p23/Tmp21 associates with protein kinase Cdelta (PKCdelta) and modulates its apoptotic function

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.

TMED2 Induces Cisplatin Resistance in Breast Cancer via Targeting the KEAP1-Nrf2 Pathway

OBJECTIVE

Cisplatin is the first-line treatment for breast cancer, but it faces challenges of drug resistance. This study investigated new molecular mechanisms underlying cisplatin resistance in breast cancer.

METHODS

We analyzed sequencing data from the TCGA database to identify potential associations between transmembrane emp24 protein transport domain containing 2 (TMED2) and breast cancer. Western blotting, real-time PCR, CCK-8, and TUNEL assays were used to measure the effects and molecular mechanism of TMED2 on cisplatin resistance in MCF-7 and MDA-MB-231 cell lines.

RESULTS

TMED2 was overexpressed in breast cancer and associated with poor prognosis. TMED2 increased cisplatin resistance in breast cancer cells in vitro via promoting ubiquitination of Kelch-like ECH-associated protein 1 (KEAP1), relieving inhibition of KEAP1 on nuclear factor erythroid 2-related factor 2 (Nrf2), and increasing expression of downstream drug resistance related genes, such as heme oxygenase 1 (HO-1) and NAD (P) H quinone oxidoreductase 1 (NQO1).

CONCLUSION

We identified a new molecular mechanism by which TMED2 affects cisplatin resistance in breast cancer. Our results provide theoretical guidance for future clinical applications.

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.

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.

Golgi Complex: A Signaling Hub in Cancer

The Golgi Complex is the central hub in the endomembrane system and serves not only as a biosynthetic and processing center but also as a trafficking and sorting station for glycoproteins and lipids. In addition, it is an active signaling hub involved in the regulation of multiple cellular processes, including cell polarity, motility, growth, autophagy, apoptosis, inflammation, DNA repair and stress responses. As such, the dysregulation of the Golgi Complex-centered signaling cascades contributes to the onset of several pathological conditions, including cancer. This review summarizes the current knowledge on the signaling pathways regulated by the Golgi Complex and implicated in promoting cancer hallmarks and tumor progression.

Multiple subcellular localizations and functions of protein kinase Cδ in liver cancer

Protein kinase Cδ (PKCδ) is a member of the PKC family, and its implications have been reported in various biological and cancerous processes, including cell proliferation, cell death, tumor suppression, and tumor progression. In liver cancer cells, accumulating reports show the bi-functional regulation of PKCδ in cell death and survival. PKCδ function is defined by various factors, such as phosphorylation, catalytic domain cleavage, and subcellular localization. PKCδ has multiple intracellular distribution patterns, ranging from the cytosol to the nucleus. We recently found a unique extracellular localization of PKCδ in liver cancer and its growth factor-like function in liver cancer cells. In this review, we first discuss the structural features of PKCδ and then focus on the functional diversity of PKCδ based on its subcellular localization, such as the nucleus, cell surface, and extracellular space. These findings improve our knowledge of PKCδ involvement in the progression of liver cancer.

The circular RNA CDR1as regulate cell proliferation via TMED2 and TMED10

Background

Circular RNAs (CircRNAs) are biologically active RNAs. CDR1as is one such circRNA previously reported to be a microRNA-7 (miR-7) sponge, thereby regulating associated gene expression. The specific underlying molecular mechanisms of CDR1as biology, however, remain largely unknown.

Methods

We performed CDR1as knockdown in order to explore its function in cell proliferation, migration, the cell cycle, and tumorigenesis. We further employed quantitative proteomic analyses and associated bioinformatics strategies to globally assess CDR1as-regulated proteins (CRPs). Western blotting and immunofluorescence staining were used to validate the proteomic results. We additionally investigated a specific link between TMED2, TMED10, and miR-7 via a dual-luciferase reporter system, and generated CDR1as knockout cell lines via CRISPR/Cas9 editing.

Results

We identified 353 proteins dysregulated upon CDR1as knockdown in 293 T cells. These CRPs were found to interact with one another and to play key roles in certain cellular pathways. Two such proteins, TMED2 and TMED10, were found to specifically contribute to the influence of CDR1as on cell proliferation. CDR1as may regulate these two TMED proteins through miR-7 sponging. We were able to further confirm these results using both CRISPRi cell lines and nude mouse models.

Conclusion

This study suggested that CDR1as may regulate cell proliferation via serving as a miR-7 sponge, thereby regulating TMED2 and TMED10 expression. These results are an invaluable template for future streamlined studies of circRNAs.

TMP21 regulates autophagy by modulating ROS production and mTOR activation

Autophagy is a catabolic cellular response to stress that has been liked to various human diseases. However, the precise involvement of autophagy in health and disease remains unclear. To explore the molecular mechanisms of autophagy, we investigated the effect of TMP21. We found that the down-regulation of TMP21 induced autophagy in SH-SY5Y cells. In addition, the enhanced autophagy observed upon TMP21 depletion was almost completely blocked in ATG5 knockout (KO) or ATG7-KO HeLa cells. Silencing of TMP21 in SH-SY5Y cells also increased the production of cellular reactive oxygen species (ROS). Accordingly, treatment with the ROS scavenger NAC suppressed autophagy activation as well as ROS production in TMP21-depleted cells. In addition, the inhibition of mTOR by treatment with Torin1 was mitigated in TMP21 overexpressing cells compared with that in control cells. Taken together, these results indicated that TMP21 could regulate autophagy by modulating ROS production and mTOR activation.

RAB21 interacts with TMED10 and modulates its localization and abundance

Membrane trafficking controls vesicular transport of cargo between cellular compartments. Vesicular trafficking is essential for cellular homeostasis and dysfunctional trafficking is linked to several pathologies such as neurodegenerative diseases. Following endocytosis, early endosomes act as sorting stations of internalized materials, routing cargo toward various fates. One important class of membrane trafficking regulators are RAB GTPases. RAB21 has been associated with multiple functions and regulates integrin internalization, endosomal sorting of specific clathrin-independent cargo and autophagy. Although RAB21 is mostly associated with early endosomes, it has been shown to mediate a specific sorting event at the Golgi. From mass spectrometry data, we identified a GTP-favored interaction between RAB21 and TMED10 and 9, essential regulators of COPI and COPII vesicles. Using RAB21 knockout cells, we describe the role of RAB21 in modulating TMED10 Golgi localization. Taken together, our study suggests a new potential function of RAB21 in modulating TMED10 trafficking, with relevance to neurodegenerative disorders.

Summary: A small early endosomal RAB GTPase is found to interact with p24 family members, with potential impacts on p24 functions.

TMP21 in Alzheimer's Disease: Molecular Mechanisms and a Potential Target

Alzheimer’s disease (AD) is the most common form of dementia in the elderly, which is characterized by progressive cognitive impairment. Neuritic plaques, neurofibrillary tangles and neuronal loss are the major neuropathological hallmarks in AD brains. TMP21 is a key molecule for protein trafficking in cells. Growing evidence indicates that TMP21 is dysregulated in AD, which plays a pivotal role in neuritic plaque formation. Therefore, we aim to review the dysregulation of TMP21 in AD, the role of TMP21 in neuritic plaque formation and underlying mechanisms. Moreover, the potential role of TMP21 in neurofibrillary tangle formation, synaptic impairment and neuronal loss is discussed. It will provide an outlook into the potential of regulating TMP21 as a therapeutic approach for AD treatment.

Down-regulated TMED10 in Alzheimer disease induces autophagy via ATG4B activation

Several studies have shown that dysfunction of macroautophagy/autophagy is associated with many human diseases, including neurodegenerative disease and cancer. To explore the molecular mechanisms of autophagy, we performed a cell-based functional screening with SH-SY5Y cells stably expressing GFP-LC3, using an siRNA library and identified TMED10 (transmembrane p24 trafficking protein 10), previously known as the γ-secretase-modulating protein, as a novel regulator of autophagy. Further investigations revealed that depletion of TMED10 induced the activation of autophagy. Interestingly, protein-protein interaction assays showed that TMED10 directly binds to ATG4B (autophagy related gene 4B cysteine peptidase), and the interaction is diminished under autophagy activation conditions such as rapamycin treatment and serum deprivation. In addition, inhibition of TMED10 significantly enhanced the proteolytic activity of ATG4B for LC3 cleavage. Importantly, the expression of TMED10 in AD (Alzheimer disease) patients was considerably decreased, and downregulation of TMED10 increased amyloid-β (Aβ) production. Treatment with Aβ increased ATG4B proteolytic activity as well as dissociation of TMED10 and ATG4B. Taken together, our results suggest that the AD-associated protein TMED10 negatively regulates autophagy by inhibiting ATG4B activity.Abbreviations: Aβ: amyloid-β; AD: Alzheimer disease; ATG: autophagy related; BECN1: beclin 1; BiFC: bimolecular fluorescence complementation; CD: cytosolic domain; GFP: green fluorescent protein; GLUC: Gaussia luciferase; IP: immunoprecipitation; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; LD: luminal domain; PD: Parkinson disease; ROS: reactive oxygen species; siRNA: small interfering RNA; SNP: single-nucleotide polymorphisms; TD: transmembrane domain; TMED10: transmembrane p24 trafficking protein 10; VC: C terminus of Venus fluorescent protein; VN: N terminus of Venus fluorescent protein.

Characterization of AJH-836, a diacylglycerol-lactone with selectivity for novel PKC isozymes

Diacylglycerol (DAG) is a key lipid second messenger downstream of cellular receptors that binds to the C1 domain in many regulatory proteins. Protein kinase C (PKC) isoforms constitute the most prominent family of signaling proteins with DAG-responsive C1 domains, but six other families of proteins, including the chimaerins, Ras-guanyl nucleotide-releasing proteins (RasGRPs), and Munc13 isoforms, also play important roles. Their significant involvement in cancer, immunology, and neurobiology has driven intense interest in the C1 domain as a therapeutic target. As with other classes of targets, however, a key issue is the establishment of selectivity. Here, using [³H]phorbol 12,13-dibutyrate ([³H]PDBu) competition binding assays, we found that a synthetic DAG-lactone, AJH-836, preferentially binds to the novel PKC isoforms PKCδ and PKCϵ relative to classical PKCα and PKCβII. Assessment of intracellular translocation, a hallmark for PKC activation, revealed that AJH-836 treatment stimulated a striking preferential redistribution of PKCϵ to the plasma membrane relative to PKCα. Moreover, unlike with the prototypical phorbol ester phorbol 12-myristate 13-acetate (PMA), prolonged exposure of cells to AJH-836 selectively down-regulated PKCδ and PKCϵ without affecting PKCα expression levels. Biologically, AJH-836 induced major changes in cytoskeletal reorganization in lung cancer cells, as determined by the formation of membrane ruffles, via activation of novel PKCs. We conclude that AJH-836 represents a C1 domain ligand with PKC-activating properties distinct from those of natural DAGs and phorbol esters. Our study supports the feasibility of generating selective C1 domain ligands that promote novel biological response patterns.

Protein kinase C in cancer: The top five unanswered questions

Few kinases have been studied as extensively as protein kinase C (PKC), particularly in the context of cancer. As major cellular targets for the phorbol ester tumor promoters and diacylglycerol (DAG), a second messenger generated by stimulation of membrane receptors, PKC isozymes play major roles in the control of signaling pathways associated with proliferation, migration, invasion, tumorigenesis, and metastasis. However, despite decades of research, fundamental questions remain to be answered or are the subject of intense controversy. Primary among these unresolved issues are the role of PKC isozymes as either tumor promoter or tumor suppressor kinases and the incomplete understanding on isozyme-specific substrates and effectors. The involvement of PKC isozymes in cancer progression needs to be reassessed in the context of specific oncogenic and tumor suppressing alterations. In addition, there are still major hurdles in addressing isozyme-specific function due to the limited specificity of most pharmacological PKC modulators and the lack of validated predictive biomarkers for response, which impacts the translation of these agents to the clinic. In this review we focus on key controversial issues and upcoming challenges, with the expectation that understanding the intricacies of PKC function will help fulfill the yet unsuccessful promise of targeting PKCs for cancer therapeutics.

TMED10 Protein Interferes with Transforming Growth Factor (TGF)-β Signaling by Disrupting TGF-β Receptor Complex Formation

The intensity and duration of TGF-β signaling determine the cellular biological response. How this is negatively regulated is not well understood. Here, we identified a novel negative regulator of TGF-β signaling, transmembrane p24-trafficking protein 10 (TMED10). TMED10 disrupts the complex formation between TGF-β type I (also termed ALK5) and type II receptors (TβRII). Misexpression studies revealed that TMED10 attenuated TGF-β-mediated signaling. A 20-amino acid-long region from Thr⁹¹ to Glu¹¹⁰ within the extracellular region of TMED10 was found to be crucial for TMED10 interaction with both ALK5 and TβRII. Synthetic peptides corresponding to this region inhibit both TGF-β-induced Smad2 phosphorylation and Smad-dependent transcriptional reporter activity. In a xenograft cancer model, where previously TGF-β was shown to elicit tumor-promoting effects, gain-of-function and loss-of-function studies for TMED10 revealed a decrease and increase in the tumor size, respectively. Thus, we determined herein that TMED10 expression levels are the key determinant for efficiency of TGF-β receptor complex formation and signaling.

p24 family proteins: key players in the regulation of trafficking along the secretory pathway

p24 family proteins have been known for a long time, but their functions have remained elusive. However, they are emerging as essential regulators of protein trafficking along the secretory pathway, influencing the composition, structure, and function of different organelles in the pathway, especially the ER and the Golgi apparatus. In addition, they appear to modulate the transport of specific cargos, including GPI-anchored proteins, G-protein-coupled receptors, or K/HDEL ligands. As a consequence, they have been shown to play specific roles in signaling, development, insulin secretion, and the pathogenesis of Alzheimer's disease. The search of new putative ligands may open the way to discover new functions for this fascinating family of proteins.

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.

Disruption of Heat Shock Protein 90 (Hsp90)-Protein Kinase Cδ (PKCδ) Interaction by (-)-Maackiain Suppresses Histamine H1 Receptor Gene Transcription in HeLa Cells

The histamine H1 receptor (H1R) gene is an allergic disease sensitive gene, and its expression level is strongly correlated with the severity of allergic symptoms. (-)-Maackiain was identified as a Kujin-derived anti-allergic compound that suppresses the up-regulation of the H1R gene. However, the underlying mechanism of H1R gene suppression remains unknown. Here, we sought to identify a target protein of (-)-maackiain and investigate its mechanism of action. A fluorescence quenching assay and immunoblot analysis identified heat shock protein 90 (Hsp90) as a target protein of (-)-maackiain. A pull-down assay revealed that (-)-maackiain disrupted the interaction of Hsp90 with PKCδ, resulting in the suppression of phorbol 12-myristate 13-acetate (PMA)-induced up-regulation of H1R gene expression in HeLa cells. Additional Hsp90 inhibitors, including 17-(allylamino)-17-demethoxygeldanamycin, celastrol, and novobiocin also suppressed PMA-induced H1R gene up-regulation. 17-(Allylamino)-17-demethoxygeldanamycin inhibited PKCδ translocation to the Golgi and phosphorylation of Tyr(311) on PKCδ. These data suggest that (-)-maackiain is a novel Hsp90 pathway inhibitor. The underlying mechanism of the suppression of PMA-induced up-regulation of H1R gene expression by (-)-maackiain and Hsp90 inhibitors is the inhibition of PKCδ activation through the disruption of Hsp90-PKCδ interaction. Involvement of Hsp90 in H1R gene up-regulation suggests that suppression of the Hsp90 pathway could be a novel therapeutic strategy for allergic rhinitis.

TMP21 modulates cell growth in papillary thyroid cancer cells by inducing autophagy through activation of the AMPK/mTOR pathway

OBJECTIVE

To investigate the role of transmembrane protein (TMP) 21 in human thyroid cancer.

METHODS

The recombinant expression vector pcDNA3.1 (+)-TMP21 and specific small interfering RNAs (siRNA) against TMP21 were transfected into a papillary thyroid cancer cell line (TPC1). After transfection, the expression of TMP21 was confirmed by quantitative real-time polymerase chain reaction (qRT-PCR) and Western blotting. Moreover, cell viability and apoptosis rate were respectively determined by 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) colorimetric assay and flow cytometry (FCM). Additionally, Western blotting was performed to analyze the adenosine monophosphate (AMP)-activated protein kinase (AMPK)/mammalian target of rapamycin (mTOR) pathways associated protein (P-AMPKα(Thr172), P-mTOR(Ser2448), light chain (LC)-II/LC3-I, and P-S6K(Thr389)) after pre-treatment with AMPK inhibitor, compound C (Com C) and siTMP21.

RESULTS

The TMP21 protein level and cell viability were significantly higher, but apoptotic rate was significantly lower by transfection with pcDNA3.1-TMP21 than those in control group (P < 0.05), and reverse results were obtained by transfection with siTMP21. However, qRT-PCR showed different results due to the feedback inhibition of mRNA. Besides, silencing of TMP21 significantly reduced the levels of P-mTOR(Ser2448) and P-S6K(Thr389) (P < 0.05), but significantly increased the levels of P-AMPKα(Thr172) and LC3-II/LC3-I compared with the control group (P < 0.01). Whereas, the levels of P-AMPKα(Thr172) and LC3-II/LC3-I were significantly decreased by Com C compared with the control group (P < 0.05).

CONCLUSION

TMP21 modulates cell growth in TPC1 cells by inducing autophagy, which may be associated with activation of AMPK/mTOR pathway.

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

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

PKCδ promotes high glucose induced renal tubular oxidative damage via regulating activation and translocation of p66Shc

Diabetic kidney disease (DKD) is a leading cause of end-stage renal disease (ESRD). Renal tubular injury by overproduction of ROS in mitochondria plays a critical role in the pathogenesis of DKD. Evidences have shown that p66Shc was involved in renal tubular injury via mitochondrial-dependent ROS production pathway, but little is known about the upstream signaling of p66Shc that leads to tubular oxidative damage under high glucose conditions. In this study, an increased PKCδ and p66Shc activation and ROS production in renal tissues of patients with diabetic nephropathy were seen and further analysis revealed a positive correlation between the tubulointerstitial damage and p-PKCδ, p-p66Shc, and ROS production. In vitro, we investigated the phosphorylation and activation of p66Shc and PKCδ during treatment of HK-2 cells with high glucose (HG). Results showed that the activation of p66Shc and PKCδ was increased in a dose- and time-dependent manner, and this effect was suppressed by Rottlerin, a pharmacologic inhibitor of PKCδ. Moreover, PKCδ siRNA partially blocked HG-induced p66Shc phosphorylation, translocation, and ROS production in HK-2 cells. Taken together, these data suggest that activation of PKCδ promotes tubular cell injury through regulating p66Shc phosphorylation and mitochondrial translocation in HG ambient.

Expression of tmp21 in normal adult human tissues

TMP21, known as p23 protein, is one important member of the p24 protein families. The degradation of TMP21 is mediated by the ubiquitin-proteasome pathway, as with the other presenilin-associated γ-secretase complex members. NFAT plays a very important role in regulation of human TMP21 gene expression. Compared with the function of TMP21, the studies about the distribution of this protein in human tissues are limited. We collected 19 normal adult human tissues from a healthy adult man died in a traffic accident and did examination of all the tissues collected for ICH, western blot and RT-PCR. It was shown that the expression of TMP21 is at high levels in heart, liver, lung, kidney and adrenal gland; moderate levels in brain, pancreas, prostate gland, testicle, small intestine, colon, stomach, gall bladder, thyroid gland and trachea; low levels in skeletal muscle, skin and lymphonodus. TMP21 is widely existed in normal adult human tissues. The current study provided for the first time a comprehensive expression of TMP21 in normal adult human tissues. It will benefit on helping in the design and interpretation of future studies focused on expounding the function of TMP21.

The type III secretion effector NleF of enteropathogenic Escherichia coli activates NF-κB early during infection

The enteric pathogens enteropathogenic Escherichia coli (EPEC) and enterohemorrhagic E. coli employ a type 3 secretion system (T3SS) to manipulate the host inflammatory response during infection. Previously, it has been reported that EPEC, in a T3SS-dependent manner, induces an early proinflammatory response through activation of NF-κB via extracellular signal-regulated kinases 1 and 2 (ERK1/2) and protein kinase Cζ (PKCζ). However, the activation of NF-κB during infection has not yet been attributed to an effector. At later time points postinfection, NF-κB signaling is inhibited through the translocation of multiple effectors, including NleE and NleC. Here we report that the highly conserved non-LEE (locus of enterocyte effacement)-encoded effector F (NleF) shows both diffuse and mitochondrial localization during ectopic expression. Moreover, NleF induces the nuclear translocation of NF-κB p65 and the expression of interleukin 8 (IL-8) following ectopic expression and during EPEC infection. Furthermore, the proinflammatory activity and localization of NleF were dependent on the C-terminal amino acids LQCG. While the C-terminal domain of NleF has previously been shown to be essential for interaction with caspase-4, caspase-8, and caspase-9, the proinflammatory activity of NleF was independent of interaction with caspase-4, -8, or -9. In conclusion, EPEC, through the T3SS-dependent translocation of NleF, induces a proinflammatory response in an NF-κB-dependent manner in the early stages of infection.

Transcriptional regulation of oncogenic protein kinase Cϵ (PKCϵ) by STAT1 and Sp1 proteins

Overexpression of PKCϵ, a kinase associated with tumor aggressiveness and widely implicated in malignant transformation and metastasis, is a hallmark of multiple cancers, including mammary, prostate, and lung cancer. To characterize the mechanisms that control PKCϵ expression and its up-regulation in cancer, we cloned an ∼ 1.6-kb promoter segment of the human PKCϵ gene (PRKCE) that displays elevated transcriptional activity in cancer cells. A comprehensive deletional analysis established two regions rich in Sp1 and STAT1 sites located between -777 and -105 bp (region A) and -921 and -796 bp (region B), respectively, as responsible for the high transcriptional activity observed in cancer cells. A more detailed mutagenesis analysis followed by EMSA and ChIP identified Sp1 sites in positions -668/-659 and -269/-247 as well as STAT1 sites in positions -880/-869 and -793/-782 as the elements responsible for elevated promoter activity in breast cancer cells relative to normal mammary epithelial cells. RNAi silencing of Sp1 and STAT1 in breast cancer cells reduced PKCϵ mRNA and protein expression, as well as PRKCE promoter activity. Moreover, a strong correlation was found between PKCϵ and phospho-Ser-727 (active) STAT1 levels in breast cancer cells. Our results may have significant implications for the development of approaches to target PKCϵ and its effectors in cancer therapeutics.

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.

Inhibiting tyrosine phosphorylation of protein kinase Cδ (PKCδ) protects the salivary gland from radiation damage

Radiation therapy for head and neck cancer can result in extensive damage to normal adjacent tissues such as the salivary gland and oral mucosa. We have shown previously that tyrosine phosphorylation at Tyr-64 and Tyr-155 activates PKCδ in response to apoptotic stimuli by facilitating its nuclear import. Here we have identified the tyrosine kinases that mediate activation of PKCδ in apoptotic cells and have explored the use of tyrosine kinase inhibitors for suppression of irradiation-induced apoptosis. We identify the damage-inducible kinase, c-Abl, as the PKCδ Tyr-155 kinase and c-Src as the Tyr-64 kinase. Depletion of c-Abl or c-Src with shRNA decreased irradiation- and etoposide-induced apoptosis, suggesting that inhibitors of these kinases may be useful therapeutically. Pretreatment with dasatinib, a broad spectrum tyrosine kinase inhibitor, blocked phosphorylation of PKCδ at both Tyr-64 and Tyr-155. Expression of "gate-keeper" mutants of c-Abl or c-Src that are active in the presence of dasatinib restored phosphorylation of PKCδ at Tyr-155 and Tyr-64, respectively. Imatinib, a c-Abl-selective inhibitor, also specifically blocked PKCδ Tyr-155 phosphorylation. Dasatinib and imatinib both blocked binding of PKCδ to importin-α and nuclear import, demonstrating that tyrosine kinase inhibitors can inhibit nuclear accumulation of PKCδ. Likewise, pretreatment with dasatinib also suppressed etoposide and radiation induced apoptosis in vitro. In vivo, pre-treatment of mice with dasatinib blocked radiation-induced apoptosis in the salivary gland by >60%. These data suggest that tyrosine kinase inhibitors may be useful prophylactically for protection of nontumor tissues in patients undergoing radiotherapy of the head and neck.

Coordinated activation of the Rac-GAP β2-chimaerin by an atypical proline-rich domain and diacylglycerol

Chimaerins, a family of GTPase activating proteins (GAPs) for the small G-protein Rac, have been implicated in development, neuritogenesis, and cancer. These Rac-GAPs are regulated by the lipid second messenger diacylglycerol (DAG) generated by tyrosine-kinases such as the epidermal growth factor receptor (EGFR). Here we identify an atypical Pro-rich motif in chimaerins that binds to the adaptor protein Nck1. Unlike most Nck1 partners, chimaerins bind to the third SH3 domain of Nck1. This association is mediated by electrostatic interactions of basic residues within the Pro-rich motif with acidic clusters in the SH3 domain. EGF promotes the binding of β2-chimaerin to Nck1 in the cell periphery in a DAG-dependent manner. Moreover, β2-chimaerin translocation to the plasma membrane and its peripheral association with Rac1 requires Nck1. Our studies underscore a coordinated mechanism for β2-chimaerin activation that involves lipid interactions via the C1 domain and protein-protein interactions via the N-terminal Pro-rich region.

Regulation of Transcriptional Networks by PKC Isozymes: Identification of c-Rel as a Key Transcription Factor for PKC-Regulated Genes

BACKGROUND

Activation of protein kinase C (PKC), a family of serine-threonine kinases widely implicated in cancer progression, has major impact on gene expression. In a recent genome-wide analysis of prostate cancer cells we identified distinctive gene expression profiles controlled by individual PKC isozymes and highlighted a prominent role for PKCδ in transcriptional activation.

PRINCIPAL FINDINGS

Here we carried out a thorough bioinformatics analysis to dissect transcriptional networks controlled by PKCα, PKCδ, and PKCε, the main diacylglycerol/phorbol ester PKCs expressed in prostate cancer cells. Despite the remarkable differences in the patterns of transcriptional responsive elements (REs) regulated by each PKC, we found that c-Rel represents the most frequent RE in promoters regulated by all three PKCs. In addition, promoters of PKCδ-regulated genes were particularly enriched with REs for CREB, NF-E2, RREB, SRF, Oct-1, Evi-1, and NF-κB. Most notably, by using transcription factor-specific RNAi we were able to identify subsets of PKCδ-regulated genes modulated by c-Rel and CREB. Furthermore, PKCδ-regulated genes condensed under the c-Rel transcriptional regulation display significant functional interconnections with biological processes such as angiogenesis, inflammatory response, and cell motility.

CONCLUSION/SIGNIFICANCE

Our study identified candidate transcription factors in the promoters of PKC regulated genes, in particular c-Rel was found as a key transcription factor in the control of PKCδ-regulated genes. The deconvolution of PKC-regulated transcriptional networks and their nodes may greatly help in the identification of PKC effectors and have significant therapeutics implications.

Expression pattern of protein kinase Cδ during mouse embryogenesis

Background

The members of the protein kinase C (PKC) family consist of serine/threonine kinases classified according to their regulatory domain. Those that belong to the novel PKC subfamily, such as PKCδ, are dependent on diacylglycerol but not Calcium when considering their catalytic activity. Although several studies have shown the importance of PKCδ in different cellular events in health and disease, the overall in vivo distribution of this PKC isoform during development is still lacking. Through Lac Z and antibody staining procedures, we show here the in vivo expression of PKCδ during mouse embryogenesis.

Results

Ganglia were the domains with most prominent expression of PKCδ in most of the stages analysed, although PKCδ could also be detected in heart and somites at earlier stages, and cartilage primordium and skin among other sites in older embryos.

Conclusions

The strong expression of PKCδ in ganglia during murine development shown in this study suggests a significant role of this isoform as well as redundancy with other PKCs within the nervous system, since PKCδ deficient mice develop normally.

ARF1-regulated coatomer directs the steady-state localization of protein kinase C epsilon at the Golgi apparatus

Protein kinase C epsilon (PKCε) contributes to multiple signaling pathways affecting human disease. The function of PKCε requires it to undergo changes in subcellular distribution in response to signaling events. While the mechanisms underlying this translocation are incompletely understood, it involves the receptor for activated C kinase protein (RACK2/β'-COP). This receptor also functions as a vesicle coat protein in the secretory pathway where it is regulated by the small GTP-binding protein ADP-ribosylation factor, ARF1. We inhibited ARF1 activation to test the requirement for RACK2/β'-COP in PKCε localization in NIH3T3 fibroblasts. We found that steady-state localization of PKCε at the Golgi complex requires ARF1-regulated RACK2/β'-COP function. By contrast, we did not observe any defects in phorbol ester-induced translocation when ARF1 was inhibited. We also found that PKCε bound to isolated membranes through two distinct mechanisms. One mechanism was dependent upon RACK2/β'-COP while a second was RACK2/β'-COP-independent and stimulated by phorbol esters. Finally, we show that RACK2/β'-COP affects the subcellular distribution of a constitutively active form of PKCε, in a manner similar to what we observed for wild-type PKCε. Together, our data support a role for RACK2/β'-COP in the steady-state localization of PKCε at the Golgi apparatus, which may be independent of its role during PKCε translocation to the cell surface.

Phosphorylation of Smooth Muscle 22α Facilitates Angiotensin II–Induced ROS Production Via Activation of the PKCδ-P47 phox Axis Through Release of PKCδ and Actin Dynamics and Is Associated With Hypertrophy and Hyperplasia of Vascular Smooth Muscle Cells In Vitro and In Vivo

Rationale:

We have demonstrated that smooth muscle (SM) 22α inhibits cell proliferation via blocking Ras-ERK1/2 signaling in vascular smooth muscle cells (VSMCs) and in injured arteries. The recent study indicates that SM22α disruption can independently promote arterial inflammation through activation of reactive oxygen species (ROS)-mediated NF-κB pathways. However, the mechanisms by which SM22α controls ROS production have not been characterized.

Objective:

To investigate how SM22α disruption promotes ROS production and to characterize the underlying mechanisms.

Methods and Results:

ROS level was measured by dihydroethidium staining for superoxide and TBA assay for malondialdehyde, respectively. We showed that downregulation and phosphorylation of SM22α were associated with angiotensin (Ang) II–induced increase in ROS production in VSMCs of rats and human. Ang II induced the phosphorylation of SM22α at Serine 181 in an Ang II type 1 receptor–PKCδ pathway–dependent manner. Phosphorylated SM22α activated the protein kinase C (PKC)δ-p47 phox axis via 2 distinct pathways: (1) disassociation of PKCδ from SM22α, and in turn binding to p47 phox , in the early stage of Ang II stimulation; and (2) acceleration of SM22α degradation through ubiquitin-proteasome, enhancing PKCδ membrane translocation via induction of actin cytoskeletal dynamics in later oxidative stress. Inhibition of SM22α phosphorylation abolished the Ang II–activated PKCδ-p47 phox axis and inhibited the hypertrophy and hyperplasia of VSMCs in vitro and in vivo, accompanied with reduction of ROS generation.

Conclusions:

These findings indicate that the disruption of SM22α plays pivotal roles in vascular oxidative stress. PKCδ-mediated SM22α phosphorylation is a novel link between actin cytoskeletal remodeling and oxidative stress and may be a potential target for the development of new therapeutics for cardiovascular diseases.

Protein kinase cδ in apoptosis: a brief overview

Protein kinase C-delta (PKCδ), a member of the lipid-regulated serine/threonine PKC family, has been implicated in a wide range of important cellular processes. In the past decade, the critical role of PKCδ in the regulation of both intrinsic and extrinsic apoptosis pathways has been widely explored. In most cases, over-expression or activation of PKCδ results in the induction of apoptosis. The phosphorylations and multiple cell organelle translocations of PKCδ initiate apoptosis by targeting multiple downstream effectors. During apoptosis, PKCδ is proteolytically cleaved by caspase-3 to generate a constitutively activated catalytic fragment, which amplifies apoptosis cascades in nucleus and mitochondria. However, PKCδ also exerts its anti-apoptotic and pro-survival roles in some cases. Therefore, the complicated role of PKCδ in apoptosis appears to be stimulus and cell type dependent. This review is mainly focused on how PKCδ gets activated in diverse ways in response to apoptotic signals and how PKCδ targets different downstream regulators to sponsor or restrain apoptosis induction.

HDAC inhibitors augmented cell migration and metastasis through induction of PKCs leading to identification of low toxicity modalities for combination cancer therapy

PURPOSE

Histone deacetylase inhibitors (HDACi) are actively explored as new-generation epigenetic drugs but have low efficacy in cancer monotherapy. To reveal new mechanism for combination therapy, we show that HDACi induce cell death but simultaneously activate tumor-progressive genes to ruin therapeutic efficacy. Combined treatments to target tumorigenesis and HDACi-activated metastasis with low toxic modalities could develop new strategies for long-term cancer therapy.

EXPERIMENTAL DESIGN

Because metastasis is the major cause of cancer mortality, we measured cell migration activity and profiled metastasis-related gene expressions in HDACi-treated cancer cells. We developed low toxic combination modalities targeting tumorigenesis and HDACi-activated metastasis for preclinical therapies in mice.

RESULTS

We showed that cell migration activity was dramatically and dose dependently enhanced by various classes of HDACi treatments in 13 of 30 examined human breast, gastric, liver, and lung cancer cell lines. Tumor metastasis was also enhanced in HDACi-treated mice. HDACi treatments activated multiple PKCs and downstream substrates along with upregulated proapoptotic p21. For targeting tumorigenesis and metastasis with immediate clinical impact, we showed that new modalities of HDACi combined drugs with PKC inhibitory agent, curcumin or tamoxifen, not only suppressed HDACi-activated tumor progressive proteins and cell migration in vitro but also inhibited tumor growth and metastasis in vivo.

CONCLUSION

Treatments of different structural classes of HDACi simultaneously induced cell death and promoted cell migration and metastasis in multiple cancer cell types. Suppression of HDACi-induced PKCs leads to development of low toxic and long-term therapeutic strategies to potentially treat cancer as a chronic disease.