Suppression of cell migration by protein kinase Cδ

Superbinder based phosphoproteomic landscape revealed PRKCD_pY313 mediates the activation of Src and p38 MAPK to promote TNBC progression

Phosphorylation proteomics is the basis for the study of abnormally activated kinase signaling pathways in breast cancer, which facilitates the discovery of new oncogenic agents and drives the discovery of potential targets for early diagnosis and therapy of breast cancer. In this study, we have explored the aberrantly active kinases in breast cancer development and to elucidate the role of PRKCD_pY313 in triple negative breast cancer (TNBC) progression. We collected 47 pairs of breast cancer and paired far-cancer normal tissues and analyzed phosphorylated tyrosine (pY) peptides by Superbinder resin and further enriched the phosphorylated serine/threonine (pS/pT) peptides using TiO2 columns. We mapped the kinases activity of different subtypes of breast cancer and identified PRKCD_pY313 was upregulated in TNBC cell lines. Gain-of-function assay revealed that PRKCD_pY313 facilitated the proliferation, enhanced invasion, accelerated metastasis, increased the mitochondrial membrane potential and reduced ROS level of TNBC cell lines, while Y313F mutation and low PRKCD_pY313 reversed these effects. Furthermore, PRKCD_pY313 significantly upregulated Src_pY419 and p38_pT180/pY182, while low PRKCD_pY313 and PRKCD_Y313F had opposite effects. Dasatinib significantly inhibited the growth of PRKCD_pY313 overexpression cells, and this effect could be enhanced by Adezmapimod. In nude mice xenograft model, PRKCD_pY313 significantly promoted tumor progression, accompanied by increased levels of Ki-67, Bcl-xl and Vimentin, and decreased levels of Bad, cleaved caspase 3 and ZO1, which was opposite to the trend of Y313F group. Collectively, the heterogeneity of phosphorylation exists in different molecular subtypes of breast cancer. PRKCD_pY313 activates Src and accelerates TNBC progression, which could be inhibited by Dasatinib.

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.

PKCδ deficiency inhibits fetal development and is associated with heart elastic fiber hyperplasia and lung inflammation in adult PKCδ knockout mice

Protein kinase C-delta (PKCδ) has a caspase-3 recognition sequence in its structure, suggesting its involvement in apoptosis. In addition, PKCδ was recently reported to function as an anti-cancer factor. The generation of a PKCδ knockout mouse model indicated that PKCδ plays a role in B cell homeostasis. However, the Pkcrd gene, which is regulated through complex transcription, produces multiple proteins via alternative splicing. Since gene mutations can result in the loss of function of molecular species required for each tissue, in the present study, conditional PKCδ knockout mice lacking PKCδI, II, IV, V, VI, and VII were generated to enable tissue-specific deletion of PKCδ using a suitable Cre mouse. We generated PKCδ-null mice that lacked whole-body expression of PKCδ. PKCδ+/- parental mice gave birth to only 3.4% PKCδ-/- offsprings that deviated significantly from the expected Mendelian ratio (χ2(2) = 101.7, P < 0.001). Examination of mice on embryonic day 11.5 (E11.5) showed the proportion of PKCδ-/- mice implanted in the uterus in accordance with Mendelian rules; however, approximately 70% of the fetuses did not survive at E11.5. PKCδ-/- mice that survived until adulthood showed enlarged spleens, with some having cardiac and pulmonary abnormalities. Our findings suggest that the lack of PKCδ may have harmful effects on fetal development, and heart and lung functions after birth. Furthermore, our study provides a reference for future studies on PKCδ deficient mice that would elucidate the effects of the multiple protein variants in mice and decipher the roles of PKCδ in various diseases.

Identification of an 11-Autophagy-Related-Gene Signature as Promising Prognostic Biomarker for Bladder Cancer Patients

Simple Summary

Human bladder cancer, one of the most common cancers worldwide, is a molecularly heterogenous and complex disease. Identifying novel prognostic biomarkers and establishing new predictive signatures are important for personalized medicine and effective treatment of bladder cancer patients. Autophagy, a cell self-maintenance process that removes damaged organelles and misfolded proteins, displays both tumor promotion and suppression activities. The aim of our study is to investigate the function of autophagy-related genes in bladder cancer with the main focus on their contribution to prognostic outcome. By analyzing data obtained from The Cancer Genome Atlas (TCGA), we identified 32 autophagy-related genes that were highly associated with overall survival of bladder cancer patients. Further statistical assessment established an 11-autophagy-related-gene signature as an effective prognostic biomarker to predict the survival outcomes of bladder cancer patients.

Abstract

Background: Survival rates for highly invasive bladder cancer (BC) patients have been very low, with a 5-year survival rate of 6%. Accurate prediction of tumor progression and survival is important for diagnosis and therapeutic decisions for BC patients. Our study aims to develop an autophagy-related-gene (ARG) signature that helps to predict the survival of BC patients. Methods: RNA-seq data of 403 BC patients were retrieved from The Cancer Genome Atlas Urothelial Bladder Carcinoma (TCGA-BLCA) database. Univariate Cox regression analysis was performed to identify overall survival (OS)-related ARGs. The Lasso Cox regression model was applied to establish an ARG signature in the TCGA training cohort (N = 203). The performance of the 11-gene ARG signature was further evaluated in a training cohort and an independent validation cohort (N = 200) using Kaplan-Meier OS curve analysis, receiver operating characteristic (ROC) analysis, as well as univariate and multivariate Cox regression analysis. Results: Our study identified an 11-gene ARG signature that is significantly associated with OS, including APOL1, ATG4B, BAG1, CASP3, DRAM1, ITGA3, KLHL24, P4HB, PRKCD, ULK2, and WDR45. The ARGs-derived high-risk bladder cancer patients exhibited significantly poor OS in both training and validation cohorts. The prognostic model showed good predictive efficacy, with the area under the ROC curve (AUCs) for 1-year, 3-year, and 5-year overall survival of 0.702 (0.695), 0.744 (0.640), and 0.794 (0.658) in the training and validation cohorts, respectively. A prognostic nomogram, which included the ARGs-derived risk factor, age and stage for eventual clinical translation, was established. Conclusion: We identified a novel ARG signature for risk-stratification and robust prediction of overall survival for BC patients.

Protein kinase C δ-dependent regulation of Ubiquitin-proteasome system function in breast cancer

Besides the crucial role of hyperinsulinemia in the development of breast cancer with Type 2 diabetes mellitus (T2DM), it has been shown that hyperglycemia could contribute to promote cancer progression. A remarkable association within hyperglycemia, PKCδ and Ubiquitin-proteasome system (UPS) has been reported, suggesting that PKCδ may mediate high glucose-induced UPS activation in breast cancer cells. Although the independent effects of PKCδ or UPS on breast cancer and T2DM are increasingly supported by experimental evidence, the complex interactional link between PKCδ and UPS is still unclear. Hence, we focus on the relationship between PKCδ and UPS in breast cancer with T2DM. We hypothesize that PKCδ may have the function to regulate the activity of UPS. Further, we speculate that PKCδ combine with proteasome α2 promoter, that indicate PKCδ regulate the function of UPS by change the composition of proteasome. Therefore, we surmise that PKCδ mediated high glucose-induced UPS activation in breast cancer cells, and specific PKCδ inhibitor rottlerin significantly suppressed elevated glucose induced the activity of UPS. We hope that our paper will stimulate further studies the relationship between PKCδ and UPS, and a new targeted therapy and early medical intervention for PKCδ could be a useful option for breast cancer cases complicated with T2DM or hyperglycemia.

Discovery of a small-molecule protein kinase Cδ-selective activator with promising application in colon cancer therapy

Protein kinase C (PKC) isozymes play major roles in human diseases, including cancer. Yet, the poor understanding of isozymes-specific functions and the limited availability of selective pharmacological modulators of PKC isozymes have limited the clinical translation of PKC-targeting agents. Here, we report the first small-molecule PKCδ-selective activator, the 7α-acetoxy-6β-benzoyloxy-12-O-benzoylroyleanone (Roy-Bz), which binds to the PKCδ-C1-domain. Roy-Bz potently inhibited the proliferation of colon cancer cells by inducing a PKCδ-dependent mitochondrial apoptotic pathway involving caspase-3 activation. In HCT116 colon cancer cells, Roy-Bz specifically triggered the translocation of PKCδ but not other phorbol ester responsive PKCs. Roy-Bz caused a marked inhibition in migration of HCT116 cells in a PKCδ-dependent manner. Additionally, the impairment of colonosphere growth and formation, associated with depletion of stemness markers, indicate that Roy-Bz also targets drug-resistant cancer stem cells, preventing tumor dissemination and recurrence. Notably, in xenograft mouse models, Roy-Bz showed a PKCδ-dependent antitumor effect, through anti-proliferative, pro-apoptotic, and anti-angiogenic activities. Besides, Roy-Bz was non-genotoxic, and in vivo it had no apparent toxic side effects. Collectively, our findings reveal a novel promising anticancer drug candidate. Most importantly, Roy-Bz opens the way to a new era on PKC biology and pharmacology, contributing to the potential redefinition of the structural requirements of isozyme-selective agents, and to the re-establishment of PKC isozymes as feasible therapeutic targets in human diseases.

Co-dependency of PKCδ and K-Ras: inverse association with cytotoxic drug sensitivity in KRAS mutant lung cancer

Recent studies suggest that the presence of a KRAS mutation may be insufficient for defining a clinically homogenous molecular group, as many KRAS mutant tumors lose reliance on K-Ras for survival. Identifying pathways that support K-Ras dependency may define clinically relevant KRAS sub-groups and lead to the identification of new drug targets. We have analyzed a panel of 17 KRAS mutant lung cancer cell lines classified as K-Ras dependent or independent, for co-dependency on PKCδ. We show that functional dependency on K-Ras and PKCδ co-segregate, and that dependency correlates with a more epithelial-like phenotype. Furthermore, we show that the pro-apoptotic and pro-tumorigenic functions of PKCδ also segregate based on K-Ras dependency, as K-Ras independent cells are more sensitive to topoisomerase inhibitors, and depletion of PKCδ in this sub-group suppresses apoptosis through increased activation of ERK. In contrast, K-Ras dependent lung cancer cells are largely insensitive to topoisomerase inhibitors, and depletion of PKCδ can increase apoptosis and decrease activation of ERK in this sub-group. We have previously shown that nuclear translocation of PKCδ is necessary and sufficient for pro-apoptotic signaling. Our current studies show that K-Ras dependent cells are refractive to PKCδ driven apoptosis. Analysis of this sub-group showed increased PKCδ expression and an increase in the nuclear:cytoplasmic ratio of PKCδ. In addition, targeting PKCδ to the nucleus induces apoptosis in K-Ras independent, but not K-Ras dependent NSCLC cells. Our studies provide tools for identification of the subset of patients with KRAS mutant tumors most amenable to targeting of the K-Ras pathway, and identify PKCδ as a potential target in this tumor population. These sub-groups are likely to be of clinical relevance, as high PKCδ expression correlates with increased overall survival and a more epithelial tumor phenotype in patients with KRAS mutant lung adenocarcinomas.

OSU-2S/Sorafenib Synergistic Antitumor Combination against Hepatocellular Carcinoma: The Role of PKCδ/p53

Background: Sorafenib (Nexavar^®) is an FDA-approved systemic therapy for advanced hepatocellular carcinoma (HCC). However, the low efficacy and adverse effects at high doses limit the clinical application of sorafenib and strongly recommend its combination with other agents aiming at ameliorating its drawbacks. OSU-2S, a PKCδ activator, was selected as a potential candidate anticancer agent to be combined with sorafenib to promote the anti-cancer activity through synergistic interaction. Methods: The antitumor effects of sorafenib, OSU-2S and their combination were assessed by MTT assay, caspase activation, Western blotting, migration/invasion assays in four different HCC cell lines. The synergistic interactions were determined by Calcusyn analysis. PKCδ knockdown was used to elucidate the role of PKCδ activation as a mechanism for the synergy. The knockdown/over-expression of p53 was used to explain the differential sensitivity of HCC cell lines to sorafenib and/or OSU-2S. Results: OSU-2S synergistically enhanced the anti-proliferative effects of sorafenib in the four used HCC cell lines with combination indices <1. This effect was accompanied by parallel increases in caspase 3/7 activity, PARP cleavage, PKCδ activation and inhibition of HCC cell migration/invasion. In addition, PKCδ knockdown abolished the synergy between sorafenib and OSU-2S. Furthermore, p53 restoration in Hep3B cells through the over-expression rendered them more sensitive to both agents while p53 knockdown from HepG2 cells increased their resistance to both agents. Conclusion: OSU-2S augments the anti-proliferative effect of sorafenib in HCC cell lines, in part, through the activation of PKCδ. The p53 status in HCC cells predicts their sensitivity toward both sorafenib and OSU-2S. The proposed combination represents a therapeutically relevant approach that can lead to a new HCC therapeutic protocol.

The role of T-box genes in the tumorigenesis and progression of cancer

The T-box (TBX) genes are part of an evolutionarily conserved family of transcription factors involved in organ development. They serve key roles in a number of molecular mechanisms, including proliferation, cell fate and organ identity. In addition, previous studies suggest that TBX genes have essential functions in the tumorigenesis and progression of various types of cancer. For example, TBX proteins served significant roles in carcinogenesis, proliferation and differentiation, senescence and apoptosis, invasion and migration, mesenchymal-epithelial and epithelial-mesenchymal transition, oncogenic signaling pathways and drug sensitivity. However, the exact mechanisms by which TBX genes carry out these functions have not yet been fully elucidated. The present review focuses on the role of TBX genes in cancer, with the aim of further clarifying their function. As altered levels of TBX proteins have detrimental consequences in numerous types of cancer, there is a need for further research into TBX genes, which this review may aid through providing a comprehensive insight into the topic.

Multifunctional roles of PKCδ: Opportunities for targeted therapy in human disease

The serine-threonine protein kinase, protein kinase C-δ (PKCδ), is emerging as a bi-functional regulator of cell death and proliferation. Studies in PKCδ-/- mice have confirmed a pro-apoptotic role for this kinase in response to DNA damage and a tumor promoter role in some oncogenic contexts. In non-transformed cells, inhibition of PKCδ suppresses the release of cytochrome c and caspase activation, indicating a function upstream of apoptotic pathways. Data from PKCδ-/- mice demonstrate a role for PKCδ in the execution of DNA damage-induced and physiologic apoptosis. This has led to the important finding that inhibitors of PKCδ can be used therapeutically to reduce irradiation and chemotherapy-induced toxicity. By contrast, PKCδ is a tumor promoter in mouse models of mammary gland and lung cancer, and increased PKCδ expression is a negative prognostic indicator in Her2+ and other subtypes of human breast cancer. Understanding how these distinct functions of PKCδ are regulated is critical for the design of therapeutics to target this pathway. This review will discuss what is currently known about biological roles of PKCδ and prospects for targeting PKCδ in human disease.

Synthesis and biological activities of the amide derivative of aplog-1, a simplified analog of aplysiatoxin with anti-proliferative and cytotoxic activities

Aplog-1 is a simplified analog of the tumor-promoting aplysiatoxin with anti-proliferative and cytotoxic activities against several cancer cell lines. Our recent findings have suggested that protein kinase Cδ (PKCδ) could be one of the target proteins of aplog-1. In this study, we synthesized amide-aplog-1 (3), in which the C-1 ester group was replaced with an amide group, to improve chemical stability in vivo. Unfortunately, 3 exhibited seventy-fold weaker binding affinity to the C1B domain of PKCδ than that of aplog-1, and negligible anti-proliferative and cytotoxic activities even at 10(-4) M. A conformational analysis and density functional theory calculations indicated that the stable conformation of 3 differed from that of aplog-1. Since 27-methyl and 27-methoxy derivatives (1, 2) without the ability to bind to PKC isozymes exhibited marked anti-proliferative and cytotoxic activities at 10(-4) M, 3 may be an inactive control to identify the target proteins of aplogs.

Protein kinase C and cancer: what we know and what we do not

Since their discovery in the late 1970s, protein kinase C (PKC) isozymes represent one of the most extensively studied signaling kinases. PKCs signal through multiple pathways and control the expression of genes relevant for cell cycle progression, tumorigenesis and metastatic dissemination. Despite the vast amount of information concerning the mechanisms that control PKC activation and function in cellular models, the relevance of individual PKC isozymes in the progression of human cancer is still a matter of controversy. Although the expression of PKC isozymes is altered in multiple cancer types, the causal relationship between such changes and the initiation and progression of the disease remains poorly defined. Animal models developed in the last years helped to better understand the involvement of individual PKCs in various cancer types and in the context of specific oncogenic alterations. Unraveling the enormous complexity in the mechanisms by which PKC isozymes have an impact on tumorigenesis and metastasis is key for reassessing their potential as pharmacological targets for cancer treatment.

Protein Kinase C (PKC) Isozymes and Cancer

Protein kinase C (PKC) is a family of phospholipid-dependent serine/threonine kinases, which can be further classified into three PKC isozymes subfamilies: conventional or classic, novel or nonclassic, and atypical. PKC isozymes are known to be involved in cell proliferation, survival, invasion, migration, apoptosis, angiogenesis, and drug resistance. Because of their key roles in cell signaling, PKC isozymes also have the potential to be promising therapeutic targets for several diseases, such as cardiovascular diseases, immune and inflammatory diseases, neurological diseases, metabolic disorders, and multiple types of cancer. This review primarily focuses on the activation, mechanism, and function of PKC isozymes during cancer development and progression.

Protein kinase C pharmacology: refining the toolbox

PKC (protein kinase C) has been in the limelight since the discovery three decades ago that it acts as a major receptor for the tumour-promoting phorbol esters. Phorbol esters, with their potent ability to activate two of the three classes of PKC isoenzymes, have remained the best pharmacological tool for directly modulating PKC activity. However, with the discovery of other phorbol ester-responsive proteins, the advent of various small-molecule and peptide modulators, and the need to distinguish isoenzyme-specific activity, the pharmacology of PKC has become increasingly complex. Not surprisingly, many of the compounds originally touted as direct modulators of PKC have subsequently been shown to hit many other cellular targets and, in some cases, not even directly modulate PKC. The complexities and reversals in PKC pharmacology have led to widespread confusion about the current status of the pharmacological tools available to control PKC activity. In the present review, we aim to clarify the cacophony in the literature regarding the current state of bona fide and discredited cellular PKC modulators, including activators, small-molecule inhibitors and peptides, and also address the use of genetically encoded reporters and of PKC mutants to measure the effects of these drugs on the spatiotemporal dynamics of signalling by specific isoenzymes.

Protein kinase Cδ is required for ErbB2-driven mammary gland tumorigenesis and negatively correlates with prognosis in human breast cancer

Protein kinase C δ (PKCδ) regulates apoptosis in the mammary gland, however, the functional contribution of PKCδ to the development or progression of breast cancer has yet to be determined. Meta-analysis of ErbB2-positive breast cancers shows increased PKCδ expression, and a negative correlation between PKCδ expression and prognosis. Here, we present in-vivo evidence that PKCδ is essential for the development of mammary gland tumors in a ErbB2-overexpressing transgenic mouse model, and in-vitro evidence that PKCδ is required for proliferative signaling downstream of the ErbB2 receptor. Mouse mammary tumor virus (MMTV)-ErbB2 mice lacking PKCδ (δKO) have increased tumor latency compared with MMTV-ErbB2 wild-type (δWT) mice, and the tumors show a dramatic decrease in Ki-67 staining. To explore the relationship between PKCδ and ErbB2-driven proliferation more directly, we used MCF-10A cells engineered to express a synthetic ligand-inducible form of the ErbB2 receptor. Depletion of PKCδ with short hairpin RNA inhibited ligand-induced growth in both two-dimensional (2D) (plastic) and three-dimensional (3D) (Matrigel) culture, and correlated with decreased phosphorylation of the ErbB2 receptor and reduced activation of Src and MAPK/ERK pathways. Similarly, in human breast cancer cell lines in which ErbB2 is overexpressed, depletion of PKCδ suppresses proliferation, Src and ERK activation. PKCδ appears to drive proliferation through the formation of an active ErbB2/PKCδ/Src signaling complex, as depletion of PKCδ disrupts association of Src with the ErbB2 receptor. Taken together, our studies present the first evidence that PKCδ is a critical regulator of ErbB2-mediated tumorigenesis, and suggest further investigation of PKCδ as a target in ErbB2-positive breast cancer.

Inhibition of S6 kinase suppresses the apoptotic effect of eIF4E ablation by inducing TGF-β-dependent G1 cell cycle arrest

The mammalian target of rapamycin complex 1 (mTORC1) is a critical regulator of cap-dependent translation through its direct activation of ribosomal protein p70 S6 kinase (S6 kinase) and indirect activation of eukaryotic initiation factor 4E (eIF4E). We recently reported that inhibition of eIF4E expression caused apoptosis in cancer cells in the absence of serum. This was indicated by treatment with the mTORC1 inhibitor rapamycin, which suppressed both S6 kinase and 4E-BP1 phosphorylation (dephosphorylated 4E-BP1 binds and inactivates eIF4E), or by knockdown of eIF4E. We report here that knockdown of eIF4E also causes apoptosis in the presence of serum. This was unexpected because rapamycin induces G1 cell cycle arrest in the presence of serum. Upon investigation, we have found that inactivated S6 kinase prevents the apoptotic effect observed by singular knockdown of eIF4E and results in G1 cell cycle arrest. This effect is dependent on TGF-β (transforming growth factor-β) signaling which contributes to G1 cell cycle arrest. Suppression of S6 kinase phosphorylation alone is insufficient to mediate cell cycle arrest, indicating that complete G1 cell cycle arrest is due to suppression of both S6 kinase and eIF4E. These data indicate that the cytostatic effect of rapamycin is suppression of both S6 kinase and eIF4E, while the cytotoxic effects are due suppression of eIF4E in the absence of S6 kinase-dependent activation of TGF-β signals. Our findings place an importance on the evaluating the activity/expression level of S6 kinase and eIF4E as readouts for rapamycin/rapalog efficacy.

Involvement of distinct PKC gene products in T cell functions

It is well established that members of the protein kinase C (PKC) family seem to have important roles in T cells. Focusing on the physiological and non-redundant PKC functions established in primary mouse T cells via germline gene-targeting approaches, our current knowledge defines two particularly critical PKC gene products, PKCθ and PKCα, as the "flavor of PKC" in T cells that appear to have a positive role in signaling pathways that are necessary for full antigen receptor-mediated T cell activation ex vivo and T cell-mediated immunity in vivo. Consistently, in spite of the current dogma that PKCθ inhibition might be sufficient to achieve complete immunosuppressive effects, more recent results have indicated that the pharmacological inhibition of PKCθ, and additionally, at least PKCα, appears to be needed to provide a successful approach for the prevention of allograft rejection and treatment of autoimmune diseases.

Regulated binding of importin-α to protein kinase Cδ in response to apoptotic signals facilitates nuclear import

PKCδ translocates into the nucleus in response to apoptotic agents and functions as a potent cell death signal. Cytoplasmic retention of PKCδ and its transport into the nucleus are essential for cell homeostasis, but how these processes are regulated is poorly understood. We show that PKCδ resides in the cytoplasm in a conformation that precludes binding of importin-α. A structural model of PKCδ in the inactive state suggests that the nuclear localization sequence (NLS) is prevented from binding to importin-α through intramolecular contacts between the C2 and catalytic domains. We have previously shown that PKCδ is phosphorylated on specific tyrosine residues in response to apoptotic agents. Here, we show that phosphorylation of PKCδ at Tyr-64 and Tyr-155 results in a conformational change that allows exposure of the NLS and binding of importin-α. In addition, Hsp90 binds to PKCδ with similar kinetics as importin-α and is required for the interaction of importin-α with the NLS. Finally, we elucidate a role for a conserved PPxxP motif, which overlaps the NLS, in nuclear exclusion of PKCδ. Mutagenesis of the conserved prolines to alanines enhanced importin-α binding to PKCδ and induced its nuclear import in resting cells. Thus, the PPxxP motif is important for maintaining a conformation that facilitates cytosplasmic retention of PKCδ. Taken together, this study establishes a novel mechanism that retains PKCδ in the cytoplasm of resting cells and regulates its nuclear import in response to apoptotic stimuli.

Signaling network state predicts twist-mediated effects on breast cell migration across diverse growth factor contexts

Epithelial-mesenchymal transition (EMT), whether in developmental morphogenesis or malignant transformation, prominently involves modified cell motility behavior. Although major advances have transpired in understanding the molecular pathways regulating the process of EMT induction per se by certain environmental stimuli, an important outstanding question is how the activities of signaling pathways governing motility yield the diverse movement behaviors characteristic of pre-induction versus postinduction states across a broad landscape of growth factor contexts. For the particular case of EMT induction in human mammary cells by ectopic expression of the transcription factor Twist, we found the migration responses to a panel of growth factors (EGF, HRG, IGF, HGF) dramatically disparate between confluent pre-Twist epithelial cells and sparsely distributed post-Twist mesenchymal cells—but that a computational model quantitatively integrating multiple key signaling node activities could nonetheless account for this full range of behavior. Moreover, motility in both conditions was successfully predicted a priori for an additional growth factor (PDGF) treatment. Although this signaling network state model could comprehend motility behavior globally, modulation of the network interactions underlying the altered pathway activities was identified by ascertaining differences in quantitative topological influences among the nodes between the two conditions.

Loss of protein kinase C delta alters mammary gland development and apoptosis

As apoptotic pathways are commonly deregulated in breast cancer, exploring how mammary gland cell death is regulated is critical for understanding human disease. We show that primary mammary epithelial cells from protein kinase C delta (PKCδ) −/− mice have a suppressed response to apoptotic agents in vitro. In the mammary gland in vivo, apoptosis is critical for ductal morphogenesis during puberty and involution following lactation. We have explored mammary gland development in the PKCδ −/− mouse during these two critical windows. Branching morphogenesis was altered in 4- to 6-week-old PKCδ −/− mice as indicated by reduced ductal branching; however, apoptosis and proliferation in the terminal end buds was unaltered. Conversely, activation of caspase-3 during involution was delayed in PKCδ −/− mice, but involution proceeded normally. The thymus also undergoes apoptosis in response to physiological signals. A dramatic suppression of caspase-3 activation was observed in the thymus of PKCδ −/− mice treated with irradiation, but not mice treated with dexamethasone, suggesting that there are both target- and tissue-dependent differences in the execution of apoptotic pathways in vivo. These findings highlight a role for PKCδ in both apoptotic and nonapoptotic processes in the mammary gland and underscore the redundancy of apoptotic pathways in vivo.

PMA-induced up-regulation of TBX3 is mediated by AP-1 and contributes to breast cancer cell migration

The T-box transcription factor TBX3 provides an important link between embryonic development and cancer. TBX3 mediates limb, mammary gland and heart development and, in humans, mutations resulting in haplo-insufficiency of TBX3 lead to ulnar-mammary syndrome. Importantly, the de-regulation of TBX3 gene expression has been linked to several cancers, where it acts to suppress senescence and promotes proliferation and tumour invasion. Despite the negative impact of de-regulated TBX3 expression as seen by developmental defects and cancer, surprisingly little is known about the regulation of the TBX3 gene. In the present paper, we show that the phorbol ester PMA increases TBX3 protein and mRNA levels in a protein kinase C-dependent manner via the AP-1 (activator protein 1) transcription factors c-Jun and JunB. Furthermore, these AP-1 factors are shown to mediate the activation of the TBX3 gene by binding a non-consensus PMA-response element in the TBX3 promoter in vitro and in vivo. We also demonstrate that TBX3 contributes to the PMA-induced migration previously observed for the MCF-7 breast epithelium cancer cell line. Our present results reveal a previously unidentified pathway that up-regulates TBX3 expression and provides additional evidence that increased levels of TBX3 contribute to metastasis.

Rottlerin inhibits migration of follicular thyroid carcinoma cells by PKCdelta-independent destabilization of the focal adhesion complex

This study examined the effect of rottlerin on the focal adhesion-mediated cell migration of CGTH W-2 human follicular thyroid carcinoma cells. Rottlerin (10 microM) resulted in decreased adhesion of CGTH W-2 cells to matrix substance, which was correlated with metastatic potential. Rottlerin treatment also resulted in a marked reduction in the migration of CGTH W-2 cells. Protein levels of integrin beta1, FAK, and paxillin were decreased by rottlerin. Consistent with this, immunostaining of FAK, vinculin, and paxillin revealed disassembly of the focal adhesions. Disruption of actin stress fibers was noted, which was compatible with reduced expression levels and activities of Rac-1 and Rho. The effect of rottlerin on cell migration was not attributable to inhibition of PKCdelta activity since siRNA knockdown of PKCdelta did not recapitulate the effects of rottlerin on cell adhesion and migration. Furthermore, activation of PKCdelta by phorbol esters failed to restore the rottlerin-inhibited migratory ability. The mitochondrial uncoupler, carbonylcyanide-4-(trifluoromethoxy)-phenylhydrazone, was able to mimic several rottlerin's effects. In summary, we demonstrated that rottlerin inhibits the migration of CGTH W-2 cells by disassembly of focal adhesion complexes in a PKCdelta-independent manner, and might play as a mitochondrial uncoupler role in these events.

Protein kinase Cdelta-mediated phosphorylation of phospholipase D controls integrin-mediated cell spreading

Integrin signaling plays critical roles in cell adhesion, spreading, and migration, and it is generally accepted that to regulate these integrin functions accurately, localized actin remodeling is required. However, the molecular mechanisms that control the targeting of actin regulation molecules to the proper sites are unknown. We previously demonstrated that integrin-mediated cell spreading and migration on fibronectin are dependent on the localized activation of phospholipase D (PLD). However, the mechanism underlying PLD activation by integrin is largely unknown. Here we demonstrate that protein kinase Cδ (PKCδ) is required for integrin-mediated PLD signaling. After integrin stimulation, PKCδ is activated and translocated to the edges of lamellipodia, where it colocalizes with PLD2. The abrogation of PKCδ activity inhibited integrin-induced PLD activation and cell spreading. Finally, we show that Thr566 of PLD2 is directly phosphorylated by PKCδ and that PLD2 mutation in this region prevents PLD2 activation, PLD2 translocation to the edge of lamellipodia, Rac translocation, and cell spreading after integrin activation. Together, these results suggest that PKCδ is a primary regulator of integrin-mediated PLD activation via the direct phosphorylation of PLD, which is essential for directing integrin-induced cell spreading.

Significance of host cell kinases in herpes simplex virus type 1 egress and lamin-associated protein disassembly from the nuclear lamina

The nuclear lamina is thought to be a steric barrier to the herpesvirus capsid. Disruption of the lamina accompanied by phosphorylation of lamina proteins is a conserved feature of herpesvirus infection. In HSV-1-infected cells, protein kinase C (PKC) alpha and delta isoforms are recruited to the nuclear membrane and PKC delta has been implicated in phosphorylation of emerin and lamin B. We tested two critical hypotheses about the mechanism and significance of lamina disruption. First, we show that chemical inhibition of all PKC isoforms reduced viral growth five-fold and inhibited capsid egress from the nucleus. However, specific inhibition of either conventional PKCs or PKC delta does not inhibit viral growth. Second, we show hyperphosphorylation of emerin by viral and cellular kinases is required for its disassociation from the lamina. These data support hypothesis that phosphorylation of lamina components mediates lamina disruption during HSV nuclear egress.

Emerging biomarkers in breast cancer care

Currently, decision-making for breast cancer treatment in the clinical setting is mainly based on clinical data, histomorphological features of the tumor tissue and a few cancer biomarkers such as steroid hormone receptor status (estrogen and progesterone receptors) and oncoprotein HER2 status. Although various therapeutic options were introduced into the clinic in recent decades, with the objective of improving surgery, radiotherapy, biochemotherapy and chemotherapy, varying response of individual patients to certain types of therapy and therapy resistance is still a challenge in breast cancer care. Therefore, since breast cancer treatment should be based on individual features of the patient and her tumor, tailored therapy should be an option by integrating cancer biomarkers to define patients at risk and to reliably predict their course of the disease and/or response to cancer therapy. Recently, candidate-marker approaches and genome-wide transcriptomic and epigenetic screening of different breast cancer tissues and bodily fluids resulted in new promising biomarker panels, allowing breast cancer prognosis, prediction of therapy response and monitoring of therapy efficacy. These biomarkers are now subject of validation in prospective clinical trials.

Protein kinase C-delta is involved in the inflammatory effect of IL-6 in mouse adipose cells

AIMS/HYPOTHESIS

The aim of the study was to address the role of protein kinase C-delta (PKCdelta) on phosphorylation of signal transducer and activator of transcription 3 (STAT3) and activation of inflammatory genes in response to IL-6 in adipose cells.

METHODS

Differentiated mouse 3T3-L1 adipocytes preincubated with the PKCdelta inhibitor rottlerin and mouse embryonic fibroblasts (MEFs) lacking PKCdelta were incubated with IL-6 and/or insulin. RNA was extracted and the gene expression was analysed by real-time PCR, while the proteins from total, nuclear and cytoplasmic lysates were analysed by immunoblotting.

RESULTS

Inhibition of PKCdelta by rottlerin significantly reduced both Ser-727 and Tyr-705 phosphorylation of STAT3. Consequently, nuclear translocation of STAT3 and the IL-6-induced gene transcription and protein release of the inflammatory molecule serum amyloid A 3 (SAA3) were reduced. Similarly, the IL-6-regulated gene transcription of Il-6 (also known as Il6) to Hp and the feedback inhibitor of IL-6, Socs3, were also attenuated by rottlerin. Furthermore, PKCdelta was found to translocate to the nucleus following IL-6 treatment and this was also reduced by rottlerin. In agreement with the effect of rottlerin, Pkcdelta (also known as Prkcd) ( -/- ) MEFs also displayed a markedly reduced ability of IL-6 to activate the transcription of Saa3, Hp, Socs3 and Il6 genes compared with wild-type MEFs. These results correlated with a reduced nuclear translocation and phosphorylation of STAT3.

CONCLUSIONS/INTERPRETATION

These results show that PKCdelta plays a key role in the inflammatory effect of IL-6 in adipose cells and may be a suitable target for novel anti-inflammatory agents.

PKC Delta (PKCdelta) promotes tumoral progression of human ductal pancreatic cancer

OBJECTIVE

Our objective was to study the role of protein kinase C delta (PKCdelta) in the progression of human pancreatic carcinoma.

METHODS

Protein kinase C delta expression in human ductal carcinoma (n = 22) was studied by immunohistochemistry. We analyzed the effect of PKCdelta overexpression on in vivo and in vitro properties of human ductal carcinoma cell line PANC1.

RESULTS

Human ductal carcinomas showed PKCdelta overexpression compared with normal counterparts. In addition, in vitro PKCdelta-PANC1 cells showed increased anchorage-independent growth and higher resistance to serum starvation and to treatment with cytotoxic drugs. Using pharmacological inhibitors, we determined that phosphatidylinositol-3-kinase and extracellular receptor kinase pathways were involved in the proliferation of PKCdelta-PANC1. Interestingly, PKCdelta-PANC1 cells showed a less in vitro invasive ability and an impairment in their ability to migrate and to secrete the proteolytic enzyme matrix metalloproteinase-2. In vivo experiments indicated that PKCdelta-PANC1 cells were more tumorigenic, as they developed tumors with a significantly lower latency and a higher growth rate with respect to the tumors generated with control cells. Besides, only PKCdelta-PANC1 cells developed lung metastasis.

CONCLUSION

Our results showed that the overexpression of PKCdelta in PANC1 cells induced a more malignant phenotype in vivo, probably through the modulation of cell proliferation and survival, involving phosphatidylinositol-3-kinase and extracellular receptor kinase signaling pathways.

Antioxidant-induced modification of INrf2 cysteine 151 and PKC-delta-mediated phosphorylation of Nrf2 serine 40 are both required for stabilization and nuclear translocation of Nrf2 and increased drug resistance

Antioxidants cause dissociation of nuclear factor erythroid 2-related factor 2 (Nrf2) from inhibitor of Nrf2 (INrf2) and so Nrf2:INrf2 can serve as a sensor of oxidative stress. Nrf2 translocates to the nucleus, binds to antioxidant response element (ARE) and activates defensive gene expression, which protects cells. Controversies exist regarding the role of antioxidant-induced modification of INrf2 cysteine 151 or protein kinase C (PKC)-mediated phosphorylation of Nrf2 serine 40 in the release of Nrf2 from INrf2. In addition, the PKC isoform that phosphorylates Nrf2S40 remains unknown. Here, we demonstrate that antioxidant-induced PKC-delta-mediated phosphorylation of Nrf2S40 leads to release of Nrf2 from INrf2. This was evident from specific chemical inhibitors of PKC isoenzymes in reporter assays, in vitro kinase assays with purified Nrf2 and PKC isoenzymes, in vivo analysis with dominant-negative mutants and siRNA against PKC isoforms, use of PKC-delta(+/+) and PKC-delta(-/-) cells, and use of Nrf2S40 phospho-specific antibody. The studies also showed that antioxidant-induced INrf2C151 modification was insufficient for the dissociation of Nrf2 from INrf2. PKC-delta-mediated Nrf2S40 phosphorylation was also required. Nrf2 and mutant Nrf2S40A both bind to INrf2. However, antioxidant treatment led to release of Nrf2 but not Nrf2S40A from INrf2. In addition, Nrf2 and mutant Nrf2S40A both failed to dissociate from mutant INrf2C151A. Furthermore, antioxidant-induced ubiquitylation of INrf2 in PKC-delta(+/+) and PKC-delta(-/-) cells occurred, but Nrf2 failed to be released in PKC-delta(-/-) cells. The antioxidant activation of Nrf2 reduced etoposide-mediated DNA fragmentation and promoted cell survival in PKC-delta(+/+) but not in PKC-delta(-/-) cells. These data together demonstrate that both modification of INrf2C151 and PKC-delta-mediated phosphorylation of Nrf2S40 play crucial roles in Nrf2 release from INrf2, antioxidant induction of defensive gene expression, promoting cell survival, and increasing drug resistance.

Protein kinase C isoforms: Multi-functional regulators of cell life and death

The protein kinase C (PKC) family consists of 10 related serine/threonine protein kinases some of which are critical regulators of cell proliferation, survival and cell death. While early studies relied on broad spectrum chemical activators or inhibitors of this family, the generation of isoform specific tools has greatly facilitated our understanding of the contribution of specific PKC isoforms to cell proliferation and apoptosis. These studies suggest that PKC-alpha, PKC-epsilon, and the atypical PKC's, PKC-lambda/iota and PKC-zeta, preferentially function to promote cell proliferation and survival, while the novel isoform, PKC-delta is an important regulator of apoptosis. The essential role of this kinase family in both cell survival and apoptosis suggests that specific isoforms may function as molecular sensors, promoting cell survival or cell death depending on environmental cues. Given their central role in cell and tissue homeostasis, it is not surprising that the expression or activity of some of these kinases is altered in human diseases, particularly cancer.

Defective TGF-beta signaling sensitizes human cancer cells to rapamycin

mTOR, the mammalian target of rapamycin, is a critical target of survival signals in many human cancers. In the absence of serum, rapamycin induces apoptosis in MDA-MB-231 human breast cancer cells. However, in the presence of serum, rapamycin induces G(1) cell cycle arrest-indicating that a factor(s) in serum suppresses rapamycin-induced apoptosis. We report here that transforming growth factor-beta (TGF-beta) suppresses rapamycin-induced apoptosis in serum-deprived MDA-MB-231 cells in a protein kinase Cdelta (PKCdelta)-dependent manner. Importantly, if TGF-beta signaling or PKCdelta was suppressed, rapamycin induced apoptosis rather than G(1) arrest in the presence of serum. And, if cells were allowed to progress into S phase, rapamycin induced apoptosis in the presence of serum. BT-549 and MDA-MB-468 breast, and SW-480 colon cancer cells have defects in TGF-beta signaling and rapamycin induced apoptosis in these cells in the presence of either serum or TGF-beta. Thus, in the absence of TGF-beta signaling, rapamycin becomes cytotoxic rather than cytostatic. Importantly, this study provides evidence indicating that tumors with defective TGF-beta signaling--common in colon and pancreatic cancers--will be selectively sensitive to rapamycin or other strategies that target mTOR.

Protein kinase C delta inhibits the production of proteolytic enzymes in murine mammary cells

In previous studies we have determined that protein kinase C (PKC) delta, a widely expressed member of the novel PKC serine-threonine kinases, induces in vitro changes associated with the acquisition of a malignant phenotype in NMuMG murine mammary cells. In this study we show that PKCdelta overexpression significantly decreases urokinase-type plasminogen activator (uPA) and matrix metalloproteinase-9 (MMP-9) production, two proteases associated with migratory and invasive capacities. This effect is markedly enhanced by treatment with phorbol 12-myristate 13-acetate (PMA). On the other hand, depletion of PKCdelta using RNAi led to a marked increase in both uPA and MMP-9 secretion, suggesting a physiological role for PKCdelta in controlling protease secretion. The MEK-1 inhibitor PD98059 reverted the characteristic pattern of proteases secretion and phospho-ERK1/2 up-regulation observed in PKCdelta overexpressors, suggesting that the PKCdelta effect is mediated by the MEK/ERK pathway. Our results suggest a dual role for PKCdelta in murine mammary cell cancer progression. While this kinase clearly promotes mitogenesis and favors malignant transformation, it also down-modulates the secretion of proteases probably limiting metastatic dissemination.

Protein kinase C and other diacylglycerol effectors in cancer

Almost three decades after the discovery of protein kinase C (PKC), we still have only a partial understanding of how this family of serine/threonine kinases is involved in tumour promotion. PKC isozymes - effectors of diacylglycerol (DAG) and the main targets of phorbol-ester tumour promoters - have important roles in cell-cycle regulation, cellular survival, malignant transformation and apoptosis. How do PKC isozymes regulate these diverse cellular processes and what are their contributions to carcinogenesis? Moreover, what is the contribution of all phorbol-ester effectors, which include PKCs and small G-protein regulators? We now face the challenge of dissecting the relative contribution of each DAG signal to cancer progression.

Phosphorylation of adducin by protein kinase Cdelta promotes cell motility

Protein kinase Cdelta (PKCdelta) has been implicated to play a crucial role in cell proliferation, differentiation and apoptosis. In this study, we have investigated the role of PKCdelta in cell motility using Madin-Darby canine kidney cells. Overexpression of PKCdelta promoted membrane protrusions, concomitant with increased cell motility. By contrast, suppression of PKCdelta expression by RNA interference inhibited cell motility. Moreover, a fraction of PKCdelta was detected at the edge of membrane protrusions in which it colocalized with adducin, a membrane skeletal protein whose phosphorylation state is important for remodeling of the cortical actin cytoskeleton. Elevated expression of PKCdelta correlated with increased phosphorylation of adducin at Ser726 in intact cells. In vitro, PKCdelta, but not PKCalpha, directly phosphorylated the Ser726 of adducin. Finally, we demonstrated that overexpression of both adducin and PKCdelta could generate a synergistic effect on promoting cell spreading and cell migration. Our results support a positive role for PKCdelta in cell motility and strongly suggest a link between PKCdelta activity, adducin phosphorylation and cell motility.

Genomics of Renal Cell Cancer: The Biology Behind and the Therapy Ahead

Renal cell cancer (RCC) is the most lethal of the urological cancers and accounts for 3% of all adult malignancies. Despite numerous recent advances in diagnostic imaging, surgical therapy, and basic molecular understanding, many patients still experience metastatic disease. For metastatic disease patients, response rates to conventional therapies rarely exceed 15% to 25% and are associated with serious adverse effects. The recent development of novel targeted therapies based on the precise biological pathways deregulated in a particular patient has paved the way for individualized, targeted patient management. Nevertheless, to achieve this goal, it is important to delineate the molecular mechanisms underlying cancer development and progression. Genomic approaches have revolutionized the field of cancer research and have led to the rapid discovery of multiple, parallel disease hypotheses, which ultimately have to be validated in large cohorts of patients and in downstream biological experiments for translation into clinical applications. The variable course of RCC and, until recently, a paucity of therapeutic options in the event of metastasis have led to the search for diagnostic and prognostic markers. We and others have used transcriptional profiling to classify different subtypes of RCC and to identify subtype- and metastasis-specific gene signatures predictive for outcome. We discuss herein recent genomic approaches to RCC and the emerging biological pathways underlying RCC development and progression. We also speculate how genomics may affect drug development and the management of patients with RCC.

Phospholipase D couples survival and migration signals in stress response of human cancer cells

MDA-MB-231 human breast cancer cells belong to a highly invasive metastatic cell line that depends on phospholipase D (PLD) activity for survival when deprived of serum growth factors. In response to the stress of serum withdrawal, there is a rapid and dramatic increase in PLD activity. Concomitant with increased PLD activity, there was an increase in the ability of MDA-MB-231 cells to both migrate and invade Matrigel. The ability of MDA-MB-231 cells to both migrate and invade Matrigel was dependent on both PLD and mTOR, a downstream target of PLD signals. Serum withdrawal also led to a PLD-dependent increase in the expression of the stress factor, hypoxia-inducible factor-1alpha. These data reveal that PLD survival signals not only prevent apoptosis but also stimulate cell migration and invasion, linking the ability to suppress apoptosis with the ability to metastasize.

Suppression of apoptosis in the protein kinase Cdelta null mouse in vivo

Protein kinase C (PKC) delta is an essential regulator of mitochondrial dependent apoptosis in epithelial cells. We have used the PKCdelta(-/-) mouse to ask if loss of PKCdelta protects salivary glands against gamma-irradiation-induced apoptosis in vivo and to explore the mechanism underlying protection from apoptosis. We show that gamma-irradiation in vivo results in a robust induction of apoptosis in the parotid glands of wild type mice, whereas apoptosis is suppressed by greater than 60% in the parotid glands of PKCdelta(-/-) mice. Primary parotid cells from PKCdelta(-/-) mice are defective in mitochondrial dependent apoptosis as indicated by suppression of etoposide-induced cytochrome c release, poly(ADP-ribose) polymerase cleavage, and caspase-3 activation. Notably, apoptotic responsiveness can be restored by re-introduction of PKCdelta by adenoviral transduction. Etoposide and gamma-irradiation-induced activation of p53 is similar in primary parotid cells and parotid glands from PKCdelta(+/+) and PKCdelta(-/-) mice, indicating that PKCdelta functions downstream of the DNA damage response. In contrast, activation of the c-Jun amino-terminal kinase is reduced in primary parotid cells from PKCdelta(-/-) cells and in parotid C5 cells, which express a dominant inhibitory mutant of PKCdelta. Similarly, c-Jun amino-terminal kinase activation is suppressed in vivo in gamma-irradiated parotid glands from PKCdelta(-/-) mice. These studies indicate an essential role for PKCdelta downstream of the p53 response and upstream of the c-Jun amino-terminal kinase activation in DNA damage-induced apoptosis in vivo and in vitro.

Phosphorylation of Coronin 1B by Protein Kinase C Regulates Interaction with Arp2/3 and Cell Motility

Coronins are a conserved family of WD repeat-containing, actin-binding proteins that regulate cell motility in a variety of model organisms. Our results show that Coronin 1B is a ubiquitously expressed member of the mammalian Coronin gene family that co-localizes with the Arp2/3 complex at the leading edge of fibroblasts, and co-immunoprecipitates with this complex. Pharmacological experiments show that the interaction between Coronin 1B and the Arp2/3 complex is regulated by protein kinase C (PKC) phosphorylation. Coronin 1B is phosphorylated by PKC both in vitro and in vivo. Using tryptic peptide mapping and mutagenesis, we have identified serine 2 (Ser-2) on Coronin 1B as the major residue phosphorylated by PKC in vivo. Rat2 fibroblasts expressing the Coronin 1B S2A mutant show enhanced ruffling in response to phorbol 12-myristate 13-acetate (PMA) and increased speed in single cell tracking assays. Cells expressing the Coronin 1B S2D mutant have attenuated PMA-induced ruffling and slower cell speed. Expression of the S2A mutant partially protects cells from the inhibitory effects of PMA on cell speed, whereas expression of the S2D mutant renders cells hypersensitive to its effects. These data demonstrate that Coronin 1B regulates leading edge dynamics and cell motility in fibroblasts, and that its ability to control motility and interactions with the Arp2/3 complex are regulated by PKC phosphorylation at Ser-2. Furthermore, Coronin 1B phosphorylation is responsible for a significant fraction of the effects of PMA on fibroblast motility.