Chromatinized protein kinase C-θ directly regulates inducible genes in epithelial to mesenchymal transition and breast cancer stem cells

Protein kinase C signaling "in" and "to" the nucleus: Master kinases in transcriptional regulation

PKC is a multifunctional family of Ser-Thr kinases widely implicated in the regulation of fundamental cellular functions, including proliferation, polarity, motility, and differentiation. Notwithstanding their primary cytoplasmic localization and stringent activation by cell surface receptors, PKC isozymes impel prominent nuclear signaling ultimately impacting gene expression. While transcriptional regulation may be wielded by nuclear PKCs, it most often relies on cytoplasmic phosphorylation events that result in nuclear shuttling of PKC downstream effectors, including transcription factors. As expected from the unique coupling of PKC isozymes to signaling effector pathways, glaring disparities in gene activation/repression are observed upon targeting individual PKC family members. Notably, specific PKCs control the expression and activation of transcription factors implicated in cell cycle/mitogenesis, epithelial-to-mesenchymal transition and immune function. Additionally, PKCs isozymes tightly regulate transcription factors involved in stepwise differentiation of pluripotent stem cells toward specific epithelial, mesenchymal, and hematopoietic cell lineages. Aberrant PKC expression and/or activation in pathological conditions, such as in cancer, leads to profound alterations in gene expression, leading to an extensive rewiring of transcriptional networks associated with mitogenesis, invasiveness, stemness, and tumor microenvironment dysregulation. In this review, we outline the current understanding of PKC signaling "in" and "to" the nucleus, with significant focus on established paradigms of PKC-mediated transcriptional control. Dissecting these complexities would allow the identification of relevant molecular targets implicated in a wide spectrum of diseases.

FRA-1 as a Regulator of EMT and Metastasis in Breast Cancer

Among FOS-related components of the dimeric AP-1 transcription factor, the oncoprotein FRA-1 (encoded by FOSL1) is a key regulator of invasion and metastasis. The well-established FRA-1 pro-invasive activity in breast cancer, in which FOSL1 is overexpressed in the TNBC (Triple Negative Breast Cancer)/basal subtypes, correlates with the FRA-1-dependent transcriptional regulation of EMT (Epithelial-to-Mesenchymal Transition). After summarizing the major findings on FRA-1 in breast cancer invasiveness, we discuss the FRA-1 mechanistic links with EMT and cancer cell stemness, mediated by transcriptional and posttranscriptional interactions between FOSL1/FRA-1 and EMT-regulating transcription factors, miRNAs, RNA binding proteins and cytokines, along with other target genes involved in EMT. In addition to the FRA-1/AP-1 effects on the architecture of target promoters, we discuss the diagnostic and prognostic significance of the EMT-related FRA-1 transcriptome, along with therapeutic implications. Finally, we consider several novel perspectives regarding the less explored roles of FRA-1 in the tumor microenvironment and in control of the recently characterized hybrid EMT correlated with cancer cell plasticity, stemness, and metastatic potential. We will also examine the application of emerging technologies, such as single-cell analyses, along with animal models of TNBC and tumor-derived CTCs and PDXs (Circulating Tumor Cells and Patient-Derived Xenografts) for studying the FRA-1-mediated mechanisms in in vivo systems of EMT and metastasis.

mTOR inhibition overcomes RSK3-mediated resistance to BET inhibitors in small cell lung cancer

Small cell lung cancer (SCLC) is a recalcitrant malignancy with limited treatment options. Bromodomain and extraterminal domain inhibitors (BETis) have shown promising preclinical activity in SCLC, but the broad sensitivity spectrum limits their clinical prospects. Here, we performed unbiased high-throughput drug combination screens to identify therapeutics that could augment the antitumor activities of BETis in SCLC. We found that multiple drugs targeting the PI-3K-AKT-mTOR pathway synergize with BETis, among which mTOR inhibitors (mTORis) show the highest synergy. Using various molecular subtypes of the xenograft models derived from patients with SCLC, we confirmed that mTOR inhibition potentiates the antitumor activities of BETis in vivo without substantially increasing toxicity. Furthermore, BETis induce apoptosis in both in vitro and in vivo SCLC models, and this antitumor effect is further amplified by combining mTOR inhibition. Mechanistically, BETis induce apoptosis in SCLC by activating the intrinsic apoptotic pathway. However, BET inhibition leads to RSK3 upregulation, which promotes survival by activating the TSC2-mTOR-p70S6K1-BAD cascade. mTORis block this protective signaling and augment the apoptosis induced by BET inhibition. Our findings reveal a critical role of RSK3 induction in tumor survival upon BET inhibition and warrant further evaluation of the combination of mTORis and BETis in patients with SCLC.

PKCθ Regulates Pituitary Adenoma Bone Invasion by Activating Osteoclast in NF-κB/IL-1β-Dependent Manner

BACKGROUND

Pituitary adenoma (PA) bone invasion results in adverse outcomes, such as reduced rates of complete surgical resection and biochemical remission as well as increased recurrence rates, though few studies have been conducted.

METHODS

We collected clinical specimens of PAs for staining and statistical analysis. Evaluation of the ability of PA cells to induce monocyte-osteoclast differentiation by coculturing PA cells with RAW264.7 in vitro. An in vivo model of bone invasion was used to simulate the process of bone erosion and evaluate the effect of different interventions in alleviating bone invasion.

RESULTS

We found an overactivation of osteoclasts in bone-invasive PAs and concomitant aggregation of inflammatory factors. Furthermore, activation of PKCθ in PAs was established as a central signaling promoting PA bone invasion through the PKCθ/NF-κB/IL-1β pathway. By inhibiting PKCθ and blocking IL1β, we were able to significantly reverse bone invasion in an in vivo study. Meanwhile, we also found that celastrol, as a natural product, can obviously reduce the secretion of IL-1β as well as alleviate the progression of bone invasion.

CONCLUSIONS

By activating the PKCθ/NF-κB/IL-1β pathway, pituitary tumors are able to induce monocyte-osteoclast differentiation in a paracrine manner and promote bone invasion, which can be alleviated by celastrol.

A Phase 1 Proof of Concept Study Evaluating the Addition of an LSD1 Inhibitor to Nab-Paclitaxel in Advanced or Metastatic Breast Cancer (EPI-PRIMED)

Objective

Lysine-Specific Demethylase-1 (LSD1) is overexpressed in breast cancer cells and facilitate mesenchymal properties which may contribute to therapeutic resistance and cancer progression. The purpose of this study was to investigate the safety of combination, nab-paclitaxel and phenelzine, an irreversible LSD1 inhibitor in patients with metastatic breast cancer (mBC).

Methods

Eligible patients with mBC were treated with nab-paclitaxel (100mg/m²) weekly for 3 weeks with one week break in a 28-day cycle. Dose escalation of phenelzine followed the Cumulative Cohort Design and phenelzine treatment commenced from day 2 of first cycle. Eleven patients were screened, and eligible patients were enrolled in cohorts with the dose of phenelzine ranging from 45mg to 90mg.

Results

The Optimum Biological Dose was established at 60mg of phenelzine daily in combination with nab-paclitaxel and considered as the recommended phase 2 dose. Most (95%) of adverse events were grade 1 or 2 with two grade 3 events being diarrhea and neutropenia at 45mg and 60mg phenelzine respectively, with no unexpected toxicity/deaths. Commonly reported toxicities were fatigue (n=4,50%), dizziness (n=6,75%), neutropenia (n=3,37.5%), peripheral neuropathy (n=3,37.5%), diarrhea (n=2,25%), and hallucination (n=2,25%). After a median follow up of 113 weeks, all patients showed disease progression on trial with 4 patients being alive at the time of data cut off, including one patient with triple negative breast cancer. Median progression-free survival was 34 weeks. Significant inhibition of LSD1 and suppression of mesenchymal markers in circulating tumor cells were noted.

Conclusion

Phenelzine in combination with nab-paclitaxel was well tolerated, without any unexpected toxicities in patients with mBC and demonstrated evidence of antitumor activity. For the first time, this proof-of-concept study showed in-vivo inhibition of LSD1 suppressed mesenchymal markers, which are known to facilitate generation of cancer stem cells with metastatic potential. Clinical Trial Registration: ClinicalTrials.Gov NCT03505528, UTN of U1111-1197-5518.

Selective Targeting of Protein Kinase C (PKC)-θ Nuclear Translocation Reduces Mesenchymal Gene Signatures and Reinvigorates Dysfunctional CD8+ T Cells in Immunotherapy-Resistant and Metastatic Cancers

Simple Summary

Some important signaling proteins that control how cells grow and behave not only act in the cytoplasm but also in the nucleus, where they tether to chromatin. This is especially true for protein kinase C (PKC)-θ, which acts in the nucleus to mediate cancer hallmarks that drive metastasis and in normal T cells. However, current PKC-θ inhibitors are either non-specific or target only its cytoplasmic function. In a bid to develop a novel class of PKC-θ inhibitor that maintains cytoplasmic signaling but inhibits its nuclear function, here we present a novel PKC-θ inhibitor (nPKC-θi2) that specifically inhibits nuclear translocation of PKC-θ without interrupting normal signaling in healthy T cells. We show for the first time that nPKC-θ mediates immunotherapy resistance via its activity in circulating tumor cells and dysfunctional CD8⁺ T cells. Our novel inhibitor provides a means to target this process by simultaneously overcoming T-cell exhaustion and cancer stem cell burden. As part of a sequential approach with other therapies, this work paves the way for improving outcomes in cancer patients with immunotherapy-resistant relapse and metastasis.

Abstract

Protein kinase C (PKC)-θ is a serine/threonine kinase with both cytoplasmic and nuclear functions. Nuclear chromatin-associated PKC-θ (nPKC-θ) is increasingly recognized to be pathogenic in cancer, whereas its cytoplasmic signaling is restricted to normal T-cell function. Here we show that nPKC-θ is enriched in circulating tumor cells (CTCs) in patients with triple-negative breast cancer (TNBC) brain metastases and immunotherapy-resistant metastatic melanoma and is associated with poor survival in immunotherapy-resistant disease. To target nPKC-θ, we designed a novel PKC-θ peptide inhibitor (nPKC-θi2) that selectively inhibits nPKC-θ nuclear translocation but not PKC-θ signaling in healthy T cells. Targeting nPKC-θ reduced mesenchymal cancer stem cell signatures in immunotherapy-resistant CTCs and TNBC xenografts. PKC-θ was also enriched in the nuclei of CD8⁺ T cells isolated from stage IV immunotherapy-resistant metastatic cancer patients. We show for the first time that nPKC-θ complexes with ZEB1, a key repressive transcription factor in epithelial-to-mesenchymal transition (EMT), in immunotherapy-resistant dysfunctional PD1⁺/CD8⁺ T cells. nPKC-θi2 inhibited the ZEB1/PKC-θ repressive complex to induce cytokine production in CD8⁺ T cells isolated from patients with immunotherapy-resistant disease. These data establish for the first time that nPKC-θ mediates immunotherapy resistance via its activity in CTCs and dysfunctional CD8⁺ T cells. Disrupting nPKC-θ but retaining its cytoplasmic function may offer a means to target metastases in combination with chemotherapy or immunotherapy.

Chronic Stress: Impacts on Tumor Microenvironment and Implications for Anti-Cancer Treatments

Chronic stress is common among cancer patients due to the psychological, operative, or pharmaceutical stressors at the time of diagnosis or during the treatment of cancers. The continuous activations of the hypothalamic-pituitary-adrenal (HPA) axis and the sympathetic nervous system (SNS), as results of chronic stress, have been demonstrated to take part in several cancer-promoting processes, such as tumorigenesis, progression, metastasis, and multi-drug resistance, by altering the tumor microenvironment (TME). Stressed TME is generally characterized by the increased proportion of cancer-promoting cells and cytokines, the reduction and malfunction of immune-supportive cells and cytokines, augmented angiogenesis, enhanced epithelial-mesenchymal transition, and damaged extracellular matrix. For the negative effects that these alterations can cause in terms of the efficacies of anti-cancer treatments and prognosis of patients, supplementary pharmacological or psychotherapeutic strategies targeting HPA, SNS, or psychological stress may be effective in improving the prognosis of cancer patients. Here, we review the characteristics and mechanisms of TME alterations under chronic stress, their influences on anti-cancer therapies, and accessory interventions and therapies for stressed cancer patients.

A 4 Gene-based Immune Signature Predicts Dedifferentiation and Immune Exhaustion in Thyroid Cancer

CONTEXT

The role of immune-related genes (IRGs) in thyroid cancer dedifferentiation and accompanying immune exhaustion remains largely unexplored.

OBJECTIVE

To construct a significant IRG-based signature indicative of dedifferentiation and immune exhaustion in thyroid cancer.

DESIGN AND SETTINGS

One exploratory cohort and 2 validation cohorts were used to identify stably dysregulated IRGs in dedifferentiated thyroid cancer (DDTC) and to obtain independent risk factors for dedifferentiation. The IRGs formed a gene signature, whose predictive value was tested by the receiver operating characteristic curve. Correlations between the signature and differentiation-related genes, immune checkpoints, and prognosis were analyzed. Gene set enrichment analyses were performed to identify related signaling pathways.

RESULTS

Four IRGs (PRKCQ, PLAUR, PSMD2, and BMP7) were found to be repeatedly dysregulated in DDTC, and they formed an IRG-based signature with a satisfactory predictive value for thyroid cancer dedifferentiation. Correlation analyses revealed that immune checkpoints were closely related to the 4 IRGs and the IRG-based signature, which was significantly associated with the histological subtype (P = 0.026), lymph node metastasis (P = 0.001), and BRAFV600E mutation (P < 0.001). The downregulated expression of PRKCQ shortened the disease-free survival for patients with thyroid cancer. Furthermore, we identified several signaling pathways inherently associated with the IRG-based signature.

CONCLUSIONS

This study suggests that IRGs participate in the dedifferentiation and immune exhaustion process of thyroid cancer and are potential biomarkers for DDTC.

Ddr1-induced neutrophil extracellular traps drive pancreatic cancer metastasis

Pancreatic ductal adenocarcinoma (PDAC) tumors are characterized by a desmoplastic reaction resulting in dense deposition of collagen that is known to promote cancer progression. A central mediator of pro-tumorigenic collagen signaling is the receptor tyrosine kinase discoid domain receptor 1 (DDR1). DDR1 is a critical driver of a mesenchymal and invasive cancer cell PDAC phenotype. Previous studies have demonstrated that genetic or pharmacologic inhibition of DDR1 reduces PDAC tumorigenesis and metastasis. Here, we investigated whether DDR1 signaling has cancer cell non-autonomous effects that promote PDAC progression and metastasis. We demonstrate that collagen-induced DDR1 activation in cancer cells is a major stimulus for CXCL5 production, resulting in the recruitment of tumor-associated neutrophils (TANs), the formation of neutrophil extracellular traps (NETs) and subsequent cancer cell invasion and metastasis. Moreover, we have identified that collagen-induced CXCL5 production was mediated by a DDR1-PKCθ-SYK-NFkB signaling cascade. Together, these results highlight the critical contribution of collagen I-DDR1 interaction in the formation of an immune microenvironment that promotes PDAC metastasis.

Targeting novel LSD1-dependent ACE2 demethylation domains inhibits SARS-CoV-2 replication

Treatment options for COVID-19 remain limited, especially during the early or asymptomatic phase. Here, we report a novel SARS-CoV-2 viral replication mechanism mediated by interactions between ACE2 and the epigenetic eraser enzyme LSD1, and its interplay with the nuclear shuttling importin pathway. Recent studies have shown a critical role for the importin pathway in SARS-CoV-2 infection, and many RNA viruses hijack this axis to re-direct host cell transcription. LSD1 colocalized with ACE2 at the cell surface to maintain demethylated SARS-CoV-2 spike receptor-binding domain lysine 31 to promote virus-ACE2 interactions. Two newly developed peptide inhibitors competitively inhibited virus-ACE2 interactions, and demethylase access to significantly inhibit viral replication. Similar to some other predominantly plasma membrane proteins, ACE2 had a novel nuclear function: its cytoplasmic domain harbors a nuclear shuttling domain, which when demethylated by LSD1 promoted importin-α-dependent nuclear ACE2 entry following infection to regulate active transcription. A novel, cell permeable ACE2 peptide inhibitor prevented ACE2 nuclear entry, significantly inhibiting viral replication in SARS-CoV-2-infected cell lines, outperforming other LSD1 inhibitors. These data raise the prospect of post-exposure prophylaxis for SARS-CoV-2, either through repurposed LSD1 inhibitors or new, nuclear-specific ACE2 inhibitors.

Crosstalk between miR-203 and PKCθ regulates breast cancer stem cell markers

INTRODUCTION

Protein kinase C theta (PKCθ) is expressed in ER-negative breast cancer and promotes cancer stem cells (CSCs) phenotype. PKCθ gene (PRKCQ) is predicted to be a target for tumor suppressor miR-203. Herein, we aim to validate this prediction and evaluate the ability of miR-203 to inhibit migration of breast cancer cell line enriched with CSCs, MDA-MB-231, via PRKCQ targeting.

METHODS

Cells were transfected with miR-203 mimic, PRKCQ siRNA and negative control; then real-time PCR, migration assay, western blotting, reporter assay, and chromatin accessibility assay were performed.

RESULTS

Our findings displayed significant decrease in PRKCQ mRNA level and luciferase signals in cells with restored miR-203 expression, therefore, validated PRKCQ as a direct target of miR-203. Additionally, inhibiting PRKCQ by siRNA led to significant inhibition of miR-203 expression and significant decrease of chromatin accessibility at miR-203 promoter region 466-291 upstream TSS. Both of miR-203 re-expression and PRKCQ suppression resulted in altering migration ability of MDA-MB-231 through regulating AKT pathway and genes involved in breast cancer stem cells, CD44 and ALDH1A3. Expression of CDK5, GIV, and NANOG was significantly downregulated in miR-203 mimic-transfected cells, while PRKCQ siRNA-transfected cells displayed downregulation of OCT3/4, SOX2, and NANOG. Furthermore, we found that miR-224 expression was enhanced while miR-150 was downregulated after ectopic expression of miR-203.

CONCLUSION

The study highlighted the negative feedback loop between miR-203 and its target PRKCQ and the interplay between them in regulating genes involved in BCSCs. The study also concluded "microRNA-mediated microRNA regulation" as an event in breast cancer cells.

The Emerging Function of PKCtheta in Cancer

Protein Kinase C theta (PKCθ) is a serine/threonine kinase that belongs to the novel PKC subfamily. In normal tissue, its expression is restricted to skeletal muscle cells, platelets and T lymphocytes in which PKCθ controls several essential cellular processes such as survival, proliferation and differentiation. Particularly, PKCθ has been extensively studied for its role in the immune system where its translocation to the immunological synapse plays a critical role in T cell activation. Beyond its physiological role in immune responses, increasing evidence implicates PKCθ in the pathology of various diseases, especially autoimmune disorders and cancers. In this review, we discuss the implication of PKCθ in various types of cancers and the PKCθ-mediated signaling events controlling cancer initiation and progression. In these types of cancers, the high PKCθ expression leads to aberrant cell proliferation, migration and invasion resulting in malignant phenotype. The recent development and application of PKCθ inhibitors in the context of autoimmune diseases could benefit the emergence of treatment for cancers in which PKCθ has been implicated.

PRKCQ inhibition enhances chemosensitivity of triple-negative breast cancer by regulating Bim

BACKGROUND

Protein kinase C theta, (PRKCQ/PKCθ) is a serine/threonine kinase that is highly expressed in a subset of triple-negative breast cancers (TNBC) and promotes their growth, anoikis resistance, epithelial-mesenchymal transition (EMT), and invasion. Here, we show that PRKCQ regulates the sensitivity of TNBC cells to apoptosis triggered by standard-of-care chemotherapy by regulating levels of pro-apoptotic Bim.

METHODS

To determine the effects of PRKCQ expression on chemotherapy-induced apoptosis, shRNA and cDNA vectors were used to modulate the PRKCQ expression in MCF-10A breast epithelial cells or triple-negative breast cancer cells (MDA-MB231Luc, HCC1806). A novel PRKCQ small-molecule inhibitor, 17k, was used to inhibit kinase activity. Viability and apoptosis of cells treated with PRKCQ cDNA/shRNA/inhibitor +/-chemotherapy were measured. Expression levels of Bcl2 family members were assessed.

RESULTS

Enhanced expression of PRKCQ is sufficient to suppress apoptosis triggered by paclitaxel or doxorubicin treatment. Downregulation of PRKCQ also enhanced the apoptosis of chemotherapy-treated TNBC cells. Regulation of chemotherapy sensitivity by PRKCQ mechanistically occurs via regulation of levels of Bim, a pro-apoptotic Bcl2 family member; suppression of Bim prevents the enhanced apoptosis observed with combined PRKCQ downregulation and chemotherapy treatment. Regulation of Bim and chemotherapy sensitivity is significantly dependent on PRKCQ kinase activity; overexpression of a catalytically inactive PRKCQ does not suppress Bim or chemotherapy-associated apoptosis. Furthermore, PRKCQ kinase inhibitor treatment suppressed growth, increased anoikis and Bim expression, and enhanced apoptosis of chemotherapy-treated TNBC cells, phenocopying the effects of PRKCQ downregulation.

CONCLUSIONS

These studies support PRKCQ inhibition as an attractive therapeutic strategy and complement to chemotherapy to inhibit the growth and survival of TNBC cells.

SETDB-1: A Potential Epigenetic Regulator in Breast Cancer Metastasis

The full epigenetic repertoire governing breast cancer metastasis is not completely understood. Here, we discuss the histone methyltransferase SET Domain Bifurcated Histone Lysine Methyltransferase 1 (SETDB1) and its role in breast cancer metastasis. SETDB1 serves as an exemplar of the difficulties faced when developing therapies that not only specifically target cancer cells but also the more elusive and aggressive stem cells that contribute to metastasis via epithelial-to-mesenchymal transition and confer resistance to therapies.

Nuclear-Biased DUSP6 Expression is Associated with Cancer Spreading Including Brain Metastasis in Triple-Negative Breast Cancer

DUSP6 is a dual-specificity phosphatase (DUSP) involved in breast cancer progression, recurrence, and metastasis. DUSP6 is predominantly cytoplasmic in HER2+ primary breast cancer cells, but the expression and subcellular localization of DUSPs, especially DUSP6, in HER2-positive circulating tumor cells (CTCs) is unknown. Here we used the DEPArray system to identify and isolate CTCs from metastatic triple negative breast cancer (TNBC) patients and performed single-cell NanoString analysis to quantify cancer pathway gene expression in HER2-positive and HER2-negative CTC populations. All TNBC patients contained HER2-positive CTCs. HER2-positive CTCs were associated with increased ERK1/ERK2 expression, which are direct DUSP6 targets. DUSP6 protein expression was predominantly nuclear in breast CTCs and the brain metastases but not pleura or lung metastases of TNBC patients. Therefore, nuclear DUSP6 may play a role in the association with cancer spreading in TNBC patients, including brain metastasis.

Lysine-Specific Histone Demethylase 1A Regulates Macrophage Polarization and Checkpoint Molecules in the Tumor Microenvironment of Triple-Negative Breast Cancer

Macrophages play an important role in regulating the tumor microenvironment (TME). Here we show that classical (M1) macrophage polarization reduced expression of LSD1, nuclear REST corepressor 1 (CoREST), and the zinc finger protein SNAIL. The LSD1 inhibitor phenelzine targeted both the flavin adenine dinucleotide (FAD) and CoREST binding domains of LSD1, unlike the LSD1 inhibitor GSK2879552, which only targeted the FAD domain. Phenelzine treatment reduced nuclear demethylase activity and increased transcription and expression of M1-like signatures both in vitro and in a murine triple-negative breast cancer model. Overall, the LSD1 inhibitors phenelzine and GSK2879552 are useful tools for dissecting the contribution of LSD1 demethylase activity and the nuclear LSD1-CoREST complex to switching macrophage polarization programs. These findings suggest that inhibitors must have dual FAD and CoREST targeting abilities to successfully initiate or prime macrophages toward an anti-tumor M1-like phenotype in triple-negative breast cancer.

Complex polymorphisms in endocytosis genes suggest alpha-cyclodextrin as a treatment for breast cancer

Most breast cancer deaths are caused by metastasis and treatment options beyond radiation and cytotoxic drugs, which have severe side effects, and hormonal treatments, which are or become ineffective for many patients, are urgently needed. This study reanalyzed existing data from three genome-wide association studies (GWAS) using a novel computational biostatistics approach (muGWAS), which had been validated in studies of 600-2000 subjects in epilepsy and autism. MuGWAS jointly analyzes several neighboring single nucleotide polymorphisms while incorporating knowledge about genetics of heritable diseases into the statistical method and about GWAS into the rules for determining adaptive genome-wide significance. Results from three independent GWAS of 1000-2000 subjects each, which were made available under the National Institute of Health's "Up For A Challenge" (U4C) project, not only confirmed cell-cycle control and receptor/AKT signaling, but, for the first time in breast cancer GWAS, also consistently identified many genes involved in endo-/exocytosis (EEC), most of which had already been observed in functional and expression studies of breast cancer. In particular, the findings include genes that translocate (ATP8A1, ATP8B1, ANO4, ABCA1) and metabolize (AGPAT3, AGPAT4, DGKQ, LPPR1) phospholipids entering the phosphatidylinositol cycle, which controls EEC. These novel findings suggest scavenging phospholipids as a novel intervention to control local spread of cancer, packaging of exosomes (which prepare distant microenvironment for organ-specific metastases), and endocytosis of β1 integrins (which are required for spread of metastatic phenotype and mesenchymal migration of tumor cells). Beta-cyclodextrins (βCD) have already been shown to be effective in in vitro and animal studies of breast cancer, but exhibits cholesterol-related ototoxicity. The smaller alpha-cyclodextrins (αCD) also scavenges phospholipids, but cannot fit cholesterol. An in-vitro study presented here confirms hydroxypropyl (HP)-αCD to be twice as effective as HPβCD against migration of human cells of both receptor negative and estrogen-receptor positive breast cancer. If the previous successful animal studies with βCDs are replicated with the safer and more effective αCDs, clinical trials of adjuvant treatment with αCDs are warranted. Ultimately, all breast cancer are expected to benefit from treatment with HPαCD, but women with triple-negative breast cancer (TNBC) will benefit most, because they have fewer treatment options and their cancer advances more aggressively.

Cytokine-mediated therapeutic resistance in breast cancer

Therapeutic resistance leading to tumor relapse is a major challenge in breast cancer (BCa) treatment. Numerous factors involved in multiple mechanisms promote the development of tumor chemo/radio-resistance. Cytokines/chemokines are important inflammatory factors and highly related to tumorigenesis, metastasis and tumors responses to treatment. A large number of studies have demonstrated that the network of cytokines activates multiple cell signaling pathways to promote tumor cell survival, proliferation, invasion, and migration. Particularly in BCa, cytokines-enhanced the epithelial-mesenchymal transition (EMT) process plays a pivotal role in the progression of metastatic phenotypes and resistance to the traditional chemo/radio-therapy. Virtually, therapeutic resistance is not entirely determined by tumor cell intrinsic characteristics but also dependent upon synchronized effects by numerous of local microenvironmental factors. Emerging evidence highlighted that exosomes secreted from various types of cells promote intercellular communication by transferring bioactive molecules including miRNAs and cytokines, suggesting that exosomes are essential for sustentation of tumor progression and therapeutic resistance within the tumor microenvironment. In this review, we discuss the mechanisms by which cytokines promote therapeutic resistance of BCa and suggest a potential approach for improving BCa therapeutics by inhibition of exosome function.

Identification of miR-34a-target interactions by a combined network based and experimental approach

Circulating miRNAs have been associated with numerous human diseases. The lack of understanding the functional roles of blood-born miRNAs limits, however, largely their value as disease marker. In a systems biology analysis we identified miR-34a as strongly associated with pathogenesis. Genome-wide analysis of miRNAs in blood cell fractions highlighted miR-34a as most significantly up-regulated in CD3+ cells of lung cancer patients. By our in silico analysis members of the protein kinase C family (PKC) were indicated as miR-34a target genes. Using a luciferase assay, we confirmed binding of miR-34a-5p to target sequences within the 3′UTRs of five PKC family members. To verify the biological effect, we transfected HEK 293T and Jurkat cells with miR-34a-5p causing reduced endogenous protein levels of PKC isozymes. By combining bioinformatics approaches with experimental validation, we demonstrate that one of the most relevant disease associated miRNAs has the ability to control the expression of a gene family.

LSD1 activation promotes inducible EMT programs and modulates the tumour microenvironment in breast cancer

Complex regulatory networks control epithelial-to-mesenchymal transition (EMT) but the underlying epigenetic control is poorly understood. Lysine-specific demethylase 1 (LSD1) is a key histone demethylase that alters the epigenetic landscape. Here we explored the role of LSD1 in global epigenetic regulation of EMT, cancer stem cells (CSCs), the tumour microenvironment, and therapeutic resistance in breast cancer. LSD1 induced pan-genomic gene expression in networks implicated in EMT and selectively elicits gene expression programs in CSCs whilst repressing non-CSC programs. LSD1 phosphorylation at serine-111 (LSD1-s111p) by chromatin anchored protein kinase C-theta (PKC-θ), is critical for its demethylase and EMT promoting activity and LSD1-s111p is enriched in chemoresistant cells in vivo. LSD1 couples to PKC-θ on the mesenchymal gene epigenetic template promotes LSD1-mediated gene induction. In vivo, chemotherapy reduced tumour volume, and when combined with an LSD1 inhibitor, abrogated the mesenchymal signature and promoted an innate, M1 macrophage-like tumouricidal immune response. Circulating tumour cells (CTCs) from metastatic breast cancer (MBC) patients were enriched with LSD1 and pharmacological blockade of LSD1 suppressed the mesenchymal and stem-like signature in these patient-derived CTCs. Overall, LSD1 inhibition may serve as a promising epigenetic adjuvant therapy to subvert its pleiotropic roles in breast cancer progression and treatment resistance.

PRKCQ promotes oncogenic growth and anoikis resistance of a subset of triple-negative breast cancer cells

Background

The protein kinase C (PKC) family comprises distinct classes of proteins, many of which are implicated in diverse cellular functions. Protein tyrosine kinase C theta isoform (PRKCQ)/PKCθ, a member of the novel PKC family, may have a distinct isoform-specific role in breast cancer. PKCθ is preferentially expressed in triple-negative breast cancer (TNBC) compared to other breast tumor subtypes. We hypothesized that PRKCQ/PKCθ critically regulates growth and survival of a subset of TNBC cells.

Methods

To elucidate the role of PRKCQ/PKCθ in regulating growth and anoikis resistance, we used both gain and loss of function to modulate expression of PRKCQ. We enhanced expression of PKCθ (kinase-active or inactive) in non-transformed breast epithelial cells (MCF-10A) and assessed effects on epidermal growth factor (EGF)-independent growth, anoikis, and migration. We downregulated expression of PKCθ in TNBC cells, and determined effects on in vitro and in vivo growth and survival. TNBC cells were also treated with a small molecule inhibitor to assess requirement for PKCθ kinase activity in the growth of TNBC cells.

Results

PRKCQ/PKCθ can promote oncogenic phenotypes when expressed in non-transformed MCF-10A mammary epithelial cells; PRKCQ/PKCθ enhances anchorage-independent survival, growth-factor-independent proliferation, and migration. PKCθ expression promotes retinoblastoma (Rb) phosphorylation and cell-cycle progression under growth factor-deprived conditions that typically induce cell-cycle arrest of MCF-10A breast epithelial cells. Proliferation and Rb phosphorylation are dependent on PKCθ-stimulated extracellular signal-related kinase (Erk)/mitogen-activated protein kinase (MAPK) activity. Enhanced Erk/MAPK activity is dependent on the kinase activity of PKCθ, as overexpression of kinase-inactive PKCθ does not stimulate Erk/MAPK or Rb phosphorylation or promote growth-factor-independent proliferation. Downregulation of PRKCQ/PKCθ in TNBC cells enhances anoikis, inhibits growth in 3-D Matrigel^TM cultures, and impairs triple-negative tumor xenograft growth. AEB071, an inhibitor of PKCθ kinase activity, also inhibits growth and invasive branching of TNBC cells in 3-D cultures, further supporting a role for PKCθ kinase activity in triple-negative cancer cell growth.

Conclusions

Enhanced PRKCQ/PKCθ expression can promote growth-factor-independent growth, anoikis resistance, and migration. PRKCQ critically regulates growth and survival of a subset of TNBC. Inhibition of PKCθ kinase activity may be an attractive therapeutic approach for TNBC, a subtype in need of improved targeted therapies.

Electronic supplementary material

The online version of this article (doi:10.1186/s13058-016-0749-6) contains supplementary material, which is available to authorized users.

Nuclear PKC-θ facilitates rapid transcriptional responses in human memory CD4+ T cells through p65 and H2B phosphorylation

Memory T cells are characterized by their rapid transcriptional programs upon re-stimulation. This transcriptional memory response is facilitated by permissive chromatin, but exactly how the permissive epigenetic landscape in memory T cells integrates incoming stimulatory signals remains poorly understood. By genome-wide ChIP-sequencing ex vivo human CD4⁺ T cells, here, we show that the signaling enzyme, protein kinase C theta (PKC-θ) directly relays stimulatory signals to chromatin by binding to transcriptional-memory-responsive genes to induce transcriptional activation. Flanked by permissive histone modifications, these PKC-enriched regions are significantly enriched with NF-κB motifs in ex vivo bulk and vaccinia-responsive human memory CD4⁺ T cells. Within the nucleus, PKC-θ catalytic activity maintains the Ser536 phosphorylation on the p65 subunit of NF-κB (also known as RelA) and can directly influence chromatin accessibility at transcriptional memory genes by regulating H2B deposition through Ser32 phosphorylation. Furthermore, using a cytoplasm-restricted PKC-θ mutant, we highlight that chromatin-anchored PKC-θ integrates activating signals at the chromatin template to elicit transcriptional memory responses in human memory T cells.

Summary: Memory T cells have a rapid transcriptional program upon re-stimulation. Chromatin-anchored PKC-θ integrates activating signals at the chromatin template to elicit this transcriptional memory in T cells.

Identification of chromatin accessibility domains in human breast cancer stem cells

Epithelial-to-mesenchymal transition (EMT) is physiological in embryogenesis and wound healing but also associated with the formation of cancer stem cells (CSCs). Many EMT signaling pathways are implicated in CSC formation, but the precise underlying mechanisms of CSC formation remain elusive. We have previously demonstrated that PKC is critical for EMT induction and CSC formation in inducible breast EMT/CSC models. Here, we used formaldehyde-assisted isolation of regulatory elements-sequencing (FAIRE-seq) to investigate DNA accessibility changes after PKC activation and determine how they influence EMT and CSC formation. During EMT, DNA accessibility principally increased in regions distant from transcription start sites, low in CpG content, and enriched with chromatin enhancer marks. ChIP-sequencing revealed that a subset of these regions changed from poised to active enhancers upon stimulation, with some even more acteylated in CSCs. While regions with increased accessibility were enriched for FOX, AP-1, TEAD, and TFAP2 motifs, those containing FOX and AP-1 motif were associated with increased expression of CSC-associated genes, while those with TFAP2 were associated with genes with increased expression in non-CSCs. Silencing of 2 members of the FOX family, FOXN2 and FOXQ1, repressed CSCs and the mesenchymal phenotype and inhibited the CSC gene signature. These novel, PKC-induced DNA accessibility regions help explain how the epigenomic plasticity of cells undergoing EMT leads to CSC gene activation.

Differential Roles for DUSP Family Members in Epithelial-to-Mesenchymal Transition and Cancer Stem Cell Regulation in Breast Cancer

Dual-specificity phosphatases (DUSPs) dephosphorylate threonine/serine and tyrosine residues on their substrates. Here we show that DUSP1, DUSP4, and DUSP6 are involved in epithelial-to-mesenchymal transition (EMT) and breast cancer stem cell (CSC) regulation. DUSP1, DUSP4, and DUSP6 are induced during EMT in a PKC pathway signal-mediated EMT model. We show for the first time that the key chromatin-associated kinase PKC-θ directly regulates a subset of DUSP family members. DUSP1, DUSP4, and DUSP6 globally but differentially co-exist with enhancer and permissive active histone post-translational modifications, suggesting that they play distinct roles in gene regulation in EMT/CSCs. We show that nuclear DUSP4 associates with the key acetyltransferase p300 in the context of the chromatin template and dynamically regulates the interplay between two key phosphorylation marks: the 1834 (active) and 89 (inhibitory) residues central to p300’s acetyltransferase activity. Furthermore, knockdown with small-interfering RNAs (siRNAs) shows that DUSP4 is required for maintaining H3K27ac, a mark mediated by p300. DUSP1, DUSP4, and DUSP6 knockdown with siRNAs shows that they participate in the formation of CD44^hi/CD24^lo/EpCAM⁺ breast CSCs: DUSP1 knockdown reduces CSC formation, while DUSP4 and DUSP6 knockdown enhance CSC formation. Moreover, DUSP6 is overexpressed in patient-derived HER2⁺ breast carcinomas compared to benign mammary tissue. Taken together, these findings illustrate novel pleiotropic roles for DUSP family members in EMT and CSC regulation in breast cancer.

Crosstalk between Wnt signaling and Phorbol ester-mediated PKC signaling in MCF-7 human breast cancer cells

Although many studies have implicated the crosstalk between the Wnt and PKC signaling pathways in tumor initiation and progression, the molecular roles of PKC isoforms in the Wnt signaling pathway remain poorly understood. In this study, we explored the contribution of PKC isoforms to canonical and noncanonical Wnt signaling pathway in mediating cell migration and an epithelial-mesenchymal transition (EMT). When MCF-7 cells were treated with 12-O-tetradecanoylphorbol-13-acetate (TPA) for up to 3 weeks, the effect of TPA on Wnt signaling pathway was dramatically different depending on the exposure time. The short term exposure (3 days) of MCF-7 cells to TPA exhibited significant induction of Wnt5a expression, along with the enhanced expression of PKC-α, to promote cell migration, which suggested that activation of noncanonical Wnt signaling pathway is associated with PKC-α. However, the chronic exposure (3 weeks) of cells to TPA completely suppressed Wnt5a expression and the expression of PKC-η and PKC-δ, whereas the expression of Wnt3a and PKC-θ were up-regulated to activate the canonical Wnt signaling pathway. Moreover, the loss of epithelial markers, including E-cadherin and GATA-3, suggested that chronic exposure of TPA stimulates EMT. Taken together, our data suggest that PKC-θ positively regulates the canonical Wnt signaling pathway, and that PKC-η and PKC-δ negatively modulate this signaling pathway.

Protein kinase C in the immune system: from signalling to chromatin regulation

Protein kinase C (PKC) form a key family of enzymes involved in signalling pathways that specifically phosphorylates substrates at serine/threonine residues. Phosphorylation by PKC is important in regulating a variety of cellular events such as cell proliferation and the regulation of gene expression. In the immune system, PKCs are involved in regulating signal transduction pathways important for both innate and adaptive immunity, ultimately resulting in the expression of key immune genes. PKCs act as mediators during immune cell signalling through the immunological synapse. PKCs are traditionally known to be cytoplasmic signal transducers and are well embedded in the signalling pathways of cells to mediate the cells' response to a stimulus from the plasma membrane to the nucleus. PKCs are also found to transduce signals within the nucleus, a process that is distinct from the cytoplasmic signalling pathway. There is now growing evidence suggesting that PKC can directly regulate gene expression programmes through a non-traditional role as nuclear kinases. In this review, we will focus on the role of PKCs as key cytoplasmic signal transducers in immune cell signalling, as well as its role in nuclear signal transduction. We will also highlight recent evidence for its newly discovered regulatory role in the nucleus as a chromatin-associated kinase.

The Role of PKC-θ in CD4+ T Cells and HIV Infection: To the Nucleus and Back Again

Protein kinase C (PKC)-θ is the only member of the PKC family that has the ability to translocate to the immunological synapse between T cells and antigen-presenting cells upon T cell receptor and MHC-II recognition. PKC-θ interacts functionally and physically with other downstream effector molecules to mediate T cell activation, differentiation, and migration. It plays a critical role in the generation of Th2 and Th17 responses and is less important in Th1 and CTL responses. PKC-θ has been recently shown to play a role in the nucleus, where it mediates inducible gene expression in the development of memory CD4+ T cells. This novel PKC (nPKC) can up-regulate HIV-1 transcription and PKC-θ activators such as Prostratin have been used in early HIV-1 reservoir eradication studies. The exact manner of the activation of virus by these compounds and the role of PKC-θ, particularly its nuclear form and its association with NF-κB in both the cytoplasmic and nuclear compartments, needs further precise elucidation especially given the very important role of NF-κB in regulating transcription from the integrated retrovirus. Continued studies of this nPKC isoform will give further insight into the complexity of T cell signaling kinases.

The role of protein kinase-C theta in control of epithelial to mesenchymal transition and cancer stem cell formation

The protein kinase C (PKC) activator phorbol 12-myristate 13-acetate (PMA) induces transition of the epithelial MCF-7 cell line to a mesenchymal phenotype. A subset of the resulting mesenchymal cells has surface markers characteristics of a cancer stem cell (CSC) population. We profiled the transcriptome changes associated with the epithelial to mesenchymal transition and those that occurred in the CSC subset. Using a siRNA knockdown strategy, we examined the extent to which these changes were dependent on the PKC family member, PKC-θ. The importance of the cytoplasmic signaling role of this kinase is well established and in this study, we have shown by PKC-θ ChIP-sequencing analysis that this kinase has a dual role with the ability to also associate with chromatin on a subset of PKC-θ dependent genes. In the associated manuscript (Zafar et al., 2014 [5]) we presented evidence for the first time showing that this nuclear role of PKC-θ is also important for gene induction and mesenchymal/CSC phenotype. Here we describe the analysis associated with the transcriptome and ChIP-seq data presented in Zafar et al. (2014) [5] and uploaded to NCBI Gene Expression Omnibus (GSE53335).