Epidermal growth factor and serum activate distinct pathways to inhibit the BH3 only protein BAD in prostate carcinoma LNCaP cells

Regulation of Kinase Signaling Pathways by α6β4-Integrins and Plectin in Prostate Cancer

Hemidesmosomes (HDs) are adhesive structures that ensure stable anchorage of cells to the basement membrane. They are formed by α6β4-integrin heterodimers and linked to intermediate filaments via plectin. It has been reported that one of the most common events during the pathogenesis of prostate cancer (PCa) is the loss of HD organization. While the expression levels of β4-integrins are strongly reduced, the expression levels of α6-integrins and plectin are maintained or even elevated, and seem to promote tumorigenic properties of PCa cells, such as proliferation, invasion, metastasis, apoptosis- and drug-resistance. In this review, we discuss the potential mechanisms of how HD components might contribute to various cellular signaling pathways to promote prostate carcinogenesis. Moreover, we summarize the current knowledge on the involvement of α6β4-integrins and plectin in PCa initiation and progression.

The role of the p90 ribosomal S6 kinase family in prostate cancer progression and therapy resistance

Prostate cancer (PCa) is the second most commonly occurring cancer in men, with over a million new cases every year worldwide. Tumor growth and disease progression is mainly dependent on the Androgen Receptor (AR), a ligand dependent transcription factor. Standard PCa therapeutic treatments include androgen-deprivation therapy and AR signaling inhibitors. Despite being successful in controlling the disease in the majority of men, the high frequency of disease progression to aggressive and therapy resistant stages (termed castrate resistant prostate cancer) has led to the search for new therapeutic targets. The p90 ribosomal S6 kinase (RSK1-4) family is a group of highly conserved Ser/Thr kinases that holds promise as a novel target. RSKs are effector kinases that lay downstream of the Ras/Raf/MEK/ERK signaling pathway, and aberrant activation or expression of RSKs has been reported in several malignancies, including PCa. Despite their structural similarities, RSK isoforms have been shown to perform nonredundant functions and target a wide range of substrates involved in regulation of transcription and translation. In this article we review the roles of the RSKs in proliferation and motility, cell cycle control and therapy resistance in PCa, highlighting the possible interplay between RSKs and AR in mediating disease progression. In addition, we summarize the current advances in RSK inhibitor development and discuss their potential clinical benefits.

Signaling Pathways That Control Apoptosis in Prostate Cancer

Prostate cancer is the second most common malignancy and the fifth leading cancer-caused death in men worldwide. Therapies that target the androgen receptor axis induce apoptosis in normal prostates and provide temporary relief for advanced disease, yet prostate cancer that acquired androgen independence (so called castration-resistant prostate cancer, CRPC) invariably progresses to lethal disease. There is accumulating evidence that androgen receptor signaling do not regulate apoptosis and proliferation in prostate epithelial cells in a cell-autonomous fashion. Instead, androgen receptor activation in stroma compartments induces expression of unknown paracrine factors that maintain homeostasis of the prostate epithelium. This paradigm calls for new studies to identify paracrine factors and signaling pathways that control the survival of normal epithelial cells and to determine which apoptosis regulatory molecules are targeted by these pathways. This review summarizes the recent progress in understanding the mechanism of apoptosis induced by androgen ablation in prostate epithelial cells with emphasis on the roles of BCL-2 family proteins and "druggable" signaling pathways that control these proteins. A summary of the clinical trials of inhibitors of anti-apoptotic signaling pathways is also provided. Evidently, better knowledge of the apoptosis regulation in prostate epithelial cells is needed to understand mechanisms of androgen-independence and implement life-extending therapies for CRPC.

A low microRNA-630 expression confers resistance to tyrosine kinase inhibitors in EGFR-mutated lung adenocarcinomas via miR-630/YAP1/ERK feedback loop

Purpose: MicroRNA-630 plays dual roles in apoptosis and drug resistance in human cancers. However, the role of miR-630 in resistance to tyrosine kinase inhibitors (TKIs) in lung adenocarcinoma remains to be elucidated.

Methods: Manipulation of miR-630 and its targeted gene YAP1 and/or combination of inhibitor treatments was performed to explore whether low miR-630 could confer TKI resistance due to de-targeting YAP1, and this could decrease proapoptotic protein Bad expression through the miR-630/YAP1/ERK feedback loop. A retrospective study was conducted to examine whether the expression of miR-630 and YAP1 could be associated with TKI therapeutic response in patients with lung adenocarcinoma.

Results: Low miR-630 expression may confer TKI resistance via increased SP1 binding to the miR-630 promoter due to ERK activation by YAP1 de-targeting. Persistent activation of ERK signaling via the miR-630/YAP1/ERK feedback loop may be responsible for TKI resistance in EGFR-mutated cells. Moreover, a decrease in Bad expression by its phosphorylation at Serine 75 through ERK activation conferred low miR-630-mediated TKI resistance by modulating the apoptotic pathway. Xenographic tumors induced by miR-630-knockdown PC9 and PC9GR cells in nude mice were nearly suppressed by the combination of gefitinib with the YAP1 inhibitor verteporfin or an MEK/ERK inhibitor AZD6244. Patients with low miR-630 and high YAP1 expressing tumors had a higher prevalence of unfavorable responses to TKI therapy and poorer outcomes when compared with their counterparts.

Conclusion: MiR-630 may be a potential biomarker for the prediction of TKI therapeutic response and outcome in patients with lung adenocarcinoma.

Bad phosphorylation as a target of inhibition in oncology

Bcl-2 agonist of cell death (BAD) is a BH3-only member of the Bcl-2 family which possesses important regulatory function in apoptosis. BAD has also been shown to possess many non-apoptotic functions closely linked to cancer including regulation of glycolysis, autophagy, cell cycle progression and immune system development. Interestingly, BAD can be either pro-apoptotic or pro-survival depending on the phosphorylation state of three specific serine residues (human S75, S99 and S118). Expression of BAD and BAD phosphorylation patterns have been shown to influence tumor initiation and progression and play a predictive role in disease prognosis, drug response and chemosensitivity in various cancers. This review aims to summarize the current evidence on the functional role of BAD phosphorylation in human cancer and evaluate the potential utility of modulating BAD phosphorylation in cancer.

Bax-interacting factor-1 inhibits cell proliferation and promotes apoptosis in prostate cancer cells

Prostate cancer (PCa) is one of the most common malignant tumors and the second leading cause of cancer-related death among males. Bax-interacting factor-1 (Bif-1) is a member of Endophilin family, which binds to and activates the BAX protein in response to the apoptosis signaling pathway. Loss of Bif-1 may suppress the intrinsic pathway of apoptosis and promote tumorigenesis, but there is also converse evidence that Bif-1 could in part be responsible for the tumorigenesis and the role of Bif-1 in PCa development is not clear. In the present study, we aimed to understand the relationships between Bif-1 expression and PCa development. The mRNA and protein expression levels of Bif-1 in PCa cell lines, benign prostatic hyperplasia (BPH) (n=100) and PCa tissues (n=100, including low Gleason-scored PCa n=43 and high Gleason-scored PCa n=57) were detected and the effects of Bif-1 overexpression on the apoptosis, proliferation and migration in LNCaP cells were explored. Bif-1 mRNA levels of PCa cell lines were analyzed by real-time PCR and the protein levels were detected by western blotting. Bif-1 expression in BPH and PCa samples was detected by immunohistochemistry. To build Bif-1 overexpression PCa cells, Bif-1 gene was transfected into LNCaP cells by pcDNA3.1(+)‑Bif-1 vector. Cell apoptosis was detected by flow cytometric analysis, cell proliferation measured by 3‑(4,5‑dimethylthiazol‑2‑yl)‑2,5‑diphenyltetrazolium bromide (MTT) assay and cell migration was analyzed by wound‑healing assay. The results proved that Bif-1 is downregulated in both PCa cell lines (P<0.01) and clinical samples (P<0.05), and Bif-1 expression is suppressed with the cancer progression (BPH vs. PCa P<0.01, and low Gleason-scored PCa vs. high Gleason-scored PCa P<0.05). Overexpression of Bif-1 could significantly inhibit cell proliferation (P<0.05) and enhancing PCa cell apoptosis (P<0.05), but it did not affect the migration ability (P>0.05). Our findings give strong evidence that Bif-1 is involved in PCa tumorigenesis and acts as a suppressor in PCa progression, and may have significance in understanding the process of PCa development.

Mesothelin confers pancreatic cancer cell resistance to TNF-α-induced apoptosis through Akt/PI3K/NF-κB activation and IL-6/Mcl-1 overexpression

Background

Previous studies showed that mesothelin (MSLN) plays important roles in survival of pancreatic cancer (PC) cells under anchorage dependent/independent conditions as well as resistance to chemotherapy. The recent success of intratumorally-injected adeno-encoded, chemo/radiation-inducible-promoter driven hTNF-α, (TNFerade) + gemcitabine in pre-clinical models of PC have renewed interest in use of TNF-α as a therapeutic component. To help find additional factors which might affect the therapy, we examined the resistance of MSLN-overexpressing pancreatic cancer cell lines to TNF-α-induced growth inhibition/apoptosis.

Methods

Stable MSLN overexpressing MIA PaCa-2 cells (MIA-MSLN), stable MSLN-silenced AsPC-1 cells (AsPC-shMSLN) and other pancreatic cells (MIA-PaCa2, Panc 28, Capan-1, BxPC3, PL 45, Hs 766T, AsPC-1, Capan-2, Panc 48) were used. NF-κB activation was examined by western blots and luciferase reporter assay. TNF-α induced growth inhibition/apoptosis was measured by MTT, TUNEL assay and caspase activation. IL-6 was measured using luminex based assay.

Results

Compared to low endogenous MSLN-expressing MIA PaCa-2 and Panc 28 cells, high endogenous MSLN-expressing Capan-1, BxPC3, PL 45, Hs 766T, AsPC-1, Capan-2, Panc 48 cells were resistant to TNF-α induced growth inhibition. Stable MSLN overexpressing MIA-PaCa2 cells (MIA-MSLN) were resistant to TNF-α-induced apoptosis while stable MSLN-silenced AsPC1 cells (AsPC-shMSLN) were sensitive. Interestingly, TNF-α-treated MIA-MSLN cells showed increased cell cycle progression and cyclin A induction, both of which were reversed by caspase inhibition. We further found that MIA-MSLN cells showed increased expression of anti-apoptotic Bcl-XL and Mcl-1; deactivated (p-Ser⁷⁵) BAD, and activated (p-Ser⁷⁰) Bcl-2. Constitutively activated NF-κB and Akt were evident in MIA-MSLN cells that could be suppressed by MSLN siRNA with a resultant increase in sensitivity of TNF-α induced apoptosis. Blocking NF-κB using IKK inhibitor wedelolactone also increased sensitivity to TNF-α-mediated cytotoxicity with concomitant decrease in Mcl-1. Blocking Akt using PI3K inhibitor also had a likewise effect presumably affecting cell cycle. MIA-MSLN cells produced increased IL-6 and were increased furthermore by TNF-α treatment. SiRNA-silencing of IL-6 increased TNF-α sensitivity of MIA-MSLN cells.

Conclusions

Our study delineates a MSLN-Akt-NF-κB-IL-6-Mcl-1 survival axis that may be operative in PC cells, and might help cancer cells' survival in the highly inflammatory milieu evident in PC. Further, for the success of TNFerade + gemcitabine to be successful, we feel the simultaneous inhibition of components of this axis is also essential.

Optic nerve and vitreal inflammation are both RGC neuroprotective but only the latter is RGC axogenic

Intravitreal inflammation, induced by either lens injury, or intravitreal injection of zymosan (IVZ), protects RGC from apoptosis and stimulates axon regeneration after optic nerve transection. Here, we investigate the differential effects of intra-optic nerve zymosan (ONZ) and IVZ injections on RGC neuroprotection and axogenesis. After both IVZ and ONZ injection, zymosan-induced inflammation promoted a similar 4-/5-fold enhancement in RGC survival, compared to optic nerve transected controls, but only IVZ promoted RGC axon regeneration. IVZ was the most effective in activating retinal astrocyte/Müller cells while regulated intramembraneous proteolysis (RIP) of p75(NTR) and inactivation of Rho (key components of the axon growth inhibitory signalling cascade) occurred in both ONZ and IVZ, but only in the latter did RGC axons regenerate. We suggest that neuroprotective factors may be transported to RGC somata by retrograde transport after ONZ and diffuse into the retina after IVZ injection, but an axogenic agent is required to initiate and maintain disinhibited RGC axon regeneration that may be an exclusive property of a Müller cell-derived factor released after IVZ.

Oncogene AF1q enhances doxorubicin-induced apoptosis through BAD-mediated mitochondrial apoptotic pathway

AF1q is an oncogenic factor involved in leukemia development, thyroid tumorigenesis, and breast cancer metastasis. In the present study, AF1q was found to be down-regulated in a doxorubicin-resistant subline of human squamous carcinoma A431 cells. Knockdown of AF1q decreased the apoptosis induced by doxorubicin, Taxol, gamma-radiation, IFN-alpha, and IFN-gamma in A431 cells. On the other hand, overexpression of AF1q increased the doxorubicin-induced apoptosis in A431 cells as well as in HepG2 and HL60 cells. Both exogenous and ectopic expression of AF1q in A431 cells increased the mRNA and protein levels of BAD, a proapoptotic BCL-2 family protein. Gene silencing of BAD by small interfering RNA suppressed the AF1q enhancement of apoptosis, suggesting that BAD is downstream of AF1q in regulation of apoptosis. Furthermore, AF1q enhanced the mitochondrial membrane depolarization, mitochondrial cytochrome c release, and activation of caspase-9 and caspase-3 on doxorubicin treatment. Collectively, AF1q increases doxorubicin-induced apoptosis in cells through activation of BAD-mediated apoptotic pathway. The study provides the first evidence that AF1q plays a critical role in the regulation of apoptosis and drug resistance.

Bax-interacting factor-1 expression in prostate cancer

BACKGROUND

Bax-interacting factor (Bif)-1 protein is a member of the endophilin B family that binds to and activates the proapoptotic Bax protein in response to apoptotic signals. Loss of Bif-1 suppresses the intrinsic pathway of apoptosis and promotes tumorigenesis. We examined the expression levels of Bif-1 protein in human prostate cancer.

MATERIALS AND METHODS

Thirty-nine archival tissue specimens of human prostate cancer, and a human prostate cancer tissue microarray containing 19 samples of normal prostate, 26 samples of benign prostatic hyperplasias (BPHs), 30 samples of high-grade prostatic intraepithelial neoplasia (PIN), and 153 samples of prostate cancer, were selected for immunohistochemical staining with Bif-1 antibody. The slides were scored by 2 independent observers.

RESULTS

Nontissue microarray samples: moderate to strong Bif-1 staining was identified in 38 of 39 prostate cancer samples. In 32 cases, foci of PIN were identified adjacent to prostate cancer samples. Of these, 29 samples (90.6%) showed strong and diffuse Bif-1 staining. Benign prostatic hyperplasias, identified in 27 cases, was weakly Bif-1 positive in 88.9% of cases. Tissue microarray samples: 38.6% (59 of 153) of prostate cancer samples showed moderate to strong Bif-1 expression, and 21.6% (33 of 153) were Bif-1 negative. Bif-1 expression was moderate to strong in 76.7% (23 of 30) of PIN. Bif-1 was weak to moderate in 53.8% (14 of 26) of BPH and negative in 46.2% (12 of 26) of them. Low to moderate Bif-1 was seen in 89.5% of normal prostate samples.

CONCLUSION

The loss of Bif-1 expression in a subset of prostate cancer samples is in agreement with the proapoptotic function of Bif-1. The significance of the increased Bif-1 in a subgroup of prostate cancer samples and in PIN remains to be determined. It seems that Bif-1 has a role in prostate cancer, providing the rationale for using Bif-1 as a target for prostate anticancer therapy.

Enzastaurin, a protein kinase C beta inhibitor, suppresses signaling through the ribosomal S6 kinase and bad pathways and induces apoptosis in human gastric cancer cells

Activation of protein kinase C (PKC) has been implicated in gastric carcinogenesis. Enzastaurin is an oral ATP-competitive inhibitor of the PKC beta isozyme. Although enzastaurin was initially advanced to the clinic based on its antiangiogenic activity, it is also known to have a direct effect on a variety of human cancer cells, inducing apoptosis by inhibiting the Akt signal pathway. However, data on enzastaurin for gastric cancer are limited. Therefore, this study was performed to assess the antitumor activity of enzastaurin on gastric cancer cells and to investigate the underlying antitumor mechanisms. Enzastaurin suppressed the proliferation of cultured gastric cancer cells and the growth of gastric carcinoma xenografts. Enzastaurin did not have an effect on gastric cancer cell cycle progression; however, it had a direct apoptosis-inducing effect through the caspase-mediated mitochondrial pathway. Glycogen synthase kinase 3beta phosphorylation, a reliable pharmacodynamic marker of enzastaurin activity, and Akt phosphorylation were both decreased after treatment with enzastaurin. Although the p90 ribosomal S6 kinase (Rsk) was also dephosphorylated, Erk phosphorylation was not affected in the enzastaurin-treated gastric cancer cells. Enzastaurin activated Bad, one of the Bcl-2 proapoptotic proteins, through dephosphorylation at Ser(112), and depletion of Bad activity resulted in resistance to enzastaurin-induced apoptosis and cytotoxicity in gastric cancer cells. These data suggest that enzastaurin induces apoptosis through Rsk-mediated and Bad-mediated pathways, besides inhibiting the Akt signal cascade. Furthermore, enzastaurin had synergistic or additive effects when combined with 5-fluorouracil, cisplatin, paclitaxel, or irinotecan. These results warrant further clinical investigation of enzastaurin for gastric cancer treatment.

Oxidative repression of NHE1 gene expression involves iron-mediated caspase activity

The mechanism of Na(+)/H(+) exchanger 1 (NHE1) gene repression upon exposure of cells to non-apoptotic concentrations of hydrogen peroxide (H(2)O(2)) was investigated. We show that continuous presence of H(2)O(2) was not required for inhibition of NHE1 promoter activity. However, the downregulation of NHE1 promoter activity and protein expression was abrogated by the presence of beta mercaptoethanol (betaME) and dithiothreitol. The pan-caspase inhibitor zVAD-fmk also blocked the effect of H(2)O(2) on NHE1 promoter activity and expression, but unlike betaME, caspase inhibition was ineffective in rescuing the early phase of NHE1 repression. Interestingly, the effect of caspase inhibition was observed only after 9 h of exposure to H(2)O(2) and completely restored NHE1 promoter activity by 18-24 h. Using tetrapeptide inhibitors of a variety of caspases and siRNA-mediated gene silencing, caspases 3 and 6 were identified as mediators of H(2)O(2)-induced NHE1 repression, independent of initiator/amplifier caspase activation. Furthermore, incubation of cells with the iron chelator, desferioxamine, not only blocked the activities of caspases 3 and 6, but also affected NHE1 promoter and protein expression in a manner similar to zVAD-fmk. These data show that a mild oxidative stress represses NHE1 promoter activity and expression via an early oxidation phase blocked by reducing agents, and a late phase requiring an iron-dependent increase in caspases 3 and 6 activities.

Bad expression influences time to androgen escape in prostate cancer

OBJECTIVE

To assess the role of selected downstream Bcl-2 family members (Bad, Bax, Bcl-2 and Bcl-xL) in the development of androgen-independent prostate cancer (AIPC), as androgen-deprivation therapy is the treatment of choice in advanced prostate cancer, yet patients generally relapse and progress to an AI state within 18-24 months.

PATIENTS, MATERIALS AND METHODS

The patient cohort was established by retrospectively selecting patients with prostate cancer who had an initial response to androgen-deprivation therapy, but subsequently relapsed with AIPC. In all, 58 patients with prostate cancer were included with matched androgen-dependent (AD) and AI prostate tumours available for immunohistochemical analysis; two independent observers using a weighted-histoscore method scored the staining. Changes in Bad, Bax, Bcl-2 and Bcl-xL expression during transition to AIPC were evaluated and then correlated to known clinical variables.

RESULTS

High Bad expression in AD tumours was associated with an increased time to biochemical relapse (P = 0.007) and a trend towards improved overall survival (P = 0.053). There were also trends towards a decrease in Bad (P = 0.068) and Bax (P = 0.055) expression with progression to AIPC. There were no significant results for Bcl-2 or Bcl-xL.

CONCLUSION

There is evidence to suggest that Bad expression levels at diagnosis influence time to biochemical relapse and overall survival, and that levels of pro-apoptotic proteins Bad and Bax fall during AIPC development. Bad might therefore represent a possible positive prognostic marker and potential therapeutic target for AIPC in the future.