regulator of Mst1 cell death, was exclusively found in the cytoplasm. As assessed by immunohistochemistry, a similar distribution of phospho-Mst1-Thr-120/Thr-183 was also observed in a prostate cancer specimen. In addition, the blockade of PI3K signaling by a small molecule inhibitor, LY294002, increased cytoplasmic phospho-Mst1-Thr-183 without having a significant effect on nuclear phospho-Mst1-Thr-120. However, the attenuation of mammalian target of rapamycin (mTOR) activity by a selective pharmacologic inhibitor, Ku0063794 or CCI-779, caused the up-regulation of nuclear phospho-Mst1-Thr-120 without affecting cytoplasmic phospho-Mst1-Thr-183. This suggests that PI3K and mTOR pathway signaling differentially regulate phospho-Mst1-Thr-120/Thr-183. Moreover, mutagenesis and RNAi data revealed that phospho-Thr-120 resulted in C4-2 cell resistance to mTOR inhibition and reduced the Mst1 suppression of cell growth and androgen receptor-driven gene expression. Collectively, these findings indicate that phospho-Thr-120 leads to the loss of Mst1 functions, supporting cancer cell growth and survival.

Nuclear factor κB predicts poor outcome in patients with hormone-naive prostate cancer with high nuclear androgen receptor

Despite recent advances in prostate cancer treatments, disease recurrence is common and associated with significant morbidity and mortality. The need for more effective antitumor agents has led researchers to target signaling pathways that drive tumorigenesis by modulating or bypassing androgen receptor signaling--attenuation or blockade of which current treatments aim to effect. The transcription factor nuclear factor κB/p65 has been implicated in prostate cancer progression; however, few studies have examined the involvement of nuclear factor κB in hormone-naive disease. We used immunohistochemistry to investigate expression of p65, androgen receptor, Ki-67, and phosphorylation status of p65 at serine 536, in 154 tumor samples taken from patients before hormone ablation or radical treatment. Nuclear p65 expression was significantly associated with disease-specific mortality: P = .005; hazard ratio, 2.2. When patients were stratified according to androgen receptor status, this relationship was abolished in low androgen receptor-expressing patients and potentiated in high androgen receptor-expressing patients: P = .002; hazard ratio, 3.1. Ki-67 expression was also prognostic of shorter disease-specific mortality: P = .001; hazard ratio, 2.3. When the cohort was stratified according to androgen receptor status, this relationship held for high androgen receptor expressers but not low expressers: P = .0003; hazard ratio, 3.5. Neither androgen receptor nor p65 phosphorylated at S536 were significantly prognostic when considered individually. These data suggest that future prostate cancer treatments that target nuclear factor κB signaling should be assigned primarily to patients with concomitant high nuclear p65 and androgen receptor expression.

Inverse relationship between PSA and IL-8 in prostate cancer: an insight into a NF-κB-mediated mechanism

Background

Prostate specific antigen (PSA) is traditionally used as an indicator for the presence of prostate cancer (PCa) and radiotherapy is generally used to treat inoperable and locally advanced PCa. However, how cellular PSA level is associated with sensitivity of PCa to radiotherapy is unknown. The previous finding that the RelB-based NF-κB alternative pathway differentially regulates PSA and interleukin-8 (IL-8) in aggressive PCa has directed our attention to the role of RelB in the response of PCa to radiotherapy.

Methodology/Principal Findings

RelB and its targets PSA and IL-8 in PCa cells were manipulated by ectopic expression in PCa cells with a low endogenous level of RelB (LNCaP) and by RNAi-based knock-down in PCa cells with a high constitutive level of RelB (PC3). The effects of RelB, PSA and IL-8 on the response of PCa to radiation treatment were examined in vitro and in xenograft tumors. RelB regulates PSA and IL-8 in an inverse manner. When the cellular levels of PSA and IL-8 were directly modulated by genetic manipulations or by the addition of recombinant proteins, the results demonstrate that up-regulation of IL-8 enhanced radioresistance of PCa cells and concurrently down-regulated PSA. In contrast, up-regulation of PSA resulted in reduced radioresistance with concurrent down-regulation of IL-8.

Conclusion/Significance

RelB plays a critical role in the response of PCa to radiotherapy and the inverse expression of IL-8 and PSA. The results identify a previously unrecognized relationship between IL-8 and PSA in the response of PCa cells to radiotherapy.

Androgen regulation of 5α-reductase isoenzymes in prostate cancer: implications for prostate cancer prevention

The enzyme 5α-reductase, which converts testosterone to dihydrotestosterone (DHT), performs key functions in the androgen receptor (AR) signaling pathway. The three isoenzymes of 5α-reductase identified to date are encoded by different genes: SRD5A1, SRD5A2, and SRD5A3. In this study, we investigated mechanisms underlying androgen regulation of 5α-reductase isoenzyme expression in human prostate cells. We found that androgen regulates the mRNA level of 5α-reductase isoenzymes in a cell type-specific manner, that such regulation occurs at the transcriptional level, and that AR is necessary for this regulation. In addition, our results suggest that AR is recruited to a negative androgen response element (nARE) on the promoter of SRD5A3 in vivo and directly binds to the nARE in vitro. The different expression levels of 5α-reductase isoenzymes may confer response or resistance to 5α-reductase inhibitors and thus may have importance in prostate cancer prevention.

Mechanisms of persistent activation of the androgen receptor in CRPC: recent advances and future perspectives

BACKGROUND

The emergence of castration resistance has remained the primary obstacle in prostate cancer therapy for several decades. Mechanisms likely to be involved in castration-resistant progression have been studied extensively, but have failed to yield many meaningful and effective targets. The re-activation of the androgen receptor (AR) in castration-resistant prostate cancer (CRPC) is now recognized as the central event in this process, and therapeutic modalities are being devised to combat it.

METHODS

A review of literature was performed to highlight the important factors that play a role in the aberrant activation of the AR in CRPC.

RESULTS

Seminal and exciting advances made in the past few years in the discovery of the roles of new intrinsic factors such as intracrine androgens, gene fusions involving the ETS oncogenes, and splice variants of the AR are reviewed. New and emerging hypotheses about the involvement of factors such as cytokines and other signaling pathways are discussed.

CONCLUSIONS

This review summarizes the most recent advances in the persistent activation of the androgen receptor signaling pathway and provides a perspective about their significance in CRPC progression.

Immunohistochemical analysis of FKBP51 in human cancers

FKBP51 is a FK506-binding immunophilin involved in the regulation of several fundamental biological processes. A growing body of data indicates that this protein has also a role in the abnormal cell growth of cancers, and could be considered as a promising new marker of tumor progression and response to radio/chemotherapy. However, the data concerning the expression of FKBP51 in cancer are not conclusive, and partially contradictory. They delineate a very complex scenario, in which many molecular FKBP51-related pathways are variously intersected among different tumors. This review reports the available data concerning FKBP51 expression in normal tissues and human malignancies, outlining the role of the immunohistochemical analysis as a fundamental tool for better understanding the role of this immunophilin in cancer biology.

MST1 is a multifunctional caspase-independent inhibitor of androgenic signaling

The MST1 serine-threonine kinase, a component of the RASSF1-LATS tumor suppressor network, is involved in cell proliferation and apoptosis and has been implicated in cancer. However, the physiologic role of MST1 in prostate cancer (PCa) is not well understood. Here, we investigated the possibility of a biochemical and functional link between androgen receptor (AR) and MST1 signaling. We showed that MST1 forms a protein complex with AR and antagonizes AR transcriptional activity as shown by coimmunoprecipitation (co-IP), promoter reporter analysis, and molecular genetic methods. In vitro kinase and site-specific mutagenesis approaches indicate that MST1 is a potent AR kinase; however, the kinase activity of MST1 and its proapoptotic functions were shown not to be involved in inhibition of AR. MST1 was also found in AR-chromatin complexes, and enforced expression of MST1 reduced the binding of AR to a well-characterized, androgen-responsive region within the prostate-specific antigen promoter. MST1 suppressed PCa cell growth in vitro and tumor growth in mice. Because MST1 is also involved in regulating the AKT1 pathway, this kinase may be an important new link between androgenic and growth factor signaling and a novel therapeutic target in PCa.

Aberrant activation of the androgen receptor by NF-kappaB2/p52 in prostate cancer cells

Prostate cancer initiation and progression are uniquely dependent on the androgen receptor (AR). Even when the cancer progresses to a castration-resistant stage, AR signaling remains active via a variety of mechanisms. In the present study, we showed that NF-kappaB/p52 can activate the AR, resulting in increased transactivation of AR-responsive genes, such as PSA and NKX3.1, in a ligand-independent manner. NF-kappaB2/p52 enhances nuclear translocation and activation of AR by interacting with its NH(2)-terminal domain and enhances the recruitment of coactivators such as p300 to the promoters of AR-dependent genes. These results were confirmed in three different prostate cancer cell lines: LAPC-4 (wild-type AR), LNCaP (mutant AR), and C4-2 (castration resistant). Transfection of p52 into LAPC-4 and LNCaP cells (which express low levels of p52) showed increased activation of the endogenous AR. Downregulation of endogenous p52 in C4-2 cells resulted in abrogation of AR constitutive activation. Comparison of the relative effects of p52 and p65 (RelA) showed that p52, but not p65, could activate the AR. Collectively, these findings, together with previous reports that the levels of NF-kappaB2/p52 are elevated in prostate cancer cells and that active NF-kappaB2/p52 promotes prostate cancer cell growth in vitro and in vivo, suggest that NF-kappaB2/p52 may play a critical role in the progression of castration-resistant prostate cancer.

Reduced tumor necrosis factor receptor-associated death domain expression is associated with prostate cancer progression

By using LNCaP and its derivative cell lines, we first observed an association between tumor necrosis factor-alpha (TNF-alpha) resistance and hormone independence. Moreover, we found that the expression of tumor necrosis factor receptor-associated death domain (TRADD) was reduced in androgen deprivation-independent cells compared with that in androgen deprivation-dependent cells. TRADD is a crucial transducer for TNF-alpha-induced nuclear factor-kappaB (NF-kappaB) activation. Knocking down TRADD expression in LNCaP cells impaired TNF-alpha-induced NF-kappaB activation and androgen receptor repression, whereas overexpression of TRADD in C4-2B cells restored their sensitivity to TNF-alpha. Finally, we found that androgen deprivation reduces TRADD expression in vitro and in vivo, suggesting that androgen deprivation therapy may promote the development of TNF-alpha resistance by reducing TRADD expression during prostate cancer progression.

Induction of neuronal apoptosis inhibitory protein expression in response to androgen deprivation in prostate cancer

A mechanism for survival of prostate cancer cells in an androgen-deprived environment remains elusive. Here, we find that expression of neuronal apoptosis inhibitory protein (NAIP) was significantly increased in vivo and in vitro in response to androgen deprivation therapy (ADT). Increased expression of NAIP corresponded to increased DNA-binding activity of NF-kappaB that physically associated to previously uncharacterized kappaB-like sites in the NAIP locus. Importantly, expression of NAIP was significantly increased (p=0.04) in clinical samples of prostate cancer from patients receiving ADT. Expression of NAIP may be associated with enhanced survival of prostate cancer in response to castration.

FKBP51 and Cyp40 are positive regulators of androgen-dependent prostate cancer cell growth and the targets of FK506 and cyclosporin A

Prostate cancer (PCa) growth is dependent on androgens and the androgen receptor (AR), which acts by modulating gene transcription. Tetratricopeptide repeat (TPR) proteins (FKBP52, FKBP51 and Cyp40) interact with AR in PCa cells, suggesting roles in AR-mediated gene transcription and cell growth. We report here that FKBP51 and Cyp40, but not FKBP52, are significantly elevated in PCa tissues and in androgen-dependent (AD) and -independent (AI) cell lines. Overexpression of FKBP51 in AD LNCaP cells increased AR transcriptional activity in the presence and absence of androgen, whereas siRNA knockdown of FKBP51 dramatically decreased AD gene transcription and proliferation. Knockdown of Cyp40 also inhibited androgen-mediated transcription and growth in LNCaP cells. However, disruption of FKBP51 and Cyp40 in the AI C4-2 cells caused only a small reduction in proliferation, indicating that Cyp40 and FKBP51 predominantly regulate AD cell proliferation. Under knock-down conditions, the inhibitory effects of TPR ligands, CsA and FK506, on AR activity were not observed, indicating that Cyp40 and FKBP51 are the targets of CsA and FK506, respectively. Our findings demonstrate that FKBP51 and Cyp40 are positive regulators of AR that can be selectively targeted by CsA and FK506 to achieve inhibition of androgen-induced cell proliferation. These proteins and their cognate ligands thus provide new strategies in the treatment of PCa

Characterization of NF-kB-mediated inhibition of catechol-O-methyltransferase

BACKGROUND

Catechol-O-methyltransferase (COMT), an enzyme that metabolizes catecholamines, has recently been implicated in the modulation of pain. Specifically, low COMT activity is associated with heightened pain perception and development of musculoskeletal pain in humans as well as increased experimental pain sensitivity in rodents.

RESULTS

We report that the proinflammatory cytokine tumor necrosis factor alpha (TNFalpha) downregulates COMT mRNA and protein in astrocytes. Examination of the distal COMT promoter (P2-COMT) reveals a putative binding site for nuclear factor kappaB (NF-kappaB), the pivotal regulator of inflammation and the target of TNFalpha. Cell culture assays and functional deletion analyses of the cloned P2-COMT promoter demonstrate that TNFalpha inhibits P2-COMT activity in astrocytes by inducing NF-kappaB complex recruitment to the specific kappaB binding site.

CONCLUSION

Collectively, our findings provide the first evidence for NF-kappaB-mediated inhibition of COMT expression in the central nervous system, suggesting that COMT contributes to the pathogenesis of inflammatory pain states.

Transcriptional regulation of the TGF-beta1 promoter by androgen receptor

TGF (transforming growth factor)-beta1 is a multifunctional cytokine that influences homoeostatic processes of various tissues. TGF-beta1 expression is inhibited by androgens in the prostate gland, whereas its expression is enhanced by androgens in highly metastatic prostate cancer cells. Here, we examined regulation of human TGF-beta1 promoter activity by androgen in prostate cancer cells. The full-length (-3363 to +110) promoter showed a high level of activity in response to androgen in PC3mm2 cells expressing AR (androgen receptor). Further deletion analysis revealed three distal and three proximal AREs (androgen-response elements) in the promoter. Gel-shift and footprint assays show that these AREs physically interact with the DNA-binding domain of AR. Chromatin immunoprecipitation assays revealed the androgen-dependent recruitment of AR to the ARE-containing regions of the TGF-beta1 gene. More importantly, a negative ARE was detected in the TGF-beta1 promoter. Both positive and negative AREs are functional in the androgen-regulated transcription of the TGF-beta1 promoter. These findings imply that androgen signalling may positively or negatively regulate TGF-beta1 expression in response to various signals or under different environmental conditions.

Androgens act synergistically to enhance estrogen-induced upregulation of human tissue kallikreins 10, 11, and 14 in breast cancer cells via a membrane bound androgen receptor

The regulation of gene expression by steroid hormones plays an important role in the normal development and function of many organs, as well as in the pathogenesis of endocrine-related cancers, especially breast cancer. However, clinical data suggest that combined testosterone and estrogen treatments on post-menopausal women increase the risk of breast cancer. Experiments have shown that many, if not all kallikreins are under steroid hormone regulation in breast cancer cell lines. Their implication as prognostic and diagnostic markers has also been well-documented. Thus, we investigated the effect of combined hormone stimulation with androgens and 17beta-estradiol on the ductal caricinoma cell line BT474. This cell line has been shown to be sensitive to both, androgens (secreting PSA) and estrogens (secreting a number of kallikreins including KLK10, 11, and KLK14). We found that PSA expression was downregulated upon combined hormone stimulation, confirming reports that estrogen can antagonize and block the activity of the androgen receptor. Upon analysis of estrogen-sensitive kallikreins 10, 11, and 14, all showed to be synergistically enhanced in their expression three- to fourfold, upon joint hormone treatment versus individual hormone stimulation. The enhancement is dependent upon the action of androgens as treatment with the androgen receptor antagonist cyproterone actetate normalized the expression of KLK10, 11, and KLK14 to estrogen-stimulation levels. The synergistic effects between estrogens and androgens on estrogen-sensitive genes may have implications on the role of the kallikreins in associated risk of breast cancer and progression.

PrLZ is expressed in normal prostate development and in human prostate cancer progression

PURPOSE

We previously reported the isolation and characterization of PrLZ, a novel prostate-specific and androgen-responsive gene of the tumor protein D52 family at chromosome 8q21.1. PrLZ is the only known gene in this locus with prostate specificity. Expression level of PrLZ was elevated specifically in cancer cells, suggesting its association with malignancy.

EXPERIMENTAL DESIGN

To define its biological function in the morphogenesis, development, and functional maturation of the prostate gland and to gain further insight into its role in prostate cancer, we examined PrLZ expression in prostate specimens during early embryonic development and in adult tissue.

RESULTS

PrLZ first appears in the nuclei of the prostate epithelia at 16 weeks of gestation before its distribution in the cytoplasm at later ages. Its expression peaks at 24 years of age, declines at 31 years of age, and maintains a minimal level in later age. On prostate cancer development, PrLZ expression is reactivated, and its expression increases from primary localized tumor to bone metastasis. Overexpression of PrLZ in prostate cancer cells accelerates their growth in vitro and tumor formation in vivo.

CONCLUSION

This work identifies PrLZ as a marker for prostate cancer progression and metastasis, and its pattern of expression is suggestive of a proto-oncogene.

Molecular cloning and preliminary analysis of the human alpha-methylacyl-CoA racemase promoter

Alpha-methylacyl-CoA racemase (AMACR) is an enzyme involved in beta-oxidation of branched-chain fatty acids and bile acid intermediates. Recent works have revealed that AMACR is overexpressed in prostate cancer and functionally important for the growth of prostate cancer cells. Despite the recent interest in AMACR as a diagnostic marker for prostate cancer, little is known about the transcriptional regulation of AMACR in prostate cancer. To elucidate the regulation of the AMACR gene, a 2.3-kb fragment of its 5' flanking region was cloned into pGL3-Basic, then using tansfection and Dual-luciferase reporter assay, a preliminary analysis on promoter activity and function of this 2.3-kb sequence was carried out. This 2.3-kb fragment represented promoter activity that consistent with the expression level in LNCaP and PC-3 cells respectively. Transfection experiments of 5'-deletion mutants into LNCaP cells revealed a positive-regulatory region located between nucleotides -423 and -93 that may be responsible for AMACR transactivation in LNCaP cells. Cotransfection experiments revealed that promoter activity of this 2.3-kb sequence was down-regulated by C/EBPalpha, p53, NF-kappaB p50. And data from luciferase-based reporter assays suggest that the promoter function of AMACR is independent of androgen receptor-mediated signaling.

Androgen receptor targets NFkappaB and TSP1 to suppress prostate tumor growth in vivo

The androgen role in the maintenance of prostate epithelium is subject to conflicting opinions. While androgen ablation drives the regression of normal and cancerous prostate, testosterone may cause both proliferation and apoptosis. Several investigators note decreased proliferation and stronger response to chemotherapy of the prostate cancer cells stably expressing androgen receptor (AR), however no mechanistic explanation was offered. In this paper we demonstrate in vivo anti-tumor effect of the AR on prostate cancer growth and identify its molecular mediators. We analyzed the effect of AR on the tumorigenicity of prostate cancer cells. Unexpectedly, the AR-expressing cells formed tumors in male mice at a much lower rate than the AR-negative controls. Moreover, the AR-expressing tumors showed decreased vascularity and massive apoptosis. AR expression lowered the angiogenic potential of cancer cells, by increasing secretion of an anti-angiogenic protein, thrombospondin-1. AR activation caused a decrease in RelA, a subunit of the pro-survival transcription factor NFkappaB, reduced its nuclear localization and transcriptional activity. This, in turn, diminished the expression of its anti-apoptotic targets, Bcl-2 and IL-6. Increased apoptosis within AR-expressing tumors was likely due to the NFkappaB suppression, since it was restricted to the cells lacking nuclear (active) NFkappaB. Thus we for the first time identified combined decrease of NFkappaB and increased TSP1 as molecular events underlying the AR anti-tumor activity in vivo. Our data indicate that intermittent androgen ablation is preferable to continuous withdrawal, a standard treatment for early-stage prostate cancer. (c) 2007 Wiley-Liss, Inc.

New insights into the functional mechanisms and clinical applications of the kallikrein-related peptidase family

The Kallikrein-related peptidase (KLK) family consists of fifteen conserved serine proteases that form the largest contiguous cluster of proteases in the human genome. While primarily recognized for their clinical utilities as potential disease biomarkers, new compelling evidence suggests that this family plays a significant role in various physiological processes, including skin desquamation, semen liquefaction, neural plasticity, and body fluid homeostasis. KLK activation is believed to be mediated through highly organized proteolytic cascades, regulated through a series of feedback loops, inhibitors, auto-degradation and internal cleavages. Gene expression is mainly hormone-dependent, even though transcriptional epigenetic regulation has also been reported. These regulatory mechanisms are integrated with various signaling pathways to mediate multiple functions. Dysregulation of these pathways has been implicated in a large number of neoplastic and non-neoplastic pathological conditions. This review highlights our current knowledge of structural/phylogenetic features, functional role and regulatory/signaling mechanisms of this important family of enzymes.

Phosphoinositide 3-kinase-independent non-genomic signals transit from the androgen receptor to Akt1 in membrane raft microdomains

The serine-threonine kinase, Akt1/protein kinase Balpha is an important mediator of growth, survival, and metabolic signaling. Recent studies have implicated cholesterol-rich, lipid raft microdomains in survival signals mediated by Akt1. Here we address the role of lipid raft membranes as a potential site of intersection of androgenic and Akt1 signaling. A subpopulation of androgen receptor (AR) was found to localize to a lipid raft subcellular compartment in LNCaP prostate cancer cells. Endogenous AR interacted with endogenous Akt1 preferentially in lipid raft fractions and androgen substantially enhanced the interaction between the two proteins. The association of AR with Akt1 was inhibited by the anti-androgen, bicalutamide, but was not affected by inhibition of phosphoinositide 3-kinase (PI3K). Androgen promoted endogenous Akt1 activity in lipid raft fractions, in a PI3K-independent manner, within 10 min of treatment. Fusion of a lipid raft targeting sequence to AR enhanced localization of the receptor to rafts, and stimulated Akt1 activity in response to androgen, while reducing the cells' dependence on constitutive signaling through PI3K for cell survival. These findings suggest that signals channeled through AR and Akt1 intersect by a mechanism involving formation within lipid raft membranes of an androgen-responsive, extranuclear AR/Akt1 complex. Our results indicate that cholesterol-rich membrane microdomains play a role in transmitting non-genomic signals involving androgen and the Akt pathway in prostate cancer cells.

NF-κB2 processing and p52 nuclear accumulation after androgenic stimulation of LNCaP prostate cancer cells

Several reports suggest that androgen signalling interferes with canonical RelA-p50 activity in androgen-sensitive cells. Whether this also occurs with non-canonical NF-kappaB subunits has not been studied. Here we report that androgenic stimulation of LNCaP cells with the androgen analogue R1881 appears to positively regulate the non-canonical NF-kappaB pathway as p52 accumulates both in the cytoplasm and nucleus after 48-72 h of stimulation. In contrast to TNF-alpha stimulation, androgen stimulation fails to induce RelB expression and is absent from nucleus of R1881-treated LNCaP cells. Electromobility shift assays reveal a time-dependent change in the nature of NF-kappaB complexes actively bound to DNA after 72 h of androgenic stimulation concomitant with the appearance of p52-containing complexes. Co-immunoprecipitation studies indicate that newly produced p52 can exist as a heterodimer with RelA or p50, but may be mainly present as a homodimer. RNAi experiments targeting IKK-alpha and IKK-beta show that the R1881-induced nuclear accumulation of p52 is IKK-alpha-dependent. These results point to a novel mechanism by which androgens regulate NF-kappaB and provide a rationale for further studies into the biological significance of non-canonical NF-kappaB signalling in prostate cancer.

Histone acetyltransferase HBO1 inhibits NF-kappaB activity by coactivator sequestration

The MYST acetyltransferase HBO1 is implicated in the regulation of DNA replication and activities of transcription factors such as the androgen receptor. Since the androgen receptor and NF-kappaB transcription factors crossmodulate their transcriptional activity, we investigated whether HBO1 regulates NF-kappaB signaling. Here, we report that in 293T cells HBO1 reduced dose-dependently NF-kappaB activity stimulated by TNFalpha, or by overexpressing p65/RelA, RelB, or cRel. Mutational analysis showed that the N-terminal serine-rich region of HBO1 but not the acetyltransferase function was required for inhibition. Electrophoretic mobility-shift assays demonstrated that HBO1 was neither perturbing the formation of p65/RelA DNA complexes nor binding itself to the kappaB consensus sequence or to p65/RelA, suggesting that HBO1 reduced NF-kappaB activity by squelching a cofactor. These data establish a novel function for HBO1 showing that it reduced NF-kappaB activity by sequestrating an essential coactivator from the NF-kappaB transcriptional complex.

Unraveling androgen receptor interactomes by an array-based method: discovery of proto-oncoprotein c-Rel as a negative regulator of androgen receptor

The androgen receptor (AR) plays a key role in the development and function of male reproductive organs. Using a high-throughput transcription factor-transcription factor (TF-TF) interaction array method, we captured the AR interactomes in androgen-responsive LNCaP cells. Several known and unknown partners of AR, including AP-2, Pax 3/5 (BSAP), c-Rel, RREB-1, LIII BP, and NPAS2 were identified. We investigated one unreported AR-associated transcription factor, the proto-oncoprotein c-Rel, in detail. C-Rel belongs to the NF-kB/Rel families and is persistently active in a number of diseases, including cancer. The presence of c-Rel transcript, protein, and its in vitro and in vivo association with AR was determined. Co-localization of c-Rel with AR both in cytoplasm and nucleus was confirmed by indirect immunofluorescence analysis. Chromatin immunoprecipitation data indicated that c-Rel, like AR, is a part of the nucleoprotein complex regulating the androgen-responsive prostate-specific antigen (PSA) promoter. Overexpression of c-Rel downregulated the promoter activity of both PSA and GRE4-TATA-Luc plasmids in LNCaP and COS cells. Analysis of AR and c-Rel protein levels indicated that the promoter downregulation was not due to reciprocal decrease in the amounts of AR or c-Rel. In summary, we have identified several new partners of AR by using the TF-TF array method and have provided the first evidence of a functional role for c-Rel in androgen-responsive human prostate cancer cells.

Post-Transcriptional Regulation of the Androgen Receptor by Mammalian Target of Rapamycin

Heparin-binding epidermal growth factor-like growth factor (HB-EGF), an ErbB1 ligand and prostate stromal growth factor, is an antagonist of androgen receptor (AR) function. In the LNCaP prostate cancer model, HB-EGF reduced AR protein levels and AR transactivation without affecting AR mRNA level or protein turnover. The signal to attenuate AR was mediated by the mammalian target of rapamycin, as shown by genetic and pharmacologic methods, and was independent of ErbB2/HER-2, extracellular signal-regulated kinase 1/2, and p38 mitogen-activated protein kinase pathways. Additional evidence suggests that AR protein levels are highly sensitive to regulation by cap-dependent mRNA translation. These findings reveal a novel mechanism for regulation of AR by a classic growth factor system and indicate that a rapamycin-sensitive post-transcriptional pathway can attenuate or possibly bypass AR-mediated signaling.

Nuclear Factor-κB Nuclear Localization Is Predictive of Biochemical Recurrence in Patients with Positive Margin Prostate Cancer

PURPOSE

Radical prostatectomy (RP) patients with positive surgical margins are at increased risk for recurrence, emphasizing the need for prognostic markers to stratify probable outcome for optimal patient management decisions. We tested the hypothesis that nuclear localization of nuclear factor (NF)-kappaB, a transcription factor involved in the regulation of cell growth, angiogenesis, invasion, and apoptosis, is associated with an increased risk of biochemical recurrence after RP.

EXPERIMENTAL DESIGN

Analyses addressed data from 42 patients (age range, 52-72 years; mean age, 63.7 years) who exhibited positive surgical margins after RP. Immunohistochemical analysis of NF-kappaB (p65) was performed on the positive margin tissue. A nuclear staining cutoff of >5% was considered positive. The relation between nuclear NF-kappaB expression and biochemical recurrence (prostate-specific antigen >0.3 ng/mL and rising) after RP was tested in univariate and multivariate Cox regression models.

RESULTS

Biochemical recurrence was recorded in 23 patients (54.8%; median follow-up, 3.2 years). Univariate Cox regression demonstrated a 4.9-fold (95% confidence interval, 1.5-16.7; P = 0.01) higher rate of recurrence in men with NF-kappaB > 5%. In the multivariate model, after controlling for primary (P = 0.004) and secondary (P = 0.7) Gleason patterns, lymph node (P = 0.06) and seminal vesicle invasion (P = 0.2), and preoperative prostate-specific antigen (P = 0.009), NF-kappaB > 5% was associated with a 6.2-fold higher risk of biochemical recurrence (95% confidence interval, 1.7-23.5; P = 0.007).

CONCLUSIONS

In univariate and multivariate analysis, NF-kappaB nuclear expression was strongly predictive of biochemical recurrence in patients with positive surgical margins after RP. We propose that nuclear NF-kappaB may serve as a useful independent molecular marker for stratifying patients at risk for recurrence.

Human Tissue Kallikreins: Physiologic Roles and Applications in Cancer

Tissue kallikreins are members of the S1 family (clan SA) of trypsin-like serine proteases and are present in at least six mammalian orders. In humans, tissue kallikreins (hK) are encoded by 15 structurally similar, steroid hormone–regulated genes (KLK) that colocalize to chromosome 19q13.4, representing the largest cluster of contiguous protease genes in the entire genome. hKs are widely expressed in diverse tissues and implicated in a range of normal physiologic functions from the regulation of blood pressure and electrolyte balance to tissue remodeling, prohormone processing, neural plasticity, and skin desquamation. Several lines of evidence suggest that hKs may be involved in cascade reactions and that cross-talk may exist with proteases of other catalytic classes. The proteolytic activity of hKs is regulated in several ways including zymogen activation, endogenous inhibitors, such as serpins, and via internal (auto)cleavage leading to inactivation. Dysregulated hK expression is associated with multiple diseases, primarily cancer. As a consequence, many kallikreins, in addition to hK3/PSA, have been identified as promising diagnostic and/or prognostic biomarkers for several cancer types, including ovarian, breast, and prostate. Recent data also suggest that hKs may be causally involved in carcinogenesis, particularly in tumor metastasis and invasion, and, thus, may represent attractive drug targets to consider for therapeutic intervention.