PKD2 and PKD3 promote prostate cancer cell invasion by modulating NF-κB- and HDAC1-mediated expression and activation of uPA

Circadian rhythm disruption and endocrine-related tumors

This review delved into the intricate relationship between circadian clocks and physiological processes, emphasizing their critical role in maintaining homeostasis. Orchestrated by interlocked clock genes, the circadian timekeeping system regulates fundamental processes like the sleep-wake cycle, energy metabolism, immune function, and cell proliferation. The central oscillator in the hypothalamic suprachiasmatic nucleus synchronizes with light-dark cycles, while peripheral tissue clocks are influenced by cues such as feeding times. Circadian disruption, linked to modern lifestyle factors like night shift work, correlates with adverse health outcomes, including metabolic syndrome, cardiovascular diseases, infections, and cancer. We explored the molecular mechanisms of circadian clock genes and their impact on metabolic disorders and cancer pathogenesis. Specific associations between circadian disruption and endocrine tumors, spanning breast, ovarian, testicular, prostate, thyroid, pituitary, and adrenal gland cancers, are highlighted. Shift work is associated with increased breast cancer risk, with PER genes influencing tumor progression and drug resistance. CLOCK gene expression correlates with cisplatin resistance in ovarian cancer, while factors like aging and intermittent fasting affect prostate cancer. Our review underscored the intricate interplay between circadian rhythms and cancer, involving the regulation of the cell cycle, DNA repair, metabolism, immune function, and the tumor microenvironment. We advocated for integrating biological timing into clinical considerations for personalized healthcare, proposing that understanding these connections could lead to novel therapeutic approaches. Evidence supports circadian rhythm-focused therapies, particularly chronotherapy, for treating endocrine tumors. Our review called for further research to uncover detailed connections between circadian clocks and cancer, providing essential insights for targeted treatments. We emphasized the importance of public health interventions to mitigate lifestyle-related circadian disruptions and underscored the critical role of circadian rhythms in disease mechanisms and therapeutic interventions.

Advances in sequencing and omics studies in prostate cancer: unveiling molecular pathogenesis and clinical applications

Background

Prostate cancer (PCa) is one of the most threatening health problems for the elderly males. However, our understanding of the disease has been limited by the research technology for a long time. Recently, the maturity of sequencing technology and omics studies has been accelerating the studies of PCa, establishing themselves as an essential impetus in this field.

Methods

We assessed Web of Science (WoS) database for publications of sequencing and omics studies in PCa on July 3rd, 2023. Bibliometrix was used to conduct ulterior bibliometric analysis of countries/affiliations, authors, sources, publications, and keywords. Subsequently, purposeful large amounts of literature reading were proceeded to analyze research hotspots in this field.

Results

3325 publications were included in the study. Research associated with sequencing and omics studies in PCa had shown an obvious increase recently. The USA and China were the most productive countries, and harbored close collaboration. CHINNAIYAN AM was identified as the most influential author, and CANCER RESEARCH exhibited huge impact in this field. Highly cited publications and their co-citation relationships were used to filtrate literatures for subsequent literature reading. Based on keyword analysis and large amounts of literature reading, 'the molecular pathogenesis of PCa' and 'the clinical application of sequencing and omics studies in PCa' were summarized as two research hotspots in the field.

Conclusion

Sequencing technology had a deep impact on the studies of PCa. Sequencing and omics studies in PCa helped researchers reveal the molecular pathogenesis, and provided new possibilities for the clinical practice of PCa.

Protein kinase D drives the secretion of invasion mediators in triple-negative breast cancer cell lines

The protein kinase D (PKD) family members regulate the fission of cargo vesicles at the Golgi complex and play a pro-oncogenic role in triple-negative breast cancer (TNBC). Whether PKD facilitates the secretion of tumor-promoting factors in TNBC, however, is still unknown. Using the pharmacological inhibition of PKD activity and siRNA-mediated depletion of PKD2 and PKD3, we identified the PKD-dependent secretome of the TNBC cell lines MDA-MB-231 and MDA-MB-468. Mass spectrometry-based proteomics and antibody-based assays revealed a significant downregulation of extracellular matrix related proteins and pro-invasive factors such as LIF, MMP-1, MMP-13, IL-11, M-CSF and GM-CSF in PKD-perturbed cells. Notably, secretion of these proteins in MDA-MB-231 cells was predominantly controlled by PKD2 and enhanced spheroid invasion. Consistently, PKD-dependent secretion of pro-invasive factors was more pronounced in metastatic TNBC cell lines. Our study thus uncovers a novel role of PKD2 in releasing a pro-invasive secretome.

Potential role for protein kinase D inhibitors in prostate cancer

Protein kinase D (PrKD), a novel serine-threonine kinase, belongs to a family of calcium calmodulin kinases that consists of three isoforms: PrKD1, PrKD2, and PrKD3. The PrKD isoforms play a major role in pathologic processes such as cardiac hypertrophy and cancer progression. The charter member of the family, PrKD1, is the most extensively studied isoform. PrKD play a dual role as both a proto-oncogene and a tumor suppressor depending on the cellular context. The duplicity of PrKD can be highlighted in advanced prostate cancer (PCa) where expression of PrKD1 is suppressed whereas the expressions of PrKD2 and PrKD3 are upregulated to aid in cancer progression. As understanding of the PrKD signaling pathways has been better elucidated, interest has been garnered in the development of PrKD inhibitors. The broad-spectrum kinase inhibitor staurosporine acts as a potent PrKD inhibitor and is the most well-known; however, several other novel and more specific PrKD inhibitors have been developed over the last two decades. While there is tremendous potential for PrKD inhibitors to be used in a clinical setting, none has progressed beyond preclinical trials due to a variety of challenges. In this review, we focus on PrKD signaling in PCa and the potential role of PrKD inhibitors therein, and explore the possible clinical outcomes based on known function and expression of PrKD isoforms at different stages of PCa.

Emerging photodynamic/sonodynamic therapies for urological cancers: progress and challenges

Photodynamic therapy (PDT), and sonodynamic therapy (SDT) that developed from PDT, have been studied for decades to treat solid tumors. Compared with other deep tumors, the accessibility of urological tumors (e.g., bladder tumor and prostate tumor) makes them more suitable for PDT/SDT that requires exogenous stimulation. Due to the introduction of nanobiotechnology, emerging photo/sonosensitizers modified with different functional components and improved physicochemical properties have many outstanding advantages in cancer treatment compared with traditional photo/sonosensitizers, such as alleviating hypoxia to improve quantum yield, passive/active tumor targeting to increase drug accumulation, and combination with other therapeutic modalities (e.g., chemotherapy, immunotherapy and targeted therapy) to achieve synergistic therapy. As WST11 (TOOKAD® soluble) is currently clinically approved for the treatment of prostate cancer, emerging photo/sonosensitizers have great potential for clinical translation, which requires multidisciplinary participation and extensive clinical trials. Herein, the latest research advances of newly developed photo/sonosensitizers for the treatment of urological cancers, and the efficacy, as well as potential biological effects, are highlighted. In addition, the clinical status of PDT/SDT for urological cancers is presented, and the optimization of the photo/sonosensitizer development procedure for clinical translation is discussed.

Exosomal RNF157 mRNA from prostate cancer cells contributes to M2 macrophage polarization through destabilizing HDAC1

Background

Exosomes have been identified to mediate the transmission of RNAs among different cells in tumor microenvironment, thus affecting the progression of different diseases. However, exosomal messenger RNAs (mRNAs) have been rarely explored. RNF157 mRNA has been found to be up-regulated in PCa patients’ exosomes, but the role of exosomal RNF157 mRNA in PCa development remains unclear.

Methods

Online databases were utilized for predicting gene expression and binding correlation between different factors. RT-qPCR and western blot assays were respectively done to analyze RNA and protein expressions. Flow cytometry analysis was implemented to analyze M2 polarization.

Results

RNF157 expression was high in PCa tissues and cells. M2 polarization of macrophages was enhanced after co-culture with PCa cells or with exosomes released by PCa cells. Upon RNF157 knockdown in PCa cells, the extracted exosomes could not lead to the facilitated M2 polarization. Mechanistically, RNF157 could bind to HDAC1 and contribute to HDAC1 ubiquitination, which led to HDAC1 degradation and resulting in promoting M2 polarization of macrophages. Animal experiments validated that exosomal RNF157 accelerated PCa tumor growth through facilitating macrophage M2 polarization.

Conclusion

Exosome-mediated RNF157 mRNA from PCa cells results in M2 macrophage polarization via destabilizing HDAC1, consequently promoting PCa tumor progression.

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.

Addressing the role of PKD3 in the T cell compartment with knockout mice

Background

The Protein kinase D3 (PKD3) has been implicated in signal transduction downstream of the T cell receptor (TCR). However, its role for the activation of primary T lymphocytes has not been elucidated so far.

Methods

Expression of PKD isoforms in primary murine T cells was determined by RT-PCR and SDS-Page. A germline PKD3-knockout mouse line was analyzed for its immune response to OVA/alum intraperitoneal immunization. Phenotyping of the T cell compartment ex vivo as well as upon stimulation in vitro was performed by flow cytometry. Additionally, cytokine expression was assessed by flow cytometry, RT-PCR and Luminex technology.

Results

PKD expression in T cells is modulated by TCR stimulation, leading to a rapid down-regulation on mRNA and on protein level. PKD3-deficient mice respond to immunization with enhanced T follicular helper cell generation. Furthermore, peripheral PKD3-deficient CD4⁺ T cells express more interleukin-2 than wild type CD4⁺ T cells upon TCR stimulation ex vivo. However, purified naïve CD4⁺ T cells do not differ in their phenotype upon differentiation in vitro from wild type T cells. Moreover, we observed a shift towards an effector/memory phenotype of splenic T cells at steady state, which might explain the contradictory results obtained with pan-T cells ex vivo and naïve-sorted T cells.

Conclusion

While PKD3-deficiency in vivo in mice leads to a skewing of the T cell compartment towards a more activated phenotype, this kinase seems to be dispensable for naïve CD4⁺ T cell differentiation in vitro.

Targeting Protein Kinases and Epigenetic Control as Combinatorial Therapy Options for Advanced Prostate Cancer Treatment

Prostate cancer (PC), the fifth leading cause of cancer-related mortality worldwide, is known as metastatic bone cancer when it spreads to the bone. Although there is still no effective treatment for advanced/metastatic PC, awareness of the molecular events that contribute to PC progression has opened up opportunities and raised hopes for the development of new treatment strategies. Androgen deprivation and androgen-receptor-targeting therapies are two gold standard treatments for metastatic PC. However, acquired resistance to these treatments is a crucial challenge. Due to the role of protein kinases (PKs) in the growth, proliferation, and metastases of prostatic tumors, combinatorial therapy by PK inhibitors may help pave the way for metastatic PC treatment. Additionally, PC is known to have epigenetic involvement. Thus, understanding epigenetic pathways can help adopt another combinatorial treatment strategy. In this study, we reviewed the PKs that promote PC to advanced stages. We also summarized some PK inhibitors that may be used to treat advanced PC and we discussed the importance of epigenetic control in this cancer. We hope the information presented in this article will contribute to finding an effective treatment for the management of advanced PC.

iTRAQ-Based Proteome Profiling of Differentially Expressed Proteins in Insulin-Resistant Human Hepatocellular Carcinoma

Recently, the incidences of insulin resistance (IR) and IR-related complications have increased throughout the world, which also associate with poor prognosis in hepatocellular carcinoma (HCC). Numerous studies had been focused on the role of IR in tumorigenesis and prognosis of HCC. The proteomic analysis of IR related hepatocellular carcinoma had not been reported by now. In the present study, 196 differentially expressed proteins (DEPs) were identified between insulin resistant HepG2 cells and their parental cells, of which 109 proteins were downregulated and 87 proteins were upregulated. Bioinformatics analysis indicated that these DEPs were highly enriched in process of tumorigenesis and tumor progression. PPI network analysis showed that SOX9, YAP1 and GSK3β as the key nodes, were involved in Wnt and Hippo signaling pathways. Survival analysis revealed that high expression of SOX9 and PRKD3 were strongly associated with reduced patient survival rate. parallel reaction monitoring (PRM) and Western blot analysis were applied to verify the protein level of these four key nodes mentioned above, which showed the same trend as quantified by isobaric tags for relative and absolute quantitation (iTRAQ) and confirmed the reliability of our Proteome Profiling analysis. Our results indicated that IR related dysregulation of protein expression might participated in tumorigenesis and malignant phenotype of hepatocarcinoma cells.

TRIM47 activates NF-κB signaling via PKC-ε/PKD3 stabilization and contributes to endocrine therapy resistance in breast cancer

Increasing attention has been paid to roles of tripartite motif-containing (TRIM) family proteins in cancer biology, often functioning as E3 ubiquitin ligases. In the present study, we focus on a contribution of TRIM47 to breast cancer biology, particularly to endocrine therapy resistance, which is a major clinical problem in breast cancer treatment. We performed immunohistochemical analysis of TRIM47 protein expression in 116 clinical samples of breast cancer patients with postoperative endocrine therapy using tamoxifen. Our clinicopathological study showed that higher immunoreactivity scores of TRIM47 were significantly associated with higher relapse rate of breast cancer patients (P = 0.012). As functional analyses, we manipulated TRIM47 expression in estrogen receptor-positive breast cancer cells MCF-7 and its 4-hydroxytamoxifen (OHT)-resistant derivative OHTR, which was established in a long-term culture with OHT. TRIM47 promoted both MCF-7 and OHTR cell proliferation. MCF-7 cells acquired tamoxifen resistance by overexpressing exogenous TRIM47. We found that TRIM47 enhances nuclear factor kappa-B (NF-κB) signaling, which further up-regulates TRIM47. We showed that protein kinase C epsilon (PKC-ε) and protein kinase D3 (PKD3), known as NF-κB-activating protein kinases, are directly associated with TRIM47 and stabilized in the presence of TRIM47. As an underlying mechanism, we showed TRIM47-dependent lysine 27-linked polyubiquitination of PKC-ε. These results indicate that TRIM47 facilitates breast cancer proliferation and endocrine therapy resistance by forming a ternary complex with PKC-ε and PKD3. TRIM47 and its associated kinases can be a potential diagnostic and therapeutic target for breast cancer refractory to endocrine therapy.

Developments in the Discovery and Design of Protein Kinase D Inhibitors

Protein kinase D (PKD) is a serine/threonine kinase family belonging to the Ca2+/calmodulin-dependent protein kinase group. Since its discovery two decades ago, many efforts have been put in elucidating PKD's structure, cellular role and functioning. The PKD family consists of three highly homologous isoforms: PKD1, PKD2 and PKD3. Accumulating cell-signaling research has evidenced that dysregulated PKD plays a crucial role in the pathogenesis of cardiac hypertrophy and several cancer types. These findings led to a broad interest in the design of small-molecule protein kinase D inhibitors. In this review, we present an extensive overview on the past and recent advances in the discovery and development of PKD inhibitors. The focus extends from broad-spectrum kinase inhibitors used in PKD signaling experiments to intentionally developed, bioactive PKD inhibitors. Finally, attention is paid to PKD inhibitors that have been identified as an off-target through large kinome screening panels.

Npas4 impairs fear memory via phosphorylated HDAC5 induced by CGRP administration in mice

The relationships among neuropeptide, calcitonin gene-related peptide (CGRP), and memory formation remain unclear. Here, we showed that the intracerebroventricular administration of CGRP impaired the traumatic fear memories, in a widely studied animal model of post-traumatic stress disorder. We found that CGRP administration suppressed fear memory by increasing neuronal PAS domain protein 4 (Npas4), phosphorylated histone deacetylase 5 (HDAC5), and protein kinase D (PKD). We also discovered that Npas4 knockdown inhibited CGRP-mediated fear memory. CGRP decreased the binding between HDAC5 and the Npas4 enhancer site and increased the binding between acetylated histone H3 and the Npas4 enhancer site. The pharmacological inhibition or knockdown of PKD attenuated the CGRP-mediated impairment of fear memory and the increased phosphorylation of HDAC5 and Npas4 expression. Our findings demonstrated that the CGRP-PKD pathway was associated with the histone H3 acetylation-Npas4 pathway. These results suggested a novel function for CGRP on fear memory, through epigenetic regulation.

Multifaceted Functions of Protein Kinase D in Pathological Processes and Human Diseases

Protein kinase D (PKD) is a family of serine/threonine protein kinases operating in the signaling network of the second messenger diacylglycerol. The three family members, PKD1, PKD2, and PKD3, are activated by a variety of extracellular stimuli and transduce cell signals affecting many aspects of basic cell functions including secretion, migration, proliferation, survival, angiogenesis, and immune response. Dysregulation of PKD in expression and activity has been detected in many human diseases. Further loss- or gain-of-function studies at cellular levels and in animal models provide strong support for crucial roles of PKD in many pathological conditions, including cancer, metabolic disorders, cardiac diseases, central nervous system disorders, inflammatory diseases, and immune dysregulation. Complexity in enzymatic regulation and function is evident as PKD isoforms may act differently in different biological systems and disease models, and understanding the molecular mechanisms underlying these differences and their biological significance in vivo is essential for the development of safer and more effective PKD-targeted therapies. In this review, to provide a global understanding of PKD function, we present an overview of the PKD family in several major human diseases with more focus on cancer-associated biological processes.

PKD3 promotes metastasis and growth of oral squamous cell carcinoma through positive feedback regulation with PD-L1 and activation of ERK-STAT1/3-EMT signalling

Oral squamous cell carcinoma (OSCC) has a high incidence of metastasis. Tumour immunotherapy targeting PD-L1 or PD-1 has been revolutionary; however, only a few patients with OSCC respond to this treatment. Therefore, it is essential to gain insights into the molecular mechanisms underlying the growth and metastasis of OSCC. In this study, we analysed the expression levels of protein kinase D3 (PKD3) and PD-L1 and their correlation with the expression of mesenchymal and epithelial markers. We found that the expression of PKD3 and PD-L1 in OSCC cells and tissues was significantly increased, which correlated positively with that of mesenchymal markers but negatively with that of epithelial markers. Silencing PKD3 significantly inhibited the growth, metastasis and invasion of OSCC cells, while its overexpression promoted these processes. Our further analyses revealed that there was positive feedback regulation between PKD3 and PD-L1, which could drive EMT of OSCC cells via the ERK/STAT1/3 pathway, thereby promoting tumour growth and metastasis. Furthermore, silencing PKD3 significantly inhibited the expression of PD-L1, and lymph node metastasis of OSCC was investigated with a mouse footpad xenograft model. Thus, our findings provide a theoretical basis for targeting PKD3 as an alternative method to block EMT for regulating PD-L1 expression and inhibiting OSCC growth and metastasis.

The oncogenic role of protein kinase D3 in cancer

Protein kinase D3 (PRKD3), a serine/threonine kinase, belongs to protein kinase D family, which contains three members: PRKD1, PRKD2, and PRKD3. PRKD3 is activated by many stimuli including phorbol esters, and G-protein-coupled receptor agonists. PRKD3 promotes cancer cell proliferation, growth, migration, and invasion in various tumor types including colorectal, gastric, hepatic, prostate, and breast cancer. Accumulating data supports that PRKD3 is a promising therapeutic target for treatment of cancer. This review discusses the functions and mechanisms of PRKD3 in promoting tumorigenesis and tumor progression of various tumor types as well as the latest developments of small-molecule inhibitors selection for PRKD/PRKD3.

Inhibiting Protein Kinase D Promotes Airway Epithelial Barrier Integrity in Mouse Models of Influenza A Virus Infection

Rationale

Protein kinase D (PKD) is a serine/threonine kinase family that is involved in a wide array of signaling pathways. Although PKD has been implicated in immune responses, relatively little is known about the function of PKD in the lung or during viral infections.

Objectives

We investigated the hypothesis that PKD is involved in multiple aspects of host response to viral infection.

Methods

The selective PKD inhibitor CRT0010166 was administered to C57BL/6 mice prior to and during challenge with either inhaled double-stranded RNA or Influenza A Virus. PKD signaling pathways were investigated in human bronchial epithelial cells treated with CRT0010166, double-stranded RNA, and/or infected with Influenza A Virus.

Measurements

Total protein and albumin accumulation in the bronchoalveolar fluid was used to asses inside/out leak. Clearance of inhaled FITC-dextran out of the airspace was used to assess outside/in leak. Cytokines and neutrophils in bronchoalveolar lavage were assayed with ELISAs and cytospins respectively. Viral RNA level was assessed with RT-PCR and protein level assessed by ELISA.

Main Results

PKD inhibition prevented airway barrier dysfunction and pro-inflammatory cytokine release. Epithelial cells express PKD3, and PKD3 siRNA knock-down inhibited polyI:C induced cytokine production. Lung epithelial-specific deletion of PKD3 (CC10-Cre x PKD3-floxed mice) partially attenuated polyI:C-induced barrier disruption in vivo. Mechanistically, we found that PKD promoted cytokine mRNA transcription, not secretion, likely through activating the transcription factor Sp1. Finally, prophylactic CRT treatment of mice promoted barrier integrity during influenza virus infection and reduced viral burden.

Conclusions

Inhibiting PKD promotes barrier integrity, limit pathogenic cytokine levels, and restrict Influenza A Virus infection. Therefore, PKD is an attractive target for novel antiviral therapeutics.

Pyruvate Kinase M2 Promotes Prostate Cancer Metastasis Through Regulating ERK1/2-COX-2 Signaling

Pyruvate kinase M2 (PKM2) is a key enzyme of glycolysis, which is highly expressed in many tumor cells, and has emerged as an important player in tumor progression and metastasis. However, the functional roles of PKM2 in tumor metastasis remain elusive. Here we showed that PKM2 promoted prostate cancer metastasis via extracellular-regulated protein kinase (ERK)-cyclooxygenase (COX-2) signaling. Based on public databases, we found that PKM2 expression was upregulated in prostate cancer and positively associated with tumor metastasis. Further analysis showed that PKM2 promoted prostate cancer cell migration/invasion and epithelial-mesenchymal transition (EMT) through upregulation of COX-2. Mechanistically, PKM2 interacted with ERK1/2 and regulated its phosphorylation, leading to phosphorylation of transcription factor c-Jun, downstream of ERK1/2, to activate COX-2 transcription by IP and ChIP assay, while inhibition of COX-2 significantly reversed the promotion effect of PKM2 on tumor metastasis in vivo. Taken together, our results suggest that a novel of PKM2-ERK1/2-c-Jun-COX-2 axis is a potential target in controlling prostate cancer metastasis.

N6-Methyladenosine modification of the TRIM7 positively regulates tumorigenesis and chemoresistance in osteosarcoma through ubiquitination of BRMS1

BACKGROUND

Metastasis is the leading cause of death in patients with osteosarcoma. Some of these patients fail to respond to chemotherapy and die of metastasis within a short period. Therefore, it is important to identify novel biomarkers to improve the diagnosis and treatment of osteosarcoma. TRIM7 is a member of the tripartite motif (TRIM) family protein that is involved in various pathological conditions including cancer; however, its role in osteosarcoma remains elusive.

METHODS

Cell proliferation, invasion and migration were measured by CCK-8 and Transwell. Immunoprecipitation and mass spectrometry analysis were used to identify candidate proteins associated with TRIM7. Immunoprecipitation, immunofluorescence, pull down and ubiquitination assay were performed to examine the regulation between TRIM7 and its candidate protein. m6A modification of TRIM7 was measured by RNA immunoprecipitation.

FINDINGS

TRIM7 expression was upregulated in osteosarcoma tissues and was an independent risk factor in predicting poor prognosis. TRIM7 regulates osteosarcoma cell migration and invasion through ubiquitination of breast cancer metastasis suppressor 1 (BRMS1). Moreover, chemoresistance was readily observed in osteosarcoma cells and in patient-derived xenograft (PDX) mice with higher TRIM7 levels. Loss of TRIM7 m6A modification was observed in osteosarcoma tissues. METTL3 and YTHDF2 were the main factors involved in the aberrant m6A modification of TRIM7.

INTERPRETATION

Overall, our findings show that TRIM7 plays a key role in regulating metastasis and chemoresistance in osteosarcoma through ubiquitination of BRMS1.

FUNDING

This work was financially supported by grants of NSFC (81001192, 81672658 and 81972521) and National Key Research Project of Science and Technology Ministry (2016YFC0106204).

Suppression of cathepsin a inhibits growth, migration, and invasion by inhibiting the p38 MAPK signaling pathway in prostate cancer

Prostate cancer has the highest incidence among men in advanced countries, as well as a high mortality rate. Despite the efforts of numerous researchers to identify a gene-based therapeutic target as an effective treatment of prostate cancer, there is still a need for further research. The cathepsin gene family is known to have a close correlation with various cancer types and is highly expressed across these cancer types. This study aimed at investigating the correlation between the cathepsin A (CTSA) gene and prostate cancer. Our findings indicated a significantly elevated level of CTSA gene expression in the tissues of patients with prostate cancer when compared with normal prostate tissues. Furthermore, the knockdown of the CTSA gene in the representative prostate cancer cell lines PC3 and DU145 led to reduced proliferation and a marked reduction in anchorage-independent colony formation, which was shown to be caused by cell cycle arrest in the S phase. In addition, CTSA gene-knockdown prostate cancer cell lines showed a substantial decrease in migration and invasion, as well as a decrease in the marker genes that promote epithelial mesenchymal transition (EMT). Such phenotypic changes in prostate cancer cell lines through CTSA gene suppression were found to be mainly caused by reduced p38 MAPK protein phosphorylation; i.e. the inactivation of the p38 MAPK cell signaling pathway. Tumorigenesis was also found to be inhibited in CTSA gene-knockdown prostate cancer cell lines when a xenograft assay was carried out using Balb/c nude mice, and the p38 MAPK phosphorylation was inhibited in tumor tissues. Thus, the CTSA gene is presumed to play a key role in human prostate cancer tissues through high-level expression, and the suppression of the CTSA gene leads to the inhibition of prostate cancer cell proliferation, colony formation, and metastasis. The mechanism, by which these effects occur, was demonstrated to be the inactivation of the p38 MAPK signaling pathway.

Protein kinase D3 regulates the expression of the immunosuppressive protein, PD‑L1, through STAT1/STAT3 signaling

Oral squamous cell carcinoma (OSCC) is capable of constructing a favorable immune escape environment through interactions of cells with cells and of cells with the environment. Programmed death ligand-1 (PD-L1) is a well-recognized inhibitor of anti-tumor immunity that plays an important role in tumor immune escape. However, the molecular mechanisms regulating PD-L1 expression are not yet fully understood. In this study, to investigate the role of protein kinase D3 (PKD3) in the regulation of PD-L1 expression, the expression and correlation of PKD3 and PD-L1 were first analyzed by the immunostaining of human OSCC tissue sections, cell experiments and TCGA gene expression databases. The expression levels of PKD3 and PD-L1 were found to be significantly higher in OSCC cells than in normal tissues or cells. In addition, the expression levels of PKD3 and PD-L1 were found to be significantly positively correlated. Subsequently, it was found that the levsel of PD-L1 expression decreased following the silencing of PKD3 and that the ability of interferon (IFN)-γ to induce PD-L1 expression was also decreased in OSCC. The opposite phenomenon occurred following the overexpression of PKD3. It was also found that the phosphorylation of signal transducer and activator of transcription (STAT)1/STAT3 was reduced by the knockdown of PKD3 in OSCC. Moreover, the expression level of PD-L1 was decreased after the use of siRNA to knockdown STAT1 or STAT3. On the whole, the findings of this study confirm that PKD3 regulates the expression of PD-L1 induced by IFN-γ by regulating the phosphorylation of STAT1/STAT3. These findings broaden the understanding of the biological function of PKD3, suggesting that PKD is a potential therapeutic target for OSCC.

Interplay of PKD3 with SREBP1 Promotes Cell Growth via Upregulating Lipogenesis in Prostate Cancer Cells

Protein kinase D (PKD) has been implicated in cancer cell survival, proliferation, migration and angiogenesis. However, it is still unknown whether PKD regulates cell proliferation through lipid metabolism in cancer cells. Here we report a novel function of PKD3, a member of PKD family, in regulating of prostate cancer cell proliferation by modulation of SREBP1-mediated de novo lipogenesis. We show that silencing of PKD3 significantly reduces lipid content and expression of the lipogenic genes encoding FASN and ATP-citrate lyase (ACLY). Moreover, endogenous PKD3 interacts with sterol regulatory element binding protein 1(SREBP1) in DU145 cells. Interestingly, PKD3 silencing decreases not only the level of matured-SREBP1 (68KD) but also the binding of SREBP1 to the promoter of fasn gene. In addition, overexpression of SREBP1 reverses the suppression of cell growth caused by PKD3 depletion. Finally, immune-histochemical staining indicate that PKD3 expression is positively correlated with expression of FASN and SREBP1 in prostate cancers. Taken together, these data suggest that targeting PKD3-mediated de novo lipogenesis may be a potential therapeutic approach to block prostate cancer progression.

Protein kinase D3 promotes gastric cancer development through p65/6-phosphofructo-2-kinase/fructose-2,6-biphosphatase 3 activation of glycolysis

Although serine/threonine-protein kinases are found to participate in a wide range of cancer progression, the involvement of protein kinase D3 (PRKD3) in gastric cancer has not been explored. Here, we investigated the role of PRKD3 in gastric cancer (GC) and its potential mechanisms. PRKD3 was over-expressed in gastric cancer tissues and cells. In vitro, PRKD3 ectopic expression accelerated the proliferation and growth of GES-1, SGC7901 and MKN-28 cells. By contrast, PRKD3 knockdown suppressed the proliferation of SGC7901 and MKN-28 GC cells. In vivo, xenograted tumorigenesis was blunted by PRKD3 silencing. Mechanistically, PRKD3 up-regulated 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase 3 (PFKFB3) and activated glycolysis as shown by increased glucose consumption and lactate production. Knockdown of PFKFB3 suppressed the glycolysis in gastric cancer cells with highly expressed PRKD3 but not in PRKD3 silenced cells. PRKD3 over-expression induced phosphorylation of p65 at serine 536 was critical for the up-regulation of glycolytic enzyme PFKFB3. Furthermore, PRKD and PFKFB3 inhibitor suppressed the viability of GC cells. Our results suggest that targeting PRKD3/p65/PFKFB3 cascade maybe a promising therapeutic strategy for gastric cancer.

Protein kinase Ds promote tumor angiogenesis through mast cell recruitment and expression of angiogenic factors in prostate cancer microenvironment

Background

Mast cells are being increasingly recognized as critical components in the tumor microenvironment. Protein Kinase D (PKD) is essential for the progression of prostate cancer, but its role in prostate cancer microenvironment remains poorly understood.

Methods

The expression of PKD, mast cells and microvessel density were examined by IHC. The clinical significance was determined by statistical analyses. The biological function of PKD and the underlying mechanisms were investigated using in vitro and in vivo models.

Results

PKD2/3 contributed to MCs recruitment and tumor angiogenesis in the prostate cancer microenvironment. Clinical data showed that increased activation of PKD at Ser744/748 in prostate cancer was correlated with mast cell infiltration and microvascular density. PKD2/3 silencing of prostate cancer cells markedly decreased MCs migration and tube formation of HUVEC cells. Moreover, PKD2/3 depletion not only reduced SCF, CCL5 and CCL11 expression in prostate cancer cells but also inhibited angiogenic factors in MCs. Conversely, exogenous SCF, CCL5 and CCL11 reversed the effect on MCs migration inhibited by PKD2/3 silencing. Mechanistically, PKD2/3 interacted with Erk1/2 and activated Erk1/2 or NF-κB signaling pathway, leading to AP-1 or NF-κB binding to the promoter of scf, ccl5 and ccl11. Finally, PKD-specific inhibitor significantly reduced tumor volume and tumor growth in mice bearing RM-1 prostate cancer cells, which was attributed to attenuation of mast cell recruitment and tumor angiogenesis.

Conclusions

These results demonstrate a novel PKDs function that contributes to tumor angiogenesis and progression through mast cells recruitment in prostate cancer microenvironment.

Electronic supplementary material

The online version of this article (10.1186/s13046-019-1118-y) contains supplementary material, which is available to authorized users.

High PKD2 predicts poor prognosis in lung adenocarcinoma via promoting Epithelial-mesenchymal Transition

Protein kinase D2 (PKD2) has been reported to be related with progression and invasion in various cancers. However, its prognostic value and the underlying mechanism in lung cancer remains unclear. Herein we evaluated the expression of PKD2 in lung adenocarcinoma and investigated its relationship with EMT. GSEA, TCGA and K-M plotter database were applied and revealed that high PKD2 expression predicted poor outcome and related with lymph nodes metastasis in lung cancer. IHC and qRT-PCR were performed and found PKD2 was elevated in lung adenocarcinoma and negatively related with OS (p = 0.015), PFS (p = 0.006) and the level of E-cadherin (p = 0.021). Experiment in lung adenocarcinoma cell lines demonstrated up-regulation of PKD2 led to high expression of mesenchymal markers (N-cadherin, vim, mmp9 et al.) and EMT transcription factors(zeb1, twist, snail), and the results were reversed when PKD2 was knocked down. Further investigation showed that abrogation of PKD2 inhibited A549 cell migration, invasion, proliferation and induced cell arrest in G2/M phase. We concluded that high expression of PKD2 was associated with poor prognosis and cancer progression in lung adenocarcinoma patients by promoting EMT.

Oncogenic functions of protein kinase D2 and D3 in regulating multiple cancer-related pathways in breast cancer

Protein Kinase D (PKD) family contains PKD1, PKD2, and PKD3 in human. Compared to consistent tumor-suppressive functions of PKD1 in breast cancer, how PKD2/3 functions in breast cancer are not fully understood. In the current study, we found that PKD2 and PKD3 but not PKD1 were preferentially overexpressed in breast cancer and involved in regulating cell proliferation and metastasis. Integrated phosphoproteome, transcriptome, and interactome showed that PKD2 was associated with multiple cancer-related pathways, including adherent junction, regulation of actin cytoskeleton, and cell cycle-related pathways. ELAVL1 was identified as a common hub-node in networks of PKD2/3-regulated phosphoproteins and genes. Silencing ELAVL1 inhibited breast cancer growth in vitro and in vivo. Direct interaction between ELAVL1 and PKD2 or PKD3 was demonstrated. Suppression of PKD2 led to ELAVL1 translocation from the cytoplasm to the nucleus without significant affecting ELAVL1 expression. Taken together, we characterized the oncogenic functions of PKD2/3 in breast cancer and their association with cancer-related pathways, which shed lights on the oncogenic roles and mechanisms of PKDs in breast cancer.

Crosstalk of protein kinase C ε with Smad2/3 promotes tumor cell proliferation in prostate cancer cells by enhancing aerobic glycolysis

Protein kinase C ε (PKCε) has emerged as an oncogenic protein kinase and plays important roles in cancer cell survival, proliferation, and invasion. It is, however, still unknown whether PKCε affects cell proliferation via glucose metabolism in cancer cells. Here we report a novel function of PKCε that provides growth advantages for cancer cells by enhancing tumor cells glycolysis. We found that either PKCε or Smad2/3 promoted aerobic glycolysis, expression of the glycolytic genes encoding HIF-1α, HKII, PFKP and MCT4, and tumor cell proliferation, while overexpression of PKCε or Smad3 enhanced aerobic glycolysis and cell proliferation in a protein kinase D- or TGF-β-independent manner in PC-3M and DU145 prostate cancer cells. The effects of PKCε silencing were reversed by ectopic expression of Smad3. PKCε or Smad3 ectopic expression-induced increase in cell growth was antagonized by inhibition of lactate transportation. Furthermore, interaction of endogenous PKCε with Smad2/3 was primarily responsible for phosphorylation of Ser213 in the Samd3 linker region, and resulted in Smad3 binding to the promoter of the glycolytic genes, thereby promoting cell proliferation. Forced expression of mutant Smad3 (S213A) attenuated PKCε-stimulated protein overexpression of the glycolytic genes. Thus, our results demonstrate a novel PKCε function that promotes cell growth in prostate cancer cells by increasing aerobic glycolysis through crosstalk between PKCε and Smad2/3.

Protein kinase D inhibitor CRT0066101 suppresses bladder cancer growth in vitro and xenografts via blockade of the cell cycle at G2/M

The protein kinase D (PKD) family of proteins are important regulators of tumor growth, development, and progression. CRT0066101, an inhibitor of PKD, has antitumor activity in multiple types of carcinomas. However, the effect and mechanism of CRT0066101 in bladder cancer are not understood. In the present study, we show that CRT0066101 suppressed the proliferation and migration of four bladder cancer cell lines in vitro. We also demonstrate that CRT0066101 blocked tumor growth in a mouse flank xenograft model of bladder cancer. To further assess the role of PKD in bladder carcinoma, we examined the three PKD isoforms and found that PKD2 was highly expressed in eight bladder cancer cell lines and in urothelial carcinoma tissues from the TCGA database, and that short hairpin RNA (shRNA)-mediated knockdown of PKD2 dramatically reduced bladder cancer growth and invasion in vitro and in vivo, suggesting that the effect of the compound in bladder cancer is mediated through inhibition of PKD2. This notion was corroborated by demonstrating that the levels of phospho-PKD2 were markedly decreased in CRT0066101-treated bladder tumor explants. Furthermore, our cell cycle analysis by flow cytometry revealed that CRT0066101 treatment or PKD2 silencing arrested bladder cancer cells at the G2/M phase, the arrest being accompanied by decreases in the levels of cyclin B1, CDK1 and phospho-CDK1 (Thr161) and increases in the levels of p27Kip1 and phospho-CDK1 (Thr14/Tyr15). Moreover, CRT0066101 downregulated the expression of Cdc25C, which dephosphorylates/activates CDK1, but enhanced the activity of the checkpoint kinase Chk1, which inhibits CDK1 by phosphorylating/inactivating Cdc25C. Finally, CRT0066101 was found to elevate the levels of Myt1, Wee1, phospho-Cdc25C (Ser216), Gadd45α, and 14-3-3 proteins, all of which reduce the CDK1-cyclin B1 complex activity. These novel findings suggest that CRT0066101 suppresses bladder cancer growth by inhibiting PKD2 through induction of G2/M cell cycle arrest, leading to the blockade of cell cycle progression.

NFkB hyperactivation causes invasion of esophageal squamous cell carcinoma with EGFR overexpression and p120-catenin down-regulation

Four out of five patients diagnosed with esophageal squamous cell carcinoma (ESCC) will die within five years. This is primarily a result of the aggressive invasive potential of the disease. Our research is focused on the interplay between tumor suppressors and oncogenes in the invasive process. Specifically, EGFR and p120-catenin (p120ctn) are commonly dysregulated genes that are indicative of poor prognosis in ESCC. In a previous study we demonstrated that in our 3D organotypic culture model, only when EGFR overexpression is combined with p120ctn inactivation do the cells transform and invade – as opposed to either event alone. The purpose of this present study was to identify the components of the molecular pathways downstream of p120ctn and EGFR that lead to invasion. Using both human esophageal keratinocytes and human ESCC cells, we have identified NFkB as a central regulator of the invasive process downstream of p120ctn down-regulation and EGFR overexpression. Interestingly, we found that NFkB is hyperactivated in cells with EGFR overexpression and p120ctn inactivation than with either EGFR or p120ctn alone. Inhibition of this NFkB hyperactivation results in complete loss of invasion, suggesting that NFkB signaling is necessary for invasion in this aggressive cell type. Furthermore, we have identified RhoA and Rho-kinase as upstream regulators of NFkB in this process. We believe the cooperation of p120ctn down-regulation and EGFR overexpression is not only important in the aggressive mechanisms of ESCC but could be broadly applicable to many other cancer types in which p120ctn and EGFR are involved.

Protein kinase D2: a versatile player in cancer biology

Protein kinase D2 (PKD2) is a serine/threonine kinase that belongs to the PKD family of calcium-calmodulin kinases, which comprises three isoforms: PKD1, PKD2, and PKD3. PKD2 is activated by many stimuli including growth factors, phorbol esters, and G-protein-coupled receptor agonists. PKD2 participation to uncontrolled growth, survival, neovascularization, metastasis, and invasion has been documented in various tumor types including pancreatic, colorectal, gastric, hepatic, lung, prostate, and breast cancer, as well as glioma multiforme and leukemia. This review discusses the versatile functions of PKD2 from the perspective of cancer hallmarks as described by Hanahan and Weinberg. The PKD2 status, signaling pathways affected in different tumor types and the molecular mechanisms that lead to tumorigenesis and tumor progression are presented. The latest developments of small-molecule inhibitors selective for PKD/PKD2, as well as the need for further chemotherapies that prevent, slow down, or eliminate tumors are also discussed in this review.

Lysophosphatidic acid via LPA-receptor 5/protein kinase D-dependent pathways induces a motile and pro-inflammatory microglial phenotype

BACKGROUND

Extracellular lysophosphatidic acid (LPA) species transmit signals via six different G protein-coupled receptors (LPAR1-6) and are indispensible for brain development and function of the nervous system. However, under neuroinflammatory conditions or brain damage, LPA levels increase, thereby inducing signaling cascades that counteract brain function. We describe a critical role for 1-oleyl-2-hydroxy-sn-glycero-3-phosphate (termed "LPA" throughout our study) in mediating a motile and pro-inflammatory microglial phenotype via LPAR5 that couples to protein kinase D (PKD)-mediated pathways.

METHODS

Using the xCELLigence system and time-lapse microscopy, we investigated the migrational response of microglial cells. Different M1 and M2 markers were analyzed by confocal microscopy, flow cytometry, and immunoblotting. Using qPCR and ELISA, we studied the expression of migratory genes and quantitated the secretion of pro-inflammatory cytokines and chemokines, respectively. Different transcription factors that promote the regulation of pro-inflammatory genes were analyzed by western blot. Reactive oxygen species (ROS) and nitric oxide (NO) production, phagocytosis, and microglial cytotoxicity were determined using commercially available assay kits.

RESULTS

LPA induces MAPK family and AKT activation and pro-inflammatory transcription factors' phosphorylation (NF-κB, c-Jun, STAT1, and STAT3) that were inhibited by both LPAR5 and PKD family antagonists. LPA increases migratory capacity, induces secretion of pro-inflammatory cytokines and chemokines and expression of M1 markers, enhances production of ROS and NO by microglia, and augments cytotoxicity of microglial cell-conditioned medium towards neurons. The PKD family inhibitor blunted all of these effects. We propose that interference with this signaling axis could aid in the development of new therapeutic approaches to control neuroinflammation under conditions of overshooting LPA production.

CONCLUSIONS

In the present study, we show that inflammatory LPA levels increased the migratory response of microglia and promoted a pro-inflammatory phenotype via the LPAR5/PKD axis. Interference with this signaling axis reduced microglial migration, blunted microglial cytotoxicity, and abrogated the expression and secretion of pro-inflammatory mediators.

Higher PKD3 expression in hepatocellular carcinoma (HCC) tissues predicts poorer prognosis for HCC patients

AIM

Protein kinase D (PKD) acts as a key mediator in several cancer development signaling pathways. The aim of this study was to investigate the clinical significance and prognostic value of PKD3 expression in hepatocellular carcinoma (HCC) patients after hepatectomy.

METHODS

PKD3 mRNA and protein expression levels in tumor and matched non-tumoral (NT) tissues, HCC cell lines were evaluated by quantitative PCR (qRT-PCR), western blotting and immunohistochemical staining (IHC). Additionally, PKD3 mRNA expression in HCC tissues correlated with clinicopathological characteristics and survival.

RESULTS

PKD3 mRNA and protein expression was elevated in HCC tissues and HCC cell lines. Our data also showed that in HCC patients after resection, a high-expression of PKD3 mRNA and protein significantly correlated with multiple tumor nodules (P=0.009, P=0.020, respectively), poor tumor differentiation (P=0.001, P=0.004, respectively), high serum AFP level (P=0.005, P=0.002, respectively), vascular invasion (P=0.006, P=0.009, respectively) and advanced AJCC stage (P=0.001, P=0.022, respectively). A Kaplan-Meier analysis indicated that an elevated PKD3 mRNA expression correlated with shorter overall survival (OS) (P<0.001) and disease-free survival (DFS) (P=0.008). Moreover, multivariate analysis showed that a high-expression of PKD3 was an independent prognostic factor for three-year overall survival rate.

CONCLUSIONS

Our findings suggest that abnormal PKD3 expression might contribute to HCC progression. Furthermore, high PKD3 expression predicts a poor prognosis in HCC patients after hepatectomy.

Src-mediated tyrosine phosphorylation of Protein Kinase D2 at focal adhesions regulates cell adhesion

Dependent on their cellular localization, Protein Kinase D (PKD) enzymes regulate different processes including Golgi transport, cell signaling and response to oxidative stress. The localization of PKD within cells is mediated by interaction with different lipid or protein binding partners. With the example of PKD2, we here show that phosphorylation events can also contribute to localization of subcellular pools of this kinase. Specifically, in the present study, we show that tyrosine phosphorylation of PKD2 at residue Y87 defines its localization to the focal adhesions and leads to activation. This phosphorylation occurs downstream of RhoA signaling and is mediated via Src. Moreover, mutation of this residue blocks PKD2's interaction with Focal Adhesion Kinase (FAK). The presence and regulation of PKD2 at focal adhesions identifies a novel function for this kinase as a modulator of cell adhesion and migration.

Detecting in vivo urokinase plasminogen activator activity with a catalyCEST MRI contrast agent

Urokinase plasminogen activator (uPA) promotes tumor invasion and metastasis. The monitoring of uPA activity using molecular imaging may have prognostic value and be predictive for response to anti-cancer therapies. However, the detection of in vivo enzyme activity with molecular imaging remains a challenge. To address this problem, we designed a nonmetallic contrast agent, GR-4Am-SA, that can be detected with chemical exchange saturation transfer (CEST) MRI. This agent has a peptide that is cleaved by uPA, which causes a CEST signal at 5.0 ppm to decrease, and also has a salicylic acid moiety that can produce a CEST signal at 9.5 ppm, which is largely unresponsive to enzyme activity. The two CEST signals were used to determine a reaction coordinate, representing the extent of enzyme-catalyzed cleavage of the GR-4Am-SA agent during an experimental study. Initial biochemical studies showed that GR-4Am-SA could detect uPA activity in reducing conditions. Subsequently, we used our catalyCEST MRI protocol with the agent to detect the uPA catalysis of GR-4Am-SA in a flank xenograft model of Capan-2 pancreatic cancer. The results showed an average reaction coordinate of 80% ± 8%, which was strongly dependent on the CEST signal at 5.0 ppm. The relative independence of the reaction coordinate on the CEST signal at 9.5 ppm showed that the detection of enzyme activity was largely independent of the concentration of GR-4Am-SA within the tumor tissue. These results demonstrated the advantages of a single CEST agent with biomarker-responsive and unresponsive signals for reliably assessing enzyme activity during in vivo cancer studies.

Protein kinase D signaling in cancer: A friend or foe?

Protein kinase D is a family of evolutionarily conserved serine/threonine kinases that belongs to the Ca⁺⁺/Calmodulin-dependent kinase superfamily. Signal transduction pathways mediated by PKD can be triggered by a variety of stimuli including G protein-coupled receptor agonists, growth factors, hormones, and cellular stresses. The regulatory mechanisms and physiological roles of PKD have been well documented including cell proliferation, survival, migration, angiogenesis, regulation of gene expression, and protein/membrane trafficking. However, its precise roles in disease progression, especially in cancer, remain elusive. A plethora of studies documented the cell- and tissue-specific expressions and functions of PKD in various cancer-associated biological processes, while the causes of the differential effects of PKD have not been thoroughly investigated. In this review, we have discussed the structural-functional properties, activation mechanisms, signaling pathways and physiological functions of PKD in the context of human cancer. Additionally, we have provided a comprehensive review of the reported tumor promoting or tumor suppressive functions of PKD in several major cancer types and discussed the discrepancies that have been raised on PKD as a major regulator of malignant transformation.

Specific tumor-derived CCL2 mediated by pyruvate kinase M2 in colorectal cancer cells contributes to macrophage recruitment in tumor microenvironment

Development of colorectal cancer has been considered as a result of imbalance of pro- and anti-inflammatory intestinal microenvironment accompanied by macrophage recruitment. Despite macrophages are implicated in remodeling tumor microenvironment, the mechanism of macrophage recruitment is not fully elucidated yet. In this study, we reported clinical association of highly expressed pyruvate kinase M2 in colorectal cancer with macrophage attraction. The conditioned medium from Caco-2 and HT-29 cells with depleted pyruvate kinase M2 dramatically reduced macrophage recruitment, which is reversed by addition of, a critical chemotaxis factor to macrophage migration, rCCL2. Silencing of endogenous pyruvate kinase M2 markedly decreased CCL2 expression and secretion by real-time quantitative polymerase chain reaction and enzyme-linked immunosorbent assay. Endogenous pyruvate kinase M2 interacted with p65 and mediated nuclear factor-κB signaling pathway and mainly regulated phosphorylation of Ser276 on p65 nuclear factor-κB. In addition, inhibition of macrophage recruitment caused by pyruvate kinase M2 silencing was rescued by ectopic expression of p65. Interestingly, pyruvate kinase M2 highly expressed in colorectal cancer tissue, which is correction with macrophage distribution. Taken together, we revealed a novel mechanism of pyruvate kinase M2 in promoting colorectal cancer progression by recruitment of macrophages through p65 nuclear factor-κB-mediated expression of CCL2.

Quercetin Has Antimetastatic Effects on Gastric Cancer Cells via the Interruption of uPA/uPAR Function by Modulating NF-κb, PKC-δ, ERK1/2, and AMPKα

Gastric cancer (GC) is a malignancy with few effective treatment options after metastasis occurs. Quercetin (Qu) intake has been associated with reduced incidence and slow development of GC, probably due to its anti-proliferative and apoptotic effects, but it is unclear whether Qu can inhibit the metastatic activity. The urokinase plasminogen activator (uPA)/uPA receptor (uPAR) system plays an important role in cancer metastasis. In this study, we measured both uPA activity and uPAR expression in GC and pericarcinous tissues, and we investigated the correlation between uPAR expression and the migratory and invasive activities of various GC cell lines. GC BGC823 and AGS cells were subjected to treatment with 10 μM Qu for 72 hours and uPAR knockdown, alone or in combination, before evaluating cell metastasis. The results showed that uPA activity and uPAR expression were higher in GC tissues than in pericarcinous tissues. Migratory and invasive activities of GC cell lines positively correlated with uPAR expression. Qu treatment decreased BGC823 and AGS cell migration and invasion, accompanied by reduced uPA and uPAR protein expression. Both Qu treatment and uPAR knockdown decreased matrix metalloproteinase-2 and -9 activity and blocked Pak1-Limk1-cofilin signaling. Qu treatment was associated with inhibition of NF-κb, PKC-δ, and ERK1/2, and with AMPKα activation. Specific inhibitors of NF-κb, PKC, and ERK1/2, and an AMPKα activator suppressed uPA and uPAR expression in GC cells. Collectively, Qu showed an antimetastatic effect on GC cells via the interruption of uPA/uPAR function and modulation of NF-κb, PKC-δ, ERK1/2, and AMPKα. This suggests that Qu is a promising agent against GC metastasis.

Id2 Collaborates with Id3 To Suppress Invariant NKT and Innate-like Tumors

Inhibitor of DNA binding (Id) proteins, including Id1-4, are transcriptional regulators involved in promoting cell proliferation and survival in various cell types. Although upregulation of Id proteins is associated with a broad spectrum of tumors, recent studies have identified that Id3 plays a tumor-suppressor role in the development of Burkitt's lymphoma in humans and hepatosplenic T cell lymphomas in mice. In this article, we report rapid lymphoma development in Id2/Id3 double-knockout mice that is caused by unchecked expansion of invariant NKT (iNKT) cells or a unique subset of innate-like CD1d-independent T cells. These populations began to expand in neonatal mice and, upon malignant transformation, resulted in mortality between 3 and 11 mo of age. The malignant cells also gave rise to lymphomas upon transfer to Rag-deficient and wild-type hosts, reaffirming their inherent tumorigenic potential. Microarray analysis revealed a significantly modified program in these neonatal iNKT cells that ultimately led to their malignant transformation. The lymphoma cells demonstrated chromosome instability along with upregulation of several signaling pathways, including the cytokine-cytokine receptor interaction pathway, which can promote their expansion and migration. Dysregulation of genes with reported driver mutations and the NF-κB pathway were found to be shared between Id2/Id3 double-knockout lymphomas and human NKT tumors. Our work identifies a distinct premalignant state and multiple tumorigenic pathways caused by loss of function of Id2 and Id3. Thus, conditional deletion of Id2 and Id3 in developing T cells establishes a unique animal model for iNKT and relevant innate-like lymphomas.

Discovery of a potent protein kinase D inhibitor: insights in the binding mode of pyrazolo[3,4-d]pyrimidine analogues

In this study, we set out to rationally optimize PKD inhibitors based on the pyrazolo[3,4-d]pyrimidine scaffold. The lead compound for this study was 1-NM-PP1, which was previously found by us and others to inhibit PKD. In our screening we identified one compound (3-IN-PP1) displaying a 10-fold increase in potency over 1-NM-PP1, opening new possibilities for specific protein kinase inhibitors for kinases that show sensitivity towards pyrazolo[3,4-d]pyrimidine derived compounds. Interestingly the observed SAR was not in complete agreement with the commonly observed binding mode where the pyrazolo[3,4-d]pyrimidine compounds are bound in a similar fashion as PKD's natural ligand ATP. Therefore we suggest an alternate binding mode where the compounds are flipped 180 degrees. This possible alternate binding mode for pyrazolo[3,4-d]pyrimidine based compounds could pave the way for a new class of specific protein kinase inhibitors for kinases sensitive towards pyrazolo[3,4-d]pyrmidines.

Protein kinase D2 contributes to TNF-α-induced epithelial mesenchymal transition and invasion via the PI3K/GSK-3β/β-catenin pathway in hepatocellular carcinoma

Although protein kinase D (PKD) has been shown to contribute to invasion and metastasis in several types of cancer, the role of PKD in the epithelial mesenchymal transition (EMT) of hepatocellular carcinoma (HCC) has remained unclear. We found that PKD2 is up-regulated in HCC and is correlated with the metastasis of HCC. PKD2 positively regulated TNF-α-induced EMT and metastasis of HCC. Mechanistic studies revealed TNF-α-induced PKD2 activation is mediated by the formation of a TNFR1/TRAF2 complex. PKD2 bound directly to the p110α and p85 subunits of PI3K and promoted the PI3K/Akt/GSK-3β signaling cascade to stimulate EMT. In conclusion, our results have uncovered a novel role for the regulation of EMT and suggest inhibition of PKD2 as a potential therapeutic strategy for HCC.

Protein Kinase D: A Potential Therapeutic Target in Prostate Cancer

Protein kinase D (PKD) belongs to a family of serine/threonine kinases in the calcium/calmodulin-dependent kinase superfamily. It modulates a number of signal transduction pathways involved in regulation of cell proliferation, survival, migration, angiogenesis, regulation of gene expression, and protein/membrane trafficking, mediated by variety of stimuli such as growth factors, hormones, and cellular stresses. Although its role in cancer progression remains elusive, current literature supports a potential tumor promoting function of the selective PKD isoforms in prostate cancer, making them promising therapeutic targets for cancer treatment.

A Novel Conserved Domain Mediates Dimerization of Protein Kinase D (PKD) Isoforms: DIMERIZATION IS ESSENTIAL FOR PKD-DEPENDENT REGULATION OF SECRETION AND INNATE IMMUNITY

Protein kinase D (PKD) isoforms are protein kinase C effectors in signaling pathways regulated by diacylglycerol. Important physiological processes (including secretion, immune responses, motility, and transcription) are placed under diacylglycerol control by the distinctive substrate specificity and subcellular distribution of PKDs. Potentially, broadly co-expressed PKD polypeptides may interact to generate homo- or heteromultimeric regulatory complexes. However, the frequency, molecular basis, regulatory significance, and physiological relevance of stable PKD-PKD interactions are largely unknown. Here, we demonstrate that mammalian PKDs 1-3 and the prototypical Caenorhabditis elegans PKD, DKF-2A, are exclusively (homo- or hetero-) dimers in cell extracts and intact cells. We discovered and characterized a novel, highly conserved N-terminal domain, comprising 92 amino acids, which mediates dimerization of PKD1, PKD2, and PKD3 monomers. A similar domain directs DKF-2A homodimerization. Dimerization occurred independently of properties of the regulatory and kinase domains of PKDs. Disruption of PKD dimerization abrogates secretion of PAUF, a protein carried in small trans-Golgi network-derived vesicles. In addition, disruption of DKF-2A homodimerization in C. elegans intestine impaired and degraded the immune defense of the intact animal against an ingested bacterial pathogen. Finally, dimerization was indispensable for the strong, dominant negative effect of catalytically inactive PKDs. Overall, the structural integrity and function of the novel dimerization domain are essential for PKD-mediated regulation of a key aspect of cell physiology, secretion, and innate immunity in vivo.

Subtilase cytotoxin produced by locus of enterocyte effacement-negative Shiga-toxigenic Escherichia coli induces stress granule formation

Subtilase cytotoxin (SubAB) is mainly produced by locus of enterocyte effacement (LEE)-negative strains of Shiga-toxigenic Escherichia coli (STEC). SubAB cleaves an endoplasmic reticulum (ER) chaperone, BiP/Grp78, leading to induction of ER stress. This stress causes activation of ER stress sensor proteins and induction of caspase-dependent apoptosis. We found that SubAB induces stress granules (SG) in various cells. Aim of this study was to explore the mechanism by which SubAB induced SG formation. Here, we show that SubAB-induced SG formation is regulated by activation of double-stranded RNA-activated protein kinase (PKR)-like endoplasmic reticulum kinase (PERK). The culture supernatant of STEC O113:H21 dramatically induced SG in Caco2 cells, although subAB knockout STEC O113:H21 culture supernatant did not. Treatment with phorbol 12-myristate 13-acetate (PMA), a protein kinase C (PKC) activator, and lysosomal inhibitors, NH4 Cl and chloroquine, suppressed SubAB-induced SG formation, which was enhanced by PKC and PKD inhibitors. SubAB attenuated the level of PKD1 phosphorylation. Depletion of PKCδ and PKD1 by siRNA promoted SG formation in response to SubAB. Furthermore, death-associated protein 1 (DAP1) knockdown increased basal phospho-PKD1(S916) and suppressed SG formation by SubAB. However, SG formation by an ER stress inducer, Thapsigargin, was not inhibited in PMA-treated cells. Our findings show that SubAB-induced SG formation is regulated by the PERK/DAP1 signalling pathway, which may be modulated by PKCδ/PKD1, and different from the signal transduction pathway that results in Thapsigargin-induced SG formation.

Protein Kinase D Enzymes as Regulators of EMT and Cancer Cell Invasion

The Protein Kinase D (PKD) isoforms PKD1, PKD2, and PKD3 are effectors of the novel Protein Kinase Cs (nPKCs) and diacylglycerol (DAG). PKDs impact diverse biological processes like protein transport, cell migration, proliferation, epithelial to mesenchymal transition (EMT) and apoptosis. PKDs however, have distinct effects on these functions. While PKD1 blocks EMT and cell migration, PKD2 and PKD3 tend to drive both processes. Given the importance of EMT and cell migration to the initiation and progression of various malignancies, abnormal expression of PKDs has been reported in multiple types of cancers, including breast, pancreatic and prostate cancer. In this review, we discuss how EMT and cell migration are regulated by PKD isoforms and the significance of this regulation in the context of cancer development.

Isoliensinine, a Bioactive Alkaloid Derived from Embryos of Nelumbo nucifera, Induces Hepatocellular Carcinoma Cell Apoptosis through Suppression of NF-κB Signaling

Isoliensinine (isolie) is an alkaloid produced by the edible plant Nelumbo nucifera. Here, we unveiled that isolie was able to provoke HepG2, Huh-7, and H22 hepatocellular carcinoma (HCC) cell apoptosis. Isolie decreased NF-κB activity and constitutive phosphorylation of NF-κB p65 subunit at Ser536 in HCC cells. Overexpression of p65 Ser536 phosphorylation mimics abrogated isolie-mediated HCC cell apoptosis. Furthermore, intraperitoneal injection of isolie inhibited the growth of Huh-7 xenografts in nude mice. Additionally, isolie given by both intraperitoneal injection and gavage diminished the proliferation of transplanted H22 cells in Kunming mice. Reduced tumor growth in vivo was associated with inhibited p65 phosphorylation at Ser536 and declined NF-κB activity in tumor tissues. Finally, we revealed that isolie was bioavailable in the blood of mice and exhibited no detectable toxic effects on tumor-bearing mice. Our data provided strong evidence for the anti-HCC effect of isolie.

Silencing of protein kinase D2 induces glioma cell senescence via p53-dependent and -independent pathways

Background

Glioblastoma multiforme (GBM) is a highly aggressive tumor of the central nervous system with a dismal prognosis for affected patients. Aberrant protein kinase C (PKC) signaling has been implicated in gliomagenesis, and a member of the PKC-activated protein kinase D (PRKD) family, PRKD2, was identified as mediator of GBM growth in vitro and in vivo.

Methods

The outcome of PRKD2 silencing and pharmacological inhibition on glioma cell proliferation was established with different glioma cell lines. Western blotting, senescence assays, co-immunoprecipitation, fluorescence activated cell sorting, quantitative PCR, and immunofluorescence microscopy were utilized to analyze downstream signaling.

Results

RNA-interference (21-mer siRNA) and pharmacological inhibition (CRT0066101) of PRKD2 profoundly inhibited proliferation of p53^wt (U87MG, A172, and primary GBM2), and p53^mut (GM133, T98G, U251, and primary Gli25) glioma cells. In a xenograft experiment, PRKD2 silencing significantly delayed tumor growth of U87MG cells. PRKD2 silencing in p53^wt and p53^mut cells was associated with typical hallmarks of senescence and cell cycle arrest in G1. Attenuated AKT/PKB phosphorylation in response to PRKD2 silencing was a common observation made in p53^wt and p53^mut GBM cells. PRKD2 knockdown in p53^wt cells induced upregulation of p53, p21, and p27 expression, decreased phosphorylation of CDK2 and/or CDK4, hypophosphorylation of retinoblastoma protein (pRb), and reduced transcription of E2F1. In p53^mut GM133 and primary Gli25 cells, PRKD2 silencing increased p27 and p15 and reduced E2F1 transcription but did not affect pRb phosphorylation.

Conclusions

PRKD2 silencing induces glioma cell senescence via p53-dependent and -independent pathways.

Functional and therapeutic significance of protein kinase D enzymes in invasive breast cancer

The protein kinase D (PKD) family members, PKD1, PKD2 and PKD3 constitute a family of serine/threonine kinases that are essential regulators of cell migration, proliferation and protein transport. Multiple types of cancers are characterized by aberrant expression of PKD isoforms. In breast cancer PKD isoforms exhibit distinct expression patterns and regulate various oncogenic processes. In highly invasive breast cancer, the leading cause of cancer-associated deaths in females, the loss of PKD1 is thought to promote invasion and metastasis, while PKD2 and upregulated PKD3 have been shown to be positive regulators of proliferation, chemoresistance and metastasis. In this review, we examine the differential expression pattern, mechanisms of regulation and contributions made by each PKD isoform to the development and maintenance of invasive breast cancer. In addition, we discuss the potential therapeutic approaches for targeting PKD in this disease.