Protein phosphatase 2A modulates the proliferation of human multiple myeloma cells via regulation of the production of reactive oxygen intermediates and anti-apoptotic factors

The TT Genotype of the KIAA1524 rs2278911 Polymorphism Is Associated with Poor Prognosis in Multiple Myeloma

Background: The KIAA1524 gene encodes an oncoprotein, CIP2A, which inhibits the phosphorylation of the Akt kinase B, stabilizes the c-Myc protein, and, through that, promotes cancerogenesis. An increase in CIP2A expression has been observed in numerous solid tumors and hematologic malignancies, including multiple myeloma (MM). The aim of our study was to evaluate the clinical impact of the functional single nucleotide polymorphisms (SNP) of the KIAA1524 gene (rs2278911, 686C > T) in MM patients. Methods: The study group consisted of 128 patients with de novo MM. EDTA venous blood samples were collected prior to the treatment. The SNPs were analyzed by Real-Time PCR with the use of specific Taqman probes. Results: Multivariable analysis revealed that variables independently associated with shorter progression-free survival (PFS) included thrombocytopenia, delTP53 and IGH/CCND1 translocation and the TT genotype of the KIAA1524 gene (686C > T) (median PFS: 6 vs. 25 months; HR = 7.18). On the other hand, autologous haematopoietic stem cell transplantation (AHSCT) was related to a lower risk of early disease progression. Moreover, light chain disease, International Staging System (ISS) 3, poor performance status, hypoalbuminemia, IGH/FGFR3 translocation and the TT genotype of the KIAA1524 gene (686C > T) were independent prognostic factors associated with shorter overall survival (OS) (median OS: 8 vs. 45 months; HR = 7.08). Conclusion: The evaluation of the SNP 686C > T of the KIAA1524 gene could be used as a diagnostic tool in MM patients at risk of early disease progression and death.

Binding and Kinetic Analysis of Human Protein Phosphatase PP2A Interactions with Caspase 9 Protein and the Interfering Peptide C9h

The serine/threonine phosphatase PP2A and the cysteine protease Caspase 9 are two proteins involved in physiological and pathological processes, including cancer and apoptosis. We previously demonstrated the interaction between Caspase 9 and PP2A and identified the C9h peptide, corresponding to the binding site of Caspase 9 to PP2A. This interfering peptide can modulate Caspase 9/PP2A interaction leading to a strong therapeutic effect in vitro and in vivo in mouse models of tumor progression. In this manuscript, we investigate (I) the peptide binding to PP2A combining docking with molecular dynamics and (II) the secondary structure of the peptide using CD spectroscopy. Additionally, we compare the binding affinity, using biolayer interferometry, of the wild-type protein PP2A with Caspase 9 and vice versa to that observed between the PP2A protein and the interfering peptide C9h. This result strongly encourages the use of peptides as new therapeutics against cancer, as shown for the C9h peptide already in clinical trial.

Upregulation of PP2Ac predicts poor prognosis and contributes to aggressiveness in hepatocellular carcinoma

Protein phosphatase 2A (PP2A) is a heterotrimeric protein phosphatase consisting of a 36-kD catalytic C subunit (PP2Ac). This study aimed to explore the prognostic and biological significance of PP2Ac in human hepatocellular carcinoma (HCC). High PP2Ac expression was significantly (P < 0.01) associated with serum hepatitis B surface antigen positivity, serum hepatitis B e antigen positivity, liver cirrhosis, moderate to poor differentiation grade, advanced disease stage, intrahepatic metastasis, and early recurrence in HCC. Multivariate analysis revealed PP2Ac as an independent prognostic factor for overall survival. Enforced expression of hepatitis B virus X protein (HBx) and its carboxyl-terminal truncated isoform induced PP2Ac expression in HCC cells. Co-immunoprecipitation assay revealed a direct interaction between PP2Ac and HBx. Small interfering RNA-mediated knockdown of PP2Ac significantly inhibited in vitro cell proliferation, colony formation, migration, and invasion and reduced tumor growth in an xenograft mouse model. In contrast, overexpression of PP2Ac promoted HCC cell proliferation, colony formation, and tumorigenesis. Additionally, silencing of PP2Ac impaired the growth-promoting effects on HepG2 HCC cells elicited by overexpression of carboxyl-terminal truncated HBx. Gene expression profiling analysis showed that PP2Ac downregulation modulated the expression of numerous genes involved in cell cycle and apoptosis regulation. Collectively, PP2Ac upregulation has a poor prognostic impact on the overall survival of HCC patients and contributes to the aggressiveness of HCC. PP2Ac may represent a potential therapeutic target for HCC.

Specific targeting of caspase-9/PP2A interaction as potential new anti-cancer therapy

PURPOSE

PP2A is a serine/threonine phosphatase critical to physiological processes, including apoptosis. Cell penetrating peptides are molecules that can translocate into cells without causing membrane damage. Our goal was to develop cell-penetrating fusion peptides specifically designed to disrupt the caspase-9/PP2A interaction and evaluate their therapeutic potential in vitro and in vivo.

EXPERIMENTAL DESIGN

We generated a peptide containing a penetrating sequence associated to the interaction motif between human caspase-9 and PP2A (DPT-C9h), in order to target their association. Using tumour cell lines, primary human cells and primary human breast cancer (BC) xenografts, we investigated the capacity of DPT-C9h to provoke apoptosis in vitro and inhibition of tumour growth (TGI) in vivo. DPT-C9h was intraperitoneally administered at doses from 1 to 25 mg/kg/day for 5 weeks. Relative Tumour Volume (RTV) was calculated.

RESULTS

We demonstrated that DPT-C9h specifically target caspase-9/PP2A interaction in vitro and in vivo and induced caspase-9-dependent apoptosis in cancer cell lines. DPT-C9h also induced significant TGI in BC xenografts models. The mouse-specific peptide DPT-C9 also induced TGI in lung (K-Ras model) and breast cancer (PyMT) models. DPT-C9h has a specific effect on transformed B cells isolated from chronic lymphocytic leukemia patients without any effect on primary healthy cells. Finally, neither toxicity nor immunogenic responses were observed.

CONCLUSION

Using the cell-penetrating peptides blocking caspase-9/PP2A interactions, we have demonstrated that DPT-C9h had a strong therapeutic effect in vitro and in vivo in mouse models of tumour progression.

QUICK identification and SPR validation of signal transducers and activators of transcription 3 (Stat3) interacting proteins

Signal transducers and activators of transcription 3 (Stat3) has been reported to be involved in the pathogenesis of various human diseases and is constitutively active in human multiple myeloma (MM) U266 cells. The Stat3-regulated mechanisms involved in these processes, however, are not fully defined. To further understand the regulation of Stat3 activity, we performed a systematic proteomic analysis of Stat3 interacting proteins in U266 cells. This analysis, termed quantitative immunoprecipitation combined with knockdown (QUICK), combines RNAi, stable isotope labeling with amino acids in cell culture (SILAC), immunoprecipitation, and quantitative MS. As a result, quantitative mass spectrometry analysis allowed us to distinguish specific Stat3 interacting proteins from background proteins and led to the identification of a total of 38 proteins. Three Stat3 interacting proteins - 14-3-3ζ, PRKCB and Hsp90 - were further confirmed by reciprocal co-immunoprecipitations and surface plasmon resonance (SPR) analysis. Our results therefore not only uncover a number of Stat3 interacting proteins that possess a variety of cellular functions, but also provide new insight into the mechanisms that regulate Stat3 activity and function in MM cells.

Cantharidin induces apoptosis of human multiple myeloma cells via inhibition of the JAK/STAT pathway

Multiple myeloma is an incurable B-cell malignancy requiring new therapeutic strategies in clinical settings. Interleukin (IL)-6 signaling pathways play a critical role in the pathogenesis of multiple myeloma. The traditional Chinese medicine cantharidin (CTD) has been shown to inhibit cellular proliferation and induce apoptosis of various cancer cells. The aim of this study was to investigate the possibility of CTD as a novel therapeutic agent for the patients with multiple myeloma. We investigated the in vitro effects of CTD for its antimyeloma activity, and further examined the molecular mechanisms of CTD-induced apoptosis. CTD inhibited the cellular growth of human myeloma cell lines as well as freshly isolated myeloma cells in patients. Cultivation with CTD induced apoptosis of myeloma cells in a cell-cycle-independent manner. Treatment with CTD induced caspase-3, -8, and -9 activities, and it was completely blocked by each caspase inhibitor. We further examined the effect of CTD on the IL-6 signaling pathway in myeloma cells, and found that CTD inhibited phosphorylation of STAT3 at tyrosine 705 residue as early as 1 h after treatment and down-regulated the expression of the antiapoptotic bcl-xL protein. STAT3 directly bound and activated the transcription of bcl-xL gene promoter, resulting in the induction of the expression of bcl-xL in myeloma cells. The essential role of STAT3 in CTD effects was confirmed by transfection with the constitutively active and dominant negative form of STAT3 in U266 cells. In conclusion, we have demonstrated that CTD is a promising candidate to be a new therapeutic agent in signal transduction therapy.

The effects of protein phosphatase inhibitors on the duration of central sensitization of rat dorsal horn neurons following injection of capsaicin

Protein kinases and phosphatases catalyze opposing reactions of phosphorylation and dephosphorylation, which may modulate the function of crucial signaling proteins in central nervous system. This is an important mechanism in the regulation of intracellular signal transduction pathways in nociceptive neurons. To explore the role of protein phosphatase in central sensitization of spinal nociceptive neurons following peripheral noxious stimulation, using electrophysiological recording techniques, we investigated the role of two inhibitors of protein phosphatase type 2A (PP2A), fostriecin and okadaic acid (OA), on the responses of dorsal horn neurons to mechanical stimuli in anesthetized rats following intradermal injection of capsaicin. Central sensitization was initiated by injection of capsaicin into the plantar surface of the left paw. A microdialysis fiber was implanted in the spinal cord dorsal horn for perfusion of ACSF and inhibitors of PP2A, fostriecin and okadaic acid. We found that in ACSF pretreated animals, the responses to innocuous and noxious stimuli following capsaicin injection increased over a period of 15 min after injection and had mostly recovered by 60 min later. However, pre- or post-treatment with the phosphatase inhibitors, fostriecin or OA, significantly enhanced the effects of capsaicin injection by prolonging the responses to more than 3 hours. These results confirm that blockade of protein phosphatase activity may potentiate central sensitization of nociceptive transmission in the spinal cord following capsaicin injection and indicate that protein phosphatase type 2A may be involved in determining the duration of capsaicin-induced central sensitization.

Redox regulation of apoptosis by members of the TNF superfamily

Tumor necrosis factor (TNF), fibroblast-associated cell surface (Fas) ligand, and TNF-related apoptosisinducing ligand (TRAIL), all members of the TNF superfamily, are arguably the most potent inducers of cell death. These cytokines induce cell death through sequential recruitment by the death receptors TNFR1- associated death domain protein (TRADD), Fas-associated death domain protein (FADD), FADD-like interleukin-1beta-converting enzyme (FLICE), and downstream caspases. Increasing evidence indicates that mitochondria play a critical role in cytokine receptor-mediated apoptosis. There is also now ample evidence that apoptosis induced by TNF and its family members is mediated through the production of reactive oxygen intermediates (also known as reactive oxygen species). Here we review the evidence linking reactive oxygen intermediates to cytokine-induced cell death mediated by TNF-alpha/beta, Fas, TRAIL, TNF-like weak inducer of apoptosis (TWEAK), and vascular endothelial cell growth inhibitor (VEGI).

In vitro Assessment of Renal Toxicity and Inflammatory Events of Two Protein Phosphatase Inhibitors Cantharidin and Nor-Cantharidin*

In China, cantharidin has been reported to be active against various human cancers, but with severe side effects such as nephrotoxicity. In order to reduce this toxicity, its demethylated analogue nor-cantharidin has been synthesized and used in cancer therapy, but with only few data regarding safety assessment. The aim of this study was to compare the in vitro effects of cantharidin and nor-cantharidin on renal toxicity and on inflammatory events associated with tumoural process where protein phosphatases could be involved (energy status, prostanoid production, glutathione and nitrite contents) on RAW 264.7 and LLC-PK1 cells. In macrophages, both cantharidin and nor-cantharidin decreased cell viability, in a concentration- and time-dependent manner. However, IC50 was lower with cantharidin than with nor-cantharidin. These two drugs significantly decreased the ATP level after 24 hr incubation. However, ATP decreased much more with cantharidin (up to 4 times) than with nor-cantharidin. When control macrophages were activated with lipopolysaccharide+interferon-gamma for 24 hr a significant increase in nitrite content and in prostanoids were observed. Addition of either drug decreased nitrite generation and prostanoids, however these decreases were greater with cantharidin than with nor-cantharidin. In LLC-PK1 cells, incubated with either cantharidin or nor-cantharidin, our results show significant differences between the two drugs, similar to those observed in peritoneal macrophages, except for GSH content with opposite variations in both cells. We provide a better understanding of the various mechanisms of cantharidin side effects, allowing an easier comparison with nor-cantharidin which could be an attractive therapeutic potential in cancer chemotherapy in western countries.

L-gamma-Glutamyl-L-cysteinyl-glycine (glutathione; GSH) and GSH-related enzymes in the regulation of pro- and anti-inflammatory cytokines: a signaling transcriptional scenario for redox(y) immunologic sensor(s)?

Of the antioxidant/prooxidant mechanisms mediating the regulation of inflammatory mediators, particularly cytokines, oxidative stress-related pathways remain a cornerstone. It is conspicuous that there is a strong association between free radical accumulation (ROS/RNS; oxidative stress) and the evolution of inflammation and inflammatory-related responses. The scenario that upholds a consensus on the aforementioned is still evolving to unravel, from an immunologic perspective, the molecular mechanisms associated with ROS/RNS-dependent inflammation. Cytokines are keynote players when it comes to defining an intimate relationship among reduction-oxidation (redox) signals, oxidative stress and inflammation. How close we are to identifying the molecular basis of this intricate association should be weighed against the involvement of specific signaling molecules and, potentially, transcription factors. L-gamma-Glutamyl-L-cysteinyl-glycine, or glutathione (GSH), an antioxidant thiol, has shaped, and still is refining, the face of oxidative signaling in terms of regulating the milieu of inflammatory mediators, ostensibly via the modulation (expression/repression) of oxygen- and redox-responsive transcription factors, hence termed redox(y)-sensitive cofactors. When it comes to the arena of oxygen sensing, oxidative stress and inflammation, nuclear factor-kappaB (NF-kappaB) and hypoxia-inducible factor-1alpha (HIF-1alpha) are key players that determine antioxidant/prooxidant responses with oxidative challenge. It is the theme therein to underlie current understanding of the molecular association hanging between oxidative stress and the evolution of inflammation, walked through an elaborate discussion on the role of transcription factors and cofactors. Would that classify glutathione and other redox signaling cofactors as potential anti-inflammatory molecules emphatically remains of particular interest, especially in the light of identifying upstream and downstream molecular pathways for conceiving therapeutic, alleviating strategy for oxidant-mediated, inflammatory-related disease conditions.

The uptake kinetics and immunotoxic effects of microcystin-LR in human and chicken peripheral blood lymphocytes in vitro

Microcystin-LR is a cyanobacterial heptapeptide that presents acute and chronic hazards to animal and human health. We investigated the influence of this toxin on human and chicken immune system modulation in vitro. Peripheral blood lymphocytes were treated with microcystin-LR at environmentally relevant doses of 1, 10 and 25 microg/ml for 12, 24, 48, 72 h (for proliferation assay cells were treated for 72 h). T-cell and B-cell proliferation as well as apoptosis and necrosis were determined in human and chicken samples. IL-2 and IL-6 production by human lymphocytes also was measured. In addition, uptake kinetics of microcystin-LR into human and chicken peripheral blood lymphocytes were calculated by Liquid Chromatography (LS) /Mass Spectrometry (MS) analysis. At the highest dose microcystin-LR decreased T-cell proliferation and all doses of microcystin-LR inhibited B-cell proliferation. The frequency of apoptotic and necrotic cells increased in a dose and time-dependent manner. Human lymphocytes responded to stimulation with microcystin-LR by increased production of IL-6 and decreased production of IL-2. Human lymphocytes were able to uptake from 0.014 to 1.663 microg/ml and chicken lymphocytes from 0.035 to 1.733 microg/ml of the microcystin-LR added to the cultures, depending on the treatment time and dose. In conclusion, microcystin-LR acted as an immunomodulator in cytokine production and down-regulated lymphocyte functions by induction of apoptosis and necrosis. However, further studies dealing with the influence of microcystin-LR on expression cytokine genes and transcription factors are necessary to confirm these hypotheses.

On the antioxidant mechanisms of Bcl-2: a retrospective of NF-kappaB signaling and oxidative stress

Antioxidant and prooxidant signaling pathways are emanating as major players in, and regulators of, cell death and apoptosis. Redox conception of the critical role of oxidative stress in determining cell fate is being established-a foundation that craves deeper than the basic understanding of physiochemical interactions to extend beyond that into the realms of deciphering the molecular codes implicated with apoptosis. The proto-oncogene Bcl-2 is no stranger being a major player and decoder in controlling apoptosis, ostensibly via the regulation of redox equilibrium and disequilibrium. One of those potential mechanisms exhibited by Bcl-2 is its ability to counteract the detrimental effects of cell damage caused by free radicals, thereby gaining its well-known property of being an antioxidant. But the question is: what are the molecular mechanisms involved with the antioxidant role of Bcl-2 in the face of cell damage and apoptosis? Currently, a stance is being upheld in that the Bcl-2 antioxidant efficacy should be weighed against its ability to manipulate transcriptional control, through the regulation of specific transcription factors. NF-kappaB is no doubt one of the best candidates when it comes to the arena of oxidative stress, inflammation, and apoptosis. Therein, current themes in the burgeoning antioxidant role of Bcl-2 are exposed within the context of transcriptional control of NF-kappaB, thereby holding potential avenues for alleviating therapeutic approaches in the regulation of apoptosis.

The effects of protein phosphatase inhibitors on nociceptive behavioral responses of rats following intradermal injection of capsaicin

The functions of crucial proteins in the nervous system are modulated by kinases and phosphatases which catalyze opposing reactions of phosphorylation and dephosphorylation. During spinal cord central sensitization, serine/threonine protein phosphatase 2A (PP2A) may play an important role in determining the excitability of nociceptive neurons in the spinal cord by modulating the phosphorylation state of some critical proteins. The effects of a general inhibitor of PP2A, okadaic acid (OA), and a specific inhibitor, fostriecin, on the behavioral responses of rats following capsaicin injection were investigated in this study. Hyperalgesia was initiated by injection of capsaicin into the plantar surface of the hindpaw of rats. An intrathecal catheter was previously implanted into the subarachnoid space of the spinal cord for the administration of a variety of drugs. Rats were tested for responses to mechanical stimuli using von Frey filaments of different bending forces applied at a site outside the area of injection. Responses to heat stimuli were detected from a site near the injection area. The responses were recorded before and after injection of capsaicin with the perfusion of ACSF, OA negative control, OA or fostriecin at different time points. The results demonstrated that secondary mechanical hyperalgesia and allodynia can be induced by the intradermal injection of capsaicin. Compared to administration of ACSF or the OA negative control, infusion of the phosphatase inhibitor OA or of fostriecin into the subarachnoid space enhanced the secondary mechanical hyperalgesia and allodynia by making the intradermal capsaicin-induced hyperalgesia and allodynia last longer.

Hydrogen sulfide induces serum-independent cell cycle entry in nontransformed rat intestinal epithelial cells

Hydrogen sulfide (H2S), produced by commensal sulfate-reducing bacteria, is an environmental insult that potentially contributes to chronic intestinal epithelial disorders. We tested the hypothesis that exposure of nontransformed intestinal epithelial cells (IEC-18) to the reducing agent sodium hydrogen sulfide (NaHS) activates molecular pathways that underlie epithelial hyperplasia, a phenotype common to both ulcerative colitis (UC) and colorectal cancer. Exposure of IEC-18 cells to NaHS rapidly increased the NADPH/NADP ratio, reduced the intracellular redox environment, and inhibited mitochondrial respiratory activity. The addition of 0.2-5 mM NaHS for 4 h increased the IEC-18 proliferative cell fraction (P<0.05), as evidenced by analysis of the cell cycle and proliferating cell nuclear antigen expression, while apoptosis occurred only at the highest concentration of NaHS. Thirty minutes of NaHS exposure increased (P<0.05) c-Jun mRNA concentrations, consistent with the observed activation of mitogen activated protein kinases (MAPK). Microarray analysis confirmed an increase (P<0.05) in MAPK-mediated proliferative activity, likely reflecting the reduced redox environment of NaHS-treated cells. These data identify functional pathways by which H2S may initiate epithelial dysregulation and thereby contribute to UC or colorectal cancer. Thus, it becomes crucial to understand how genetic background may affect epithelial responsiveness to this bacterial-derived environmental insult.