NF-kappaB controls cell growth and differentiation through transcriptional regulation of cyclin D1

Cyclin D1 repression of peroxisome proliferator-activated receptor gamma expression and transactivation

The cyclin D1 gene is overexpressed in human breast cancers and is required for oncogene-induced tumorigenesis. Peroxisome proliferator-activated receptor gamma (PPAR gamma) is a nuclear receptor selectively activated by ligands of the thiazolidinedione class. PPAR gamma induces hepatic steatosis, and liganded PPAR gamma promotes adipocyte differentiation. Herein, cyclin D1 inhibited ligand-induced PPAR gamma function, transactivation, expression, and promoter activity. PPAR gamma transactivation induced by the ligand BRL49653 was inhibited by cyclin D1 through a pRB- and cdk-independent mechanism, requiring a region predicted to form an helix-loop-helix (HLH) structure. The cyclin D1 HLH region was also required for repression of the PPAR gamma ligand-binding domain linked to a heterologous DNA binding domain. Adipocyte differentiation by PPAR gamma-specific ligands (BRL49653, troglitazone) was enhanced in cyclin D1(-/-) fibroblasts and reversed by retroviral expression of cyclin D1. Homozygous deletion of the cyclin D1 gene, enhanced expression by PPAR gamma ligands of PPAR gamma and PPAR gamma-responsive genes, and cyclin D1(-/-) mice exhibit hepatic steatosis. Finally, reduction of cyclin D1 abundance in vivo using ponasterone-inducible cyclin D1 antisense transgenic mice, increased expression of PPAR gamma in vivo. The inhibition of PPAR gamma function by cyclin D1 is a new mechanism of signal transduction cross talk between PPAR gamma ligands and mitogenic signals that induce cyclin D1.

Activation of cyclin D1 expression by the ERK5 cascade

Transcriptional activation of the cyclin D1 gene is a key step in cell proliferation. Accordingly, cyclin D1 overexpression is frequently an early step in neoplastic transformation, particularly in mammary epithelium. Numerous studies have linked elevated cyclin D1 promoter activity to a sustained activation of the ERK1/2 cascade. Here we show that the ERK5 cascade, a distinct mitogen-induced MAPK pathway, can also drive cyclin D1 expression. In CCL39 cells, serum induces a strong, prolonged peak of ERK1/2 and ERK5 phosphorylation, and subsequently elevates cyclin D1 mRNA and protein levels. Overexpression of constitutively active MEK5 and wt ERK5 induces a cyclin D1 reporter gene (D1 -973-luciferase) at least as well as constitutively active MEK1. Activation is blocked by kinase-dead mutants of ERK5 and ERK2, respectively. Mutation of the CRE at -50 in the cyclin D1 promoter decreases activation by the ERK5 but not the ERK1/2 cascade. Importantly, expression of kinase-dead ERK5 diminishes endogenous cyclin D1 protein induction by serum in CCL39 cells and the breast cancer cell lines MCF-7 and HS579. These data identify the cyclin D1 gene as a novel target of the ERK5 cascade, an observation with important implications in cancers involving cyclin D1 deregulation.

The clinical significance between activation of nuclear factor kappa B transcription factor and overexpression of HER-2/neu oncoprotein in Taiwanese patients with breast cancer

BACKGROUND

This study investigated the role of nuclear factor-kappa B (NF-kappaB) activity in human breast cancer with overexpression of HER-2/neu oncoprotein, as well as its role on expression of different histological grades of cancer cells taken from Taiwanese breast cancer patients.

MATERIALS AND METHODS

Specimens were collected from 82 female breast cancer patients. The HER-2/neu oncoprotein was measured by immunohistochemistry. NF-kappaB activity expression was assessed by the electrophoretic mobility shift assay, and confirmed by the supershift technique using anti-P65 antibody in both breast cancer tissue and the adjacent normal tissue. The histological grades were measured by Modified Bloom-Richardson Grading Scheme.

RESULTS

Of the 82 cancer specimens, 81 (98.7%) showed higher or equal expressions of NF-kappaB activity when compared to the adjacent normal tissue. Fifty-five cases (67.1%) had higher levels of NF-kappaB activity in the cancerous tissue than in the adjacent normal tissue (p<0.005). With regard to tumor size, steroid receptors, stages, histological types, and node status, there were no statistically significant differences in NF-kappaB activity between cancerous tissues and adjacent normal tissues. However, significantly higher expressions of NF-kappaB activity were seen in those cases with positive HER2/neu oncoprotein, poorly differentiated histological grades, high nuclear pleomorphisms, and high mitotic counts (p<0.05). Positive HER-2/neu overexpression of oncoprotein had higher NF-kappaB activity (86%) than negative overexpression (60%) (p<0.05). It has been shown that the NF-kappaB activity increases in the HER-2/neu oncoprotein overexpression in human breast cancer.

CONCLUSION

Overexpression of HER-2/neu gene could induce NF-kappaB activity in human breast cancer cells, as has been confirmed in other research on cell lines.

Distinctions between c-Rel and other NF-kappaB proteins in immunity and disease

c-Rel is a proto-oncogene first identified as the cellular counterpart of the v-Rel oncogene derived from the avian reticuloendotheliosis retrovirus (REV-T). It was subsequently discovered that c-Rel belongs to the NF-kappaB/Rel transcription factor family whose members share a common DNA recognition motif and similar signaling pathways. Despite the similarities, however, each NF-kappaB/Rel member possesses unique properties with regard to tissue expression pattern, response to receptor signals and target gene specificity. These differences are fairly evident from the non-redundant phenotypes exhibited by individual NF-kappaB/Rel knockout mice. Hence the work described in this review will compare and contrast the various physiological functions of c-Rel to those of other NF-kappaB members, particularly with respect to the regulation of proliferation, survival and effector functions in multiple hematopoietic and immunological cell types. The study of c-Rel knockout mice in several disease models will also be discussed as they reveal an important role for c-Rel in response to allergens, auto-antigens, allo-antigens and pathogenic infection.

Mouse mammary tumor virus c-rel transgenic mice develop mammary tumors

Amplification, overexpression, or rearrangement of the c-rel gene, encoding the c-Rel NF-kappaB subunit, has been reported in solid and hematopoietic malignancies. For example, many primary human breast cancer tissue samples express high levels of nuclear c-Rel. While the Rev-T oncogene v-rel causes tumors in birds, the ability of c-Rel to transform in vivo has not been demonstrated. To directly test the role of c-Rel in breast tumorigenesis, mice were generated in which overexpression of mouse c-rel cDNA was driven by the hormone-responsive mouse mammary tumor virus long terminal repeat (MMTV-LTR) promoter, and four founder lines identified. In the first cycle of pregnancy, the expression of transgenic c-rel mRNA was observed, and levels of c-Rel protein were increased in the mammary gland. Importantly, 31.6% of mice developed one or more mammary tumors at an average age of 19.9 months. Mammary tumors were of diverse histology and expressed increased levels of nuclear NF-kappaB. Analysis of the composition of NF-kappaB complexes in the tumors revealed aberrant nuclear expression of multiple subunits, including c-Rel, p50, p52, RelA, RelB, and the Bcl-3 protein, as observed previously in human primary breast cancers. Expression of the cancer-related NF-kappaB target genes cyclin D1, c-myc, and bcl-xl was significantly increased in grossly normal transgenic mammary glands starting the first cycle of pregnancy and increased further in mammary carcinomas compared to mammary glands from wild-type mice or virgin transgenic mice. In transient transfection analysis in untransformed breast epithelial cells, c-Rel-p52 or -p50 heterodimers either potently or modestly induced cyclin D1 promoter activity, respectively. Lastly, stable overexpression of c-Rel resulted in increased cyclin D1 and NF-kappaB p52 and p50 subunit protein levels. These results indicate for the first time that dysregulated expression of c-Rel, as observed in breast cancers, is capable of contributing to mammary tumorigenesis.

Effect of a single dose of polychlorinated biphenyls on hepatic cell proliferation and the DNA binding activity of NF-kappaB and AP-1 in rats

Polychlorinated biphenyls (PCBs) are environmental pollutants that, because of their persistence and biomagnification, raise concerns about the health consequences of long-term exposure. PCB mixtures induce hepatocellular carcinomas in rodents, but the mechanism of their promoting activity is not clear. Previous studies have shown that oxidative stress occurs after PCB administration, with the induction of lipid peroxidation and oxidative DNA damage, which may contribute to their promoting activity. In this study, we examined whether the oxidative stress-sensitive transcription factors NF-kappaB or AP-1 were activated by PCBs in the liver. Male Sprague-Dawley rats were injected i.p. with corn oil, 2,2',4,4',5,5'-hexachlorobiphenyl (PCB-153, 30, 150, or 300 micromol/kg), 3,3',4,4'-tetrachlorobiphenyl (PCB-77, 30, 150, or 300 micromol/kg), or both PCBs (each 30 or 150 micromol/kg). Rats were euthanized 2, 6, or 24 h, or 2, 6, and 10 d after the PCB injection. Electrophoretic mobility shift assays (EMSAs) were performed to determine NF-kappaB and AP-1 DNA binding activities. The highest NF-kappaB DNA binding activity was observed in rats receiving higher doses of PCB-153 (150 and 300 micromol/kg), with peak activation occurring 2 d after injection. AP-1 activation was not detected at any timepoint. Hepatocyte proliferation, as measured by the labeling index, was increased only in groups receiving the highest dose of PCB-153 or the combination of two PCBs (150 micromol/kg each) at day 2, and not by any other PCB treatment at any timepoint. These results show that PCB-153, but not PCB-77, can induce hepatocyte proliferation and hepatic NF-kappaB activation after a single dose.

TNF-alpha is a mitogen in skeletal muscle

Emerging evidence suggests that tumor necrosis factor (TNF)-alpha plays a role in muscle repair. To determine whether TNF-alpha modulates satellite cell proliferation, the current study evaluated TNF-alpha effects on DNA synthesis in primary myoblasts and on satellite cell activation in adult mouse muscle. Exposure to recombinant TNF-alpha increased total DNA content in rat primary myoblasts dose-dependently over a 24-h period and increased the number of primary myoblasts incorporating 5-bromo-2'-deoxyuridine (BrdU) during a 30-min pulse labeling. Systemic injection of TNF-alpha stimulated BrdU incorporation by satellite cells in muscles of adult mice, whereas no BrdU was incorporated by satellite cells in control mice. TNF-alpha stimulated serum response factor (SRF) binding to the serum response element (SRE) present in the c-fos gene promoter and stimulated reporter gene expression controlled by the same element. Our data suggest that TNF-alpha activates satellite cells to enter the cell cycle and accelerates G1-to-S phase transition, and these actions may involve activation of early response genes via SRF.

jumonji downregulates cardiac cell proliferation by repressing cyclin D1 expression

Spatiotemporal regulation of cell proliferation is necessary for normal tissue development. The molecular mechanisms, especially the signaling pathways controlling the cell cycle machinery, remain largely unknown. Here, we demonstrate a negative relationship between the spatiotemporal patterns of jumonji (jmj) expression and cardiac myocyte proliferation. cyclin D1 expression and cell proliferation are enhanced in the cardiac myocytes of jmj-deficient mutant embryos. In contrast, jmj overexpression represses cyclin D1 expression in cardiac cells, and Jmj protein binds to cyclin D1 promoter in vivo and represses its transcriptional activity. cyclin D1 overexpression causes hyperproliferation in the cardiac myocytes, but the absence of cyclin D1 in jmj mutant embryos rescues the hyperproliferation. Therefore, Jmj might control cardiac myocyte proliferation and consequently cardiac morphogenesis by repressing cyclin D1 expression.

p53 represses cyclin D1 transcription through down regulation of Bcl-3 and inducing increased association of the p52 NF-kappaB subunit with histone deacetylase 1

The p53 and NF-kappaB transcription factor families are important, multifunctional regulators of the cellular response to stress. Here we have investigated the regulatory mechanisms controlling p53-dependent cell cycle arrest and cross talk with NF-kappaB. Upon induction of p53 in H1299 or U-2 OS cells, we observed specific repression of cyclin D1 promoter activity, correlating with a decrease in cyclin D1 protein and mRNA levels. This repression was dependent on the proximal NF-kappaB binding site of the cyclin D1 promoter, which has been shown to bind the p52 NF-kappaB subunit. p53 inhibited the expression of Bcl-3 protein, a member of the IkappaB family that functions as a transcriptional coactivator for p52 NF-kappaB and also reduced p52/Bcl-3 complex levels. Concomitant with this, p53 induced a significant increase in the association of p52 and histone deacetylase 1 (HDAC1). Importantly, p53-mediated suppression of the cyclin D1 promoter was reversed by coexpression of Bcl-3 and inhibition of p52 or deacetylase activity. p53 therefore induces a transcriptional switch in which p52/Bcl-3 activator complexes are replaced by p52/HDAC1 repressor complexes, resulting in active repression of cyclin D1 transcription. These results reveal a unique mechanism by which p53 regulates NF-kappaB function and cell cycle progression.

Current status of thalidomide and its role in the treatment of metastatic prostate cancer

Following the discovery of its anti-angiogenic properties and despite its tragic history, thalidomide has re-surfaced in the field of oncology. Concurrent with its evaluation in various clinical trials for cancer, thalidomide's mechanism of action is sought and new analogues with improved efficacy and pharmacological profile are emerging. This review is a critical evaluation of thalidomide metabolism, molecular targets, anti-angiogenic activity and clinical efficacy with an emphasis on metastatic prostate cancer.

Differential signaling through NFkappaB does not ameliorate skeletal myoblast apoptosis during differentiation

During 23A2 skeletal myoblast differentiation, roughly 30% of the population undergoes apoptosis. Further, constitutive signaling by G12V:H-Ras or Raf:CAAX abrogates this apoptosis. In this study, we demonstrate an increase in NFkappaB activity in myoblasts that have survived and are expressing muscle-specific genes. NFkappaB activity is also elevated in myoblasts expressing constitutively active G12V:H-Ras but not Raf:CAAX. Expression of a dominant negative IkappaB (IkappaB-SR) sufficient to eliminate this elevated level of NFkappaB activity, in either the 23A2 myoblasts or their G12V:H-Ras-expressing counterparts, however, does not affect survival. Furthermore, expression of a constitutively active IkappaB kinase in 23A2 myoblasts does not protect these cells from the apoptosis associated with differentiation. Since signaling by IkappaB kinase can abrogate differentiation, this result demonstrates that abrogated differentiation and abrogated apoptosis are separable phenotypes.

A prominent role for airway epithelial NF-kappa B activation in lipopolysaccharide-induced airway inflammation

To reveal the causal role of airway epithelial NF-kappaB activation in evoking airway inflammation, a transgenic mouse was created expressing a mutant version of the inhibitory protein I-kappaBalpha. This I-kappaBalpha superrepressor (I-kappaBalpha(SR)) acts to repress NF-kappaB activation exclusively in airway epithelial cells, under the transcriptional control of the rat CC10 promoter (CC10-I-kappaBalpha(SR)). Compared with transgene-negative littermates, intranasal instillation of LPS did not induce nuclear translocation of NF-kappaB in airway epithelium of CC10-I-kappaBalpha(SR) transgenic mice. Consequently, the influx of neutrophils into the airways and secretion of the NF-kappaB-regulated neutrophilic chemokine, macrophage-inflammatory protein-2, and the inflammatory cytokine, TNF-alpha, were markedly reduced in CC10-I-kappaBalpha(SR) mice relative to the transgene-negative mice exposed to LPS. Despite an inability to activate NF-kappaB in airway epithelium, resident alveolar macrophages from transgene-positive mice were capable of activating NF-kappaB in a manner indistinguishable from transgene-negative mice. These findings demonstrate that airway epithelial cells play a prominent role in orchestrating the airway inflammatory response to LPS and suggest that NF-kappaB signaling in these cells is important for modulating innate immune responses to microbial products.

Adenoma growth stimulation by the trans-10, cis-12 isomer of conjugated linoleic acid (CLA) is associated with changes in mucosal NF-kappaB and cyclin D1 protein levels in the Min mouse

Conjugated linoleic acid (CLA) is a term used to describe the different conjugated isomers of linoleic acid. CLA has been found to be anticarcinogenic in mammary cancer, but its effects on colon carcinogenesis are still inconclusive. In this study, the isomer-specific effects of the cis-9, trans-11 and trans-10, cis-12 CLA isomers were investigated in the Min mouse model for intestinal carcinogenesis. The Min mice (n = 10/group) were fed either an AIN-93G control diet or a diet containing 1 g/100 g cis-9, trans-11 or trans-10, cis-12 CLA for 8 wk. The number and size of adenomas were measured and the proteins from the small intestinal tissues extracted for immunoblotting analysis. The number of adenomas did not differ, but the size of the adenomas was greater in the distal part of the small intestine in mice fed the trans-10, cis-12 isomer than in controls (1.19 +/- 0.16 vs. 0.94 +/- 0.21 mm, mean +/- SD, P < 0.01). The same isomer caused an increase in lipid peroxidation, measured as urinary 8-iso-prostaglandin (PG)F(2alpha). Nuclear p65 protein of the mucosal tissue was not detectable in the trans-10, cis-12 group, which differed (P < 0.05) from the control group. Cyclin D1, a target for the nuclear factor (NF)-kappaB pathway, was elevated in the trans-10, cis-12 group compared with the control group (P < 0.01), but cyclooxygenase-2 levels were not higher. There was no difference in beta-catenin protein levels between the groups. The results indicate that the trans-10, cis-12 isomer of CLA can act as a cancer promoter in colon carcinogenesis possibly through pathways affecting NF-kappaB and cyclin D1.

In vivo analysis of the cyclin D1 promoter during early embryogenesis in Xenopus

Cyclin D1 plays an important role in the regulation of G1 progression of the somatic cell cycle by functioning as a regulatory subunit of cdk4 and 6. Since both cyclin D1-mRNA and -protein turn over very rapidly, the expression of cyclin D1 is mostly regulated at the transcription level. Detection of the cyclin D1-specific mRNA during early embryogenesis in Xenopus laevis revealed that expression was induced soon after the midblastula stage but not during the cleavage stage, and was mainly found in the neural plate and eye vesicles. The recently-developed transgenic frog technique enabled us to analyze the frog cyclin D1 promoter activity in vivo by using green fluorescent protein (GFP) as a marker. During early embryogenesis, a GFP signal was detected at the neural plate in the neurula of the transgenic embryos. Transgenic analysis using sequential-deletion and point mutants of the cyclin D1 promoter revealed that a single, putative TCF/LEF binding site, located approximately 3.5 kb upstream of the transcriptional initiation site, was required for neural plate-specific expression. Our results suggest that the TCF/LEF signaling pathway participates in the regulation of cyclin D1 induction during the generation of the dorsal nervous system in early frog embryogenesis.

TNF-alpha increases ubiquitin-conjugating activity in skeletal muscle by up-regulating UbcH2/E220k

In some inflammatory diseases, TNF-alpha is thought to stimulate muscle catabolism via an NF-kappaB-dependent process that increases ubiquitin conjugation to muscle proteins. The transcriptional mechanism of this response has not been determined. Here we studied the potential role of UbcH2, a ubiquitin carrier protein and homologue of murine E220k. We find that UbcH2 is constitutively expressed by human skeletal and cardiac muscles, murine limb muscle, and cultured myotubes. TNF-alpha stimulates UbcH2 expression in mouse limb muscles in vivo and in cultured myotubes. The UbcH2 promoter region contains a functional NF-kappaB binding site; NF-kappaB binding to this sequence is increased by TNF-alpha stimulation. A dominant negative inhibitor of NF-kappaB activation blocks both UbcH2 up-regulation and the increase in ubiquitin-conjugating activity stimulated by TNF-alpha. In extracts from TNF-alpha-treated myotubes, ubiquitin-conjugating activity is limited by UbcH2 availability; activity is inhibited by an antiserum to UbcH2 or a dominant negative mutant of UbcH2 and is enhanced by wild-type UbcH2. Thus, UbcH2 up-regulation is a novel response to TNF-alpha/NF-kappaB signaling in skeletal muscle that appears to be essential for the increased ubiquitin conjugation induced by this cytokine.

Erythroid gene suppression by NF-kappa B

NF-kappa B/Rel transcription factors play essential roles to mediate the immune response and apoptosis, and they have also been implicated in cellular differentiation such as erythropoiesis. To elucidate the possible role(s) of NF-kappa B in erythroid gene regulation and erythropoiesis, we have carried out transient transfection studies of the human embryonic/fetal erythroid cell line K562 and mouse adult erythroid MEL cells. It is shown that tumor necrosis factor-alpha represses the transcription activity directed by either alpha or zeta globin promoter in a dose-dependent manner. Furthermore, different NF-kappa B family members could effectively repress the transfected alpha-like globin promoters in K562 as well as in MEL cells. The involvement of NF-kappa B pathway is supported by the ability of a NF-kappa B-specific, dominant negative mutant to block the tumor necrosis factor-alpha or p65-mediated suppression of the alpha-like globin promoter activities. The suppression appears to be mediated through cis-linked HS-40 enhancer. Finally, stably transfected K562 cells overexpressing p65 contain reduced amounts of the p45/NF-E2 RNA and functional NF-E2 proteins. Our studies have identified a new set of targets of NF-kappa B. We suggest that the relatively high activity of the NF-kappa B pathway in early erythroid progenitors is involved in the suppression of erythroid-specific genes. Later in differentiation, together with other changes, the decline of the amounts of the NF-kappa B family of factors leads to derepression and consequent increase of NF-E2, which in turn would activate a subset of erythroid-specific genes.

Glucocorticoid receptor functions as a potent suppressor of mouse skin carcinogenesis

Glucocorticoids are effective inhibitors of epidermal proliferation and skin tumorigenesis. Glucocorticoids affect cellular functions via glucocorticoid receptor (GR), a well-known transcription factor. Recently, we generated skin-targeted transgenic mice overexpressing GR under control of the keratin5 promoter (K5-GR mice). To test the hypothesis that GR plays a role as a tumor suppressor in skin, we bred K5-GR transgenic mice with Tg.AC transgenic mice, which express v-Ha-ras oncogene in the skin, and compared the susceptibility of F1 offspring to TPA-induced skin carcinogenesis. GR overexpression in the epidermis dramatically inhibited skin tumor development. In K5-GR/ras+ double transgenic mice papillomas developed later and the average number of tumors per animal was 15% (in males) and 40% (in females) of the number seen in wild type (w.t./ras+) littermates. In addition, the papillomas in w.t./ras+ animals were eight to nine times larger. GR overexpression resulted in a decrease in keratinocyte proliferation combined with a modest increase in apoptosis and differentiation of keratinocytes in K5-GR/ras+ papillomas. Our data clearly indicate that interference of GR transgenic protein with nuclear factor kappa B (NF-kappaB) transcription factor had resulted in NF-kappaB blockage in K5-GR/ras+ tumors. We discuss the role of NF-kappaB blockage in tumor-suppressor effect of GR.

Dual mechanisms for lysophosphatidic acid stimulation of human ovarian carcinoma cells

BACKGROUND

Lysophosphatidic acid (LPA), at concentrations present in ascitic fluid, indirectly stimulates the growth of malignant ovarian tumors by increasing the expression of vascular endothelial growth factor (VEGF) in ovarian cancer cells. We investigated whether LPA could also directly promote ovarian tumor growth by increasing the level of cyclin D1, a key G1-phase checkpoint regulator, which thereby increases cell proliferation.

METHODS

Expression of cyclin D1 and LPA receptors (EDG4 and EDG7) was determined in six ovarian cancer cell lines (including OVCAR-3 cells) and immortalized ovarian surface epithelial cells (IOSE-29). Cyclin D1 promoter activity was measured in LPA-treated OVCAR-3 cells cotransfected with cyclin D1 promoter-driven luciferase constructs and cDNA expression plasmids for IkappaBalphaM (a nuclear factor kappaB [NFkappaB] super-repressor).

RESULTS

Four of six cancer cell lines, including OVCAR-3, overexpressed cyclin D1 protein relative to levels in IOSE-29 cells. LPA treatment increased cyclin D1 protein in a dose- and time-dependent manner in OVCAR-3 cells but not in IOSE-29 cells. LPA stimulated cyclin D1 promoter activity (3.0-fold, 95% confidence interval [CI] = 2.7-fold to 3.3-fold). Mutation of the NFkappaB-binding site in the cyclin D1 promoter to block NFkappaB binding and expression of IkappaBalphaM, which binds NFkappaB and inhibits its binding to the promoter, markedly diminished LPA stimulation of cyclin D1 promoter activity (activity stimulated only 1.4-fold, 95% CI = 1.1-fold to 1.7-fold, and 0.7-fold, 95% CI = 0.6-fold to 0.8-fold, respectively). EDG4 was overexpressed in all cancer cell lines studied relative to that in IOSE-29 cells, but EDG7 was overexpressed in only two lines.

CONCLUSIONS

Dual mechanisms are probably involved in LPA stimulation of ovarian tumor growth in vivo. In addition to the previously characterized indirect mechanism that increases angiogenesis via VEGF, LPA may directly increase the level of cyclin D1 in ovarian cancer cells, increasing their proliferation.

NF-kappa B-dependent induction of cyclin D1 by retinoblastoma protein (pRB) family proteins and tumor-derived pRB mutants

The retinoblastoma protein (pRB) and its homologues, p107 and p130, prevent cell cycle progression from G(0)/G(1) to S phase by forming complexes with E2F transcription factors. Upon phosphorylation by G(1) cyclin-cyclin-dependent kinase (Cdk) complexes such as cyclin D1-Cdk4/6 and cyclin E-Cdk2, they lose the ability to bind E2F, and cells are thereby allowed to progress into S phase. Functional loss of one or more of the pRB family members, as a result of genetic mutation or deregulated phosphorylation, is considered to be an essential prerequisite for cellular transformation. In this study, we found that pRB family proteins have the ability to stimulate cyclin D1 transcription by activation of the NF-kappaB transcription factor. The cyclin D1-inducing activity of pRB is abolished by adenovirus E1A oncoprotein but not by the deletion of the A-box, the B-box, or the C-terminal region of the pocket, indicating that multiple pocket sequences are independently involved in cyclin D1 activation. Intriguingly, tumor-derived pRB pocket mutants retain the cyclin D1-inducing activity. Our results reveal a novel role of pRB family proteins as potential activators of NF-kappaB and inducers of G(1) cyclin. Certain pRB pocket mutants may give rise to a cellular situation in which deregulated E2F and cyclin D1 cooperatively promote abnormal cell proliferation.

Ethanol induces redox-sensitive cell-cycle inhibitors and inhibits liver regeneration after partial hepatectomy

BACKGROUND

Doses of ethanol (EtOH) that are not overtly cytotoxic inhibit mitogen-induced hepatocyte proliferation and delay liver regeneration after 70% partial hepatectomy (PH). The mechanisms for this are poorly understood. This study evaluates the hypothesis that EtOH inhibits hepatocyte proliferation after PH by inducing redox-sensitive factors, such as p38 mitogen-activated protein kinase (MAPK) and p21 (WAF1/CIP1), that protect cells from oxidative stress but prevent cell-cycle progression by inhibiting cyclin D1.

METHODS

Mechanisms that regulate the transition from the prereplicative G1 phase of the cell cycle into S phase were compared in EtOH-fed mice and normal pair-fed mice after PH.

RESULTS

Prior EtOH exposure significantly increases p38 MAPK and p21 after PH. This is accompanied by reduced expression of cyclin D1 messenger RNA and protein, increases in other cell-cycle regulators (such as signal transducer and activator of transcription-3 and p27) that are normally inhibited by cyclin D1, and hepatocyte G1 arrest.

CONCLUSIONS

EtOH amplifies G1 checkpoint mechanisms that are induced by oxidative stress and promotes hepatic accumulation of factors, including p38 MAPK, p21, and signal transducer and activator of transcription-3, that enhance cellular survival after oxidant exposure. Therefore, cell-cycle inhibition may be an adaptive response that helps EtOH-exposed livers survive situations, such as PH, that acutely increase reactive oxygen species in hepatocytes.

Downstream effectors of oncogenic ras in multiple myeloma cells

Ectopic expression of mutated K-ras or N-ras in the interleukin 6 (IL-6)-dependent ANBL6 multiple myeloma cell line induces cytokine-independent growth. To investigate the signaling pathways activated by oncogenic ras that may stimulate IL-6-independent growth, we compared ANBL6 cells stably transfected with mutated K or N-ras genes with wild-type ras-expressing control cells identically transfected with an empty vector. Upon depletion of IL-6, both mutated ras-containing myeloma lines demonstrated constitutive activation of mitogen-activated extracellular kinase 2(MEK)/extracellular signal-regulated kinase (ERK), phosphatidylinositol-3 kinase (PI3-kinase)/AKT, mammalian target of rapamycin (mTOR)/p70S6-kinase, and nuclear factor kappa B (NF-kappa B) pathways. In contrast, signal transducer and activator of transcription-3 (STAT-3) was not constitutively tyrosine phosphorylated in mutant ras-expressing cells. We used several maneuvers in attempts to selectively target these constitutively active pathways. The mTOR inhibitors rapamycin and CCI-779, the PI3-kinase inhibitor LY294002, and the MEK inhibitor PD98059 all significantly curtailed growth of mutant ras-containing cells. Farnesyl transferase inhibitors, used to target ras itself, had modest effects only against mutant N-ras-containing cells. Growth of mutant N-ras-containing myeloma cells was also inhibited by acute expression of the IKB superrepressor gene, which abrogated NF-kappa B activation. These results indicate that several pathways contributing to stimulation of cytokine-independent growth are activated downstream of oncogenic ras in myeloma cells. They also suggest that therapeutic strategies that target these pathways may be particularly efficacious in patients whose myeloma clones contain ras mutations.

Divergent gene regulation and growth effects by NF-kappa B in epithelial and mesenchymal cells of human skin

NF-kappa B regulates normal and pathological processes, including neoplasia, in a tissue-context-dependent manner. In skin, NF-kappa B is implicated in epidermal homeostasis as well as in the pathogenesis of squamous cell carcinoma; however, its function in the underlying mesenchymal dermis has been unclear. To gain insight into NF-kappa B roles in these two adjacent cutaneous tissue compartments, NF-kappa B effects on expression of 12 435 genes were determined in epidermal keratinocytes and dermal fibroblasts. Although NF-kappa B induced proinflammatory and antiapoptotic genes in both settings, it exhibited divergent effects on growth regulatory genes. In keratinocytes, but not in fibroblasts, NF-kappa B induced p21(CIP1), which was sufficient to inhibit growth of both cell types. Levels of growth inhibitory factor (GIF), in contrast, were increased by NF-kappa B in both settings but inhibited growth only in keratinocytes. These findings indicate that transcription factors such as NF-kappa B can program tissue-selective effects via both differential target gene induction as well as by inducing common targets that exert differing effects depending on cellular lineage.

NF-kappaB in mammary gland development and breast cancer

Nuclear factor of kappaB (NF-kappaB) is a group of sequence-specific transcription factors that is best known as a key regulator of the inflammatory and innate immune responses. Recent studies of genetically engineered mice have clearly indicated that NF-kappaB is also required for proper organogenesis of several epithelial tissues, including the mammary gland. Mice have shown severe lactation deficiency when NF-kappaB activation is specifically blocked in the mammary gland. In addition, there are strong suggestions that NF-kappaB may play an important role in the etiology of breast cancer. Elevated NF-kappaB DNA-binding activity is detected in both mammary carcinoma cell lines and primary human breast cancer tissues.

Glioma cell-associated sustained activation of the transcription factor, nuclear factor-kappa B, was inhibited by neomycin

Experimental evidence suggests that the transcription factor nuclear factor-Kappa B (NF-kappa B) plays an important role in tumor cell invasion, apoptosis suppression and growth. Malignant glioma is one of the most intractable tumors because of its invasiveness to surrounding brain tissue. Our study investigated the role of neomycin on NF-kappa B activity in glioma cell cultures. We performed immunocytochemical analysis of cells with the antibody NF-kappa Bp65 which results show that neomycin decreases significantly the activation of NF-kappa B when added to glioma cultures for 30 min. This finding supports an important role for neomycin in glioma invasion, apoptosis and growth. Collectively, these data suggest a rationale for clinical trials with neomycin in the treatment of gliomas.

The nuclear localization of NFkappaB and p53 is positively correlated with HPV16 E7 level in laryngeal squamous cell carcinoma

The interaction between the HPV (human papilloma virus) 16 E7 and other cell growth factors, such as p53 and NFkappaB in laryngeal cancer is not clearly understood. The aim of this study was to examine the expression of these three proteins in tumor and non-tumor laryngeal tissues from patients with laryngeal squamous cell carcinoma. These three proteins were dominantly expressed in the nucleus and their levels were higher in the tumor tissue than in the non-tumor tissue, although the comparison between the tumor and non-tumor tissues of p53 staining did not reach significance. The intensity of the nuclear stain of E7 and p53 was stronger than that of p65, a subunit of NFkappaB. Correlation analysis revealed that there was a positive relationship between the level of HPV16 E7 and the expression of p65. The correlation between E7 and p53 was also significant, although to a lesser degree. The finding of nuclear localization of p65 suggests that NFkappaB is constantly activated in the laryngeal cancer cells, whereas the sequestration of p53 in the nucleus may represent a mutated form of p53, which is probably inactivated by HPV16 oncoproteins. In conclusion, this study suggests that the nuclear localization of NFkappaB and p53 may play a role in the development of human laryngeal squamous cell carcinoma infected with HPV16.

Enhanced myogenic differentiation by extracellular matrix is regulated at the early stages of myogenesis

Myogenic cell lines have been used extensively in the study of skeletal muscle development, regeneration, and homeostasis. To induce myogenic differentiation, culture media composed of a wide variety of growth factors and other additives have been used. Because the diversity in these components may modulate the differentiation process differentially, we describe a differentiation protocol that does not require the introduction of any factors to the differentiation media (DM) other than those present in the growth media. By culturing C2C12 skeletal myocytes on a coating of diluted Matrigel, a soluble basement membrane, consisting of collagen IV, laminin, heparan sulfate proteoglycans, and entactin, myogenic differentiation was accomplished by mere serum reduction. Assessment of myotube formation, creatine kinase activity, myosin heavy chain-fast, and myogenin demonstrated that the kinetics and extent of myogenic differentiation were superior using this protocol, compared with a commonly used differentiation protocol, in which an extracellular matrix is not provided and the DM contains horse serum. In addition, the elevated transactivation of a troponin-I promoter reporter construct suggested that myogenesis was enhanced at the transcriptional level. Finally, assessment of genomic deoxyribonucleic acid content revealed that the Matrigel differentiation protocol resulted in lowered proliferation. This protocol may aid studies aimed at elucidating mechanisms of myogenic differentiation, where a homogeneous population of myotubes is preferred.

NF-kappa B1 is required for optimal CD4+ Th1 cell development and resistance to Leishmania major

The NF-kappaB family of transcription factors regulates the expression of a wide range of immune response genes involved in immunity to pathogens. However, the need for individual family members in regulating innate and adaptive immune responses in vivo has yet to be clearly defined. We investigated the role of NF-kappaB1 in the induction of protective IL-12-dependent Th1 cell responses following infection with the intracellular protozoan parasite Leishmania major. Whereas wild-type C57BL/6 mice controlled parasite replication, NF-kappaB1 knockout (KO) mice were susceptible to infection, developing chronic unresolving lesions associated with persistent parasites. There was a profound defect in Ag-specific CD4(+) T cell proliferation and IFN-gamma production in infected KO mice, although innate responses-including IL-12 production and control of intracellular parasite replication by macrophages-were intact. In vitro polyclonal stimulation of purified naive KO T cells revealed an intrinsic defect in CD4(+) T cell proliferation associated with reduced IL-2 receptor expression, but operating independently of APC function and IL-2 production. Critically, the frequency of proliferating KO CD4(+) T cells secreting IFN-gamma matched that of wild-type cells, suggesting that NF-kappaB1 was not required for efficient transcription of the IFN-gamma gene. Taken together, these results identify a novel role for NF-kappaB1 in CD4(+) T cell proliferation and the development of Th1 cell responses required for protective immunity against intracellular pathogens.

Activation of the transcription factor NF-kappaB in Schwann cells is required for peripheral myelin formation

Peripheral myelin formation is initiated by axonal cues that trigger a differentiation program in associated Schwann cells. Here, we define one essential differentiation signal: activation of the transcription factor NF-kappaB. In rat sciatic nerves, NF-kappaB was highly upregulated in pre-myelinating Schwann cells, and then its expression progressively declined until it was nearly absent in adults. Similarly, in co-cultures of Schwann cells and sensory neurons, NF-kappaB activation paralleled myelination, and blocking its activity or using cells from mice lacking the NF-kappaB subunit p65 markedly attenuated myelination. Inhibiting NF-kappaB also prevented activation of Oct-6, a transcription factor induced by axonal contact and required for proper myelin formation. These results show that the activation of NF-kappaB is an essential signal for the progression of axon-associated Schwann cells into a myelinating phenotype.

Inhibition of IkappaB kinase by a new class of retinoid-related anticancer agents that induce apoptosis

The transcription factor NF-kappaB is overexpressed or constitutively activated in many cancer cells, where it induces expression of antiapoptotic genes correlating with resistance to anticancer therapies. Small molecules that inhibit the NF-kappaB signaling pathway could therefore be used to induce apoptosis in NF-kappaB-overexpressing tumors and potentially serve as anticancer agents. We found that retinoid antagonist MX781 inhibited the activation of NF-kappaB-dependent transcriptional activity in different tumor cell lines. MX781 was able to completely inhibit tumor necrosis factor alpha-mediated activation of IkappaB kinase (IKK), the upstream regulator of NF-kappaB. Inhibition of IKK activity resulted from direct binding of MX781 to the kinase, as demonstrated by in vitro inhibition studies. Two other molecules, MX3350-1 and CD2325, which are retinoic acid receptor gamma-selective agonists, were capable of inhibiting IKK in vitro, although they exerted variable inhibition of IKK and NF-kappaB activities in intact cells in a cell type-specific manner. However, N-(4-hydroxyphenyl)-retinamide, another apoptosis-inducing retinoid, and retinoic acid as well as other nonapoptotic retinoids did not inhibit IKK. Inhibition of IKK by the retinoid-related compounds and other small molecules correlated with reduced cell proliferation and increased apoptosis. Reduced cell viability was also observed after overexpression of an IKKbeta kinase-dead mutant or the IkappaBalpha superrepressor. The induction of apoptosis by the retinoid-related molecules that inhibited IKK was dependent on caspase activity but independent of the retinoid receptors. Thus, the presence of an excess of retinoic acid or a retinoid antagonist did not prevent the inhibition of IKK activation by MX781 and CD2325, indicating a retinoid receptor-independent mechanism of action.

NF-kappaB activation in cancer: a challenge for ubiquitination- and proteasome-based therapeutic approach

Nuclear factor-kappa B (NF-kappaB) activation relies primarily on ubiquitin-mediated degradation of its inhibitor IkappaB. NF-kappaB plays an important role in many aspects of tumor development, progression, and therapy. Some types of cancer are characterized by constitutive NF-kappaB activity, whereas in others such activity is induced following chemotherapy. NF-kappaB-harboring tumors are generally resistant to chemotherapy and their eradication requires NF-kappaB inhibition. Here we describe the mechanisms of NF-kappaB activation in normal and tumor cells, review prevalent notions regarding the factor's contribution to tumorigenicity and discuss present and future options for NF-kappaB inhibition in cancer. The ubiquitination-mediated activation of NF-kappaB is intersected by another cancer-associated protein, beta-catenin. We, therefore, compare the related activation pathways and discuss the possibility of differential targeting of the involved ubiquitination machinery.

Tumor necrosis factor-regulated biphasic activation of NF-kappa B is required for cytokine-induced loss of skeletal muscle gene products

NF-kappaB activation is classically defined as a transient response initiated by the degradation of IkappaB inhibitor proteins leading to nuclear import of NF-kappaB and culminating with the resynthesis of IkappaBalpha and subsequent inactivation of the transcription factor. Although this type of regulation is considered the paradigm for NF-kappaB activation, other regulatory profiles are known to exist. By far the most common of these is chronic or persistent activation of NF-kappaB. In comparison, regulation of NF-kappaB in a biphasic manner represents a profile that is scarcely documented and whose biological significance remains poorly understood. Here we show using differentiated skeletal muscle cells, that tumor necrosis factor (TNF) induces NF-kappaB activation in a biphasic manner. Unlike the first transient phase, which is terminated within 1 h of cytokine addition, the second phase persists for an additional 24-36 h. Biphasic activation is mediated at both the levels of NF-kappaB DNA binding and transactivation function, and both phases are dependent on the IKK/26 S proteasome pathway. We find that regulation of the first transient phase is mediated by the degradation and subsequent resynthesis of IkappaBalpha, as well as by a TNF-induced expression of A20. Second phase activity correlates with persistent down-regulation of both IkappaBalpha and IkappaBbeta proteins, derived from a continuous TNF signal. Finally, we demonstrate that inhibition of NF-kappaB prior to initiation of the second phase of activity inhibits cytokine-mediated loss of muscle proteins. We propose that the biphasic activation of NF-kappaB in response to TNF may play a key regulatory role in skeletal muscle wasting associated with cachexia.

The biologic role for nuclear factor-kappaB in disease and its potential involvement in mucosal injury associated with anti-neoplastic therapy

Oral mucosal barrier injury (mucositis) is a frequent, painful, serious, dose-limiting toxicity associated with many anti-neoplastic drugs and radiation to the head and neck. Results of recent studies suggest that mucositis is the result of a complex series of interactive biological events that take place in the submucosa and epithelium. The nuclear transcription factor NF-kappaB has been implicated in the control of a broad range of biological responses, the activation of a large number of specific cellular genes, and the determination of the fate of cells exposed to ionizing radiation and anti-neoplastic drugs. Of particular importance to mucositis is the fact that NF-kappaB regulates key elements in the apparent sequence that leads to normal tissue toxicity. Not the least of these is the effect that NF-kappaB activation has on apoptosis. In particular, a paradox exists between the potential pro-apoptotic effect NF-kappaB exerts on normal cells, and the anti-apoptotic and cytoprotective effect it causes in tumor cells. This paper provides a review of the structure and function of NF-kappaB and speculates how its apparent enigmatic effect on normal and tumor cells may occur.

Nuclear transport as a target for cell growth

The function of many key proteins and transcription factors involved in cell growth can be regulated by their cellular localization. Such proteins include the tumor suppressor p53 and the nuclear factor kappaB. Although the idea of trapping such proteins in either the nucleus or cytoplasm has been introduced as a potential therapeutic target, only two nuclear transport inhibitors have been reported. Here, we explore the roles of small-molecule inhibitors that cause target proteins to sequester in either the nucleus or cytoplasm. Methods of artificially targeting proteins to the nucleus or cytoplasm using peptide aptamer technology are also discussed.

Regulation of RelA (p65) function by the large subunit of replication factor C

The RelA (p65) subunit of NF-kappaB is an important regulator of inflammation, proliferation, and apoptosis. We have discovered that the large subunit, p140, of replication factor C (RFC) can function as a regulator of RelA. RFC is a clamp loader, facilitating the addition and removal of proliferating-cell nuclear antigen from DNA during replication and repair but can also interact directly with the retinoblastoma tumor suppressor protein and the transcription factor C/EBPalpha. We find that RFC (p140) interacts with RelA both in vitro and in vivo and stimulates RelA transactivation. In contrast, coexpression of fragments of RFC (p140) that mediate the interaction with RelA results in transcriptional inhibition. The significance of this regulation was confirmed by using short interfering RNA oligonucleotides targeted to RFC (p140). Down regulation of endogenous RFC (p140) inhibits expression from a chromosomally integrated reporter plasmid induced by endogenous, TNF-alpha-activated NF-kappaB. Dominant negative fragments of RFC (p140) also cooperate with overexpressed RelA to induce cell death. Interestingly, RFC (p140) also interacts with the tumor suppressor p53. Taken together, these observations suggest that, in addition to its previously described function in DNA replication and repair, RFC (p140) has an important role as a regulator of transcription and NF-kappaB activity.

Low-dose TNF-alpha protects against hepatic ischemia-reperfusion injury in mice: implications for preconditioning

Tumor necrosis factor alpha (TNF-alpha) is implicated in the pathogenesis of hepatic ischemia reperfusion injury but can also prime hepatocytes to enter the cell cycle. Ischemic preconditioning protects against ischemia-reperfusion (IR) liver injury and is associated with activation of nuclear factor kappaB (NF-kappaB) and cell cycle entry. We examined the pattern of TNF-alpha release during hepatic IR in the presence or absence of ischemic preconditioning, and we tested whether a single low-dose injection of TNF could mimic the biologic effects of ischemic preconditioning. In naïve mice, hepatic and plasma levels of TNF-alpha rose during hepatic ischemia, reaching high levels after 90 minutes; values remained elevated during reperfusion until 44 hours. Following the ischemic preconditioning stimulus, there was an early rise in hepatic and serum TNF-alpha levels, but, during a second prolonged ischemic interval peak, TNF-alpha values were lower than in naïve mice and declined to negligible levels by 2 hours reperfusion. An injection with 1 microg or 5 microg/kg body weight TNF-alpha 30 minutes prior to hepatic IR substantially reduced liver injury determined by liver histology and serum alanine aminotransferase (ALT) levels. As in ischemic preconditioning, TNF-alpha pretreatment activated NF-kappaB DNA binding, STAT3, cyclin D1, cyclin-dependent kinase 4 (cdk4) expression, and cell cycle entry, determined by proliferating cell nuclear antigen (PCNA) staining of hepatocyte nuclei. In conclusion, the hepatoprotective effects of "preconditioning" can be simulated by TNF-alpha injection, which has identical downstream effects on cell cycle entry. We propose that transient increases in TNF-alpha levels may substitute for, as well as, mediate the hepatoprotective effects of ischemic preconditioning against hepatic IR injury.

Ubiquitin-dependent proteolysis of cyclin D1 is associated with coxsackievirus-induced cell growth arrest

Coxsackievirus group B3 (CVB3) replication is influenced by host cell cycle status. However, the effect of CVB3 infection on cell cycle regulation and the mechanisms involved are not precisely defined. In this study, we examined cell cycle progression and regulation when the infection was initiated in late G(1) phase of the cell cycle. Analysis of cellular DNA synthesis in infected cells by thymidine incorporation assays showed a significant reduction in [(3)H]thymidine uptake compared to that of sham-infected cells. To further clarify the effects of CVB3 on the host cell cycle, we examined the cell cycle regulatory proteins involved in G(1) progression and G(1)/S transition. Infection resulted in dephosphorylation of retinoblastoma protein and reduced G(1) cyclin-dependent kinase activities, accompanied by decreased levels of G(1) cyclin protein expression (cyclin D1 and cyclin E). We further investigated the mechanisms by which CVB3 infection down-regulates cyclin D1 expression. Northern blotting showed that cyclin D1 mRNA levels were modestly increased following CVB3 infection, suggesting that cyclin D1 regulation occurs by a posttranscriptional mechanism. Viral infection resulted in only a 20 to 30% inhibition of cyclin D1 protein synthesis 3 h postinfection. However, the proteasome inhibitors MG132 and lactacystin prevent CVB3-induced cyclin D1 reduction, indicating that CVB3-induced down-regulation of cyclin D1 is facilitated by ubiquitin-proteasome proteolysis. Finally, using GSK3beta pathway inhibitors, we showed that the reduction of cyclin D1 is GSK3beta independent. Taken together, our results demonstrate that CVB3 infection disrupts host cell homeostasis by blocking the cell cycle at the G(1)/S boundary and induces cell cycle arrest in part through an increase in ubiquitin-dependent proteolysis of cyclin D1.

Curcumin-induced suppression of cell proliferation correlates with down-regulation of cyclin D1 expression and CDK4-mediated retinoblastoma protein phosphorylation

Cyclin D1 is a proto-oncogene that is overexpressed in many cancers including breast and prostate. It plays a role in cell proliferation through activation of cyclin-dependent kinases. Curcumin, a diferuloylmethane, is a chemopreventive agent known to inhibit the proliferation of several breast and prostate cancer cell lines. It is possible that the effect of curcumin is mediated through the regulation of cyclin D1. In the present report we show that inhibition of the proliferation of various prostate, breast and squamous cell carcinoma cell lines by curcumin correlated with the down-regulation of the expression of cyclin D1 protein. In comparison, the down-regulation by curcumin of cyclin D2 and cyclin D3 was found only in selective cell lines. The suppression of cyclin D1 by curcumin led to inhibition of CDK4-mediated phosphorylation of retinoblastoma protein. We found that curcumin-induced down-regulation of cyclin D1 was inhibited by lactacystin, an inhibitor of 26S proteosome, suggesting that curcumin represses cyclin D1 expression by promoting proteolysis. We found that curcumin also down-regulated mRNA expression, thus suggesting transcriptional regulation. Curcumin also inhibited the activity of the cyclin D1 promoter-dependent reporter gene expression. Overall our results suggest that curcumin down-regulates cyclin D1 expression through activation of both transcriptional and post-transcriptional mechanisms, and this may contribute to the antiproliferative effects of curcumin against various cell types.

Transforming pathways activated by the v-Abl tyrosine kinase

The Abelson Murine Leukemia Virus (A-MuLV) is the acute transforming retrovirus encoding the v-abl oncogene. Two isolates of the virus encoding proteins of p120 Kd and 160 Kd have been extensively studied. These viral isolates have been found to transform both hematopoietic and fibroblastic cells in vitro, while inducing predominantly pre-B cell leukemias in vivo. Both p120(v-Abl) and p160(v-Abl) are plasma membrane-associated non-receptor tyrosine kinases and the transforming activity of these proteins requires their tyrosine kinase activity. A-MuLV infection of hematopoietic cells has often been found to result in the abrogation of their cytokine-dependence for growth. In addition, v-Abl expressing hematopoietic cells often lose their ability to differentiate in response to appropriate cytokines. This review discusses some of the early transformation studies of A-MuLV, as well as some of the findings concerning the structure and biochemical activity of the v-Abl protein. Finally, we discuss the mechanisms associated with v-Abl mediated transformation through examination of the various signal transduction pathways activated by this oncogene.

Role for cellular Src kinase in myoblast proliferation

In this study, a role for cellular Src in muscle cell proliferation and differentiation was investigated. Pharmacological inhibition of Src-class kinases repressed proliferation and promoted differentiation of the C2C12 muscle cell line, even when the cells were cultured under growth-inducing conditions of high serum. Pharmacological inhibition of Src-class kinases also affected cellular components that regulate proliferation and differentiation in muscle; cyclin D1 levels were reduced while, myogenin was increased. Suppression of cyclin D1 and enhancement of myogenin levels also occurred upon expression of a dominant negative Src, corroborating a role for Src kinases in regulating proliferation and differentiation. Inhibition of Src-family kinases also blocked fibroblast growth factor (FGF) induced proliferation but, notably, did not reverse the effect of FGF to inhibit differentiation. Evidence for the Src-class kinase Src in myoblast mitogenesis was obtained by determining the pattern of protein expression and activity for this kinase. Under all conditions examined, Src's expression and enzymatic activity were high in cultures of myoblasts and down-regulated during differentiation. Importantly, Src's activity was rapidly stimulated by mitogen-containing serum and attenuated when myoblasts were switched to low serum-containing differentiation medium. These data indicate that Src is important for maintaining muscle cell proliferation.

Rocaglamide derivatives are potent inhibitors of NF-kappa B activation in T-cells

Crude extracts from different Aglaia species are used as anti-inflammatory remedies in the traditional medicine of several countries from Southeast Asia. Because NF-kappaB transcription factors represent key regulators of genes involved in immune and inflammatory responses, we supposed that the anti-inflammatory effects of Aglaia extracts are mediated by the inhibition of NF-kappaB activity. Purified compounds of Aglaia species, namely 1H-cyclopenta[b]benzofuran lignans of the rocaglamide type as well as one aglain congener were tested for their ability to inhibit NF-kappaB activity. We show that a group of rocaglamides represent highly potent and specific inhibitors of tumor necrosis factor-alpha (TNFalpha) and phorbol 12-myristate 13-acetate (PMA)-induced NF-kappaB-dependent reporter gene activity in Jurkat T cells with IC(50) values in the nanomolar range. Some derivatives are less effective, and others are completely inactive. Rocaglamides are able to suppress the PMA-induced expression of NF-kappaB target genes and sensitize leukemic T cells to apoptosis induced by TNFalpha, cisplatin, and gamma-irradiation. The suppression of NF-kappaB activation correlated with the inhibition of induced IkappaB(alpha) degradation and IkappaB(alpha) kinase activation. The level of interference was determined and found to be localized upstream of the IkappaB kinase complex but downstream of the TNF receptor-associated protein 2. Our data suggest that rocaglamide derivatives could serve as lead structures in the development of anti-inflammatory and tumoricidal drugs.

Cyclosporine inhibits growth through the activating transcription factor/cAMP-responsive element-binding protein binding site in the cyclin D1 promoter

The immunosuppressive agent cyclosporine affects proliferation depending on the cellular system used. In an attempt to study the inhibitory effect of cyclosporine on proliferation of pancreatic acinar cells, we used AR42J cells as a model system. Here we demonstrate that cyclosporine inhibits growth of these cells by inducing G(1) cell cycle arrest. This effect is mediated by the 5' regulatory region of the cyclin D1 gene and leads to a reduction of cyclin D1 mRNA expression and protein abundance. We show that in AR42J cells the proximal cyclin D1 promoter contains a cis-regulated element, which is important for the maintenance of basal transcriptional activity. This element overlaps the described cAMP-responsive element (CRE) and confers cyclosporine sensitivity to the cyclin D1 promoter. Furthermore, the DNA binding activity of the CRE-binding protein (CREB) decreases through cyclosporine treatment and this is mediated by cyclosporine-induced reduction of CREB steady-state levels. These results demonstrate that cyclosporine can inhibit proliferation of acinar cells by targeting the cyclin D1 promoter at the proximal CRE via a reduction of CREB protein abundance.

Galectin-3 enhances cyclin D(1) promoter activity through SP1 and a cAMP-responsive element in human breast epithelial cells

Galectin-3 is a multifunctional carbohydrate-binding protein found in the nucleus, cytoplasm and the extracellular milieu. Nuclear galectin-3 expression is associated with cell proliferation, and its role in pre-mRNA splicing has been suggested. In this report, we investigated the role of galectin-3 on cyclin D(1) gene expression, a critical inducer of the cell cycle and a potential oncogene in human cancer. We found that galectin-3 induces cyclin D(1) promoter activity in human breast epithelial cells independent of cell adhesion through multiple cis-elements, including the SP1 and CRE sites. We present evidence that galectin-3 induction of the cyclin D(1) promoter may result from enhancement/stabilization of nuclear protein-DNA complex formation at the CRE site of the cyclin D(1) promoter. We also show that galectin-3 co-operates with, but does not depend on, pRb for cyclin D(1) promoter activation. The present study reveals a growth promoting activity of galectin-3 through cyclin D(1) induction, and suggests a novel function of nuclear galectin-3 in the regulation of gene transcription.

Tumor necrosis factor alpha induces three-dimensional cytomorphologic differentiation of human anaplastic thyroid carcinoma cells through activation of nuclear factor kappaB

BACKGROUND

Anaplastic thyroid carcinoma is almost uniformly fatal. Microvilli are an important three-dimensional (3-D) cytomorphologic feature of thyrocyte differentiation, because fewer microvilli are seen in less differentiated tumors. Differentiation therapies, such as retinoic acid and somatostatin, have been tested previously in experimental models of differentiated thyroid carcinoma but not in anaplastic thyroid carcinoma. The objective of this study was to determine whether tumor necrosis factor alpha (TNF-alpha) is capable of inducing 3-D cytomorphologic differentiation of anaplastic thyroid carcinoma cells, and, if so, to investigate the mechanism involved.

METHODS

Anaplastic thyroid carcinoma cells were treated with TNF-alpha and examined for evidence of cytomorphologic differentiation using electron microscopy. To study the mechanism of differentiation, immunoblotting was used to analyze inhibitory kappaB (I-kappaB) proteins and electrophoretic mobility shift assays to analyze nuclear factor kappaB (NF-kappaB) activation. The effect of NF-kappaB SN50, a NF-kappaB translocation inhibitor, on cytomorphologic changes induced in anaplastic thyroid carcinoma cells by TNF-alpha also was studied. In addition, levels of thyroglobulin and vascular endothelial growth factor (VEGF) secreted into the culture medium were measured.

RESULTS

The results showed that TNF-alpha can induce activation of NF-kappaB and that the activation and translocation of NF-kappaB into the nucleus is responsible for promoting the 3-D cytomorphologic differentiation of anaplastic thyroid carcinoma cells, which was inhibited by the NF-kappaB translocation inhibitor, NF-kappaB SN50. TNF-alpha also induced increased thyroglobulin secretion and reduced VEGF secretion by anaplastic tumor cells.

CONCLUSIONS

The current data suggest that TNF-alpha can induce thyrocyte differentiation in anaplastic thyroid carcinoma cells through NF-kappaB and that it merits investigation as differentiation therapy for the treatment of patients with anaplastic thyroid carcinoma. The authors also found that microvilli were useful markers for studying thyrocyte differentiation in anaplastic thyroid carcinoma cells.

Role of NF-kappaB on liver cold ischemia-reperfusion injury

The role of NF-kappaB, the rapid-response transcription factor for multiple genes, in cold ischemia-reperfusion (I/R) injury was examined after syngeneic transplantation of liver grafts. Lewis rat recipients were killed 1-48 h after reperfusion of three different liver grafts: 1) uninfected control, 2) infected ex vivo with control adenoviral vector (AdEGFP), and 3) infected ex vivo with AdIkappaB. In uninfected control livers, NF-kappaB was activated biphasically at 1-3 and 12 h after reperfusion with aspartate transaminase (AST) levels of 4,244 +/- 691 IU/l. The first peak of NF-kappaB activation associated with an increase of mRNA for TNF-alpha, IL-1beta, and IL-10. AdEGFP transfection resulted in similar outcomes. Interestingly, AdIkappaB-transfected liver grafts suffered more severe I/R injury (AST >9,000 IU/l). Transfected IkappaB was detected in transplanted livers as early as 6 h, and this correlated with the abrogation of the second, but not the first, peak of NF-kappaB activation at 12-48 h and increased apoptosis. Thus inhibition of the second wave of NF-kappaB activation in IkappaB-transfected livers resulted in an increase of liver injury, suggesting that NF-kappaB may have a dual role during liver I/R injury.

Oct-1 potentiates CREB-driven cyclin D1 promoter activation via a phospho-CREB- and CREB binding protein-independent mechanism

Cyclin D1, the regulatory subunit for mid-G(1) cyclin-dependent kinases, controls the expression of numerous cell cycle genes. A cyclic AMP-responsive element (CRE), located upstream of the cyclin D1 mRNA start site, integrates mitogenic signals that target the CRE-binding factor CREB, which can recruit the transcriptional coactivator CREB-binding protein (CBP). We describe an alternative mechanism for CREB-driven cyclin D1 induction that involves the ubiquitous POU domain protein Oct-1. In the breast cancer cell line MCF-7, overexpression of Oct-1 or its POU domain strongly increases transcriptional activation of cyclin D1 and GAL4 reporter genes that is specifically dependent upon CREB but independent of Oct-1 DNA binding. Gel retardation and chromatin immunoprecipitation assays confirm that POU forms a complex with CREB bound to the cyclin D1 CRE. In solution, CREB interaction with POU requires the CREB Q2 domain and, notably, occurs with CREB that is not phosphorylated on Ser 133. Accordingly, Oct-1 also potently enhances transcriptional activation mediated by a Ser133Ala CREB mutant. Oct-1/CREB synergy is not diminished by the adenovirus E1A 12S protein, a repressor of CBP coactivator function. In contrast, E1A strongly represses CBP-enhanced transactivation by CREB phosphorylated on Ser 133. Our observation that Oct-1 potentiates CREB-dependent cyclin D1 transcriptional activity independently of Ser 133 phosphorylation and E1A-sensitive coactivator function offers a new paradigm for the regulation of cyclin D1 induction by proliferative signals.

Negative regulation of Epstein-Barr virus latent membrane protein 1-mediated functions by the bone morphogenetic protein receptor IA-binding protein, BRAM1

The latent membrane protein 1 (LMP1) of Epstein-Barr virus causes cellular transformation and activates several intracellular signals, including NF-kappaB and c-Jun N-terminal kinase. Using yeast two-hybrid screening with the LMP1 C-terminal sequence as bait, we demonstrate that BRAM1 (bone morphogenetic protein receptor-associated molecule 1) is an LMP1-interacting protein. BRAM1 associates with LMP1, both in vitro and in vivo, as revealed by confocal microscopy, glutathione S-transferase pull-down, and co-immunoprecipitation assays. This association mainly involves the C-terminal half of BRAM1 comprising the MYND domain and the CTAR2 region of LMP1, which is critical in LMP1-mediated signaling pathways. We show that BRAM1 interferes with LMP1-mediated NF-kappaB activation but not the JNK signaling pathway. Because the CTAR2 region interacts with the tumor necrosis factor (TNF-alpha receptor-associated death domain protein, it is interesting to find that BRAM1 also interferes with NF-kappaB activation mediated by TNF-alpha. BRAM1 interferes LMP1-mediated and TNF-alpha-induced NF-kappaB activation by targeting IkappaBalpha molecules. Moreover, BRAM1 inhibits the resistance of LMP1-expressing cells to TNF-alpha-induced cytotoxicity. We therefore propose that the BRAM1 molecule associates with LMP1 and functions as a negative regulator of LMP1-mediated biological functions.

Linking cyclins to transcriptional control

Cell cycle activation is coordinated by D-type cyclins which are rate limiting and essential for the progression through the G1 phase of the cell cycle. D-type cyclins bind to and activate the cyclin-dependent kinases Cdk4 and Cdk6, which in turn phosphorylate their downstream target, the retinoblastoma protein Rb. Upon Rb phosphorylation, the E2F transcription factors activate the expression of S-phase genes and thereby induce cell cycle progression. The raise of cyclin D levels in early G1 also serves to titrate Kip/Cip proteins away from cyclinE/Cdk2 complexes, further accelerating cell cycle progression. Therefore, cyclin D plays essential roles in the response to mitogens, transmitting their signal to the Rb/E2F pathway. Surprisingly, cyclin D1-deficient animals are viable and have developmental abnormalities limited to restricted tissues, such as retina, the nervous system and breast epithelium. This observation, combined with several other studies, have raised the possibility that cyclin D1 may have new activities that are unrelated to its function as a cdk regulatory subunit and as regulator of Rb. Effectively, cyclin D has been reported to have transcriptional functions since it interacts with several transcription factors to regulate their activity. Most often, this effect does not rely on the kinase function of Cdk4, indicating that this function is probably independent of cell cycle progression. Further extending its role in gene regulation, cyclin D interacts with histone acetylases such as P/CAF or NcoA/SRC1a but also with components of the transcriptional machinery such as TAF(II)250. Therefore, these studies suggest that the functions of cyclin D might need to be reevaluated. They have established a new cdk-independent role of cyclin D1 as a transcriptional regulator, indicating that cyclin D1 can act via two different mechanisms, as a cdk activator it regulates cell cycle progression and as a transcriptional regulator, it modulates the activity of transcription factors.