Stable expression of constitutively-activated STAT3 in benign prostatic epithelial cells changes their phenotype to that resembling malignant cells

Second-Generation Jak2 Inhibitors for Advanced Prostate Cancer: Are We Ready for Clinical Development?

Simple Summary

Prostate Cancer (PC) is currently estimated to affect 1 in 9 men and is the second leading cause of cancer in men in the US. While androgen deprivation therapy, which targets the androgen receptor, is one of the front-line therapies for advanced PC and for recurrence of organ-confined PC treated with surgery, lethal castrate-resistant PC develops consistently in patients. PC is a multi-focal cancer with different grade carcinoma areas presenting simultaneously. Jak2-Stat5 signaling pathway has emerged as a potentially highly effective molecular target in PCs with positive areas for activated Stat5 protein. Activated Jak2-Stat5 signaling can be readily targeted by the second-generation Jak2-inhibitors that have been developed for myeloproliferative and autoimmune disorders and hematological malignancies. In this review, we analyze and summarize the Jak2 inhibitors that are currently in preclinical and clinical development.

Abstract

Androgen deprivation therapy (ADT) for metastatic and high-risk prostate cancer (PC) inhibits growth pathways driven by the androgen receptor (AR). Over time, ADT leads to the emergence of lethal castrate-resistant PC (CRPC), which is consistently caused by an acquired ability of tumors to re-activate AR. This has led to the development of second-generation anti-androgens that more effectively antagonize AR, such as enzalutamide (ENZ). However, the resistance of CRPC to ENZ develops rapidly. Studies utilizing preclinical models of PC have established that inhibition of the Jak2-Stat5 signaling leads to extensive PC cell apoptosis and decreased tumor growth. In large clinical cohorts, Jak2-Stat5 activity predicts PC progression and recurrence. Recently, Jak2-Stat5 signaling was demonstrated to induce ENZ-resistant PC growth in preclinical PC models, further emphasizing the importance of Jak2-Stat5 for therapeutic targeting for advanced PC. The discovery of the Jak2V617F somatic mutation in myeloproliferative disorders triggered the rapid development of Jak1/2-specific inhibitors for a variety of myeloproliferative and auto-immune disorders as well as hematological malignancies. Here, we review Jak2 inhibitors targeting the mutated Jak2V617F vs. wild type (WT)-Jak2 that are currently in the development pipeline. Among these 35 compounds with documented Jak2 inhibitory activity, those with potency against WT-Jak2 hold strong potential for advanced PC therapy.

STAT3 is required for Smo-dependent signaling and mediates Smo-targeted treatment resistance and tumorigenesis in Shh medulloblastoma

Sonic hedgehog (Shh)‐driven medulloblastoma (Shh MB) cells are dependent on constitutive Shh signaling, but targeted treatment of Shh MB has been ineffective due to drug resistance. The purpose of this study was to address the critical role of signal transducer and activator of transcription 3 (STAT3) in Shh signaling and drug resistance in Shh MB cells. Herein, we show that STAT3 is required for Smoothened (Smo)‐dependent Shh signaling and, in turn, is reciprocally regulated by Shh signaling, and demonstrate that STAT3 activity is critical for expression of HCK proto‐oncogene, Src family tyrosine kinase (Hck) in Shh MB. We also demonstrate that maintained STAT3 activity suppresses p21 expression and promotes colony formation of Shh MB cells, whereas dual treatment with inhibitors of both Smo and STAT3 results in marked synergistic killing and overcomes drug resistance in vitro of Smo antagonist‐resistant Shh MB cells. Finally, STAT3 inhibitor treatment significantly prevents in vivo tumor formation in genetically engineered Shh MB mice. Collectively, we show that STAT3 is necessary to maintain Shh signaling and thus is a potential therapeutic target to treat Shh MB and overcome anti‐Smo drug resistance.

Inflammatory repercussions in female steroid responsive glands after perinatal exposure to bisphenol A and 17-β estradiol

The mammary gland (MG) and female prostate are plastic reproductive organs which are highly responsive to hormones. Thus, endocrine disruptors, such as bisphenol A (BPA) and exogenous estrogens, negatively affect glandular homeostasis. In addition to previously described alterations, changes in inflammatory markers expression also trigger the development of a microenvironment that contributes to tumor progression. The current work aimed to evaluate the inflammatory responses of the MG and prostate gland to BPA (50 µg/kg) and 17-β estradiol (35 µg/kg) exposure during the perinatal window of susceptibility. The results showed that at 6 months of age there was an increase in the number of phospho-STAT3 (P-STAT3) positive cells in the female prostate from animals perinatally exposed to 50 µg/kg BPA daily. In addition, the number of macrophages increased in these animals in comparison with nonexposed animals, as shown by the F4/80 marker. Despite an increase in the incidence of lobuloalveolar and intraductal hyperplasia, the MG did not show any difference in the expression of the four inflammatory markers evaluated: tumor necrosis factor-α, COX-2, P-STAT3, and F4/80. Analysis of both glands from the same animal led to the conclusion that exposure to endocrine disruptors during the perinatal window of susceptibility leads to different inflammatory responses in different reproductive organs. As the prostate is more susceptible to these inflammatory mechanisms, it is reasonable to affirm that possible neoplastic alterations in this organ are related to changes in the inflammatory pattern of the stroma, a characteristic that is not evident in the MG.

High-Fat Diet Induced Gut Microbiota Alterations Associating With Ghrelin/Jak2/Stat3 Up-Regulation to Promote Benign Prostatic Hyperplasia Development

The role of high-fat diet (HFD) induced gut microbiota alteration and Ghrelin as well as their correlation in benign prostatic hyperplasia (BPH) were explored in our study. The gut microbiota was analyzed by 16s rRNA sequencing. Ghrelin levels in serum, along with Ghrelin and Ghrelin receptor in prostate tissue of mice and patients with BPH were measured. The effect of Ghrelin on cell proliferation, apoptosis, and induction of BPH in mice was explored. Our results indicated that BPH mice have the highest ratio of Firmicutes and Bacteroidetes induced by HFD, as well as Ghrelin level in serum and prostate tissue was significantly increased compared with control. Elevated Ghrelin content in the serum and prostate tissue of BPH patients was also observed. Ghrelin promotes cell proliferation while inhibiting cell apoptosis of prostate cells. The effect of Ghrelin on enlargement of the prostate was found almost equivalent to that of testosterone propionate (TP) which may be attenuated by Ghrelin receptor antagonist YIL-781. Ghrelin could up-regulate Jak2/pJak2/Stat3/pStat3 expression in vitro and in vivo. Our results suggested that Gut microbiota may associate with Ghrelin which plays an important role in activation of Jak2/Stat3 in BPH development. Gut microbiota and Ghrelin might be pathogenic factors for BPH and could be used as a target for mediation.

Capsazepine inhibits JAK/STAT3 signaling, tumor growth, and cell survival in prostate cancer

Persistent STAT3 activation is seen in many tumor cells and promotes malignant transformation. Here, we investigated whether capsazepine (Capz), a synthetic analogue of capsaicin, exerts anticancer effects by inhibiting STAT3 activation in prostate cancer cells. Capz inhibited both constitutive and induced STAT3 activation in human prostate carcinoma cells. Capz also inhibited activation of the upstream kinases JAK1/2 and c-Src. The phosphatase inhibitor pervanadate reversed Capz-induced STAT3 inhibition, indicating that the effect of Capz depends on a protein tyrosine phosphatase. Capz treatment increased PTPε protein and mRNA levels. Moreover, siRNA-mediated knockdown of PTPε reversed the Capz-induced induction of PTPε and inhibition of STAT3 activation, indicating that PTPε is crucial for Capz-dependent STAT3 dephosphorylation. Capz also decreased levels of the protein products of various oncogenes, which in turn inhibited proliferation and invasion and induced apoptosis. Finally, intraperitoneal Capz administration decreased tumor growth in a xenograft mouse prostate cancer model and reduced p-STAT3 and Ki-67 expression. These data suggest that Capz is a novel pharmacological inhibitor of STAT3 activation with several anticancer effects in prostate cancer cells.

Total glucosides of paeony inhibits lipopolysaccharide-induced proliferation, migration and invasion in androgen insensitive prostate cancer cells

Previous studies demonstrated that inflammatory microenvironment promoted prostate cancer progression. This study investigated whether total glucosides of paeony (TGP), the active constituents extracted from the root of Paeonia Lactiflora Pall, suppressed lipopolysaccharide (LPS)-stimulated proliferation, migration and invasion in androgen insensitive prostate cancer cells. PC-3 cells were incubated with LPS (2.0 μg/mL) in the absence or presence of TGP (312.5 μg /mL). As expected, cells at S phase and nuclear CyclinD1, the markers of cell proliferation, were increased in LPS-stimulated PC-3 cells. Migration activity, as determined by wound-healing assay and transwell migration assay, and invasion activity, as determined by transwell invasion assay, were elevated in LPS-stimulated PC-3 cells. Interestingly, TGP suppressed LPS-stimulated PC-3 cells proliferation. Moreover, TGP inhibited LPS-stimulated migration and invasion of PC-3 cells. Additional experiment showed that TGP inhibited activation of nuclear factor kappa B (NF-κB) and mitogen-activated protein kinase (MAPK)/p38 in LPS-stimulated PC-3 cells. Correspondingly, TGP attenuated upregulation of interleukin (IL)-6 and IL-8 in LPS-stimulated PC-3 cells. In addition, TGP inhibited nuclear translocation of signal transducer and activator of transcription 3 (STAT3) in LPS-stimulated PC-3 cells. These results suggest that TGP inhibits inflammation-associated STAT3 activation and proliferation, migration and invasion in androgen insensitive prostate cancer cells.

Interleukin 6 alters localization of hMSH3, leading to DNA mismatch repair defects in colorectal cancer cells

BACKGROUND & AIMS

Elevated microsatellite alterations at selected tetranucleotide repeats (EMAST) is the most common DNA mismatch repair defect in colorectal cancers, observed in approximately 60% of specimens. This acquired genotype correlates with metastasis and poor outcomes for patients, and is associated with intra-epithelial inflammation and heterogeneous nuclear levels of the mismatch repair protein hMSH3. Inflammation and accompanying oxidative stress can cause hMSH3 to change its intracellular location, but little is known about the source of oxidative stress in cancer cells. We investigated whether cytokines mediate this process.

METHODS

We analyzed levels of interleukin 6 (IL6) and its receptor (IL6R) in human colon and lung cancer cell lines by flow cytometry and enzyme-linked immunosorbent assay; proteins were localized by immunofluorescence and immunoblot analyses. IL6 signaling was blocked with antibodies against IL6, soluble glycoprotein 130 Fc fragments, and the signal transducers and activators of transcription 3 inhibitor NSC74859; a constitutively active form of STAT3 was expressed in colon and lung cancer cell lines to replicate IL6R signaling. EMAST was detected by DNA fragment analysis. Immunohistochemistry was used to examine levels of IL6 in 20 colorectal tumor and adjacent nontumor tissues.

RESULTS

Incubation of colon and lung cancer cell lines with IL6, but not other cytokines, caused hMSH3, but no other mismatch repair proteins, to move from the nucleus to the cytosol after generation of oxidative stress; inhibition of IL6 signaling prevented this shift. Expression of constitutively active STAT3 also caused hMSH3 to translocate from the nucleus to the cytoplasm in cancer cell lines. Incubation of cells with IL6 led to tetranucleotide frameshifts, the signature for EMAST. EMAST-positive colorectal tumors had significantly higher levels of IL6 than EMAST-negative tumors.

CONCLUSIONS

IL6 signaling disrupts the nuclear localization of hMSH3 and DNA repair, leading to EMAST in cancer cell lines. Inflammatory cytokines might therefore promote genetic alterations in human cancer cells.

Radiotherapy-induced plasticity of prostate cancer mobilizes stem-like non-adherent, Erk signaling-dependent cells

Fractionated ionizing radiation combined with surgery or hormone therapy represents the first-choice treatment for medium to high-risk localized prostate carcinoma. One of the main reasons for the failure of radiotherapy in prostate cancer is radioresistance and further dissemination of surviving cells. In this study, exposure of four metastasis-derived human prostate cancer cell lines (DU145, PC-3, LNCaP and 22RV1) to clinically relevant daily fractions of ionizing radiation (35 doses of 2 Gy) resulted in generation of two radiation-surviving populations: adherent senescent-like cells expressing common senescence-associated markers and non-adherent anoikis-resistant stem cell-like cells with active Notch signaling and expression of stem cell markers CD133, Oct-4, Sox2 and Nanog. While a subset of the radiation-surviving adherent cells resumed proliferation shortly after completion of the irradiation regimen, the non-adherent cells started to proliferate only on their reattachment several weeks after the radiation-induced loss of adhesion. Like the parental non-irradiated cells, radiation-surviving re-adherent DU145 cells were tumorigenic in immunocompromised mice. The radiation-induced loss of adhesion was dependent on expression of Snail, as siRNA/shRNA-mediated knockdown of Snail prevented cell detachment. On the other hand, survival of the non-adherent cells required active Erk signaling, as chemical inhibition of Erk1/2 by a MEK-selective inhibitor or Erk1/2 knockdown resulted in anoikis-mediated death in the non-adherent cell fraction. Notably, whereas combined inhibition of Erk and PI3K-Akt signaling triggered cell death in the non-adherent cell fraction and blocked proliferation of the adherent population of the prostate cancer cells, such combined treatment had only marginal if any impact on growth of control normal human diploid cells. These results contribute to better understanding of radiation-induced stress response and heterogeneity of human metastatic prostate cancer cells, document treatment-induced plasticity and phenotypically distinct cell subsets, and suggest the way to exploit their differential sensitivity to radiosensitizing drugs in overcoming radioresistance.

Reconstruction and analysis of transcription factor-miRNA co-regulatory feed-forward loops in human cancers using filter-wrapper feature selection

BACKGROUND

As one of the most common types of co-regulatory motifs, feed-forward loops (FFLs) control many cell functions and play an important role in human cancers. Therefore, it is crucial to reconstruct and analyze cancer-related FFLs that are controlled by transcription factor (TF) and microRNA (miRNA) simultaneously, in order to find out how miRNAs and TFs cooperate with each other in cancer cells and how they contribute to carcinogenesis. Current FFL studies rely on predicted regulation information and therefore suffer the false positive issue in prediction results. More critically, FFLs generated by existing approaches cannot represent the dynamic and conditional regulation relationship under different experimental conditions.

METHODOLOGY/PRINCIPAL FINDINGS

In this study, we proposed a novel filter-wrapper feature selection method to accurately identify co-regulatory mechanism by incorporating prior information from predicted regulatory interactions with parallel miRNA/mRNA expression datasets. By applying this method, we reconstructed 208 and 110 TF-miRNA co-regulatory FFLs from human pan-cancer and prostate datasets, respectively. Further analysis of these cancer-related FFLs showed that the top-ranking TF STAT3 and miRNA hsa-let-7e are key regulators implicated in human cancers, which have regulated targets significantly enriched in cellular process regulations and signaling pathways that are involved in carcinogenesis.

CONCLUSIONS/SIGNIFICANCE

In this study, we introduced an efficient computational approach to reconstruct co-regulatory FFLs by accurately identifying gene co-regulatory interactions. The strength of the proposed feature selection method lies in the fact it can precisely filter out false positives in predicted regulatory interactions by quantitatively modeling the complex co-regulation of target genes mediated by TFs and miRNAs simultaneously. Moreover, the proposed feature selection method can be generally applied to other gene regulation studies using parallel expression data with respect to different biological contexts.

Cyclin-dependent kinase 5 modulates STAT3 and androgen receptor activation through phosphorylation of Ser⁷²⁷ on STAT3 in prostate cancer cells

Cyclin-dependent kinase 5 (Cdk5) is known to regulate prostate cancer metastasis. Our previous results indicated that Cdk5 activates androgen receptor (AR) and supports prostate cancer growth. We also found that STAT3 is a target of Cdk5 in promoting thyroid cancer cell growth, whereas STAT3 may play a role as a regulator to AR activation under cytokine control. In this study, we investigated the regulation of Cdk5 and its activator p35 on STAT3/AR signaling in prostate cancer cells. Our results show that Cdk5 biochemically interacts with STAT3 and that this interaction depends on Cdk5 activation in prostate cancer cells. The phosphorylation of STAT3 at Ser⁷²⁷ (p-Ser⁷²⁷-STAT3) is regulated by Cdk5 in cells and xenograft tumors. The mutant of STAT3 S727A reduces its interaction with Cdk5. We further show that the nuclear distribution of p-Ser⁷²⁷-STAT3 and the expression of STAT3-regulated genes (junB, c-fos, c-myc, and survivin) are regulated by Cdk5 activation. STAT3 mutant does not further decrease cell proliferation upon Cdk5 inhibition, which implies that the role of STAT3 regulated by Cdk5 correlates to cell proliferation control. Interestingly, Cdk5 may regulate the interaction between STAT3 and AR through phosphorylation of Ser⁷²⁷-STAT3 and therefore upregulate AR protein stability and transactivation. Correspondingly, clinical evidence shows that the level of p-Ser⁷²⁷-STAT3 is significantly correlated with Gleason score and the levels of upstream regulators (Cdk5 and p35) as well as downstream protein (AR). In conclusion, this study demonstrates that Cdk5 regulates STAT3 activation through Ser⁷²⁷ phosphorylation and further promotes AR activation by protein-protein interaction in prostate cancer cells.

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.

Genetic ablation of PKC epsilon inhibits prostate cancer development and metastasis in transgenic mouse model of prostate adenocarcinoma

Protein kinase C epsilon (PKCε), a novel PKC isoform, is overexpressed in prostate cancer (PCa) and correlates with disease aggressiveness. However, the functional contribution of PKCε to development or progression of PCa remained to be determined. Here we present the first in vivo genetic evidence that PKCε is essential for both the development and metastasis of PCa in the transgenic mouse model of prostate adenocarcinoma (TRAMP). Heterozygous or homozygous genetic deletions of PKCε in FVB/N TRAMP inhibited PCa development and metastasis as analyzed by positron emission tomography/computed tomography, tumor weight determinations, and histopathology. We also examined biomarkers associated with tumor progression in this model, including markers of survival, proliferation, angiogenesis, inflammation, and metastatic progression. To find clues about the genes regulated by PKCε and linked to the Stat3 signaling pathway, we carried out focused PCR arrays of JAK/STAT signaling in excised PCa tissues from PKCε wild-type and nullizygous TRAMP mice. Notably, PKCε loss was associated with significant downregulation of proliferative and metastatic genes C/EBPβ (CCAAT/enhancer binding protein β), CRP (C-reactive protein), CMK, EGFR (epidermal growth factor receptor), CD64, Jun B, and gp130. Taken together, our findings offer the first genetic evidence of the role of PKCε in PCa development and metastasis. PKCε may be potential target for prevention and/or treatment of PCa.

Diallyl trisulfide inhibits activation of signal transducer and activator of transcription 3 in prostate cancer cells in culture and in vivo

Signal transducer and activator of transcription 3 (STAT3) is an oncogenic transcription factor implicated in prostate carcinogenesis. The present study shows that diallyl trisulfide (DATS), a promising cancer-chemopreventive constituent of processed garlic, inhibits phosphorylation of STAT3 in prostate cancer cells in culture and in vivo. Exposure of DU145 and LNCaP human prostate cancer cells to growth-suppressive and pharmacologically relevant concentrations of DATS (20 and 40 μmol/L) resulted in suppression of constitutive (DU145) as well as interleukin-6 (IL-6)-induced (LNCaP) phosphorylation of STAT3 (Tyr(705)), which correlated with inhibition of Janus-activated kinase 2 phosphorylation. Constitutive and/or IL-6-induced nuclear translocation of pSTAT3 and STAT3 dimerization was also markedly inhibited on treatment with DATS in both cell lines. Inhibition of prostate cancer development in transgenic adenocarcinoma of mouse prostate mice by gavage of DATS correlated with a visible decrease in the levels of pSTAT3. Interestingly, the IL-6-mediated activation of STAT3 largely failed to confer protection against proapoptotic response to DATS in both cells. Likewise, DATS-mediated inhibition of cell migration was either not affected or minimally reversed by IL-6 treatment or ectopic expression of constitutively active STAT3. In conclusion, the present study indicates that DATS treatment suppresses STAT3 phosphorylation in prostate cancer cells in culture and in vivo, but activation of this oncogenic transcription factor is largely dispensable for cellular responses to DATS. Ability of DATS to overcome STAT3 activation is a therapeutic advantage for this chemopreventive agent.

Antagonists of growth hormone-releasing hormone inhibit the proliferation of human benign prostatic hyperplasia cells

BACKGROUND

Growth hormone-releasing hormone (GHRH), besides stimulating the secretion of GH from the pituitary gland, acts as an autocrine/paracrine growth factor in many cancers. Antagonists of GHRH inhibit growth of experimental human tumors, but their effects on benign prostatic hyperplasia (BPH) have not been studied.

MATERIALS AND METHODS

We evaluated the effects of GHRH and GHRH antagonists JMR-132, MZ-5-156, MIA-601, and MIA-479 on the proliferation rate of human BPH-1 cells. We also measured by Western blot the influence of GHRH and GHRH antagonist JMR-132 on the expression of the PCNA and the activation of ERK1/2 and JAK/STAT3.

RESULTS

BPH-1 cells express GHRH and GHRH-receptor proteins. The proliferation rate of BPH-1 cells is increased by GHRH and inhibited by all the GHRH antagonists, the latest analogs MIA-601 and MIA-479 being the most potent. The stimulatory effect of GHRH is nullified by GHRH antagonists. GHRH strongly activates and GHRH antagonists significantly suppress the expression of the PCNA and the phosphorylation of ERK1/2 and JAK2/STAT3 pathways in these cells. Treatment with JAK2 inhibitor (AG490) decreases the proliferation rate of BPH-1 cells, and AG490 does nullify the effect of GHRH.

CONCLUSION

This study demonstrates for the first time that GHRH can act as a growth factor in BPH-1 cells and that GHRH antagonists can reverse its stimulatory effect. New observations are provided on the mechanism of action of GHRH antagonists in BPH. Our findings support the merit of further work on the development of GHRH antagonists for therapy of BPH.

A novel small molecule, LLL12, inhibits STAT3 phosphorylation and activities and exhibits potent growth-suppressive activity in human cancer cells

Constitutive activation of signal transducer and activator of transcription 3 (STAT3) signaling is frequently detected in cancer, promoting its emergence as a promising target for cancer treatment. Inhibiting constitutive STAT3 signaling represents a potential therapeutic approach. We used structure-based design to develop a nonpeptide, cell-permeable, small molecule, termed as LLL12, which targets STAT3. LLL12 was found to inhibit STAT3 phosphorylation (tyrosine 705) and induce apoptosis as indicated by the increases of cleaved caspase-3 and poly (ADP-ribose) polymerase in various breast, pancreatic, and glioblastoma cancer cell lines expressing elevated levels of STAT3 phosphorylation. LLL12 could also inhibit STAT3 phosphorylation induced by interleukin-6 in MDA-MB-453 breast cancer cells. The inhibition of STAT3 by LLL12 was confirmed by the inhibition of STAT3 DNA binding activity and STAT3-dependent transcriptional luciferase activity. Downstream targets of STAT3, cyclin D1, Bcl-2, and survivin were also downregulated by LLL12 at both protein and messenger RNA levels. LLL12 is a potent inhibitor of cell viability, with half-maximal inhibitory concentrations values ranging between 0.16 and 3.09 microM, which are lower than the reported JAK2 inhibitor WP1066 and STAT3 inhibitor S3I-201 in six cancer cell lines expressing elevated levels of STAT3 phosphorylation. In addition, LLL12 inhibits colony formation and cell migration and works synergistically with doxorubicin and gemcitabine. Furthermore, LLL12 demonstrated a potent inhibitory activity on breast and glioblastoma tumor growth in a mouse xenograft model. Our results indicate that LLL12 may be a potential therapeutic agent for human cancer cells expressing constitutive STAT3 signaling.

Sulforaphane inhibits constitutive and interleukin-6-induced activation of signal transducer and activator of transcription 3 in prostate cancer cells

D,L-sulforaphane (SFN), a synthetic analogue of broccoli-derived L-isomer, inhibits viability of human prostate cancer cells and prevents development of prostate cancer and distant site metastasis in a transgenic mouse model. However, the mechanism underlying the anticancer effect of SFN is not fully understood. We now show that SFN inhibits constitutive and interleukin-6 (IL-6)-inducible activation of signal transducer and activator of transcription 3 (STAT3), which is an oncogenic transcription factor activated in many human malignancies, including prostate cancer. Growth-suppressive concentrations of SFN (20 and 40 micromol/L) decreased constitutive (DU145 cells) and IL-6-induced (DU145 and LNCaP cells) phosphorylation of STAT3 (Tyr(705)) as well as its upstream regulator Janus-activated kinase 2 (Tyr(1007/1008)). Exposure of DU145 and LNCaP cells to SFN resulted in suppression of (a) IL-6-induced transcriptional activity of STAT3 as judged by luciferase reporter assay and (b) nuclear translocation of phospho-STAT3 as revealed by immunofluorescence microscopy. Levels of many STAT3-regulated gene products, including Bcl-2, cyclin D1, and survivin, were also reduced in SFN-treated cells. The IL-6-mediated activation of STAT3 conferred partial but marked protection against SFN-induced apoptosis as evidenced by cytoplasmic histone-associated DNA fragmentation and cleavage of poly(ADP-ribose) polymerase and procaspase-3. Furthermore, knockdown of STAT3 protein using small interfering RNA resulted in a modest yet statistically significant increase in SFN-induced apoptotic DNA fragmentation in DU145 cells. Suppression of STAT3 activation was also observed in cells treated with naturally occurring analogues of SFN. In conclusion, the present study indicates that inhibition of STAT3 partially contributes to the proapoptotic effect of SFN.

Transcription factor Stat3 stimulates metastatic behavior of human prostate cancer cells in vivo, whereas Stat5b has a preferential role in the promotion of prostate cancer cell viability and tumor growth

Identification of the molecular changes that promote viability and metastatic behavior of prostate cancer is critical for the development of improved therapeutic interventions. Stat5a/b and Stat3 are both constitutively active in locally-confined and advanced prostate cancer, and both transcription factors have been reported to be critical for the viability of prostate cancer cells. We recently showed that Stat3 promotes metastatic behavior of human prostate cancer cells not only in vitro but also in an in vivo experimental metastases model. In this work, we compare side-by-side Stat5a/b versus Stat3 in the promotion of prostate cancer cell viability, tumor growth, and induction of metastatic colonization in vivo. Inhibition of Stat5a/b induced massive death of prostate cancer cells in culture and reduced both subcutaneous and orthotopic prostate tumor growth, whereas Stat3 had a predominant role over Stat5a/b in promoting metastases formation of prostate cancer cells in vivo in nude mice. The molecular mechanisms underlying the differential biological effects induced by these two transcription factors involve largely different sets of genes regulated by Stat5a/b versus Stat3 in human prostate cancer model systems. Of the two Stat5 homologs, Stat5b was more important for supporting growth of prostate cancer cells than Stat5a. This work provides the first mechanistic comparison of the biological effects induced by transcription factors Stat5a/b versus Stat3 in prostate cancer.

Iron complexation to oxygen rich marine natural products: a computational study

The natural products kahalalide F, halichondrin B, and discodermolide are relatively large structures that were originally harvested from marine organisms. They are oxygen rich structures that, to varying degrees, should have the ability to bind iron (II or III) by Fe-O and/or Fe-N bonds. In this semi empirical study, the binding of these natural products to iron (II) is studied and the aqueous stability factor (ASF) is used to determine which bonding configuration is most stable. The energy, the complex charge (+1), the average Fe-O (or Fe-N) bond distances and the dipole moments are used to calculate the ASF. The ASF provides insight to which complex will be the most stable and water soluble, important for a medicinal application. The ability of a molecule with a more than six oxygen and/or nitrogen atoms to bind iron (hexavalent, octahedral) by shifting which six atoms (O/N) are bound to the iron qualifies it as a polarity adaptive molecule.

Pathway biomarker profiling of localized and metastatic human prostate cancer reveal metastatic and prognostic signatures

Reverse phase protein microarray technology was used to study key signaling pathways thought to be involved in the progression of benign epithelium to the lethal phenotype of prostate cancer. Specimens of androgen-stimulated localized prostate cancer (N = 21) and androgen-deprivation therapy-recurrent local (N = 4) or metastatic (N = 11) prostate cancer were laser capture microdissected prior to analysis. The results showed significant increases in protein expression levels in malignant epithelial cells and patient-matched stromal tissue, which included higher levels of the apoptotic proteins Bax and Smac/Diablo and increased phosphorylation of Bcl2 (S70). The mitochondrial protein Smac/Diablo and the transcription regulatory protein STAT3 (Y705) correlated with Gleason sum and differed statistically in high Gleason grade (8-10) prostate cancers. Distinct metastasis-specific pathways were activated by caspase cleavage activation, ErbB2 phosphorylation, Bax total protein and Bcl-2 phosphorylation while phosphorylation of all three members of the MAPK family, ERK, p38, and SAP/JNK, were reduced significantly in metastatic lesions compared to primary cancers. This study, the most comprehensive pathway analysis ever performed for human prostate cancer, presents evidence of specific pathway biomarkers that may be useful for assessment of prognosis and stratification for therapy if validated in larger clinical study sets.

Expression of activated signal transducer and activator of transcription-3 predicts poor prognosis in cervical squamous-cell carcinoma

BACKGROUND

Stat3 is a member of the Janus-activated kinase/STAT signalling pathway. It normally resides in the cytoplasm and can be activated through phosphorylation. Activated Stat3 (p-Stat3) translocates to the nucleus to activate the transcription of several molecules involved in cell survival and proliferation. The constitutive activation of Stat3 has been shown in various types of malignancies, and its expression has been reported to indicate a poor prognosis. However, the correlation between the constitutive activation of Stat3 and the prognosis of cervical cancer patients has not been reported.

METHODS

The immunohistochemical analysis of p-Stat3 expression was performed on tissues from 125 cervical squamous-cell carcinoma patients who underwent extended hysterectomy and pelvic lymphadenectomy, and the association of p-Stat3 expression with several clinicopathological factors and survival was investigated.

RESULTS

Positive p-Stat3 expression was observed in 71 of 125 (56.8%) cases and was significantly correlated with lymph node metastasis, lymph vascular space invasion, and large tumour diameter (>4 cm) by Fisher's exact test. Kaplan-Meier survival analysis showed that p-Stat3 expression was statistically indicative of a poor prognosis for overall survival (P=0.006) and disease-free survival (P=0.010) by log-rank test.

CONCLUSION

These data showed that p-Stat3 expression in cervical cancer acts as a predictor of poor prognosis.

Alternative implication of CXCR4 in JAK2/STAT3 activation in small cell lung cancer

Small cell lung cancer (SCLC) is an aggressive, rapidly metastasising tumour. Previously, we demonstrated the influence of CXCL12–CXCR4 interaction on processes involved in metastasis and chemoresistance in SCLC. We show here that STAT3 is expressed in both primary SCLC tumour tissues and SCLC cell lines. We investigated the function of STAT3 upon CXCL12 stimulation in SCLC cell lines. Small cell lung cancer cell lines present constitutive phosphorylation of STAT3, and in the reference cell lines NCI-H69 and NCI-H82 constitutive phosphorylation was further increased by CXCL12 stimulation. Further investigating this signalling cascade, we showed that it involves interactions between CXCR4 and JAK2 in both cell lines. However CXCL12-induced adhesion to VCAM-1 could be completely inhibited by the JAK2 inhibitor AG490 only in NCI-H82. Furthermore, CXCR4 antagonist but not AG490 inhibited cell adhesion whereas both antagonisms were shown to inhibit growth of the cells in soft agar, indicating the central involvement of this signalling in anchorage-independent growth of SCLC cells. Most interestingly, while using primary tumour material, we observed that in contrast to non-small-cell lung cancer samples from primary tumour tissues, all analysed samples from SCLC were strongly positive for tyrosine-phosphorylated STAT3. Taken together, these data indicate that STAT3 is constitutively phosphorylated in SCLC and is important in SCLC growth and spreading thus presenting an interesting target for therapy.

S-glutathionylation impairs signal transducer and activator of transcription 3 activation and signaling

S-glutathionylation is a physiological, reversible protein modification of cysteine residues with glutathione in response to mild oxidative stress. Because the key cell growth regulator signal transducer and activator of transcription (STAT) 3 is particularly susceptible to redox regulation, we hypothesized that oxidative modification of cysteine residues of STAT3 by S-glutathionylation may occur. Herein, we show that the cysteine residues of STAT3 are modified by a thiol-alkylating agent and are the targets of S-glutathionylation. STAT3 protein thiol reactivity was reversibly attenuated with concomitant increase in the S-glutathionylation of STAT3 upon treatment of human HepG2 hepatoma cells with pyrrolidine dithiocarbamate, glutathione disulfide, or diamide. Under these conditions there was a marked reduction in IL-6-dependent STAT3 signaling, including decreased STAT3 tyrosine phosphorylation, loss in nuclear accumulation of STAT3, and impaired expression of target genes, such as fibrinogen-gamma. In a cell-free system, diamide induced glutathionylation of STAT3, which was decreased upon addition of glutaredoxin (GRX)-1, a deglutathionylation enzyme, or the reducing agent, dithiothreitol. Glutathionylated STAT3 was a poor Janus protein tyrosine kinase 2 substrate in vitro, and it exhibited low DNA-binding activity. Cellular GRX-1 activity was inhibited by diamide and pyrrolidine dithiocarbamate treatment; however, ectopic expression of GRX-1 was accompanied by a modest increase in phosphorylation, nuclear translocation, and DNA-binding ability of STAT3 in response to IL-6. These results are the first to show S-glutathionylation of STAT3, a modification that may exert regulatory function in STAT3 signaling.

LLL-3 inhibits STAT3 activity, suppresses glioblastoma cell growth and prolongs survival in a mouse glioblastoma model

Persistent activation of the signal transducer and activator of transcription 3 (STAT3) signalling has been linked to oncogenesis and the development of chemotherapy resistance in glioblastoma and other cancers. Inhibition of the STAT3 pathway thus represents an attractive therapeutic approach for cancer. In this study, we investigated the inhibitory effects of a small molecule compound known as LLL-3, which is a structural analogue of the earlier reported STAT3 inhibitor, STA-21, on the cell viability of human glioblastoma cells, U87, U373, and U251 expressing constitutively activated STAT3. We also investigated the inhibitory effects of LLL-3 on U87 glioblastoma cell growth in a mouse tumour model as well as the impact it had on the survival time of the treated mice. We observed that LLL-3 inhibited STAT3-dependent transcriptional and DNA binding activities. LLL-3 also inhibited viability of U87, U373, and U251 glioblastoma cells as well as induced apoptosis of these glioblastoma cell lines as evidenced by increased poly (ADP-ribose) polymerase (PARP) and caspase-3 cleavages. Furthermore, the U87 glioblastoma tumour-bearing mice treated with LLL-3 exhibited prolonged survival relative to vehicle-treated mice (28.5 vs 16 days) and had smaller intracranial tumours and no evidence of contralateral invasion. These results suggest that LLL-3 may be a potential therapeutic agent in the treatment of glioblastoma with constitutive STAT3 activation.

Plumbagin, a medicinal plant-derived naphthoquinone, is a novel inhibitor of the growth and invasion of hormone-refractory prostate cancer

Prostate cancer (PCa) is the second leading cause of cancer-related deaths in men. Hormone-refractory invasive PCa is the end stage and accounts for the majority of PCa patient deaths. We present here that plumbagin (PL), a quinoid constituent isolated from the root of the medicinal plant Plumbago zeylanica L., may be a potential novel agent in the control of hormone-refractory PCa. Specific observations are the findings that PL inhibited PCa cell invasion and selectively induced apoptosis in PCa cells but not in immortalized nontumorigenic prostate epithelial RWPE-1 cells. In addition, i.p. administration of PL (2 mg/kg body weight), beginning 3 days after ectopic implantation of hormone-refractory DU145 PCa cells, delayed tumor growth by 3 weeks and reduced both tumor weight and volume by 90%. Discontinuation of PL treatment in PL-treated mice for as long as 4 weeks did not result in progression of tumor growth. PL, at concentrations as low as 5 micromol/L, inhibited in both cultured PCa cells and DU145 xenografts (a) the expression of protein kinase Cepsilon (PKCepsilon), phosphatidylinositol 3-kinase, phosphorylated AKT, phosphorylated Janus-activated kinase-2, and phosphorylated signal transducer and activator of transcription 3 (Stat3); (b) the DNA-binding activity of transcription factors activator protein-1, nuclear factor-kappaB, and Stat3; and (c) Bcl-xL, cdc25A, and cyclooxygenase-2 expression. The results indicate for the first time, using both in vitro and in vivo preclinical models, that PL inhibits the growth and invasion of PCa. PL inhibits multiple molecular targets including PKCepsilon, a predictive biomarker of PCa aggressiveness. PL may be a novel agent for therapy of hormone-refractory PCa.

Stat3 promotes metastatic progression of prostate cancer

There are currently no effective therapies for metastatic prostate cancer because the molecular mechanisms that underlie the metastatic spread of primary prostate cancer are unclear. Transcription factor Stat3 is constitutively active in malignant prostate epithelium, and its activation is associated with high histological grade and advanced cancer stage. In this work, we hypothesized that Stat3 stimulates metastatic progression of prostate cancer. We show that Stat3 is active in 77% of lymph node and 67% of bone metastases of clinical human prostate cancers. Importantly, adenoviral gene delivery of wild-type Stat3 (AdWTStat3) to DU145 human prostate cancer cells increased the number of lung metastases by 33-fold in an experimental metastasis assay compared with controls. Using various methods to inhibit Stat3, we demonstrated that Stat3 promotes human prostate cancer cell migration. Stat3 induced the formation of lamellipodia in both DU145 and PC-3 cells, further supporting the concept that Stat3 promotes a migratory phenotype of human prostate cancer cells. Moreover, Stat3 caused the rearrangement of cytoplasmic actin stress fibers and microtubules in both DU145 and PC-3 cells. Finally, inhibition of the Jak2 tyrosine kinase decreased both activation of Stat3 and prostate cancer cell motility. Collectively, these data indicate that transcription factor Stat3 is involved in metastatic behavior of human prostate cancer cells and may provide a therapeutic target to prevent metastatic spread of primary prostate cancer.

The PIM1 kinase is a critical component of a survival pathway activated by docetaxel and promotes survival of docetaxel-treated prostate cancer cells

A defining characteristic of solid tumors is the capacity to divide aggressively and disseminate under conditions of nutrient deprivation, limited oxygen availability, and exposure to cytotoxic drugs or radiation. Survival pathways are activated within tumor cells to cope with these ambient stresses. We here describe a survival pathway activated by the anti-cancer drug docetaxel in prostate cancer cells. Docetaxel activates STAT3 phosphorylation and transcriptional activity, which in turns induces expression of the PIM1 gene, encoding a serine-threonine kinase activated by many cellular stresses. Expression of PIM1 improves survival of docetaxel-treated prostate cancer cells, and PIM1 knockdown or expression of a dominant-negative PIM1 protein sensitize cells to the cytotoxic effects of docetaxel. PIM1 in turn mediates docetaxel-induced activation of NFkappaB transcriptional activity, and PIM1 depends in part on RELA/p65 proteins for its prosurvival effects. The PIM1 kinase plays a critical role in this STAT3 --> PIM1 --> NFkappaB stress response pathway and serves as a target for intervention to enhance the therapeutic effects of cytotoxic drugs such as docetaxel.

TNF-alpha stimulation inhibits siRNA-mediated RNA interference through a mechanism involving poly-(A) tail stabilization

The control of mRNA stability is a complex biological process that involves numerous factors, including microRNA (miRNA) and short interfering RNA (siRNA). Here, we show that short interfering RNA (siRNA) and microRNA share some similarities in their response to cellular stress. miR16 expedites the degradation of mRNAs containing AU-rich elements (ARE) in their 3' untranslated region (UTR). si20 is an siRNA designed to target a non-ARE sequence in the TNF 3'UTR. We found that both si20 and miR16/ARE-mediated degradation of mRNAs can be inhibited by stimulating cells with different stresses. By analyzing TNF-alpha stimulation-mediated stabilization of si20- and miR16-targeted mRNA, we show that this stabilization is not caused by modifying si20 and miR16 loading into Ago2 complexes, or mRNA targeting to Ago2, but by inhibiting mRNA deadenylation. This is the first report showing that a specific siRNA-mediated mRNA degradation can be regulated by inflammatory stimuli, and that deadenylation is involved in this siRNA-mediated mRNA decay.

Galiellalactone is a novel therapeutic candidate against hormone-refractory prostate cancer expressing activated Stat3

BACKGROUND

Signal transducer and activator of transcription 3 (Stat3) is constitutively active (phosphorylated) in several forms of cancer, including prostate cancer (PCa). Stat3 signaling may be an interesting target for cancer therapy since inhibition of this pathway mediates growth inhibition and apoptosis of these cells. In this study we investigated the in vitro and in vivo effects of the fungal metabolite galiellalactone, a direct inhibitor of Stat3, on PCa cells.

METHODS

The human PCa cell lines DU145, PC-3, and LNCaP were used. Nude mice with subcutaneous PCa cell xenografts were subjected to daily intraperitoneal injections of galiellalactone for 3 weeks. The effect of galiellalactone on the induction of apoptosis of cultured PCa cells was investigated by Western blot analysis, immunocytochemistry, and annexin V staining. Effects of galiellalactone on Stat3 signaling were investigated by a luciferase reporter gene assay. Expression of Stat3 associated proteins and mRNA was investigated by Western blot and real-time quantitative PCR analysis.

RESULTS

Galiellalactone induced apoptosis of p-Stat3 positive PCa cells (androgen-insensitive DU145 and PC-3) but not in cells lacking p-Stat3 (androgen-sensitive LNCaP). Galiellalactone inhibited Stat3-mediated luciferase activity (IC(50) approximately 5 microM) and reduced the expression of Bcl-2, Bcl-x(L), c-myc, and cyclin D1. Furthermore, galiellalactone significantly suppressed DU145 xenograft growth in vivo (42% growth reduction; P<0.002) and reduced the relative mRNA expression of Bcl-x(L) and Mcl-1.

CONCLUSIONS

Galiellalactone induced growth inhibition and apoptosis in androgen-insensitive PCa cells expressing p-Stat3. We suggest that galiellalactone is a potential anti-tumor lead against hormone-refractory PCa with constitutively active Stat3.

Epidermal growth factor receptor activation in prostate cancer by three novel missense mutations

While epidermal growth factor receptor (EGFR) dysregulation is known to play a critical role in prostate carcinogenesis, there has been no direct evidence indicating EGFR mutations induce tumorigenesis in prostate cancer. We previously identified four novel EGFR somatic mutations in the EGFR tyrosine kinase domain of prostate cancer patients: G735S, G796S, E804G and R841K. In this study, we investigated the oncogenic potential of these somatic mutations by establishing stable clonal NIH3T3 cells expressing these four mutations and WT EGFR to determine their ability to increase cell proliferation and invasion. In the absence of the EGF ligand, cell proliferation was readily increased in G735S, G796S and E804G mutants compared to WT EGFR. The addition of EGF ligand greatly increased cell growth and transforming ability of these same EGFR mutants. Matrigel invasion assays showed enhanced invasion with G735S, G796S and E804G mutants. Western blot analysis showed that these EGFR mutations enhanced cell growth and invasion via constitutive and hyperactive tyrosine phosphorylation and led to the activation of mitogen-activated protein kinase (MAPK), signal transducer and activator of transcription 3 (STAT3) and Akt pathways. Our findings demonstrate the oncogenic activation of three novel EGFR somatic missense mutations in prostate cancer. Molecules that regulate the mechanisms of their oncogenic activation represent novel targets for limiting tumor cell progression, and further elucidation of these mutations will have utility in prostate cancer treatment.

Protein kinase Cepsilon interacts with Stat3 and regulates its activation that is essential for the development of skin cancer

Protein kinase C (PKC) represents a large family of phosphatidylserine (PS)-dependent serine/threonine protein kinases. At least six PKC isoforms (alpha, delta, epsilon, eta, micro, and zeta) are expressed in epidermis. PKC is a major intracellular receptor for 12-O-tetradecanoylphorbol-13-acetate (TPA) and is also activated by a variety of stress factors including ultraviolet radiation (UVR). PKC isozymes (alpha, delta, epsilon, and eta), exhibit specificities to the development of skin cancer. PKCepsilon, a calcium-insensitive PKC isoform, is linked to the development of squamous cell carcinoma (SCC) elicited either by the 7,12-Dimethylbenzanthracene (DMBA)-TPA protocol or by repeated exposures to UVR. PKCepsilon overexpressing transgenic mice, when treated either with TPA or exposed to UVR, elicit similar responses such as inhibition of apoptosis, promotion of cell survival, and development of SCC. PKCepsilon overexpression increases Stat3 activation after either TPA treatment or UVR exposure. Both PKCepsilon and signal transducers and activators of transcription-3 (Stat3) are implicated in the development of SCC. However, the link between PKCepsilon and Stat3 remains elusive. We found that PKCepsilon interacts with Stat3. PKCepsilon interaction with Stat3 was dependent upon UVR treatment. In reciprocal immunoprecipitation/blotting experiments, Stat3 coimmunoprecipitated with PKCepsilon. Colocalization of PKCepsilon with Stat3 was confirmed by double immunofluorescence staining. PKCepsilon interaction with Stat3 was PKCepsilon isoform specific and was not observed with other protein kinases. As observed in vitro with immunocomplex kinase assay with immunopurified PKCepsilon and Stat3, PKCepsilon phosphorylated Stat3 at the serine 727 residue. PKCepsilon depletion prevented Stat3Ser727 phosphorylation, Stat3 DNA binding, and transcriptional activity. The results presented indicate that PKCepsilon mediates Stat3 activation.

Constitutively activated Stat3 induces tumorigenesis and enhances cell motility of prostate epithelial cells through integrin beta 6

The persistent activation of signal transducer and activator of transcription 3 (Stat3) is a common feature of prostate cancer. However, little is known about the Stat3 targets that may mediate prostate tumorigenesis. The introduction of an activating mutant form of Stat3 (Stat3-C) into immortalized prostate epithelial cells resulted in tumorigenesis. Stat3-C-expressing cells had decreased E-cadherin levels, increased numbers of lamellipodia and stress fibers, and enhanced migratory capacities compared to vector control-expressing cells, with a concomitant increase in the expression of integrin beta6 and its ligand, fibronectin (FN). Exogenously added FN increased cellular migration, with a concomitant loss of E-cadherin expression. The blockade of integrin alphavbeta6 in Stat3-C-expressing cells inhibited migration, increased E-cadherin levels, and reduced colony formation in soft agar. These results demonstrate the sufficiency of constitutively activated Stat3 in mediating prostate tumorigenesis and identify novel Stat3 targets that are involved in promoting cell migration and transformation.

The role of constitutively active signal transducer and activator of transcription 3 in ovarian tumorigenesis and prognosis

BACKGROUND

Signal transducer and activator of transcription 3 (Stat3), which is a latent transcription factor that participates in the transcriptional activation of apoptosis and cell cycle progression, has been implicated as an oncogene in several neoplastic diseases. However, the specific role of Stat3 in ovarian carcinogenesis remains poorly understood. The objectives of the current study were to examine the effect of Stat3 activation on the phenotypic transformation of an immortalized, nontumorigenic ovarian epithelial cell line and to evaluate the expression of tyrosine-activated Stat3 (pStat3) in tissue microarrays from 303 ovarian carcinomas to determine its prognostic relevance and to correlate its expression with several upstream oncogenes of Stat3 and with the oncogenes involved in apoptosis and proliferation.

METHODS

Overexpression of pStat3 was weakly tumorigenic and produced measurable tumors in mice in 1 of 3 clones. Using tissue microarrays from a large group of patients with primary ovarian carcinoma, the expression of pStat3 was correlated with the expression of growth factor receptors (HER-2/neu and epidermal growth factor receptor [EGFR]), interleukin 6, and the proliferation and apoptosis markers Ki-67, Bcl-2, and Bcl-xL and with clinicopathologic variables and patient survival.

RESULTS

High pStat3 expression in the tumor tissue microarray was associated with high levels of HER-2/neu, EGFR, and Ki-67. No correlation was observed between overall pStat3 levels and any other clinicopathologic variables tested. High nuclear expression of pStat3 (>10% of positive-stained cells) was linked with poor overall survival.

CONCLUSIONS

The activation and translocation of pStat3 to the nucleus are frequent events in ovarian carcinoma that are associated with a poor prognosis. Further studies are needed to elucidate the mechanism of activation of Stat3, its effects on downstream targets, and its role in the neoplastic transformation of epithelial ovarian cells.

Molecular markers in the diagnosis of prostate cancer

The genetic alterations leading to prostate cancer are gradually being discovered. A wide variety of genes have been associated with prostate cancer development as well as tumor progression. Knowledge of gene polymorphisms associated with disease aid in the understanding of important pathways involved in this process and may result in the near future in clinical applications. Urinary molecular markers will soon be available to aid in the decision of repeat prostate biopsies. Recent findings suggest the importance of androgen signaling in disease development and progression. The further understanding of interaction of inflammation, diet, and genetic predisposition will improve risk stratification in the near future.

Genistein-induced neuroendocrine differentiation of prostate cancer cells

BACKGROUND

Neuroendocrine (NE) cells are present in normal prostate and their number appears to be increased in advanced prostate cancer (PCA). In this study, we studied the effect of the phytoestrogen, genistein, on NE differentiation of LNCaP cells in vitro.

METHODS

Neuroendocrine marker expression of LNCaP cells exposed to genistein was measured by immunohistochemistry, Western blot, and real-time PCR methods. Western blot analysis was used to study cell cycle and signaling pathways induced by genistein treatment.

RESULTS

Six days after continuous genistein treatment, the majority of genistein-surviving cancer cells underwent transdifferentiation into a NE-like phenotype overexpressing the NE markers chromogranin A, synaptophysin, serotonin, and beta-III tubulin. This NE differentiation process was associated with upregulation of the cell cycle modulators p21, p27, and p53, and activation of the MAPK and STAT3 pathways.

CONCLUSION

Our data indicate that genistein evokes not only apoptosis but also NE transdifferentiation of PCA cells.

Stat3 cleavage by caspases: impact on full-length Stat3 expression, fragment formation, and transcriptional activity

Stat3 and its isoforms belong to a family of cytoplasmic transcription factors that affect the synthesis of various proteins. Caspases are cysteinyl-aspartate proteases that function under apoptotic and non-apoptotic conditions. We now report that, in addition to transcriptional splicing, Stat3 fragmentation can be mediated by caspases. Caspase activation in DU145 cells was achieved by staurosporine (STS) exposure, and Western analysis revealed a reduction in full-length Stat3 (fl-Stat3) expression that was caspase-mediated. This proteolytic relationship was further studied by exposing purified Stat3 protein to a mixture of active caspases under cell-free conditions. This demonstrated that caspases directly cleaved Stat3 and Stat3 cleavage was accompanied by the apparent formation of cleavage fragment(s). Stat3 cleavage fragments, reflecting multiple caspase cleavage sites, also were observed in vitro following STS exposure in DU145 cells and in HEK293T cells transfected to express Stat3 truncation mutants. The impact of cleavage on Stat3 transcriptional activity next was assessed and revealed that cleavage of fl-Stat3 was accompanied by reductions in Stat3-DNA binding, Stat3-driven reporter protein (luciferase) activity, and the expression of selected Stat3-dependent genes. Further, reduced Stat3 expression correlated with increased sensitivity to apoptotic stimuli. In concomitant experiments, reporter activity was assessed in Stat3 truncation mutant-expressing HEK293T cells and revealed that, under non-apoptotic conditions, expression of different Stat3 fragments induced differential effects on Stat3-driven luciferase activity. These findings demonstrate that fl-Stat3 undergoes proteolytic processing by caspases that reduces its expression and leads to the formation of cleavage fragments that may modulate Stat3 transcriptional activity.

Tocopherol-associated protein suppresses prostate cancer cell growth by inhibition of the phosphoinositide 3-kinase pathway

Epidemiologic studies suggested that vitamin E has a protective effect against prostate cancer. We showed here that tocopherol-associated protein (TAP), a vitamin E-binding protein, promoted vitamin E uptake and facilitated vitamin E antiproliferation effect in prostate cancer cells. Interestingly, without vitamin E treatment, overexpression of TAP in prostate cancer cells significantly suppressed cell growth; knockdown of endogenous TAP by TAP small interfering RNA (siRNA) in nonmalignant prostate HPr-1 cells increased cell growth. Further mechanism dissection studies suggested that the tumor suppressor function of TAP was via down-regulation of phosphoinositide 3-kinase (PI3K)/Akt signaling, but not by modulating cell cycle arrest or androgen receptor signaling. Immunoprecipitation results indicated that TAP inhibited the interaction of PI3K subunits, p110 with p85, and subsequently reduced Akt activity. Constitutively active Akt could negate the TAP-suppressive activity on prostate cancer cell growth. Moreover, stable transfection of TAP in LNCaP cells suppressed LNCaP tumor incidence and growth rate in nude mice. Furthermore, TAP mRNA and protein expression levels were significantly down-regulated in human prostate cancer tissue samples compared with benign prostate tissues as measured by reverse transcription-PCR, in situ hybridization, and immunohistochemistry. Together, our data suggest that TAP not only mediates vitamin E absorption to facilitate vitamin E antiproliferation effect in prostate cancer cells, but also functions like a tumor suppressor gene to control cancer cell viability through a non-vitamin E manner. Therefore, TAP may represent a new prognostic marker for prostate cancer progression.

Clinical and pathologic significance of activation of signal transducer and activator of transcription 3 in prostate cancer

OBJECTIVES

To evaluate the association of signal transducer and activator of transcription 3 (STAT3) with the invasiveness and aggressiveness of localized prostate cancer.

METHODS

Paraffin-embedded specimens from 92 patients with clinically localized prostate cancer who underwent radical prostatectomy without neoadjuvant treatment were analyzed by immunohistochemistry using two antibodies: anti-phospho-specific STAT3 (p-STAT3) antibody, which recognized only activated STAT3, and anti-total STAT3 antibody, which recognized both activated and inactivated STAT3. The patients were separated into one of four groups according to the percentage of the cells with positive nuclear staining using a 0 to 3+ scoring system. The associations between the immunostaining and invasiveness and aggressiveness of clinically localized prostate cancer were analyzed.

RESULTS

Pathologically, 66 patients (71.7%) had organ-confined disease. Of the 92 tumors examined, 8, 20, 23, and 41 showed staining patterns for p-STAT3 of 0, 1+, 2+, and 3+, respectively. In addition, 0, 3, 2, and 87 tumors showed staining patterns for STAT3 of 0, 1+, 2+, and 3+, respectively. The staining patterns for p-STAT3 correlated significantly with pathologic stage, Gleason score, and extracapsular extension. No significant correlation was found between p-STAT3 immunostaining and microvascular invasion, perineural invasion, or seminal vesicle invasion. Patients with 3+ immunostaining of p-STAT3 had a significantly greater biochemical prostate-specific antigen failure rate than those with 2+ or less immunostaining.

CONCLUSIONS

Increased p-STAT3 immunoreactivity showed a highly invasive and aggressive potential in patients with localized prostate cancer treated with radical prostatectomy. This suggests that STAT3 signaling contributes to the invasiveness and aggressiveness of prostate cancer.