NF-kappaB/RelA transactivation is required for atypical protein kinase C iota-mediated cell survival

PKCα and PKCδ: Friends and Rivals

PKC comprises a large family of serine/threonine kinases that share a requirement for allosteric activation by lipids. While PKC isoforms have significant homology, functional divergence is evident among subfamilies and between individual PKC isoforms within a subfamily. Here, we highlight these differences by comparing the regulation and function of representative PKC isoforms from the conventional (PKCα) and novel (PKCδ) subfamilies. We discuss how unique structural features of PKCα and PKCδ underlie differences in activation and highlight the similar, divergent, and even opposing biological functions of these kinases. We also consider how PKCα and PKCδ can contribute to pathophysiological conditions and discuss challenges to targeting these kinases therapeutically.

New Therapeutic Opportunities for the Treatment of Squamous Cell Carcinomas: A Focus on Novel Driver Kinases

Squamous cell carcinomas of the lung, head and neck, esophagus, and cervix account for more than two million cases of cancer per year worldwide with very few targetable therapies available and minimal clinical improvement in the past three decades. Although these carcinomas are differentiated anatomically, their genetic landscape shares numerous common genetic alterations. Amplification of the third chromosome's distal portion (3q) is a distinguishing genetic alteration in most of these carcinomas and leads to copy-number gain and amplification of numerous oncogenic proteins. This area of the chromosome harbors known oncogenes involved in squamous cell fate decisions and differentiation, including TP63, SOX2, ECT2, and PIK3CA. Furthermore, novel targetable oncogenic kinases within this amplicon include PRKCI, PAK2, MAP3K13, and TNIK. TCGA analysis of these genes identified amplification in more than 20% of clinical squamous cell carcinoma samples, correlating with a significant decrease in overall patient survival. Alteration of these genes frequently co-occurs and is dependent on 3q-chromosome amplification. The dependency of cancer cells on these amplified kinases provides a route toward personalized medicine in squamous cell carcinoma patients through development of small-molecules targeting these kinases.

Transcription co-activator P300 activates Elk1-aPKC-ι signaling mediated epithelial-to-mesenchymal transition and malignancy in hepatocellular carcinoma

Epithelial-to-mesenchymal transition (EMT) plays an important role in invasion and metastasis of hepatocellular carcinoma (HCC). Our previous study found that atypical protein kinase C-ι (aPKC-ι) promoted the EMT process in HCC. However, how the aPKC-ι signaling pathway is regulated in HCC has not been elucidated. In this study, vector transfection was utilized to study the invasion of HCC cells, and the mechanism between P300 and aPKC-ι signaling pathways in regulating the EMT process of HCC was further elucidated in vitro and in vivo. We found both P300 and aPKC-ι were highly expressed in HCC and they were correlated with tumor progression and poor survival in HCC patients. P300 knockdown inhibited EMT, invasion and other malignant events of HCC cells but promoted cell apoptosis and cycle arrest. However, the effects mediated by P300 knockdown were abolished by aPKC-ι overexpression. Further studies showed that P300 upregulates aPKC-ι expression through increasing the transcription of Elk1, a transcriptional activator of aPKC-ι, and stabilizing Elk1 protein and its phosphorylation. In conclusion, our work uncovered the molecular mechanism by which oncogenic aPKC-ι is upregulated in HCC and suggests that P300, like aPKC-ι, may be used as a prognostic biomarker and therapeutic target in patients with HCC.

The Dual Roles of the Atypical Protein Kinase Cs in Cancer

Atypical protein kinase C (aPKC) isozymes, PKCλ/ι and PKCζ, are now considered fundamental regulators of tumorigenesis. However, the specific separation of functions that determine their different roles in cancer is still being unraveled. Both aPKCs have pleiotropic context-dependent functions that can translate into tumor-promoter or -suppressive functions. Here, we review early and more recent literature to discuss how the different tumor types, and their microenvironments, might account for the selective signaling of each aPKC isotype. This is of clinical relevance because a better understanding of the roles of these kinases is essential for the design of new anti-cancer treatments.

Deciphering the mechanism of Indirubin and its derivatives in the inhibition of Imatinib resistance using a "drug target prediction-gene microarray analysis-protein network construction" strategy

Background

The introduction of imatinib revolutionized the treatment of chronic myeloid leukaemia (CML), substantially extending patient survival. However, imatinib resistance is currently a clinical problem for CML. It is very importantto find a strategy to inhibit imatinib resistance.

Methods

(1) We Identified indirubin and its derivatives and predicted its putative targets; (2) We downloaded data of the gene chip GSE2810 from the Gene Expression Omnibus (GEO) database and performed GEO2R analysis to obtain differentially expressed genes (DEGs); and (3) we constructed a P-P network of putative targets and DEGs to explore the mechanisms of action and to verify the results of molecular docking.

Result

We Identified a total of 42 small-molecule compounds, of which 15 affected 11 putative targets, indicating the potential to inhibit imatinib resistance; the results of molecular docking verified these results. Six biomarkers of imatinib resistance were characterised by analysing DEGs.

Conclusion

The 15 small molecule compounds inhibited imatinib resistance through the cytokine-cytokine receptor signalling pathway, the JAK-stat pathway, and the NF-KB signalling pathway. Indirubin and its derivatives may be new drugsthat can combat imatinib resistance.

Electronic supplementary material

The online version of this article (10.1186/s12906-019-2471-2) contains supplementary material, which is available to authorized users.

The signaling axis atypical protein kinase C λ/ι-Satb2 mediates leukemic transformation of B-cell progenitors

Epigenetically regulated transcriptional plasticity has been proposed as a mechanism of differentiation arrest and resistance to therapy. BCR-ABL leukemias result from leukemic stem cell/progenitor transformation and represent an opportunity to identify epigenetic progress contributing to lineage leukemogenesis. Primary human and murine BCR-ABL⁺ leukemic progenitors have increased activation of Cdc42 and the downstream atypical protein kinase C (aPKC). While the isoform aPKCζ behaves as a leukemic suppressor, aPKCλ/ι is critically required for oncogenic progenitor proliferation, survival, and B-cell differentiation arrest, but not for normal B-cell lineage differentiation. In vitro and in vivo B-cell transformation by BCR-ABL requires the downregulation of key genes in the B-cell differentiation program through an aPKC λ/ι-Erk dependent Etv5/Satb2 chromatin repressive signaling complex. Genetic or pharmacological targeting of aPKC impairs human oncogenic addicted leukemias. Therefore, the aPKCλ/ι-SATB2 signaling cascade is required for leukemic BCR-ABL⁺ B-cell progenitor transformation and is amenable to non-tyrosine kinase inhibition.

The upstream pathways regulating leukemic transcriptional plasticity for differentiation arrest and resistance to therapy are unclear. Here the authors show that aPKC λ/ι-controls leukemic B-cell precursor differentiation arrest trough RAC/MEK/ERK/SATB2 epigenetic repression

Preclinical testing of 5-amino-1-((1R,2S,3S,4R)-2,3-dihydroxy-4-methylcyclopentyl)-1H-imidazole-4-carboxamide: a potent protein kinase C-ι inhibitor as a potential prostate carcinoma therapeutic

Protein kinase C-iota (PKC-ι) is an oncogene overexpressed in many cancer cells including prostate, breast, ovarian, melanoma, and glioma. Previous in-vitro studies have shown that 5-amino-1-((1R,2S,3S,4R)-2,3-dihydroxy-4-methylcyclopentyl)-1H-imidazole-4-carboxamide (ICA-1s), a PKC-ι specific inhibitor, is effective against some cancer cell lines by decreasing cell growth and inducing apoptosis. To assess ICA-1s as a possible therapeutic, in-vivo studies using a murine model were performed. ICA-1s was tested for stability in blood serum and results demonstrated that ICA-1s was stable in human plasma at 25 and 37°C over a course of 2 h. Toxicity of ICA-1s was tested for both acute and subacute exposure. The acute exposure showed patient surviving after 48 h of doses ranging from 5 to 5000 mg/kg. Subacute tests exposed the patients to 14 days of treatment and were followed by serum and tissue collection. Aspartate aminotransferase, alkaline phosphatase, γ-glutamyl transpeptidase, troponin, and C-reactive protein serum levels were measured to assess organ function. ICA-1s in plasma serum was measured over the course of 24 h for both oral and intravenous treatments. Heart, liver, kidney, and brain tissues were analyzed for accumulation of ICA-1s. Finally, athymic nude mice were xenografted with DU-145 prostate cancer cells. After tumors reached ~0.2 cm², they were either treated with ICA-1s or left as control and measured for 30 days or until the tumor reached 2 cm². Results showed tumors in treated mice grew at almost half the rate as untreated tumors, showing a significant reduction in growth. In conclusion, ICA-1s is stable, shows low toxicity, and is a potential therapeutic for prostate carcinoma tumors.

Pentamethinium salts as ligands for cancer: Sulfated polysaccharide co-receptors as possible therapeutic target

A series of pentamethinium salts with benzothiazolium and indolium side units comprising one or two positive charges were designed and synthesized to determine the relationships among the molecular structure, charge density, affinity to sulfated polysaccharides, and biological activity. Firstly, it was found that the affinity of the pentamethinium salts to sulfated polysaccharides correlated with their biological activity. Secondly, the side heteroaromates displayed a strong effect on the cytotoxicity and selectivity towards cancer cells. Finally, doubly charged pentamethinium salts possessing benzothiazolium side units exhibited remarkably high efficacy against a taxol-resistant cancer cell line.

Two novel PRKCI polymorphisms and prostate cancer risk in an Eastern Chinese Han population

The atypical protein kinase C (aPKCι), encoded by the PRKCI gene, has been recently found to be a unique human oncoprotein, compared with some other diverse PKC isozymes. Genetic variations in PRKCI have also been reported to be associated with prostate cancer (PCa) risk in Caucasian populations, but no similar studies have been reported for Chinese populations. We genotyped two well-described PRKCI single nucleotide polymorphisms (SNPs) rs546950 and rs4955720 in 1015 PCa patients and 1044 cancer-free controls of Eastern Chinese men. SNPs in the vicinity of those two variants of PRKCI were evaluated using the in silico analysis. Logistic regression was then used to estimate their associations with and interactions in PCa risk. Although no significant main effects were found for the two tested SNPs in the single locus analysis, individuals carrying homozygote wide-type form of these two SNPs had slightly reduced PCa risk (adjusted OR = 0.63, 95% CI = 0.40-0.99, P = 0.045), compared with those carrying any of heterozygous or homozygous variant genotypes. Our results indicated that the two PRKCI SNPs were jointly associated with PCa risk in an Eastern Chinese population. Larger studies with multiethnic groups are warranted to confirm these findings and to explore the role of PRKCI SNPs in the etiology of PCa.

Role of calcium-dependent protein kinases in chronic myeloid leukemia: combined effects of PKC and BCR-ABL signaling on cellular alterations during leukemia development

Calcium-dependent protein kinases (PKCs) function in a myriad of cellular processes, including cell-cycle regulation, proliferation, hematopoietic stem cell differentiation, apoptosis, and malignant transformation. PKC inhibitors, when targeted to these pathways, have demonstrated efficacy against several types of solid tumors as well as leukemia. Chronic myeloid leukemia (CML) represents 20% of all adult leukemia. The aberrant Philadelphia chromosome has been reported as the main cause of CML development in hematopoietic stem cells, due to the formation of the BCR-ABL oncogene. PKCs and BCR-ABL coordinate several signaling pathways that are crucial to cellular malignant transformation. Experimental and clinical evidence suggests that pharmacological approaches using PKC inhibitors may be effective in the treatment of CML. This mini review summarizes articles from the National Center for Biotechnology Information website that have shown evidence of the involvement of PKC in CML.

The aPKCι blocking agent ATM negatively regulates EMT and invasion of hepatocellular carcinoma

Epithelial-to-mesenchymal transition (EMT) has an important role in invasion and metastasis of hepatocellular carcinoma (HCC). To explore the regulatory mechanism of atypical protein kinase C ι (aPKCι) signaling pathways to HCC development, and find an agent for targeted therapy for HCC, immortalized murine hepatocytes were employed to establish an EMT cell model of HCC, MMH-RT cells. Our study showed that EMT took place in MMH-R cells under the effect of transforming growth factor-β1 (TGF-β1) overexpressing aPKCι. Furthermore, we showed that the aPKCι blocking agent aurothiomalate (ATM) inhibited EMT and decreased invasion of hepatocytes. Moreover, ATM selectively inhibited proliferation of mesenchymal cells and HepG2 cells and induced apoptosis. However, ATM increased proliferation of epithelial cells and had little effect on apoptosis and invasion of epithelial cells. In conclusion, our result suggested that aPKCι could be an important bio-marker of tumor EMT, and used as an indicator of invasion and malignancy. ATM might be a promising agent for targeted treatment of HCC.

Atypical protein kinase Cι as a human oncogene and therapeutic target

Protein kinase inhibitors represent a major class of targeted therapeutics that has made a positive impact on treatment of cancer and other disease indications. Among the promising kinase targets for further therapeutic development are members of the Protein Kinase C (PKC) family. The PKCs are central components of many signaling pathways that regulate diverse cellular functions including proliferation, cell cycle, differentiation, survival, cell migration, and polarity. Genetic manipulation of individual PKC isozymes has demonstrated that they often fulfill distinct, nonredundant cellular functions. Participation of PKC members in different intracellular signaling pathways reflects responses to varying extracellular stimuli, intracellular localization, tissue distribution, phosphorylation status, and intermolecular interactions. PKC activity, localization, phosphorylation, and/or expression are often altered in human tumors, and PKC isozymes have been implicated in various aspects of transformation, including uncontrolled proliferation, migration, invasion, metastasis, angiogenesis, and resistance to apoptosis. Despite the strong relationship between PKC isozymes and cancer, to date only atypical PKCiota has been shown to function as a bona fide oncogene, and as such is a particularly attractive therapeutic target for cancer treatment. In this review, we discuss the role of PKCiota in transformation and describe mechanism-based approaches to therapeutically target oncogenic PKCiota signaling in cancer.

Par-complex aPKC and Par3 cross-talk with innate immunity NF-κB pathway in epithelial cells

Components of the Par-complex, atypical PKC and Par3, have been found to be downregulated upon activation of NF-κB in intestinal epithelial cells. To determine their possible role in pro-inflammatory responses we transduced Caco-2 human colon carcinoma cells with constitutively active (ca) PKCι or anti-Par3 shRNA-expressing lentiviral particles. Contrary to previous reports in other cell types, ca-PKCι did not activate, but rather decreased, baseline NF-κB activity in a luminiscence reporter assay. An identical observation applied to a PB1 domain deletion PKCι, which fails to localize to the tight-junction. Conversely, as expected, the same ca-PKCι activated NF-κB in non-polarized HEK293 cells. Likewise, knockdown of Par3 increased NF-κB activity and, surprisingly, greatly enhanced its response to TNFα, as shown by transcription of IL-8, GRO-1, GRO-2 and GRO-3. We conclude that aPKC and Par3 are inhibitors of the canonical NF-κB activation pathway, although perhaps acting through independent pathways, and may be involved in pro-inflammatory responses.

PKC phosphorylates HEXIM1 and regulates P-TEFb activity

The positive transcription elongation factor b (P-TEFb) regulates RNA polymerase II elongation. In cells, P-TEFb partitions between small active and larger inactive states. In the latter, HEXIM1 binds to 7SK snRNA and recruits as well as inactivates P-TEFb in the 7SK snRNP. Several stimuli can affect this P-TEFb equilibrium. In this study, we demonstrate that protein kinase C (PKC) phosphorylates the serine at position158 (S158) in HEXIM1. This phosphorylated HEXIM1 protein neither binds to 7SK snRNA nor inhibits P-TEFb. Phorbol esters or the engagement of the T cell antigen receptor, which activate PKC and the expression of the constitutively active (CA) PKCθ protein, which is found in T cells, inhibit the formation of the 7SK snRNP. All these stimuli increase P-TEFb-dependent transcription. In contrast, the kinase-negative PKCθ and the mutant HEXIM1 (S158A) proteins block effects of these PKC-activating stimuli. These results indicate that the phosphorylation of HEXIM1 by PKC represents a major regulatory step of P-TEFb activity in cells.

Protein kinase Cι expression and oncogenic signaling mechanisms in cancer

Accumulating evidence demonstrates that PKCι is an oncogene and prognostic marker that is frequently targeted for genetic alteration in many major forms of human cancer. Functional data demonstrate that PKCι is required for the transformed phenotype of lung, pancreatic, ovarian, prostate, colon, and brain cancer cells. Future studies will be required to determine whether PKCι is also an oncogene in the many other cancer types that also overexpress PKCι. Studies of PKCι using genetically defined models of tumorigenesis have revealed a critical role for PKCι in multiple stages of tumorigenesis, including tumor initiation, progression, and metastasis. Recent studies in a genetic model of lung adenocarcinoma suggest a role for PKCι in transformation of lung cancer stem cells. These studies have important implications for the therapeutic use of aurothiomalate (ATM), a highly selective PKCι signaling inhibitor currently undergoing clinical evaluation. Significant progress has been made in determining the molecular mechanisms by which PKCι drives the transformed phenotype, particularly the central role played by the oncogenic PKCι-Par6 complex in transformed growth and invasion, and of several PKCι-dependent survival pathways in chemo-resistance. Future studies will be required to determine the composition and dynamics of the PKCι-Par6 complex, and the mechanisms by which oncogenic signaling through this complex is regulated. Likewise, a better understanding of the critical downstream effectors of PKCι in various human tumor types holds promise for identifying novel prognostic and surrogate markers of oncogenic PKCι activity that may be clinically useful in ongoing clinical trials of ATM.

Viral induction of the zinc finger antiviral protein is IRF3-dependent but NF-kappaB-independent

The zinc finger antiviral protein (ZAP) is an interferon-stimulated gene that restricts the replication of retroviruses, alphaviruses, and filoviruses. Relatively little is known, however, regarding the detailed mechanism of ZAP induction during viral infections. We show that, although being inducible by either interferon or virus, expression of ZAP is more efficiently activated by virus than are several other classical interferon-stimulated genes and that viral induction of ZAP occurs under the direct control of interferon regulatory factor 3 (IRF3) independent of interferon paracrine/autocrine signaling. ZAP was up-regulated in cells unresponsive to type I and III interferons upon engagement of TLR3, retinoic inducible gene I/melanoma differentiation-associated gene 5 pathways, or ectopic expression of a constitutively active IRF3 mutant. Conversely, induction of ZAP by virus or dsRNA was severely impaired in cells expressing a dominant-negative mutant IRF3 and completely abrogated in cells lacking IRF3. In contrast to IRF3, ZAP induction was independent of NF-kappaB activity. Mutational analysis of the human ZAP promoter revealed that multiple interferon-stimulated response elements far distal to the transcription start site serve redundantly to control IRF3-dependent induction of ZAP transcription. Chromatin immunoprecipitation assays demonstrated that IRF3 selectively binds the distal interferon-stimulated response elements in human ZAP promoter following viral infection. Collectively, these data suggest that ZAP is a direct target gene of IRF3 action in cellular antiviral responses.

High expression of atypical protein kinase C lambda/iota in gastric cancer as a prognostic factor for recurrence

BACKGROUND

The atypical protein kinase C lambda/iota (aPKClambda/iota) is involved in several signal transduction pathways that influence cell growth, apoptosis, and the establishment and maintenance of epithelial cell polarity. Overexpression of aPKClambda/iota has been reported in several cancers and been shown to be associated with oncogenesis. However, the expression and role of aPKClambda/iota in gastric cancer, one of the commonest cancers in Asia, have not so far been investigated. This study aimed to clarify the relationship between aPKClambda/iota expression and the clinicopathological features of gastric cancer.

PATIENTS AND METHODS

Gastric adenocarcinoma samples were obtained from 177 patients who underwent gastrectomy at the Yokohama City University Hospital between 1999 and 2004. Expression of aPKClambda/iota and E: -cadherin was examined immunohistochemically and compared with clinicopathological features of the tumors. Univariate and multivariate analyses were performed for both disease-specific and relapse-free survival.

RESULTS

Overexpression of aPKClambda/iota protein was detected in 126 of the 177 (71.2%) gastric cancers. Immunohistological staining for aPKClambda/iota was stronger in gastric adenocarcinoma of intestinal type than diffuse type (p = 0.036), but was not correlated with E: -cadherin expression. A multivariate analysis suggested that nodal metastasis and aPKClambda/iota overexpression were prognostic factors for disease recurrence.

CONCLUSIONS

Our results suggested that aPKClambda/iota overexpression was a strong prognostic factor for gastric adenocarcinoma recurrence. As well as being a new prognostic indicator, aPKClambda/iota is also likely to be a novel therapeutic target for gastric cancer.

aPKClambda/iota promotes growth of prostate cancer cells in an autocrine manner through transcriptional activation of interleukin-6

Understanding the mechanism by which hormone refractory prostate cancer (HRPC) develops remains a major issue. Alterations in HRPC include androgen receptor (AR) changes. In addition, the AR is activated by cytokines such as interleukin-6 (IL-6). Atypical protein kinase C (aPKClambda/iota) has been implicated in the progression of several cancers. Herein, we provide evidence that aPKClambda/iota expression correlates with prostate cancer recurrence. Experiments in vitro and in vivo revealed aPKClambda/iota to be involved in prostate cancer cell growth through secretion of IL-6. Further, aPKClambda/iota activates transcription of the IL-6 gene through NFkappaB and AP-1. We conclude that aPKClambda/iota promotes the growth of hormone independent prostate cancer cells by stimulating IL-6 production in an autocrine manner. Our findings not only explain the link between aPKClambda/iota and IL-6, implicated in the progression a variety of cancers, but also establish a molecular change involved in the development of HRPC. Further, aPKClambda/iota expression might be a biomarker for prostate cancer progression.

Non-histone nuclear factor HMGB1 is phosphorylated and secreted in colon cancers

The high mobility group box 1 (HMGB1) protein, a non-histone nuclear factor, is overexpressed and localizes to the cytoplasm in some cancer cells. However, the mechanism of cytoplasmic HMGB1 transport, extracellular secretion, and its role in cancer progression is not clear. To simulate the activated state of HMGB1, we mutated serine residues of nuclear localization signals (NLSs) to glutamic acid and performed transfection assays. We carried out a kinase inhibitor study and evaluated the cell migration by invasion assay. We showed that phosphorylated HMGB1 localizes in the cytoplasm of colon cancer cells and also showed the interaction of PKC and HMGB1 by immunoprecipitation analysis. Concurrent mutations at six serine residues (35, 39, 42, 46, 53, and 181) to glutamic acid induced the nuclear to cytoplasmic transport of HMGB1, which was detected in the culture medium. We also observed that the secretion of HMGB1 correlated with increased cancer cell invasiveness. Our results suggest that phosphorylated HMGB1 is transported to the cytoplasm, is subsequently secreted from the cell, and has a role in tumor progression through the activation of genes related to cell migration.

Role of protein kinase C-iota in transformed non-malignant RWPE-1 cells and androgen-independent prostate carcinoma DU-145 cells

Prostate cancer is one of the leading causes of death among men in the USA.

OBJECTIVE

In this study, we investigated the role of atypical protein kinase C-iota (PKC-iota) in androgen independent prostate DU-145 carcinoma cellscompared to transformed non-malignant prostate RWPE-1 cells.

MATERIALS AND METHODS

Western blotting and immunoprecipitations demonstrated that PKC-iotaisassociated with cyclin-dependent kinase activating kinase (CAK/Cdk7) in RWPE-1 cells, but not in DU-145 cells.

RESULTS

Treatment of prostate RWPE-1 cells with PKC-iota silencing RNA (siRNA) decreased cell viability,cell-cycle accumulation at G2/M phase, and phosphorylation of Cdk7 and Cdk2. In addition, PKC-iota siRNA treatment caused less phosphorylation ofBad at ser-155, ser-136, and greater Bad/Bcl-xL heterodimerization, leading to apoptosis. In DU-145 cells, PKC-iota was anti-apoptotic and was required for cell survival. Treatment with PKC-iota siRNA blocked increase in cell number, and inhibited G1/S transition by accumulation of cells in G0/G1phase. In addition to cell-cycle arrest, both RWPE-1 and DU-145 cells underwent apoptosis due to mitochondrial dysfunction and apoptosis cascades, such as release of cytochrome c,activation of caspase-7, and poly (ADP-ribose)polymerase (PARP) cleavage.

CONCLUSION

Our results suggest that PKC-iota is required for cell survival in both transformed non-malignant prostate RWPE-1 cells and androgen-independent malignant prostate DU-145 cells, whereas suppressing PKC-iota lead to apoptosis in DU-145 prostate cells.

Circulating heat shock protein 70 and progression in patients with chronic myeloid leukemia

We evaluated the association of circulating levels of heat shock protein 70 (Hsp70) in plasma with clinical behavior and progression in 139 chronic myeloid leukemia (CML) patients. Circulating Hsp70 levels did not differ significantly between CML patients in the chronic phase (n=93; median 33.24 ng/mL, range 3.89-128.2 ng/mL) and those in the accelerated/blast phase (n=46; median 26.57 ng/mL, range 4.5-114.7 ng/mL). However, overall CML patients had significantly higher levels of Hsp70 than healthy subjects (n=95, median 4.17 ng/mL, range 1.75-24.7 ng/mL) (P<0.001). In chronic phase CML patients, Hsp70 levels above the median were associated with a higher rate of progression to the accelerated/blast phase and a tendency toward shorter survival. Plasma Hsp70 thus could be a potential marker for predicting disease progression in patients with chronic phase CML.

Atypical protein kinase C phosphorylates IKKalphabeta in transformed non-malignant and malignant prostate cell survival

Mechanistic pathways involving atypical protein kinase C-iota (aPKC-iota) have been targeted in various cancer cells such as lung cancer, brain and prostate due to PKCiota's antiapoptotic function, and role in cell proliferation and cell survival. In the current study, we examined the involvement of PKC-iota in the NF-kappaB pathway following treatment of prostate cells with the pro-inflammatory cytokine tumor necrosis factor alpha (TNFalpha). Results demonstrated that androgen-independent DU-145 prostate carcinoma is insensitive to TNFalpha while transformed non-tumorigenic prostate RWPE-1 cells showed a slight sensitivity to TNFalpha. However, androgen-dependent LNCaP prostate cells are more sensitive to TNFalpha treatment and undergo apoptosis. Results demonstrated that in DU-145 cells, TNFalpha-induced PKC-iota in phosphorylation of IKKalphabeta. In RWPE-1 cells, PKC-zeta phosphorylates IKKalphabeta. Degradation of IkappaBalpha was observed in all three cell lines, allowing NF-kappaB/p65 translocation to the nucleus. Although, IKKalpha is weakly activated in LNCaP cells, the upstream kinase phosphorylation of IKKalphabeta via aPKCs was not observed. Hence, aPKCs may play a role in activation of NFkappaB pathway in prostate cancer cells.

RelA Ser276 phosphorylation is required for activation of a subset of NF-kappaB-dependent genes by recruiting cyclin-dependent kinase 9/cyclin T1 complexes

NF-kappaB plays a central role in cytokine-inducible inflammatory gene expression. Previously we empirically determined the identity of 92 members of the genetic network under direct NF-kappaB/RelA control that show marked heterogeneity in magnitude of transcriptional induction and kinetics of peak activation. To investigate this network further, we have applied a recently developed two-step chromatin immunoprecipitation assay that accurately reflects association and disassociation of RelA binding to its chromatin targets. Although inducible RelA binding occurs with similar kinetics on all NF-kappaB-dependent genes, serine 276 (Ser(276))-phosphorylated RelA binding is seen primarily on a subset of genes that are rapidly induced by tumor necrosis factor (TNF), including Gro-beta, interleukin-8 (IL-8), and IkappaBalpha. Previous work has shown that TNF-inducible RelA Ser(276) phosphorylation is controlled by a reactive oxygen species (ROS)-protein kinase A signaling pathway. To further understand the role of phospho-Ser(276) RelA in target gene expression, we inhibited its formation by ROS scavengers and antioxidants, treatments that disrupt phospho-Ser(276) formation but not the translocation and DNA binding of nonphosphorylated RelA. Here we find that phospho-Ser(276) RelA is required only for activation of IL-8 and Gro-beta, with IkappaBalpha being unaffected. These data were confirmed in experiments using RelA(-/-) murine embryonic fibroblasts reconstituted with a RelA Ser(276)Ala mutation. In addition, we observe that phospho-Ser(276) RelA binds the positive transcription elongation factor b (P-TEFb), a complex containing the cyclin-dependent kinase 9 (CDK-9) and cyclin T1 subunits. Inhibition of P-TEFb activity by short interfering RNA (siRNA)-mediated knockdown shows that the phospho-Ser(276) RelA-P-TEFb complex is required for IL-8 and Gro-beta gene activation but not for IkappaBalpha gene activation. These studies indicate that TNF induces target gene expression by heterogeneous mechanisms. One is mediated by phospho-Ser(276) RelA formation and chromatin targeting of P-TEFb controlling polymerase II (Pol II) recruitment and carboxy-terminal domain phosphorylation on the IL-8 and Gro-beta genes. The second involves a phospho-Ser(276) RelA-independent activation of genes preloaded with Pol II, exemplified by the IkappaBalpha gene. Together, these data suggest that the binding kinetics, selection of genomic targets, and mechanisms of promoter induction by RelA are controlled by a phosphorylation code influencing its interactions with coactivators and transcriptional elongation factors.

Targeting the oncogenic protein kinase Ciota signalling pathway for the treatment of cancer

PKC (protein kinase C) isoenzymes are key signalling components involved in the regulation of normal cell proliferation, differentiation, polarity and survival. The aberrant regulation of PKC isoenzymes has been implicated in the development of many human diseases including cancer [Fields and Gustafson (2003) Methods Mol. Biol. 233, 519-537]. To date, however, only one PKC isoenzyme, the aPKC [atypical PKCiota (protein kinase Ciota)], has been identified as a human oncogene [Regala, Weems, Jamieson, Khoor, Edell, Lohse and Fields (2005) Cancer Res. 65, 8905-8911]. PKCiota has also proven to be a useful prognostic marker and legitimate target for the development of novel pharmacological agents for the treatment of cancer. The PKCiota gene resides at chromosome 3q26 and is a frequent target of tumour-specific gene amplification in multiple forms of human cancer. PKCiota gene amplification in turn drives PKCiota overexpression in these cancers. Genetic disruption of PKCiota expression blocks multiple aspects of the transformed phenotype of human cancer cells including transformed growth in soft agar, invasion through Matrigel and growth of subcutaneous tumours in nude mice. Genetic dissection of oncogenic PKCiota signalling mechanisms demonstrates that PKCiota drives transformed growth by activating a PKCiota --> Rac1 --> PAK (p21-activated kinase) --> MEK [MAPK (mitogen-activated protein kinase) 1,2/ERK (extracellular-signal-regulated kinase) kinase] 1,2 signalling pathway [Regala, Weems, Jamieson, Copland, Thompson and Fields (2005) J. Biol. Chem. 280, 31109-31115]. The transforming activity of PKCiota requires the N-terminal PB1 (Phox-Bem1) domain of PKCiota, which serves to couple PKCiota with downstream effector molecules. Hence, there exists a strong rationale for developing novel cancer therapeutics that target the PB1 domain of PKCiota and thereby disrupt its interactions with effector molecules. Using a novel high-throughput drug screen, we identified compounds that can disrupt PB1-PB1 domain interactions between PKCiota and the adaptor molecule Par6 [Stallings-Mann, Jamieson, Regala, Weems, Murray and Fields (2006) Cancer Res. 66, 1767-1774]. Our screen identified the gold compounds ATG (aurothioglucose) and ATM (aurothiomalate) as specific inhibitors of the PB1-PB1 domain interaction between PKCiota and Par6 that exhibit anti-tumour activity against NSCLC (non-small-cell lung cancer) both in vitro and in vivo. Structural analysis, site-directed mutagenesis and modelling indicate that ATM specifically targets the PB1 domain of PKCiota to mediate its anti-tumour activity [Erdogan, Lamark, Stallings-Mann, Lee, Pellechia, Thompson, Johansen and Fields (2006) J. Biol. Chem. 281, 28450-28459]. Taken together, our recent work demonstrates that PKCiota signalling is required for transformed growth of human tumours and is an attractive target for development of mechanism-based cancer therapies. ATM is currently in Phase I clinical trials for the treatment of NSCLC.

Protein kinase C iota: human oncogene, prognostic marker and therapeutic target

The protein kinase C (PKC) family of serine/threonine kinases has been the subject of intensive study in the field of cancer since their initial discovery as major cellular receptors for the tumor promoting phorbol esters nearly 30 years ago. However, despite these efforts, the search for a direct genetic link between members of the PKC family and human cancer has yielded only circumstantial evidence that any PKC isozyme is a true cancer gene. This situation changed in the past year with the discovery that atypical protein kinase C iota (PKC iota) is a bonafide human oncogene. PKC iota is required for the transformed growth of human cancer cells and the PKC iota gene is the target of tumor-specific gene amplification in multiple forms of human cancer. PKC iota participates in multiple aspects of the transformed phenotype of human cancer cells including transformed growth, invasion and survival. Herein, we review pertinent aspects of atypical PKC structure, function and regulation that relate to the role of these enzymes in oncogenesis. We discuss the evidence that PKC iota is a human oncogene, review mechanisms controlling PKC iota expression in human cancers, and describe the molecular details of PKC iota-mediated oncogenic signaling. We conclude with a discussion of how oncogenic PKC iota signaling has been successfully targeted to identify a novel, mechanism-based therapeutic drug currently entering clinical trials for treatment of human lung cancer. Throughout, we identify key unanswered questions and exciting future avenues of investigation regarding this important oncogenic molecule.

NF-kappaB as a potential molecular target for cancer therapy

Nuclear factor kappaB (NF-kappaB), a transcription factor, plays an important role in carcinogenesis as well as in the regulation of immune and inflammatory responses. NF-kappaB induces the expression of diverse target genes that promote cell proliferation, regulate apoptosis, facilitate angiogenesis and stimulate invasion and metastasis. Furthermore, many cancer cells show aberrant or constitutive NF-kappaB activation which mediates resistance to chemo- and radio-therapy. Therefore, the inhibition of NF-kappaB activation and its signaling pathway offers a potential cancer therapy strategy. In addition, recent studies have shown that NF-kappaB can also play a tumor suppressor role in certain settings. In this review, we focus on the role of NF-kappaB in carcinogenesis and the therapeutic potential of targeting NF-kappaB in cancer therapy.

PKC inhibition is involved in trichosanthin-induced apoptosis in human chronic myeloid leukemia cell line K562

Trichosanthin (TCS), a type I ribosome-inactivating protein, induces cell death in various cell types including several tumor cell lines. However, the mechanism remains largely uncharacterized. In this study, we investigated the possible mechanism underlying its cytotoxicity by using human chronic myeloid leukemia cell line K562. We found that TCS induced apoptosis in K562 cells in a time- and concentration-dependent manner and can be blocked by caspase-3 inhibitors. Interestingly, TCS treatment induced a transient elevation in intracellular calcium concentration and a slow increase in reactive oxygen species production, while calcium chelators and antioxidants had no obvious effect on TCS-induced apoptosis, suggesting that calcium changes and reactive oxygen species may not be involved in TCS-mediated apoptosis in K562 cells. Instead we found that TCS partly inhibited PKC activity. Indeed, the PKC activator, PMA, inhibited while the PKC inhibitor, calphostin c, enhanced TCS-induced apoptosis. These PKC modulators had similar effects on TCS-induced cleavage of caspase-3, and caspase-3 inhibitors prevented calphostin c-enhanced apoptosis induced by TCS. In summary, we conclude that TCS induces apoptosis in K562 cells partly via PKC inhibition and caspase-3 activation.

Differential signaling networks induced by mild and lethal hemorrhagic fever virus infections

The family Arenaviridae includes several National Institutes of Allergy and Infections Diseases category A select agents which cause hemorrhagic fever. There are few vaccines available, and treatment is limited to ribavirin, which varies in efficacy. Development of new antiviral compounds has been hindered by a lack of understanding of the molecular basis of pathogenesis. We used two variants of Pichinde virus, one attenuated and one virulent in the guinea pig model, to delineate the host determinants which lead to either viral clearance or lethal disease. By analyzing protein level changes using pathway analysis, we have identified key intermediates which may be targets for therapeutic intervention.

Protection of glioblastoma cells from cisplatin cytotoxicity via protein kinase Ciota-mediated attenuation of p38 MAP kinase signaling

Glioblastoma multiforme is an aggressive form of brain cancer that responds poorly to chemotherapy and is generally incurable. The basis for the poor response of this cancer to chemotherapy is not well understood. The atypical protein kinases C (PKCiota and PKCzeta) have previously been implicated in leukaemia cell chemoresistance. To assess the role of atypical PKC in glioblastoma cell chemoresistance, RNA interference was used to deplete human glioblastoma cells of PKCiota. Transfection of cells with either of two different RNA duplexes specific for PKCiota caused a partial sensitisation to cell death induced by the chemotherapy agent cisplatin. To screen for possible mechanisms for PKCiota-mediated chemoresistance, microarray analysis of gene expression was performed on RNA from glioblastoma cells that were either untreated or depleted of PKCiota. This identified sets of genes that were regulated either positively or negatively by PKCiota. Within the set of genes that were negatively regulated by PKCiota, the function of the gene coding for GMFbeta, an enhancer of p38 mitogen-activated protein kinase (MAP kinase) signaling, was investigated further, as the p38 MAP kinase pathway has been previously identified as a key mediator of cisplatin cytotoxicity. The expression of both GMFbeta mRNA and protein increased upon PKCiota depletion, and this was accompanied by an increase in cisplatin-activated p38 MAP kinase signaling. Transient overexpression of GMFbeta increased cisplatin-activated p38 MAP kinase signaling and also sensitised cells to cisplatin cytotoxicity. The increase in cisplatin cytotoxicity seen with PKCiota depletion was blocked by the p38 MAP kinase inhibitor SKF86002. These data show that PKCiota can confer partial resistance to cisplatin in glioblastoma cells by suppressing GMFbeta-mediated enhancement of p38 MAP kinase signaling.

Atypical protein kinase C iota is an oncogene in human non-small cell lung cancer

Protein kinase C (PKC) isozymes have long been implicated in carcinogenesis. However, little is known about the functional significance of these enzymes in human cancer. We recently showed that the atypical PKC (aPKC) isozyme PKCiota is overexpressed in human non-small cell lung cancer (NSCLC) cells and that PKCiota plays a critical role in the transformed growth of the human lung adenocarcinoma A549 cell line in vitro and tumorigenicity in vivo. Here we provide compelling evidence that PKCiota is an oncogene in NSCLC based on the following criteria: (a) aPKCiota is overexpressed in the vast majority of primary NSCLC tumors; (b) tumor PKCiota expression levels predict poor survival in patients with NSCLC; (c) the PKCiota gene is frequently amplified in established NSCLC cell lines and primary NSCLC tumors; (d) gene amplification drives PKCiota expression in NSCLC cell lines and primary NSCLC tumors; and (e) disruption of PKCiota signaling with a dominant negative PKCiota allele blocks the transformed growth of human NSCLC cells harboring PKCiota gene amplification. Taken together, our data provide conclusive evidence that PKCiota is required for the transformed growth of NSCLC cells and that the PKCiota gene is a target for tumor-specific genetic alteration by amplification. Interestingly, PKCiota expression predicts poor survival in NSCLC patients independent of tumor stage. Therefore, PKCiota expression profiling may be useful in identifying early-stage NSCLC patients at elevated risk of relapse. Our functional data indicate that PKCiota is an attractive target for development of novel, mechanism-based therapeutics to treat NSCLC.

Atypical protein kinase Ciota plays a critical role in human lung cancer cell growth and tumorigenicity

Atypical protein kinase C (aPKC) isozymes function in epithelial cell polarity, proliferation, and survival and have been implicated in cellular transformation. However, the role of these enzymes in human cancer is largely unexplored. Here, we report that aPKCiota is highly expressed in human non-small cell lung cancer cell lines, whereas the closely related aPKC isozyme PKCzeta is undetectable in these cells. Disruption of PKCiota signaling reveals that PKCiota is dispensable for adherent growth of non-small cell lung cancer cells but is required for transformed growth in soft agar in vitro and for tumorigenicity in vivo. Molecular dissection of signaling down-stream of PKCiota demonstrates that Rac1 is a critical molecular target for PKCiota-dependent transformation, whereas PKCiota is not necessary for NFkappaB activation in vitro or in vivo. Expression of the PB1 domain of PKCiota (PKCiota-(1-113)) blocks PKCiota-dependent Rac1 activity and inhibits cellular transformation indicating a role for this domain in the transforming activity of PKCiota. Taken together, our data demonstrate that PKCiota is a critical lung cancer gene that activates a Rac1-->Pak-->Mek1,2-->Erk1,2 signaling pathway required for transformed growth. Our data indicate that PKCiota may be an attractive molecular target for mechanism-based therapies for treatment of lung cancer.

Novel functions of the phospholipase D2-Phox homology domain in protein kinase Czeta activation

It has been established that protein kinase Czeta (PKCzeta) participates in diverse signaling pathways and cellular functions in a wide variety of cells, exhibiting properties relevant to cellular survival and proliferation. Currently, however, the regulation mechanism of PKCzeta remains elusive. Here, for the first time, we determine that phospholipase D2 (PLD2) enhances PKCzeta activity through direct interaction in a lipase activity-independent manner. This interaction of the PLD2-Phox homology (PX) domain with the PKCzeta-kinase domain also induces the activation loop phosphorylation of PKCzeta and downstream signal stimulation, as measured by p70 S6 kinase phosphorylation. Furthermore, only the PLD2-PX domain directly stimulates PKCzeta activity in vitro, and it is necessary for the formation of the ternary complex with phosphoinositide-dependent kinase 1 and PKCzeta. The mutant that substitutes the triple lysine residues (Lys101, Lys102, and Lys103) within the PLD2-PX domain with alanine abolishes interaction with the PKCzeta-kinase domain and activation of PKCzeta. Moreover, breast cancer cell viability is significantly affected by PLD2 silencing. Taken together, these results suggest that the PLD2-mediated PKCzeta activation is induced by its PX domain performing both direct activation of PKCzeta and assistance of activation loop phosphorylation. Furthermore, we find it is an important factor in the survival of breast cancer cells.

Identification of direct genomic targets downstream of the nuclear factor-kappaB transcription factor mediating tumor necrosis factor signaling

Tumor necrosis factor (TNF) is a pro-inflammatory cytokine that controls expression of inflammatory genetic networks. Although the nuclear factor-kappaB (NF-kappaB) pathway is crucial for mediating cellular TNF responses, the complete spectrum of NF-kappaB-dependent genes is unknown. In this study, we used a tetracycline-regulated cell line expressing an NF-kappaB inhibitor to systematically identify NF-kappaB-dependent genes. A microarray data set generated from a time course of TNF stimulation in the presence or absence of NF-kappaB signaling was analyzed. We identified 50 unique genes that were regulated by TNF (Pr(F)<0.001) and demonstrated a change in signal intensity of+/-3-fold relative to control. Of these, 28 were NF-kappaB-dependent, encoding proteins involved in diverse cellular activities. Quantitative real-time PCR assays of eight characterized NF-kappaB-dependent genes and five genes not previously known to be NF-kappaB-dependent (Gro-beta and-gamma, IkappaBepsilon, interleukin (IL)-7R, and Naf-1) were used to determine whether they were directly or indirectly NF-kappaB regulated. Expression of constitutively active enhanced green fluorescent.NF-kappaB/Rel A fusion protein transactivated all but IL-6 and IL-7R in the absence of TNF stimulation. Moreover, TNF strongly induced all 12 genes in the absence of new protein synthesis. High probability NF-kappaB sites in novel genes were predicted by binding site analysis and confirmed by electrophoretic mobility shift assay. Chromatin immunoprecipitation assays show the endogenous IkappaBalpha/epsilon, Gro-beta/gamma, and Naf-1 promoters directly bound NF-kappaB/Rel A in TNF-stimulated cells. Together, these studies systematically identify the direct NF-kappaB-dependent gene network downstream of TNF signaling, extending our knowledge of biological processes regulated by this pathway.

Nuclear βII-Tubulin Associates with the Activated Notch Receptor to Modulate Notch Signaling

The Notch signal pathway plays important roles in proliferation, apoptosis, and differentiation. Abnormalities in Notch signaling are linked to many human diseases. After ligand binding, Notch signaling is activated through the cleavage of Notch receptors to release and translocate the Notch intracellular domain into the nucleus. The Notch1 receptor intracellular domain (N1IC), the activated form of the Notch1 receptor, can modulate downstream target genes via C promoter-binding factor 1-dependent and -independent pathways. To further dissect the Notch1 signaling pathway, we screened the N1IC-associated proteins using a yeast two-hybrid system and identified nuclear beta(II)-tubulin as a candidate for the N1IC-associated proteins. It was suggested that the presence of beta(II)-tubulin in nuclei might be correlated with the cancerous state of cells. However, the function of beta(II)-tubulin locating in the nucleus still is unknown. Herein, we show that the complex of alpha- and beta(II)-tubulin is associated with N1IC in cancer cells by a coimmunoprecipitation analysis. The ankyrin domain of the Notch1 receptor alone was sufficient to associate with beta(II)-tubulin. Furthermore, alpha- and beta(II)-tubulin were localized in the nucleus and formed a complex with N1IC. Treatment with Taxol increased the amounts of nuclear alpha- and beta(II)-tubulin in K562 and HeLa cells and promoted the C promoter-binding factor 1-dependent transactivation activity of N1IC. We also show that nuclear beta(II)-tubulin was bound on the C promoter-binding factor 1 response elements via the association with N1IC. These results suggest that nuclear beta(II)-tubulin can modulate Notch signaling through interaction with N1IC in cancer cells.

Bryostatin-1 enhances the maturation and antigen-presenting ability of murine and human dendritic cells

In this study, we investigated the effect of bryostatin-1 (Bryo-1), an antineoplastic agent, on dendritic cell (DC) maturation, activation, and functions. Murine bone marrow-derived DCs on culture with Bryo-1 alone, Bryo-1 + calcium ionophore (CI), but not CI alone exhibited morphologic changes characteristic of mature DCs and expressed increased levels of CD40, CD80, and CD86. Moreover, Bryo-1 + CI-treated DCs exhibited enhanced antigen-presenting ability to naive and antigen-specific T cells and alloreactive T cells. Bryo-1 + CI-mediated activation of DCs involved protein kinase C (PKC), especially PKC-alpha, -delta, and -iota, and addition of PKC inhibitors impaired their ability to activate T cells. Bryo-1 + CI treatment of DCs did not activate mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase, p38 MAPK, or stress-activated protein kinase/c-Jun NH2-terminal kinase pathways. Finally, treatment of DCs with Bryo-1 alone and Bryo-1 + CI, but not CI alone, induced nuclear translocation of nuclear factor kappaB as studied by confocal microscopy. DCs generated from human peripheral blood monocytes or from human cord blood CD34+ hematopoietic stem cells, when cultured with Bryo-1 + CI, also showed maturation and increased T-cell stimulatory activity. Bryo-1 + CI was more potent in inducing maturation and activation of DCs when compared with other agents such as tumor necrosis factor alpha, lipopolysaccharide, or phorbol 12-myristate 13-acetate + CI. Collectively, the current study shows for the first time that Bryo-1 alone or in combination with CI may promote the maturation of DCs and therefore may be useful in development of DC-based cancer immunotherapy.

Protein kinase Ciota is required for Ras transformation and colon carcinogenesis in vivo

Protein kinase C ι (PKCι) has been implicated in Ras signaling, however, a role for PKCι in oncogenic Ras-mediated transformation has not been established. Here, we show that PKCι is a critical downstream effector of oncogenic Ras in the colonic epithelium. Transgenic mice expressing constitutively active PKCι in the colon are highly susceptible to carcinogen-induced colon carcinogenesis, whereas mice expressing kinase-deficient PKCι (kdPKCι) are resistant to both carcinogen- and oncogenic Ras-mediated carcinogenesis. Expression of kdPKCι in Ras-transformed rat intestinal epithelial cells blocks oncogenic Ras-mediated activation of Rac1, cellular invasion, and anchorage-independent growth. Constitutively active Rac1 (RacV12) restores invasiveness and anchorage-independent growth in Ras-transformed rat intestinal epithelial cells expressing kdPKCι. Our data demonstrate that PKCι is required for oncogenic Ras- and carcinogen-mediated colon carcinogenesis in vivo and define a procarcinogenic signaling axis consisting of Ras, PKCι, and Rac1.

Bcr-Abl-mediated molecular mechanism for apoptotic suppression in multipotent haemopoietic cells: a role for PKCbetaII

Bcr-Abl protein tyrosine kinase (PTK) activity is a feature of chronic myeloid leukaemia and confers a survival advantage on haemopoietic progenitor cells. We have expressed conditional mutant of the Bcr-Abl PTK in the FDCP-Mix A4 multipotent haematopoietic cell line in order to examine the molecular mechanisms whereby Bcr-Abl PTK leads to enhanced cell survival under conditions in which normal cells die. Activation of Bcr-Abl PTK does not phosphorylate or activate either ERK-1/2 or JAK-2/STAT-5b, suggesting that these signal transduction pathways are not involved in Abl PTK-mediated suppression of apoptosis in FDCP-Mix cells. However, protein kinase C (PKC) does have a role to play. Inhibition of PKC results in a reversal of Bcr-Abl PTK-mediated survival in the absence of growth factor and Bcr-Abl stimulates translocation of the PKCbetaII isoform to the nucleus. Furthermore, expression of a constitutively activated PKCbetaII in haemopoietic progenitor FDCP-Mix cells stimulates enhanced cell survival when IL-3 is withdrawn. However, expression of this constitutively activated PKC isoform does not suppress cytotoxic drug-induced apoptosis. Thus Bcr-Abl PTK has pleiotropic effects which can suppress cell death induced by a number of stimuli.

Genomic Mechanisms of p210BCR-ABL Signaling

Chronic myelogenous leukemia (CML) results from a t(9,22) translocation, producing the p210(BCR-ABL) oncoprotein, a tyrosine kinase that causes transformation and chemotherapy resistance. To further understand mechanisms mediating chemotherapy resistance, we identified 556 differentially regulated genes in HL-60 cells stably expressing p210(BCR-ABL) versus those expressing an empty vector using cDNA macro- and oligonucleotide microarrays. These BCR-ABL-regulated gene products play diverse roles in cellular function including apoptosis, cell cycle regulation, intracellular signaling, transcription, and cellular adhesion. In particular, we identified up-regulation of the inducible form of heat shock protein 70 (Hsp70), and further explored the mechanism for its up-regulation. In HL-60/BCR-ABL and K562 cells (expressing p210(BCR-ABL)), abundant cytoplasmic Hsp70 expression was detected by immunoblot analysis. Moreover, cells isolated from bone marrow aspirates of patients in different stages of CML (chronic, aggressive, and blast crisis) express Hsp70. Expression of p210(BCR-ABL) in BCR-ABL negative cells induced transcription of the proximal Hsp70 promoter. Mutational analysis mapped the major p210(BCR-ABL) responsive element to a high affinity 5'(A/T)GATA(A/G)-3' "GATA" response element (GATA-RE) that binds GATA-1 in CML cells. The GATA-RE was sufficient to confer p210(BCR-ABL)- and p185(BCR-ABL)-mediated trans-activation to an inert promoter. Short interfering RNA mediated "knockdown" of Hsp70 expression in K562 cells induced marked sensitivity to paclitaxel-induced apoptosis. Together these findings indicate that BCR-ABL confers chemotherapeutic resistance through intracellular signaling to the GATA-RE element found in the promoter region of the anti-apoptotic Hsp70 protein. We suggest that down-regulation of the GATA-Hsp70 pathway may be useful in the treatment of chemotherapy-resistant CML.

Modulating protein kinase C (PKC) to increase the efficacy of chemotherapy: stepping into darkness

The identification of molecules that promote chemotherapeutic resistance would allow rationally designed approaches to abrogate this resistance, thereby possibly improving clinical outcomes for patients with cancer. In this regard, the PKC family is attractive for targeting, because it is comprised of a family of isoforms that play key roles in multiple cellular processes and can contribute to cellular transformation. Encouraging in vitro data originally showed that approaches to modulate PKC activity through small-molecule inhibitors or genetic manipulation could affect tumor cell survival. Recently, some of these approaches have begun clinical testing. Early-stage clinical trials revealed scattered clinical responses to these agents, but the most recent clinical trials have shown that combining modulators of PKC with standard chemotherapy does not improve outcome over chemotherapy alone. In this review, we will trace the development of these approaches, and discuss possible explanations for the recent negative results. Importantly, we will suggest guidelines for the clinical evaluation of PKC modulators.

Bcr-Abl regulates protein kinase Ciota (PKCiota) transcription via an Elk1 site in the PKCiota promoter

The protein kinase C (PKC) family of serine/threonine kinases plays an important role in numerous cancer signaling pathways, including those downstream of the bcr-abl oncogene. We demonstrated previously that atypical PKCiota is required for Bcr-Abl-mediated resistance of human K562 chronic myelogenous leukemia (CML) cells to Taxol-induced apoptosis. Here, we report that the pattern of PKC isozyme expression characteristic of CML cells is regulated by Bcr-Abl. When Bcr-Abl was expressed in Bcr-Abl-negative HL-60 promyelocytic leukemia cells, expression of the PKCbetaI, PKCbetaII, and PKCiota genes was induced, whereas expression of the PKCdelta gene was reduced to levels similar to those found in CML cells. Given the importance of PKCiota in Bcr-Abl-mediated transformation, we characterized the mechanism by which Bcr-Abl regulates PKCiota expression. A 1200-bp PKCiota promoter construct isolated from genomic DNA was highly active in Bcr-Abl-positive K562 cells and was activated when Bcr-Abl-negative cells were transfected with Bcr-Abl. Bcr-Abl-mediated induction of the PKCiota promoter was dependent upon MEK1/2 activity, but not phosphatidylinositol 3-kinase or p38 MAPK activity. Mutational analysis of the PKCiota promoter revealed a region between 97 and 114 bp upstream of the transcriptional start site that is responsible for Bcr-Abl-mediated regulation. Mutation of a consensus Elk1-binding site within this region abolished Bcr-Abl-mediated regulation. We conclude that Bcr-Abl regulates PKCiota expression through the MEK-dependent activation of an Elk1 element within the proximal PKCiota promoter. Our results indicate that Bcr-Abl-mediated transformation involves transcriptional activation of the PKCiota gene, which in turn is required for Bcr-Abl-mediated chemoresistance.

NF-kappaB activation plays an antiapoptotic role in human leukemic K562 cells exposed to ionizing radiation

Exposure of cells to ionizing radiation (IR) determines cellular lesions, such as DNA and membrane damage, which involve a coordinate network of signal transduction pathways responsible for resistance to or delay of apoptosis, depending on cell type and administered dose. Since, after IR exposure, the apoptotic profile appeared different in the two chosen cell lines K562 and Jurkat along with caspase-3 activation, we paid attention to the influence exerted by Protein kinase C delta on transcription factor NF-kappaB activation. Interestingly, K562 resist to IR carrying out a survival strategy which includes PKC delta/NF-kappaB pathway activation, probably mediated by novel IKKs and a role for PI-3-kinase in activating PKC delta at Thr 505 by PDK-1 phosphorylation is suggested. In addition, since caspase-3 is not activated in these cells upon ionizing radiation exposure, it could be supposed that NF-kappaB antagonizes apoptosis induction interfering with pathways which lead to caspase activation, may be by inducing expression of IAP, caspases 3, 7, 9, inhibitor. Thus NF-kappaB activation explains the resistance displayed by K562 to IR and drug potential interference directed to this protein could overcome apoptosis resistance in clinical settings.

Involvement of Akt kinase in the action of STI571 on chronic myelogenous leukemia cells

To elucidate the role of mitogen-activated protein kinases (MAPKs) and Akt kinase in leukemogenesis caused by the breakpoint cluster region (BCR)-Abelson (ABL) tyrosine kinase oncoprotein, we examined the activities of MAPKs and Akt kinase and their roles in the action of STI571, a specific inhibitor of BCR-ABL tyrosine kinase, in chronic myelogenous leukemia (CML) cells. We found that extracellular signal-regulated kinase (ERK) 1/2 and Akt kinase are constitutively active in the chronic phase of CML, blast crisis of CML, and the CML-derived K562 cell line. Both interferon-alpha and STI571 suppressed ERK1/2 activity in K562 cells. In contrast, Akt kinase activity was inhibited only by STI571. K562 cell proliferation was markedly suppressed by LY294002, a specific inhibitor of PI3K/Akt kinase, and STI571 but not by PD98059, a specific inhibitor of MEK1/2. In addition, caspase-3 was activated by treatment of cells with STI571 and LY294002 but not with PD98059. These data indicate that Akt kinase may play a role in the proliferation of CML leukemia cells and the action of STI571. Primary leukemia cells from patients with CML blast crisis did not show inhibition of ERK1/2 or Akt kinase activity and were resistant to caspase-3-associated apoptosis after treatment with STI571. These findings suggest that STI571 does not effectively block signaling molecules downstream of the BCR-ABL tyrosine kinase in some cases of CML blast crisis.

Essential role of Src-family protein tyrosine kinases in NF-kappaB activation during B cell development

The nature of signals that govern the development of immunoglobulin heavy chain-dependent B cells is largely unknown. Using mice deficient for the B cell-expressed Src-family protein tyrosine kinases (SFKs) Blk, Fyn and Lyn, we show an essential role of these kinases in pre-B cell receptor (pre-BCR)- mediated NF-kappaB activation and B cell development. This signaling defect is SFK specific, as a deficiency in Syk, which controls pre-B cell development, does not affect NF-kappaB induction. Impaired NF-kappaB induction was overcome by the activation of protein kinase C (PKC)-lambda, thus suggesting the involvement of PKC-lambda in pre-BCR-mediated SFK-dependent activation of NF-kappaB. Our data show the existence of a functionally distinct SFK signaling module responsible for pre-BCR-mediated NF-kappaB activation and B cell development.

Identification of NF-kappaB-dependent gene networks in respiratory syncytial virus-infected cells

Respiratory syncytial virus (RSV) is a mucosa-restricted virus that is a leading cause of epidemic respiratory tract infections in children. In epithelial cells, RSV replication activates nuclear translocation of the inducible transcription factor nuclear factor kappaB (NF-kappaB) through proteolysis of its cytoplasmic inhibitor, IkappaB. In spite of a putative role in mediating virus-inducible gene expression, the spectrum of NF-kappaB-dependent genes induced by RSV infection has not yet been determined. To address this, we developed a tightly regulated cell system expressing a nondegradable, epitope-tagged IkappaBalpha isoform (Flag-IkappaBalpha Mut) whose expression could be controlled by exogenous addition of nontoxic concentrations of doxycycline. Flag-IkappaBalpha Mut expression potently inhibited IkappaBalpha proteolysis, NF-kappaB binding, and NF-kappaB-dependent gene transcription in cells stimulated with the prototypical NF-kappaB-activating cytokine tumor necrosis factor alpha (TNF-alpha) and in response to RSV infection. High-density oligonucleotide microarrays were then used to profile constitutive and RSV-induced gene expression in the absence or presence of Flag-IkappaBalpha Mut. Comparison of these profiles revealed 380 genes whose expression was significantly changed by the dominant-negative NF-kappaB. Of these, 236 genes were constitutive (not RSV regulated), and surprisingly, only 144 genes were RSV regulated, representing numerically approximately 10% of the total population of RSV-inducible genes at this time point. Hierarchical clustering of the 144 RSV- and Flag-IkappaBalpha Mut-regulated genes identified two discrete gene clusters. The first group had high constitutive expression, and its expression levels fell in response to RSV infection. In this group, constitutive mRNA expression was increased by Flag-IkappaBalpha Mut expression, and the RSV-induced decrease in expression was partly inhibited. In the second group, constitutive expression was very low (or undetectable) and, after RSV infection, expression levels strongly increased. In this group, NF-kappaB was required for RSV-inducible expression because Flag-IkappaBalpha Mut expression blocked their induction by RSV. This latter cluster includes chemokines, transcriptional regulators, intracellular proteins regulating translation and proteolysis, and secreted proteins (complement components and growth factor regulators). These data suggest that NF-kappaB action induces global cellular responses after viral infection.

Functional cooperation among Ras, STAT5, and phosphatidylinositol 3-kinase is required for full oncogenic activities of BCR/ABL in K562 cells

BCR/ABL tyrosine kinase generated from the chromosomal translocation t(9;22) causes chronic myelogenous leukemia and acute lymphoblastic leukemia. To examine the roles of BCR/ABL-activated individual signaling molecules and their cooperation in leukemogenesis, we inducibly expressed a dominant negative (DN) form of Ras, phosphatidylinositol 3-kinase, and STAT5 alone or in combination in p210 BCR/ABL-positive K562 cells. The inducibly expressed DN Ras (N17), STAT5 (694F), and DN phosphatidylinositol 3-kinase (Delta p85) inhibited the growth by 90, 55, and 40%, respectively. During the growth inhibition, the expression of cyclin D2 and cyclin D3 was suppressed by N17, 694F, or Delta p85; that of cyclin E by N17; and that of cyclin A by Delta p85. In addition, N17 induced apoptosis in a small proportion of K562, whereas 694F and Delta p85 were hardly effective. In contrast, coexpression of two DN mutants in any combinations induced severe apoptosis. During these cultures, the expression of Bcl-2 was suppressed by N17, 694F, or Delta p85, and that of Bcl-XL by N17. Furthermore, although K562 was resistant to interferon-alpha- and dexamethasone-induced apoptosis, disruption of one pathway by N17, 694F, or Delta p85 sensitized K562 to these reagents. These results suggested that cooperation among these molecules is required for full leukemogenic activities of BCR/ABL.