VHL expression in renal cell carcinoma sensitizes to bortezomib (PS-341) through an NF-kappaB-dependent mechanism

APOBEC3C-mediated NF-κB activation enhances clear cell renal cell carcinoma progression

Renowned as the predominant form of kidney cancer, clear cell renal cell carcinoma (ccRCC) exhibits susceptibility to immunotherapies due to its specific expression profile as well as notable immune cell infiltration. Despite this, effectively treating metastatic ccRCC remains a significant challenge, necessitating a more profound comprehension of the underlying molecular mechanisms governing its progression. Here, we unveil that the enhanced expression of the RNA-binding protein DNA dC → dU-editing enzyme APOBEC-3C (APOBEC3C; also known as A3C) in ccRCC tissue and ccRCC-derived cell lines serves as a catalyst for tumor growth by amplifying nuclear factor-kappa B (NF-κB) activity. By employing RNA-sequencing and cell-based assays in ccRCC-derived cell lines, we determined that A3C is a stress-responsive factor and crucial for cell survival. Furthermore, we identified that A3C binds and potentially stabilizes messenger RNAs (mRNAs) encoding positive regulators of the NF-κB pathway. Upon A3C depletion, essential subunits of the NF-κB family are abnormally restrained in the cytoplasm, leading to deregulation of NF-κB target genes. Our study illuminates the pivotal role of A3C in promoting ccRCC tumor development, positioning it as a prospective target for future therapeutic strategies.

Panels of mRNAs and miRNAs for decoding molecular mechanisms of Renal Cell Carcinoma (RCC) subtypes utilizing Artificial Intelligence approaches

Renal Cell Carcinoma (RCC) encompasses three histological subtypes, including clear cell RCC (KIRC), papillary RCC (KIRP), and chromophobe RCC (KICH) each of which has different clinical courses, genetic/epigenetic drivers, and therapeutic responses. This study aimed to identify the significant mRNAs and microRNA panels involved in the pathogenesis of RCC subtypes. The mRNA and microRNA transcripts profile were obtained from The Cancer Genome Atlas (TCGA), which were included 611 ccRCC patients, 321 pRCC patients, and 89 chRCC patients for mRNA data and 616 patients in the ccRCC subtype, 326 patients in the pRCC subtype, and 91 patients in the chRCC for miRNA data, respectively. To identify mRNAs and miRNAs, feature selection based on filter and graph algorithms was applied. Then, a deep model was used to classify the subtypes of the RCC. Finally, an association rule mining algorithm was used to disclose features with significant roles to trigger molecular mechanisms to cause RCC subtypes. Panels of 77 mRNAs and 73 miRNAs could discriminate the KIRC, KIRP, and KICH subtypes from each other with 92% (F1-score ≥ 0.9, AUC ≥ 0.89) and 95% accuracy (F1-score ≥ 0.93, AUC ≥ 0.95), respectively. The Association Rule Mining analysis could identify miR-28 (repeat count = 2642) and CSN7A (repeat count = 5794) along with the miR-125a (repeat count = 2591) and NMD3 (repeat count = 2306) with the highest repeat counts, in the KIRC and KIRP rules, respectively. This study found new panels of mRNAs and miRNAs to distinguish among RCC subtypes, which were able to provide new insights into the underlying responsible mechanisms for the initiation and progression of KIRC and KIRP. The proposed mRNA and miRNA panels have a high potential to be as biomarkers of RCC subtypes and should be examined in future clinical studies.

High-speed fluorescence image-enabled cell sorting

Fast and selective isolation of single cells with unique spatial and morphological traits remains a technical challenge. Here, we address this by establishing high-speed image-enabled cell sorting (ICS), which records multicolor fluorescence images and sorts cells based on measurements from image data at speeds up to 15,000 events per second. We show that ICS quantifies cell morphology and localization of labeled proteins and increases the resolution of cell cycle analyses by separating mitotic stages. We combine ICS with CRISPR-pooled screens to identify regulators of the nuclear factor κB (NF-κB) pathway, enabling the completion of genome-wide image-based screens in about 9 hours of run time. By assessing complex cellular phenotypes, ICS substantially expands the phenotypic space accessible to cell-sorting applications and pooled genetic screening.

Role of the KEAP1-NRF2 Axis in Renal Cell Carcinoma

NRF2 is a transcription factor that coordinates the antioxidant response in many different tissues, ensuring cytoprotection from endogenous and exogenous stress stimuli. In the kidney, its function is essential in appropriate cellular response to oxidative stress, however its aberrant activation supports progression, metastasis, and resistance to therapies in renal cell carcinoma, similarly to what happens in other nonrenal cancers. While at the moment direct inhibitors of NRF2 are not available, understanding the molecular mechanisms that regulate its hyperactivation in specific tumor types is crucial as it may open new therapeutic perspectives. Here, we focus our attention on renal cell carcinoma, describing how NRF2 hyperactivation can contribute to tumor progression and chemoresistance. Furthermore, we highlight the mechanism whereby the many pathways that are generally altered in these tumors converge to dysregulation of the KEAP1-NRF2 axis.

Nobiletin inhibits hypoxia-induced epithelial-mesenchymal transition in renal cell carcinoma cells

Hypoxia is a universal characteristic of solid tumor and involving cancer metastasis via epithelial-mesenchymal transition (EMT). Nobiletin (3',4',5,6,7,8-hexamethoxyflavone), a dietary polymethoxylated flavonoid found in citrus fruits, has been reported to have anticancer effects. However, the possible role of nobiletin in renal cell carcinoma (RCC) remains unclear. Thus, the aim of this study was to identify the effect of nobiletin on hypoxia-induced EMT in RCC cells. We found that nobiletin significantly inhibited the migration and invasion induced by hypoxia in RCC cells. In addition, nobiletin reversed the hypoxia-induced EMT process in RCC cells. Furthermore, nobiletin suppressed the activation of NF-κB and Wnt/β-catenin signaling pathways in hypoxia-stimulated RCC cells. In conclusion, these findings demonstrate that nobiletin inhibits hypoxia-induced EMT in human RCC cells via the inactivation of the NF-κB and Wnt/β-catenin signaling pathways.

The von Hippel–Lindau Tumor Suppressor Protein

The von Hippel–Lindau (VHL) gene is a two-hit tumor suppressor gene and is linked to the development of the most common form of kidney cancer, clear cell renal carcinoma; blood vessel tumors of the retina, cerebellum, and spinal cord called hemangioblastomas; and tumors of the sympathoadrenal nervous system called paragangliomas. The VHL gene product, pVHL, is the substrate recognition subunit of a cullin-dependent ubiquitin ligase that targets the α subunits of hypoxia-inducible factor (HIF) for destruction when oxygen is plentiful. Mounting evidence implicates HIF2 in the pathogenesis of pVHL-defective tumors and has provided a conceptual foundation for the development of drugs to treat them that inhibit HIF2-responsive gene products such as VEGF and, more recently, HIF2 itself. pVHL has additional, noncanonical functions that are cancer relevant, including roles related to the primary cilium, chromosome stability, extracellular matrix formation, and survival signaling.

USP9X destabilizes pVHL and promotes cell proliferation

Numerous mutations of the Von Hippel-Lindau (VHL) gene have been reported to cause dysfunction of VHL protein (pVHL) and lead to processes related to tumor progression. pVHL acts as an E3 ligase and degrades downstream targets, such as hypoxia-inducible transcription factor (HIF) which is essential for tumor growth. Previous studies reported reduction of VHL protein, rather than mRNA in VHL-related tumor patients, suggesting that instability of the pVHL protein itself is a primary cause of dysfunction. Regulation of pVHL stability has therefore been a major focus of research. We report that ubiquitin-specific protease 9X (USP9X), which is a deubiquitinase binds and promotes degradation of both wild-type and mutants of pVHL that retain E3 ligase function, thus activating the HIF pathway. USP9X degrades pVHL through protection of its substrate, the newly identified pVHL E3 ligase Smurf1. In addition, USP9X activates glycolysis and promotes cell proliferation through pVHL. Treatment with a USP9X inhibitor shows an effect similar to USP9X knockdown in pVHL induction, and suppresses HIF activity. Our findings demonstrate that USP9X is a novel regulator of pVHL stability, and USP9X may be a therapeutic target for treatment of VHL-related tumors.

The HIF and other quandaries in VHL disease

Mutations in VHL underlie von Hippel-Lindau (VHL) disease, a hereditary cancer syndrome with several subtypes depending on the risk of developing certain combination of classic features, such as clear cell renal cell carcinoma (ccRCC), hemangioblastoma and pheochromocytoma. Although numerous potential substrates and functions of pVHL have been described over the past decade, the best-defined role of pVHL has remained as the negative regulator of the heterodimeric hypoxia-inducible factor (HIF) transcription factor via the oxygen-dependent ubiquitin-mediated degradation of HIF-α subunit. Despite the seminal discoveries that led to the molecular elucidation of the mammalian oxygen-sensing VHL-HIF axis, which have provided several rational therapies, the mechanisms underlying the complex genotype-phenotype correlation in VHL disease are unclear. This review will discuss and highlight the studies that have provided interesting insights as well as uncertainties to the underlying mechanisms governing VHL disease.

VHL promotes immune response against renal cell carcinoma via NF-κB-dependent regulation of VCAM-1

Labrousse-Arias et al. show that VHL expression leads to increased VCAM-1 levels in renal cell carcinoma through an NF-κB–dependent mechanism that seems to contribute to the antitumoral immune response. This study also suggests that VCAM-1 levels might serve as a marker of ccRCC progression in human patients.

Vascular cell adhesion molecule 1 (VCAM-1) is an adhesion molecule assigned to the activated endothelium mediating immune cells adhesion and extravasation. However, its expression in renal carcinomas inversely correlates with tumor malignancy. Our experiments in clear cell renal cell carcinoma (ccRCC) cell lines demonstrated that von Hippel Lindau (VHL) loss, hypoxia, or PHD (for prolyl hydroxylase domain–containing proteins) inactivation decreased VCAM-1 levels through a transcriptional mechanism that was independent of the hypoxia-inducible factor and dependent on the nuclear factor κB signaling pathway. Conversely, VHL expression leads to high VCAM-1 levels in ccRCC, which in turn leads to better outcomes, possibly by favoring antitumor immunity through VCAM-1 interaction with the α4β1 integrin expressed in immune cells. Remarkably, in ccRCC human samples with VHL nonmissense mutations, we observed a negative correlation between VCAM-1 levels and ccRCC stage, microvascular invasion, and symptom presentation, pointing out the clinical value of VCAM-1 levels as a marker of ccRCC progression.

pVHL mediates K63-linked ubiquitination of IKKβ, leading to IKKβ inactivation

Nuclear factor (NF)-κB is a transcription factor that plays an important role in many biological functions. Regulation of NF-κB activity is complicated, and ubiquitination is essential for NF-κB activation. Hypoxia can activate NF-κB. However, the underlying mechanism remains unclear. pVHL is a tumour suppressor and functions as an adaptor of E3-ligase. In this study, we demonstrated that pVHL inhibits NF-κB by mediating K63-ubiquitination of IKKβ, which is dependent on oxygen. We found that pVHL mediates K63-linked ubiquitination of IKKβ, which is an upstream regulator of NF-κB. The pVHL-mediated K63-ubiquitination of IKKβ prevents TAK1 binding, which leads to the inhibition of IKKβ phosphorylation and NF-κB activation. pVHL-mediated K63-ubiquitination of IKKβ is inhibited under hypoxia. DMOG, which is a specific inhibitor of prolyl hydroxylases, also suppresses K63-ubiquitination of IKKβ. Prolyl hydroxylase (PHD) 1 enhances K63-ubiquitination of IKKβ and inhibits IKKβ phosphorylation. These results suggest a novel function for pVHL in mediating K63-linked ubiquitination of IKKβ, which plays a role in the regulation of IKK/NF-κB signalling. The results also provide new insight into the mechanism of NF-κB activation through hypoxia.

The NF-κB Pathway and Cancer Stem Cells

The NF-κB transcription factor pathway is a crucial regulator of inflammation and immune responses. Additionally, aberrant NF-κB signaling has been identified in many types of cancer. Downstream of key oncogenic pathways, such as RAS, BCR-ABL, and Her2, NF-κB regulates transcription of target genes that promote cell survival and proliferation, inhibit apoptosis, and mediate invasion and metastasis. The cancer stem cell model posits that a subset of tumor cells (cancer stem cells) drive tumor initiation, exhibit resistance to treatment, and promote recurrence and metastasis. This review examines the evidence for a role for NF-κB signaling in cancer stem cell biology.

Combined Analyses of the VHL and Hypoxia Signaling Axes in an Isogenic Pairing of Renal Clear Cell Carcinoma Cells

The loss of function of the Von Hippel-Lindau (VHL) tumor suppressor leads to the development of hypervascular tumors, exemplified by clear-cell-type renal cell carcinoma (RCC). VHL governs the adaptive responses to fluctuation of oxygen levels largely through the regulated suppression of hypoxia inducible factors (HIFs). Here, we combine proteome and phospho-proteomic analysis of isogenic 786-O RCC (±VHL) cells to compare signatures that reflect hypoxia and/or loss of VHL. VHL-independent hypoxic responses, notably include up-regulation of phosphorylation at Ser232 on the pyruvate dehydrogenase α subunit that is known to promote glycolysis. Hypoxic responses governed by VHL include up-regulation of known biomarkers of RCC (e.g., GLUT1, NDRG1) and the signaling adaptor molecule IRS-2. Notably, we also observe down-regulation of linked-components associated with the Jacobs-Stewart cycle, including the intracellular carbonic anhydrase II (CA2), which governs cellular response to CO2 fluctuations that often accompany hypoxia in tumors. Further studies indicate an unusual mechanism of control for CA2 expression that, at least in part, reflects enhanced activity of the NFκB pathway, which is associated with loss of VHL.

Pomegranate extract inhibits EMT in clear cell renal cell carcinoma in a NF-κB and JNK dependent manner

Objective

Clear cell renal cell carcinoma (ccRCC) is the most common subtype of renal cell carcinoma (RCC) and is characterized by biallelic inactivation of the von Hippel-Lindau (VHL) tumor suppressor gene. One effect of VHL inactivation is hypoxia inducible factor alpha (HIFα)-independent constitutive activation of nuclear factor kappa B (NF-κB) and c-jun N-terminal kinase (JNK). Both NF-κB and JNK drive ccRCC growth and epithelial to mesenchymal transition (EMT). The purpose of this study was to determine the biochemical effects of pomegranate juice extracts (PE) on RCC cell lines.

Methods

The pre-clinical effects of PE on NF-κB, JNK, and the EMT phenotype were assayed, including its effect on proliferation, anchorage-independent growth, and invasion of pVHL-deficient RCCs.

Results

PE inhibits the NF-κB and JNK pathways and consequently inhibits the EMT phenotype of pVHL-deficient ccRCCs. The effects of PE are concentration-dependent and affect not only biochemical markers of EMT (i.e., cadherin expression) but also functional manifestations of EMT, such as invasion. These effects are manifested within days of exposure to PE when diluted 2000-fold. Highly dilute concentrations of PE (10⁶ dilution), which do not impact these pathways in the short term, were found to have NF-κB and JNK inhibitory effects and ability to reverse the EMT phenotype following prolonged exposure.

Conclusion

These findings suggest that PE may mediate inhibition growth of pVHL-deficient ccRCCs and raises the possibility of its use as a dietary adjunct to managing patients with active surveillance for small, localized, incidentally identified renal tumors so as to avoid more invasive procedures such as nephrectomy.

VHL, the story of a tumour suppressor gene

Since the Von Hippel-Lindau (VHL) disease tumour suppressor gene VHL was identified in 1993 as the genetic basis for a rare disorder, it has proved to be of wide medical and scientific interest. VHL tumour suppressor protein (pVHL) plays a key part in cellular oxygen sensing by targeting hypoxia-inducible factors for ubiquitylation and proteasomal degradation. Early inactivation of VHL is commonly seen in clear-cell renal cell carcinoma (ccRCC), and insights gained from the functional analysis of pVHL have provided the foundation for the routine treatment of advanced-stage ccRCC with novel targeted therapies. However, recent sequencing studies have identified additional driver genes that are involved in the pathogenesis of ccRCC. As our understanding of the importance of VHL matures, it is timely to review progress from its initial description to current knowledge of VHL biology, as well as future prospects for novel medical treatments for VHL disease and ccRCC.

The apoptosis repressor with a CARD domain (ARC) gene is a direct hypoxia-inducible factor 1 target gene and promotes survival and proliferation of VHL-deficient renal cancer cells

The induction of hypoxia-inducible factors (HIFs) is essential for the adaptation of tumor cells to a low-oxygen environment. We found that the expression of the apoptosis inhibitor ARC (apoptosis repressor with a CARD domain) was induced by hypoxia in a variety of cancer cell types, and its induction is primarily HIF1 dependent. Chromatin immunoprecipitation (ChIP) and reporter assays also indicate that the ARC gene is regulated by direct binding of HIF1 to a hypoxia response element (HRE) located at bp -190 upstream of the transcription start site. HIFs play an essential role in the pathogenesis of renal cell carcinoma (RCC) under normoxic conditions, through the loss of the Von Hippel-Lindau gene (VHL). Accordingly, our results show that ARC is not expressed in normal renal tissue but is highly expressed in 65% of RCC tumors, which also express high levels of carbonic anhydrase IX (CAIX), a HIF1-dependent protein. Compared to controls, ARC-deficient RCCs exhibited decreased colony formation and increased apoptosis in vitro. In addition, loss of ARC resulted in a dramatic reduction of RCC tumor growth in SCID mice in vivo. Thus, HIF-mediated increased expression of ARC in RCC can explain how loss of VHL can promote survival early in tumor formation.

SQSTM1 is a pathogenic target of 5q copy number gains in kidney cancer

Clear cell renal cell carcinoma (ccRCC) is the most common form of kidney cancer and is often linked to loss of chromosome 3p, which harbors the VHL tumor suppressor gene, loss of chromosome 14q, which includes HIF1A, and gain of chromosome 5q. The relevant target(s) on chromosome 5q is not known. Here, we show that 5q amplification leads to overexpression of the SQSTM1 oncogene in ccRCC lines and tumors. Overexpression of SQSTM1 in ccRCC lines promoted resistance to redox stress and increased soft agar growth, while downregulation of SQSTM1 decreased resistance to redox stress, impaired cellular fitness, and decreased tumor formation. Therefore, the selection pressure to amplify 5q in ccRCC is driven, at least partly, by SQSTM1.

Meta-analysis identifies NF-κB as a therapeutic target in renal cancer

OBJECTIVE

To determine the expression patterns of NF-κB regulators and target genes in clear cell renal cell carcinoma (ccRCC), their correlation with von Hippel Lindau (VHL) mutational status, and their association with survival outcomes.

METHODS

Meta-analyses were carried out on published ccRCC gene expression datasets by RankProd, a non-parametric statistical method. DEGs with a False Discovery Rate of < 0.05 by this method were considered significant, and intersected with a curated list of NF-κB regulators and targets to determine the nature and extent of NF-κB deregulation in ccRCC.

RESULTS

A highly-disproportionate fraction (~40%; p < 0.001) of NF-κB regulators and target genes were found to be up-regulated in ccRCC, indicative of elevated NF-κB activity in this cancer. A subset of these genes, comprising a key NF-κB regulator (IKBKB) and established mediators of the NF-κB cell-survival and pro-inflammatory responses (MMP9, PSMB9, and SOD2), correlated with higher relative risk, poorer prognosis, and reduced overall patient survival. Surprisingly, levels of several interferon regulatory factors (IRFs) and interferon target genes were also elevated in ccRCC, indicating that an 'interferon signature' may represent a novel feature of this disease. Loss of VHL gene expression correlated strongly with the appearance of NF-κB- and interferon gene signatures in both familial and sporadic cases of ccRCC. As NF-κB controls expression of key interferon signaling nodes, our results suggest a causal link between VHL loss, elevated NF-κB activity, and the appearance of an interferon signature during ccRCC tumorigenesis.

CONCLUSIONS

These findings identify NF-κB and interferon signatures as clinical features of ccRCC, provide strong rationale for the incorporation of NF-κB inhibitors and/or and the exploitation of interferon signaling in the treatment of ccRCC, and supply new NF-κB targets for potential therapeutic intervention in this currently-incurable malignancy.

Interferon-γ-induced necrosis: an antitumor biotherapeutic perspective

Interferon (IFN)-γ-like the well-known antitumor biotherapeutic IFN-α-is a powerful antiproliferative and immune modulatory cytokine, but mixed results from clinical trials, together with issues of systemic toxicity, have dampened enthusiasm for its use in the treatment of cancer. We suggest that at least 2 factors reduce the antitumor efficacy of IFN-γ: (1) poorly understood survival mechanisms that protect most tumor cells from IFN-γ-induced direct cytotoxicity, and (2) the short half-life of IFN-γ in serum. In this review, we outline avenues to overcome both these limitations. First, we have identified the transcription factor nuclear factor-kappa B (NF-κB) as a protective mechanism against IFN-γ-induced necrosis, and disabling NF-κB allows IFN-γ to trigger RIP1 kinase-dependent programmed necrosis (or necroptosis) in otherwise resistant cells. Second, we propose that fusing IFN-γ to tumor-specific antibodies will stabilize IFN-γ in serum and target this cytokine to tumor cells. We expect that such IFN-γ-antibody chimeras (called immunocytokines), when combined with agents that neutralize tumor-intrinsic survival signals such as NF-κB, will exert potent tumoricidal activity with minimized systemic side effects. Although this review will focus on exploiting IFN-γ-induced necrosis for treatment of renal cell carcinoma, these approaches are also directly applicable to several human cancers in which IFNs have shown therapeutic potential.

Hyperactivated JNK is a therapeutic target in pVHL-deficient renal cell carcinoma

Clear cell renal cell carcinomas (RCC), the major histologic subtype of RCC accounting for more than 80% of cases, are typified by biallelic inactivation of the von Hippel-Lindau (VHL) tumor suppressor gene. Although accumulation of hypoxia-inducible factor alpha (HIF-α) is the most well-studied effect of VHL inactivation, direct inhibition of HIFα or restoration of wild-type pVHL protein expression has not proved readily feasible, given the limitations associated with pharmacologic targeting of transcription factors (i.e., HIF-α) and gene replacement therapy of tumor suppressor genes (i.e., VHL). Here, we have established that phosphorylated c-Jun, a substrate of the c-Jun-NH(2)-kinase (JNK), is selectively activated in clear cell RCC patient specimens. Using multiple isogenic cell lines, we show that HIF-α-independent JNK hyperactivation is unique to the pVHL-deficient state. Importantly, pVHL-deficient RCCs are dependent upon JNK activity for in vitro and in vivo growth. A multistep signaling pathway that links pVHL loss to JNK activation involves the formation of a CARD9/BCL10/TRAF6 complex as a proximal signal to sequentially stimulate TAK1 (MAPKKK), MKK4 (MAPKK), and JNK (MAPK). JNK stimulates c-Jun phosphorylation, activation, and dimerization with c-Fos to form a transcriptionally competent AP1 complex that drives transcription of the Twist gene and induces epithelial-mesenchymal transition. Thus, JNK represents a novel molecular target that is selectively activated in and drives the growth of pVHL-deficient clear cell RCCs. These findings can serve as the preclinical foundation for directed efforts to characterize potent pharmacologic inhibitors of the JNK pathway for clinical translation.

Overexpression of von Hippel-Lindau protein synergizes with doxorubicin to suppress hepatocellular carcinoma in mice

BACKGROUND & AIMS

Hypoxia-inducible factors (HIFs) and nuclear factor-κB (NF-κB) regulate genes involved in carcinogenesis and progression of cancers including hepatocellular carcinoma (HCC). The von Hippel-Lindau (VHL) protein (pVHL) targets HIFα subunits for destruction and participates in modulating the activity of NF-κB. The present study aimed to investigate whether the overexpression of pVHL synergizes with doxorubicin in the treatment of HCC.

METHODS

Overexpression of pVHL was induced by infecting mouse HCC Hepa1-6 and H22 cells, or injecting subcutaneous Hepa1-6 tumors in C57BL/c mice, with adenoviral vectors encoding mouse VHL gene. Cell proliferation, apoptosis, tumoral angiogenesis, and gene expression and DNA-binding activity of NF-κB were examined. The therapeutic effects of pVHL were also evaluated in orthotopic Hepa1-6 tumors by intraportal delivery of Ad-VHL.

RESULTS

Ad-VHL enhanced the anti-tumor activity of doxorubicin by inhibiting cell proliferation, and causing cell cycle arrest and apoptosis. The Ad-VHL infection downregulated HIF-1α and HIF-2α expression, and inhibited NF-κB activity and the expression of genes involved in apoptosis, proliferation, angiogenesis, invasion, and metastasis. Injection of Ad-VHL into HCC tumors augmented doxorubicin-induced suppression of tumor growth by inhibiting cell proliferation and tumor angiogenesis, and by inducing cell apoptosis. Effects on the expression of HIFαs, activity of NF-κB, and their downstream genes were in accordance with the in vitro findings. Intraportal injection of Ad-VHL enhanced the efficacy of doxorubicin to suppress the growth of orthotopic liver tumors.

CONCLUSIONS

By targeting HIF and NF-κB, overexpression of pVHL enhances the efficacy of doxorubicin, and warrants consideration as a potential therapeutic strategy for treating HCC.

New insights into the biology of renal cell carcinoma

Ninety percent or more of kidney cancers are believed to be of epithelial cell origin, and are referred to as renal cell carcinoma (RCC), which are further subdivided based on histology into clear-cell RCC (75%), papillary RCC (15%), chromophobe tumor (5%), and oncocytoma (5%). Some genes confer an increased risk of these various histologic RCC subtypes. In practice, there is some overlap among the histologic subtypes, and there are some shared molecular features among these tumor types. This review focuses primarily on the most common form of RCC, clear-cell renal carcinoma, noting some recent advances in the other histologic subtypes.

NF-kappaB-dependent plasticity of the epithelial to mesenchymal transition induced by Von Hippel-Lindau inactivation in renal cell carcinomas

The critical downstream signaling consequences contributing to renal cancer as a result of loss of the tumor suppressor gene von Hippel-Lindau (VHL) have yet to be fully elucidated. Here, we report that VHL loss results in an epithelial to mesenchymal transition (EMT). In studies of paired isogenic cell lines, VHL silencing increased the levels of N-cadherin and vimentin and reduced the levels of E-cadherin relative to the parental VHL(+) cell line, which displayed the opposite profile. VHL(+) cells grew as clusters of cuboidal and rhomboid cells, whereas VHL-silenced cells took on an elongated, fibroblastoid morphology associated with a more highly invasive character in Matrigel chamber assays. Based on earlier evidence that VHL loss can activate NF-kappaB, a known mediator of EMT, we tested whether NF-kappaB contributed to VHL-mediated effects on EMT. On pharmacologic or molecular inhibition of NF-kappaB, VHL-silenced cells regained expression of E-cadherin, lost expression of N-cadherin, and reversed their highly invasive phenotype. Introducing a pVHL-resistant hypoxia-inducible factor 1alpha (HIF1alpha) mutant (HIFalpha(M)) into VHL(+) cells heightened NF-kappaB activity, phenocopying EMT effects produced by VHL silencing. Conversely, inhibiting the heightened NF-kappaB activity in this setting reversed the EMT phenotype. Taken together, these results suggest that VHL loss induces an EMT that is largely dependent on HIFalpha-induced NF-kappaB. Our findings rationalize targeting the NF-kappaB pathway as a therapeutic strategy to treat renal tumors characterized by biallelic VHL inactivation.

Von Hippel-Lindau methylation status in patients with multiple myeloma: a potential predictive factor for the development of bone disease

It has been suggested that during multiple myeloma (MM) progression, a proangiogenesis stress response occurs, but the mechanistic basis of this has not been established. It is an attractive hypothesis that loss of expression of the von Hippel-Lindau (VHL) gene, resulting in constitutive activation of hypoxia-inducible factor-1alpha (HIF-1alpha), contributes to increased angiogenesis in MM. Because aberrant methylation in the VHL CpG island could cause downregulation of VHL transcription, we prospectively studied the methylation status of the VHL CpG island in 45 individuals with multiple myeloma (MM; 25 men, 20 women; mean age, 66.4 years) and in 10 individuals with borderline thrombocytopenia, who were proven to have no malignancy and served as controls. Methylation was found in 15 of 45 patients with MM at diagnosis (33.3%). The presence of methylation in the VHL CpG island was significantly associated with the development of bone disease (odds ratio, 7.5; P = .018). Patients with bone disease had an increased risk of death compared with those with no bone lytic lesions (hazard ratio [HR], 5.1; P = .13). VHL methylation was not a predictor of excess mortality (HR, 0.92; P = .91). Our data imply that methylation in the VHL CpG island is a frequent event in patients with MM and might be a potential biomarker of bone disease. Methylation in the VHL CpG island, leading to transcriptional silencing and hence decreased HIF-1alpha proteolysis, could be a possible mechanism of increased angiogenesis and altered bone marrow microenvironment that is more supportive for survival and growth of MM cells, contributing to MM bone disease. Whether it represents an early or late event of the disease merits additional study. Additional studies regarding the serum levels of HIF-1alpha and vascular endothelial growth factor would be mechanistically interesting.

Treatment of kidney cancer: insights provided by the VHL tumor-suppressor protein

Germline inactivation of the VHL tumor suppressor gene is associated with an increased risk of clear cell carcinoma of the kidney in the context of von Hippel-Lindau (VHL) disease. Somatic VHL mutations are also common in nonhereditary (sporadic) clear cell carcinomas. The VHL protein (pVHL) has multiple functions that might be linked to tumor suppression, including targeting the hypoxia inducible factor (HIF) transcription factor for polyubiquitylation and proteasomal degradation. HIF, especially HIF2alpha, appears to play a causal role in clear cell renal carcinogenesis based on genotype-phenotype correlations in VHL disease, laboratory experiments with human VHL-/- renal carcinoma cell lines, and genetically engineered mouse models. Deregulation of HIF almost certainly accounts for the high levels of vascular endothelial growth factor (VEGF) observed in kidney cancer and relates to their sensitivity to VEGF inhibitors. In addition, the beneficial effects of mammalian target of rapamycin (mTOR) inhibitors are likely due to, at least partly, their ability to down-regulate HIF. pVHL, in a HIF-independent manner, also regulates a specialized structure called the primary cilium and regulates apoptosis via factors such as NFkappaB. Loss of the primary cilium probably facilitates the development of preneoplastic renal cysts, whereas increased NFkappaB might contribute to the resistance of kidney cancers to conventional cytotoxic agents.

HIF-1alpha-dependent gene expression program during the nucleic acid-triggered antiviral innate immune responses

Recent studies suggest a novel role of HIF-1alpha under non-hypoxic conditions, including antibacterial and antiviral innate immune responses. However, the identity of the pathogen-associated molecular pattern which triggers HIF-1alpha activation during the antiviral response remains to be identified. Here, we demonstrate that cellular administration of double-stranded nucleic acids, the molecular mimics of viral genomes, results in the induction of HIF-1alpha protein level as well as the increase in HIF-1alpha target gene expression. Whole-genome DNA microarray analysis revealed that double-stranded nucleic acid treatment triggers induction of a number of hypoxia-inducible genes, and induction of these genes are compromised upon siRNA-mediated HIF-1alpha knock-down. Interestingly, HIF-1alpha knock-down also resulted in down-regulation of a number of genes involved in antiviral innate immune responses. Our study demonstrates that HIF-1alpha activation upon nucleic acid-triggered antiviral innate immune responses plays an important role in regulation of genes involved in not only hypoxic response, but also immune response.

Subcellular dynamics of the VHL tumor suppressor: on the move for HIF degradation

The von Hippel–Lindau (VHL) tumor suppressor protein, the recognition component of an E3 ubiquitin ligase complex, recruits the α-subunit of the hypoxia-inducible factor (HIFα) for oxygen-dependent degradation. The ability of VHL to mediate efficient degradation of HIFα is also dependent on its oxygen/pH-regulated subcellular trafficking. Under aerobic conditions, VHL engages in nuclear–cytoplasmic trafficking that requires ongoing transcription and is mediated by a novel nuclear export motif, the transcription-dependent nuclear export motif (TD-NEM). Disease-causing mutations targeting TD-NEM restrain VHL from mediating efficient oxygen-dependent degradation of HIFα by altering its subcellular dynamics. In addition, decreasing the extracellular pH, during anaerobic metabolism, stabilizes HIFα by triggering the relocalization and static detention of VHL to nucleoli. Together, these recent findings support the critical role of subcellular trafficking and dynamic properties for the function of VHL in promoting HIF regulation and tumor suppression.

A molecule targeting VHL-deficient renal cell carcinoma that induces autophagy

Renal cell carcinomas (RCCs) are refractory to standard therapies. The von Hippel-Lindau (VHL) tumor suppressor gene is inactivated in 75% of RCCs. By screening for small molecules selectively targeting VHL-deficient RCC cells, we identified STF-62247. STF-62247 induces cytotoxicity and reduces tumor growth of VHL-deficient RCC cells compared to genetically matched cells with wild-type VHL. STF-62247-stimulated toxicity occurs in a HIF-independent manner through autophagy. Reduction of protein levels of essential autophagy pathway components reduces sensitivity of VHL-deficient cells to STF-62247. Using a yeast deletion pool, we show that loss of proteins involved in Golgi trafficking increases killing by STF-62247. Thus, we have found a small molecule that selectively induces cell death in VHL-deficient cells, representing a paradigm shift for targeted therapy.

pVHL: a multipurpose adaptor protein

Mutations in the von Hippel-Lindau tumor suppressor gene VHL occur in various inherited and sporadically occurring tumors. The protein encoded by VHL--pVHL--bears no known enzymatic activities but interacts with numerous protein partners. With the identification of distinct pVHL-containing multiprotein complexes, a refined portrait of pVHL tumor suppressor function has arisen. In general, pVHL acts as a multipurpose adaptor protein that controls a diverse array of gene expression programs, as well as extracellular matrix assembly and microtubule-based processes, by linking various target proteins to appropriate enzymatic activities. These findings provide an evermore complex but coherent view of how pVHL functions molecularly and of the consequences of dysregulation of these diverse molecular activities on tumor formation.

pVHL acts as an adaptor to promote the inhibitory phosphorylation of the NF-kappaB agonist Card9 by CK2

The VHL tumor suppressor protein (pVHL) is part of an E3 ubiquitin ligase that targets HIF for destruction. pVHL-defective renal carcinoma cells exhibit increased NF-kappaB activity but the mechanism is unclear. NF-kappaB affects tumorigenesis and therapeutic resistance in some settings. We found that pVHL associates with the NF-kappaB agonist Card9 but does not target Card9 for destruction. Instead, pVHL serves as an adaptor that promotes the phosphorylation of the Card9 C terminus by CK2. Elimination of these sites markedly enhanced Card9's ability to activate NF-kappaB in VHL(+/+) cells, and Card9 siRNA normalized NF-kappaB activity in VHL(-/-) cells and restored their sensitivity to cytokine-induced apoptosis. Furthermore, downregulation of Card9 in VHL(-/-) cancer cells reduced their tumorigenic potential. Therefore pVHL can serve as an adaptor for both a ubiquitin conjugating enzyme and a kinase. The latter activity, which promotes Card9 phosphorylation, links pVHL to control of NF-kappaB activity and tumorigenesis.

Targeting the nuclear factor-kappaB rescue pathway has promising future in human renal cell carcinoma therapy

Metastatic renal cell carcinoma (RCC) remains refractory to therapies. The nuclear factor-kappaB (NF-kappaB) transcription factor is involved in cell growth, cell motility, and vascularization. We evaluated whether targeting NF-kappaB could be of therapeutic and prognostic values in human RCC. The activation of the NF-kappaB pathway in human RCC cells and tumors was investigated by Western blot. In vitro, the effects of BAY 11-7085 and sulfasalazine, two NF-kappaB inhibitors, on tumor cell growth were investigated by cell counting, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide analysis, terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling, and fluorescence-activated cell sorting. Their specificity toward NF-kappaB was analyzed by Western blot, confocal microscopy, NF-kappaB small interfering RNA, and NF-kappaB transcription assay. In vivo, the effects of BAY 11-7085 on the growth of human RCC tumors were investigated in nude mice. A tissue microarray (TMA) containing 241 cases of human RCC with 12 to 22 years of clinical follow-up and corresponding normal tissues was built up to assess prognostic significance of activated NF-kappaB. NF-kappaB is constitutively activated in cultured cells expressing or not the von Hippel-Lindau (VHL) tumor suppressor gene as a consequence of Akt kinase activation and in tumors. In vitro and in vivo NF-kappaB inhibition blocked tumor cell growth by inducing cell apoptosis. On the TMA, NF-kappaB activation was correlated with tumor dimension but was not found to be an independent prognostic factor for patient survival. This report provides strong evidence that the mechanisms responsible for the intrinsic resistance of RCC cells to apoptosis converge on NF-kappaB independently of VHL expression and that targeting this pathway has great anticancer potential.

Genetics and epigenetics of renal cell cancer

Renal cell carcinoma (RCC) is not a single disease, but comprises a group of tumors of renal epithelial origin, each with a different histology, displaying a different clinical course and caused by different genetic alterations. Since cure rates are inversely associated with stage and response to the available treatment regimes is limited to a subgroup of patients, diagnostic methods facilitating early detection and new therapeutic modalities are necessary. Increased knowledge of the underlying pathophysiology of RCC has resulted in the identification of genetic alterations involved in renal cell cancer carcinogenesis. Promising agents to target these pathways, especially the angiogenesis pathway, are being developed, some of which are already standard of care. In addition to genetics, knowledge on epigenetics in the process of renal tumorigenesis has been significantly increased in the last decades. Epigenetics will play an increasing role in the development of new therapeutic modalities and may deliver new prognostic and early diagnostic markers. In this review we discuss the background of RCC and the clinical applications of RCC genetics and epigenetics.

Antimicrobial and cytotoxic activity of agelasine and agelasimine analogs

Agelasine and agelasimine derivatives with substantially less complicated terpenoid side chains compared to the naturally occurring compounds have been synthesized and their ability to inhibit growth of microorganisms and cancer cells has been studied. Compounds with excellent activity against cancer cell lines (MIC ca. 1 microM for the most potent compounds), including a drug resistant renal cell line, have been identified. Most compounds studied also exhibited broad spectrum antimicrobial activity including activity against Mycobacterium tuberculosis.

Epidermal growth factor receptor inhibition sensitizes renal cell carcinoma cells to the cytotoxic effects of bortezomib

In renal cell carcinoma (RCC) models, maximal cytotoxicity of the proteasome inhibitor bortezomib is dependent on efficient blockade of constitutive nuclear factor kappaB (NF-kappaB) activity. Signaling through the epidermal growth factor receptor (EGFR) has been shown to result in NF-kappaB activation. Thus, we sought to investigate whether inhibition of the EGFR sensitizes RCC cells to the cytotoxic effects of bortezomib. We first established that constitutive NF-kappaB activity is dependent on signaling through the EGFR in RCC cells. Indeed, blockade of EGFR signaling with an EGFR tyrosine kinase inhibitor (TKI) resulted in inhibition of NF-kappaB activity. Using pharmacologic and genetic approaches, we also showed that EGFR-mediated NF-kappaB activation occurs through the phosphotidylinositol-3-OH kinase/AKT pathway. Combinations of the EGFR-TKI and bortezomib resulted in synergistic cytotoxic effects when RCC cells were pretreated with the EGFR-TKI, but an antagonistic interaction was observed with bortezomib pretreatment. Evaluation of the effects of drug sequencing on inhibition of NF-kappaB activity revealed that EGFR-TKI pretreatment markedly augmented the NF-kappaB inhibitory effect of bortezomib, whereas bortezomib preexposure resulted in suboptimal NF-kappaB blockade and thus provides a biochemical explanation for the drug interaction results. We conclude that the constitutive NF-kappaB activity observed in RCC cells is mediated, at least in part, through an EGFR/phosphotidylinositol-3-OH kinase/AKT signaling cascade. Pretreatment with an EGFR-TKI sensitizes to bortezomib-mediated cytotoxicity by inhibiting constitutive NF-kappaB activity. The combination of bortezomib and a currently approved EGFR inhibitor warrants clinical investigation.

The von Hippel-Lindau tumor suppressor protein and clear cell renal carcinoma

Germ line VHL tumor suppressor gene loss-of-function mutations cause von Hippel-Lindau disease, which is associated with an increased risk of central nervous system hemangioblastomas, clear cell renal carcinomas, and pheochromocytomas. Somatic VHL mutations are also common in sporadic clear cell renal carcinomas. The VHL gene product, pVHL, is part of a ubiquitin ligase complex that targets the alpha-subunits of the heterodimeric transcription factor hypoxia-inducible factor (HIF) for polyubiquitylation, and hence, proteasomal degradation, when oxygen is available. pVHL-defective clear cell renal carcinomas overproduce a variety of mRNAs that are under the control of HIF, including the mRNAs that encode vascular endothelial growth factor, platelet-derived growth factor B, and transforming growth factor alpha. In preclinical models, down-regulation of HIF-alpha, especially HIF-2alpha, is both necessary and sufficient for renal tumor suppression by pVHL. These observations are probably relevant to the demonstrated clinical activity of vascular endothelial growth factor antagonists in clear cell renal carcinoma and form a foundation for the testing of additional agents that inhibit HIF, or HIF-responsive gene products, in this disease.

Sorafenib (BAY 43-9006) inhibits tumor growth and vascularization and induces tumor apoptosis and hypoxia in RCC xenograft models

PURPOSE

New research findings have revealed a key role for vascular endothelial growth factor (VEGF) in the stimulation of angiogenesis in clear cell renal carcinoma (RCC) which is a highly vascularized and treatment-resistant tumor. Sorafenib (BAY 43-9006, Nexavar) is a multi-kinase inhibitor which targets receptor tyrosine and serine/threonine kinases involved in tumor progression and tumor angiogenesis. The effect of sorafenib on tumor growth and tumor histology was assessed in both ectopic and orthotopic mouse models of RCC.

METHODS

Sorafenib was administered orally to mice bearing subcutaneous (SC, ectopic) or sub-renal capsule (SRC, orthotopic) tumors of murine (Renca) or human (786-O) RCC. Treatment efficacy was determined by measurements of tumor volume and tumor growth delay. In mechanism of action studies, using the 786-O and Renca RCC tumor models, the effect of sorafenib was assessed after dosing for 3 or 5 days in the SC models and 21 days in the SRC models. Inhibition of tumor angiogenesis was assessed by measuring level of CD31 and alpha-smooth muscle actin (alphaSMA) staining by immunohistochemistry (IHC). The effect of sorafenib on MAPK signaling, cell cycle progression and cell proliferation was also assessed by IHC by measuring levels of phospho-ERK, phospho-histone H3 and Ki-67 staining, respectively. The extent of tumor apoptosis was measured by terminal deoxynucleotidyl transferase-mediated nick-end labeling (TUNEL) assays. Finally, the effects of sorafenib on tumor hypoxia was assessed in 786-O SC model by injecting mice intravenously with pimonidazole hydrochloride 1 h before tumor collection and tumor sections were stained with a FITC-conjugated Hypoxyprobe antibody.

RESULTS

Sorafenib produced significant tumor growth inhibition (TGI) and a reduction in tumor vasculature of both ectopic and orthotopic Renca and 786-O tumors, at a dose as low as 15 mg/kg when administered daily. Inhibition of tumor vasculature was observed as early as 3 days post-treatment, and this inhibition of angiogenesis correlated with increased level of tumor apoptosis (TUNEL-positive) and central necrosis. Consistent with these results, a significant increase in tumor hypoxia was also observed 3 days post-treatment in 786-O SC model. However, no significant effect of sorafenib on phospho-ERK, phospho-histone H3 or Ki-67 levels in either RCC tumor model was observed.

CONCLUSION

Our results show the ability of sorafenib to potently inhibit the growth of both ectopically- and orthotopically-implanted Renca and 786-O tumors. The observed tumor growth inhibition and tumor stasis or stabilization correlated strongly with decreased tumor angiogenesis, which was due, at least in part, to inhibition of VEGF and PDGF-mediated endothelial cell and pericyte survival. Finally, sorafenib-mediated inhibition of tumor growth and angiogenesis occurred at concentrations equivalent to those achieved in patients in the clinic.

Prolyl hydroxylase-1 negatively regulates IkappaB kinase-beta, giving insight into hypoxia-induced NFkappaB activity

Hypoxia is a feature of the microenvironment of a growing tumor. The transcription factor NFkappaB is activated in hypoxia, an event that has significant implications for tumor progression. Here, we demonstrate that hypoxia activates NFkappaB through a pathway involving activation of IkappaB kinase-beta (IKKbeta) leading to phosphorylation-dependent degradation of IkappaBalpha and liberation of NFkappaB. Furthermore, through increasing the pool and/or activation potential of IKKbeta, hypoxia amplifies cellular sensitivity to stimulation with TNFalpha. Within its activation loop, IKKbeta contains an evolutionarily conserved LxxLAP consensus motif for hydroxylation by prolyl hydroxylases (PHDs). Mimicking hypoxia by treatment of cells with siRNA against PHD-1 or PHD-2 or the pan-prolyl hydroxylase inhibitor DMOG results in NFkappaB activation. Conversely, overexpression of PHD-1 decreases cytokine-stimulated NFkappaB reporter activity, further suggesting a repressive role for PHD-1 in controlling the activity of NFkappaB. Hypoxia increases both the expression and activity of IKKbeta, and site-directed mutagenesis of the proline residue (P191A) of the putative IKKbeta hydroxylation site results in a loss of hypoxic inducibility. Thus, we hypothesize that hypoxia releases repression of NFkappaB activity through decreased PHD-dependent hydroxylation of IKKbeta, an event that may contribute to tumor development and progression through amplification of tumorigenic signaling pathways.

Interfering with cell-survival signalling as a treatment strategy for prostate cancer

Authors from Australia describe how interfering with cell survival is increasingly being chosen as a method of developing a treatment strategy for hormone-resistant prostate cancer. The authors show how several developmental drug candidates have preclinical and clinical activity against cell survival proteins, and that these might be worth considering as possible clinical entities in this condition. The commonly stated argument that laparoscopy has advanced the cause of donor nephrectomy in renal transplantation is examined by authors from the UK. They present a review of the published reports and show that the evidence base is poor for drawing a conclusion as to whether laparoscopic or open nephrectomy is best.

(+)-agelasine D: improved synthesis and evaluation of antibacterial and cytotoxic activities

An improved synthesis of (+)-agelasine D (10) from (+)-manool is reported together with cytotoxic and antibacterial data for agelasine D and structurally close synthetic analogues. These compounds display a broad spectrum of antibacterial activities including effects on M. tuberculosis and Gram-positive and Gram-negative bacteria (both aerobes and anaerobes). They exhibit profound cytotoxic activity against several cancer cells, including a multidrug-resistant cell line. (+)-Agelasine D (10) has been isolated earlier from a marine sponge (Agelas sp.).

Mechanism of von Hippel-Lindau protein-mediated suppression of nuclear factor kappa B activity

Biallelic inactivating mutations of the von Hippel-Lindau tumor suppressor gene (VHL) are a hallmark of clear cell renal cell carcinoma (CCRCC), the most common histologic subtype of RCC. Biallelic VHL loss results in accumulation of hypoxia-inducible factor alpha (HIFalpha). Restoring expression of the wild-type protein encoded by VHL (pVHL) in tumors with biallelic VHL inactivation (VHL(-)(/)(-)) suppresses tumorigenesis, and pVHL-mediated degradation of HIFalpha is necessary and sufficient for VHL-mediated tumor suppression. The downstream targets of HIFalpha that promote renal carcinogenesis have not been completely elucidated. Recently, VHL loss was shown to activate nuclear factor kappa B (NF-kappaB), a family of transcription factors that promotes tumor growth. Here we show that VHL loss drives NF-kappaB activation by resulting in HIFalpha accumulation, which induces expression of transforming growth factor alpha, with consequent activation of an epidermal growth factor receptor/phosphatidylinositol-3-OH kinase/protein kinase B (AKT)/IkappaB-kinase alpha/NF-kappaB signaling cascade. We also show that components of this signaling pathway promote the growth of VHL(-)(/)(-) tumor cells. Members of this pathway represent viable drug targets in VHL(-)(/)(-) tumors, such as those associated with CCRCC.

Real-time imaging of ligand-induced IKK activation in intact cells and in living mice

The transcription factor NF-kappaB is a key regulator of cellular activation, proliferation and apoptosis. Defects in the NF-kappaB pathway contribute to a broad array of malignant, neurodegenerative and chronic inflammatory diseases. IKK-dependent IkappaB alpha degradation by the 26S proteasome is a critical NF-kappaB regulatory control point, which is emerging as an important target for drug development. To directly monitor regulation of IKK activation in intact organisms, we engineered an IkappaB alpha-firefly luciferase (IkappaB alpha-FLuc) fusion reporter. In cultured cells and living animals, the reporter provided a continuous, noninvasive readout of the kinetics of ligand-induced IKK activation and the pharmacodynamics of selective inhibitors of both IKK and the 26S proteasome. This IkappaB alpha-FLuc reporter now permits continuous readout of IKK activation in vivo, facilitates development and validation of target-specific therapeutics, and complements conventional NF-kappaB transcriptional reporters for more complete temporal and regional investigations of the NF-kappaB signaling pathway in health and disease.