Regulation of the proapoptotic functions of prostate apoptosis response-4 (Par-4) by casein kinase 2 in prostate cancer cells

Inhibition of extracellular traps by spores of Trichoderma stromaticum on neutrophils obtained from human peripheral blood

Although the genus Trichoderma is widely used as a biocontrol agent in crops, little is known about its potential impact on the human immune system. In mice, our group has shown that exposition to T. asperelloides spores lead to reduced neutrophil counts in the peripheral blood and in the peritoneal cavity. In addition, T. stromaticum spores produced an inflammatory infiltrate on mice lungs, reducing the levels of IFN-γ and IL-10 cytokines, reactive oxygen species, and receptors of microbial patterns. Here we demonstrate that the interaction of human peripheral neutrophils with T. stromaticum spores also leads to a reduced release of neutrophil extracellular traps (NETs) after induction with the NET-inducer agent phorbol 12-myristate 13-acetate. This interaction also reduced the expression levels of multiple microRNAs, such as miR-221, miR-222, miR-223 and miR-27a, as well as genes related to NETs, such as ELANE, MPO and PADI4. Furthermore, T. stromaticum spores affected the expression of the genes SOCS3, TLR4, CSNK2A1, GSDMD, and NFFKBIA, related to the activation of inflammatory immune responses in neutrophils. Overall, our results suggest T. stromaticum as a potential NET inhibitor and as an immunomodulatory agent. Since this fungus is used as biocontrol in crops, our findings point to the importance of advancing our knowledge on the effects of this bioagent on the human immune system. Finally, the study of the active compounds produced by the fungus is also important for the prospection of new drugs that could be used to block the exacerbation of inflammatory immune responses present in several human diseases.

In Vivo Evaluation of Combined CK2 Inhibition and Irradiation in Human WiDr Tumours

BACKGROUND/AIM

Casein kinase 2 (CK2) which sustains multiple pro-survival functions in cellular DNA-damage response, is strictly regulated in normal cells but elevated in cancer. CK2 is considered as a potential therapeutic target, and its inhibition has been associated with radiosensitization in mammalian cells in vitro. Here, we investigated potential radiosensitization by CK2 inhibition in vivo.

MATERIALS AND METHODS

The effect of CK2 inhibition in vivo was investigated in human WiDr-xenograft tumours grown subcutaneously on BALB/c nu/nu mice with and without fractionated irradiation. CK2 inhibition was performed using the specific inhibitor tetra-bromobenzotriazole (TBB). Histological examinations included staining for apoptosis and double-strand breaks.

RESULTS

Both TBB treatment alone and radiation alone significantly reduced tumour growth, which was reflected by increased apoptosis rates. However, TBB treatment did not boost radiation-induced tumour growth suppression in combined treatment, although the apoptosis rate increased and repair of double-strand breaks was reduced. This was in stark contrast to previous data on in vitro radiosensitization.

CONCLUSION

The absence of radiosensitization by CK2 inhibition should be investigated in different tumour models.

Structural Analysis of the cl-Par-4 Tumor Suppressor as a Function of Ionic Environment

Prostate apoptosis response-4 (Par-4) is a proapoptotic tumor suppressor protein that has been linked to a large number of cancers. This 38 kilodalton (kDa) protein has been shown to be predominantly intrinsically disordered in vitro. In vivo, Par-4 is cleaved by caspase-3 at Asp-131 to generate the 25 kDa functionally active cleaved Par-4 protein (cl-Par-4) that inhibits NF-κB-mediated cell survival pathways and causes selective apoptosis in tumor cells. Here, we have employed circular dichroism (CD) spectroscopy and dynamic light scattering (DLS) to assess the effects of various monovalent and divalent salts upon the conformation of cl-Par-4 in vitro. We have previously shown that high levels of sodium can induce the cl-Par-4 fragment to form highly compact, highly helical tetramers in vitro. Spectral characteristics suggest that most or at least much of the helical content in these tetramers are non-coiled coils. Here, we have shown that potassium produces a similar effect as was previously reported for sodium and that magnesium salts also produce a similar conformation effect, but at an approximately five times lower ionic concentration. We have also shown that anion identity has far less influence than does cation identity. The degree of helicity induced by each of these salts suggests that the "Selective for Apoptosis in Cancer cells" (SAC) domain-the region of Par-4 that is most indispensable for its apoptotic function-is likely to be helical in cl-Par-4 under the studied high salt conditions. Furthermore, we have shown that under medium-strength ionic conditions, a combination of high molecular weight aggregates and smaller particles form and that the smaller particles are also highly helical, resembling at least in secondary structure, the tetramers found at high salt.

Prostate apoptosis response-4 and tumor suppression: it's not just about apoptosis anymore

The tumor suppressor prostate apoptosis response-4 (Par-4) has recently turned ‘twenty-five’. Beyond its indisputable role as an apoptosis inducer, an increasing and sometimes bewildering, new roles for Par-4 are being reported. These roles include its ability to regulate autophagy, senescence, and metastasis. This growing range of responses to Par-4 is reflected by our increasing understanding of the various mechanisms through which Par-4 can function. In this review, we summarize the existing knowledge on Par-4 tumor suppressive mechanisms, and discuss how the interaction of Par-4 with different regulators influence cell fate. This review also highlights the new secretory pathway that has emerged and the likely discussion on its clinical implications.

Withania somnifera (L.) Dunal: A potential therapeutic adjuvant in cancer

ETHNOPHARMACOLOGICAL RELEVANCE

Withania somnifera (L.) Dunal (WS) is one of the moststudied Rasayana botanicals used in Ayurveda practice for its immunomodulatory, anti-aging, adaptogenic, and rejuvenating effects. The botanical is being used for various clinical indications, including cancer. Several studies exploring molecular mechanisms of WS suggest its possible role in improving clinical outcomes in cancer management. Therefore, research on WS may offer new insights in rational development of therapeutic adjuvants for cancer.

AIM OF THIS REVIEW

The review aims at providing a detailed analysis of in silico, in vitro, in vivo, and clinical studies related to WS and cancer. It suggests possible role of WS in regulating molecular mechanisms associated with carcinogenesis. The review discusses potential of WS in cancer management in terms of cancer prevention, anti-cancer activity, and enhancing efficacy of cancer therapeutics.

MATERIAL AND METHODS

The present narrative review offers a critical analysis of published literature on WS studies in cancer. The reported studies were analysed in the context of pathophysiology of cancer, commonly referred as 'cancer hallmarks'. The review attempts to bridge Ayurveda knowledge with biological insights into molecular mechanisms of cancer.

RESULTS

Critical analysisof the published literature suggests an anti-cancer potential of WS with a key role in cancer prevention. The possible mechanisms for these effects are associated with the modulation of apoptotic, proliferative, and metastatic markers in cancer. WS can attenuate inflammatory responses and enzymes involved in invasion and metastatic progression of cancer.The properties of WS are likely to be mediated through withanolides, which may activate tumor suppressor proteins to restrict proliferation of cancer cells. Withanolides also regulate the genomic instability, and energy metabolism of cancer cells. The reported studies indicate the need for deeper understanding of molecular mechanisms of WS in inhibiting angiogenesis and promoting immunosurveillance. Additionally, WS can augment efficacy and safety of cancer therapeutics.

CONCLUSION

The experimentally-supported evidence of immunomodulatory, anti-cancer, adaptogenic, and regenerative attributes of WS suggest its therapeutic adjuvant potential in cancer management. The adjuvant properties of withanolides can modulate multidrug resistance and reverse chemotherapy-induced myelosuppression. These mechanisms need to be further explored in systematically designed translational and clinical studies that will pave the way for integration of WS as a therapeutic adjuvant in cancer management.

Coordinated targeting of CK2 and KIT in gastrointestinal stromal tumours

Background

Most gastrointestinal stromal tumours (GIST) are driven by activating oncogenic mutations of KIT/PDGFRA, which provide a compelling therapeutic target. Our previous studies showed that CDC37, regulated by casein kinase 2 (CK2), is a crucial HSP90 cofactor for KIT oncogenic function and a promising and more selective therapeutic target in GIST.

Methods

Biologic mechanisms of CK2-mediated CDC37 regulation were assessed in GISTs by immunoblotting, immunoprecipitations, knockdown and inactivation assays. The effects of a combination of KIT and CK2 inhibition were assessed by immunoblotting, cell viability, colony growth, cell cycle analysis, apoptosis, migration and invasiveness.

Results

CK2 overexpression was demonstrated by immunoblotting in GIST cell lines and patient biopsies. Treatment with a specific CK2 inhibitor, CX4945, leads to CDC37 dephosphorylation and inhibits KIT signalling in imatinib-sensitive and in imatinib-resistant GIST cell lines. Immunoprecipitation demonstrated that CK2 inhibition blocks KIT:HSP90:CDC37 interaction in GIST cells. Coordinated inhibition of CK2 and KIT by CX4945 (or CK2 shRNA) and imatinib, respectively, leads to increased apoptosis, anti-proliferative effects and cell cycle arrest and decreased p-AKT and p-S6 expression, migration and invasiveness in all GIST cell lines compared with either intervention alone, indicating additive effects of inhibiting these two important regulators of GIST biology.

Conclusion

Our findings suggest that combinatorial inhibition of CK2 and KIT warrants evaluation as a novel therapeutic strategy in GIST, especially in imatinib-resistant GIST.

Par-4 overexpression impedes leukemogenesis in the Eµ-TCL1 leukemia model through downregulation of NF-κB signaling

Prostate apoptosis response 4 (Par-4) is a tumor suppressor that prevents proliferation and induces cell death in several solid tumors. However, its role in B-cell malignancies has not been elucidated. To describe the role of Par-4 in chronic lymphocytic leukemia (CLL) pathogenesis, we developed a B-cell-specific human Par-4-overexpressing mouse model of CLL using the TCL1 leukemia model. While Par-4 transgenic mice did not display any obvious defects in B-cell development or function, disease burden as evidenced by abundance of CD19⁺CD5⁺ B cells in the peripheral blood was significantly reduced in Par-4 × TCL1 mice compared with TCL1 littermates. This conferred a survival advantage on the Par-4-overexpressing mice. In addition, a B-cell-specific knockout model displayed the opposite effect, where lack of Par-4 expression resulted in accelerated disease progression and abbreviated survival in the TCL1 model. Histological and flow cytometry-based analysis of spleen and bone marrow upon euthanasia revealed comparable levels of malignant B-cell infiltration in Par-4 × TCL1 and TCL1 individuals, indicating delayed but pathologically normal disease progression in Par-4 × TCL1 mice. In vivo analysis of splenic B-cell proliferation by 5-ethynyl-2-deoxyuridine incorporation indicated >50% decreased expansion of CD19⁺CD5⁺ cells in Par-4 × TCL1 mice compared with TCL1 littermates. Moreover, reduced nuclear p65 levels were observed in Par-4 × TCL1 splenic B cells compared with TCL1, suggesting suppressed NF-κB signaling. These findings have identified an in vivo antileukemic role for Par-4 through an NF-κB-dependent mechanism in TCL1-mediated CLL-like disease progression.

A Naturally Generated Decoy of the Prostate Apoptosis Response-4 Protein Overcomes Therapy Resistance in Tumors

Primary tumors are often heterogeneous, composed of therapy-sensitive and emerging therapy-resistant cancer cells. Interestingly, treatment of therapy-sensitive tumors in heterogeneous tumor microenvironments results in apoptosis of therapy-resistant tumors. In this study, we identify a prostate apoptosis response-4 (Par-4) amino-terminal fragment (PAF) that is released by diverse therapy-sensitive cancer cells following therapy-induced caspase cleavage of the tumor suppressor Par-4 protein. PAF caused apoptosis in cancer cells resistant to therapy and inhibited tumor growth. A VASA segment of Par-4 mediated its binding and degradation by the ubiquitin ligase Fbxo45, resulting in loss of Par-4 proapoptotic function. Conversely, PAF, which contains this VASA segment, competitively bound to Fbxo45 and rescued Par-4-mediated induction of cancer cell-specific apoptosis. Collectively, our findings identify a molecular decoy naturally generated during apoptosis that inhibits a ubiquitin ligase to overcome therapy resistance in tumors. Cancer Res; 77(15); 4039-50. ©2017 AACR.

A journey beyond apoptosis: new enigma of controlling metastasis by pro-apoptotic Par-4

Prostate apoptotic response 4 (Par-4) is coined as a therapeutic protein since owing to its diverse physiologically relevant properties, especially in the cancer perspective. Albeit, Par-4 expression is not restricted to any specific tissue/organ, apart from cell death promotion (due to challenging threats), the other biological role of Par-4 is convincingly emerging. In the recent years, several laboratories have intended to dissect the signaling or mechanisms involved in Par-4 activation to augment apoptosis cascades but new developments in Par-4 research have widened its therapeutic potential. One of these important avenues is the prevention of metastasis by pro-apoptotic Par-4. In this review, we will focus on the therapeutic perspective of Par-4 with a special reference to its (Par-4) virgin prospect of devastating metastasis control.

CK2α' Drives Lung Cancer Metastasis by Targeting BRMS1 Nuclear Export and Degradation

Breast cancer metastasis suppressor 1 (BRMS1) is decreased in non-small cell lung cancer (NSCLC) and other solid tumors, and its loss correlates with increased metastases. We show that BRMS1 is posttranslationally regulated by TNF-induced casein kinase 2 catalytic subunit (CK2α') phosphorylation of nuclear BRMS1 on serine 30 (S30), resulting in 14-3-3ε-mediated nuclear exportation, increased BRMS1 cytosolic expression, and ubiquitin-proteasome-induced BRMS1 degradation. Using our in vivo orthotopic mouse model of lung cancer metastases, we found that mutation of S30 in BRMS1 or the use of the CK2-specific small-molecule inhibitor CX4945 abrogates CK2α'-induced cell migration and invasion and decreases NSCLC metastasis by 60-fold. Analysis of 160 human NSCLC specimens confirmed that tumor CK2α' and cytoplasmic BRMS1 expression levels are associated with increased tumor recurrence, metastatic foci, and reduced disease-free survival. Collectively, we identify a therapeutically exploitable posttranslational mechanism by which CK2α-mediated degradation of BRMS1 promotes metastases in lung cancer. Cancer Res; 76(9); 2675-86. ©2016 AACR.

Inhibition of AKT promotes FOXO3a-dependent apoptosis in prostate cancer

Growth factor-induced activation of protein kinase-B (PKB), also known as AKT, induces pro-survival signaling and inhibits activation of pro-apoptotic signaling molecules including the Forkhead box O-3a (FOXO3a) transcription factor and caspase in transformed prostate cells in vitro. Earlier we reported that Withaferin-A (WA), a small herbal molecule, induces pro-apoptotic response-4 (Par-4) mediated apoptosis in castration-resistant prostate cancer (CRPC) cells. In the present study, we demonstrate that inhibition of AKT facilitates nuclear shuttling of FOXO3a where it regulates Par-4 transcription in CRPC cells. FOXO3a is upstream of Par-4 signaling, which is required for induction of apoptosis in CRPC cells. Promoter bashing studies and Ch-IP analysis confirm a direct interaction of FOXO3a and Par-4; a sequential deletion of FOXO3a-binding sites in the Par-4 promoter fails to induce Par-4 activation. To confirm these observations, we either overexpressed AKT or silenced FOXO3a activation in CRPC cells. Both methods inhibit Par-4 function and apoptosis is significantly compromised. In xenograft tumors derived from AKT-overexpressed CRPC cells, FOXO3a and Par-4 expression is downregulated, leading to aggressive tumor growth. Oral administration of WA to mice with xenograft tumors restores FOXO3a-mediated Par-4 functions and results in inhibited tumor growth. Finally, an inverse correlation of nuclear localization of AKT expression corresponds to cytoplasmic Par-4 localization in human prostate tissue array. Our studies suggest that Par-4 is one of the key transcriptional targets of FOXO3a, and Par-4 activation is required for induction of apoptosis in CRPC cells. Activation of FOXO3a appears to be an attractive target for the treatment of CRPC and molecules such as WA can be explored further for the treatment of CRPC.