Protein kinase Cdelta signaling downstream of the EGF receptor mediates migration and invasiveness of prostate cancer cells

Multiple subcellular localizations and functions of protein kinase Cδ in liver cancer

Protein kinase Cδ (PKCδ) is a member of the PKC family, and its implications have been reported in various biological and cancerous processes, including cell proliferation, cell death, tumor suppression, and tumor progression. In liver cancer cells, accumulating reports show the bi-functional regulation of PKCδ in cell death and survival. PKCδ function is defined by various factors, such as phosphorylation, catalytic domain cleavage, and subcellular localization. PKCδ has multiple intracellular distribution patterns, ranging from the cytosol to the nucleus. We recently found a unique extracellular localization of PKCδ in liver cancer and its growth factor-like function in liver cancer cells. In this review, we first discuss the structural features of PKCδ and then focus on the functional diversity of PKCδ based on its subcellular localization, such as the nucleus, cell surface, and extracellular space. These findings improve our knowledge of PKCδ involvement in the progression of liver cancer.

Co-administration of tyrosine kinase inhibitors with rottlerin in metastatic prostate cancer cells

After prostatectomy due to prostate carcinoma, patients often develop metastases. Although prostate cancer is susceptible to hormonal manipulation, many patients become castration-resistant. Therefore, new therapies are the focus of investigations. We analyzed the effect of the tyrosine kinase inhibitors (TKIs), sorafenib and sunitinib, in combination with rottlerin, a PKCδ inhibitor, on metastatic mechanisms in prostate carcinoma cells. LNCaP and PC-3 prostate carcinoma cells were treated with sorafenib or sunitinib alone at various concentrations (1-20 µM) or in combination with rottlerin (10 µM) for 24 h. Then, cell toxicity (MTT test) and cell proliferation (BrdU incorporation assay) were quantified. The study demonstrated a dose-dependent inhibitory effect of sorafenib and sunitinib on PC-3 and LNCaP cell activity and proliferation. Both agents showed significantly stronger cytotoxic effects in LNCaP cells. At the highest concentrations, sorafenib and sunitinib inhibited the viability of LNCaP cells up to 2 % and 31 %, respectively, and the viability of PC-3 cell line up to 20 % and 43 %, respectively. The proliferation of both cell lines was significantly stronger inhibited by sorafenib than by sunitinib. In LNCaP cells, sorafenib and sunitinib at the highest concentrations inhibited cell proliferation up to 46 % and 49 %, respectively, and the proliferation of PC-3 line up to 40 % and 47 %, respectively. Rottlerin reduced the viability and proliferation of PC3 cells to 81 % and 42 %, whereas the viability and proliferation of LNCaP cells were reduced to 25 % and 57 %, respectively. Sorafenib and sunitinib at low concentrations partly neutralized the inhibitory effect of rottlerin on cell viability and proliferation. On the other hand, in PC-3 cells, rottlerin reduced the inhibitory effects of sorafenib and sunitinib at the highest concentrations on cell viability from 20 % to 30 % and from 43 % to 61 %, respectively. An additive effect on cell activity was observed after treating LNCaP cells with both sunitinib at high concentrations and rottlerin. This combination increased the cytotoxic effect from 31 % to 13 % at the highest sunitinib concentration. Our results showed that monotherapy with sorafenib was the most efficient in both PCa cell lines. A marginally additive effect of rottlerin was only observed in LNCaP cells treated with sunitinib at a high concentration. Sorafenib and sunitinib reduced cell migration in PC-3 cells to 10 % and 32 % of untreated cells, respectively. Co-treatment with sorafenib/sunitinib and rottlerin did not result in a significantly stronger anti-migratory effect than the treatment with each TKI alone. Given the strong cytotoxic effect of TKIs, especially sorafenib, on LNCaP cells, the results of the migration assay in this line were severely biased and not considered in the analysis. Unlike in other malignancies, combination therapy with TKI and rottlerin seems not beneficial in prostate cancer. More promising seems to be monotherapy with rottlerin, but further studies are needed to confirm this observation.

Rottlerin, BDNF, and the impairment of inhibitory avoidance memory

RATIONALE AND OBJECTIVE

As a eukaryotic elongation factor 2 kinase (eEF2K) inhibitor and a mitochondrial uncoupler, oncologists have extensively studied rottlerin. Neuroscientists, however, have accumulated scarce data on the role of rottlerin in affective and cognitive functions. Only two prior studies have, respectively, documented its antidepressant-like effect and how it impairs psychostimulant-supported memory. Whether or not rottlerin would affect aversive memory remains unknown. Hence, we sought to investigate the effects of rottlerin on aversive memory in the inhibitory avoidance (IA) task in mice.

MATERIALS AND METHODS

Male C57BL/6J mice were trained to acquire the IA task. Rottlerin (5 mg/kg, i.p. or 3 μg bilaterally in the hippocampus) or the vehicle was administered before footshock training (acquisition), after footshock training (consolidation), after the memory reactivation (reconsolidation), and before the test (retrieval) in the IA task.

RESULTS

Systemic and intrahippocampal rottlerin impaired the acquisition, consolidation, and retrieval of IA memory, without affecting the reconsolidation process. Rottlerin (5 mg/kg, i.p.) induced a fast-onset and long-lasting increase in the brain-derived neurotrophic factor (BDNF) protein levels in the mouse hippocampus. Systemic injection of 7,8-dihydroxyflavone (7,8-DHF, 30 mg/kg), a BDNF tropomyosin receptor kinase B (TrkB) agonist impaired IA memory consolidation, and treatment with K252a (5 μg/kg), a Trk receptor antagonist, reversed the suppressing effect of rottlerin on IA memory consolidation.

CONCLUSION

Rottlerin impairs IA memory consolidation through the enhancement of BDNF signaling in the mouse hippocampus. Excessive brain BDNF levels can be detrimental to cognitive function. Rottlerin is likely to affect the original memory-associated neuroplasticity. Thus, it can be combined with exposure therapy to facilitate the forgetting of maladaptive aversive memory, such as post-traumatic stress disorder (PTSD).

Missing Selectivity of Targeted 4β-Phorbol Prodrugs Expected to be Potential Chemotherapeutics

Targeting cytotoxic 4β-phorbol esters toward cancer tissue was attempted by conjugating a 4β-pborbol derivative with substrates for the proteases prostate-specific antigen (PSA) and prostate-specific membrane antigen (PSMA) expressed in cancer tissue. The hydrophilic peptide moiety was hypothesized to prevent penetration of the prodrugs into cells and prevent interaction with PKC. Cleavage of the peptide in cancer tumors was envisioned to release lipophilic cytotoxins, which subsequently penetrate into cancer cells. The 4β-phorbol esters were prepared from 4β-phorbol isolated from Croton tiglium seeds, while the peptides were prepared by solid-phase synthesis. Cellular assays revealed activation of PKC by the prodrugs and efficient killing of both peptidase positive as well as peptidase negative cells. Consequently no selectivity for enzyme expressing cells was found.

miR-26a regulates extracellular vesicle secretion from prostate cancer cells via targeting SHC4, PFDN4, and CHORDC1

Extracellular vesicles (EVs) are involved in intercellular communication during cancer progression; thus, elucidating the mechanism of EV secretion in cancer cells will contribute to the development of an EV-targeted cancer treatment. However, the biogenesis of EVs in cancer cells is not fully understood. MicroRNAs (miRNAs) regulate a variety of biological phenomena; thus, miRNAs could regulate EV secretion. Here, we performed high-throughput miRNA-based screening to identify the regulators of EV secretion using an ExoScreen assay. By using this method, we identified miR-26a involved in EV secretion from prostate cancer (PCa) cells. In addition, we found that SHC4, PFDN4, and CHORDC1 genes regulate EV secretion in PCa cells. Furthermore, the progression of the PCa cells suppressing these genes was inhibited in an in vivo study. Together, our findings suggest that miR-26a regulates EV secretion via targeting SHC4, PFDN4, and CHORDC1 in PCa cells, resulting in the suppression of PCa progression.

Differential role of PTEN in transforming growth factor β (TGF-β) effects on proliferation and migration in prostate cancer cells

BACKGROUND

Transforming growth factor-β (TGF-β) acts as a tumor suppressor in normal epithelial cells but as a tumor promoter in advanced prostate cancer cells. PI3-kinase pathway mediates TGF-β effects on prostate cancer cell migration and invasion. PTEN inhibits PI3-kinase pathway and is frequently mutated in prostate cancers. We investigated possible role(s) of PTEN in TGF-β effects on proliferation and migration in prostate cancer cells.

METHODS

Expression of PTEN mRNA and proteins were determined using RT-PCR and Western blotting in RWPE1 and DU145 cells. We also studied the role of PTEN in TGF-β effects on cell proliferation and migration in DU145 cells after transient silencing of endogenous PTEN. Conversely, we determined the role of PTEN in cell proliferation and migration after over-expression of PTEN in PC3 cells which lack endogenous PTEN.

RESULTS

TGF-β1 and TGF-β3 had no effect on PTEN mRNA levels but both isoforms increased PTEN protein levels in DU145 and RWPE1 cells indicating that PTEN may mediate TGF-β effects on cell proliferation. Knockdown of PTEN in DU145 cells resulted in significant increase in cell proliferation which was not affected by TGF-β isoforms. PTEN overexpression in PC3 cells inhibited cell proliferation. Knockdown of endogenous PTEN enhanced cell migration in DU145 cells, whereas PTEN overexpression reduced migration in PC3 cells and reduced phosphorylation of AKT in response to TGF-β.

CONCLUSION

We conclude that PTEN plays a role in inhibitory effects of TGF-β on cell proliferation whereas its absence may enhance TGF-β effects on activation of PI3-kinase pathway and cell migration.

Phosphorylation of E-cadherin at threonine 790 by protein kinase Cδ reduces β-catenin binding and suppresses the function of E-cadherin

Proper control of cell-cell adhesion is crucial for embryogenesis and tissue homeostasis. In this study, we show that protein kinase C (PKC)δ, a member of the novel PKC subfamily, localizes at cell-cell contacts of epithelial cells through its C2-like domain in an F-actin-dependent manner. Upon hepatocyte growth factor stimulation, PKCδ is phosphorylated and activated by Src, which then phosphorylates E-cadherin at Thr790. Phosphorylation of E-cadherin at Thr790 diminishes its interaction with β-catenin and impairs the homophilic interaction between the ectodomains of E-cadherin. The suppression of PKCδ by its dominant-negative mutants or specific short-hairpin RNA inhibits the disruption of cell-cell adhesions induced by hepatocyte growth factor. Elevated PKCδ expression in cancer cells is correlated with increased phosphorylation of E-cadherin at Thr790, reduced binding of E-cadherin to β-catenin, and poor homophilic interaction between E-cadherin. Analysis of surgical specimens confirmed that PKCδ is overexpressed in cervical cancer tissues, accompanied by increased phosphorylation of E-cadherin at Thr790. Together, our findings unveil a negative role for PKCδ in cell-cell adhesion through phosphorylation of E-cadherin.

Co-dependency of PKCδ and K-Ras: inverse association with cytotoxic drug sensitivity in KRAS mutant lung cancer

Recent studies suggest that the presence of a KRAS mutation may be insufficient for defining a clinically homogenous molecular group, as many KRAS mutant tumors lose reliance on K-Ras for survival. Identifying pathways that support K-Ras dependency may define clinically relevant KRAS sub-groups and lead to the identification of new drug targets. We have analyzed a panel of 17 KRAS mutant lung cancer cell lines classified as K-Ras dependent or independent, for co-dependency on PKCδ. We show that functional dependency on K-Ras and PKCδ co-segregate, and that dependency correlates with a more epithelial-like phenotype. Furthermore, we show that the pro-apoptotic and pro-tumorigenic functions of PKCδ also segregate based on K-Ras dependency, as K-Ras independent cells are more sensitive to topoisomerase inhibitors, and depletion of PKCδ in this sub-group suppresses apoptosis through increased activation of ERK. In contrast, K-Ras dependent lung cancer cells are largely insensitive to topoisomerase inhibitors, and depletion of PKCδ can increase apoptosis and decrease activation of ERK in this sub-group. We have previously shown that nuclear translocation of PKCδ is necessary and sufficient for pro-apoptotic signaling. Our current studies show that K-Ras dependent cells are refractive to PKCδ driven apoptosis. Analysis of this sub-group showed increased PKCδ expression and an increase in the nuclear:cytoplasmic ratio of PKCδ. In addition, targeting PKCδ to the nucleus induces apoptosis in K-Ras independent, but not K-Ras dependent NSCLC cells. Our studies provide tools for identification of the subset of patients with KRAS mutant tumors most amenable to targeting of the K-Ras pathway, and identify PKCδ as a potential target in this tumor population. These sub-groups are likely to be of clinical relevance, as high PKCδ expression correlates with increased overall survival and a more epithelial tumor phenotype in patients with KRAS mutant lung adenocarcinomas.

PKCδ regulates integrin αVβ3 expression and transformed growth of K-ras dependent lung cancer cells

We have previously shown that Protein Kinase C delta (PKCδ) functions as a tumor promoter in non-small cell lung cancer (NSCLC), specifically in the context of K-ras addiction. Here we define a novel PKCδ -> integrin α_Vβ₃->Extracellular signal-Regulated Kinase (ERK) pathway that regulates the transformed growth of K-ras dependent NSCLC cells. To explore how PKCδ regulates tumorigenesis, we performed mRNA expression analysis in four KRAS mutant NSCLC cell lines that stably express scrambled shRNA or a PKCδ targeted shRNA. Analysis of PKCδ-dependent mRNA expression identified 3183 regulated genes, 210 of which were specifically regulated in K-ras dependent cells. Genes that regulate extracellular matrix and focal adhesion pathways were most highly represented in this later group. In particular, expression of the integrin pair, α_Vβ₃, was specifically reduced in K-ras dependent cells with depletion of PKCδ, and correlated with reduced ERK activation and reduced transformed growth as assayed by clonogenic survival. Re-expression of PKCδ restored ITGAV and ITGB3 mRNA expression, ERK activation and transformed growth, and this could be blocked by pretreatment with a α_Vβ₃ function-blocking antibody, demonstrating a requirement for integrin α_Vβ₃ downstream of PKCδ. Similarly, expression of integrin α_V restored ERK activation and transformed growth in PKCδ depleted cells, and this could also be inhibited by pretreatment with PD98059. Our studies demonstrate an essential role for α_Vβ₃ and ERK signalingdownstream of PKCδ in regulating the survival of K-ras dependent NSCLC cells, and identify PKCδ as a novel therapeutic target for the subset of NSCLC patients with K-ras dependent tumors.

Multifunctional roles of PKCδ: Opportunities for targeted therapy in human disease

The serine-threonine protein kinase, protein kinase C-δ (PKCδ), is emerging as a bi-functional regulator of cell death and proliferation. Studies in PKCδ-/- mice have confirmed a pro-apoptotic role for this kinase in response to DNA damage and a tumor promoter role in some oncogenic contexts. In non-transformed cells, inhibition of PKCδ suppresses the release of cytochrome c and caspase activation, indicating a function upstream of apoptotic pathways. Data from PKCδ-/- mice demonstrate a role for PKCδ in the execution of DNA damage-induced and physiologic apoptosis. This has led to the important finding that inhibitors of PKCδ can be used therapeutically to reduce irradiation and chemotherapy-induced toxicity. By contrast, PKCδ is a tumor promoter in mouse models of mammary gland and lung cancer, and increased PKCδ expression is a negative prognostic indicator in Her2+ and other subtypes of human breast cancer. Understanding how these distinct functions of PKCδ are regulated is critical for the design of therapeutics to target this pathway. This review will discuss what is currently known about biological roles of PKCδ and prospects for targeting PKCδ in human disease.

Non-muscle myosin II in disease: mechanisms and therapeutic opportunities

The actin motor protein non-muscle myosin II (NMII) acts as a master regulator of cell morphology, with a role in several essential cellular processes, including cell migration and post-synaptic dendritic spine plasticity in neurons. NMII also generates forces that alter biochemical signaling, by driving changes in interactions between actin-associated proteins that can ultimately regulate gene transcription. In addition to its roles in normal cellular physiology, NMII has recently emerged as a critical regulator of diverse, genetically complex diseases, including neuronal disorders, cancers and vascular disease. In the context of these disorders, NMII regulatory pathways can be directly mutated or indirectly altered by disease-causing mutations. NMII regulatory pathway genes are also increasingly found in disease-associated copy-number variants, particularly in neuronal disorders such as autism and schizophrenia. Furthermore, manipulation of NMII-mediated contractility regulates stem cell pluripotency and differentiation, thus highlighting the key role of NMII-based pharmaceuticals in the clinical success of stem cell therapies. In this Review, we discuss the emerging role of NMII activity and its regulation by kinases and microRNAs in the pathogenesis and prognosis of a diverse range of diseases, including neuronal disorders, cancer and vascular disease. We also address promising clinical applications and limitations of NMII-based inhibitors in the treatment of these diseases and the development of stem-cell-based therapies.

Phosphorylation-independent mTORC1 inhibition by the autophagy inducer Rottlerin

We recently found that Rottlerin not only inhibits proliferation but also causes Bcl-2- and Beclin 1-independent autophagic death in apoptosis-resistant breast adenocarcinoma MCF-7 cells. Having excluded a role for canonical signaling pathways, the current study was aimed to investigate the contribution of the AMPK/mTOR axis in autophagy induction and to search for the upstream signaling molecules potentially targeted by Rottlerin. Using several enzyme inhibitors, Western blotting analysis, mTOR siRNA and pull down assay, we demonstrate that the Rottlerin-triggered autophagy is mediated by inhibition of mTORC1 activity through a novel AMPK and mTORC1 phosphorylation-independent mechanism, likely mediated by the direct interaction between Rottlerin and mTOR.

Protein kinase C and cancer: what we know and what we do not

Since their discovery in the late 1970s, protein kinase C (PKC) isozymes represent one of the most extensively studied signaling kinases. PKCs signal through multiple pathways and control the expression of genes relevant for cell cycle progression, tumorigenesis and metastatic dissemination. Despite the vast amount of information concerning the mechanisms that control PKC activation and function in cellular models, the relevance of individual PKC isozymes in the progression of human cancer is still a matter of controversy. Although the expression of PKC isozymes is altered in multiple cancer types, the causal relationship between such changes and the initiation and progression of the disease remains poorly defined. Animal models developed in the last years helped to better understand the involvement of individual PKCs in various cancer types and in the context of specific oncogenic alterations. Unraveling the enormous complexity in the mechanisms by which PKC isozymes have an impact on tumorigenesis and metastasis is key for reassessing their potential as pharmacological targets for cancer treatment.

Protein Kinase C (PKC) Isozymes and Cancer

Protein kinase C (PKC) is a family of phospholipid-dependent serine/threonine kinases, which can be further classified into three PKC isozymes subfamilies: conventional or classic, novel or nonclassic, and atypical. PKC isozymes are known to be involved in cell proliferation, survival, invasion, migration, apoptosis, angiogenesis, and drug resistance. Because of their key roles in cell signaling, PKC isozymes also have the potential to be promising therapeutic targets for several diseases, such as cardiovascular diseases, immune and inflammatory diseases, neurological diseases, metabolic disorders, and multiple types of cancer. This review primarily focuses on the activation, mechanism, and function of PKC isozymes during cancer development and progression.

Gαs protein expression is an independent predictor of recurrence in prostate cancer

Background. T393C polymorphism in the gene GNAS1, which encodes the G-protein alpha s subunit (Gαs) of heterotrimeric G protein, is significantly associated with the clinical outcome of patients suffering from several cancers. However, studies on the role and protein expression of Gαs subunit in prostate cancer were still unavailable. Methods. The immunohistochemical staining was used to assess Gαs expression through tissue microarray procedure of 56 metastatic PCas, 291 localized PCas, and 67 benign hyperplasia (BPH). Gαs expression was semiquantitatively scored and evaluated the correlation with pathologic parameters and biochemical recurrence of prostate-specific antigen (PSA). Results. Gαs expression was localized in nuclear and cytoplasm in prostate cancer cells and downregulated in metastatic PCa compared to localized PCa and BPH (P < 0.001). Gαs was inversely associated with PSA level and Gleason scores; patients with low expression of Gαs had adverse clincopathological features. In multivariable Cox regression analysis, high Gαs expression and Gleason scores were independent predictors of both PSA progression-free and overall survival. Conclusions. Gαs down-expression is associated with adverse pathologic features and clinical PSA biochemical recurrence of prostate cancer. Gαs is an independent predictor to help determine the risk of PSA progression and death.

Regulation of Transcriptional Networks by PKC Isozymes: Identification of c-Rel as a Key Transcription Factor for PKC-Regulated Genes

BACKGROUND

Activation of protein kinase C (PKC), a family of serine-threonine kinases widely implicated in cancer progression, has major impact on gene expression. In a recent genome-wide analysis of prostate cancer cells we identified distinctive gene expression profiles controlled by individual PKC isozymes and highlighted a prominent role for PKCδ in transcriptional activation.

PRINCIPAL FINDINGS

Here we carried out a thorough bioinformatics analysis to dissect transcriptional networks controlled by PKCα, PKCδ, and PKCε, the main diacylglycerol/phorbol ester PKCs expressed in prostate cancer cells. Despite the remarkable differences in the patterns of transcriptional responsive elements (REs) regulated by each PKC, we found that c-Rel represents the most frequent RE in promoters regulated by all three PKCs. In addition, promoters of PKCδ-regulated genes were particularly enriched with REs for CREB, NF-E2, RREB, SRF, Oct-1, Evi-1, and NF-κB. Most notably, by using transcription factor-specific RNAi we were able to identify subsets of PKCδ-regulated genes modulated by c-Rel and CREB. Furthermore, PKCδ-regulated genes condensed under the c-Rel transcriptional regulation display significant functional interconnections with biological processes such as angiogenesis, inflammatory response, and cell motility.

CONCLUSION/SIGNIFICANCE

Our study identified candidate transcription factors in the promoters of PKC regulated genes, in particular c-Rel was found as a key transcription factor in the control of PKCδ-regulated genes. The deconvolution of PKC-regulated transcriptional networks and their nodes may greatly help in the identification of PKC effectors and have significant therapeutics implications.

TGF-β effects on prostate cancer cell migration and invasion are mediated by PGE2 through activation of PI3K/AKT/mTOR pathway

TGF-β plays an important role in the progression of prostate cancer. It exhibits both tumor suppressor and tumor-promoting activities. Correlations between cyclooxygenase (COX)-2 overexpression and enhanced production of prostaglandin (PG)E2 have been implicated in cancer progression; however, there are no studies indicating that TGF-β effects in prostate cancer cells involve PGE2 synthesis. In this study, we investigated TGF-β regulation of COX-1 and COX-2 expression in prostate cancer cells and whether the effects of TGF-β on cell proliferation and migration are mediated by PGE2. COX-1 protein was ubiquitously expressed in prostate cells; however, COX-2 protein levels were detected only in prostate cancer cells. TGF-β treatment increased COX-2 protein levels and PGE2 secretion in PC3 cells. Exogenous PGE2 and PGF2α had no effects on cell proliferation in LNCaP, DU145, and PC3 cells whereas PGE2 and TGF-β induced migration and invasive behavior in PC3 cells. Only EP2 and EP4 receptors were detected at mRNA levels in prostate cells. The EP4-targeting small interfering RNA inhibited PGE2 and TGF-β-induced migration of PC3 cells. TGF-β and PGE2 induce activation of PI3K/AKT/mammalian target of rapamycin pathway as indicated by increased AKT, p70S6K, and S6 phosphorylation. Rapamycin completely blocked the effects of TGF-β and PGE2 on phosphorylation of p70S6K and S6 but not on AKT phosphorylation. PGE2 and TGF-β induced phosphorylation of AKT, which was blocked by antagonists of PGE2 (EP4) receptors (L161982, AH23848) and PI3K inhibitor (LY294002) in PC3 cells. Pretreatment with L161982 or AH23848 blocked the stimulatory effects of PGE2 and TGF-β on cell migration, whereas LY294002 or rapamycin completely eliminated PGE2, TGF-β, and epidermal growth factor-induced migration in PC3 cells. We conclude that TGF-β increases COX-2 levels and PGE2 secretion in prostate cancer cells which, in turn, mediate TGF-β effects on cell migration and invasion through the activation of PI3K/AKT/mammalian target of rapamycin pathway.

PTPL1 and PKCδ contribute to proapoptotic signalling in prostate cancer cells

PTPL1 is a non-receptor protein tyrosine phosphatase involved in apoptosis regulation, although controversial findings have been reported in different cancer types. We report here a proapoptotic role for PTPL1 in PC3 and LNCaP prostate cancer cells, as its absence induces apoptosis resistance upon treatment with different drugs. In PC3 cells, PTPL1 silencing by small interfering RNA influences the expression levels of Bcl-xL and Mcl-1_S proteins as well as final events in the apoptotic process such as activation of caspases and caspase-mediated cleavage of proteins like Mcl-1 or poly (ADP-ribose) polymerase. We have identified PKCδ as an intermediary of PTPL1-mediated apoptotic signalling and that phosphorylation status of NF-κB and IκBα is influenced by PTPL1 and PKCδ. Furthermore, the loss of PTPL1 and PKCδ expression in poorly differentiated, more aggressive human prostate cancers also indicate that their absence could be related to apoptosis resistance and tumour progression.

PKC-dependent phosphorylation of p27 at T198 contributes to p27 stabilization and cell cycle arrest

In this manuscript, we present experimental evidence that PKCs phosphorylate p27 at T198 in vitro and in vivo, resulting in p27 stabilization and cell cycle arrest in MCF-7 and HeLa cells. Our findings indicate that (1) recombinant PKCα, βII, δ, η and θ isoforms phosphorylate, in in vitro kinase assays, wild-type recombinant p27 protein expressed in E. coli and wild-type p27 protein immunoprecpitated from transfected HEK-293 cells but not the T198A mutant, (2) adoptive expressed PKCα and δ phosphorylate both transfected and endogenous p27 at T198 in HEK-293 cells, (3) T198 phosphorylation of transfected and endogenous p27 is increased by PKC activators [Phorbol 12-myristate 13-acetate (PMA)] and suppressed by PKC inhibitors (Rottlerin A, G06976, Calphostin C), (4) in parallel with increased T198 phosphorylation, PMA induces stabilization of p27 protein in HeLa cells, whereas PKC inhibitors induce a decrease in p27 stability and, finally, (5) PMA-induced p27 upregulation is necessary for growth arrest of HeLa and MCF-7 cells induced by PKC activation by PMA.   Overall, these results suggest that PKC-dependent upregulation of p27 induced by its phosphorylation at T198 represents a mechanism that mediates growth arrest promoted by PMA and provide novel insights on the ability of different PKC isoforms to play a role in controlling cell cycle progression.

Human periprostatic adipose tissue promotes prostate cancer aggressiveness in vitro

Background

Obesity is associated with prostate cancer aggressiveness and mortality. The contribution of periprostatic adipose tissue, which is often infiltrated by malignant cells, to cancer progression is largely unknown. Thus, this study aimed to determine if periprostatic adipose tissue is linked with aggressive tumor biology in prostate cancer.

Methods

Supernatants of whole adipose tissue (explants) or stromal vascular fraction (SVF) from paired fat samples of periprostatic (PP) and pre-peritoneal visceral (VIS) anatomic origin from different donors were prepared and analyzed for matrix metalloproteinases (MMPs) 2 and 9 activity. The effects of those conditioned media (CM) on growth and migration of hormone-refractory (PC-3) and hormone-sensitive (LNCaP) prostate cancer cells were measured.

Results

We show here that PP adipose tissue of overweight men has higher MMP9 activity in comparison with normal subjects. The observed increased activities of both MMP2 and MMP9 in PP whole adipose tissue explants, likely reveal the contribution of adipocytes plus stromal-vascular fraction (SVF) as opposed to SVF alone. MMP2 activity was higher for PP when compared to VIS adipose tissue. When PC-3 cells were stimulated with CM from PP adipose tissue explants, increased proliferative and migratory capacities were observed, but not in the presence of SVF. Conversely, when LNCaP cells were stimulated with PP explants CM, we found enhanced motility despite the inhibition of proliferation, whereas CM derived from SVF increased both cell proliferation and motility. Explants culture and using adipose tissue of PP origin are most effective in promoting proliferation and migration of PC-3 cells, as respectively compared with SVF culture and using adipose tissue of VIS origin. In LNCaP cells, while explants CM cause increased migration compared to SVF, the use of PP adipose tissue to generate CM result in the increase of both cellular proliferation and migration.

Conclusions

Our findings suggest that the PP depot has the potential to modulate extra-prostatic tumor cells' microenvironment through increased MMPs activity and to promote prostate cancer cell survival and migration. Adipocyte-derived factors likely have a relevant proliferative and motile role.

Rottlerin and cancer: novel evidence and mechanisms

Because cancers are caused by deregulation of hundreds of genes, an ideal anticancer agent should target multiple gene products or signaling pathways simultaneously. Recently, extensive research has addressed the chemotherapeutic potential of plant-derived compounds. Among the ever-increasing list of naturally occurring anticancer agents, Rottlerin appears to have great potentiality for being used in chemotherapy because it affects several cell machineries involved in survival, apoptosis, autophagy, and invasion. The underlying mechanisms that have been described are diverse, and the final, cell-specific, Rottlerin outcome appears to result from a combination of signaling pathways at multiple levels. This paper seeks to summarize the multifocal signal modulatory properties of Rottlerin, which merit to be further exploited for successful prevention and treatment of cancer.

Expression of nodal and nodal receptors in prostate stem cells and prostate cancer cells: autocrine effects on cell proliferation and migration

BACKGROUND

Nodal, a TGFβ like growth factor, functions as an embryonic morphogen that maintains the pluripotency of embryonic stem cells. Nodal has been implicated in cancer progression; however, there is no information on expression and functions of Nodal in prostate cancer. In this study, we have investigated the expression of Nodal, its receptors, and its effects on proliferation and migration of human prostate cells.

METHODS

RT-PCR, qPCR, and Western blot analyses were performed to analyze expression of Nodal and Nodal receptors and its effects on phosphorylation of Smad2/3 in prostate cells. The effects on proliferation and migration were determined by (3) H-Thymidine incorporation and cell migration assays in the presence or absence of Nodal receptor inhibitor (SB431542).

RESULTS

Nodal was highly expressed in WPE, DU145, LNCaP, and LNCaP-C81 cells with low expression in RWPE1 and RWPE2 cells, but not in PREC, PC3 and PC3M cells. Nodal receptors are expressed at varying levels in all prostate cells. Treatment with exogenous Nodal induced phosphorylation of Smad2/3 in WPE, DU145, and PC3 cells, which was blocked by SB431542. Nodal dose-dependently inhibited proliferation of WPE, RWPE1 and DU145 cells, but not LNCaP and PC3 cells. Nodal induced cell migration in PC3 cells, which was inhibited by SB431542; Nodal had no effect on cell migration in WPE and DU145 cells. The effects of Nodal on cell proliferation and migration are mediated via ALK4 and ActRII/ActRIIB receptors and Smad 2/3 phosphorylation.

CONCLUSIONS

Nodal may function as an autocrine regulator of proliferation and migration of prostate cancer cells.

Nitric oxide counters the inhibitory effects of uremic toxin indoxyl sulfate on endothelial cells by governing ERK MAP kinase and myosin light chain activation

Uremic toxins such as indoxyl sulfate (IS) accumulate at a high level in end stage renal disease (ESRD) and can exhibit significant systemic endothelial toxicity leading to accelerated cardiovascular events. The precise molecular mechanisms by which IS causes endothelial dysfunction are unknown. We tested the hypothesis that IS negatively influences properties of endothelial cells, such as migration and tube formation, by depleting nitric oxide (NO) bioavailability, and that an NO donor can reverse these inhibitory effects. IS inhibited human umbilical vein endothelial cell (HUVEC) migration and formation of tubes on matrigel. Mechanistically, IS inhibited VEGF-induced NO release from HUVECs. An NO donor, SNAP, reversed IS-mediated inhibition of HUVEC migration as well as tube-formation. IS inhibited ERK 1/2 MAP kinase activity in a dose-dependent manner, but this was preserved by SNAP. Inhibition of ERK 1/2 with a pharmacological inhibitor (U0126) decreased HUVEC migration and tube formation; these effects too were prevented by SNAP. Further, IS stimulated activation of myosin light chain (MLC), potentially stimulating endothelial contractility, while SNAP decreased MLC activation. Thus, we conclude that the negative effects of IS on endothelial cells are prevented, to a major extent, by NO, via its divergent actions on ERK MAP kinase and MLC.

Interplay between FAK, PKCδ, and p190RhoGAP in the regulation of endothelial barrier function

Disruption of either intercellular or extracellular junctions involved in maintaining endothelial barrier function can result in increased endothelial permeability. Increased endothelial permeability, in turn, allows for the unregulated movement of fluid and solutes out of the vasculature and into the surrounding connective tissue, contributing to a number of disease states, including stroke and pulmonary edema (Ermert et al., 1995; Lee and Slutsky, 2010; van Hinsbergh, 1997; Waller et al., 1996; Warboys et al., 2010). Thus, a better understanding of the molecular mechanisms by which endothelial cell junction integrity is controlled is necessary for development of therapies aimed at treating such conditions. In this review, we will discuss the functions of three signaling molecules known to be involved in regulation of endothelial permeability: focal adhesion kinase (FAK), protein kinase C delta (PKCδ), and p190RhoGAP (p190). We will discuss the independent functions of each protein, as well as the interplay that exists between them and the effects of such interactions on endothelial function.

Transcriptional regulation of pro-apoptotic protein kinase Cdelta: implications for oxidative stress-induced neuronal cell death

We previously demonstrated that protein kinase Cδ (PKCδ; PKC delta) is an oxidative stress-sensitive kinase that plays a causal role in apoptotic cell death in neuronal cells. Although PKCδ activation has been extensively studied, relatively little is known about the molecular mechanisms controlling PKCδ expression. To characterize the regulation of PKCδ expression, we cloned an ∼2-kbp 5'-promoter segment of the mouse Prkcd gene. Deletion analysis indicated that the noncoding exon 1 region contained multiple Sp sites, including four GC boxes and one CACCC box, which directed the highest levels of transcription in neuronal cells. In addition, an upstream regulatory region containing adjacent repressive and anti-repressive elements with opposing regulatory activities was identified within the region -712 to -560. Detailed mutagenesis studies revealed that each Sp site made a positive contribution to PKCδ promoter expression. Overexpression of Sp family proteins markedly stimulated PKCδ promoter activity without any synergistic transactivating effect. Furthermore, experiments in Sp-deficient SL2 cells indicated long isoform Sp3 as the essential activator of PKCδ transcription. Importantly, both PKCδ promoter activity and endogenous PKCδ expression in NIE115 cells and primary striatal cultures were inhibited by mithramycin A. The results from chromatin immunoprecipitation and gel shift assays further confirmed the functional binding of Sp proteins to the PKCδ promoter. Additionally, we demonstrated that overexpression of p300 or CREB-binding protein increases the PKCδ promoter activity. This stimulatory effect requires intact Sp-binding sites and is independent of p300 histone acetyltransferase activity. Finally, modulation of Sp transcriptional activity or protein level profoundly altered the cell death induced by oxidative insult, demonstrating the functional significance of Sp-dependent PKCδ gene expression. Collectively, our findings may have implications for development of new translational strategies against oxidative damage.

Protein kinase C δ is a downstream effector of oncogenic K-ras in lung tumors

Oncogenic activation of K-ras occurs commonly in non-small cell lung cancer (NSCLC), but strategies to therapeutically target this pathway have been challenging to develop. Information about downstream effectors of K-ras remains incomplete, and tractable targets are yet to be defined. In this study, we investigated the role of protein kinase C δ (PKCδ) in K-ras-dependent lung tumorigenesis by using a mouse carcinogen model and human NSCLC cells. The incidence of urethane-induced lung tumors was decreased by 69% in PKCδ-deficient knockout (δKO) mice compared with wild-type (δWT) mice. δKO tumors are smaller and showed reduced proliferation. DNA sequencing indicated that all δWT tumors had activating mutations in KRAS, whereas only 69% of δKO tumors did, suggesting that PKCδ acts as a tumor promoter downstream of oncogenic K-ras while acting as a tumor suppressor in other oncogenic contexts. Similar results were obtained in a panel of NSCLC cell lines with oncogenic K-ras but which differ in their dependence on K-ras for survival. RNA interference-mediated attenuation of PKCδ inhibited anchorage-independent growth, invasion, migration, and tumorigenesis in K-ras-dependent cells. These effects were associated with suppression of mitogen-activated protein kinase pathway activation. In contrast, PKCδ attenuation enhanced anchorage-independent growth, invasion, and migration in NSCLC cells that were either K-ras-independent or that had WT KRAS. Unexpectedly, our studies indicate that the function of PKCδ in tumor cells depends on a specific oncogenic context, as loss of PKCδ in NSCLC cells suppressed transformed growth only in cells dependent on oncogenic K-ras for proliferation and survival.

Rottlerin inhibits migration of follicular thyroid carcinoma cells by PKCdelta-independent destabilization of the focal adhesion complex

This study examined the effect of rottlerin on the focal adhesion-mediated cell migration of CGTH W-2 human follicular thyroid carcinoma cells. Rottlerin (10 microM) resulted in decreased adhesion of CGTH W-2 cells to matrix substance, which was correlated with metastatic potential. Rottlerin treatment also resulted in a marked reduction in the migration of CGTH W-2 cells. Protein levels of integrin beta1, FAK, and paxillin were decreased by rottlerin. Consistent with this, immunostaining of FAK, vinculin, and paxillin revealed disassembly of the focal adhesions. Disruption of actin stress fibers was noted, which was compatible with reduced expression levels and activities of Rac-1 and Rho. The effect of rottlerin on cell migration was not attributable to inhibition of PKCdelta activity since siRNA knockdown of PKCdelta did not recapitulate the effects of rottlerin on cell adhesion and migration. Furthermore, activation of PKCdelta by phorbol esters failed to restore the rottlerin-inhibited migratory ability. The mitochondrial uncoupler, carbonylcyanide-4-(trifluoromethoxy)-phenylhydrazone, was able to mimic several rottlerin's effects. In summary, we demonstrated that rottlerin inhibits the migration of CGTH W-2 cells by disassembly of focal adhesion complexes in a PKCdelta-independent manner, and might play as a mitochondrial uncoupler role in these events.

Elevated expression of protein kinase C delta induces cell scattering upon serum deprivation

Tumor metastasis might be evoked in response to microenvironmental stress, such as a shortage of oxygen. Although the cellular response to hypoxia has been well established, we know little about how tumors adapt themselves to deprivation of growth factor. Protein kinase Cdelta (PKCdelta), a stress-sensitive protein kinase, has been implicated in tumor progression. In this study, we demonstrate that elevated expression of PKCdelta in Madin-Darby canine kidney cells induces a scatter response upon serum starvation, a condition that mimics growth-factor deprivation. Serum starvation stimulates the catalytic activity and Y311 phosphorylation of PKCdelta through reactive oxygen species (ROS) and the Src family kinases. Mutation of PKCdelta at Y311 and Y322, both of which are phosphorylation sites for Src, impairs its activation and ability to promote cell scattering upon serum deprivation. Once activated by ROS, PKCdelta itself activates ROS production at least partially through NADPH oxidase. In addition, the c-Jun N-terminal kinase is identified as a crucial downstream mediator of ROS and PKCdelta for induction of cell scattering upon serum deprivation. We demonstrate that the C1B domain of PKCdelta is essential not only for its localization at the Golgi complex, but also for its activation and ability to induce cell scattering upon serum deprivation. Finally, depletion of PKCdelta in human bladder carcinoma T24 cells restores their cell-cell contacts, which thereby reverses a scattered growth pattern to an epithelial-like growth pattern. Collectively, our results suggest that elevated expression of PKCdelta might facilitate the scattering of cells in order to escape stress induced by growth-factor deprivation.

Oxytocin induces the migration of prostate cancer cells: involvement of the Gi-coupled signaling pathway

Expression of genes that encode oxytocin (OXT) and vasopressin (AVP) and their cognate receptors in normal and diseased prostates are only partially characterized. Reverse transcription and PCR were used to examine the expression of these genes in normal prostate epithelial and stromal cell lines, k-ras-transformed prostate epithelial cell lines, and in four prostate cancer cell lines. Secreted and cell-associated OXT peptide was measured by an enzyme immunoassay. OXT and its receptor (OXTR) were expressed in all eight prostate cell lines. Cell-associated OXT peptide was also found in all prostate epithelial cell lines except in DU145 cells. Neither AVP nor its cognate receptors (V1a receptor and V2 receptor) were expressed in any prostate cell line examined. These data point to the OXTR as the primary target of OXT and AVP, and suggest that OXT might be an autocrine/paracrine regulator in human prostate. We found that OXT induces the migration of PC3 and PC3M, but not DU145 prostate cancer cells. The effect of OXT is distinct from the epidermal growth factor (EGF)-induced migration of prostate cancer cells, in which ERK1/2 and EGF receptor kinase activities were required. When cells were pretreated with pertussis toxin, the effect of OXT, but not EGF, on cell migration was abolished. Pretreatment with the cyclic AMP analogue, 8-Br-cAMP, did not affect OXT-induced cell migration, which eliminated the nonspecific effect of pertussis toxin. We conclude that a Gi-dependent mechanism is involved in OXTR-mediated migration of prostate cancer cells, and indicates a role for OXTR in prostate cancer metastasis.

Claudin-1 acts through c-Abl-protein kinase Cdelta (PKCdelta) signaling and has a causal role in the acquisition of invasive capacity in human liver cells

Claudins are identified as members of the tetraspanin family of proteins, which are integral to the structure and function of tight junction. Recent studies showed an increase in expression of claudins during tumorigenesis, which is associated with loss of cell-cell contact, dedifferentiation, and invasiveness. However, the molecular basis for the causal relationship between claudin expression and cancer progression is not fully understood yet. In this study, we show that claudin-1 plays a causal role in the acquisition of invasive capacity in human liver cells and that c-Abl-protein kinase Cdelta (PKCdelta) signaling is critical for the malignant progression induced by claudin-1. Overexpression of claudin-1 clearly induced expression of matrix metalloproteinase-2 (MMP-2) and cell invasion and migration in normal liver cells as well as in non-invasive human hepatocellular carcinoma (HCC) cells. Conversely, small interfering RNA targeting of claudin-1 in invasive HCC cells completely inhibited cell invasion. Both c-Abl and PKCdelta are found to be activated in normal liver cell line clones that stably overexpress claudin-1. Inhibition of either c-Abl or PKCdelta alone clearly attenuated MMP-2 activation and impeded cell invasion and migration in both human HCC and normal liver cells expressing claudin-1. These results indicate that claudin-1 is both necessary and sufficient to induce invasive behavior in human liver cells and that activation of c-Abl-PKCdelta signaling pathway is critically required for the claudin-1-induced acquisition of the malignant phenotype. The present observations raise the possibility of exploiting claudin-1 as a potential biomarker for the spread of liver cancer and might provide pivotal points for therapeutic intervention in HCC.

Annexins--modulators of EGF receptor signalling and trafficking

At the cell surface, activation of the epidermal growth factor (EGF) receptor triggers a complex network of signalling events that regulate a variety of cellular processes. For signal termination, the activated EGF receptor is internalised and targeted to lysosomes for degradation. Microdomain localization at the plasma membrane and endocytic transport of the EGFR is important for the formation of compartment-specific signalling complexes and is regulated by scaffolding and targeting proteins. This includes Ca2+-effector proteins, such as calmodulin and annexins (Anx), in particular AnxA1, AnxA2, AnxA6 and as shown recently,AnxA8. Given that these annexins show differences in their expression patterns, subcellular localization and mode of action, they are likely to differentially contribute and cooperate in the fine-tuning of EGFR activity. In support of this hypothesis, current literature suggests these annexins to be involved in different steps that control the endocytic transport and signalling of the EGF receptor. This review summarizes how the coordinated activity of AnxA1, AnxA2, AnxA6 and AnxA8 can contribute to regulate EGF receptor localization and activity.

Functional suppression of E-cadherin by protein kinase Cdelta

Protein kinase C (PKC) delta, a member of the novel PKC subfamily, has been shown to have an important role in cell proliferation, differentiation, apoptosis and cell motility. In this study, we investigated the effect of green fluorescent protein (GFP)-PKCdelta and GFP-PKCalpha on cell-cell junctions of Madin-Darby canine kidney (MDCK) cells and found that only GFP-PKCdelta suppressed the homophilic interactions between the ectodomains of E-cadherins, accompanied by a weaker cell-cell adhesion. The kinase-deficient mutant of GFP-PKCdelta retained its localization at cell-cell junctions but failed to suppress the function of E-cadherin. In addition, we demonstrated that the hinge region (residues 280-347) that links the regulatory domain and the catalytic domain of PKCdelta is essential for both its kinase activity and the targeting of cell-cell junctions. A PKCdelta mutant with the deletion of amino acids 280-323 within the hinge region, which is catalytically active but defective in the targeting of cell-cell junctions, failed to suppress the function of E-cadherin. Moreover, expression of GFP-PKCdelta in MDCK cells expedited the detachment of cells from their neighbors and facilitated cell scatter induced by hepatocyte growth factor. By contrast, the GFP-PKCdelta mutants including the kinase-deficient mutant and the truncated mutant lacking residues 280-323 suppressed hepatocyte-growth-factor-induced cell scattering. Finally, siRNA-mediated knockdown of endogenous PKCdelta in MDCK cells was found to delay the onset of cell-cell detachment and cell scattering induced by hepatocyte growth factor. Taken together, our results demonstrate that the catalytic activity of PKCdelta and its localization to cell-cell junctions are necessary for PKCdelta to suppress the function of E-cadherin, which thereby facilitates scattering of epithelial cells in response to extracellular cues.

Phorbol 12-myristate 13-acetate inhibits FRO anaplastic human thyroid cancer cell proliferation by inducing cell cycle arrest in G1/S phase: evidence for an effect mediated by PKCdelta

Phorbol 12-myristate 13-acetate (PMA) is known to affect a variety of cellular processes, including cell proliferation, differentiation, and migration. PMA has been shown to promote antiproliferative and antimigratory effects in many types of cancer cells. Our findings show that PMA induced a strong antiproliferative effect in two anaplastic (FRO and ARO) and one follicular (ML-1) thyroid cancer cell lines, and increased the fraction of FRO cells in G1 phase of the cell cycle. The fractions in the S and G2 phases were decreased. Moreover, PMA evoked a significant increase in the levels of the cell cycle regulators p21Waf1/Cip1 and p27Kip1. The levels of cyclin D3 and the cyclin-dependent kinases cdk4 and cdk6 decreased, as did the phosphorylation of the Rb-protein. PMA did not induce apoptosis. PMA stimulated the translocation of protein kinase C (PKC) alpha, betaI and delta isoforms to the cell membrane. PKCdelta small interfering RNA attenuated the PMA-induced antiproliferative effect and prevented the upregulation of p21Waf1/Cip1 and p27Kip1. Prolonged stimulation with PMA decreased the phosphorylation of mitogen-activated protein (MAP) kinase. PMA also decreased the phosphorylation of Akt and evoked a biphasic change in the phosphorylation of the forkhead box class-O protein (FOXO): an increase in phosphorylation, followed by a dephosphorylation. In addition, PMA inhibited FRO, ARO and ML-1 cell migration toward serum. The inactive phorbol ester analog 4alpha-phorbol and the diacylglycerol analog 1,2-dioctanoyl-sn-glycerol were without an effect on proliferation and migration. The results indicate that PMA is an effective inhibitor of thyroid cancer cell proliferation and migration by a mechanism involving PKC-MAP kinase/Akt and FOXO signaling.

Atypical protein kinase C phosphorylates IKKalphabeta in transformed non-malignant and malignant prostate cell survival

Mechanistic pathways involving atypical protein kinase C-iota (aPKC-iota) have been targeted in various cancer cells such as lung cancer, brain and prostate due to PKCiota's antiapoptotic function, and role in cell proliferation and cell survival. In the current study, we examined the involvement of PKC-iota in the NF-kappaB pathway following treatment of prostate cells with the pro-inflammatory cytokine tumor necrosis factor alpha (TNFalpha). Results demonstrated that androgen-independent DU-145 prostate carcinoma is insensitive to TNFalpha while transformed non-tumorigenic prostate RWPE-1 cells showed a slight sensitivity to TNFalpha. However, androgen-dependent LNCaP prostate cells are more sensitive to TNFalpha treatment and undergo apoptosis. Results demonstrated that in DU-145 cells, TNFalpha-induced PKC-iota in phosphorylation of IKKalphabeta. In RWPE-1 cells, PKC-zeta phosphorylates IKKalphabeta. Degradation of IkappaBalpha was observed in all three cell lines, allowing NF-kappaB/p65 translocation to the nucleus. Although, IKKalpha is weakly activated in LNCaP cells, the upstream kinase phosphorylation of IKKalphabeta via aPKCs was not observed. Hence, aPKCs may play a role in activation of NFkappaB pathway in prostate cancer cells.

Functions of normal and malignant prostatic stem/progenitor cells in tissue regeneration and cancer progression and novel targeting therapies

This review summarizes the recent advancements that have improved our understanding of the functions of prostatic stem/progenitor cells in maintaining homeostasis of the prostate gland. We also describe the oncogenic events that may contribute to their malignant transformation into prostatic cancer stem/progenitor cells during cancer initiation and progression to metastatic disease stages. The molecular mechanisms that may contribute to the intrinsic or the acquisition of a resistant phenotype by the prostatic cancer stem/progenitor cells and their differentiated progenies with a luminal phenotype to the current therapies and disease relapse are also reviewed. The emphasis is on the critical functions of distinct tumorigenic signaling cascades induced through the epidermal growth factor system, hedgehog, Wnt/beta-catenin, and/or stromal cell-derived factor-1/CXC chemokine receptor-4 pathways as well as the deregulated apoptotic signaling elements and ATP-binding cassette multidrug transporter. Of particular therapeutic interest, we also discuss the potential beneficial effects associated with the targeting of these signaling elements to overcome the resistance to current treatments and prostate cancer recurrence. The combined targeted strategies toward distinct oncogenic signaling cascades in prostatic cancer stem/progenitor cells and their progenies as well as their local microenvironment, which could improve the efficacy of current clinical chemotherapeutic treatments against incurable, androgen-independent, and metastatic prostate cancers, are also described.

Effects of a novel tyrosine kinase inhibitor in rheumatoid arthritis synovial fibroblasts

OBJECTIVE

Biologicals have revolutionised the treatment of rheumatoid arthritis (RA). However, progressive joint destruction can still be observed in many patients and the search for novel molecular therapies targeting specific signalling pathways is ongoing. In the present study, we investigated the effects of GW282974, a novel compound directed against tyrosine kinase activity with respect to the potential suppression of inflammation and destruction.

METHODS

Synovial tissue specimens were obtained from RA patients undergoing surgical joint replacement. Rheumatoid arthritis synovial fibroblasts (RASFs) were stimulated with cytokines and GW282974 was added in different concentrations. Gene expression was checked by TaqMan PCR, using 18S as housekeeping gene. Protein analysis was quantified by ELISA. Cell growth and proliferation was measured using the "ViaLight" proliferation assay.

RESULTS

EGF had no effect on the gene expression profile of RASFs when used as single stimulatory agent. In combination with pro-inflammatory mediators however, EGF showed a synergistic effect. The expression of matrix metalloproteinases, inflammatory cytokines and cyclooxygenase-2 on mRNA levels was strongly increased, whereas the addition of GW282974 abrogated these effects in a dose-dependent manner. These data could be confirmed on protein/lipid levels analysing the supernatants of RASFs by ELISA. Similarly, cell growth and proliferation of RASFs were inhibited by GW282974 in a dose- and time-dependent manner. By contrast, no cytotoxic effects were seen within the concentrations used.

DISCUSSION

GW282974 appears to interfere with the inflammatory and the destructive pathways in RASFs and might therefore be used as novel therapeutic strategy for the treatment of RA.

Cell surface restriction of EGFR by a tenascin cytotactin-encoded EGF-like repeat is preferential for motility-related signaling

The 14th EGFL-repeat (Ten14) of human tenascin cytotactin activates the epidermal growth factor receptor (EGFR) with micromolar affinity; however, unlike EGF, Ten14-mediated activation of EGFR does not lead to receptor internalization. As the divergent signaling pathways downstream of EGFR have been shown to be triggered from plasma membrane and cytosolic locales, we investigated whether Ten14-mediated surface restriction of EGFR resulted in altered biochemical and cellular responses as compared to EGF. Molecules associated with migratory cascades were activated to a relatively greater extent in response to Ten14, with very weak activation of proliferation-associated cascades. Activation of phospholipase C gamma (PLCgamma) and m-calpain, associated with lamellipod protrusion and tail retraction, respectively, were noted at even at sub-saturating doses of Ten14. However, activation of ERK/MAPK, p90RSK, and Elk1, factors affecting proliferation, remained low even at high Ten14 concentrations. Similar activation profiles were observed for EGF-treated cells at 4 degrees C, a maneuver that limits receptor internalization. We demonstrate a concurrent effect of such altered signaling on biophysical responses-sustained migration was observed at levels of Ten14 that activated PLCgamma, but did not stimulate proliferation significantly. Here, we present a novel class of EGFR ligands that can potentially signal as a part of the extracellular matrix, triggering specific intracellular signaling cascades leading to a directed cellular response from an otherwise pleiotropic receptor. This work extends the signaling paradigm of EGFL repeat being presented in a restricted fashion as part of the extracellular matrix.

Cellular responses to EGFR inhibitors and their relevance to cancer therapy

EGFR is a trans-membrane receptor tyrosine kinase that belongs to the HER family of receptors. The EGFR family plays an essential role in normal organ development by mediating morphogenesis and differentiation. Unlike normal cells that have tight regulatory mechanisms controlling EGFR pathways, tumor cells often have dysregulated EGFR signaling through receptor overexpression and/or mutation. This leads to proliferation under adverse conditions, invasion of surrounding tissues, and increased angiogenesis as well as resistance to radiation and chemotherapy. Therefore, EGFR is a legitimate therapeutic target. Numerous EGFR inhibitors are under development, but to date only four of them are FDA-approved, including two that inhibit the receptor's intracellular tyrosine kinase activity (gefitinib and erlotinib) and two that block extracellular ligand binding (cetuximab, and most recently panitumumab). In this review, we focus on how these different inhibitors affect EGFR signaling and the mechanisms by which they potentiate the effects of chemotherapy and radiation therapy. Numerous clinical trials have been conducted with these agents either as monotherapy, in combination with chemotherapy, or concurrently with radiation. Unfortunately, many of the clinical trials reported so far have shown at best limited gains; therefore, understanding the actions of these agents is essential to improving their efficacy in the treatment of cancers.

Identification of novel androgen receptor target genes in prostate cancer

BACKGROUND

The androgen receptor (AR) plays critical roles in both androgen-dependent and castrate-resistant prostate cancer (PCa). However, little is known about AR target genes that mediate the receptor's roles in disease progression.

RESULTS

Using Chromatin Immunoprecipitation (ChIP) Display, we discovered 19 novel loci occupied by the AR in castrate resistant C4-2B PCa cells. Only four of the 19 AR-occupied regions were within 10-kb 5'-flanking regulatory sequences. Three were located up to 4-kb 3' of the nearest gene, eight were intragenic and four were in gene deserts. Whereas the AR occupied the same loci in C4-2B (castrate resistant) and LNCaP (androgen-dependent) PCa cells, differences between the two cell lines were observed in the response of nearby genes to androgens. Among the genes strongly stimulated by DHT in C4-2B cells--D-dopachrome tautomerase (DDT), Protein kinase C delta (PRKCD), Glutathione S- transferase theta 2 (GSTT2), Transient receptor potential cation channel subfamily V member 3 (TRPV3), and Pyrroline-5-carboxylate reductase 1 (PYCR1)--most were less strongly or hardly stimulated in LNCaP cells. Another AR target gene, ornithine aminotransferase (OAT), was AR-stimulated in a ligand-independent manner, since it was repressed by AR siRNA knockdown, but not stimulated by DHT. We also present evidence for in vivo AR-mediated regulation of several genes identified by ChIP Display. For example, PRKCD and PYCR1, which may contribute to PCa cell growth and survival, are expressed in PCa biopsies from primary tumors before and after ablation and in metastatic lesions in a manner consistent with AR-mediated stimulation.

CONCLUSION

AR genomic occupancy is similar between LNCaP and C4-2B cells and is not biased towards 5' gene flanking sequences. The AR transcriptionally regulates less than half the genes nearby AR-occupied regions, usually but not always, in a ligand-dependent manner. Most are stimulated and a few are repressed. In general, response is stronger in C4-2B compared to LNCaP cells. Some of the genes near AR-occupied regions appear to be regulated by the AR in vivo as evidenced by their expression levels in prostate cancer tumors of various stages. Several AR target genes discovered in the present study, for example PRKCD and PYCR1, may open avenues in PCa research and aid the development of new approaches for disease management.