Cells lacking IKKα show nuclear cyclin D1 overexpression and a neoplastic phenotype: role of IKKα as a tumor suppressor.

The catalytic subunits of IκB kinase (IKK) complex, IKKα and IKKß, are involved in activation of NF-κB and in mediating a variety of other biological functions. Though these proteins have a high-sequence homology, IKKα exhibits different functional characteristics as compared with IKKß. Earlier, we have shown that cyclin D1 is overexpressed and predominantly localized in the nucleus of IKKα(-/-) cells, indicating that IKKα regulates turnover and subcellular distribution of cyclin D1, which is mediated by IKKα-induced phosphorylation of cyclin D1. Because cyclin D nuclear localization is implicated in tumor development, we examined whether the absence of IKKα leads to tumor development as well. In the current study, we show that IKKα plays a critical role in tumorigenesis. Though IKKα(-/-) MEF cells show a slower anchorage-dependent growth, they are clonogenic in soft agar. These cells are tumorigenic in nude mice. Microarray analysis of IKKα(-/-) cells indicates a differential expression of genes involved in proliferation and apoptosis. Furthermore, analysis of microarray data of human lung cancer cell lines revealed decreased IKKα RNA expression level as compared with cell lines derived from normal bronchial epithelium. These results suggest that IKKα may function as a tumor suppressor gene. Absence of IKKα may induce tumorigenicity by nuclear localization of cyclin D1 and modulating the expression of genes involved in neoplastic transformation.

Soluble and insoluble nickel compounds exert a differential inhibitory effect on cell growth through IKKalpha-dependent cyclin D1 down-regulation.

It is well-known that insoluble nickel compounds possess much more potent carcinogenic activities as compared with soluble nickel compounds. Although it is assumed that the different entry and clearance rate are responsible for the difference, the mechanisms underlying the different carcinogenic activities are still not well understood yet. In the present study, we found that exposure to soluble, but not insoluble nickel compounds, caused a significant inhibition of cell growth and G1/G0 cell cycle arrest, which was concomitant with a marked down-regulation of cylin D1, an essential nuclear protein for controlling G1/S transition, while both soluble and insoluble nickel compounds showed similar effects on NFkappaB activation, HIF-1alpha protein accumulation and TNF-alpha transcription and CAP43 protein expression at same doses range. The down-regulation of cyclin D1 is due to protein degradation rather than inhibition of transcription, because the nickel compounds treatment did not change cyclin D1 mRNA level, while MG132, the proteasome inhibitor, can rescue the degradation of cyclin D1 caused by soluble nickel compound. Moreover, the soluble nickel-induced cyclin D1 degradation is dependent on its Thr286 residue and requires IKKalpha, but not HIF-1alpha, which are both reported to be involved in cyclin D1 down-regulation. Taken together, we demonstrate that soluble, but not insoluble nickel compound, is able to cause cyclin D1 degradation and a cell growth arrest in an IKKalpha-dependent manner. Given the role of cyclin D1 and cell proliferation in carcinogenesis, we anticipate that the different effects of soluble and insoluble nickel compounds on cyclin D1 degradation and cell growth arrest may at least partially account for their different carcinogenic activities.

Phase I dose escalation study with irinotecan, capecitabine, epirubicin, and granulocyte colony-stimulating factor support for patients with solid malignancies.

OBJECTIVES: Preclinical studies using sequences of topoisomerase I and II inhibitors suggested synergism; preliminary clinical studies, resulting in enhanced antitumor responses, confirm this in selected malignancies. This study determined the maximum-tolerated dose (MTD), toxicity, and pharmacokinetics of irinotecan (CPT-11), capecitabine, and epirubicin in patients with metastatic adenocarcinoma of lung, breast, or gastrointestinal tract. Correlation of topoisomerase IIbeta was also done. METHODS: Eligibility criteria included the following: documented adenocarcinoma of the lung, breast, or gastrointestinal tract, <3 prior chemotherapy regimens, Eastern Cooperative Oncology Group (ECOG) performance status 0 to 2, age > or =18 years, adequate organ function, and signed informed consent. Irinotecan was administered at 250 mg/m2 intravenously day 1 every 21-day cycle, but was reduced to 180 mg/m2 in cohort 2 due to toxicity. Capecitabine was administered at 750 mg/m2 twice daily days 2 to 14 in cohort 1 but only on days 2 to 7 from cohort 2 due to early neutropenia and to allow for prophylactic granulocyte colony-stimulating factor (GCSF) support. Epirubicin was administered at 40 mg/m2 in cohort 1, but reduced to 30 mg/m2 in cohort 2, then reescalated until the MTD was reached. RESULTS: Toxicity was assessed in 21 patients; response was assessed in 17 patients. The most common grade 3 to 4 toxicities included neutropenia (57.1%) and anemia (28.6%). The MTD of epirubicin was 50 mg/m2. In evaluable patients, there were 2 partial responses (11.8%) and 13 stable disease (76.5%); these correlated well with topoisomerase IIbeta. CONCLUSIONS: The recommended doses for phase II studies: irinotecan 180 mg/m2 day 1, epirubicin 50 mg/m2 day 2, and capecitabine 750 mg/m2 twice daily days 2 to 7 of each 21-day cycle. This combination is reasonably active and warrants evaluation in the phase II setting.

Efficacy of sequential treatment of HCT116 colon cancer monolayers and xenografts with docetaxel, flavopiridol, and 5-fluorouracil.

AIM: Clinical treatment of solid tumors with docetaxel, flavopiridol, or 5-fluorouracil (5-FU) often encounters undesirable side effects and drug resistance. This study aims to evaluate the potential role of combination therapy with docetaxel, flavopiridol, or 5-FU in modulating chemosensitivity and better understand how they might be used clinically. METHODS: HCT116 colon cancer cells were treated with docetaxel, flavopiridol, and 5-FU in several different administrative schedules in vitro, either sequentially or simultaneously. Cell survival was measured by MTT assay. The activity of caspase-3 was determined by caspase-3 assays and the soft agar colony assay was used to test the colony formation of HCT116 cells in soft agar. We also established xenograft models to extend in vitro observations to an in vivo system. RESULTS: The maximum cytotoxicity was found when human colon cancer HCT116 cells were treated with docetaxel for 1 h followed by flavopiridol for 24 h and 5-FU for another 24 h. This sequential combination therapy not only inhibits tumor cell growth more strongly compared to other combination therapies but also significantly reduces colony formation in soft agar and augments apoptosis of HCT116 cells. Sequencing of docetaxel followed 1 h later by flavopiridol, followed 24 h later by 5-FU in xenograft models, also resulted in delayed tumor growth and higher survival rate. CONCLUSION: These results highlight the importance of an administrative schedule when combining docetaxel with flavopiridol and 5-FU, providing a rationale explanation for its development in clinical trials.

IkappaB kinase alpha regulates subcellular distribution and turnover of cyclin D1 by phosphorylation.

IkappaB kinases (IKKs), IKKalpha and IKKbeta, with a regulatory subunit IKKgamma/NEMO constitute a high molecular weight IKK complex that regulates NF-kappaB activity. Although IKKalpha and IKKbeta share structural and biochemical similarities, IKKalpha has been shown to have distinct biological roles. Here we show that IKKalpha plays a critical role in regulating cyclin D1 during the cell cycle. Analysis of IKKalpha-/- mouse embryo fibroblast cells showed that cyclin D1 is overexpressed and localized in the nucleus compared with parental mouse embryo fibroblasts. IKKalpha associates with and phosphorylates cyclin D1. Analysis on cyclin D1 mutants demonstrated that IKKalpha phosphorylates cyclin D1 at Thr286. Reconstitution of IKKalpha in knockout cells leads to nuclear export and increased degradation of cyclin D1. Further, RNAi-mediated knockdown of IKKalpha results in similar changes as observed in IKKalpha-/- cells. These results suggest a novel role of IKKalpha in regulating subcellular localization and proteolysis of cyclin D1 by phosphorylation of cyclin D1 at Thr286, the same residue earlier found to be a target for glycogen synthase kinase-3beta-induced phosphorylation.

Enhanced chemosensitivity to irinotecan by RNA interference-mediated down-regulation of the nuclear factor-kappaB p65 subunit.

In preclinical tumor models, inhibition of nuclear factor-kappaB (NF-kappaB) has been associated with increased sensitivity to chemotherapeutic agents such as irinotecan (CPT-11). This is based on the fact that a variety of chemotherapy agents such as CPT-11 activate NF-kappaB to result in the expression of genes such as c-IAP1 and c-IAP2 that might be responsible for the inhibition of chemotherapy-induced apoptosis. In this study, RNA interference [small interfering RNA (siRNA)] was used to down-regulate the NF-kappaB p65 subunit in the HCT116 colon cancer cell line, and its role, in the presence and absence of CPT-11, was assessed on cell growth and apoptosis. Reduction of endogenous p65 by siRNA treatment significantly impaired CPT-11-mediated NF-kappaB activation, enhanced apoptosis, and reduced colony formation in soft agar. Furthermore, the in vivo administration of p65 siRNA reduced HCT116 tumor formation in xenograft models in the presence but not the absence of CPT-11 administration. These data indicate that the administration of siRNA directed against the p65 subunit of NF-kappaB can effectively enhance in vitro and in vivo sensitivity to chemotherapeutic agents.

Nuclear role of I kappa B Kinase-gamma/NF-kappa B essential modulator (IKK gamma/NEMO) in NF-kappa B-dependent gene expression.

The I kappa B kinase (IKK) complex, which is composed of the two kinases IKK alpha and IKK beta and the regulatory subunit IKK gamma/nuclear factor-kappa B (NF-kappa B) essential modulator (NEMO), is important in the cytokine-induced activation of the NF-kappa B pathway. In addition to modulation of IKK activity, the NF-kappa B pathway is also regulated by other processes, including the nucleocytoplasmic shuttling of various components of this pathway and the post-translational modification of factors bound to NF-kappa B-dependent promoters. In this study, we explored the role of the nucleocytoplasmic shuttling of components of the IKK complex in the regulation of the NF-kappa B pathway. IKK gamma/NEMO was demonstrated to shuttle between the cytoplasm and the nucleus and to interact with the nuclear coactivator cAMP-responsive element-binding protein-binding protein (CBP). Using both in vitro and in vivo analysis, we demonstrated that IKK gamma/NEMO competed with p65 and IKK alpha for binding to the N terminus of CBP, inhibiting CBP-dependent transcriptional activation. These results indicate that, in addition to the key role of IKK gamma/NEMO in regulating cytokine-induced IKK activity, its ability to shuttle between the cytoplasm and the nucleus and to bind to CBP can lead to transcriptional repression of the NF-kappa B pathway.

Histone H3 phosphorylation by IKK-alpha is critical for cytokine-induced gene expression.

Cytokine-induced activation of the IkappaB kinases (IKK) IKK-alpha and IKK-beta is a key step involved in the activation of the NF-kappaB pathway. Gene-disruption studies of the murine IKK genes have shown that IKK-beta, but not IKK-alpha, is critical for cytokine-induced IkappaB degradation. Nevertheless, mouse embryo fibroblasts deficient in IKK-alpha are defective in the induction of NF-kappaB-dependent transcription. These observations raised the question of whether IKK-alpha might regulate a previously undescribed step to activate the NF-kappaB pathway that is independent of its previously described cytoplasmic role in the phosphorylation of IkappaBalpha. Here we show that IKK-alpha functions in the nucleus to activate the expression of NF-kappaB-responsive genes after stimulation with cytokines. IKK-alpha interacts with CREB-binding protein and in conjunction with Rel A is recruited to NF-kappaB-responsive promoters and mediates the cytokine-induced phosphorylation and subsequent acetylation of specific residues in histone H3. These results define a new nuclear role of IKK-alpha in modifying histone function that is critical for the activation of NF-kappaB-directed gene expression.

Small interfering RNAs directed against beta-catenin inhibit the in vitro and in vivo growth of colon cancer cells.

The beta-catenin and APC genes are key components of the Wnt signaling pathway. Mutation of these genes results in increased levels of the beta-catenin protein, which is associated with enhanced cellular proliferation and the development of both colon polyps and colon cancer. Recently, a technique known as RNA interference has been successfully adapted to mammalian cells so that it is now possible to specifically decrease the expression of cellular genes after transfection of annealed small interfering 21-mer RNAs. In the current study, we used small interfering RNA (siRNA) directed against beta-catenin to determine the effects of decreasing the high constitutive levels of this protein in colon cancer cell lines with mutations in either beta-catenin or APC. Our studies demonstrate that siRNA directed against beta-catenin markedly decreased beta-catenin-dependent gene expression and inhibited cellular proliferation as reflected in the reduced growth of these colon cancer cells both in soft agar and in nude mice. These results indicate that siRNA can target specific factors whose expression is altered in malignancy and may have the potential as a therapeutic modality to treat human cancer.

Sulindac enhances tumor necrosis factor-alpha-mediated apoptosis of lung cancer cell lines by inhibition of nuclear factor-kappaB.

Programmed cell death (apoptosis) is induced by certain anticancer therapies, and resistance to apoptosis is a major mechanism by which tumors evade these therapies. The transcription factor nuclear factor (NF)-kappaB, which is frequently activated by treatment of cancer cells with different chemotherapeutic agents, promotes cell survival, whereas its inhibition leads to enhanced apoptosis. Recently, sulindac and other nonsteroidal anti-inflammatory drugs have been shown to inhibit tumor necrosis factor (TNF)-alpha-mediated NF-kappaB activation. Here, we demonstrate that treatment of the non-small cell lung carcinoma cells NCI-H157 and NCI-H1299 with sulindac greatly enhances TNF-alpha-mediated apoptosis. We further show that sulindac inhibits TNF-alpha-mediated activation of NF-kappaB DNA binding and nuclear translocation of NF-kappaB. These results suggest that sulindac and other nonsteroidal anti-inflammatory drug inhibitors of NF-kappaB activation may serve as useful agents in cancer chemotherapy.