A kinase inhibitor screen reveals protein kinase C-dependent endocytic recycling of ErbB2 in breast cancer cells

Assembly and disassembly dynamics of nonmuscle myosin II control endosomal fission

Endocytic vesicular trafficking requires merging of two lipid bilayers, but how the two lipid bilayers can come close together during fusion and fission in endocytic trafficking is not well explored. Here, we establish that knocking down nonmuscle myosin IIs (NM IIs) by small interfering RNA (siRNA) or inhibition of their activities by (-) blebbistatin causes the formation of a ring-like assembly of early endosomes (raEE). Inhibition of NM II assembly by an inhibitor of regulatory light-chain (RLC) kinase results in the formation of raEE, whereas inhibition of NM II disassembly by inhibitors of heavy chain kinases, protein kinase C (PKC) and casein kinase 2 (CK2), causes the dispersion of early endosomes. The raEEs retain EEA1, Rab7, and LAMP2 markers. Overexpression of an assembly incompetent form, RLC-AA, and disassembly incompetent form, NMHCIIB-S6A or NMHCIIA-1916A, induces such defects, respectively. Altogether, these data support that NM II assembly and disassembly dynamics participate in endocytic trafficking by regulating fission to maintain the size of early endosomes.

EHD2 overexpression promotes tumorigenesis and metastasis in triple-negative breast cancer by regulating store-operated calcium entry

With nearly all cancer deaths a result of metastasis, elucidating novel pro-metastatic cellular adaptations could provide new therapeutic targets. Here, we show that overexpression of the EPS15-Homology Domain-containing 2 (EHD2) protein in a large subset of breast cancers (BCs), especially the triple-negative (TNBC) and HER2+ subtypes, correlates with shorter patient survival. The mRNAs for EHD2 and Caveolin-1/2, structural components of caveolae, show co-overexpression across breast tumors, predicting shorter survival in basal-like BC. EHD2 shRNA knockdown and CRISPR-Cas9 knockout with mouse Ehd2 rescue, in TNBC cell line models demonstrate a major positive role of EHD2 in promoting tumorigenesis and metastasis. Mechanistically, we link these roles of EHD2 to store-operated calcium entry (SOCE), with EHD2-dependent stabilization of plasma membrane caveolae ensuring high cell surface expression of the SOCE-linked calcium channel Orai1. The novel EHD2-SOCE oncogenic axis represents a potential therapeutic target in EHD2- and CAV1/2-overexpressing BC.

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.

CAF08 adjuvant enables single dose protection against respiratory syncytial virus infection in murine newborns

Respiratory syncytial virus is a leading cause of morbidity and mortality in children, due in part to their distinct immune system, characterized by impaired induction of Th 1 immunity. Here we show application of cationic adjuvant formulation CAF08, a liposomal vaccine formulation tailored to induce Th 1 immunity in early life via synergistic engagement of Toll-like Receptor 7/8 and the C-type lectin receptor Mincle. We apply quantitative phosphoproteomics to human dendritic cells and reveal a role for Protein Kinase C-δ for enhanced Th1 cytokine production in neonatal dendritic cells and identify signaling events resulting in antigen cross-presentation. In a murine in vivo model a single immunization at birth with CAF08-adjuvanted RSV pre-fusion antigen protects newborn mice from RSV infection by induction of antigen-specific CD8+ T-cells and Th1 cells. Overall, we describe a pediatric adjuvant formulation and characterize its mechanism of action providing a promising avenue for development of early life vaccines against RSV and other respiratory viral pathogens.

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.

PKC-mediated phosphorylation and activation of the MEK/ERK pathway as a mechanism of acquired trastuzumab resistance in HER2-positive breast cancer

Protein expression, activation and stability are regulated through inter-connected signal transduction pathways resulting in specific cellular states. This study sought to differentiate between the complex mechanisms of intrinsic and acquired trastuzumab resistance, by quantifying changes in expression and activity of proteins (phospho-protein profile) in key signal transduction pathways, in breast cancer cellular models of trastuzumab resistance. To this effect, we utilized a multiplex, bead-based protein assay, DigiWest^®, to measure around 100 proteins and protein modifications using specific antibodies. The main advantage of this methodology is the quantification of multiple analytes in one sample, utilising input volumes of a normal western blot. The intrinsically trastuzumab-resistant cell line JIMT-1 showed the largest number of concurrent resistance mechanisms, including PI3K/Akt and RAS/RAF/MEK/ERK activation, β catenin stabilization by inhibitory phosphorylation of GSK3β, cell cycle progression by Rb suppression, and CREB-mediated cell survival. MAPK (ERK) pathway activation was common to both intrinsic and acquired resistance cellular models. The overexpression of upstream RAS/RAF, however, was confined to JIMT 1; meanwhile, in a cellular model of acquired trastuzumab resistance generated in this study (T15), entry into the ERK pathway seemed to be mostly mediated by PKCα activation. This is a novel observation and merits further investigation that can lead to new therapeutic combinations in HER2-positive breast cancer with acquired therapeutic resistance.

Angiopoietin-like protein 4 is a chromatin-bound protein that enhances mammosphere formation in vitro and experimental triple-negative breast cancer brain and liver metastases in vivo

INTRODUCTION:

Metastatic progression in triple-negative breast cancer (TNBC) patients occurs primarily because of nuclear reprogramming that includes chromatin remodeling and epigenetic modifications. The existing and most successful chemotherapies available for metastatic TNBC target nuclear proteins or damage DNA. The objectives here are to investigate an undescribed role for the molecular biology of nuclear angiopoietin-like protein 4 (ANGPTL4) and to characterize the effect of ectopic overexpression of ANGPTL4 in the metastatic biology of TNBC.

MATERIALS AND METHODS:

Lentiviral-mediated transduction was used to overexpress ANGPTL4 in the TNBC cell line MD Anderson–metastatic breast cancer 231. The overexpression of ANGPTL4 was confirmed by western blot and ELISA. Subcellular fractionation, western blot, and immunofluorescence microscopy were used to characterize the intracellular localization of ANGPTL4. Mammosphere culture and the anchorage-independent growth assay analyzed the metastatic potential of the cell line. Xenograft assays assessed the effect of ANGPTL4 overexpression on TNBC metastases in vivo.

RESULTS:

The ANGPTL4 overexpressing cell line formed larger mammospheres and anchorage-independent colonies in vitro and developed larger primary tumors, more liver metastases, and brain metastatic outgrowth in vivo in comparison to a cell line that expressed endogenous levels of ANGPTL4. ANGPTL4, aurora kinase A (AURKA), a mitotic kinase, and Tat-interacting protein p60 kDa (Tip60), a lysine acetyltransferase, associated with chromatin in the ANGPTL4 overexpressing cells but not in cells that expressed endogenous levels of ANGPTL4.

CONCLUSIONS:

The ANGPTL4 overexpressing cell line showed in vitro and in vivo activities that suggest that nuclear ANGPTL4, AURKA, and Tip60 may cooperatively modulate TNBC metastases within chromatin-remodeling complexes or DNA-associated machinery.

The complexities of PKCα signaling in cancer

Protein kinase C α (PKCα) is a ubiquitously expressed member of the PKC family of serine/threonine kinases with diverse functions in normal and neoplastic cells. Early studies identified anti-proliferative and differentiation-inducing functions for PKCα in some normal tissues (e.g., regenerating epithelia) and pro-proliferative effects in others (e.g., cells of the hematopoietic system, smooth muscle cells). Additional well documented roles of PKCα signaling in normal cells include regulation of the cytoskeleton, cell adhesion, and cell migration, and PKCα can function as a survival factor in many contexts. While a majority of tumors lose expression of PKCα, others display aberrant overexpression of the enzyme. Cancer-related mutations in PKCα are uncommon, but rare examples of driver mutations have been detected in certain cancer types (e. g., choroid gliomas). Here we review the role of PKCα in various cancers, describe mechanisms by which PKCα affects cancer-related cell functions, and discuss how the diverse functions of PKCα contribute to tumor suppressive and tumor promoting activities of the enzyme. We end the discussion by addressing mutations and expression of PKCα in tumors and the clinical relevance of these findings.

Phosphorylation of PKCδ by FER tips the balance from EGFR degradation to recycling

Receptor degradation terminates signaling by activated receptor tyrosine kinases. Degradation of EGFR occurs in lysosomes and requires the switching of RAB5 for RAB7 on late endosomes to enable their fusion with the lysosome, but what controls this critical switching is poorly understood. We show that the tyrosine kinase FER alters PKCδ function by phosphorylating it on Y374, and that phospho-Y374-PKCδ prevents RAB5 release from nascent late endosomes, thereby inhibiting EGFR degradation and promoting the recycling of endosomal EGFR to the cell surface. The rapid association of phospho-Y374-PKCδ with EGFR-containing endosomes is diminished by PTPN14, which dephosphorylates phospho-Y374-PKCδ. In triple-negative breast cancer cells, the FER-dependent phosphorylation of PKCδ enhances EGFR signaling and promotes anchorage-independent cell growth. Importantly, increased Y374-PKCδ phosphorylation correlating with arrested late endosome maturation was identified in ∼25% of triple-negative breast cancer patients, suggesting that dysregulation of this pathway may contribute to their pathology.

Activated Protein Kinase C (PKC) Is Persistently Trafficked with Epidermal Growth Factor (EGF) Receptor

Protein kinase Cs (PKCs) are activated by lipids in the plasma membrane and bind to a scaffold assembled on the epidermal growth factor (EGF) receptor (EGFR). Understanding how this complex is routed is important, because this determines whether EGFR is degraded, terminating signaling. Here, cells were preincubated in EGF-tagged gold nanoparticles, then allowed to internalize them in the presence or absence of a phorbol ester PKC activator. PKC colocalized with EGF-tagged nanoparticles within 5 min and migrated with EGFR-bearing vesicles into the cell. Two conformations of PKC-epsilon were distinguished by different primary antibodies. One, thought to be enzymatically active, was on endosomes and displayed a binding site for antibody RR (R&D). The other, recognized by Genetex green (GG), was soluble, on actin-rich structures, and loosely bound to vesicles. During a 15-min chase, EGF-tagged nanoparticles entered large, perinuclear structures. In phorbol ester-treated cells, vesicles bearing EGF-tagged nanoparticles tended to enter this endocytic recycling compartment (ERC) without the GG form. The correlation coefficient between the GG (inactive) and RR conformations on vesicles was also lower. Thus, active PKC has a Charon-like function, ferrying vesicles to the ERC, and inactivation counteracts this function. The advantage conferred on cells by aggregating vesicles in the ERC is unclear.

Knockdown Of CCDC132 Attenuates Gastric Cancer Cells Proliferation And Tumorigenesis By Facilitating DNA Damage Signaling

Background

Aberrant endocytic recycling has fundamental functions on plasma membrane component turnover. Recent studies have identified an uncharacterized protein, CCDC132, in the endosome-associated recycling protein complex. Besides, our preliminary data first showed that CCDC132 was elevated in malignant neoplasms, especially in esophagus/stomach cancers. However, the functions and the underlying mechanisms of CCDC132 in gastric cancer (GC) biology remain unclear.

Methods

The CCDC132 mRNA expression in 4 GC cell lines and normal gastric epithelial cell lines was detected by qRT-PCR. Then, CCDC132 was downregulated in AGS and MGC-803 cells by lentivirus-induced RNA interfere, and cell viability assay, clone formation assay and apoptosis assay were carried out. The mechanism of CCDC132 on cell proliferation and apoptosis activation was explored using PathScan^® Stress, apoptosis signaling arrays and Western blot. We further investigated the pro-oncogenesis of CCDC132 in vivo. Meanwhile, immunohistochemistry was utilized to analyze the association between CCDC132 expression and clinicopathological features and prognosis. Finally, the correlation between CCDC132 and p53 was analyzed by Spearman’s rank correlation analysis.

Results

In this study, knockdown of CCDC132 significantly decreased cell proliferation and clone formation ability and facilitated apoptosis, and increased phosphorylation of p53 and Chk2 and protein levels of γ-H2AX, 53BP1, cleaved Caspase 3 and cleaved PARP. Additionally, knockdown of CCDC132 attenuated tumorigenesis and tumor growth of MGC-803 cell xenografts. CCDC132 expression was significantly higher in GC tissues compared with that in adjacent normal tissues and was positively correlated with nodal metastasis and TNM stage and negatively associated with prognosis. The survival rate of CCDC132 positive patients was lower than that of CCDC132-negative patients. Furthermore, CCDC132 expression was negatively related to p53.

Conclusion

This study unravels that knockdown of CCDC132 attenuates GC cell proliferation and tumorigenesis by facilitating DNA damage signaling, indicating that CCDC132 may serve as a potential target for GC therapy.

Protein kinase C regulates ErbB3 turnover

ErbB3, which belongs to the epidermal growth factor receptor (EGFR) or ErbB family of receptor tyrosine kinases, is involved in progression of several human cancers and a tight regulation of its expression is crucial. An important mechanism for regulation of ErbB proteins is endocytosis and we recently showed that ErbB3, contrary to other ErbB proteins, like EGFR and ErbB2, is constitutively internalized and degraded. Several studies show that protein kinase C (PKC) can regulate the activation, localization and stability of EGFR and ErbB2. Activation of PKC causes their down-regulation from the plasma membrane, but instead of being degraded the receptors accumulate in an endosomal recycling compartment. Since little is known about possible connections between ErbB3 and PKC, we have in the present study investigated effects PKC activity has on ErbB3 stability and intracellular trafficking. While PKC inhibition tends to increase ErbB3 degradation, activation of PKC causes ErbB3 stabilization. The stabilization was not due to inhibited internalization, on the contrary we find that expression of ErbB3 at the plasma membrane is reduced upon PMA-induced PKC activation. However, while endocytosed ErbB3 under normal conditions and upon PKC inhibition is found in early endosomal antigen 1 (EEA1) positive early endosomes and lysosomal-associated membrane protein 1 (LAMP1) positive late endosomes/lysosomes, indicating that it follows the classic degradative pathway, ErbB3 localizes to EEA1 and LAMP1 negative compartments upon PMA-induced activation of PKC. Altogether this shows that PKC regulates the stability of ErbB3, and knockdown experiments show that PKCδ is essential in this process. A likely explanation is that PKC regulates endosomal sorting of ErbB3 and that activated PKC sorts ErbB3 away from the degradative pathway.

Release of transcriptional repression via ErbB2-induced, SUMO-directed phosphorylation of myeloid zinc finger-1 serine 27 activates lysosome redistribution and invasion

HER2/ErbB2 activation turns on transcriptional processes that induce local invasion and lead to systemic metastasis. The early transcriptional changes needed for ErbB2-induced invasion are poorly understood. Here, we link ErbB2 activation to invasion via ErbB2-induced, SUMO-directed phosphorylation of a single serine residue, S27, of the transcription factor myeloid zinc finger-1 (MZF1). Utilizing an antibody against MZF1-pS27, we show that the phosphorylation of S27 correlates significantly (p < 0.0001) with high-level expression of ErbB2 in primary invasive breast tumors. Phosphorylation of MZF1-S27 is an early response to ErbB2 activation and results in increased transcriptional activity of MZF1. It is needed for the ErbB2-induced expression of MZF1 target genes CTSB and PRKCA, and invasion of single-cells from ErbB2-expressing breast cancer spheroids. The phosphorylation of MZF1-S27 is preceded by poly-SUMOylation of K23, which can make S27 accessible to efficient phosphorylation by PAK4. Based on our results, we suggest for an activation mechanism where phosphorylation of MZF1-S27 triggers MZF1 dissociation from its transcriptional repressors such as the CCCTC-binding factor (CTCF). Our findings increase understanding of the regulation of invasive signaling in breast cancer by uncovering a detailed biological mechanism of how ErbB2 activation can rapidly lead to its invasion-promoting target gene expression and invasion.

Inhibition of ezrin causes PKCα-mediated internalization of erbb2/HER2 tyrosine kinase in breast cancer cells

Unlike other ErbB family members, HER2 levels are maintained on the cell surface when the receptor is activated, allowing prolonged signaling and contributing to its transforming ability. Interactions between HER2, HSP90, PMCA2, and NHERF1 within specialized plasma membrane domains contribute to the membrane retention of HER2. We hypothesized that the scaffolding protein ezrin, which has been shown to interact with NHERF1, might also help stabilize the HER2-PMCA2-NHERF1 complex at the plasma membrane. Therefore, we examined ezrin expression and its relationship with HER2, NHERF1, and PMCA2 levels in murine and human breast cancers. We also used genetic knockdown and/or pharmacologic inhibition of ezrin, HSP90, NHERF1, PMCA2, and HER2 to examine the functional relationships between these factors and membrane retention of HER2. We found ezrin to be expressed at low levels at the apical surface of normal mammary epithelial cells, but its expression is up-regulated and correlates with HER2 expression in hyperplasia and tumors in murine mammary tumor virus-Neu mice, in human HER2-positive breast cancer cell lines, and in ductal carcinoma in situ and invasive breast cancers from human patients. In breast cancer cells, ezrin co-localizes and interacts with HER2, NHERF1, PMCA2, and HSP90 in specialized membrane domains, and inhibiting ezrin disrupts interactions between HER2, PMCA2, NHERF1, and HSP90, inhibiting HER2 signaling and causing PKCα-mediated internalization and degradation of HER2. Inhibition of ezrin synergizes with lapatinib in a PKCα-dependent fashion to inhibit proliferation and promote apoptosis in HER2-positive breast cancer cells. We conclude that ezrin stabilizes a multiprotein complex that maintains active HER2 at the cell surface.

Protein kinase C mediated internalization of ErbB2 is independent of clathrin, ubiquitination and Hsp90 dissociation

Overexpression of ErbB2 is frequent in cancer and understanding the mechanisms which regulate its expression is important. ErbB2 is considered endocytosis resistant. It has no identified ligand, but upon heterodimerization it is a potent mediator of proliferative signaling. A recent study established a role for protein kinase C (PKC) in internalization and recycling of ErbB2. We have now further investigated the molecular mechanisms involved in PKC-mediated downregulation of ErbB2. We confirm that PMA-induced PKC activation causes ErbB2 internalization, but while the Hsp90 inhibitor 17-AAG induced ErbB2 degradation, PMA had no such effect. When combined with 17-AAG, PMA had additive effect on ErbB2 internalization indicating that Hsp90 inhibition and PKC activation induce internalization by alternative mechanisms. We confirm that while 17-AAG-induced internalization was clathrin-mediated, PMA-induced internalization was clathrin independent. This difference may be explained by while both 17-AAG and PMA reduced the constitutive tyrosine phosphorylation of ErbB2, only 17-AAG induced Hsp90 dissociation, Hsp70 recruitment and ubiquitination of ErbB2. Importantly, since PMA induced internalization of ErbB2, but not dissociation of Hsp90, Hsp90 does not per se retain ErbB2 at the plasma membrane. The morphology of the compartment into which receptors are sorted upon PKC activation has not previously been identified. By immuno-electron microscopy, we show that PMA sorts ErbB2 into a complex tubulovesicular or cisternal organelle resembling a previously described endocytic recycling compartment.

Identification of an HSP90 modulated multi-step process for ERBB2 degradation in breast cancer cells

The receptor tyrosine kinase ERBB2 interacts with HSP90 and is overexpressed in aggressive breast cancers. Therapeutic HSP90 inhibitors, i.e. Geldanamycin (GA), target ERBB2 to degradation. We have previously shown that HSP90 is responsible for the missorting of recycling ERBB2 to degradation compartments. In this study, we used biochemical, immunofluorescence and electron microscopy techniques to demonstrate that in SKBR3 human breast cancer cells, GA strongly induces polyubiquitination and internalization of the full-length p185-ERBB2, and promotes its cleavage, with the formation of a p116-ERBB2 form in EEA1-positive endosomes (EE). p116-ERBB2 corresponds to a non-ubiquitinated, signaling-impaired, membrane-bound fragment, which is readily sorted to lysosomes and degraded. To define the sequence of events leading to p116-ERBB2 degradation, we first blocked the EE maturation/trafficking to late endosomes/lysosomes with wortmannin, and found an increase in GA-dependent formation of p116-ERBB2; we then inhibited the proteasome activity with MG-132 or lactacystin, and observed an efficient block of p185-ERBB2 cleavage, and its accumulation in EE, suggesting that p185-ERBB2 polyubiquitination is necessary for proteasome-dependent p116-ERBB2 generation occurring in EE. As polyubiquitination has also been implicated in autophagy-mediated degradation of ERBB2 under different experimental conditions, we exploited this possibility and demonstrate that GA strongly inhibits early autophagy, and reduces the levels of the autophagy markers atg5-12 and LC3-II, irrespective of GA-induced ERBB2 polyubiquitination, ruling out a GA-dependent autophagic degradation of ERBB2. In conclusion, we propose that HSP90 inhibition fosters ERBB2 polyubiquitination and proteasome-dependent generation of a non-ubiquitinated and inactive p116-ERBB2 form in EE, which is trafficked from altered EE to lysosomes.

Proteolytic cleavages in the extracellular domain of receptor tyrosine kinases by membrane-associated serine proteases

The epithelial extracellular membrane-associated serine proteases matriptase, hepsin, and prostasin are proteolytic modifying enzymes of the extracellular domain (ECD) of the epidermal growth factor receptor (EGFR). Matriptase also cleaves the ECD of the vascular endothelial growth factor receptor 2 (VEGFR2) and the angiopoietin receptor Tie2. In this study we tested the hypothesis that these serine proteases may cleave the ECD of additional receptor tyrosine kinases (RTKs). We co-expressed the proteases in an epithelial cell line with Her2, Her3, Her4, insulin receptor (INSR), insulin-like growth factor I receptor (IGF-1R), the platelet-derived growth factor receptors (PDGFRs) α and β, or nerve growth factor receptor A (TrkA). Western blot analysis was performed to detect the carboxyl-terminal fragments (CTFs) of the RTKs. Matriptase and hepsin were found to cleave the ECD of all RTKs tested, while TMPRSS6/matriptase-2 cleaves the ECD of Her4, INSR, and PDGFR α and β. Prostasin was able to cleave the ECD of Her3 and PDGFRα. Matriptase cleaves phosphorylated Her2 at Arg558 and Arg599 and the Arg599 cleavage produces a CTF not recognized by the monoclonal antibody trastuzumab/Herceptin. Her2 cleavages by matriptase can be inhibited by the hepatocyte growth factor activator inhibitor 1 (HAI-1) in the MDA-MB-231 human breast cancer cells. Matriptase silencing in the Her2, matriptase, and HAI-1 triple-positive SKBR3 human breast cancer cells enhanced Her2 protein down-regulation induced by a sustained exposure to phorbol 12-myristate 13-acetate (PMA), which down-regulated matriptase protein. The novel Her2 cleavage and expression regulation mechanisms mediated by matriptase may have potential impacts in Her2-targeting therapies.

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.

Inhibition of PKCα reduces the ability of migration of kidney cancer cells but has no impact on cell apoptosis

Kidney cancer is among the most important causes of cancer-associated mortality worldwide. The present study aimed to evaluate protein kinase C α (PKCα) expression in kidney cancer tissues and cell lines, and its significance in apoptosis and migration. Expression of PKCα was analyzed using quantitative polymerase chain reaction and western blotting. In addition, the inhibitor of PKCα (calphostin C and GO6976) was used to treat kidney cancer cells. The ACHN cell line was generated with PKCα-small-interfering RNA (siRNA) and a stable expression of PKCα, in order to facilitate the analysis of apoptosis and migration of PKCα during knockdown and inactivation. Flow cytometry was used to determine the rates of apoptosis. Immunohistochemical staining was used to identify the localization of PKCα in renal clear cell carcinoma and normal sections. PKCα expression in normal tissues was found to be greater than in cancerous tissues. Furthermore, apoptosis was not promoted with PKCα inhibitors or PKCα-siRNA treatment, and a decrease of the migration ability was observed following transfection with PKCα-dominant negative. The results indicated that inhibition of PKCα might not contribute to apoptosis progression in kidney carcinoma.

Plasmodium falciparum ligand binding to erythrocytes induce alterations in deformability essential for invasion

The most lethal form of malaria in humans is caused by Plasmodium falciparum. These parasites invade erythrocytes, a complex process involving multiple ligand-receptor interactions. The parasite makes initial contact with the erythrocyte followed by dramatic deformations linked to the function of the Erythrocyte binding antigen family and P. falciparum reticulocyte binding-like families. We show EBA-175 mediates substantial changes in the deformability of erythrocytes by binding to glycophorin A and activating a phosphorylation cascade that includes erythrocyte cytoskeletal proteins resulting in changes in the viscoelastic properties of the host cell. TRPM7 kinase inhibitors FTY720 and waixenicin A block the changes in the deformability of erythrocytes and inhibit merozoite invasion by directly inhibiting the phosphorylation cascade. Therefore, binding of P. falciparum parasites to the erythrocyte directly activate a signaling pathway through a phosphorylation cascade and this alters the viscoelastic properties of the host membrane conditioning it for successful invasion.

CSF-1 receptor signalling is governed by pre-requisite EHD1 mediated receptor display on the macrophage cell surface

Colony stimulating factor-1 receptor (CSF-1R), a receptor tyrosine kinase (RTK), is the master regulator of macrophage biology. CSF-1 can bind CSF-1R resulting in receptor activation and signalling essential for macrophage functions such as proliferation, differentiation, survival, polarization, phagocytosis, cytokine secretion, and motility. CSF-1R activation can only occur after the receptor is presented on the macrophage cell surface. This process is reliant upon the underlying macrophage receptor trafficking machinery. However, the mechanistic details governing this process are incompletely understood. C-terminal Eps15 Homology Domain-containing (EHD) proteins have recently emerged as key regulators of receptor trafficking but have not yet been studied in the context of macrophage CSF-1R signalling. In this manuscript, we utilize primary bone-marrow derived macrophages (BMDMs) to reveal a novel function of EHD1 as a regulator of CSF-1R abundance on the cell surface. We report that EHD1-knockout (EHD1-KO) macrophages cell surface and total CSF-1R levels are significantly decreased. The decline in CSF-1R levels corresponds with reduced downstream macrophage functions such as cell proliferation, migration, and spreading. In EHD1-KO macrophages, transport of newly synthesized CSF-1R to the macrophage cell surface was reduced and was associated with the shunting of the receptor to the lysosome, which resulted in receptor degradation. These findings reveal a novel and functionally important role for EHD1 in governing CSF-1R signalling via regulation of anterograde transport of CSF-1R to the macrophage cell surface.

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.

Protein Kinase C-α is a Critical Protein for Antisense Oligonucleotide-mediated Silencing in Mammalian Cells

We have identified the existence of a productive, PKC-α-dependent endocytotic silencing pathway that leads gymnotically-delivered locked nucleic acid (LNA)-gapmer phosphorothioate antisense oligonucleotides (ASOs) into late endosomes. By blocking the maturation of early endosomes to late endosomes, silencing the expression of PKC-α results in the potent reduction of ASO silencing ability in the cell. We have also demonstrated that silencing of gene expression in the cytoplasm is vitiated when PKC-α expression is reduced. Restoring PKC-α expression via a reconstitution experiment reinstates the ability of ASOs to silence. These results advance our understanding of intracellular ASO trafficking and activity following gymnotic delivery, and further demonstrate the existence of two distinct silencing pathways in mammalian cells, one in the cytoplasmic and the other in the nuclear compartment.

Marked enhancement of lysosomal targeting and efficacy of ErbB2-targeted drug delivery by HSP90 inhibition

Targeted delivery of anticancer drugs to tumor cells using monoclonal antibodies against oncogenic cell surface receptors is an emerging therapeutic strategy. These strategies include drugs directly conjugated to monoclonal antibodies through chemical linkers (Antibody-Drug Conjugates, ADCs) or those encapsulated within nanoparticles that in turn are conjugated to targeting antibodies (Antibody-Nanoparticle Conjugates, ANPs). The recent FDA approval of the ADC Trastuzumab-TDM1 (Kadcyla; Genentech; San Francisco) for the treatment of ErbB2-overexpressing metastatic breast cancer patients has validated the strong potential of these strategies. Even though the activity of ANPs and ADCs is dependent on lysosomal traffic, the roles of the endocytic route traversed by the targeted receptor and of cancer cell-specific alterations in receptor dynamics on the efficiency of drug delivery have not been considered in these new targeted therapies. For example, constitutive association with the molecular chaperone HSP90 is thought to either retard ErbB2 endocytosis or to promote its recycling, traits undesirable for targeted therapy with ANPs and ADCs. HSP90 inhibitors are known to promote ErbB2 ubiquitination, targeting to lysosome and degradation. We therefore hypothesized that ErbB2-targeted drug delivery using Trastuzumab-conjugated nanoparticles could be significantly improved by HSP90 inhibitor-promoted lysosomal traffic of ErbB2. Studies reported here validate this hypothesis and demonstrate, both in vitro and in vivo, that HSP90 inhibition facilitates the intracellular delivery of Trastuzumab-conjugated ANPs carrying a model chemotherapeutic agent, Doxorubicin, specifically into ErbB2-overexpressing breast cancer cells, resulting in improved antitumor activity. These novel findings highlight the need to consider oncogene-specific alterations in receptor traffic in the design of targeted drug delivery strategies. We suggest that combination of agents that enhance receptor endocytosis and lysosomal routing can provide a novel strategy to significantly improve therapy with ANPs and ADCs.

Mining for Candidate Genes Related to Pancreatic Cancer Using Protein-Protein Interactions and a Shortest Path Approach

Pancreatic cancer (PC) is a highly malignant tumor derived from pancreas tissue and is one of the leading causes of death from cancer. Its molecular mechanism has been partially revealed by validating its oncogenes and tumor suppressor genes; however, the available data remain insufficient for medical workers to design effective treatments. Large-scale identification of PC-related genes can promote studies on PC. In this study, we propose a computational method for mining new candidate PC-related genes. A large network was constructed using protein-protein interaction information, and a shortest path approach was applied to mine new candidate genes based on validated PC-related genes. In addition, a permutation test was adopted to further select key candidate genes. Finally, for all discovered candidate genes, the likelihood that the genes are novel PC-related genes is discussed based on their currently known functions.

PKCα Attenuates Jagged-1-Mediated Notch Signaling in ErbB-2-Positive Breast Cancer to Reverse Trastuzumab Resistance

PURPOSE

Breast cancer is the second leading cause of cancer mortality among women worldwide. The major problem with current treatments is tumor resistance, recurrence, and disease progression. ErbB-2-positive breast tumors are aggressive and frequently become resistant to trastuzumab or lapatinib. We showed previously that Notch-1 is required for trastuzumab resistance in ErbB-2-positive breast cancer.

EXPERIMENTAL DESIGN

Here, we sought to elucidate mechanisms by which ErbB-2 attenuates Notch signaling and how this is reversed by trastuzumab or lapatinib.

RESULTS

The current study elucidates a novel Notch inhibitory mechanism by which PKCα downstream of ErbB-2 (i) restricts the availability of Jagged-1 at the cell surface to transactivate Notch, (ii) restricts the critical interaction between Jagged-1 and Mindbomb-1, an E3 ligase that is required for Jagged-1 ubiquitinylation and subsequent Notch activation, (iii) reverses trastuzumab resistance in vivo, and (iv) predicts better outcome in women with ErbB-2-positive breast cancer.

CONCLUSIONS

The clinical impact of these studies is PKCα is potentially a good prognostic marker for low Notch activity and increased trastuzumab sensitivity in ErbB-2-positive breast cancer. Moreover, women with ErbB-2-positive breast tumors expressing high Notch activation and low PKCα expression could be the best candidates for anti-Notch therapy.