Protein kinase D2 induces invasion of pancreatic cancer cells by regulating matrix metalloproteinases

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.

Protein kinase D1 - A targetable mediator of pancreatic cancer development

Members of the Protein kinase D (PKD) kinase family each play important cell-specific roles in the regulation of normal pancreas functions. In pancreatic diseases PKD1 is the most widely characterized isoform with roles in pancreatitis and in induction of pancreatic cancer and its progression. PKD1 expression and activation increases in pancreatic acinar cells through macrophage secreted factors, Kirsten rat sarcoma viral oncogene homolog (KRAS) signaling, and reactive oxygen species (ROS), driving the formation of precancerous lesions. In precancerous lesions PKD1 regulates cell survival, growth, senescence, and generation of doublecortin like kinase 1 (DCLK1)-positive cancer stem cells (CSCs). Within tumors, regulation by PKD1 includes chemoresistance, apoptosis, proliferation, CSC features, and the Warburg effect. Thus, PKD1 plays a critical role throughout pancreatic disease initiation and progression.

Golgi retention and oncogenic KIT signaling via PLCγ2-PKD2-PI4KIIIβ activation in gastrointestinal stromal tumor cells

Most gastrointestinal stromal tumors (GISTs) develop due to gain-of-function mutations in the tyrosine kinase gene, KIT. We recently showed that mutant KIT mislocalizes to the Golgi area and initiates uncontrolled signaling. However, the molecular mechanisms underlying its Golgi retention remain unknown. Here, we show that protein kinase D2 (PKD2) is activated by the mutant, which causes Golgi retention of KIT. In PKD2-inhibited cells, KIT migrates from the Golgi region to lysosomes and subsequently undergoes degradation. Importantly, delocalized KIT cannot trigger downstream activation. In the Golgi/trans-Golgi network (TGN), KIT activates the PKD2-phosphatidylinositol 4-kinase IIIβ (PKD2-PI4KIIIβ) pathway through phospholipase Cγ2 (PLCγ2) to generate a PI4P-rich membrane domain, where the AP1-GGA1 complex is aberrantly recruited. Disruption of any factors in this cascade results in the release of KIT from the Golgi/TGN. Our findings show the molecular mechanisms underlying KIT mislocalization and provide evidence for a strategy for inhibition of oncogenic signaling.

Endothelial Protein kinase D1 is a major regulator of post-traumatic hyperinflammation

Trauma is a major cause of death worldwide. The post-traumatic immune response culminates in the release of pro-inflammatory mediators, translating in the infiltration of neutrophils (PMNs) at injury sites. The extent of this inflammation is determined by multiple factors, such as PMN adhesion to the endothelium, transendothelial migration, endothelial barrier integrity as well as PMN swarming, mass infiltration and activation. This process is initiated by secondary lipid mediators, such as leukotriene B₄ (LTB₄). We here provide evidence that Protein kinase D1 (PRKD1) in endothelial cells is implicated in all these processes. Endothelial PRKD1 is activated by pro-inflammatory stimuli and amplifies PMN-mediated inflammation by upregulation of cytokine and chemokines as well as adhesion molecules, such as ICAM-1, VCAM-1 and E-selectin. This induces enhanced PMN adhesion and trans-migration. PRKD1 activation also destabilizes endothelial VE-cadherin adhesion complexes and thus the endothelial barrier, fostering PMN infiltration. We even describe a yet unrecognized PRKD1-dependant mechanism to induce biosynthesis of the PMN-swarming mediator LTB₄ directed via intercellular communication through small extracellular vesicles (sEVs) and enhanced CXCL8 secretion from activated endothelial cells. These endothelial sEVs transfer the LTB₄ biosynthesis enzyme LTA₄ hydrolase (LTA₄H) to prime PMNs, while initiating biosynthesis also requires additional signals, like CXCL8. We further demonstrate the respective LTA₄H-positive sEVs in the serum of polytrauma patients, peaking 12 h post injury. Therefore, PRKD1 is a key regulator in the coordinated communication of the endothelium with PMNs and a vital signaling node during post-traumatic inflammation.

Combination therapy of doxorubicin and Sildenafil inhibits the growth of pediatric rhabdomyosarcoma

BACKGROUND

Overexpression of phosphodiesterase type 5 (PDE5) has been detected in many types of malignant tumors. Sildenafil, a potent and selective inhibitor of a cGMP-specific PDE5, has been found to enhance the cytotoxic activity of different chemotherapeutic agents including doxorubicin. The combined therapy of doxorubicin with Sildenafil might reduce the possible side effects of chemotherapy while maintaining synergistic anticancer activity. The present study explored for the first time the effects of Sildenafil, alone and in combination with doxorubicin, on pediatric RMS cells.

METHODS

Human RMS cells lines RH30 and RD were used. Western blotting and RT-PCR were performed to analyze PDE5 expression in RMS cells. Cell viability was determined using MTT assay. Cell migration was analyzed via transwell chambers, clonal growth and mitotic cell death were analyzed using the clonogenic assay. FACS analysis was performed to evaluate reactive oxygen species (ROS) and apoptosis.

RESULTS

Sildenafil significantly decreased cell viability and migration of RD and RH30 cells. The exposure of RMS cells to doxorubicin resulted in a dose-dependent decrease in their viability. Simultaneous administration of Sildenafil enhanced this effect. The incubation of the RMS cells with Sildenafil in the presence of doxorubicin significantly increased the proportion of apoptotic cells and ROS production compared to the treatment with Sildenafil alone.

CONCLUSIONS

The results of our study indicate a link between PDE5 inhibition by Sildenafil and decreased calcium signalling leading to significantly impaired viability, migration, and colony forming of RMS cells. Increased ROS production and apoptosis are mechanisms relevantly contributing to this observation.

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.

Overarching roles of diacylglycerol signaling in cancer development and antitumor immunity

Diacylglycerol (DAG) is a lipid second messenger that is generated in response to extracellular stimuli and channels intracellular signals that affect mammalian cell proliferation, survival, and motility. DAG exerts a myriad of biological functions through protein kinase C (PKC) and other effectors, such as protein kinase D (PKD) isozymes and small GTPase-regulating proteins (such as RasGRPs). Imbalances in the fine-tuned homeostasis between DAG generation by phospholipase C (PLC) enzymes and termination by DAG kinases (DGKs), as well as dysregulation in the activity or abundance of DAG effectors, have been widely associated with tumor initiation, progression, and metastasis. DAG is also a key orchestrator of T cell function and thus plays a major role in tumor immunosurveillance. In addition, DAG pathways shape the tumor ecosystem by arbitrating the complex, dynamic interaction between cancer cells and the immune landscape, hence representing powerful modifiers of immune checkpoint and adoptive T cell-directed immunotherapy. Exploiting the wide spectrum of DAG signals from an integrated perspective could underscore meaningful advances in targeted cancer therapy.

Sildenafil triggers tumor lethality through altered expression of HSP90 and degradation of PKD2

The repurposing of existing drugs has emerged as an attractive additional strategy to the development of novel compounds in the fight against cancerous diseases. Inhibition of phosphodiesterase 5 (PDE5) has been claimed as a potential approach to target various cancer subtypes in recent years. However, data on the treatment of tumors with PDE5 inhibitors as well as the underlying mechanisms are as yet very scarce. Here, we report that treatment of tumor cells with low concentrations of Sildenafil was associated with decreased cancer cell proliferation and augmented apoptosis in vitro and resulted in impaired tumor growth in vivo. Notably, incubation of cancer cells with Sildenafil was associated with altered expression of HSP90 chaperone followed by degradation of protein kinase D2, a client protein previously reported to be involved in tumor growth. Furthermore, the involvement of low doses of PU-H71, an HSP90 inhibitor currently under clinical evaluation, in combination with low concentrations of Sildenafil, synergistically and negatively impacted on the viability of cancer cells in vivo. Taken together, our study suggests that repurposing of already approved drugs, alone or in combination with oncology-dedicated compounds, may represent a novel cancer therapeutic strategy.

High expression of MMP28 indicates unfavorable prognosis in pancreatic cancer

To investigate the expression pattern and diagnostic performance of matrix metalloproteinase 28 (MMP28) in pancreatic cancer (PC).The RNA-seq data of PC and normal pancreas tissue were acquired from The Cancer Genome Atlas (TCGA) and Genotype-Tissue Expression. Clinical information of PC that included prognostic data was obtained from TCGA. Later, Fisher exact test was applied for comparison of different clinicopathological features between high and low expression of MMP28 in PC. Afterwards, Kaplan-Meier survival analysis and Cox analysis (univariate and multivariate analysis) were used to explore the prognostic performance of MMP28 in PC cohort. Finally, gene set enrichment analysis (GSEA) revealed the potential signaling pathways related to high expression of MMP28 in PC.Upregulation of MMP28 was identified in PC tissue compared to normal pancreas tissue (P < .001). Overexpression of MMP28 was related to histological grade (P < .001), M classification (P = .014), and survival status (P = .028). Kaplan-Meier survival analysis revealed that high level of MMP28 implied unfavorable prognosis in PC (P = .002). Multivariate analysis confirmed that MMP28 was an independent risk factor in PC (hazard rate = 1.308, P = .018). Our GSEA analysis found that signaling pathways including glycolysis, p53 pathway, notch signaling, estrogen response late, cholesterol homeostasis, estrogen response early, mitotic spindle, and transforming growth factor beta signaling were enriched in the group with higher MMP28 expression.High expression of MMP28 could be identified in PC, which also served as an independent risk element for PC.

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.

Sildenafil beyond erectile dysfunction and pulmonary arterial hypertension: Thinking about new indications

Sildenafil, approved two decades ago, is the inhibitor of phosphodiesterase 5 (PDE5). First of all, it was designated for angina pectoris, but soon it showed a wonderful efficacy in erectile dysfunction (ED) and then pulmonary arterial hypertension (PAH). Due to the distribution of phosphodiesterase (PDE) in almost all organs, maybe it effects other diseases. Hence, a great number of investigations began to understand the role of PDEi in different organs. Preliminary research on sildenafil in cell culture and animal models has yielded promising results. Soon, a greater number of animal researches and clinical trials joined them. The results disclosed sildenafil can have beneficial effects in each organ such as heart, liver, kidney, brain, and intestines. Furthermore, it has significantly improved the prognosis of organ ischemia in various animal models. Clinical trials in several diseases, such as recurrent spontaneous miscarriage, fatty liver disease, bronchopulmonary dysplasia (BPD), heart failure, and premature ejaculation (PE) brought promising results. Although some clinical trials are available on the effects of sildenafil on various diseases, further studies on humans are needed to consolidate the ultimate effects of sildenafil. The aim of this review was to describe the effects of sildenafil on each organ and explain its mechanisms of action. Further, other PDE inhibitors such as tadalafil and vardenafil have been briefly discussed in parts of this review.

Protein Kinase D1, Reduced in Human Pancreatic Tumors, Increases Secretion of Small Extracellular Vesicles From Cancer Cells That Promote Metastasis to Lung in Mice

BACKGROUND & AIMS

Pancreatic tumor cells release small extracellular vesicles (sEVs, exosomes) that contain lipids and proteins, RNA, and DNA molecules that might promote formation of metastases. It is not clear what cargo these vesicles contain and how they are released. Protein kinase D1 (PRKD1) inhibits cell motility and is believed to be dysregulated in pancreatic ductal adenocarcinomas. We investigated whether it regulates production of sEVs in pancreatic cancer cells and their ability to form premetastatic niches for pancreatic cancer cells in mice.

METHODS

We analyzed data from UALCAN and human pancreatic tissue microarrays to compare levels of PRKD1 between tumor and nontumor tissues. We studied mice with pancreas-specific disruption of Prkd1 (PRKD1^KO mice), mice that express oncogenic KRAS (KC mice), and KC mice with disruption of Prkd1 (PRKD1^KO-KC mice). Subcutaneous xenograft tumors were grown in NSG mice from Panc1 cells; some mice were then given injections of sEVs. Pancreata and lung tissues from mice were analyzed by histology, immunohistochemistry, and/or quantitative polymerase chain reaction; we performed nanoparticle tracking analysis of plasma sEVs. The Prkd1 gene was disrupted in Panc1 cells using CRISPR-Cas9 or knocked down with small hairpin RNAs, or PRKD1 activity was inhibited with the selective inhibitor CRT0066101. Pancreatic cancer cell lines were analyzed by gene-expression microarray, quantitative polymerase chain reaction, immunoblot, and immunofluorescence analyses. sEVs secreted by Panc1 cell lines were analyzed by flow cytometry, transmission electron microscopy, and mass spectrometry.

RESULTS

Levels of PRKD1 were reduced in human pancreatic ductal adenocarcinoma tissues compared with nontumor tissues. PRKD1^KO-KC mice developed more pancreatic intraepithelial neoplasia, at a faster rate, than KC mice, and had more lung metastases and significantly shorter average survival time. Serum from PRKD1^KO-KC mice had increased levels of sEVs compared with KC mice. Pancreatic cancer cells with loss or inhibition of PRKD1 increased secretion of sEVs; loss of PRKD1 reduced phosphorylation of its substrate, cortactin, resulting in increased F-actin levels at the plasma membrane. sEVs from cells with loss or reduced expression of PRKD1 had altered content, and injection of these sEVs into mice increased metastasis of xenograft tumors to lung, compared with sEVs from pancreatic cells that expressed PRKD1. PRKD1-deficient pancreatic cancer cells showed increased loading of integrin α6β4 into sEVs-a process that required CD82.

CONCLUSIONS

Human pancreatic ductal adenocarcinoma has reduced levels of PRKD1 compared with nontumor pancreatic tissues. Loss of PRKD1 results in reduced phosphorylation of cortactin in pancreatic cancer cell lines, resulting in increased in F-actin at the plasma membrane and increased release of sEVs, with altered content. These sEVs promote metastasis of xenograft and pancreatic tumors to lung in mice.

Histo-genomics: digital pathology at the forefront of precision medicine

The toughest challenge OMICs face is that they provide extremely high molecular resolution but poor spatial information. Understanding the cellular/histological context of the overwhelming genetic data is critical for a full understanding of the clinical behavior of a malignant tumor. Digital pathology can add an extra layer of information to help visualize in a spatial and microenvironmental context the molecular information of cancer. Thus, histo-genomics provide a unique chance for data integration. In the era of a precision medicine, a four-dimensional (4D) (temporal/spatial) analysis of cancer aided by digital pathology can be a critical step to understand the evolution/progression of different cancers and consequently tailor individual treatment plans. For instance, the integration of molecular biomarkers expression into a three-dimensional (3D) image of a digitally scanned tumor can offer a better understanding of its subtype, behavior, host immune response and prognosis. Using advanced digital image analysis, a larger spectrum of parameters can be analyzed as potential predictors of clinical behavior. Correlation between morphological features and host immune response can be also performed with therapeutic implications. Radio-histomics, or the interface of radiological images and histology is another emerging exciting field which encompasses the integration of radiological imaging with digital pathological images, genomics, and clinical data to portray a more holistic approach to understating and treating disease. These advances in digital slide scanning are not without technical challenges, which will be addressed carefully in this review with quick peek at its future.

Elevated matrix metalloproteinase 7 expression promotes the proliferation, motility and metastasis of tongue squamous cell carcinoma

BACKGROUND

Matrix metalloproteinase 7 (MMP7), as the smallest member of the matrix metalloproteinase family, has been verified to be implicated in cancer progression, especially metastasis. However, its expression pattern and function in tongue cancer is not clear.

METHODS

The expression of MMP7 in human tongue squamous cell carcinoma (TSCC) specimens compared with their respective paired nontumour tissues by real-time PCR and immunohistochemical staining. The effect of MMP7 on the proliferation, apoptosis, migration, invasion of tongue cancer cells was tested in appropriate ways after MMP7 siRNA knockdown or overexpression. The effect of MMP7 on lymph node metastasis in vivo was analyzed using a high-metastasis orthotopic nude mouse tongue transplanted tumour model.

RESULTS

We found markedly elevated expression of MMP7 in human TSCC specimens compared with their respective paired nontumour tissues, and this high expression was correlated with the patients' lymph node metastasis. Furthermore, the results of molecular functional assays confirmed that MMP7 promotes cell proliferation, migration and invasion of TSCC cells. Knockdown of MMP7 inhibited lymph nodes metastasis in vivo.

CONCLUSIONS

MMP7 plays an oncogenic role in carcinogenesis and metastasis of tongue cancer, and may serve as a potential therapeutic target for tongue cancer.

Concerted regulation of actin polymerization during constitutive secretion by cortactin and PKD2

Constitutive secretion from the trans-Golgi-network (TGN) is facilitated by a concerted regulation of vesicle biogenesis and fission processes. The protein kinase D family (PKD) has been previously described to enhance vesicle fission by modifying the lipid environment. PKD also phosphorylates the actin regulatory protein cortactin at S298 to impair synergistic actin polymerization. We here report additional functions for PKD2 (also known as PRKD2) and cortactin in the regulation of actin polymerization during the fission of transport carriers from the TGN. Phosphorylation of cortactin at S298 impairs the interaction between WIP (also known as WIPF1) and cortactin. WIP stabilizes the autoinhibited conformation of N-WASP (also known as WASL). This leads to an inhibition of synergistic Arp2/3-complex-dependent actin polymerization at the TGN. PKD2 activity at the TGN is controlled by active CDC42-GTP which directly activates N-WASP, inhibits PKD2 and shifts the balance to non-S298-phosphorylated cortactin, which can in turn sequester WIP from N-WASP. Consequently, synergistic actin polymerization at the TGN and constitutive secretion are enhanced.

Physical plasma-triggered ROS induces tumor cell death upon cleavage of HSP90 chaperone

HSP90 is a ubiquitously expressed molecular chaperone implicated in the correct folding and maturation of a plethora of proteins including protein kinases and transcription factors. While disruption of chaperone activity was associated with augmented cancer cell death and decreased tumor growth both in vitro and in vivo, the regulation of HSP90 is not clearly understood. Here we report that treatment of cancer cells with cold physical plasma, an emerging and less aggressive tumor therapy, resulted in ROS generation which subsequently triggered the cleavage of HSP90. Notably, cleavage of HSP90 was followed by the degradation of PKD2, a crucial regulator of tumor growth and angiogenesis. Pre-sensitization of cancer cells with subliminal doses of PU-H71, an HSP90 inhibitor currently under clinical evaluation, followed by treatment with cold-plasma, synergistically and negatively impacted on the viability of cancer cells. Taken together, cold-plasma can be used in conjunction with pharmacologic treatment in order to target the expression and activity of HSP90 and the downstream client proteins implicated in various cancer cell capabilities.

The phosphorylation status of PIP5K1C at serine 448 can be predictive for invasive ductal carcinoma of the breast

Phosphatidylinositol-4-phosphate 5-kinase type-1C (PIP5K1C) is a lipid kinase that regulates focal adhesion dynamics and cell attachment through site-specific formation of phosphatidylinositol-4,5-bisphosphate (PI4,5P₂). By comparing normal breast tissue to carcinoma in situ and invasive ductal carcinoma subtypes, we here show that the phosphorylation status of PIP5K1C at serine residue 448 (S448) can be predictive for breast cancer progression to an aggressive phenotype, while PIP5K1C expression levels are not indicative for this event. PIP5K1C phosphorylation at S448 is downregulated in invasive ductal carcinoma, and similarly, the expression levels of PKD1, the kinase that phosphorylates PIP5K1C at this site, are decreased. Overall, since PKD1 is a negative regulator of cell migration and invasion in breast cancer, the phosphorylation status of this residue may serve as an indicator of aggressiveness of breast tumors.

PKD regulates actin polymerization, neutrophil deformability, and transendothelial migration in response to fMLP and trauma

Neutrophils are important mediators of the innate immune defense and of the host response to a physical trauma. Because aberrant infiltration of injured sites by neutrophils was shown to cause adverse effects after trauma, we investigated how neutrophil infiltration could be modulated at the cellular level. Our data indicate that protein kinase D (PKD) is a vital regulator of neutrophil transmigration. PKD phosphorylates the Cofilin-phosphatase Slingshot-2L (SSH-2L). SSH-2L in turn dynamically regulates Cofilin activity and actin polymerization in response to a chemotactic stimulus for neutrophils, for example, fMLP. Here, we show that inhibition of PKD by two specific small molecule inhibitors results in broad, unrestricted activation of Cofilin and strongly increases the F-actin content of neutrophils even under basal conditions. This phenotype correlates with a significantly impaired neutrophil deformability as determined by optical stretcher analysis. Consequently, inhibition of PKD impaired chemotaxis as shown by reduced extravasation of neutrophils. Consequently, we demonstrate that transendothelial passage of both, neutrophil-like NB4 cells and primary PMNs recovered from a hemorrhagic shock trauma model was significantly reduced. Thus, inhibition of PKD may represent a promising modulator of the neutrophil response to trauma.

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.

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.

Activation of the ROCK1/MMP-9 pathway is associated with the invasion and poor prognosis in papillary thyroid carcinoma

Rho-associated protein kinase 1 (ROCK1), a serine/threonine kinase, has previously been shown to be over-expressed in various types of human malignant tumors and to play an important role in cancer development and progression. Although ROCK1 has gained growing prominence as an important protein kinase in cancer biology, its potential as a predictive biomarker and a therapeutic target in papillary thyroid carcinoma (PTC) remains unknown. In the present study, ROCK1 expression was examined in 356 formalin-fixed, paraffin-embedded papillary thyroid carcinoma tissues using immunohistochemistry, and its clinical implications and prognostic significance were analyzed. Our results showed that ROCK1 expression was significantly increased in PTC compared with normal tissues, and was significantly associated with tumor size, lymphatic metastasis, distant organ metastasis, extrathyroid invasion, vascular invasion and tumor, node and metastasis (TNM) stage. Patients with strong ROCK1 expression had lower overall survival, disease-free survival, lymph node recurrence-free survival and distant recurrence-free survival rates than those with weak expression. Furthermore, overexpression of ROCK1 in papillary thyroid carcinoma cells was found to increase their invasiveness. Silencing ROCK1 by siRNA, however, caused an inhibition of cell invasion. Knockdown of ROCK1 decreased the volume and weight of the xenograft tumors, while overexpression of ROCK1 showed a proliferative tendency with significantly greater tumor volume and weight in vivo. Moreover, the upregulation of ROCK1 increased the expression of MMP-9, and levels of MMP-9 positively correlated with the ROCK1 levels in PTC tissues, implicating that MMP-9 may be involved in the mechanism of ROCK1 in the development and progression of PTC. These data suggest that ROCK1 might be a potential prognostic marker and therapeutic target for the treatment of PTC.

The armadillo protein p0071 controls KIF3 motor transport

We here report a novel function of the armadillo protein p0071 (also known as PKP4) during transport mediated by the KIF3 transport complex. Secretion of chromogranin A and matrix metallopeptidase 9 from pancreatic neuroendocrine tumor cells or pancreatic cancer cells, respectively, was substantially reduced following knockdown of p0071. Vesicle tracking indicated that there was impaired directional persistence of vesicle movement upon p0071 depletion. This suggests a disturbed balance between plus- and minus-end directed microtubule transport in cells lacking p0071. p0071 directly interacts with the KIF3 motor subunit KIF3B. Our data indicate that p0071 also interacts with the kinesin cargo adaptor protein KAP3 (also known as KIFAP3) acting as a stabilizing linker between KIF3B and its KAP3 cargo-binding entity. Thus, p0071 is required for directional vesicle movement and secretion of different KIF3-transported carriers, thereby regulating the transport of intracellular membrane vesicles along microtubules.

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.

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.

Frequent low-level mutations of protein kinase D2 in angiolipoma

Tumours displaying differentiation towards normal fat constitute the most common subgroup of soft tissue neoplasms. A series of such tumours was investigated by whole-exome sequencing followed by targeted ultra-deep sequencing. Eighty per cent of angiolipomas, but not any other tumour type, displayed mutations in the protein kinase D2 (PRKD2) gene, typically in the part encoding the catalytic domain. The absence of other aberrations at the chromosome or RNA level suggests that PRKD2 mutations are critical for angiolipoma development. Consistently, the mutated PRKD2 alleles were present at low (3-15%) frequencies, indicating that only a subset of the tumour cells is affected. Indeed, by sequencing mature fat cells and other cells separately, the former typically showed the highest mutation frequencies. Thus, we hypothesize that altered PRKD2 signalling in the adipocytic cells drives tumourigenesis and, in agreement with its pivotal role in angiogenesis, induces the vessel formation that is characteristic for angiolipoma. Copyright © 2016 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Identifying the crosstalk of dysfunctional pathways mediated by lncRNAs in breast cancer subtypes

Crosstalk among abnormal pathways widely occurs in human cancer and generally leads to insensitivity to cancer treatment. How long non-coding RNAs (lncRNAs) participate in the regulation of an abnormal pathway crosstalk in human cancer is largely unknown. Here, we proposed a strategy that integrates mRNA and lncRNA expression profiles for systematic identification of lncRNA-mediated crosstalk among risk pathways in different breast cancer subtypes. We identified 12 to 44 crosstalking pathway pairs mediated by 28 to 49 lncRNAs in four breast cancer subtypes. An LncRNA-mediated crosstalking pathway network in each breast cancer subtype was then constructed. We observed a number of breast cancer subtype-specific crosstalks of risk pathways. These subtype-specific lncRNA-mediated pathway crosstalks largely determined subtype-selective functions. Notably, we observed that lncRNAs mediated the crosstalk of pathways by cooperating with known important protein-coding genes, which play core roles in the deterioration of breast cancer. And we also identified key lncRNAs contributing to the crosstalk network in each subtype. As an example, the low expression of LIFR-AS1 was associated with poor survival in LumB subtype, and its cooperated genes IL1R and TGFBR located at the most upstream of the MAPK signaling pathway shared a common cascade path (p38 MAPKs-MEF2C) that can result in proliferation, differentiation and apoptosis. In summary, we offer an effective way to characterize complex crosstalks mediated by lncRNAs in breast cancer subtypes, which can be applied to other diseases and provide useful information for understanding the pathogenesis of human cancer.

Helicobacter pylori-induced changes in microtubule dynamics conferred by α-tubulin phosphorylation on Ser/Tyr mediate gastric mucosal secretion of matrix metalloproteinase-9 (MMP-9) and its modulation by ghrelin

Regulation of matrix metalloproteinase-9 (MMP-9) secretion in response to proinflammatory challenge remains under a strict control of factors that affect the stability dynamics of the major cytoskeleton polymeric structures, microtubules (MTs). In this study, we report that H. pylori LPS-elicited induction gastric mucosal MMP-9 secretion is accompanied by the enhancement in MT stabilization as evidenced by the increase in α-tubulin acetylation and detyrosination while the modulatory influence of hormone, ghrelin, is associated with MT destabilization and reflected in a decrease in α-tubulin acetylation and detyrosination. Further, we reveal that the LPS-induced enhancement in MT stabilization and up-regulation in MMP-9 secretion as well as the modulatory influence of ghrelin occur with the involvement of PKCδ and SFK. The LPS effect is reflected in a marked increase in PKCδ-mediated α-tubulin phosphorylation on Ser, while the modulatory effect of ghrelin on MT dynamics and MMP-9 secretion is manifested by the SFK-dependent phosphorylation of α-tubulin on Tyr. Moreover, the changes in α-tubulin phosphorylation and MT stabilization dynamics occur in concert with the Golgi recruitment and activation of PKD2 and Arf-GEF. The findings demonstrate that the enhancement in gastric mucosal MMP-9 secretion in response to H. pylori and its modulation by ghrelin are the result of changes in MT dynamics conferred by PKCδ/SFK- mediated α-tubulin Ser/Tyr phosphorylation.

Role of protein kinase D2 phosphorylation on Tyr in modulation by ghrelin of Helicobacter pylori-induced up-regulation in gastric mucosal matrix metalloproteinase-9 (MMP-9) secretion

Matrix metalloproteinas-9 (MMP-9) is a glycosylated endopeptidase associated with host reaction to microbial endotoxins and also characterizes gastric mucosal inflammatory response to H. pylori infection. Here, we report on the factors involved in gastric mucosal MMP-9 secretion in response to H. pylori LPS, and the effect of hormone, ghrelin. We show that both the LPS-elicited induction in MMP-9 secretion and also the modulatory influence of ghrelin occur at the level of MMP-9 processing between the endoplasmic reticulum (ER) and Golgi. Further, we demonstrate that the LPS effect is associated with up-regulation in the activation of Arf1, a small GTPase of the ADP-ribosylation factor family, and the recruitment and phosphorylation of protein kinase D2 (PKD2), involved in the secretory cargo processing in the Golgi. Moreover, we reveal that the LPS-induced up-regulation in MMP-9 secretion is reflected in a marked increase in PKCδ-mediated PKD2 phosphorylation on Ser, while the modulatory effect of ghrelin is manifested by the SFK-PTKs-dependent phosphorylation of PKD2 on Tyr. Thus, our findings demonstrate the role of Arf1/PKD2 in mediation of H. pylori LPS-induced up-regulation in gastric mucosal MMP-9 secretion and suggest the modulatory mechanism of ghrelin action.

Cortactin is a scaffolding platform for the E-cadherin adhesion complex and is regulated by protein kinase D1 phosphorylation

Dynamic regulation of cell-cell adhesion by the coordinated formation and dissolution of E-cadherin-based adherens junctions is crucial for tissue homeostasis. The actin-binding protein cortactin interacts with E-cadherin and enables F-actin accumulation at adherens junctions. Here, we were interested to study the broader functional interactions of cortactin in adhesion complexes. In line with literature, we demonstrate that cortactin binds to E-cadherin, and that a posttranslational modification of cortactin, RhoA-induced phosphorylation by protein kinase D1 (PKD1; also known as PRKD1) at S298, impairs adherens junction assembly and supports their dissolution. Two new S298-phosphorylation-dependent interactions were also identified, namely, that phosphorylation of cortactin decreases its interaction with β-catenin and the actin-binding protein vinculin. In addition, binding of vinculin to β-catenin, as well as linkage of vinculin to F-actin, are also significantly compromised upon phosphorylation of cortactin. Accordingly, we found that regulation of cell-cell adhesion by phosphorylation of cortactin downstream of RhoA and PKD1 is vitally dependent on vinculin-mediated protein interactions. Thus, cortactin, unexpectedly, is an important integration node for the dynamic regulation of protein complexes during breakdown and formation of adherens junctions.

Protein Kinase D1 Signaling in Angiogenic Gene Expression and VEGF-Mediated Angiogenesis

Protein kinase D 1 (PKD-1) is a signaling kinase important in fundamental cell functions including migration, proliferation, and differentiation. PKD-1 is also a key regulator of gene expression and angiogenesis that is essential for cardiovascular development and tumor progression. Further understanding molecular aspects of PKD-1 signaling in the regulation of angiogenesis may have translational implications in obesity, cardiovascular disease, and cancer. The author will summarize and provide the insights into molecular mechanisms by which PKD-1 regulates transcriptional expression of angiogenic genes, focusing on the transcriptional regulation of CD36 by PKD-1-FoxO1 signaling axis along with the potential implications of this axis in arterial differentiation and morphogenesis. He will also discuss a new concept of dynamic balance between proangiogenic and antiangiogenic signaling in determining angiogenic switch, and stress how PKD-1 signaling regulates VEGF signaling-mediated angiogenesis.

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.

A bright future for protein kinase D1 as a drug target to prevent or treat pancreatic cancer

Pancreatic ductal adenocarcinoma originates from acinar cells that undergo acinar-to-ductal metaplasia (ADM). ADM is initiated in response to growth factors, inflammation, and oncogene activation and leads to a de-differentiated, duct-like phenotype. Our recent publication demonstrated a transforming growth factor α-Kras(G12D)-protein kinase D1-Notch1 signaling axis driving the induction of ADM and further progression to pancreatic intraepithelial neoplasia. This suggests that protein kinase D1 might be an early marker for tumor development and a potential target for drug development.

Protein Kinase D2 Assembles a Multiprotein Complex at the Trans-Golgi Network to Regulate Matrix Metalloproteinase Secretion

Vesicle formation and fission are tightly regulated at the trans-Golgi network (TGN) during constitutive secretion. Two major protein families regulate these processes: members of the adenosyl-ribosylation factor family of small G-proteins (ARFs) and the protein kinase D (PKD) family of serine/threonine kinases. The functional relationship between these two key regulators of protein transport from the TGN so far is elusive. We here demonstrate the assembly of a novel functional protein complex at the TGN and its key members: cytosolic PKD2 binds ARF-like GTPase (ARL1) and shuttles ARL1 to the TGN. ARL1, in turn, localizes Arfaptin2 to the TGN. At the TGN, where PKD2 interacts with active ARF1, PKD2, and ARL1 are required for the assembly of a complex comprising of ARF1 and Arfaptin2 leading to secretion of matrix metalloproteinase-2 and -7. In conclusion, our data indicate that PKD2 is a core factor in the formation of this multiprotein complex at the TGN that controls constitutive secretion of matrix metalloproteinase cargo.

A time frame permissive for Protein Kinase D2 activity to direct angiogenesis in mouse embryonic stem cells

The protein kinase D isoenzymes PKD1/2/3 are prominent downstream targets of PKCs (Protein Kinase Cs) and phospholipase D in various biological systems. Recently, we identified PKD isoforms as novel mediators of tumour cell-endothelial cell communication, tumour cell motility and metastasis. Although PKD isoforms have been implicated in physiological/tumour angiogenesis, a role of PKDs during embryonic development, vasculogenesis and angiogenesis still remains elusive. We investigated the role of PKDs in germ layer segregation and subsequent vasculogenesis and angiogenesis using mouse embryonic stem cells (ESCs). We show that mouse ESCs predominantly express PKD2 followed by PKD3 while PKD1 displays negligible levels. Furthermore, we demonstrate that PKD2 is specifically phosphorylated/activated at the time of germ layer segregation. Time-restricted PKD2-activation limits mesendoderm formation and subsequent cardiovasculogenesis during early differentiation while leading to branching angiogenesis during late differentiation. In line, PKD2 loss-of-function analyses showed induction of mesendodermal differentiation in expense of the neuroectodermal germ layer. Our in vivo findings demonstrate that embryoid bodies transplanted on chicken chorioallantoic membrane induced an angiogenic response indicating that timed overexpression of PKD2 from day 4 onwards leads to augmented angiogenesis in differentiating ESCs. Taken together, our results describe novel and time-dependent facets of PKD2 during early cell fate determination.

Effective Targeting of Estrogen Receptor-Negative Breast Cancers with the Protein Kinase D Inhibitor CRT0066101

Invasive ductal carcinomas (IDC) of the breast are associated with altered expression of hormone receptors (HR), amplification or overexpression of HER2, or a triple-negative phenotype. The most aggressive cases of IDC are characterized by a high proliferation rate, a great propensity to metastasize, and their ability to resist to standard chemotherapy, hormone therapy, or HER2-targeted therapy. Using progression tissue microarrays, we here demonstrate that the serine/threonine kinase protein kinase D3 (PKD3) is highly upregulated in estrogen receptor (ER)-negative (ER(-)) tumors. We identify direct binding of the ER to the PRKD3 gene promoter as a mechanism of inhibition of PKD3 expression. Loss of ER results in upregulation of PKD3, leading to all hallmarks of aggressive IDC, including increased cell proliferation, migration, and invasion. This identifies ER(-) breast cancers as ideal for treatment with the PKD inhibitor CRT0066101. We show that similar to a knockdown of PKD3, treatment with this inhibitor targets all tumorigenic processes in vitro and decreases growth of primary tumors and metastasis in vivo. Our data strongly support the development of PKD inhibitors for clinical use for ER(-) breast cancers, including the triple-negative phenotype.

Mapping spatial heterogeneity in the tumor microenvironment: a new era for digital pathology

The emergent field of digital pathology employing automated image analysis techniques is to revolutionize traditional pathology at the center of clinical diagnostics. Histological images provide important tumor features unavailable in molecular profiling or omics data- the spatial context of tumor and stromal cells at single-cell resolution. Methods to map the spatial and morphological patterns of cancer and normal cells can contribute to a more comprehensive understanding of the highly heterogeneous tumor microenvironment. This review focuses on methods that help expand our knowledge of intra-tumoral spatial heterogeneity of the tumor microenvironment and their potential synergies with molecular profiling technologies.

Protein kinase D2 silencing reduced motility of doxorubicin-resistant MCF7 cells

Success of chemotherapy is generally impaired by multidrug resistance, intrinsic resistance, or acquired resistance to functionally and structurally irrelevant drugs. Multidrug resistance emerges via distinct mechanisms: increased drug export, decreased drug internalization, dysfunctional apoptotic machinery, increased DNA damage repair, altered cell cycle regulation, and increased drug detoxification. Several reports demonstrated that multidrug resistance is a multifaceted problem such that multidrug resistance correlates with increased aggressiveness and metastatic potential. Here, we tested the involvement of protein kinase D2, a serine/threonine kinase that was previously implicated in proliferation, drug resistance, and motility in doxorubicin-resistant MCF7 (MCF7/DOX) cell line, which served as an in vitro model for drug resistance and invasiveness. We showed that basal level activity of protein kinase D2 (PKD2) was higher in MCF7/DOX cells than parental MCF7 cells. To elucidate the roles of PKD2 MCF7/DOX, PKD2 expression was reduced via small interfering RNA (siRNA)-mediated knockdown. Results showed that acquired resistance of MCF7/DOX to doxorubicin was not affected by PKD2 silencing, while motility of MCF7/DOX cells was reduced. The results implied that PKD2 silencing might inhibit migration of MCF7/DOX cells without affecting chemoresistance significantly.

Protein kinase D enzymes: novel kinase targets in pancreatic cancer

Pancreatic ductal adenocarcinoma (PDA) is characterized by advanced stage desmoplastic tumors with a high prevalence of genetic abnormalities. Occurrence of PDA is linked to activating Kras mutations and aberrant epidermal growth factor receptor signaling, leading to additional activation of wild-type Kras. As Kras is difficult to target, there is a constant need to identify novel targets acting downstream of this molecule in driving the formation or progression of PDA. Recently, it was shown that protein kinase D enzymes not only are increasingly expressed in PDA but also causatively linked to the development and progression of this cancer. They act downstream of both mutant Kras and growth factors and therefore may represent ideal novel targets.

HSP90 supports tumor growth and angiogenesis through PRKD2 protein stabilization

The kinase PRKD2 (protein kinase D) is a crucial regulator of tumor cell-endothelial cell communication in gastrointestinal tumors and glioblastomas, but its mechanistic contributions to malignant development are not understood. Here, we report that the oncogenic chaperone HSP90 binds to and stabilizes PRKD2 in human cancer cells. Pharmacologic inhibition of HSP90 with structurally divergent small molecules currently in clinical development triggered proteasome-dependent degradation of PRKD2, augmenting apoptosis in human cancer cells of various tissue origins. Conversely, ectopic expression of PRKD2 protected cancer cells from the apoptotic effects of HSP90 abrogation, restoring blood vessel formation in two preclinical models of solid tumors. Mechanistic studies revealed that PRKD2 is essential for hypoxia-induced accumulation of hypoxia-inducible factor-1α (HIF1α) and activation of NF-κB in tumor cells. Notably, ectopic expression of PRKD2 was able to partially restore HIF1α and secreted VEGF-A levels in hypoxic cancer cells treated with HSP90 inhibitors. Taken together, our findings indicate that signals from hypoxia and HSP90 pathways are interconnected and funneled by PRKD2 into the NF-κB/VEGF-A signaling axis to promote tumor angiogenesis and tumor growth.

Protein kinase D2 promotes the proliferation of glioma cells by regulating Golgi phosphoprotein 3

Protein kinase D2 (PKD2) has been demonstrated to promote tumorigenesis in many types of cancers. However, how PKD2 regulates cancer cell growth is largely unknown. In this study, we found that over-expression of PKD2 promoted glioma cell growth but down-regulation of PKD2 inhibited it. Further investigation indicated that PKD2 down-regulation decreased the protein level of Golgi phosphoprotein 3(GOLPH3) as well as p-AKT level. On the contrary, over-expression of PKD2 increased the protein level of GOLPH3 and p-AKT. In addition, GOLPH3 exhibited similar effect on glioma cell growth to that of PKD2. Importantly, GOLPH3 down-regulation partially abolished glioma cell proliferation induced by PKD2 over-expression, while over-expression of GOLPH3 also partially rescued the inhibition effect of PKD2 down-regulation on glioma cell growth. Interestingly, the level of PKD2 and GOLPH3 significantly increased and was positively correlated in a cohort of glioma patients, as well as in patients from TCGA database. Taken together, these results reveal that PKD2 promotes glioma cell proliferation by regulating GOLPH3 and then AKT activation. Our findings indicate that both PKD2 and GOLPH3 play important roles in the progression of human gliomas and PKD2-GOLPH3-AKT signaling pathway might be a potential glioma therapeutic target.

Protein Kinase D family kinases: roads start to segregate

Highly invasive pancreatic tumors are often recognized in late stages due to a lack of clear symptoms and pose major challenges for treatment and disease management. Broad-band Protein Kinase D (PKD) inhibitors have recently been proposed as additional treatment option for this disease. PKDs are implicated in the control of cancer cell motility, angiogenesis, proliferation and metastasis. In particular, PKD2 expression is elevated in pancreatic cancer, whereas PKD1 expression is comparably lower. In our recent study we report that both kinases control PDAC cell invasive properties in an isoform-specific, but opposing manner. PKD1 selectively mediates anti-migratory/anti-invasive features by preferential regulation of the actin-regulatory Cofilin-phosphatase Slingshot1L (SSH1L). PKD2, on the other hand enhances invasion and angiogenesis of PDAC cells in 3D-ECM cultures and chorioallantois tumor models by stimulating expression and secretion of matrix-metalloproteinase 7 and 9 (MMP7/9). MMP9 also enhances PKD2-mediated tumor angiogenesis releasing extracellular matrix-bound VEGF-A. We thus suggest high PKD2 expression and loss of PKD1 may be beneficial for tumor cells to enhance their matrix-invading abilities. In our recent study we demonstrate for the first time PKD1 and 2 isoform-selective effects on pancreatic cancer cell invasion, in-vitro and in-vivo, defining isoform-specific regulation of PKDs as a major future issue.