Protein kinase D1 promotes anchorage-independent growth, invasion, and angiogenesis by human pancreatic cancer cells

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.

Membrane trafficking in breast cancer progression: protein kinase D comes into play

Protein kinase D (PKD) is a serine/threonine kinase family that controls important cellular functions, most notably playing a key role in the secretory pathway at the trans-Golgi network. Aberrant expression of PKD isoforms has been found mainly in breast cancer, where it promotes various cellular processes such as growth, invasion, survival and stem cell maintenance. In this review, we discuss the isoform-specific functions of PKD in breast cancer progression, with a particular focus on how the PKD controlled cellular processes might be linked to deregulated membrane trafficking and secretion. We further highlight the challenges of a therapeutic approach targeting PKD to prevent breast cancer progression.

Statins inhibit protein kinase D (PKD) activation in intestinal cells and prevent PKD1-induced growth of murine enteroids

We examined the impact of statins on protein kinase D (PKD) activation by G protein-coupled receptor (GPCR) agonists. Treatment of intestinal IEC-18 cells with cerivastatin inhibited PKD autophosphorylation at Ser916 induced by angiotensin II (ANG II) or vasopressin in a dose-dependent manner with half-maximal inhibition at 0.2 µM. Cerivastatin treatment inhibited PKD activation stimulated by these agonists for different times (5-60 min) and blunted HDAC5 phosphorylation, a substrate of PKD. Other lipophilic statins, including simvastatin, atorvastatin, and fluvastatin also prevented PKD activation in a dose-dependent manner. Using IEC-18 cell lines expressing PKD1 tagged with EGFP (enhanced green fluorescent protein), cerivastatin or simvastatin blocked GPCR-mediated PKD1-EGFP translocation to the plasma membrane and its subsequent nuclear accumulation. Similar results were obtained in IEC-18 cells expressing PKD3-EGFP. Mechanistically, statins inhibited agonist-dependent PKD activation rather than acting directly on PKD catalytic activity since exposure to cerivastatin or simvastatin did not impair PKD autophosphorylation or PKD1-EGFP membrane translocation in response to phorbol dibutyrate, which bypasses GPCRs and directly stimulates PKC and PKD. Furthermore, cerivastatin did not inhibit recombinant PKD activity determined via an in vitro kinase assay. Using enteroids generated from intestinal crypt-derived epithelial cells from PKD1 transgenic mice as a model of intestinal regeneration, we show that statins oppose PKD1-mediated increase in enteroid area, complexity (number of crypt-like buds), and DNA synthesis. Our results revealed a previously unappreciated inhibitory effect of statins on receptor-mediated PKD activation and in opposing the growth-promoting effects of PKD1 on intestinal epithelial cells.

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.

B Cell Receptor Signaling and Protein Kinase D2 Support Regulatory B Cell Function in Pancreatic Cancer

B cells can act as potent suppressors of anti-tumor T cell immunity, presenting a mechanism of resistance to immunotherapy. In pancreatic ductal adenocarcinoma, B cells can display a T cell-suppressive or regulatory phenotype centered on the expression of the cytokine Interleukin 35 (IL-35). While B cell-mediated immunosuppression presents a barrier to anti-tumorigenic T cell function, it is not clear how regulatory B cell function could be targeted, and the signals that promote this suppressive phenotype in B cells are not well understood. Here we use a novel IL-35 reporter model to understand which signaling pathways are important for immunosuppressive properties in B cells. In vitro analysis of IL-35 reporter B cells revealed a synergy between the BCR and TLR4 signaling pathways is sufficient to induce IL-35 expression. However, in vivo, B cell receptor activation, as opposed to MyD88 signaling in B cells, is central to B cell-mediated suppression and promotion of pancreatic cancer growth. Further analysis identified protein kinase D2 (PKD2) as being a key downstream regulator of IL-35 expression in B cells. Regulatory B cells with an inactivating mutation in PKD2 failed to produce IL-35 or fully suppress effector T cell function in vitro. Furthermore, inhibition of PKD in B cells decreased tumor growth and promoted effector T cell function upon adoptive transfer into B cell-deficient mice. Collectively, these data provide insight into how regulatory B cell function is promoted in pancreatic cancer and identify potential therapeutic targets to restrain this function.

Higher tumor protein kinase D1 correlates with increased tumor size, BCLC stage, CA199 level, AFP level and worse overall survival in hepatocellular carcinoma patients

OBJECTIVE

Hepatocellular carcinoma (HCC) is one of the most common cancers worldwide. Protein kinase D1 (PKD1) is recognized as a key regulator in the progression in several solid cancers, while its clinical role in HCC is unclear. This study aimed to evaluate the correlation of PKD1 with clinical features and prognosis in HCC patients.

METHODS

A total of 218 HCC patients who underwent resection were retrospectively enrolled. PKD1 expression in tumor (N = 218) and adjacent (N = 110) tissues was detected by immunohistochemical staining, scored by a semi-quantitative scoring method ranging from 0 to 12, and further classified as PKD1-, PKD1+, PKD1++ and PKD1+++ for analysis. Meanwhile, patients' clinical features and survival data were acquired from the database.

RESULTS

PKD1 was elevated in tumor tissues compared with adjacent tissues. Meanwhile, higher tumor PKD1 was correlated with elevated tumor size, Barcelona Clinic Liver Cancer (BCLC) stage, carbohydrate antigen 199 (CA199) level and alpha fetoprotein (AFP) level; while no correlation was found in tumor PKD1 with patients' basic features or liver function indexes. Moreover, higher tumor PKD1 was correlated with worse overall survival (OS) in HCC patients, then further validated as an independent predictive factor for worse OS by multivariate Cox's regression model analysis. Additionally, in Child-Pugh stage A, Child-Pugh stage B, BCLC stage 0/A, and BCLC stage B subgroups, higher tumor PKD1 was also correlated with worse OS.

CONCLUSION

Higher PKD1 in tumor tissues correlates with elevated BCLC stage, bigger tumor size, increased CA199 level, higher AFP level and worse OS in HCC patients.

Therapy-Naïve and Radioresistant 3-Dimensional Pancreatic Cancer Cell Cultures Are Effectively Radiosensitized by β1 Integrin Targeting

PURPOSE

Pancreatic ductal adenocarcinoma (PDAC) is a cancer with unmet needs. The role of highly conformal radiation therapy is still under debate for PDAC. Owing to its desmoplastic nature, integrin-mediated interactions between PDAC cells and extracellular matrix (ECM) profoundly contribute to PDAC therapy resistance. In this study, we investigated the radiochemosensitizing potential of β1 integrin targeting in therapy-naïve and radioresistant PDAC cell cultures grown in 3-dimensional (3D) ECM.

METHODS AND MATERIALS

In a panel of 3D, ECM-based PDAC cell cultures, β1 integrin was inhibited by antibodies or siRNA-mediated knockdown. Together with x-ray irradiation and specific chemotherapies, we determined 3D colony formation capacity in therapy-naïve and radioresistant PDAC cultures. We used kinome profiling, Western blotting, and immunofluorescence stainings to characterize these cell lines. Various siRNA screens were conducted to identify novel therapeutic targets.

RESULTS

We found a significant radiosensitizing potential of β1 integrin inhibition both in therapy-naïve and radioresistant PDAC cell cultures. Kinome profiling upon β1 integrin targeting identified a generally declined tyrosine and serine/threonine kinase activity, which presented less prominent in radioresistant than in therapy-naïve PDAC cells. siRNA screens employing the top 34 deregulated kinases in combination with β1 integrin inhibition revealed less efficacy and less radiosensitization in radioresistant relative to therapy-naïve PDAC cell cultures. Triple inhibition of β1 integrin, protein kinase D1, and rearranged during transfection turned out to be most effective in reducing 3D colony formation of radioresistant PDAC cells.

CONCLUSIONS

Our study clearly shows that β1 integrins are robust targets for overcoming radioresistance in PDAC. This seems to apply equally to therapy-sensitive and radioresistant cells. Concerning tumor heterogeneity, this dual therapy-sensitizing potential might be exploitable for a significant improvement of patient survival.

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.

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.

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.

Protein Kinase D1 Is Increased in Tumor Tissue, Correlates With Advanced Tumor Features and Worse Prognosis of Non-Small Cell Lung Cancer

OBJECTIVE

This study aimed to assess protein kinase D1 expression and its association with tumor characteristics as well as prognosis in patients with non-small cell lung cancer.

METHODS

Protein kinase D1 expression in tumor tissues and adjacent tissues from 172 patients with non-small cell lung cancer who underwent surgical resection were analyzed by immunohistochemical staining. Based on the total immunohistochemical score, protein kinase D1 expression was classified as protein kinase D1 high expression (further divided into protein kinase D1 high+++, protein kinase D1 high++, and protein kinase D1 high+ expressions) and protein kinase D1 low expression. Clinical characteristics of patients with non-small cell lung cancer were acquired from the database. Accumulating disease-free survival and overall survival were calculated based on patients' relapse/survival status.

RESULTS

Protein kinase D1 expression was increased in tumor tissues compared to adjacent tissues (P < .001). Tumor protein kinase D1 high expression correlated with poorer pathological differentiation (P = .041), increased tumor size (P = .003), the presence of lymph node metastasis (P = .001), and elevated tumor, nodes and metastases stage (P < .001). Besides, both accumulating disease-free survival and overall survival were decreased in patients with tumor protein kinase D1 high expression compared to patients with tumor protein kinase D1 low expression (P = .010 for disease-free survival and P = 0.005 for overall survival). Moreover, they were lowest in patients with tumor protein kinase D1 high+++ expression, followed by patients with tumor protein kinase D1 high++ expression, then patients with tumor protein kinase D1 high+ expression, and highest in patients with tumor protein kinase D1 low expression (P < .001 for disease-free survival and P = .001 for overall survival). Notably, higher tumor protein kinase D1 expression was an independent predictive factor for decreased disease-free survival (P = .001) and overall survival (P = .004).

CONCLUSIONS

Protein kinase D1 might be a potential marker to identify patients with non-small cell lung cancer with worse tumor features and prognosis.

Protein kinase D1 regulates metabolic switch in pancreatic cancer via modulation of mTORC1

BACKGROUND

Protein kinase D1 (PKD1) is a serine-threonine kinase that regulates various functions within the cell. Herein, we report the significance of PKD1 expression in glucose metabolism resulting in pancreatic cancer (PanCa) progression and chemo-resistance.

METHODS

PKD1 expression in PanCa was investigated by using immunohistochemistry. Functional and metabolic assays were utilised to analyse the effect of PKD1 expression/knockdown on associated cellular/molecular changes.

RESULTS

PKD1 expression was detected in human pancreatic intraepithelial neoplasia lesions (MCS = 12.9; P < 0.0001) and pancreatic ductal adenocarcinoma samples (MCS = 15, P < 0.0001) as compared with faint or no expression in normal pancreatic tissues (MCS = 1.54; P < 0.0001). Our results determine that PKD1 enhances glucose metabolism in PanCa cells, by triggering enhanced tumorigenesis and chemo-resistance. We demonstrate that mTORC1 activation by PKD1 regulates metabolic alterations in PanCa cells. siRNA knockdown of Raptor or treatment with rapamycin inhibited PKD1-accelerated lactate production as well as glucose consumption in cells, which confirms the association of mTORC1 with PKD1-induced metabolic alterations.

CONCLUSION

This study suggests a novel role of PKD1 as a key modulator of the glucose metabolism in PanCa cells accelerating tumorigenesis and chemo-resistance. The remodelling of PKD1-dysregulated glucose metabolism can be achieved by regulation of mTORC1 for development of novel therapeutic strategies.

Deciphering the Role of Protein Kinase D1 (PKD1) in Cellular Proliferation

Protein kinase D1 (PKD1) is a serine/threonine kinase that belongs to the calcium/calmodulin-dependent kinase family, and is involved in multiple mechanisms implicated in tumor progression such as cell motility, invasion, proliferation, protein transport, and apoptosis. While it is expressed in most tissues in the normal state, PKD1 expression may increase or decrease during tumorigenesis, and its role in proliferation is context-dependent and poorly understood. In this review, we present and discuss the current landscape of studies investigating the role of PKD1 in the proliferation of both cancerous and normal cells. Indeed, as a potential therapeutic target, deciphering whether PKD1 exerts a pro- or antiproliferative effect, and under what conditions, is of paramount importance.

Analysis of oncogenic activities of protein kinase D1 in head and neck squamous cell carcinoma

BACKGROUND

Head and neck squamous cell carcinoma (HNSCC) is the sixth leading cause of cancer death in the US. The protein kinase D (PKD) family has emerged as a promising target for cancer therapy with PKD1 being most intensively studied; however, its role in HNSCC has not been investigated.

METHODS

The expression of PKD was evaluated in human HNSCC by quantitative RT-PCR, Western blot and immunohistochemistry. Cell proliferation, wound healing, and matrigel invasion assays were performed upon siRNA-mediated knockdown of PKD1 in HNSCC cells, and subcutaneous xenograft mouse model was established by implantation of the stable doxycycline (Dox)-inducible PKD1 expression cell lines for analysis of tumorigenic activity in vivo.

RESULTS

PKD1 was frequently downregulated in HNSCC cell lines at both transcript and protein levels. In human HNSCC tissues, PKD1 was significantly down-regulated in localized tumors and metastases, and in patient-paired tumor tissues as compared to their normal counterparts, which was in part due to epigenetic modification of the PRKD1 gene. The function of PKD1 in HNSCC was analyzed using stable doxycycline-inducible cell lines that express native or constitutive-active PKD1. Upon induction, the rate of proliferation, survival, migration and invasion of HNSCC cells did not differ significantly between the control and PKD1 overexpressing cells in the basal state, and depletion of endogenous PKD1 did not impact the proliferation of HNSCC cells. However, the median growth rate of the subcutaneous HNSCC tumor xenografts over time was elevated with PKD1 induction, and the final tumor weight was significantly increased in Dox-induced vs. the non-induced tumors. Moreover, induced expression of PKD1 promoted bombesin-induced cell proliferation of HNSCC and resulted in sustained ERK1/2 activation in response to gastrin-releasing peptide or bombesin stimulation, suggesting that PKD1 potentiates GRP/bombesin-induced mitogenic response through the activation of ERK1/2 in HSNCC cells.

CONCLUSIONS

Our study has identified PKD1 as a frequently downregulated gene in HNSCC, and functionally, under certain cellular context, may play a role in GRP/bombesin-induced oncogenesis in HNSCC.

Improved GMP compliant approach to manipulate lipoaspirates, to cryopreserve stromal vascular fraction, and to expand adipose stem cells in xeno-free media

Background

The stromal vascular fraction (SVF) derived from adipose tissue contains adipose-derived stromal/stem cells (ASC) and can be used for regenerative applications. Thus, a validated protocol for SVF isolation, freezing, and thawing is required to manage product administration. To comply with Good Manufacturing Practice (GMP), fetal bovine serum (FBS), used to expand ASC in vitro, could be replaced by growth factors from platelet concentrates.

Methods

Throughout each protocol, GMP-compliant reagents and devices were used. SVF cells were isolated from lipoaspirates by a standardized enzymatic protocol. Cells were cryopreserved in solutions containing different albumin or serum and dimethylsulfoxide (DMSO) concentrations. Before and after cryopreservation, we analyzed: cell viability (by Trypan blue); immunophenotype (by flow cytometry); colony-forming unit-fibroblast (CFU-F) formation; and differentiation potential. ASC, seeded at different densities, were expanded in presence of 10% FBS or 5% supernatant rich in growth factors (SRGF) from platelets. The differentiation potential and cell transformation grade were tested in expanded ASC.

Results

We demonstrated that SVF can be obtained with a consistent yield (about 185 × 10³ cells/ml lipoaspirate) and viability (about 82%). Lipoaspirate manipulation after overnight storage at +4 °C reduced cell viability (−11.6%). The relative abundance of ASC (CD34⁺CD45⁻CD31^–) and endothelial precursors (CD34⁺CD45⁻CD31⁺) in the SVF product was about 59% and 42%, respectively. A period of 2 months cryostorage in autologous serum with added DMSO minimally affected post-thaw SVF cell viability as well as clonogenic and differentiation potentials. Viability was negatively affected when SVF was frozen at a cell concentration below 1.3 × 10⁶ cells/ml. Cell viability was not significantly affected after a freezing period of 1 year.

Independent of seeding density, ASC cultured in 5% SRGF exhibited higher growth rates when compared with 10% FBS. ASC expanded in both media showed unaltered identity (by flow cytometry) and were exempt from genetic lesions. Both 5% SRGF- and 10% FBS-expanded ASC efficiently differentiated to adipocytes, osteocytes, and chondrocytes.

Conclusions

This paper reports a GMP-compliant approach for freezing SVF cells isolated from adipose tissue by a standardized protocol. Moreover, an ASC expansion method in controlled culture conditions and without involvement of animal-derived additives was reported.

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.

KRAS, YAP, and obesity in pancreatic cancer: A signaling network with multiple loops

Pancreatic ductal adenocarcinoma (PDAC) continues to be a lethal disease with no efficacious treatment modalities. The incidence of PDAC is expected to increase, at least partially because of the obesity epidemic. Increased efforts to prevent or intercept this disease are clearly needed. Mutations in KRAS are initiating events in pancreatic carcinogenesis supported by genetically engineered mouse models of the disease. However, oncogenic KRAS is not entirely sufficient for the development of fully invasive PDAC. Additional genetic mutations and/or environmental, nutritional, and metabolic stressors, e.g. inflammation and obesity, are required for efficient PDAC formation with activation of KRAS downstream effectors. Multiple factors "upstream" of KRAS associated with obesity, including insulin resistance, inflammation, changes in gut microbiota and GI peptides, can enhance/modulate downstream signals. Multiple signaling networks and feedback loops "downstream" of KRAS have been described that respond to obesogenic diets. We propose that KRAS mutations potentiate a signaling network that is promoted by environmental factors. Specifically, we envisage that KRAS mutations increase the intensity and duration of the growth-promoting signaling network. As the transcriptional activator YAP plays a critical role in the network, we conclude that the rationale for targeting the network (at different points), e.g. with FDA approved drugs such as statins and metformin, is therefore compelling.

Androgen suppresses protein kinase D1 expression through fibroblast growth factor receptor substrate 2 in prostate cancer cells

In prostate cancer, androgen/androgen receptor (AR) and their downstream targets play key roles in all stages of disease progression. The protein kinase D (PKD) family, particularly PKD1, has been implicated in prostate cancer biology. Here, we examined the cross-regulation of PKD1 by androgen signaling in prostate cancer cells. Our data showed that the transcription of PKD1 was repressed by androgen in androgen-sensitive prostate cancer cells. Steroid depletion caused up regulation of PKD1 transcript and protein, an effect that was reversed by the AR agonist R1881 in a time- and concentration-dependent manner, thus identifying PKD1 as a novel androgen-repressed gene. Kinetic analysis indicated that the repression of PKD1 by androgen required the induction of a repressor protein. Furthermore, inhibition or knockdown of AR reversed AR agonist-induced PKD1 repression, indicating that AR was required for the suppression of PKD1 expression by androgen. Downstream of AR, we identified fibroblast growth factor receptor substrate 2 (FRS2) and its downstream MEK/ERK pathway as mediators of androgen-induced PKD1 repression. In summary, PKD1 was identified as a novel androgen-suppressed gene and could be downregulated by androgen through a novel AR/FRS2/MEK/ERK pathway. The upregulation of prosurvival PKD1 by anti-androgens may contribute to therapeutic resistance in prostate cancer treatment.

Investigation of the Role of Protein Kinase D in Human Rhinovirus Replication

Picornavirus replication is known to cause extensive remodeling of Golgi and endoplasmic reticulum membranes, and a number of the host proteins involved in the viral replication complex have been identified, including oxysterol binding protein (OSBP) and phosphatidylinositol 4-kinase III beta (PI4KB). Since both OSBP and PI4KB are substrates for protein kinase D (PKD) and PKD is known to be involved in the control of Golgi membrane vesicular and lipid transport, we hypothesized that PKD played a role in viral replication. We present multiple lines of evidence in support of this hypothesis. First, infection of HeLa cells with human rhinovirus (HRV) induced the phosphorylation of PKD. Second, PKD inhibitors reduced HRV genome replication, protein expression, and titers in a concentration-dependent fashion and also blocked the replication of poliovirus (PV) and foot-and-mouth disease virus (FMDV) in a variety of cells. Third, HRV replication was significantly reduced in HeLa cells overexpressing wild-type and mutant forms of PKD1. Fourth, HRV genome replication was reduced in HAP1 cells in which the PKD1 gene was knocked out by clustered regularly interspaced short palindromic repeats (CRISPR)-Cas9. Although we have not identified the molecular mechanism through which PKD regulates viral replication, our data suggest that this is not due to enhanced interferon signaling or an inhibition of clathrin-mediated endocytosis, and PKD inhibitors do not need to be present during viral uptake. Our data show for the first time that targeting PKD with small molecules can inhibit the replication of HRV, PV, and FMDV, and therefore, PKD may represent a novel antiviral target for drug discovery.

IMPORTANCE Picornaviruses remain an important family of human and animal pathogens for which we have a very limited arsenal of antiviral agents. HRV is the causative agent of the common cold, which in itself is a relatively trivial infection; however, in asthma and chronic obstructive pulmonary disease (COPD) patients, this virus is a major cause of exacerbations resulting in an increased use of medication, worsening symptoms, and, frequently, hospital admission. Thus, HRV represents a substantial health care and economic burden for which there are no approved therapies. We sought to identify a novel host target as a potential anti-HRV therapy. HRV infection induces the phosphorylation of PKD, and inhibitors of this kinase effectively block HRV replication at an early stage of the viral life cycle. Moreover, PKD inhibitors also block PV and FMDV replication. This is the first description that PKD may represent a target for antiviral drug discovery.

Insulin Receptor and GPCR Crosstalk Stimulates YAP via PI3K and PKD in Pancreatic Cancer Cells

We examined the impact of crosstalk between the insulin receptor and G protein-coupled receptor (GPCR) signaling pathways on the regulation of Yes-associated protein (YAP) localization, phosphorylation, and transcriptional activity in the context of human pancreatic ductal adenocarcinoma (PDAC). Stimulation of PANC-1 or MiaPaCa-2 cells with insulin and neurotensin, a potent mitogenic combination of agonists for these cells, promoted striking YAP nuclear localization and decreased YAP phosphorylation at Ser¹²⁷ and Ser³⁹⁷ Challenging PDAC cells with either insulin or neurotensin alone modestly induced the expression of YAP/TEAD-regulated genes, including connective tissue growth factor (CTGF), cysteine-rich angiogenic inducer 61 (CYR61), and CXCL5, whereas the combination of neurotensin and insulin induced a marked increase in the level of expression of these genes. In addition, siRNA-mediated knockdown of YAP/TAZ prevented the increase in the expression of these genes. A small-molecule inhibitor (A66), selective for the p110α subunit of PI3K, abrogated the increase in phosphatidylinositol 3,4,5-trisphosphate production and the expression of CTGF, CYR61, and CXCL5 induced by neurotensin and insulin. Furthermore, treatment of PDAC cells with protein kinase D (PKD) family inhibitors (CRT0066101 or kb NB 142-70) or with siRNAs targeting the PKD family prevented the increase of CTGF, CYR61, and CXCL5 mRNA levels in response to insulin and neurotensin stimulation. Thus, PI3K and PKD mediate YAP activation in response to insulin and neurotensin in pancreatic cancer cells.Implications: Inhibitors of PI3K or PKD disrupt crosstalk between insulin receptor and GPCR signaling systems by blocking YAP/TEAD-regulated gene expression in pancreatic cancer cells. Mol Cancer Res; 15(7); 929-41. ©2017 AACR.

Bradykinin stimulates protein kinase D-mediated colonic myofibroblast migration via cyclooxygenase-2 and heat shock protein 27

BACKGROUND

Inflammatory bowel disease is characterized by episodic intestinal injury and repair. Myofibroblasts are gastrointestinal tract stromal cells that regulate the reparative process and are known targets of inflammatory mediators including bradykinin (BK). However, the mechanisms through which inflammation regulates myofibroblast-induced wound healing remain incompletely understood. Here, we demonstrate, for the first time, that BK stimulates myofibroblast migration through protein kinase D (PKD)-mediated activation of the cyclooxygenase-2 (COX-2) and heat shock protein 27 (Hsp27) pathways.

MATERIALS AND METHODS

CCD-18Co is a human colonic myofibroblast cell line used from passages 8 to 14. An in vitro scratch assay assessed the effect of BK (100 nM) on myofibroblast migration over 24 h in the presence or absence of several inhibitors (CID755673 [10 μM] and NS398 [10 μM]). Hsp27 small interfering RNA evaluated the effect of Hsp27 on colonic myofibroblast migration. Antibodies to pPKD, pHsp27, and COX-2 evaluated expression levels by Western blot.

RESULTS

BK stimulated myofibroblast migration over 24 h. BK also led to rapid and sustained phosphorylation of PKD at Ser-916, rapid phosphorylation of Hsp27 at Ser-82, and increased COX-2 expression over 4 h. BK-mediated COX-2 expression and Hsp27 phosphorylation were both inhibited by the PKD inhibitor CID755673. Similarly, BK-induced myofibroblast migration was significantly inhibited by CID755673 (P < 0.05), by the direct COX-2 inhibitor NS398 (P < 0.05), and by Hsp27 small interfering RNA (P < 0.05).

CONCLUSIONS

BK stimulates myofibroblast migration through PKD-mediated activation of COX-2 and Hsp27. PKD, COX-2, and Hsp27 all appear to regulate myofibroblast cell migration, a stromal population that may play an important role in mucosal healing in the setting of inflammation.

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.

Positive cross talk between protein kinase D and β-catenin in intestinal epithelial cells: impact on β-catenin nuclear localization and phosphorylation at Ser552

Given the fundamental role of β-catenin signaling in intestinal epithelial cell proliferation and the growth-promoting function of protein kinase D1 (PKD1) in these cells, we hypothesized that PKDs mediate cross talk with β-catenin signaling. The results presented here provide several lines of evidence supporting this hypothesis. We found that stimulation of intestinal epithelial IEC-18 cells with the G protein-coupled receptor (GPCR) agonist angiotensin II (ANG II), a potent inducer of PKD activation, promoted endogenous β-catenin nuclear localization in a time-dependent manner. A significant increase was evident within 1 h of ANG II stimulation (P< 0.01), peaked at 4 h (P< 0.001), and declined afterwards. GPCR stimulation also induced a marked increase in β-catenin-regulated genes and phosphorylation at Ser(552) in intestinal epithelial cells. Exposure to preferential inhibitors of the PKD family (CRT006610 or kb NB 142-70) or knockdown of the isoforms of the PKD family prevented the increase in β-catenin nuclear localization and phosphorylation at Ser(552) in response to ANG II. GPCR stimulation also induced the formation of a complex between PKD1 and β-catenin, as shown by coimmunoprecipitation that depended on PKD1 catalytic activation, as it was abrogated by cell treatment with PKD family inhibitors. Using transgenic mice that express elevated PKD1 protein in the intestinal epithelium, we detected a marked increase in the localization of β-catenin in the nucleus of crypt epithelial cells in the ileum of PKD1 transgenic mice, compared with nontransgenic littermates. Collectively, our results identify a novel cross talk between PKD and β-catenin in intestinal epithelial cells, both in vitro and in vivo.

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.

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.

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.

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.

Protein kinase D1 regulates ERα-positive breast cancer cell growth response to 17β-estradiol and contributes to poor prognosis in patients

About 70% of human breast cancers express and are dependent for growth on estrogen receptor α (ERα), and therefore are sensitive to antiestrogen therapies. However, progression to an advanced, more aggressive phenotype is associated with acquisition of resistance to antiestrogens and/or invasive potential. In this study, we highlight the role of the serine/threonine-protein kinase D1 (PKD1) in ERα-positive breast cancers. Growth of ERα-positive MCF-7 and MDA-MB-415 human breast cancer cells was assayed in adherent or anchorage-independent conditions in cells overexpressing or depleted for PKD1. PKD1 induces cell growth through both an ERα-dependent manner, by increasing ERα expression and cell sensitivity to 17β-estradiol, and an ERα-independent manner, by reducing cell dependence to estrogens and conferring partial resistance to antiestrogen ICI 182,780. PKD1 knockdown in MDA-MB-415 cells strongly reduced estrogen-dependent and independent invasion. Quantification of PKD1 mRNA levels in 38 cancerous and non-cancerous breast cell lines and in 152 ERα-positive breast tumours from patients treated with adjuvant tamoxifen showed an association between PKD1 and ERα expression in 76.3% (29/38) of the breast cell lines tested and a strong correlation between PKD1 expression and invasiveness (P < 0.0001). In tamoxifen-treated patients, tumours with high PKD1 mRNA levels (n = 77, 50.66%) were significantly associated with less metastasis-free survival than tumours with low PKD1 mRNA expression (n = 75, 49.34%; P = 0.031). Moreover, PKD1 mRNA levels are strongly positively associated with EGFR and vimentin levels (P < 0.0000001). Thus, our study defines PKD1 as a novel attractive prognostic factor and a potential therapeutic target in breast cancer.

Mechanistic target of rapamycin (mTOR): a point of convergence in the action of insulin/IGF-1 and G protein-coupled receptor agonists in pancreatic cancer cells

Pancreatic ductal adenocarcinoma (PDAC), the most common form of pancreatic cancer, is one of the most lethal human diseases. PDAC is now the fourth leading cause of cancer mortality in both men and women and deaths due to PDAC are projected to increase dramatically. Novel targets and agents for chemoprevention are urgently needed and will most likely arise from a more detailed understanding of the signaling mechanisms that stimulate the promotion and progression of sub-malignant cells into pancreatic cancer cells and from the identification of modifiable risk factors for PDAC. Many epidemiological studies have linked obesity and long-standing type 2 diabetes mellitus (T2DM) with increased risk and worse clinical outcomes for developing PDAC. These diet-related metabolic disorders are multifaceted but characterized by peripheral insulin resistance, compensatory overproduction of insulin and increased bioavailability of insulin-like growth factor-1 (IGF-1). Mounting evidence indicates that the insulin/IGF-1 receptor system plays a critical role in PDAC development and multiple studies support the notion that crosstalk between the insulin receptor and heptahelical G protein-coupled receptor (GPCR) signaling systems is an important element in the biological responses elicited by these signaling systems, including cell proliferation. This article highlights the central role of the mechanistic target of rapamycin (mTOR) in mediating crosstalk between insulin/IGF-1 and GPCR signaling in pancreatic cancer cells and proposes strategies, including the use of metformin, to target this signaling system in PDAC cells.

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.

Polyserase-1/TMPRSS9 induces pro-tumor effects in pancreatic cancer cells by activation of pro-uPA

Polyserase-1/TMPRSS9 is a type II transmembrane serine protease showing a complex molecular architecture characterized by the presence of three tandem serine protease domains in its amino acid sequence. This protease is widely expressed in mouse and human tissues, however, its functional significance is unknown in both normal and pathological conditions. In the present study, we evaluated the possible role of polyserase-1 in cancer progression. First, we showed that polyserase-1 increased the invasive capacities of PANC-1 and SK-PC-3 pancreatic cancer cells. Moreover, the presence of polyserase-1 enhanced anchorage-independent growth and diminished the adhesion capability of PANC-1 cells to different extracellular matrix components. These effects were mediated by the efficient conversion of pro-uPA to active uPA and high phosphorylation levels of ERK detected in the PANC-1 cells expressing exogenous polyserase-1. Collectively, our data suggest that polyserase-1 may be involved in cancer progression and, similarly to what has been proposed for the closely related serine proteases matriptase and TMPRSS4, inhibition of TMPRSS9 activity may contribute to the inhibition of tumor growth.

Glutathione peroxidase 7 has potential tumour suppressor functions that are silenced by location-specific methylation in oesophageal adenocarcinoma

OBJECTIVE

To investigate the potential tumour suppressor functions of glutathione peroxidase 7 (GPX7) and examine the interplay between epigenetic and genetic events in regulating its expression in oesophageal adenocarcinomas (OAC).

DESIGN

In vitro and in vivo cell models were developed to investigate the biological and molecular functions of GPX7 in OAC.

RESULTS

Reconstitution of GPX7 in OAC cell lines, OE33 and FLO-1, significantly suppressed growth as shown by the growth curve, colony formation and EdU proliferation assays. Meanwhile, GPX7-expressing cells displayed significant impairment in G1/S progression and an increase in cell senescence. Concordant with the above functions, Western blot analysis displayed higher levels of p73, p27, p21 and p16 with a decrease in phosphorylated retinoblastoma protein (RB), indicating its increased tumour suppressor activities. On the contrary, knockdown of GPX7 in HET1A cells (an immortalised normal oesophageal cell line) rendered the cells growth advantage as indicated with a higher EdU rate, lower levels of p73, p27, p21 and p16 and an increase in phosphorylated RB. We confirmed the tumour suppressor function in vivo using GPX7-expressing OE33 cells in a mouse xenograft model. Pyrosequencing of the GPX7 promoter region (-162 to +138) demonstrated location-specific hypermethylation between +13 and +64 in OAC (69%, 54/78). This was significantly associated with the downregulation of GPX7 (p<0.01). Neither mutations in the coding exons of GPX7 nor DNA copy number losses were frequently present in the OAC examined (<5%).

CONCLUSIONS

Our data suggest that GPX7 possesses tumour suppressor functions in OAC and is silenced by location-specific promoter DNA methylation.

New pyrazolopyrimidine inhibitors of protein kinase d as potent anticancer agents for prostate cancer cells

The emergence of protein kinase D (PKD) as a potential therapeutic target for several diseases including cancer has triggered the search for potent, selective, and cell-permeable small molecule inhibitors. In this study, we describe the identification, in vitro characterization, structure-activity analysis, and biological evaluation of a novel PKD inhibitory scaffold exemplified by 1-naphthyl PP1 (1-NA-PP1). 1-NA-PP1 and IKK-16 were identified as pan-PKD inhibitors in a small-scale targeted kinase inhibitor library assay. Both screening hits inhibited PKD isoforms at about 100 nM and were ATP-competitive inhibitors. Analysis of several related kinases indicated that 1-NA-PP1 was highly selective for PKD as compared to IKK-16. SAR analysis showed that 1-NA-PP1 was considerably more potent and showed distinct substituent effects at the pyrazolopyrimidine core. 1-NA-PP1 was cell-active, and potently blocked prostate cancer cell proliferation by inducing G2/M arrest. It also potently blocked the migration and invasion of prostate cancer cells, demonstrating promising anticancer activities on multiple fronts. Overexpression of PKD1 or PKD3 almost completely reversed the growth arrest and the inhibition of tumor cell invasion caused by 1-NA-PP1, indicating that its anti-proliferative and anti-invasive activities were mediated through the inhibition of PKD. Interestingly, a 12-fold increase in sensitivity to 1-NA-PP1 could be achieved by engineering a gatekeeper mutation in the active site of PKD1, suggesting that 1-NA-PP1 could be paired with the analog-sensitive PKD1^M659G for dissecting PKD-specific functions and signaling pathways in various biological systems.

Multi-level control of actin dynamics by protein kinase D

Dynamic actin remodeling is fundamental to processes such as cell motility, vesicle trafficking, and cytokinesis. Protein kinase D (PKD) is a serine-threonine kinase known to be involved in diverse biological functions ranging from vesicle fission at the Golgi complex to regulation of cell motility and invasion. This review addresses the role of PKD in the organization of the actin cytoskeleton with a particular emphasis on the substrates associated with this function. We further highlight the multi-level control of actin dynamics by PKD and suggest that the tight spatio-temporal control of PKD activity is critical for the coordination of directed cell migration.

Protein kinase D1 mRNA level may predict cancer-specific survival in heavy smokers with esophageal squamous cell cancers

Protein kinase D1 (PRKD1) is a kinase that regulates various pathways, which involve in cell proliferation, apoptosis, cell adhesion and invasion. Although PRKD1 expression has been observed in many cancers, its role in esophageal squamous cell cancer (ESCC) has not been well reported. As its dysregulation in cancers is organ specific, we sought to investigate the potential role of PRKD1 in the progression of ESCC. Samples were collected from 178 patients with completely resected ESCCs at Sun Yat-sen University Cancer Center, including 47 pairs of tumorous and non-tumorous tissues. PRKD1 mRNA expression was investigated by quantitative real-time polymerase chain reaction. Receiver operating characteristic (ROC) curve analysis was used to search for a feasible cut-off point of PRKD1 mRNA levels for predicting cancer-specific survival. Kaplan-Meier and multivariate Cox regression analysis were used to assess the prognostic value of PRKD1 mRNA level in ESCC patients. In result, upregulation of PRKD1 mRNA was detected in 55.3% (26/47) of ESCC tissues compared with paired non-tumorous ones (P = 0.011). ROC analysis indicated 3.28 as a cut-off point, and thus 72 and 106 tumors with low and high PRKD1 mRNA expression were categorized. High-PRKD1 mRNA expression in tumors appeared with more frequency in heavy smokers (P = 0.002) and patients with advanced pathological T category (P = 0.034). Kaplan-Meier analysis indicated that patients with low-PRKD1 mRNA had a longer cancer-specific survival than the ones with high-PRKD1 level (P = 0.044). Multivariate analysis showed that tumorous PRKD1 mRNA expression was an independent prognostic factor (hazard ratio: 1.538, 95% confidence interval: 1.018-2.323, P = 0.041) in resected ESCC. Subgroup analysis revealed that the discernibility of PRKD1 mRNA level on ESCC outcomes was only pronounced in heavy smokers (P = 0.002), but not in non-heavy smokers (P = 0.870). PRKD1 might play a potential oncogenic role in ESCC. It might be an independent biomarker to predict prognosis in heavy smokers with ESCC.

Protein kinase D2 regulates migration and invasion of U87MG glioblastoma cells in vitro

Glioblastoma multiforme (GBM) is the most common malignant brain tumor, which, despite combined modality treatment, reoccurs and is invariably fatal for affected patients. Recently, a member of the serine/threonine protein kinase D (PRKD) family, PRKD2, was shown to be a potent mediator of glioblastoma growth. Here we studied the role of PRKD2 in U87MG glioblastoma cell migration and invasion in response to sphingosine-1-phosphate (S1P), an activator of PRKD2 and a GBM mitogen. Time-lapse microscopy demonstrated that random cell migration was significantly diminished in response to PRKD2 silencing. The pharmacological PRKD family inhibitor CRT0066101 decreased chemotactic migration and invasion across uncoated or matrigel-coated Transwell inserts. Silencing of PRKD2 attenuated migration and invasion of U87MG cells even more effectively. In terms of downstream signaling, CRT0066101 prevented PRKD2 autophosphorylation and inhibited p44/42 MAPK and to a smaller extent p54/46 JNK and p38 MAPK activation. PRKD2 silencing impaired activation of p44/42 MAPK and p54/46 JNK, downregulated nuclear c-Jun protein levels and decreased c-Jun^S73 phosphorylation without affecting the NFκB pathway. Finally, qPCR array analyses revealed that silencing of PRKD2 downregulates mRNA levels of integrin alpha-2 and -4 (ITGA2 and -4), plasminogen activator urokinase (PLAU), plasminogen activator urokinase receptor (PLAUR), and matrix metallopeptidase 1 (MMP1). Findings of the present study identify PRKD2 as a potential target to interfere with glioblastoma cell migration and invasion, two major determinants contributing to recurrence of glioblastoma after multimodality treatment.

•

Sphingosine-1-phosphate induces glioma cell migration and invasion.

•

Part of the effects is mediated by protein kinase D2 (PRKD2) activation.

•

Inactivation of PRKD2 attenuates glioblastoma cell migration and invasion.

•

Both, RNAi and pharmacological inhibition of PRKD2 inhibits MAPK signaling.

•

PRKD2 regulates transcription of gene products implicated in migration and invasion.

Ectopic expression of the heterotrimeric G15 protein in pancreatic carcinoma and its potential in cancer signal transduction

G15 is a heterotrimeric G protein selectively expressed in immature cell lineages in adult tissues that feature higher cell renewal potential. It promiscuously couples a wide variety of G protein-coupled receptors (GPCRs) to phospholipase C. Intriguingly, G15 is poorly affected by GPCR desensitization. We show here that G15 α-subunit (Gα15) supports sustained stimulation of PKD1 by a constitutively desensitized GPCR co-transfected over a negative cell background. Based on the fact that PKD1 is a multifunctional protein kinase activated by PKC and known for promoting oncogenic signaling, we hypothesized that, if expressed out of its natural cell context, G15 might promote tumor growth. A screening for Gα15 mRNA expression pointed to pancreatic carcinoma among different human cancer cell types and revealed significant expression in human tumor biopsies xenografted in mice. In addition, G15 ectopic presence could functionally contribute to the transformation process since siRNA-induced depletion of Gα15 in pancreatic carcinoma cell lines dramatically inhibited anchorage-independent growth and resistance to the lack of nutrients. Altogether, our findings suggest that G15 supports tumorigenic signaling in pancreas and hence it may be considered as a novel potential target for the therapy of this form of cancer.

PKD controls αvβ3 integrin recycling and tumor cell invasive migration through its substrate Rabaptin-5

Integrin recycling is critical for cell migration. Protein kinase D (PKD) mediates signals from the platelet-derived growth factor receptor (PDGF-R) to control αvβ3 integrin recycling. We now show that Rabaptin-5, a Rab5 effector in endosomal membrane fusion, is a PKD substrate. PKD phosphorylates Rabaptin-5 at Ser407, and this is both necessary and sufficient for PDGF-dependent short-loop recycling of αvβ3, which in turn inhibits α5β1 integrin recycling. Rab4, but not Rab5, interacts with phosphorylated Rabaptin-5 toward the front of migrating cells to promote delivery of αvβ3 to the leading edge, thereby driving persistent cell motility and invasion that is dependent on this integrin. Consistently, disruption of Rabaptin-5 Ser407 phosphorylation reduces persistent cell migration in 2D and αvβ3-dependent invasion. Conversely, invasive migration that is dependent on α5β1 integrin is promoted by disrupting Rabaptin phosphorylation. These findings demonstrate that the PKD pathway couples receptor tyrosine kinase signaling to an integrin switch via Rabaptin-5 phosphorylation.

In vitro cytotoxicity, pharmacokinetics, tissue distribution, and metabolism of small-molecule protein kinase D inhibitors, kb-NB142-70 and kb-NB165-09, in mice bearing human cancer xenografts

PURPOSE

Protein kinase D (PKD) mediates diverse biological responses including cell growth and survival. Therefore, PKD inhibitors may have therapeutic potential. We evaluated the in vitro cytotoxicity of two PKD inhibitors, kb-NB142-70 and its methoxy analogue, kb-NB165-09, and examined their in vivo efficacy and pharmacokinetics.

METHODS

The in vitro cytotoxicities of kb-NB142-70 and kb-NB165-09 were evaluated by MTT assay against PC-3, androgen-independent prostate cancer cells, and CFPAC-1 and PANC-1, pancreatic cancer cells. Efficacy studies were conducted in mice bearing either PC-3 or CPFAC-1 xenografts. Tumor-bearing mice were euthanized between 5 and 1,440 min after iv dosing, and plasma and tissue concentrations were measured by HPLC-UV. Metabolites were characterized by LC-MS/MS.

RESULTS

kb-NB142-70 and kb-NB165-09 inhibited cellular growth in the low-mid μM range. The compounds were inactive when administered to tumor-bearing mice. In mice treated with kb-NB142-70, the plasma C (max) was 36.9 nmol/mL, and the PC-3 tumor C (max) was 11.8 nmol/g. In mice dosed with kb-NB165-09, the plasma C (max) was 61.9 nmol/mL, while the PANC-1 tumor C (max) was 8.0 nmol/g. The plasma half-lives of kb-NB142-70 and kb-NB165-09 were 6 and 14 min, respectively. Both compounds underwent oxidation and glucuronidation.

CONCLUSIONS

kb-NB142-70 and kb-NB165-09 were rapidly metabolized, and concentrations in tumor were lower than those required for in vitro cytotoxicity. Replacement of the phenolic hydroxyl group with a methoxy group increased the plasma half-life of kb-NB165-09 2.3-fold over that of kb-NB142-70. Rapid metabolism in mice suggests that next-generation compounds will require further structural modifications to increase potency and/or metabolic stability.

A targeted library screen reveals a new inhibitor scaffold for protein kinase D

Protein kinase D (PKD) has emerged as a potential therapeutic target in multiple pathological conditions, including cancer and heart diseases. Potent and selective small molecule inhibitors of PKD are valuable for dissecting PKD-mediated cellular signaling pathways and for therapeutic application. In this study, we evaluated a targeted library of 235 small organic kinase inhibitors for PKD1 inhibitory activity at a single concentration. Twenty-eight PKD inhibitory chemotypes were identified and six exhibited excellent PKD1 selectivity. Five of the six lead structures share a common scaffold, with compound 139 being the most potent and selective for PKD vs PKC and CAMK. Compound 139 was an ATP-competitive PKD1 inhibitor with a low double-digit nanomolar potency and was also cell-active. Kinase profiling analysis identified this class of small molecules as pan-PKD inhibitors, confirmed their selectivity again PKC and CAMK, and demonstrated an overall favorable selectivity profile that could be further enhanced through structural modification. Furthermore, using a PKD homology model based on similar protein kinase structures, docking modes for compound 139 were explored and compared to literature examples of PKD inhibition. Modeling of these compounds at the ATP-binding site of PKD was used to rationalize its high potency and provide the foundation for future further optimization. Accordingly, using biochemical screening of a small number of privileged scaffolds and computational modeling, we have identified a new core structure for highly potent PKD inhibition with promising selectivity against closely related kinases. These lead structures represent an excellent starting point for the further optimization and the design of selective and therapeutically effective small molecule inhibitors of PKD.

Rapid protein kinase D1 signaling promotes migration of intestinal epithelial cells

We have examined the role of protein kinase D1 (PKD1) signaling in intestinal epithelial cell migration. Wounding monolayer cultures of intestinal epithelial cell line IEC-18 or IEC-6 induced rapid PKD1 activation in the cells immediately adjacent to the wound edge, as judged by immunofluorescence microscopy with an antibody that detects the phosphorylated state of PKD1 at Ser(916), an autophosphorylation site. An increase in PKD1 phosphorylation at Ser(916) was evident as early as 45 s after wounding, reached a maximum after 3 min, and persisted for ≥15 min. PKD1 autophosphorylation at Ser(916) was prevented by the PKD family inhibitors kb NB 142-70 and CRT0066101. A kb NB 142-70-sensitive increase in PKD autophosphorylation was also elicited by wounding IEC-6 cells. Using in vitro kinase assays after PKD1 immunoprecipitation, we corroborated that wounding IEC-18 cells induced rapid PKD1 catalytic activation. Further results indicate that PKD1 signaling is required to promote migration of intestinal epithelial cells into the denuded area of the wound. Specifically, treatment with kb NB 142-70 or small interfering RNAs targeting PKD1 markedly reduced wound-induced migration in IEC-18 cells. To test whether PKD1 promotes migration of intestinal epithelial cells in vivo, we used transgenic mice that express elevated PKD1 protein in the small intestinal epithelium. Enterocyte migration was markedly increased in the PKD1 transgenic mice. These results demonstrate that PKD1 activation is one of the early events initiated by wounding a monolayer of intestinal epithelial cells and indicate that PKD1 signaling promotes the migration of these cells in vitro and in vivo.

Protein kinase D1 mediates anchorage-dependent and -independent growth of tumor cells via the zinc finger transcription factor Snail1

We here identify protein kinase D1 (PKD1) as a major regulator of anchorage-dependent and -independent growth of cancer cells controlled via the transcription factor Snail1. Using FRET, we demonstrate that PKD1, but not PKD2, efficiently interacts with Snail1 in nuclei. PKD1 phosphorylates Snail1 at Ser-11. There was no change in the nucleocytoplasmic distribution of Snail1 using wild type Snail1 and Ser-11 phosphosite mutants in different tumor cells. Regardless of its phosphorylation status or following co-expression of constitutively active PKD, Snail1 was predominantly localized to cell nuclei. We also identify a novel mechanism of PKD1-mediated regulation of Snail1 transcriptional activity in tumor cells. The interaction of the co-repressors histone deacetylases 1 and 2 as well as lysyl oxidase-like protein 3 with Snail1 was impaired when Snail1 was not phosphorylated at Ser-11, which led to reduced Snail1-associated histone deacetylase activity. Additionally, lysyl oxidase-like protein 3 expression was up-regulated by ectopic PKD1 expression, implying a synergistic regulation of Snail1-driven transcription. Ectopic expression of PKD1 also up-regulated proliferation markers such as Cyclin D1 and Ajuba. Accordingly, Snail1 and its phosphorylation at Ser-11 were required and sufficient to control PKD1-mediated anchorage-independent growth and anchorage-dependent proliferation of different tumor cells. In conclusion, our data show that PKD1 is crucial to support growth of tumor cells via Snail1.

Inducible silencing of protein kinase D3 inhibits secretion of tumor-promoting factors in prostate cancer

Protein kinase D (PKD) acts as a major mediator of several signaling pathways related to cancer development. Aberrant PKD expression and activity have been shown in multiple cancers, and novel PKD inhibitors show promising anticancer activities. Despite these advances, the mechanisms through which PKD contributes to the pathogenesis of cancer remain unknown. Here, we establish a novel role for PKD3, the least studied member of the PKD family, in the regulation of prostate cancer cell growth and motility through modulation of secreted tumor-promoting factors. Using both a stable inducible knockdown cell model and a transient knockdown system using multiple siRNAs, we show that silencing of endogenous PKD3 significantly reduces prostate cancer cell proliferation, migration, and invasion. In addition, conditioned medium from PKD3-knockdown cells exhibits less migratory potential compared with that from control cells. Further analysis indicated that depletion of PKD3 blocks secretion of multiple key tumor-promoting factors including matrix metalloproteinase (MMP)-9, interleukin (IL)-6, IL-8, and GROα but does not alter mRNA transcript levels for these factors, implying impairment of the secretory pathway. More significantly, inducible depletion of PKD3 in a subcutaneous xenograft model suppresses tumor growth and decreases levels of intratumoral GROα in mice. These data validate PKD3 as a promising therapeutic target in prostate cancer and shed light on the role of secreted tumor-promoting factors in prostate cancer progression.

Protein kinase D: coupling extracellular stimuli to the regulation of cell physiology

Protein kinase D (PKD) mediates the actions of stimuli that promote diacylglycerol (DAG) biogenesis. By phosphorylating effectors that regulate transcription, fission and polarized transport of Golgi vesicles, as well as cell migration and survival after oxidative stress, PKDs substantially expand the range of physiological processes controlled by DAG. Dysregulated PKDs have been linked to pathologies including heart hypertrophy and cancer invasiveness. Our understanding of PKD regulation by trans- and autophosphorylation, as well as the subcellular dynamics of PKD substrate phosphorylation, have increased markedly. Selective PKD inhibitors provide new, powerful tools for elucidating the physiological roles of PKDs and potentially treating cardiac disease and cancer.

Protein kinase D signaling: multiple biological functions in health and disease

Protein kinase D (PKD) is an evolutionarily conserved protein kinase family with structural, enzymological, and regulatory properties different from the PKC family members. Signaling through PKD is induced by a remarkable number of stimuli, including G-protein-coupled receptor agonists and polypeptide growth factors. PKD1, the most studied member of the family, is increasingly implicated in the regulation of a complex array of fundamental biological processes, including signal transduction, cell proliferation and differentiation, membrane trafficking, secretion, immune regulation, cardiac hypertrophy and contraction, angiogenesis, and cancer. PKD mediates such a diverse array of normal and abnormal biological functions via dynamic changes in its spatial and temporal localization, combined with its distinct substrate specificity. Studies on PKD thus far indicate a striking diversity of both its signal generation and distribution and its potential for complex regulatory interactions with multiple downstream pathways, often regulating the subcellular localization of its targets.