Inhibition of Cdk2 activation by selected tyrphostins causes cell cycle arrest at late G1 and S phase

ERCC6L, a DNA helicase, is involved in cell proliferation and associated with survival and progress in breast and kidney cancers

By analyzing 4987 cancer transcriptomes from The Cancer Genome Atlas (TCGA), we identified that excision repair cross-complementation group 6 like (ERCC6L), a newly discovered DNA helicase, is highly expressed in 12 solid cancers. However, its role and mechanism in tumorigenesis are largely unknown. In this study, we found that ERCC6L silencing by small interring RNA (siRNA) or short hairpin RNA (shRNA) significantly inhibited the proliferation of breast (MCF-7, MDA-MB-231) and kidney cancer cells (786-0). Furthermore, ERCC6L silencing induced cell cycle arrest at G0/G1 phase without affecting apoptosis. We then performed RNA sequencing (RNA-seq) analysis after ERCC6L silencing and identified that RAB31 was markedly downregulated at both the transcriptional and translational levels. Its downstream protein, phosphorylated MAPK and CDK2 were also inhibited by ERCC6L silencing. The xenograft experiment showed that silencing of ERCC6L strikingly inhibited tumor growth from the 7th day after xenograft in nude mice. In addition, higher ERCC6L expression was found to be significantly associated with worse clinical survival in breast and kidney cancers. In conclusion, our results suggest that ERCC6L may stimulates cancer cell proliferation by promoting cell cycle through a way of RAB31-MAPK-CDK2, and it could be a potential biomarker for cancer prognosis and target for cancer treatment.

Information theoretic sub-network mining characterizes breast cancer subtypes in terms of cancer core mechanisms

A breast cancer subtype classification scheme, PAM50, based on genetic information is widely accepted for clinical applications. On the other hands, experimental cancer biology studies have been successful in revealing the mechanisms of breast cancer and now the hallmarks of cancer have been determined to explain the core mechanisms of tumorigenesis. Thus, it is important to understand how the breast cancer subtypes are related to the cancer core mechanisms, but multiple studies are yet to address the hallmarks of breast cancer subtypes. Therefore, a new approach that can explain the differences among breast cancer subtypes in terms of cancer hallmarks is needed.

We developed an information theoretic sub-network mining algorithm, differentially expressed sub-network and pathway analysis (DeSPA), that retrieves tumor-related genes by mining a gene regulatory network (GRN) of transcription factors and miRNAs. With extensive experiments of the cancer genome atlas (TCGA) breast cancer sequencing data, we showed that our approach was able to select genes that belong to cancer core pathways such as DNA replication, cell cycle, p53 pathways while keeping the accuracy of breast cancer subtype classification comparable to that of PAM50. In addition, our method produces a regulatory network of TF, miRNA, and their target genes that distinguish breast cancer subtypes, which is confirmed by experimental studies in the literature.

Characterization of phytochemicals and evaluation of anti-cancer potential of Blumea eriantha DC

The aim of the present study was to evaluate the in vitro anti-cancer and anti-oxidant potential of methanol extract of Blumea eriantha as well as its phytochemical characterization. The in vitro cytotoxic and antiproliferative activities of B. eriantha methanolic extract of leaves were evaluated using MTT assay on HeLa and B16F10 cell lines, and wound scratch and colony formation assays on B16F10 cell lines. The expressions of p53 and Bcl-2 genes were also determined by reverse transcriptase-polymerase chain reaction to establish apoptosis. Isolation and identification of chemical constituents were carried out by various chromatographic and spectroscopic analytical techniques including HPTLC and LC-MS. The methanol extract of the leaves of B. eriantha showed potent in vitro antioxidant and anticancer properties. Moreover, the extract showed significant loss of wound healing, thus suggesting that it could prevent a possible metastasis. Hence, B. eriantha could be explored as a potential anticancer plant with antimetastatic properties.

CRIF1 interacting with CDK2 regulates bone marrow microenvironment-induced G0/G1 arrest of leukemia cells

Background

To assess the level of CR6-interacting factor 1 (CRIF1), a cell cycle negative regulator, in patients with leukemia and investigate the role of CRIF1 in regulating leukemia cell cycle.

Methods

We compared the CRIF1 level in bone marrow (BM) samples from healthy and acute myeloid leukemia (AML), iron deficiency anemia (IDA) and AML-complete remission (AML-CR) subjects. We also manipulated CRIF1 level in the Jurkat cells using lentivirus-mediated overexpression or siRNA-mediated depletion. Co-culture with the BM stromal cells (BMSCs) was used to induce leukemia cell cycle arrest and mimic the BM microenvironment.

Results

We found significant decreases of CRIF1 mRNA and protein in the AML group. CRIF1 overexpression increased the proportion of Jurkat cells arrested in G0/G1, while depletion of endogenous CRIF1 decreased cell cycle arrest. Depletion of CRIF1 reversed BMSCs induced cell cycle arrest in leukemia cells. Co-immunoprecipitation showed a specific binding of CDK2 to CRIF1 in Jurkat cells during cell cycle arrest. Co-localization of two proteins in both nucleus and cytoplasm was also observed with immunofluorescent staining.

Conclusion

CRIF1 may play a regulatory role in the BM microenvironment-induced leukemia cell cycle arrest possibly through interacting with CDK2 and acting as a cyclin-dependent kinase inhibitor.

The Use of JAK-specific inhibitors as chemical biology tools

The JAK family of protein tyrosine kinases are now recognized as important participants in a wide range of pathologies, from cancer to inflammatory diseases. In the last decade, the drive to develop drugs targeting members of this family has begun to deliver a panel of small molecule inhibitors of JAK family members, with a range of potencies and specificities. A number of these compounds have already found widespread use as biochemical tools in the elucidation of JAK activity in specific signaling and disease processes; however, many of the first generation compounds are poorly characterized with suboptimal potencies and selectivities.Herein, we present the data for those small molecule JAK inhibitors that have been described in the peer-reviewed literature and the benefits and potential issues that may be associated with the use of these tool compounds.

Small-molecule inhibitors of signal transducer and activator of transcription 3 protect against angiotensin II-induced vascular dysfunction and hypertension

Angiotensin II (Ang II) is known to promote vascular disease and hypertension in part by formation of cytokines, such as interleukin-6. However, the role of signal transducer and activator of transcription 3 (STAT3) in these processes and Ang II/interleukin-6 signaling is unclear. Using 2 models, we tested the hypothesis that STAT3 is essential for Ang II-induced vascular dysfunction and hypertension. Incubation of isolated carotid arteries from C57BL/6J mice with Ang II overnight increased superoxide ≈2-fold and reduced vasodilator responses to the endothelium-dependent agonist acetylcholine by ≈50% versus controls (P<0.05). These effects were prevented by the addition of small-molecular inhibitors of STAT3 activation (S3I-201 or STATTIC). In vivo, administration of Ang II (1.4 mg kg(-1) day(-1)) using osmotic minipumps increased arterial pressure by ≈40 mm Hg at day 14 compared with vehicle-treated mice, and this effect was prevented by S3I-201 treatment (5 mg/kg IP, QOD). After systemic treatment with Ang II, dilator responses to acetylcholine were reduced by ≈30% to 50% in carotid artery and basilar arteries, whereas S3I-201 treatment prevented most of this impairment (P<0.05). In contrast to effects on vascular function and blood pressure, S31-201 did not prevent Ang II-induced hypertrophy in the carotid artery. These findings provide the first evidence that inhibitors of STAT3 activation protect against Ang II-induced oxidative stress, endothelial dysfunction, and hypertension. Because Ang II promotes vascular disease in the presence of multiple cardiovascular risk factors, these results suggest that selective targeting of STAT3 may have substantial therapeutic potential.

Cyclin E drives human keratinocyte growth into differentiation

Human epidermis is continuously exposed to environmental mutagenic hazard and is the most frequent target of human cancer. How the epidermis coordinates proliferation with differentiation to maintain homeostasis, even in hyperproliferative conditions, is unclear. For instance, overactivation of the proto-oncogene MYC in keratinocytes stimulates differentiation. Here we explore the cell cycle regulation as proliferating human keratinocytes commit to terminal differentiation upon loss of anchorage or overactivation of MYC. The S-phase of the cell cycle is deregulated as mitotic regulators are inhibited in the onset of differentiation. Experimental inhibition of mitotic kinase cdk1 or kinases of the mitosis spindle checkpoint Aurora B or Polo-like Kinase, triggered keratinocyte terminal differentiation. Furthermore, hyperactivation of the cell cycle by overexpressing the DNA replication regulator Cyclin E induced mitosis failure and differentiation. Inhibition of Cyclin E by shRNAs attenuated the induction of differentiation by MYC. In addition, we present evidence that Cyclin E induces DNA damage and the p53 pathway. The results provide novel clues for the mechanisms committing proliferative keratinocytes to differentiate, with implications for tissue homeostasis maintenance, HPV amplification and tumorigenesis.

A46, a benzothiophene-derived compound, suppresses Jak2-mediated pathologic cell growth

Hyperkinetic Jak2 tyrosine kinase signaling has been implicated in several hematological disorders, including myeloproliferative neoplasms. Effective Jak2 inhibitors can have significant therapeutic potential. Here, using structure-based virtual screening, we identified a benzothiophene-derived Jak2 inhibitor named A46. We hypothesized that this compound would inhibit Jak2-V617F-mediated pathologic cell growth. To test this, A46 was analyzed for its ability to inhibit recombinant Jak2 protein catalysis; suppress Jak2-mediated pathogenic cell growth in vitro; inhibit the aberrant ex vivo growth of Jak2-V617F-expressing primary human bone marrow cells; and inhibit Jak2-mediated pathogenesis in vivo. To this end, we found that A46 selectively inhibited Jak2-V617F protein when compared to wild-type Jak2 protein. The drug also selectively inhibited the proliferation of Jak2-V617F-expressing cells in both a time- and dose-dependent manner, and this correlated with decreased Jak2 and signal transducers and activators of transcription 5 phosphorylation within treated cells. The Jak2-V617F cell growth inhibition correlated with an induction of cell cycle arrest and promotion of apoptosis. A46 also inhibited the pathologic growth of primary Jak2-V617F-expressing bone marrow cells ex vivo. Lastly, using a mouse model of Jak2-V617F-mediated myeloproliferative neoplasia. A46 significantly reduced the splenomegaly and megakaryocytic hyperplasia in the spleens of treated mice and the levels of interleukin-6 in the plasma. Collectively, our data demonstrate that the benzothiophene-based compound, A46, suppresses Jak2-mediated pathogenesis, thereby making it a potential candidate drug against Jak2-mediated disorders.

Vascular smooth muscle Jak2 mediates angiotensin II-induced hypertension via increased levels of reactive oxygen species

AIMS

Angiotensin II (Ang II) type AT(1) receptors expressed on vascular smooth muscle cells (VSMCs) couple to the Jak2 signalling pathway. However, the importance of this tissue-specific coupling is poorly understood. The purpose of this investigation was to determine the importance of VSMC-derived Jak2 in angiotensin II-mediated hypertension.

METHODS AND RESULTS

The Cre-loxP system was used to conditionally eliminate Jak2 tyrosine kinase expression within the smooth muscle cells of mice. Following chronic Ang II infusion, the resulting increase in mean arterial pressure (MAP) was significantly attenuated in the Jak2 null mice when compared with littermate controls. The VSMC Jak2 null mice were also protected from the Ang II-induced vascular remodelling. Aortic rings from the VSMC Jak2 null mice exhibited reduced Ang II-induced contraction and enhanced endothelial-dependent relaxation via increased nitric oxide (NO) bioavailability. When compared with controls, the VSMC Jak2 nulls also had lower levels of hydrogen peroxide, Rho kinase activity, and intracellular Ca(2+) in response to Ang II.

CONCLUSIONS

The data indicate that VSMC Jak2 expression is involved in the pathogenesis of Ang II-dependent hypertension due to the increased presence of reactive oxygen species (ROS). As such, VSMC-derived Jak2 tyrosine kinase modulates overall vascular tone via multiple, non-redundant mechanisms.

Identification of a novel inhibitor of JAK2 tyrosine kinase by structure-based virtual screening

Janus kinase 2 (JAK2) plays a crucial role in the pathomechanism of myeloproliferative disorders and hematologic malignancies. A somatic mutation of JAK2 (Val617Phe) was previously shown to occur in 98% of patients with polycythemia vera and 50% of patients with essential thrombocythemia and primary myelofibrosis. Thus, effective JAK2 kinase inhibitors may be of significant therapeutic importance. Here, we applied a structure-based virtual screen to identify novel JAK2 inhibitors. One JAK2 inhibitor in particular, G6, demonstrated remarkable potency as well as specificity, which makes it as a potential lead candidate against diseases related to elevated JAK2 tyrosine kinase activity.

Z3, a novel Jak2 tyrosine kinase small-molecule inhibitor that suppresses Jak2-mediated pathologic cell growth

Jak2 tyrosine kinase is essential for animal development and hyperkinetic Jak2 function has been linked to a host of human diseases. Control of this pathway using Jak2-specific inhibitors would therefore potentially serve as a useful research tool and/or therapeutic agent. Here, we used a high-throughput program called DOCK to predict the ability of 20,000 small molecules to interact with a structural pocket adjacent to the ATP-binding site of murine Jak2. One small molecule, 2-methyl-1-phenyl-4-pyridin-2-yl-2-(2-pyridin-2-ylethyl)butan-1-one (herein designated as Z3), bound to Jak2 with a favorable energy score. Z3 inhibited Jak2-V617F and Jak2-WT autophosphorylation in a dose-dependent manner but was not cytotoxic to cells at concentrations that inhibited kinase activity. Z3 selectively inhibited Jak2 kinase function with no effect on Tyk2 or c-Src kinase function. Z3 significantly inhibited proliferation of the Jak2-V617F-expressing, human erythroleukemia cell line, HEL 92.1.7. The Z3-mediated reduction in cell proliferation correlated with reduced Jak2 and STAT3 tyrosine phosphorylation levels as well as marked cell cycle arrest. Finally, Z3 inhibited the growth of hematopoietic progenitor cells isolated from the bone marrow of an essential thrombocythemia patient harboring the Jak2-V617F mutation and a polycythemia vera patient carrying a Jak2-F537I mutation. Collectively, the data suggest that Z3 is a novel specific inhibitor of Jak2 tyrosine kinase.

[(2-Phenylindol-3-yl)methylene]propanedinitriles inhibit the growth of breast cancer cells by cell cycle arrest in G2/M phase and apoptosis

Cell cycle arrest of malignant cells is an important option for cancer treatment. In this study, we modified the structure of antimitotic 2-phenylindole-3-carbaldehydes by condensation with malononitrile. The resulting methylene propanedinitriles inhibited the growth of MDA-MB 231 and MCF-7 breast cancer cells with IC(50) values below 100 nM. Though they exhibited similar structure-activity relationships as the aldehydes, they did not inhibit tubulin polymerization but were capable of blocking the cell cycle in G(2)/M phase. The cell cycle arrest was accompanied by apoptosis as demonstrated by the activation of caspases 3 and 9. Since the new 2-phenylindole derivatives also inhibited the growth of transplanted MXT mouse mammary tumors, they are interesting candidates for further development.

Gö6976 is a potent inhibitor of the JAK 2 and FLT3 tyrosine kinases with significant activity in primary acute myeloid leukaemia cells

Aberrant activation of Janus kinase/signal transducers and activators of transcription (JAK/STAT) signalling is implicated in a number of haematological malignancies and effective JAK inhibitors may be therapeutically useful. We found that Gö6976, an indolocarbazole inhibitor of the calcium-dependent isozymes of protein kinase C (PKC), inhibited interleukin 3/granulocyte-macrophage colony-stimulating factor-induced signalling, proliferation and survival whereas Gö6983, a broad spectrum PKC inhibitor, had no such effects. Gö6976 was found to be a direct and potent inhibitor of JAK2 in vitro. Gö6976 also inhibited signalling, survival and proliferation in cells expressing the leukaemia-associated TEL-JAK2 fusion protein and the myeloproliferative disorder (MPD)-associated JAK2 V617F mutant. In primary acute myeloid leukaemia (AML) cells, incubation with Gö6976 reduced constitutive STAT activity in all cases studied. In addition, Akt and mitogen-activated protein kinase phosphorylation were reduced in 4/5 FLT3-internal tandem duplication (ITD) positive AML cases and 7/13 FLT3-wild-type (WT) cases. Expression of FLT3-WT, ITD and D835Y in 32D cells showed that Gö6976 is also a potent inhibitor of WT and mutant FLT3. In AML cells, Gö6976 reduced the survival to 55 +/- 5% of control in FLT3-ITD cases and to 69 +/- 5% in FLT3-WT samples. These data may help identify clinically useful compounds based on the structure of Gö6976, which can be employed for the treatment of MPDs as well as AML.

Janus kinase 3: a novel target for selective transplant immunosupression

Existing immunosuppressants inhibit lymphocyte activation and T cell cytokine signal transduction pathways, reducing the rate of acute rejection episodes to < 10%. However, the widespread tissue distribution of their molecular targets engenders pleiotropic toxicities. One strategy to address this problem seeks to identify compounds that selectively inhibit a target restricted in distribution to the lymphoid system. Janus kinase (Jak) 3 is such a molecule; it mediates signal transduction via the gamma common chain of lymphokine surface receptors. Disruption of this lymphoid-restricted enzyme would not be predicted to produce collateral damage in other organ systems. Development of selective Jak3 inhibitors has been difficult due to crossreactivity with its homologue, Jak2. In contrast to all other putative antagonists, which are discussed in detail herein, one Jak3 inhibitor, NC1153, shows at least 40-fold greater selective inhibition for Jak3 than for Jak2, is robustly synergistic with calcineurin antagonists, and, either alone or in combination with cyclosporin, produces no adverse effects in rodents preconditioned to be at heightened risk for nephrotoxicity, bone marrow suppression, or altered lipid metabolism.

Identification of 1,2,3,4,5,6-hexabromocyclohexane as a small molecule inhibitor of jak2 tyrosine kinase autophosphorylation [correction of autophophorylation]

The commercially available Jak2 inhibitor, alpha-cyano-3,4-dihydroxy-N-benzylcinnamide (AG490), has been used extensively to study Jak2 kinase function. While alpha-cyano-3,4-dihydroxy-N-benzylcinnamide is a potent Jak2 inhibitor, it can inhibit a number of other kinase signaling pathways as well. To circumvent this problem, we sought to identify novel small molecule inhibitors of Jak2 tyrosine kinase activity. For this, we constructed a homology model of the Jak2 kinase domain and identified solvent accessible pockets on the surface of the structure. Using the DOCK program, we tested 6451 compounds of known chemical structure in silico for their ability to interact with a pocket positioned adjacent to the activation loop. We attained the top seven scoring compounds from the National Cancer Institute and tested their ability to inhibit Jak2 autophosphorylation in vitro. Using Western blot analysis, we found that one of the compounds, 1,2,3,4,5,6-hexabromocyclohexane, was able to potently, and directly, inhibit Jak2 autophosphorylation. Characterization of this compound revealed that it inhibits Jak2 tyrosine autophosphorylation in both a time- and concentration-dependent manner. It greatly reduced growth hormone-mediated Jak2 autophosphorylation but did not block autophosphorylation of the epidermal growth factor receptor. Furthermore, doses as high as 100 muM were not toxic to cells as measured by their ability to exclude propidium iodide. As such, we believe that this compound could serve as a lead compound for a new generation of Jak2 inhibitors and, perhaps, be useful in elucidating the mechanisms of Jak2 kinase function.

Use of mRNA- and protein-destabilizing elements to develop a highly responsive reporter system

Reporter assays are widely used in applications that require measurement of changes in gene expression over time (e.g. drug screening). With standard reporter vectors, the measurable effect of a treatment or compound (altered reporter activity) is substantially diluted and delayed, compared with its true effect (altered transcriptional activity). This problem is caused by the relatively long half-lives of both the reporter protein and its mRNA. As a result, the activities of compounds, ligands or treatments that have a relatively minor effect, or a substantial but transient effect, often remain undetected. To circumvent this problem, we introduced modular protein- and mRNA-destabilizing elements into a range of commonly used reporters. Our data show that both elements are required for maximal responses to both increases and decreases in transcriptional activity. The double-destabilized reporter vectors showed markedly improved performance in drug screening, kinetic assays and dose–response titrations.

Enhancer role of STAT5 in CD2 activation of IFN-gamma gene expression

IFN-gamma is an important immunoregulatory protein with tightly controlled expression in activated T and NK cells. Three potential STAT binding regions have been recognized within the IFN-gamma promoter: 1) an IL-12-mediated STAT4 binding site at -236 bp; 2) a newly identified IL-2-induced STAT5 binding element at -3.6 kb; and 3) CD2-mediated STAT1 and STAT4 binding to an intronic element in mucosal T cells. However, functional activation of these sites remains unclear. In this study we demonstrate CD2-mediated activation of the newly characterized -3.6-kb IFN-gamma STAT5 binding region. CD2 signaling of human PBMC results in activation of the -3.6-kb IFN-gamma promoter, whereas mutation of the -3.6-kb STAT5 site attenuates promoter activity. Functional activation is accompanied by STAT5A but little STAT5B nucleoprotein binding to the IFN-gamma STAT5 site, as determined by competition and supershift assays. STAT5 activation via CD2 occurs independent of IL-2. Western and FACS analysis shows increased phospho-STAT5 following CD2 signaling. AG490, a tyrosine kinase inhibitor affecting Jak proteins, inhibits CD2-mediated IFN-gamma mRNA expression, secretion, and nucleoprotein binding to the IFN-gamma STAT5 site in a dose-dependent fashion. This report is the first to describe CD2-mediated activation of STAT5 and supports STAT5 involvement in regulation of IFN-gamma expression.

AG490 inhibits G1-S traverse in BALB/c-3T3 cells following either mitogenic stimulation or exogenous expression of E2F-1

AG490, a member of the tryphostin family of protein kinase inhibitors, repressed G0-G1 traverse in BALB/c-3T3 cells. While the early induction of STAT activity was repressed by AG490, extracellular signal-regulated kinase (ERK) activation was unaffected and a pattern of gene expression suggested that cells exited G0 in the presence of the inhibitor. Although AG490 did not alter the induction of cyclin D1 protein, neither cyclin D1- nor cyclin D3-associated kinase activity was observed in growth-inhibited cells. Surprisingly, p130 was partially phosphorylated, and E2F3A protein was expressed in mitogen-stimulated AG490-treated cells despite the lack of cyclin D-associated kinase activity. These data suggest that AG490 inhibits a cellular pathway required for mid-G0-G1 traverse that is located after the induction of early processes potentially mediated by E2F (although independent of cyclin D-associated kinase activity) but before the late G1 increase in E2F-dependent transcription. Infection of AG490-treated cells with an E2F-1 adenovirus caused the induction of cyclin A, but could not overcome the drug-induced cell cycle arrest that was coincident with the repression of cyclin-dependent kinase 2 (cdk2)-associated kinase activation. We conclude that cdk2-associated kinase activity is modulated by a cellular process repressed by AG490. Furthermore, this cdk2-associated kinase activity is required for G0-G1 traverse in some role other than the regulation of E2F-dependent transcription.

Jak2 Tyrosine Kinase Mediates Angiotensin II-dependent Inactivation of ERK2 via Induction of Mitogen-activated Protein Kinase Phosphatase 1

Previous work has shown that inhibition of Jak2 via the pharmacological compound AG490 blocks the angiotensin II (Ang II)-dependent activation of ERK2, thereby suggesting an essential role of Jak2 in ERK activation. However, recent studies have thrown into question the specificity of AG490 and therefore the role of Jak2 in ERK activation. To address this, we reconstituted an Ang II signaling system in a Jak2-/-cell line and measured the ability of Ang II to activate ERK2 in these cells. Controls for this study were the same cells expressing Jak2 via the addition of a Jak2 expression plasmid. In the cells expressing Jak2, Ang II induced a marked increase in ERK2 activity as measured by Western blot analysis and in vitro kinase assays. ERK2 activity returned to basal levels within 30 min. However, in the cells lacking Jak2, Ang II treatment resulted in ERK2 activation that did not return to basal levels until 120 min after ligand addition. Analysis of phosphatase gene expression revealed that Ang II induced mitogen-activated protein kinase phosphatase 1 (MKP-1) expression in cells expressing Jak2 but failed to induce MKP-1 expression in cells lacking Jak2. Therefore, our results suggest that Jak2 is not required for Ang II-induced ERK2 activation. Rather Jak2 is required for Ang II-induced ERK2 inactivation via induction of MKP-1 gene expression.

Small interfering RNA (siRNA) inhibits the expression of the Her2/neu gene, upregulates HLA class I and induces apoptosis of Her2/neu positive tumor cell lines

Silencing of a specific mRNA using double stranded RNA oligonucleotides represents one of the newest technologies for suppressing a specific gene product. Small interfering RNA (siRNA) are 21 nucleotides long, double stranded RNA fragments that are identical in sequence to the target mRNA. We designed 3 such siRNA against the Her2/neu (HER2) gene. The HER2 gene is known to play an important role in the oncogenesis of several types of cancers, such as breast, ovarian, colon and gastric cancers. Introduction of the siRNA into HER2 positive tumor lines in vitro greatly reduced the cell surface expression of the HER2 protein. Concurrently, a range of effects on cell physiology, such as growth inhibition or apoptosis, was observed. The expression of HLA class I was observed to be upregulated when HER2 was silenced with siRNA. Treatment of SKBr3 and MCF7/HER2 tumor cell lines with the HER2 siRNA resulted in growth arrest of cells in the late G(1)/S-phase. Our results suggest that siRNA may be an effective method of abrogating the effect of HER2 in tumorigenesis.

Tyrphostin AG 555 inhibits bovine papillomavirus transcription by changing the ratio between E2 transactivator/repressor function

The tyrosine kinase inhibitor (tyrphostin) AG 555 selectively interferes with viral transcription in bovine papillomavirus type 1 (BPV-1)-transformed fibroblasts and induces suppression of cyclin-dependent kinase activity and cell cycle arrest. Concomitant with inhibition of viral transcription, c-Jun was strongly up-regulated, which was consistent with the observation that AG 555 treatment also led to an activation of the mitogen-activated protein kinase pathway by enhancing phosphorylation of JNK and p38. Increased JNK and p38 activity resulted in higher phosphorylation of the AP-1 family members c-Jun and activating transcription factor 2. Scanning the BPV-1 genome for potential binding sequences, an intragenic AP-1 site (BAP-1) within the E7 open reading frame was detected. Enhanced dimerization of phosphorylated activating transcription factor 2 together with c-Jun and binding to BAP-1 seem to be responsible for viral dysregulation because both suppression of BPV-1 and induction of c-Jun mRNA could be almost entirely abrogated by simultaneous treatment with SB 203580, an inhibitor of p38 mitogen-activated protein kinase activity. Moreover, dissecting the complex transcriptional pattern of episomal BPV-1 with specific primer sets for reverse transcription-PCR analysis, the repressive effect could be attributed to a selective down-regulation of the mRNA encoding the E2 transactivator function in favor of the E2 repressor, whose mRNA level remained constant during AG 555 treatment. These data indicate that tyrphostin AG 555 disturbs the balance of negative and positive regulatory factors necessary to maintain the homeostasis of a virus-transformed phenotype.

Janus kinase 2 is involved in lipopolysaccharide-induced activation of macrophages

The mechanisms by which lipopolysaccharide (LPS) is recognized, and how such recognition leads to innate immune responses, are poorly understood. Stimulation with LPS induces the activation of a variety of proteins, including mitogen-activated protein kinases (MAPKs) and NF-kappaB. Activation of protein tyrosine kinases (PTKs) is also necessary for a number of biological responses to LPS. We used a murine macrophage-like cell line, RAW264.7, to demonstrate that Janus kinase (JAK)2 is tyrosine phosphorylated immediately after LPS stimulation. Anti-Toll-like receptor (TLR)4 neutralization antibody inhibits the phosphorylation of JAK2 and the c-Jun NH2-terminal protein kinase (JNK). Both the JAK inhibitor AG490 and the kinase-deficient JAK2 protein reduce the phosphorylation of JNK and phosphatidylinositol 3-kinase (PI3K) via LPS stimulation. Pharmacological inhibition of the kinase activity of PI3K with LY-294002 decreases the phosphorylation of JNK. Finally, we show that JAK2 is involved in the production of IL-1beta and IL-6. PI3K and JNK are also important for the production of IL-1beta. These results suggest that LPS induces tyrosine phosphorylation of JAK2 via TLR4 and that JAK2 regulates phosphorylation of JNK mainly through activation of PI3K. Phosphorylation of JAK2 via LPS stimulation is important for the production of IL-1beta via the PI3K/JNK cascade. Thus JAK2 plays a pivotal role in LPS-induced signaling in macrophages.

Association between the cell cycle and neural crest delamination through specific regulation of G1/S transition

Delamination of premigratory neural crest cells from the dorsal neural tube depends both upon environmental signals and cell-intrinsic mechanisms and is a prerequisite for cells to engage in migration. Here we show that avian neural crest cells synchronously emigrate from the neural tube in the S phase of the cell cycle. Furthermore, specific inhibition of the transition from G1 to S both in ovo and in explants blocks delamination, whereas arrest at the S or G2 phases has no immediate effect. Thus, the events taking place during G1 that control the transition from G1 to S are necessary for the epithelial to mesenchymal conversion of crest precursors.

Effects of receptor tyrosine kinase inhibitor A47 on estrogen and growth factor-dependent breast cancer cell proliferation and apoptosis in vitro

BACKGROUND AND OBJECTIVES

We propose that a growth factor receptor tyrosine kinase (RTK) inhibitor, such as tyrphostin A47, could serve as an adjunct to estrogen replacement therapy (ERT) for postmenopausal breast cancer survivors. Tyrphostins have been shown to block estrogen (E2)-induced proliferation in the human breast cancer MCF-7 cell line. Therefore, the effects of A47 on signal transduction, cell cycle progression, and apoptosis in E2-mediated breast cancer cell growth in vitro were investigated.

METHODS

Cell growth was determined by MTT proliferation assay, cell cycle analysis assessed by flow cytometry, and RTK activation by Western blot. Apoptosis assays included nuclear staining, TdT-mediated dUTP-X nick end labeling, and caspase 3 activation.

RESULTS

We find A47 selectively inhibits epidermal growth factor (EGF) and basic fibroblast growth factor but not insulin growth factor-1 proliferation. Although A47 inhibits EGF-induced phosphorylation of the EGF receptor in A431 cells, it does not consistently block MAP kinase phosphorylation.

CONCLUSIONS

Taken together, A47 blocks E2/EGF-induced activation of EGFR and therefore interferes with the proximal EGFR signaling pathway. A47 also arrests the cells at the G1-S transition of the cell cycle and induces cell death by apoptosis. Thus, a growth factor RTK may be useful in blocking hormone-dependent tumor growth in an elevated E2 environment.

Perspectives for cancer therapies with cdk2 inhibitors

Modern anticancer strategies are designed against specific molecular targets with the goal of sparing normal, non-neoplastic tissues. Choosing specific molecular targets, however, is problematic. Cdk2 (Cyclin dependent kinase 2, cell division kinase 2, p33) is an important candidate target for therapeutic intervention. Phosphorylation of retinoblastoma protein (pRb) by Cdk2 is the penultimate step in the transition from G1 to S phase. Inhibition of this step could potentially result in inhibition of proliferation, cytostasis and possibly apoptosis in human tumors. Cdk2 also plays a critical role in the transition through S phase and the S to G2 transition as well. Inhibitors of the cyclin dependent kinases, such as flavopiridol and UCN-01, are currently in clinical trials. While demonstrating clinical activity, neither acts specifically against Cdk2. Other more specific Cdk2 inhibitors are currently in preclinical development. Further studies to explore the therapeutic worth of such agents are warranted.

Role of NAD(P)H oxidase in angiotensin II-induced JAK/STAT signaling and cytokine induction

Inflammatory processes involve both synthesis of inflammatory cytokines, such as interleukin-6 (IL-6), and the activation of their distinct signaling pathways, eg, the janus kinases (JAKs) and signal transducers and activators of transcription (STAT). Superoxide (O(2)(-)) anions activate this signaling cascade, and the vasoconstrictor angiotensin II (Ang II) enhances the formation of O(2)(-) anions via the NAD(P)H oxidase system in rat aortic smooth muscle cells. Ang II activates the JAK/STAT cascade via its type 1 (AT(1)) receptor and induces synthesis and release of IL-6. Therefore, we investigated the role of O(2)(-) anions generated by the NAD(P)H oxidase system on the Ang II activation of the JAK/STAT cascade and its impact on IL-6 synthesis. Ang II stimulation of rat aortic smooth muscle cells induced a rapid increase in O(2)(-) anions determined by laser fluoroscopy, which can be abolished by DPI, a flavoprotein inhibitor. Ang II-induced phosphorylation of JAK2, STAT1alpha/ss, STAT3, and IL-6-synthesis can be abolished by DPI, as determined by immunoprecipitations and Northern blot analysis. Electroporation of neutralizing antisera targeted against p47(phox), a NAD(P)H oxidase subunit, abolished Ang II-induced JAK/STAT activation and IL-6 synthesis. Inhibition of JAK2 by its inhibitor AG490 (10 micromol/L) blocked not only JAK2 activation but also IL-6 synthesis. These results suggest that stimulation of the JAK/STAT cascade by Ang II requires O(2)(-) anions generated by the NAD(P)H oxidase system, and O(2)(-) anion-dependent activation of the JAK/STAT cascade seems to be additionally involved in Ang II-induced IL-6 synthesis. Thus, Ang II-induced inflammatory effects seem to require O(2)(-) anions generated by the NAD(P)H oxidase system.

Hyperoxia induces S-phase cell-cycle arrest and p21(Cip1/Waf1)-independent Cdk2 inhibition in human carcinoma T47D-H3 cells

Little is known about cell-cycle checkpoint activation by oxidative stress in mammalian cells. The effects of hyperoxia on cell-cycle progression were investigated in asynchronous human T47D-H3 cells, which contain mutated p53 and fail to arrest at G1/S in response to DNA damage. Hyperoxic exposure (95% O(2), 40-64 h) induced an S-phase arrest associated with acute inhibition of Cdk2 activity and DNA synthesis. In contrast, exit from G2/M was not inhibited in these cells. After 40 h of hyperoxia, these effects were partially reversible during recovery under normoxic conditions. The inhibition of Cdk2 activity was not due to degradation of Cdk2, cyclin E or A, nor impairment of Cdk2 complex formation with cyclin A or E and p21(Cip1). The loss of Cdk2 activity occurred in the absence of induction and recruitment of cdk inhibitor p21(Cip1) or p27(Kip1) in cyclin A/Cdk2 or cyclin E/Cdk2 complexes. In contrast, Cdk2 inhibition was associated with increased Cdk2-Tyr15 phosphorylation, increased E2F-1 recruitment, and decreased PCNA contents in Cdk2 complexes. The latter results indicate a p21(Cip1)/p27(Kip1)-independent mechanism of S-phase checkpoint activation in the hyperoxic T47D cell model investigated.

The cell cycle and drug discovery: the promise and the hope

In recent years, there have been major developments in the understanding of the cell cycle. It is now known that normal cellular proliferation is tightly regulated by the activation and deactivation of a series of proteins that constitute the cell cycle machinery. The expression and activity of components of the cell cycle can be altered during the development of a variety of diseases where aberrant proliferation contributes to the pathology of the illness. Apart from yielding a new source of untapped therapeutic targets, it is likely that manipulating the activity of such proteins in diseased states will provide an important route for treating proliferative disorders, and the opportunity to develop a novel class of future medicines.

Targeting signal transduction for disease therapy

With the advance in the molecular understanding of cancers and proliferative disorders new approaches to managing these diseases may become feasible. It has been recognized that a key feature of these diseases is the pathological alteration in the molecular machineries of signalling pathways. This recognition which began to emerge in the early 1980s induced us to explore the possibility of targetting the aberrant signalling pathways for disease therapy. I now present evidence for the validity of the approach.