p38MAPK activation is involved in androgen-independent proliferation of human prostate cancer cells by regulating IL-6 secretion

Human antigen R is positively associated with malignant aggressiveness via upregulation of cell proliferation, migration, and vascular endothelial growth factors and cyclooxygenase-2 in prostate cancer

Limited information is available on the pathologic significance of human antigen R (HuR) in prostate cancer (PCa). The main aim of this study was to clarify the relationship between HuR expression and malignant aggressiveness, outcome, and expression of cancer-related molecules in PCa. In vitro proliferation, colony formation, and migration assays were performed on LNCaP and PC-3 cells. HuR expression was knocked down (KD) using small interfering RNA. The relationships between HuR expression and the expression of vascular endothelial growth factors (VEGFs), cyclooxygenase (COX)-2, and heme oxygenase (HO)-1 were investigated in PCa cell lines using Western blotting. On KD of HuR, cell proliferation and migration were suppressed in both LNCaP and PC-3 cells, whereas expression of VEGF-A to -D and COX-2 was suppressed in PC-3 but not in LNCaP cells. In addition, expression of these cancer-related factors was analyzed in 182 hormone-naïve PCa and 23 castration-resistant prostate cancer (CRPC) human tissues in vivo. Cytoplasmic (C)-HuR expression was significantly higher in CRPC > hormone-naïve PCa > nontumoral cells. C-HuR expression was positively associated with Gleason score, T stage, and metastasis, and it was considered to be a useful predictor of biochemical recurrence after radical prostatectomy. C-HuR expression was correlated with COX-2 expression in hormone-naïve PCa, and with the expression of VEGF-A, VEGF-C, and COX-2 in CRPC tissues. Our results demonstrated that HuR plays important roles in determining malignant aggressiveness and outcome in PCa, especially in androgen-independent PCa cells, via the regulation of cell proliferation, migration, and expression of VEGF-A, -C, and COX-2.

Inhibition of FOXC2 restores epithelial phenotype and drug sensitivity in prostate cancer cells with stem-cell properties

Advanced prostate adenocarcinomas enriched in stem-cell features, as well as variant androgen receptor (AR)-negative neuroendocrine (NE)/small-cell prostate cancers are difficult to treat, and account for up to 30% of prostate cancer-related deaths every year. While existing therapies for prostate cancer such as androgen deprivation therapy (ADT), destroy the bulk of the AR-positive cells within the tumor, eradicating this population eventually leads to castration-resistance, owing to the continued survival of AR^-/lo stem-like cells. In this study, we identified a critical nexus between p38MAPK signaling, and the transcription factor Forkhead Box Protein C2 (FOXC2) known to promote cancer stem-cells and metastasis. We demonstrate that prostate cancer cells that are insensitive to ADT, as well as high-grade/NE prostate tumors, are characterized by elevated FOXC2, and that targeting FOXC2 using a well-tolerated p38 inhibitor restores epithelial attributes and ADT-sensitivity, and reduces the shedding of circulating tumor cells in vivo with significant shrinkage in the tumor mass. This study thus specifies a tangible mechanism to target the AR^-/lo population of prostate cancer cells with stem-cell properties.

The changing natural history of metastatic prostate cancer

Since 1941, the understanding of prostate cancer pathogenesis and therapy has undergone a significant transformation. Rigorous translational research has identified multiple mechanisms underlying castration resistance, the fatal clinical state of the disease. Therapeutic approaches targeting these mechanisms in metastatic castration-resistant prostate cancer have now been clinically validated in the clinic including high-potency androgen signaling inhibition, novel cytotoxic chemotherapy, and bone-targeted therapies. Despite these advances, cure remains an elusive goal. The natural history of metastatic prostate cancer has evolved particularly in the last 2 decades in step with improved management of age-associated comorbidities, improved imaging, and the expansion of novel therapies, thus providing new opportunities and challenges. It is also important to note that the advent of prostate-specific antigen testing caused a stage shift in the disease spectrum, thus leading to earlier interventions and potentially positively impacting survival. The optimal sequencing and combinations of available therapies, predictive biomarkers, and better understanding of mechanisms of resistance remain high priority. Further refinement of the clinical niche for novel therapies in hormone-sensitive and castration-resistant disease through rationally designed clinical trials incorporating molecular, clinical, and imaging biomarkers and quality-of-life correlatives is of paramount importance.

miTALOS: analyzing the tissue-specific regulation of signaling pathways by human and mouse microRNAs

MicroRNAs (miRNAs) are an important class of post-transcriptional regulators of gene expression that are involved in various cellular and phenotypic processes. A number of studies have shown that miRNA expression is induced by signaling pathways. Moreover, miRNAs emerge as regulators of signaling pathways. Here, we present the miTALOS web resource, which provides insight into miRNA-mediated regulation of signaling pathways. As a novel feature, miTALOS considers the tissue-specific expression signatures of miRNAs and target transcripts to improve the analysis of miRNA regulation in biological pathways. MiTALOS identifies potential pathway regulation by (i) an enrichment analysis of miRNA targets genes and (ii) by using a proximity score to evaluate the functional role of miRNAs in biological pathways by their network proximity. Moreover, miTALOS integrates five different miRNA target prediction tools and two different signaling pathway resources (KEGG and NCI). A graphical visualization of miRNA targets in both KEGG and NCI PID signaling pathways is provided to illustrate their respective pathway context. We perform a functional analysis on prostate cancer-related miRNAs and are able to infer a model of miRNA-mediated regulation on tumor proliferation, mobility and anti-apoptotic behavior. miTALOS provides novel features that accomplish a substantial support to systematically infer regulation of signaling pathways mediated by miRNAs. The web-server is freely accessible at http://hmgu.de/cmb/mitalos.

Analyzing serum-stimulated prostate cancer cell lines after low-fat, high-fiber diet and exercise intervention

Serum from men undergoing a low-fat, high-fiber diet and exercise intervention has previously been shown to decrease growth and increase apoptosis in serum-stimulated, androgen-dependent LNCaP cells associated with a reduction in serum IGF-I. Here we sought to determine the underlying mechanisms for these anticancer effects. Again, the intervention slowed growth and increased apoptosis in LNCaP cells; responses that were eliminated when IGF-I was added back to the post-intervention samples. The p53 protein content was increased and NFκB activation reduced in the post serum-stimulated LNCaP cells. Similar results were observed when the IGF-I receptor was blocked in the pre-intervention serum. In androgen-independent PC-3 cells, growth was reduced while none of the other factors were changed by the intervention. We conclude that diet and exercise intervention might help prevent clinical PCa as well as aid in the treatment of PCa during the early stages of development.

Benign prostatic hyperplasia: does lifestyle play a role?

Benign prostatic hyperplasia (BPH) is a very common condition in older men, affecting up to 80% of men aged >or= 80 years in the United States. It typically leads to lower urinary tract symptoms, which often require medical management. The exact cause of BPH is unknown, and the only 2 established factors associated with BPH are age and the presence of androgens. Although the presence of testosterone is required for the development of BPH, testosterone is not thought to be the underlying factor causing BPH because testosterone levels decrease in older men. Recent studies have reported that BPH is associated with elevations in plasma estradiol/testosterone ratio, insulin, and insulin-like growth factor-I. Daily aerobic exercise can reduce all of these plasma factors, particularly when combined with a low-fat, high-fiber diet consisting of whole grains, fruits, and vegetables. In cell culture studies, this type of lifestyle regimen has recently been shown to reduce the growth of serum-stimulated prostate epithelial cells and the growth of androgen-dependent prostate cancer cell lines.

Hypoxia-associated p38 mitogen-activated protein kinase-mediated androgen receptor activation and increased HIF-1alpha levels contribute to emergence of an aggressive phenotype in prostate cancer

Androgen receptor (AR) signaling is involved in the development and progression of prostate cancer. Tumor microvasculature contributes to continual exposure of prostate cancer cells to hypoxia-reoxygenation, however, the role of hypoxia-reoxygenation in prostate cancer progression and modulation of AR signaling is not understood. In this study, we evaluated the effects of hypoxia-reoxygenation in LNCaP cells, a line of hormone responsive human prostate cancer cells. Our results demonstrate that hypoxia-reoxygenation resulted in increased survival, higher clonogenicity and enhanced invasiveness of these cells. Moreover, hypoxia-reoxygenation was associated with an increased AR activity independent of androgens as well as increased hypoxia inducible factor (HIF-1alpha) levels and activity. We also observed that the activation of p38 mitogen-activated protein (MAP) kinase pathway was an early response to hypoxia, and inhibition of p38 MAP kinase pathway by variety of approaches abolished hypoxia-reoxygenation induced increased AR activity as well as increased survival, clonogenicity and invasiveness. These results demonstrate a critical role for hypoxia-induced p38 MAP kinase pathway in androgen-independent AR activation in prostate cancer cells, and suggest that hypoxia-reoxygenation may select for aggressive androgen-independent prostate cancer phenotype.

Riboflavin inhibits IL-6 expression and p38 activation in islet cells

Riboflavin is a water-soluble vitamin that reduces the production of proinflammatory mediators and oxygen radicals. Because islet beta-cells are very sensitive to oxidative stress and to cytokines, we investigated the possible cytoprotective effects of riboflavin on insulinoma NIT-1 cells and on isolated rodent islets. NIT-1 cells and islets cultured in the presence or absence of 10 microM riboflavin were studied at baseline and after exposure to cytokines (TNF-alpha, IL-1beta, INF-gamma). Riboflavin treatment did not affect islet cell viability as assessed by flow cytometry for caspases activation. However, riboflavin prevented the cytokine-induced increase in IL-6 mRNA expression and p38 phosphorylation analyzed by real-time PCR and immunoassay, respectively. In summary, nontoxic doses of riboflavin prevent cytokines-induced p38 phosphorylation and IL-6 upregulation in islet cells. This observation, together with the safety profile of riboflavin in the clinical setting, makes it an appealing agent for islet cytoprotection in islet transplantation protocols.

Tumor necrosis factor receptor 1 induces interleukin-6 upregulation through NF-kappaB in a rat neuropathic pain model

Peripheral nerve injury resulting in neuropathic pain induces the upregulation of interleukin (IL)-6 and tumor necrosis factor-alpha, which binds to tumor necrosis factor receptor 1 (TNFR1) and induces NF-kappaB and p38 MAPK activation in the spinal cord and dorsal root ganglia (DRG). We here investigated whether TNFR1 regulates IL-6 expression through NF-kappaB or p38 MAPK activations in the spinal cord and DRG in rats with chronic constriction injury (CCI) of the sciatic nerve. Intrathecal treatment with a TNFR1 antisense oligonucleotide (ASO) significantly inhibited CCI-elevated IKKs phosphorylation, IkB-alpha degradation, the nuclear translocation, phosphorylation, and DNA-binding activity of NF-kappaB, p38 MAPK activation, and IL-6 mRNA and protein expression in the spinal cord and DRG. Interestingly, CCI remarkably elevated IKKalpha and p65 phosphorylations in the spinal cord rather than in the DRG. In addition, NF-kappaB decoy, but not p38 MAPK inhibitor, SB203580 reduced CCI-elevated IL-6 expression in the spinal cord and DRG. Therefore, these data suggest that TNFR1 induces IL-6 upregulation and neuropathic pain through NF-kappaB, but not p38 MAPK activation in the spinal cord and DRG and that the NF-kappaB/IL-6 pathways in the DRG may be less dependent on TNFR1 than the spinal cord pathway.

MAP kinase pathways and calcitonin influence CD44 alternate isoform expression in prostate cancer cells

Background

Dysregulated expression and splicing of cell adhesion marker CD44 is found in many types of cancer. In prostate cancer (PC) specifically, the standard isoform (CD44s) has been found to be downregulated compared with benign tissue whereas predominant variant isoform CD44v7-10 is upregulated. Mitogen-activated protein kinase pathways and paracrine calcitonin are two common factors linked to dysregulated expression and splicing of CD44 in cancer. Calcitonin has been found to increase proliferation and invasion in PC acting through the protein kinase A pathway.

Methods

In androgen-independent PC with known high CD44v7-10 expression, CD44 total and CD44v7-10 RNA or protein were assessed in response to exogenous and endogenous calcitonin and to inhibitors of protein kinase A, MEK, JNK, or p38 kinase. Benign cells and calcitonin receptor-negative PC cells were also tested.

Results

MEK or p38 but not JNK reduced CD44 total RNA by 40%–65% in cancer and benign cells. Inhibition of protein kinase A reduced CD44 total and v7-10 protein expression. In calcitonin receptor-positive cells only, calcitonin increased CD44 variant RNA and protein by 3 h and persisting to 48 h, apparently dependent on an uninhibited p38 pathway. Cells with constitutive CT expression showed an increase in CD44v7-10 mRNA but a decrease in CD44 total RNA.

Conclusion

The MEK pathway increases CD44 RNA, while calcitonin, acting through the protein kinase A and p38 pathway, facilitates variant splicing. These findings could be used in the formulation of therapeutic methods for PC targeting CD44 alternate splicing.

A cross-talk between the androgen receptor and the epidermal growth factor receptor leads to p38MAPK-dependent activation of mTOR and cyclinD1 expression in prostate and lung cancer cells

In androgen sensitive LNCaP prostate cancer cells, the proliferation induced by the epidermal growth factor (EGF) involves a cross-talk between the EGF receptor (EGFR) and the androgen receptor (AR). In lung cancer the role of the EGF-EGFR transduction pathway has been documented, whereas androgen activity has received less attention. Here we demonstrate that in LNCaP and A549 non-small cell lung cancer (NSCLC), AR and EGFR are required for either 5alpha-dihydrotestosterone (DHT) or EGF-stimulated cell growth. Only EGF activated ERK signaling and up-regulated early gene expression, while DHT triggered the expression of classical AR-responsive genes with the exception of the EGF-induced PSA transcript in A549 cells. DHT and EGF up-regulated cyclinD1 (CD1) at both mRNA and protein levels in A549 cells, while in LNCaP cells each mitogen increased only CD1 protein expression. In both cell contexts, CD1 up-regulation was prevented by selective inhibitors as well as by knock-down of either AR or EGFR and also inhibiting p38MAPK and the mammalian target of rapamycin (mTOR) pathways. Interestingly, p38MAPK and mTOR repression prevented the activation of the mTOR target ribosomal p70S6 kinase induced by DHT and EGF, indicating that p38MAPK acts as an upstream mTOR regulator. In addition, the proliferative effects promoted by both DHT and EGF in LNCaP and A549 cancer cells were no longer observed blocking either p38MAPK or mTOR activity. Hence, our data suggest that p38MAPK-dependent activation of the mTOR/CD1 pathway may represent a mechanism through which AR and EGFR cross-talk contributes to prostate and lung cancer progression.

Androgen signaling and its interactions with other signaling pathways in prostate cancer

Prostate cancer is the most frequently diagnosed non-skin cancer and the third leading cause of cancer mortality in men. In the initial stages, prostate cancer is dependent on androgens for growth, which is the basis for androgen ablation therapy. However, in most cases, prostate cancer progresses to a hormone refractory phenotype for which there is no effective therapy available at present. The androgen receptor (AR) is required for prostate cancer growth in all stages, including the relapsed, "androgen-independent" tumors in the presence of very low levels of androgens. This review focuses on AR function and AR-target genes and summarizes the major signaling pathways implicated in prostate cancer progression, their crosstalk with each other and with AR signaling. This complex network of interactions is providing a deeper insight into prostate carcinogenesis and may form the basis for novel diagnostic and therapeutic strategies.

Apoptosis induced by capsaicin in prostate PC-3 cells involves ceramide accumulation, neutral sphingomyelinase, and JNK activation

Numerous studies have recently focused on the anticarcinogenic, antimutagenic, or chemopreventive activities of the main pungent component of red pepper, capsaicin (N-vanillyl-8-methyl-1-nonenamide). We have previously shown that, in the androgen-independent prostate cancer PC-3 cells, capsaicin inhibits cell growth and induces apoptosis through reactive oxygen species (ROS) generation [Apoptosis 11 (2006) 89-99]. In the present study, we investigated the signaling pathways involved in the antiproliferative effect of capsaicin. Here, we report that capsaicin apoptotic effect was mediated by ceramide generation which occurred by sphingomyelin hydrolysis. Using siRNA, we demonstrated that N-SMase expression is required for the effect of capsaicin on prostate cell viability. We then investigated the role of MAP kinase cascades, extracellular signal-regulated protein kinase (ERK), c-Jun N-terminal kinase (JNK), and p38 MAPK, in the antiproliferative effect of capsaicin, and we confirmed that capsaicin could activate ERK and JNK but not p38 MAPK. Pharmacological inhibition of JNK kinase, as well as inhibition of ROS by the reducing agent N-acetylcysteine, prevented ceramide accumulation and capsaicin-induced cell death. However, inhibition of ceramide accumulation by the SMase inhibitor D609 did not modify JNK activation. These data reveal JNK as an upstream regulator of ceramide production. Capsaicin-promoted activation of ERK was prevented with all the inhibitors tested. We conclude that capsaicin induces apoptosis in PC-3 cells via ROS generation, JNK activation, ceramide accumulation, and second, ERK activation.

Attenuation of p38 MAPK activity upon contact inhibition in fibroblasts

The molecular events, which govern growth control upon contact inhibition have not yet been clearly defined. Previous work has indicated that there is an increase in the expression of mitogen-activated protein kinase phosphatases (MKPs) upon the attainment of contact inhibition in normal fibroblasts, concurrently with a decrease in ERK activity. To investigate the potential role of p38 and JNK in the transition to a contact-inhibited state, normal human fibroblasts (BJ) were grown to subconfluent and confluent densities. The total levels and phosphorylation states of p38 and JNK were assayed, and were compared to protein levels seen in HT-1080 fibrosarcoma cells, which lack contact-inhibited growth control. Activation of JNK was not apparent in these cells, though p38 was found to be active in proliferating cells, but attenuated in contact-inhibited cultures. Such fluctuations in p38 activity were not seen in cultures of fibrosarcoma cells of increasing density. This alteration in p38 activity was also reflected by attenuated activation of the downstream transcription factor ATF-2 upon contact inhibition. Overexpression of MKP-1 in fibrosarcoma cells and fibroblasts reduced proliferation, while expression of a phosphatase-resistant p38 protein (p38(N316)) enhanced proliferation of normal fibroblasts. Taken together, these results suggest the involvement of negative regulation of p38 in contact-inhibited growth control.

Dextran sulfate sodium enhances interleukin-1 beta release via activation of p38 MAPK and ERK1/2 pathways in murine peritoneal macrophages

Interleukin (IL)-1 beta is a pro-inflammatory cytokine that has been shown to play a pivotal role in the onset of inflammatory bowel disease (IBD), however, the molecular mechanisms underlying the production of IL-1 beta in IBD are not fully understood. We investigated dextran sulfate sodium (DSS)-induced IL-1 beta production and caspase-1 activities in murine peritoneal macrophages (pM phi). Further, the activation status of p38 mitogen-activated protein kinase (MAPK), extracellular signal-regulated kinase 1/2 (ERK1/2), and c-Jun NH(2)-terminal kinase (JNK1/2), as well as their upstream target kinases, were examined by Western blotting. In addition, mRNA expression was assessed by RT-PCR and CXC chemokine ligand 16 (CXCL16) protein was detected by immunocytochemistry. DSS-treated pM phi released IL-1 beta protein in a time-dependent manner without affecting mRNA levels during 3-24 h, and caspase-1 activity peaked at 5 min (29-fold). IL-1 beta release and caspase-1 activity induced by DSS were significantly inhibited by a MAPK kinase 1/2 inhibitor, a p38 MAPK inhibitor, and NAC, however, not by JNK1/2 or a protein kinase C inhibitor. In addition, DSS strikingly induced the phosphorylation of p38 MAPK and ERK1/2 within 2 and 10 min, respectively. DSS also induced intracellular generation of reactive oxygen species (ROS). Pre-treatment with anti-CXCL16 for 24 h, but not anti-scavenger receptor-A, anti-CD36, or anti-CD68 antibodies, significantly suppressed DSS-induced IL-1 beta production. Our results suggest that DSS triggers the release of IL-1 beta protein from murine pM phi at a post-translational level through binding with CXCL16, ROS generation, and resultant activation of both p38 MAPK and ERK1/2 pathways, and finally caspase-1 activation.