RAF and antioxidants prevent cell death induction after growth factor abrogation through regulation of Bcl-2 proteins

Rigosertib-Activated JNK1/2 Eliminate Tumor Cells through p66Shc Activation

Rigosertib, via reactive oxygen species (ROS), stimulates cJun N-terminal kinases 1/2 (JNK1/2), which inactivate RAS/RAF signaling and thereby inhibit growth and survival of tumor cells. JNK1/2 are not only regulated by ROS—they in turn can also control ROS production. The prooxidant and cell death function of p66Shc requires phosphorylation by JNK1/2. Here, we provide evidence that establishes p66Shc, an oxidoreductase, as a JNK1/2 effector downstream of Rigosertib-induced ROS production, DNA damage, and cell death. This may provide a common pathway for suppression of tumor cell growth by Rigosertib.

Metabolism of Reactive Oxygen Species in Osteosarcoma and Potential Treatment Applications

Background: The present study was designed to explore the underlying role of hypoxia-inducible factor 1α (HIF-1α) in reactive oxygen species (ROS) formation and apoptosis in osteosarcoma (OS) cells induced by hypoxia. Methods: In OS cells, ROS accumulated and apoptosis increased within 24 h after exposure to low HIF-1α expression levels. A co-expression analysis showed that HIF was positively correlated with Forkhead box class O1 (FoxO1) expression and negatively correlated with CYP-related genes from the National Center for Biotechnology Information’s Gene Expression Omnibus (NCBI GEO) datasets. Hypoxia also considerably increased HIF-1α and FoxO1 expression. Moreover, the promoter region of FoxO1 was directly regulated by HIF-1α. We inhibited HIF-1α via siRNA and found that the ROS accumulation and apoptosis induced by hypoxia in OS cells decreased. In this study, a murine xenograft model of BALB-c nude mice was adopted to test tumour growth and measure the efficacy of 2-ME + As₂O₃ treatment. Results: Ad interim knockdown of HIF-1α also inhibited manganese-dependent superoxide dismutase (MnSOD), catalase and sestrin 3 (Sesn3) expression in OS cells. Furthermore, hypoxia-induced ROS formation and apoptosis in OS cells were associated with CYP450 protein interference and were ablated by HIF-1α silencing via siRNA. Conclusions: Our data reveal that HIF-1α inhibits ROS accumulation by directly regulating FoxO1 in OS cells, which induces MnSOD, catalase and Sesn3 interference, thus resulting in anti-oxidation effects. The combination of an HIF-1α inhibitor (2-mercaptoethanol,2-ME) and ROS inducer (arsenous oxide, As₂O₃) can prohibit proliferation and migration and promote apoptosis in MG63 cells in vitro while inhibiting tumour growth in vivo.

The oxidoreductase p66Shc acts as tumor suppressor in BRAFV600E-transformed cells

Metabolic reprogramming, as exemplified by the shift from oxidative phosphorylation to glycolysis, is a common feature of transformed cells. In many tumors, altered metabolism is also reflected in increased reactive oxygen species (ROS) levels, which contribute to proliferation and survival signaling. However, despite high ROS levels, cancer cells can be efficiently killed by further increasing ROS production. We have shown previously that both wild‐type and oncogenic CRAF and BRAF prevent excessive mitochondrial ROS production. Subsequently, it has been demonstrated that raising ROS levels in BRAFV600E‐transformed melanoma cells by inhibiting BRAF or MEK rendered them susceptible to cell death induction. To understand how oncogenic BRAF affects mitochondrial ROS production in melanoma, we studied the mitochondrial ROS‐producing oxidoreductase p66Shc, which is frequently overexpressed in tumors. Using NIH 3T3 BRAFV600E fibroblasts and the melanoma cell lines A375 and M238 carrying the same BRAF mutation, we show that under treatment with the ROS‐inducing agent phenethyl isothiocyanate (PEITC), oncogenic BRAF renders cells refractory to p66ShcS36 phosphorylation, which is essential for p66Shc activation and mitochondrial ROS production. Consistent with this, the activation of JNK1/2, which phosphorylate S36, was blunted, while other mitogen‐activated protein kinases were not affected. Inhibition of JNK1/2 efficiently prevented ROS production, while BRAF and MEK inhibitors increased ROS levels. Vemurafenib‐resistant M238R melanoma cells were impaired in S36 phosphorylation and ROS production following PEITC treatment. Moreover, they failed to increase ROS levels after MEK/BRAF inhibition. Finally, shRNA‐mediated knockdown of p66Shc led to increased growth of BRAFV600E‐transformed NIH 3T3 cells in soft agar assay. Taken together, these data suggest that phosphorylation‐activated p66Shc functions as a tumor suppressor in melanoma cells.

Mcl-1 regulates reactive oxygen species via NOX4 during chemotherapy-induced senescence

Mcl-1, a Bcl-2 family member, is highly expressed in a variety of human cancers and is believed to enhance tumorigenic potential and chemotherapy resistance through the inhibition of apoptosis and senescence. We previously reported that Mcl-1′s regulation of chemotherapy-induced senescence (CIS) is dependent on its ability to prevent reactive oxygen species (ROS) generation. In this report, we demonstrate that Mcl-1-regulated CIS requires not only ROS, but specifically mitochondrial ROS, and that these events are upstream of activation of the DNA damage response, another necessary step toward senescence. Mcl-1′s anti-senescence activity also involves the unique ability to inhibit ROS formation by preventing the upregulation of pro-oxidants. Specifically, we found that NADPH oxidases (NOXs) are regulated by Mcl-1 and that NOX4 expression in particular is a required step for CIS induction that is blocked by Mcl-1. Lastly, we illustrate that by preventing expression of NOX4, Mcl-1 limits its availability in the mitochondria, thereby lowering the production of mitochondrial ROS during CIS. Our studies not only define the essential role of Mcl-1 in chemoresistance, but also for the first time link a key pro-survival Bcl-2 family member with the NOX protein family, both of which have significant ramifications in cancer progression.

Novel Insights into the PKCβ-dependent Regulation of the Oxidoreductase p66Shc

Dysfunctional mitochondria contribute to the development of many diseases and pathological conditions through the excessive production of reactive oxygen species (ROS), and, where studied, ablation of p66Shc (p66) was beneficial. p66 translocates to the mitochondria and oxidizes cytochrome c to yield H₂O₂, which in turn initiates cell death. PKCβ-mediated phosphorylation of serine 36 in p66 has been implicated as a key regulatory step preceding mitochondrial translocation, ROS production, and cell death, and PKCβ thus may provide a target for therapeutic intervention. We performed a reassessment of PKCβ regulation of the oxidoreductase activity of p66. Although our experiments did not substantiate Ser³⁶ phosphorylation by PKCβ, they instead provided evidence for Ser¹³⁹ and Ser²¹³ as PKCβ phosphorylation sites regulating the pro-oxidant and pro-apoptotic function of p66. Mutation of another predicted PKCβ phosphorylation site also located in the phosphotyrosine binding domain, threonine 206, had no phenotype. Intriguingly, p66 with Thr²⁰⁶ and Ser²¹³ mutated to glutamic acid showed a gain-of-function phenotype with significantly increased ROS production and cell death induction. Taken together, these data argue for a complex mechanism of PKCβ-dependent regulation of p66 activation involving Ser¹³⁹ and a motif surrounding Ser²¹³.

cJun N-terminal kinase (JNK) phosphorylation of serine 36 is critical for p66Shc activation

p66Shc-dependent ROS production contributes to many pathologies including ischemia/reperfusion injury (IRI) during solid organ transplantation. Inhibiting p66Shc activation may provide a novel therapeutic approach to prevent damage, which is poorly managed by antioxidants in vivo. Previous work suggested that pro-oxidant and a pro-apoptotic function of p66Shc required mitochondrial import, which depended on serine 36 phosphorylation. PKCß has been proposed as S36 kinase but cJun N-terminal kinases (JNKs) may also phosphorylate this residue. To simulate the early stages of ischemia/reperfusion (IR) we either used H2O2 treatment or hypoxia/reoxygenation (HR). As during reperfusion in vivo, we observed increased JNK and p38 activity in mouse embryonic fibroblasts (MEFs) and HL-1 cardiomyocytes along with significantly increased p66ShcS36 phosphorylation, ROS production and cell damage. Application of specific inhibitors caused a pronounced decrease in p66ShcS36 phosphorylation only in the case of JNK1/2. Moreover, S36 phosphorylation of recombinant p66Shc by JNK1 but not PKCß was demonstrated. We further confirmed JNK1/2-dependent regulation of p66ShcS36 phosphorylation, ROS production and cell death using JNK1/2 deficient MEFs. Finally, the low ROS phenotype of JNK1/2 knockout MEFs was reversed by the phosphomimetic p66ShcS36E mutant. Inhibiting JNK1/2-regulated p66Shc activation may thus provide a therapeutic approach for the prevention of oxidative damage.

T24 HRAS transformed NIH/3T3 mouse cells (GhrasT-NIH/3T3) in serial tumorigenic in vitro/in vivo passages give rise to increasingly aggressive tumorigenic cell lines T1-A and T2-A and metastatic cell lines T3-HA and T4-PA

Cancer cells often arise progressively from "normal" to "pre-cancer" to "transformed" to "local metastasis" to "metastatic disease" to "aggressive metastatic disease". Recent whole genome sequencing (WGS) and spectral karyotyping (SKY) of cancer cells and tumorigenic models have shown this progression involves three major types of genome rearrangements: ordered small step-wise changes, more dramatic "punctuated evolution" (chromoplexy), and large catastrophic steps (chromothripsis) which all occur in random combinations to generate near infinite numbers of stochastically rearranged metastatic cancer cell genomes. This paper describes a series of mouse cell lines developed sequentially to mimic this type of progression. This starts with the new GhrasT-NIH/Swiss cell line that was produced from the NIH/3T3 cell line that had been transformed by transfection with HRAS oncogene DNA from the T24 human bladder carcinoma. These GhrasT-NIH/Swiss cells were injected s.c. into NIH/Swiss mice to produce primary tumors from which one was used to establish the T1-A cell line. T1-A cells injected i.v. into the tail vein of a NIH/Swiss mouse produced a local metastatic tumor near the base of the tail from which the T2-A cell line was established. T2-A cells injected i.v. into the tail vein of a nude NIH/Swiss mouse produced metastases in the liver and one lung from which the T3-HA (H=hepatic) and T3-PA (P=pulmonary) cell lines were developed, respectively. T3-HA cells injected i.v. into a nude mouse produced a metastasis in the lung from which the T4-PA cell line was established. PCR analysis indicated the human T24 HRAS oncogene was carried along with each in vitro/in vivo transfer step and found in the T2-A and T4-PA cell lines. Light photomicrographs indicate that all transformed cells are morphologically similar. GhrasT-NIH/Swiss cells injected s.c. produced tumors in 4% of NIH/Swiss mice in 6-10 weeks; T1-A cells injected s.c. produced tumors in 100% of NIH/Swiss mice in 7-10 days. T1-A, T-2A, T3-HA and T4-PA cells when injected i.v. into the tail produced local metastasis in non-nude or nude NIH/Swiss mice. T4-PA cells were more widely metastatic than T3-HA cells when injected i.v. into nude mice. Evaluation of the injected mice indicated a general increase in metastatic potential of each cell line in the progression as compared to the GhrasT-NIH/3T3 transformed cells. A new photomicrographic technique to follow growth rates within six preselected 2×2mm(2) grids per plate is described. Average doubling times of the transformed cells GhrasT-NIH/3T3 (17h), T1A (17.5h), T2A (15.5h), T3-HA (17.5h) and T4-PA (18.5h) (average 17.2h) were significantly faster (P=0.006) than NIH Swiss primary embryonic cells and NIH/3T3 cells (22 h each). This cell series is currently used in this lab for studies of cancer cell inhibitors, mitochondrial biogenesis and gene expression and is available for further study by other investigators for intra- and inter-laboratory comparisons of WGS, transcriptome sequencing, SKY and other analyses. The genome rearrangements in these cells together with their phenotypic properties may help provide more insights into how one tumorigenic progression occurred to produce the various cell lines that led to the highly metastatic T4-PA cell line.

C-Raf deficiency leads to hearing loss and increased noise susceptibility

The family of RAF kinases transduces extracellular information to the nucleus, and their activation is crucial for cellular regulation on many levels, ranging from embryonic development to carcinogenesis. B-RAF and C-RAF modulate neurogenesis and neuritogenesis during chicken inner ear development. C-RAF deficiency in humans is associated with deafness in the rare genetic insulin-like growth factor 1 (IGF-1), Noonan and Leopard syndromes. In this study, we show that RAF kinases are expressed in the developing inner ear and in adult mouse cochlea. A homozygous C-Raf deletion in mice caused profound deafness with no evident cellular aberrations except for a remarkable reduction of the K⁺ channel Kir4.1 expression, a trait that suffices as a cause of deafness. To explore the role of C-Raf in cellular protection and repair, heterozygous C-Raf^+/− mice were exposed to noise. A reduced C-RAF level negatively affected hearing preservation in response to noise through mechanisms involving the activation of JNK and an exacerbated apoptotic response. Taken together, these results strongly support a role for C-RAF in hearing protection.

Alpha2beta1 integrin promotes T cell survival and migration through the concomitant activation of ERK/Mcl-1 and p38 MAPK pathways

Integrin-mediated attachment to extracellular matrix (ECM) is crucial for cancer progression. Malignant T cells such as acute lymphoblastic leukemia (T-ALL) express β1 integrins, which mediate their interactions with ECM. However, the role of these interactions in T-ALL malignancy is still poorly explored. In the present study, we investigated the effect of collagen; an abundant ECM, on T-ALL survival and migration. We found that collagen through α2β1 integrin promotes the survival of T-ALL cell lines in the absence of growth factors. T-ALL cell survival by collagen is associated with reduced caspase activation and maintenance of Mcl-1 levels. Collagen activated both ERK and p38 MAPKs but only MAPK/ERK was required for collagen-induced T-ALL survival. However, we found that α2β1 integrin promoted T-ALL migration via both ERK and p38. Together these data indicate that α2β1 integrin signaling can represent an important signaling pathway in T-ALL pathogenesis and suggest that its blockade could be beneficial in T-ALL treatment.

RNA-seq based transcriptome analysis of hepatitis E virus (HEV) and hepatitis B virus (HBV) replicon transfected Huh-7 cells

Pathogenesis of hepatitis B virus (HBV) and hepatitis E virus (HEV) infection is as varied as they appear similar; while HBV causes an acute and/or chronic liver disease and hepatocellular carcinoma, HEV mostly causes an acute self-limiting disease. In both infections, host responses are crucial in disease establishment and/or virus clearance. In the wake of worsening prognosis described during HEV super-infection over chronic HBV hepatitis, we investigated the host responses by studying alterations in gene expression in liver cells (Huh-7 cell line) by transfection with HEV replicon only (HEV-only), HBV replicon only (HBV-only) and both HBV and HEV replicons (HBV+HEV). Virus replication was validated by strand-specific real-time RT-PCR for HEV and HBsAg ELISA of the culture supernatants for HBV. Indirect immunofluorescence for the respective viral proteins confirmed infection. Transcription profiling was carried out by RNA Sequencing (RNA-Seq) analysis of the poly-A enriched RNA from the transfected cells. Averages of 600 million bases within 5.6 million reads were sequenced in each sample and ∼15,800 genes were mapped with at least one or more reads. A total of 461 genes in HBV+HEV, 408 in HBV-only and 306 in HEV-only groups were differentially expressed as compared to mock transfection control by two folds (p<0.05) or more. Majority of the significant genes with altered expression clustered into immune-associated, signal transduction, and metabolic process categories. Differential gene expression of functionally important genes in these categories was also validated by real-time RT-PCR based relative gene-expression analysis. To our knowledge, this is the first report of in vitro replicon transfected RNA-Seq based transcriptome analysis to understand the host responses against HEV and HBV.