Plasma protein kinase C (PKC)alpha as a biomarker for the diagnosis of cancers

Research progress on the antitumor effects of astragaloside IV

One of the most important and effective components of Astragalus membranaceus is astragaloside IV (AS-IV), which can exert anti-tumor effects through various pathways. For instance, AS-IV exerts an anti-tumor effect by acting at the cellular level, regulating the phenotype switch of tumor-associated macrophages, or inhibiting the development of tumor cells. Furthermore, AS-IV inhibits tumor cell progression by enhancing its sensitivity to antitumor drugs or reversing the drug resistance of tumor cells. This article reviews the different mechanisms of AS-IV inhibition of epithelial-mesenchymal transition (EMT), migration, proliferation, and invasion of tumor cells, inducing apoptosis and improving the sensitivity of anti-tumor drugs. This review summarizes recent progress in the current research into AS-IV anti-tumor effect and provides insight on the next anti-tumor research of AS-IV.

Protein Kinase C (PKC) Isozymes as Diagnostic and Prognostic Biomarkers and Therapeutic Targets for Cancer

Protein kinase C (PKC) is a large family of calcium- and phospholipid-dependent serine/threonine kinases that consists of at least 11 isozymes. Based on their structural characteristics and mode of activation, the PKC family is classified into three subfamilies: conventional or classic (cPKCs; α, βI, βII, and γ), novel or non-classic (nPKCs; δ, ε, η, and θ), and atypical (aPKCs; ζ, ι, and λ) (PKCλ is the mouse homolog of PKCι) PKC isozymes. PKC isozymes play important roles in proliferation, differentiation, survival, migration, invasion, apoptosis, and anticancer drug resistance in cancer cells. Several studies have shown a positive relationship between PKC isozymes and poor disease-free survival, poor survival following anticancer drug treatment, and increased recurrence. Furthermore, a higher level of PKC activation has been reported in cancer tissues compared to that in normal tissues. These data suggest that PKC isozymes represent potential diagnostic and prognostic biomarkers and therapeutic targets for cancer. This review summarizes the current knowledge and discusses the potential of PKC isozymes as biomarkers in the diagnosis, prognosis, and treatment of cancers.

Role of alternatively spliced, pro-survival Protein Kinase C delta VIII (PKCδVIII) in ovarian cancer

Ovarian cancer is the deadliest malignant disease in women. Protein Kinase C delta (PRKCD; PKCδ) is serine/threonine kinase extensively linked to various cancers. In humans, PKCδ is alternatively spliced to PKCδI and PKCδVIII. However, the specific function of PKCδ splice variants in ovarian cancer has not been elucidated yet. Hence, we evaluated their expression in human ovarian cancer cell lines (OCC): SKOV3 and TOV112D, along with the normal T80 ovarian cells. Our results demonstrate a marked increase in PKCδVIII in OCC compared to normal ovarian cells. Therefore, we elucidated the role of PKCδVIII and the underlying mechanism of its expression in OCC. Using overexpression and knockdown studies, we demonstrate that PKCδVIII increases cellular survival and migration in OCC. Further, overexpression of PKCδVIII in T80 cells resulted in increased expression of Bcl2 and knockdown of PKCδVIII in OCC decreased Bcl2 expression. Using co-immunoprecipitations and immunocytochemistry, we demonstrate nuclear localization of PKCδVIII in OCC and further show increased association of PKCδVIII with Bcl2 and Bcl-xL in OCC. Using PKCδ splicing minigene, mutagenesis, siRNA and antisense oligonucleotides, we demonstrate that increased levels of alternatively spliced PKCδVIII in OCC is regulated by splice factor SRSF2. Finally, we verified that PKCδVIII levels are elevated in samples of human ovarian cancer tissue. The data presented here demonstrate that the alternatively spliced, signaling kinase PKCδVIII is a viable target to develop therapeutics to combat progression of ovarian cancer.

Identification of Activated Protein Kinase Cα (PKCα) in the Urine of Orthotopic Bladder Cancer Xenograft Model as a Potential Biomarker for the Diagnosis of Bladder Cancer

Bladder cancer has a high recurrence rate; therefore, frequent and effective monitoring is essential for disease management. Cystoscopy is considered the gold standard for the diagnosis and continuous monitoring of bladder cancer. However, cystoscopy is invasive and relatively expensive. Thus, there is a need for non-invasive, relatively inexpensive urinary biomarker-based diagnoses of bladder cancer. This study aimed to investigate the presence of activated protein kinase Cα (PKCα) in urine samples and the possibility of PKCα as a urinary biomarker for bladder cancer diagnosis. Activated PKCα was found to be present at higher levels in bladder cancer tissues than in normal bladder tissues. Furthermore, high levels of activated PKCα were observed in urine samples collected from orthotopic xenograft mice carrying human bladder cancer cells compared to urine samples from normal mice. These results suggest that activated PKCα can be used as a urinary biomarker to diagnose bladder cancer. To the best of our knowledge, this is the first report describing the presence of activated PKCα in the urine of orthotopic xenograft mice.

Protein kinase C-α and the regulation of diverse cell responses

Protein kinase C (PKC) comprises a family of lipid-sensitive enzymes that have been involved in a broad range of cellular functions. PKC-α is a member of classical PKC with ubiquitous expression and different cellular localization. This unique PKC isoform is activated by various signals which evoke lipid hydrolysis, after activation it interacts with various adapter proteins and is localized to specific cellular compartments where it is devised to work. The universal expression and activation by various stimuli make it a perfect player in uncountable cellular functions including differentiation, proliferation, apoptosis, cellular transformation, motility, adhesion and so on. However, these functions are not intrinsic properties of PKC-α, but depend on cell types and conditions. The activities of PKC-α are managed by the various pharmacological activators/inhibitors and antisense oligonucleotides. The aim of this review is to elaborate the structural feature, and provide an insight into the mechanism of PKC-α activation and regulation of its key biological functions in different cellular compartments to develop an effective pharmacological approach to regulate the PKC-α signal array.

PKCα promotes local advancement via its dual roles in nasopharyngeal carcinoma

CONCLUSION

In patients with nasopharyngeal carcinoma (NPC), PKCα is linked to local advancement and plays dual roles in tumorigenesis. Moreover, positive PKCα is associated with 2-year overall survival of NPC.

OBJECTIVE

This study seeks to investigate the role of PKCα to identify different sub-types in NPC.

METHODS

PKCα expression levels were detected in a collection of NPC samples. CT and MRI scans of the corresponding patients were used to assess adjacent tissue invasion and lymph node metastasis. The correlation of tumour invasion and PKCα levels was evaluated by statistical analysis. The correlation between expression level of PKCα and 2-year overall survival was analysed by the Kaplan-Meier curves. Moreover, a multivariate Cox proportional hazard regression analysis was used to identify the independent prognostic factors for NPC.

RESULTS

PKCα is linked to the invasion of adjacent tissues, especially in the skull base. However, down-regulation of PKCα is a risk factor for regional lymph node metastasis. The 2-year overall survival of the PKCα negative group is better than that of the PKCα positive group (PKCα negative group 100%, PKCα positive group 88.5%, p = 0.034). Based on the multivariate Cox proportional hazard regression analysis, age was identified as a risk factor.

5-(Bis(3-(2-hydroxyethyl)-1H-indol-2-yl)methyl)-2-hydroxybenzoic acid (BHIMHA): showing a strategy of designing drug to block lung metastasis of tumors

Early metastasis is still the most recalcitrant factor in the treatment of lung cancer patients. By analyzing the structures and comparing the docking scores of the known pharmacophores, the authors of this paper designed 5-(bis(3-(2-hydroxyethyl)-1H-indol-2-yl)methyl)-2-hydroxybenzoic acid (BHIMHA) as a promising lead compound to develop metastasis inhibitors. In vitro 5, 10, and 20 µM of BHIMHA concentration dependently inhibited the migration and invasion of A549 cells. In vivo 0.4, 2.0, and 8.9 µmol/kg of BHIMHA dose dependently inhibited the metastasis of LLC (Lewis Lung Carcinoma) toward lung. In vivo, 2 µmol/kg of BHIMHA showed additional actions of slowing the growth of the primary tumor of C57BL/6 mice and S180 mice as well as inhibiting xylene-induced ear edema of the mice. Therefore, BHIMHA simultaneously blocked tumor metastasis toward lung, slowed the primary tumor growth, and limited the inflammation. These pharmacological actions were correlated with the inhibition of PKCα and NF-κB expression.

Proteomic database mining opens up avenues utilizing extracellular protein phosphorylation for novel therapeutic applications

Recent advances in extracellular signaling suggest that extracellular protein phosphorylation is a regulatory mechanism outside the cell. The list of reported active extracellular protein kinases and phosphatases is growing, and phosphorylation of an increasing number of extracellular matrix molecules and extracellular domains of trans-membrane proteins is being documented. Here, we use public proteomic databases, collagens – the major components of the extracellular matrix, extracellular signaling molecules and proteolytic enzymes as examples to assess what the roles of extracellular protein phosphorylation may be in health and disease. We propose that novel tools be developed to help assess the role of extracellular protein phosphorylation and translate the findings for biomedical applications. Furthermore, we suggest that the phosphorylation state of extracellular matrix components as well as the presence of extracellular kinases be taken into account when designing translational medical applications.

Ectokinases as novel cancer markers and drug targets in cancer therapy

While small-molecule kinase inhibitors became the most prominent anticancer drugs, novel combinatorial strategies need to be developed as the fight against cancer is not yet won. We review emerging literature showing that the release of several ectokinases is significantly upregulated in body fluids from cancer patients and that they leave behind their unique signatures on extracellular matrix (ECM) proteins. Our analysis of proteomic data reveals that fibronectin is heavily phosphorylated in cancer tissues particularly within its growth factor binding sites and on domains that regulate fibrillogenesis. We are thus making the case that cancer is not only a disease of cells but also of the ECM. Targeting extracellular kinases or the extracellular signatures they leave behind might thus create novel opportunities in cancer diagnosis as well as new avenues to interfere with cancer progression and malignancy.

Effect of peptide content on the regulation of transgene expression by protein kinase Cα-responsive linear polyethylenimine-peptide conjugates

We examined a series of linear polyethylenimine (LPEI)-based nanocarriers that activate transgene expression in response to cancer-specific protein kinase Cα (PKCα). Eight types of LPEI-peptide conjugate differing in peptide content and number were synthesized using click chemistry. The conjugates could form polyplexes with pDNA through electrostatic interaction, but the degree of pDNA condensation, sizes, and surface charges of the resulting polyplexes depended on the pendant-peptide content and number. None of the polyplexes showed significant cytotoxicity toward human hepatoma cells (HepG2). Furthermore, pendant peptide content and number markedly affected transgene activation in response to PKCα. To achieve an all-or-none response to PKCα, we determined the optimum peptide content and number in LPEI-peptide conjugates as ≈6 mol% and ≈40 peptides/conjugate.

Astragaloside IV inhibits migration and invasion in human lung cancer A549 cells via regulating PKC-α-ERK1/2-NF-κB pathway

The migration and invasion characteristics that are related to inflammatory response play important roles in the development of lung cancer. Astagaloside IV (AS-IV), an effective saponin component isolated from Astragali Radix, has been reported to inhibit metastasis of tumor cells. However, little is known about the underlying mechanism of AS-IV on inhibiting the migration and invasion characteristics of lung cancer cells. In the present study, cell proliferation was assessed by MTT colorimetric assay. Wound-healing assay and transwell chambers assay were used to detect the effects of AS-IV on the migration capacity and invasiveness of A549 cells. Metastasis-related bio-markers expressions were detected by Western blot analysis. Levels of inflammatory factors including transforming growth factor-β1 (TGF-β1), tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) in cell supernatant were tested by enzyme linked immunosorbent assay (ELISA). The expressions of PKC-α, ERK1/2 and NF-κB were analyzed by Western blot analysis. The results showed that the migration and invasion ability of A549 has been suppressed in presence of AS-IV. The levels of MMP-2, MMP-9 and integrin β1 were decreased significantly, whereas E-cadherin was increased by the treatment of different concentrations AS-IV. Furthermore, AS-IV also significantly decreased TGF-β1, TNF-α and IL-6 levels. Interestingly, PKC pathway inhibitor AEB071 (Sotrastaurin) (0.1 μM) or ERK inhibitor U0126 (1 μM) or NF-κB inhibitor PDTC (1 μM) could affect suppression of AS-IV on cell invasion, at least partially. Our results suggested that the migration and invasion of AS-IV in A549 cells might be related to the PKC-α-ERK1/2-NF-κB pathway. The result indicated that AS-IV could be used as a candidate for the inhibition of metastasis of human lung cancer.

Ecto-protein kinases and phosphatases: an emerging field for translational medicine

Progress in translational research has led to effective new treatments of a large number of diseases. Despite this progress, diseases including cancer and cardiovascular disorders still are at the top in death statistics and disorders such as osteoporosis and osteoarthritis represent an increasing disease burden in the aging population. Novel strategies in research are needed more than ever to overcome such diseases. The growing field of extracellular protein phosphorylation provides excellent opportunities to make major discoveries of disease mechanisms that can lead to novel therapies. Reversible phosphorylation/dephosphorylation of sites in the extracellular domains of matrix, cell-surface and trans-membrane proteins is emerging as a critical regulatory mechanism in health and disease. Moreover, a new concept is emerging from studies of extracellular protein phosphorylation: in cells where ATP is stored within secretory vesicles and released by exocytosis upon cell-stimulation, phosphorylation of extracellular proteins can operate as a messenger operating uniquely in signaling pathways responsible for long-term cellular adaptation. Here, we highlight new concepts that arise from this research, and discuss translation of the findings into clinical applications such as development of diagnostic disease markers and next-generation drugs.

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.

Branched polyethylenimine-based PKCα-responsive gene carriers

We examined in vitro performance of the branched polyethylenimine (bPEI)-based gene carriers which respond to cancer-specific activation of protein kinase Cα (PKCα) to express plasmid DNA. The carriers were synthesized straightforward by using amide bond formation between a peptide terminal carboxyl and a primary amine group of bPEI. To examine the effect of the peptide contents in the carrier, we prepared several carriers with various peptide contents. The obtained polymers form polyplexes with tighter condensation of plasmid DNA than our previous gene carriers. After internalization of the polyplexes via endocytosis, the polyplexes effectively escaped from the endosome into cytosol. Then, the polyplexes showed a clear-cut response to PKCα to release plasmid DNA for gene expression. We determined the optimum contents of the peptides in carriers as 5 mol% to achieve the clear-cut response to PKCα.

Tight junctions in human pancreatic duct epithelial cells

Tight junctions of the pancreatic duct are essential regulators of physiologic secretion of the pancreas and disruption of the pancreatic ductal barrier is known to contribute to the pathogenesis of pancreatitis and progression of pancreatic cancer. Various inflammatory mediators and carcinogens can trigger tight junction disassembly and disruption of the pancreatic barrier, however signaling events that mediates such barrier dysfunctions remain poorly understood. This review focuses on structure and regulation of tight junctions in normal pancreatic epithelial cells and mechanisms of junctional disruption during pancreatic inflammation and cancer. We will pay special attention to a novel model of human telomerase reverse transcriptase-transfected human pancreatic ductal epithelial cells and will describe the roles of major signaling molecules such as protein kinase C and c-Jun N-terminal kinase in formation and disassembly of the pancreatic ductal barrier.

PKCα is involved in the progression of kidney carcinoma through regulating netrin-1/UNC5B signaling pathway

With a special interest towards a better understanding of signal pathways, we attempted to discover a safer and more effective therapeutic strategy for kidney carcinoma. Recent studies had suggested a role mediated by PKCα for netrin-1 and its receptors in the initiation and progression of tumors. Real-time PCR and western blotting were used to determine the expression levels of netrin-1 and UNC5B. We made use of the agonist of PKCα (phorbol-12-myristate 13-acetate-PMA) and the inhibitor of PKCα (calphostin C) to treat renal cell carcinoma (RCC) cells, and MTT assays were used to measure cell proliferation. By immunofluorescence, we identified the localization of netrin-1 and UNC5B in RCC cell lines 769-P and ACHN. The expression of UNC5B in tumor tissues was significantly downregulated compared to the corresponding normal tissues in which netrin-1 was upregulated. In low grade tumors, UNC5B expression was more prominent while netrin-1 expression was the opposite when compared with high grade ones. Proliferation of ACHN cells was concentration dependent in the presence of PMA and calphostin C. Netrin-1 and UNC5B expressions were upregulated in cells treated with PMA while calphostin C reversed this upregulation. By immunofluorescence, we identified that netrin-1 was highly expressed in the nuclear but none of UNC5B. Our data highly suggested that PMA-induced upregulation and calphostin C-induced reversion of netrin-1 and UNC5B in kidney carcinoma were accompanied by the activation of the netrin-1/UNC5B pathways.

Protein kinase Cα inhibitor protects against downregulation of claudin-1 during epithelial-mesenchymal transition of pancreatic cancer

Protein kinase Cα (PKCα) is highly expressed in pancreatic cancer. However, the effects of PKCα on Snail and claudin-1, which play crucial roles in epithelial cell polarity during epithelial-mesenchymal transition (EMT), remain unclear. In this study, we investigated the mechanisms of regulation of Snail and claudin-1 via a PKCα signal pathway during EMT in pancreatic cancer cells and in normal human pancreatic duct epithelial cells (HPDEs). By immunostaining, overexpression of PKCα and downregulation of claudin-1 were observed in poorly differentiated human pancreatic cancer tissues and the pancreatic cancer cell line PANC-1. Treatment with the PKCα inhibitor Gö6976 transcriptionally decreased Snail and increased claudin-1 in PANC-1 cells. The PKCα inhibitor prevented upregulation of Snail and downregulation of claudin-1 during EMT induced by transforming growth factor-β1 (TGF-β1) treatment and under hypoxia in PANC-1 cells. The effects of the PKCα inhibitor were in part regulated via an extracellular signal-regulated kinase (ERK) signaling pathway. The PKCα inhibitor also prevented downregulation of the barrier function and fence function during EMT in well-differentiated pancreatic cancer cell line HPAC. In normal HPDEs, the PKCα inhibitor transcriptionally induced not only claudin-1 but also claudin-4, -7 and occludin without a change of Snail. Treatment with the PKCα inhibitor in normal HPDEs prevented downregulation of claudin-1 and occludin by TGF-β1 treatment and enhanced upregulation of claudin-1, -4, -7 and occludin under hypoxia. These findings suggest that PKCα regulates claudin-1 via Snail- and mitogen-activated protein kinase/ERK-dependent pathways during EMT in pancreatic cancer. Thus, PKCα inhibitors may be potential therapeutic agents against the malignancy of human pancreatic cancer cells.

Protein kinase Cα inhibitor enhances the sensitivity of human pancreatic cancer HPAC cells to Clostridium perfringens enterotoxin via claudin-4

Protein kinase C (PKC) is overexpressed in cancer, including pancreatic cancer, compared with normal tissue. Moreover, PKCα is considered one of the biomarkers for the diagnosis of cancers. In several human cancers, the claudin tight junction molecules are abnormally regulated and are thus promising molecular targets for diagnosis and therapy with Clostridium perfringens enterotoxin (CPE). In order to investigate the changes of tight junction functions of claudins via PKCα activation in pancreatic cancer cells, the well-differentiated human pancreatic cancer cell line HPAC, with its highly expressed tight junction molecules and well-developed barrier function, was treated with the PKC activator 12-O-tetradecanoylphorbol 13-acetate (TPA). Treatment with TPA modified the activity of phosphoPKCα and caused an increase of the Snail family members Snail, Slug and Smad-interacting protein 1 and a decrease of E-cadherin. In HPAC cells treated with TPA, downregulation of claudin-1 and mislocalization of claudin-4 and occludin around the nuclei were observed, together with a decrease in the numbers of tight junction strands and an increase in phosphorylation of claudin-4. The barrier function and the cytotoxicity of CPE were significantly decreased on TPA treatment. All such changes after TPA treatment were prevented by inhibitors of panPKC and PKCα. These findings suggest that, in human pancreatic cancer cells, PKCα activation downregulates tight junction functions as a barrier and as a receptor of CPE via the modification of claudin-1 and -4 during epithelial to mesenchymal transition-like changes. PKCα inhibitors might represent potential therapeutic agents against human pancreatic cancer cells by use of CPE cytotoxicity via claudin-4.

Synthesis and biological activity of novel organoselenium derivatives targeting multiple kinases and capable of inhibiting cancer progression to metastases

The present study reports synthesis and biological activity of novel benzoisoselenazolone compounds derived from ebselen and conjugated to a sugar molecule. Cell proliferation assay using cancer cells combined with in vitro biochemical assays revealed that benzoisoselenazolone 2d, 5a, and 6a exerted anti-proliferative activity, which correlated with selective in vitro inhibition of focal adhesion kinase, AKT-1, and protein kinase C-α. Active molecules were able to significantly inhibit cell migration and invasion in vitro compared to cells treated with the vehicle alone or ebselen. Moreover, in vivo anticancer activity focusing on lead compound 2d and using an invasive human breast cancer orthotopic mouse model revealed a potent anti-metastatic activity at well-tolerated doses. In summary, these novel benzoisoselenazolones we report herein target multiple kinases with established roles in cancer progression and possess anti-invasive and anti-metastatic activity in preclinical models supporting a potential for therapeutic application for human disease.

A hydrophilic polymer grafted with a histone tail peptide as an artificial gene regulator

In chromatin, gene transcription is regulated through posttranslational modifications on the histone N-terminal tail sequences, typically an acetyl group modification on lysine residues. To realize a simple model of the gene regulation of chromatin, we designed a hydrophilic polymer grafted with histone H3 tail peptides. The polyplex formed from the polymer and DNA suppressed the gene expression effectively although the polyplex was weaker than the polyplex of poly-L-lysine and DNA. This weaker polyplex afforded the acetylation of the lysine residue of the grafted peptides by histone acetyltransferase. Subsequently, the gene expression was activated due to the relaxation of the polyplex which was brought by a cationic charge decrease in the grafted peptides. This molecular system is the first functional model of the gene regulation of the chromatin.