Potent and selective disruption of protein kinase D functionality by a benzoxoloazepinolone

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.

Targeting PKD2 aggravates ferritinophagy-mediated ferroptosis via promoting autophagosome-lysosome fusion and enhances efficacy of carboplatin in lung adenocarcinoma

Ferroptosis is an iron-dependent cell death and affects efficacies of multiple antitumor regimens, showing a great potential in cancer therapy. Protein kinase D2 (PKD2) plays a crucial role in regulating necrosis and apoptosis. However, the relationship of PKD2 and ferroptosis is still elusive. In this study, we mainly analyzed the roles of PKD2 on ferroptosis and chemotherapy in lung adenocarcinoma (LUAD). We found PKD2 was highly expressed in LUAD and silencing PKD2 could promote erastin-induced reactive oxygen species (ROS), malondialdehyde (MDA) accumulation, intracellular iron content and LUAD cells death. Mechanistically, augmenting PKD2 could prevent autophagic degradation of ferritin, which could be impaired by bafilomycin A1. We further found that PKD2 overexpression would promote LC3B-II, p62/SQSTM1 accumulation and block autophagosome-lysosome fusion in a TFEB-independent manner, which could be impaired by bafilomycin A1. Bafilomycin A1 stimulation could weaken ferroptosis promotion by PKD2 abrogation. Silencing ferritin heavy chain-1 (FTH1) could reverse the resistance to ferroptosis by PKD2 overexpression. Additionally, in vitro and vivo experiments validated PKD2 promoted proliferation, migration and invasion of LUAD cells. PKD2 knockdown or pharmacological inhibition by CRT0066101 could enhance efficacy of carboplatin in LUAD via ferroptosis and apoptosis. Collectively, our study revealed that abrogation of PKD2 could aggravate ferritinophagy-mediated ferroptosis by promoting autophagosome-lysosome fusion and enhance efficacy of carboplatin in LUAD. Targeting PKD2 to induce ferroptosis may be a promising strategy for LUAD therapy.

Protein kinase D activity is a risk biomarker in prostate cancer that drives cell invasion by a Snail/ERK dependent mechanism

Protein kinase D (PKD) family members play controversial roles in prostate cancer (PC). Thus, PKD1 is nearly absent in advanced tumours, where PKD2 and PKD3 are upregulated. Additionally, consequences of activation of these kinases on PC progression remain largely unclear. Here, we first investigated PKD function on PC cell motility, analysing the underlying molecular mechanisms. We find a striking decrease of Snail levels after PKD inhibition followed by cell migration and invasion impairment, demonstrating an unprecedented role of PKD activity on the regulation of this key transcription factor in PC progression. Specifically, we show that PKD2 activity mediates the effects of MEK/ERK pathway on Snail expression, establishing a joint function of ERK/PKD2/Snail cascade in PC cell invasion regulation. These results led us to address the clinical relevance of the correlation between PKD2 and ERK activities with Snail abundance in samples from PC patients at different stages, analysing its impact on tumour prognosis and patients´ survival. Importantly, this is the first study defining a direct correlation between active PKD2 and Snail levels, further linked to ERK activity. We also evidence that PKD2 activity is associated with important poor prognostic factors. Thus, PC patients with the expression pattern: active PKD2high/active ERKhigh/Snailhigh exhibit increased invasiveness and metastasis, and decreased survival. Our findings provide new insights for understanding the molecular mechanisms involved in PC progression, pinpointing the combination of active PKD2 and Snail levels, with the additional measurement of active ERK, as a confident biomarker to predict clinical outcome of patients with advanced PC.

The role of PKC and PKD in CXCL12 and CXCL13 directed malignant melanoma and acute monocytic leukemic cancer cell migration

Cancer metastasis is the leading cause of cancer related mortality. Chemokine receptors and proteins in their downstream signalling axis represent desirable therapeutic targets for the prevention of metastasis. Despite this, current therapeutics have experienced limited success in clinical trials due to a lack of insight into the downstream signalling pathway of specific chemokine receptor cascades in different tumours. In this study, we investigated the role of protein kinase C (PKC) and protein kinase D (PKD) in CXCL12 and CXCL13 stimulated SK-MEL-28 (malignant melanoma) and THP-1 (acute monocytic leukaemia) cell migration. While PKC and PKD had no active role in CXCL12 or CXCL13 stimulated THP-1 cell migration, PKC and PKD inhibition reduced CXCL12 stimulated migration and caused profound effects upon the cytoskeleton of SK-MEL-28 cells. Furthermore, only PKC and not PKD inhibition reduced CXCL13 stimulated migration in SK-MEL-28 cells however PKC inhibition failed to stimulate any changes to the actin cytoskeleton. These findings indicate that PKC inhibitors would be a useful therapeutic for the prevention of both CXCL12 and CXCL13 stimulated migration and PKD inhibitors for CXCL12 stimulated migration in malignant melanoma.

Small molecule inhibitor CRT0066101 inhibits cytokine storm syndrome in a mouse model of lung injury

Pneumonia is an acute inflammation of the lungs induced by pathogenic microorganisms, immune damage, physical and chemical factors, and other factors, and the latest outbreak of novel coronavirus pneumonia is also an acute lung injury (ALI) induced by viral infection. However, there are currently no effective treatments for inflammatory cytokine storms in patients with ALI/acute respiratory distress syndrome (ARDS). Protein kinase D (PKD) is a highly active kinase that has been shown to be associated with the production of inflammatory cytokines. Therefore, small-molecule compounds that inhibit PKD may be potential drugs for the treatment of ALI/ARDS. In the present study, we evaluated the ability of the small-molecule inhibitor CRT0066101 to attenuate lipopolysaccharide (LPS)-induced inflammatory cytokine production through in vitro cell experiments and a mouse pneumonia model. We found that CRT0066101 significantly reduced the protein and mRNA levels of LPS-induced cytokines (e.g., IL-6, TNF-α, and IL-1β). CRT0066101 inhibited MyD88 and TLR4 expression and reduced NF-κB, ERK, and JNK phosphorylation. CRT0066101 also reduced NLRP3 activation, inhibited the assembly of the inflammasome complex, and attenuated inflammatory cell infiltration and lung tissue damage. Taken together, our data indicate that CRT0066101 exerts anti-inflammatory effects on LPS-induced inflammation through the TLR4/MyD88 signaling pathway, suggesting that CRT0066101 may have therapeutic value in acute lung injury and other MyD88-dependent inflammatory diseases.

Protein Kinase D2 and D3 Promote Prostate Cancer Cell Bone Metastasis by Positively Regulating Runx2 in a MEK/ERK1/2-Dependent Manner

Advanced-stage prostate tumors metastasize to the bone, often causing death. The protein kinase D (PKD) family has been implicated in prostate cancer development; however, its role in prostate cancer metastasis remains elusive. This study examined the contribution of PKD, particularly PKD2 and PKD3 (PKD2/3), to the metastatic potential of prostate cancer cells and the effect of PKD inhibition on prostate cancer bone metastasis in vivo. Depletion of PKD2/3 by siRNAs or inhibition by the PKD inhibitor CRT0066101 in AR-positive and AR-negative castration-resistant prostate cancer cells potently inhibited colony formation and cell migration. Depletion or inhibition of PKD2/3 significantly blocked tumor cell invasion and suppressed the expression of genes related to bone metastasis in the highly invasive PC3-ML cells. The reduced invasive activity resulting from PKD2/3 depletion was in part mediated by the transcription factor Runx2, as its silencing decreased PKD2/3-mediated metastatic gene expression through the mitogen-activated protein kinase kinase/extracellular signal-regulated kinase 1/2 signaling axis. Furthermore, inhibition of PKD by CRT0066101 potently decreased the frequency of bone micrometastases in a mouse model of bone metastasis based on intracardiac injection of PC3-ML cells. These results indicate that PKD2/3 plays an important role in the bone metastasis of prostate cancer cells, and its inhibition may be beneficial for the treatment of advanced prostate cancer.

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.

Multiparameter phenotypic screening for endogenous TFEB and TFE3 translocation identifies novel chemical series modulating lysosome function

The accumulation of toxic protein aggregates in multiple neurodegenerative diseases is associated with defects in the macroautophagy/autophagy-lysosome pathway. The amelioration of disease phenotypes across multiple models of neurodegeneration can be achieved through modulating the master regulator of lysosome function, TFEB (transcription factor EB). Using a novel multi-parameter high-throughput screen for cytoplasmic:nuclear translocation of endogenous TFEB and the related transcription factor TFE3, we screened the Published Kinase Inhibitor Set 2 (PKIS2) library as proof of principle and to identify kinase regulators of TFEB and TFE3. Given that TFEB and TFE3 are responsive to cellular stress we have established assays for cellular toxicity and lysosomal function, critical to ensuring the identification of hit compounds with only positive effects on lysosome activity. In addition to AKT inhibitors which regulate TFEB localization, we identified a series of quinazoline-derivative compounds that induced TFEB and TFE3 translocation. A novel series of structurally-related analogs was developed, and several compounds induced TFEB and TFE3 translocation at higher potency than previously screened compounds. KINOMEscan and cell-based KiNativ kinase profiling revealed high binding for the PRKD (protein kinase D) family of kinases, suggesting good selectivity for these compounds. We describe and utilize a cellular target-validation platform using CRISPRi knockdown and orthogonal PRKD inhibitors to demonstrate that the activity of these compounds is independent of PRKD inhibition. The more potent analogs induced subsequent upregulation of the CLEAR gene network and cleared pathological HTT protein in a cellular model of proteinopathy, demonstrating their potential to alleviate neurodegeneration-relevant phenotypes. Abbreviations: AD: Alzheimer disease; AK: adenylate kinase; CLEAR: coordinated lysosomal expression and regulation; CQ: chloroquine; HD: Huntington disease; PD: Parkinson disease; PKIS2: Published Kinase Inhibitor Set 2; PRKD: protein kinase D; TFEB: transcription factor EB.

Protein kinase D1 promotes the survival of random-pattern skin flaps in rats

BACKGROUND

In reconstructive surgery, random skin flaps are commonly used tools to cover skin defects, however, their applicability and size are limited by post-operative complications such as marginal ischemia-reperfusion injury and flap necrosis. Protein kinase D1 (PKD1), a calcium/calmodulin-dependent serine/threonine kinase, is known to induce angiogenesis and has been shown to mitigate ischemia in cardiovascular diseases. However, the role of PKD1 has not been investigated in skin flaps.

METHOD

Seventy-five male Sprague-Dawley rats with skin flaps were randomly divided into three groups: control, PKD1, and CID755673. Seven days following surgery, we assessed the general view and survival rate of the flap using histological analysis. Laser Doppler and lead oxide/gelatin angiography were used to evaluate microcirculation blood flow. Histopathological changes, neovascularization and microvascular density (MVD). were examined and calculated using microscopy after H&E staining. Protein expression levels were determined using immunoblotting and immunohistochemistry techniques.

RESULT

PKD1 significantly improved flap survival by upregulating angiogenic factors VEGF and cadherin5 and increasing antioxidant enzymes SOD, eNOS, and HO1, as well as reducing caspase 3, cytochrome c, and Bax expression, and attenuating IL-1β, IL-6, and TNF-α. In the PKD1 group, PKD1 increased neovascularization, and blood flow and flap survival areas were larger as compared to the control and CID755673 groups.

CONCLUSION

These findings show that PKD1 accelerates angiogenesis, reduces oxidative stress, and impedes apoptosis and inflammation, thus resulting in improved flap survival. Our observations indicated that PKD1 could be a therapeutic target for flap failure treatment.

Small Molecule Inhibitors of Protein Kinase D: Early Development, Current Approaches, and Future Directions

Now entering its fourth decade, research on the biological function, small molecule inhibition, and disease relevance of the three known isoforms of protein kinase D, PKD1, PKD2, and PKD3, has entered a mature development stage. This mini-perspective focuses on the medicinal chemistry that provided a structurally diverse set of mainly active site inhibitors, which, for a brief time period, moved through preclinical development stages but have yet to be tested in clinical trials. In particular, between 2006 and 2012, a rapid expansion of synthetic efforts led to several moderately to highly PKD-selective chemotypes but did not yet achieve PKD subtype selectivity or resolve general toxicity and pharmacokinetic challenges. In addition to cancer, other unresolved medical needs in cardiovascular, inflammatory, and metabolic diseases would, however, benefit from a renewed focus on potent and selective PKD modulators.

Chemical Modification of Phage-Displayed Helix-Loop-Helix Peptides to Construct Kinase-Focused Libraries

Conformationally constrained peptides hold promise as molecular tools in chemical biology and as a new modality in drug discovery. The construction and screening of a target-focused library could be a promising approach for the generation of de novo ligands or inhibitors against target proteins. Here, we have prepared a protein kinase-focused library by chemically modifying helix-loop-helix (HLH) peptides displayed on phage and subsequently tethered to adenosine. The library was screened against aurora kinase A (AurA). The selected HLH peptide Bip-3 retained the α-helical structure and bound to AurA with a KD value of 13.7 μM. Bip-3 and the adenosine-tethered peptide Bip-3-Adc provided IC50 values of 103 μM and 7.7 μM, respectively, suggesting that Bip-3-Adc bivalently inhibited AurA. In addition, the selectivity of Bip-3-Adc to several protein kinases was tested, and was highest against AurA. These results demonstrate that chemical modification can enable the construction of a kinase-focused library of phage-displayed HLH peptides.

His domain protein tyrosine phosphatase and Rabaptin-5 couple endo-lysosomal sorting of EGFR with endosomal maturation

His domain protein tyrosine phosphatase (HD-PTP; also known as PTPN23) collaborates with endosomal sorting complexes required for transport (ESCRTs) to sort endosomal cargo into intralumenal vesicles, forming the multivesicular body (MVB). Completion of MVB sorting is accompanied by maturation of the endosome into a late endosome, an event that requires inactivation of the early endosomal GTPase Rab5 (herein referring to generically to all isoforms). Here, we show that HD-PTP links ESCRT function with endosomal maturation. HD-PTP depletion prevents MVB sorting, while also blocking cargo from exiting Rab5-rich endosomes. HD-PTP-depleted cells contain hyperphosphorylated Rabaptin-5 (also known as RABEP1), a cofactor for the Rab5 guanine nucleotide exchange factor Rabex-5 (also known as RABGEF1), although HD-PTP is unlikely to directly dephosphorylate Rabaptin-5. In addition, HD-PTP-depleted cells exhibit Rabaptin-5-dependent hyperactivation of Rab5. HD-PTP binds directly to Rabaptin-5, between its Rabex-5- and Rab5-binding domains. This binding reaction involves the ESCRT-0/ESCRT-III binding site in HD-PTP, which is competed for by an ESCRT-III peptide. Jointly, these findings indicate that HD-PTP may alternatively scaffold ESCRTs and modulate Rabex-5–Rabaptin-5 activity, thereby helping to coordinate the completion of MVB sorting with endosomal maturation.

Summary: Sorting of endocytic cargo to the multivesicular body is accompanied by endosomal maturation. Here, we provide a potential mechanism by which these two processes are linked.

Decoding the Cardiac Actions of Protein Kinase D Isoforms

Protein kinase D (PKD) consists of a family of three structurally related enzymes that play key roles in a wide range of biological functions that contribute to the evolution of cardiac hypertrophy and heart failure. PKD1 (the founding member of this enzyme family) has been implicated in the phosphorylation of substrates that regulate cardiac hypertrophy, contraction, and susceptibility to ischemia/reperfusion injury, and de novo PRKD1 (protein kinase D1 gene) mutations have been identified in patients with syndromic congenital heart disease. However, cardiomyocytes coexpress all three PKDs. Although stimulus-specific activation patterns for PKD1, PKD2, and PKD3 have been identified in cardiomyocytes, progress toward identifying PKD isoform-specific functions in the heart have been hampered by significant gaps in our understanding of the molecular mechanisms that regulate PKD activity. This review incorporates recent conceptual breakthroughs in our understanding of various alternative mechanisms for PKD activation, with an emphasis on recent evidence that PKDs activate certain effector responses as dimers, to consider the role of PKD isoforms in signaling pathways that drive cardiac hypertrophy and ischemia/reperfusion injury. The focus is on whether the recently identified activation mechanisms that enhance the signaling repertoire of PKD family enzymes provide novel therapeutic strategies to target PKD enzymes and prevent or slow the evolution of cardiac injury and pathological cardiac remodeling. SIGNIFICANCE STATEMENT: PKD isoforms regulate a large number of fundamental biological processes, but the understanding of the biological actions of individual PKDs (based upon studies using adenoviral overexpression or gene-silencing methods) remains incomplete. This review focuses on dimerization, a recently identified mechanism for PKD activation, and the notion that this mechanism provides a strategy to develop novel PKD-targeted pharmaceuticals that restrict proliferation, invasion, or angiogenesis in cancer and prevent or slow the evolution of cardiac injury and pathological cardiac remodeling.

Small-Molecule Inhibitor Targeting Protein Kinase D: A Potential Therapeutic Strategy

The protein kinase D (PKD) family is a family of serine-threonine kinases that are members of the calcium/calmodulin-dependent kinase (CaMK) superfamily. PKDs have been increasingly implicated in multiple pivotal cellular processes and pathological conditions. PKD dysregulation is associated with several diseases, including cancer, inflammation, and obesity. Over the past few years, small-molecule inhibitors have emerged as alternative targeted therapy with fewer adverse side effects than currently available chemotherapy, and these specifically targeted inhibitors limit non-specific toxicities. The successful development of PKD inhibitors would significantly suppress the growth and proliferation of various cancers and inhibit the progression of other diseases. Various PKD inhibitors have been studied in the preclinical setting. In this context, we summarize the PKD inhibitors under investigation and their application for different kinds of diseases.

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.

Inhibition of protein kinase D by CID755673 promotes maintenance of the pluripotency of embryonic stem cells

The identification of novel mechanisms to maintain embryonic stem cell (ESC) pluripotency is of crucial importance, because the currently used culture conditions are not suitable for ESCs from all species. In this study, we show that the protein kinase D (PKD) inhibitor CID755673 (CID) is able to maintain the undifferentiated state of mouse ESCs in combination with the mitogen-activated protein kinase kinase (MEK) inhibitor. The expression levels of PKD members, including PKD1, PKD2 and PKD3, were low in mouse ESCs but significantly increased under differentiation conditions. Therefore, depletion of three PKD genes was able to phenocopy PKD inhibition. Mechanistically, PKD inhibition activated PI3K/AKT signaling by increasing the level of AKT phosphorylation, and the addition of a PI3K/AKT signaling pathway inhibitor partially reduced the cellular response to PKD inhibition. Importantly, the self-renewal-promoting effect of CID was maintained in human ESCs. Simultaneous knockdown of the three human PKD isoforms enabled short-term self-renewal in human ESCs, whereas PI3K/AKT signaling inhibition eliminated this self-renewal ability downstream of the PKD inhibitor. These findings expand our understanding of the gene regulatory network of ESC pluripotency.

Unveiling the Structural Insights into the Selective Inhibition of Protein Kinase D1

BACKGROUND

Although protein kinase D1 (PKD1) has been proved to be an efficient target for anticancer drug development, lack of structural details and substrate binding mechanisms are the main obstacles for the development of selective inhibitors with therapeutic benefits.

OBJECTIVE

The present study described the in silico dynamics behaviors of PKD1 in binding with selective and non-selective inhibitors and revealed the critical binding site residues for the selective kinase inhibition.

METHODS

Here, the three dimensional model of PKD1 was initially constructed by homology modeling along with binding site characterization to explore the non-conserved residues. Subsequently, two known inhibitors were docked to the catalytic site and the detailed ligand binding mechanisms and post binding dyanmics were investigated by molecular dynamics simulation and binding free energy calculations.

RESULTS

According to the binding site analysis, PKD1 serves several non-conserved residues in the G-loop, hinge and catalytic subunits. Among them, the residues including Leu662, His663, and Asp665 from hinge region made polar interactions with selective PKD1 inhibitor in docking simulation, which were further validated by the molecular dynamics simulation. Both inhibitors strongly influenced the structural dynamics of PKD1 and their computed binding free energies were in accordance with experimental bioactivity data.

CONCLUSION

The identified non-conserved residues likely to play critical role on molecular reorganization and inhibitor selectivity. Taken together, this study explained the molecular basis of PKD1 specific inhibition, which may help to design new selective inhibitors for better therapies to overcome cancer and PKD1 dysregulated disorders.

β-catenin stimulates Tcf7l1 degradation through recruitment of casein kinase 2 in mouse embryonic stem cells

Activation of the Wnt/β-catenin signaling pathway by the inhibition of glycogen synthase kinase-3 (GSK-3) will induce Tcf7l1 protein degradation to effectively promote embryonic stem cell (ESC) self-renewal. However, the exact mechanism remains unclear. Here, we found that inhibition of casein kinase 2 (Csnk2) by TBB or DMAT was sufficient to block the reduction of the Tcf7l1 protein induced by CHIR99021, a specific inhibitor of GSK-3. Similarly, downregulation of Csnk2 increased the Tcf7l1 level. In contrast, overexpression of Csnk2 significantly decreased Tcf7l1 protein stability in mouse ESCs. Notably, Csnk2α1 controls Tcf7l1 turnover to a greater degree than the other two isoforms of Csnk2, Csnk2α2 and Csnk2β, as Csnk2α1-overexpressing mouse ESCs exhibited the lowest level of Tcf7l1. Csnk2α1 interacted with and phosphorylated Tcf7l1. In addition, the association of Csnk2α1 and Tcf7l1 was enhanced by CHIR99021. Our study demonstrated, for the first time, that Csnk2 is involved in Tcf7l1 turnover mediated by the Wnt/β-catenin signaling pathway. These results expand our understanding of the function and circuit of Wnt/β-catenin signaling pathway in ESCs.

Protein Kinase D3 promotes the cell proliferation by activating the ERK1/c-MYC axis in breast cancer

Breast cancer is the second leading death cause of cancer death for all women. Previous study suggested that Protein Kinase D3 (PRKD3) was involved in breast cancer progression. In addition, the protein level of PRKD3 in triple‐negative breast adenocarcinoma was higher than that in normal breast tissue. However, the oncogenic mechanisms of PRKD3 in breast cancer is not fully investigated. Multi‐omic data showed that ERK1/c‐MYC axis was identified as a major pivot in PRKD3‐mediated downstream pathways. Our study provided the evidence to support that the PRKD3/ERK1/c‐MYC pathway play an important role in breast cancer progression. We found that knocking out PRKD3 by performing CRISPR/Cas9 genome engineering technology suppressed phosphorylation of both ERK1 and c‐MYC but did not down‐regulate ERK1/2 expression or phosphorylation of ERK2. The inhibition of ERK1 and c‐MYC phosphorylation further led to the lower protein level of c‐MYC and then reduced the expression of the c‐MYC target genes in breast cancer cells. We also found that loss of PRKD3 reduced the rate of the cell proliferation in vitro and tumour growth in vivo, whereas ectopic (over)expression of PRKD3, ERK1 or c‐MYC in the PRKD3‐knockout breast cells reverse the suppression of the cell proliferation and tumour growth. Collectively, our data strongly suggested that PRKD3 likely promote the cell proliferation in the breast cancer cells by activating ERK1‐c‐MYC axis.

Inhibition of protein kinase D disrupts spindle formation and actin assembly during porcine oocyte maturation

Protein kinase D (PKD) subfamily which includes PKD1, PKD2 and PKD3 is a novel family of serine/threonine kinases. PKD has been widely implicated in the regulation of multiple physiological effects including immune responses, apoptosis and cell proliferation. However, the roles of PKD in oocytes have not been fully clarified. In this study we investigated the regulatory functions of PKD during porcine oocyte maturation. Our results indicated that PKD expressed in porcine oocytes and the inhibition of PKD family activity led to the failure of meiosis resumption and the first polar body extrusion. Further analysis indicated that the spindle assembly and chromosome alignment were disrupted after PKD family inhibition, and this might be through its regulatory role on MAPK phosphorylation. We also found that PKD phosphorylated cofilin for actin assembly, which further affected cortical actin distribution, indicating the roles of PKD family on cytoskeleton. In addition, a decreased expression of PKD in postovulatory aging porcine oocytes was observed, which might connect PKD with cytoskeleton defects in aged oocytes. Taken together, these results suggest that PKD possesses important functions in porcine oocyte maturation by regulating spindle organization and actin assembly.

Twist1-Induced Epithelial Dissemination Requires Prkd1 Signaling

Dissemination is an essential early step in metastasis but its molecular basis remains incompletely understood. To define the essential targetable effectors of this process, we developed a 3D mammary epithelial culture model, in which dissemination is induced by overexpression of the transcription factor Twist1. Transcriptomic analysis and ChIP-PCR together demonstrated that protein kinase D1 (Prkd1) is a direct transcriptional target of Twist1 and is not expressed in the normal mammary epithelium. Pharmacologic and genetic inhibition of Prkd1 in the Twist1-induced dissemination model demonstrated that Prkd1 was required for cells to initiate extracellular matrix (ECM)-directed protrusions, release from the epithelium, and migrate through the ECM. Antibody-based protein profiling revealed that Prkd1 induced broad phosphorylation changes, including an inactivating phosphorylation of β-catenin and two microtubule depolymerizing phosphorylations of Tau, potentially explaining the release of cell-cell contacts and persistent activation of Prkd1. In patients with breast cancer, TWIST1 and PRKD1 expression correlated with metastatic recurrence, particularly in basal breast cancer. Prkd1 knockdown was sufficient to block dissemination of both murine and human mammary tumor organoids. Finally, Prkd1 knockdown in vivo blocked primary tumor invasion and distant metastasis in a mouse model of basal breast cancer. Collectively, these data identify Prkd1 as a novel and targetable signaling node downstream of Twist1 that is required for epithelial invasion and dissemination. SIGNIFICANCE: Twist1 is a known regulator of metastatic cell behaviors but not directly targetable. This study provides a molecular explanation for how Twist1-induced dissemination works and demonstrates that it can be targeted. GRAPHICAL ABSTRACT: http://cancerres.aacrjournals.org/content/canres/80/2/204/F1.large.jpg.

Lysosomal degradation of newly formed insulin granules contributes to β cell failure in diabetes

Compromised function of insulin-secreting pancreatic β cells is central to the development and progression of Type 2 Diabetes (T2D). However, the mechanisms underlying β cell failure remain incompletely understood. Here, we report that metabolic stress markedly enhances macroautophagy-independent lysosomal degradation of nascent insulin granules. In different model systems of diabetes including of human origin, stress-induced nascent granule degradation (SINGD) contributes to loss of insulin along with mammalian/mechanistic Target of Rapamycin (mTOR)-dependent suppression of macroautophagy. Expression of Protein Kinase D (PKD), a negative regulator of SINGD, is reduced in diabetic β cells. Pharmacological activation of PKD counters SINGD and delays the onset of T2D. Conversely, inhibition of PKD exacerbates SINGD, mitigates insulin secretion and accelerates diabetes. Finally, reduced levels of lysosomal tetraspanin CD63 prevent SINGD, leading to increased insulin secretion. Overall, our findings implicate aberrant SINGD in the pathogenesis of diabetes and suggest new therapeutic strategies to prevent β cell failure.

Impaired beta-cell insulin secretion is a key pathological feature of type 2 diabetes. Here, the authors describe metabolic stress induced lysosomal degradation of newly formed insulin granules, independent of macroautophagy, as a potential mechanism for beta-cell dysfunction.

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.

Angiogenic function of astragaloside IV in rats with myocardial infarction occurs via the PKD1-HDAC5-VEGF pathway

The current study aimed to assess the role and mechanism of astragaloside IV (AS-IV) in myocardial infarction. A myocardial infarction model was established via the ligation of the left anterior descending artery. Rats were randomly divided into sham, DMSO, model, AS-IV, AS-IV-CID755673 and CID755673 inhibitor groups. Rats were then sacrificed following 4 weeks of treatment and segmental heart samples were obtained for hematoxylin and eosin, and masson staining. The expression of PKD1, HDAC5 and VEGF were analyzed using immunohistochemistry, reverse transcription polymerase chain reaction and western blotting. Compared with the sham and DMSO groups, the morphology of myocardium in the model and CID755673 inhibitor groups were disordered and exhibited necrotic myocardial cells and collagen tissues. Following treatment with AS-IV, the morphology of the myocardium was markedly improved and the number of new blood vessels increased. However, following treatment with CID755673, the myocardial tissue of rats became disordered, with an increased number of necrotic cells and the closure of certain vessels. The expression of PKD1, HDAC5 and VEGF mRNA and protein in myocardial tissue of model group and CID755673 inhibitor group were significantly lower than the other four groups (P<0.05), whereas these levels in the AS-IV group were significantly higher than those in the other five groups (P<0.01). Additionally, the AS-IV-CID755673 group exhibited significantly higher levels of PKD1, HDAC5 and VEGF mRNA and protein than the sham, DMSO, CID755673 inhibitor and model groups (P<0.05). Furthermore, the protein expression of pS205 PKD1, pS259 HDAC5 and pTyr951 VEGF in the myocardium of rats was comparable with that of PKD1, HDAC5 and VEGF. AS-IV may partly promote the angiogenesis of myocardial tissue in rats with myocardial infarction via the PKD1-HDAC5-VEGF pathway.

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

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

Bifunctional N-heterocyclic carbene catalyzed [3 + 4] annulation of enals with azadienes: enantioselective synthesis of benzofuroazepinones

The bifunctional N-heterocyclic carbene catalyzed [3 + 4] annulation of enals with aurone-derived azadienes was developed to afford benzofuroazepinones with excellent enantioselectivities.

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.

PKD1 is a potential biomarker and therapeutic target in triple-negative breast cancer

Protein Kinase D1 (PKD1) is a serine/threonine kinase encoded by the PRKD1 gene. PKD1 has been previously shown to be a prognostic factor in ERα+ tamoxifen-resistant breast tumors and PKD1 overexpression confers estrogen independence to ERα+ MCF7 cells. In the present study, our goal was to determine whether PKD1 is a prognostic factor and/or a relevant therapeutic target in breast cancer. We analyzed PRKD1 mRNA levels in 527 primary breast tumors. We found that high PRKD1 mRNA levels were significantly and independently associated with a low metastasis-free survival in the whole breast cancer population and in the triple-negative breast cancer (TNBC) subtype specifically. High PRKD1 mRNA levels were also associated with a low overall survival in TNBC. We identified novel PKD1 inhibitors and assessed their antitumor activity in vitro in TNBC cell lines and in vivo in a TNBC patient-derived xenograft (PDX) model. Pharmacological inhibition and siRNA-mediated depletion of PKD1 reduced colony formation in MDA-MB-436 TNBC cells. PKD1 inhibition also reduced tumor growth in vivo in a TNBC PDX model. Together, these results establish PKD1 as a poor prognostic factor and a potential therapeutic target in TNBC.

Hippocampal protein kinase D1 is necessary for DHPG-induced learning and memory impairments in rats

Background

Understanding molecular mechanisms underlying the induction of learning and memory impairments remains a challenge. Recent investigations have shown that the activation of group I mGluRs (mGluR1 and mGluR5) in cultured hippocampal neurons by application of (S)-3,5-Dihydroxyphenylglycine (DHPG) causes the regulated internalization of N-methyl-D-aspartate receptors (NMDARs), which subsequently activates protein kinase D1 (PKD1). Through phosphorylating the C-terminals of the NMDAR GluN2 subunits, PKD1 down-regulates the activity of remaining (non-internalized) surface NMDARs. The knockdown of PKD1 does not affect the DHPG-induced inhibition of AMPA receptor-mediated miniature excitatory post-synaptic currents (mEPSCs) but prevents the DHPG-induced inhibition of NMDAR-mediated mEPSCs in vitro. Thus, we investigated the in vivo effects of bilateral infusions of DHPG into the hippocampal CA1 area of rats in the Morris water maze (MWM) and the novel object discrimination (NOD) tests.

Methods

A total of 300 adult male Sprague Dawley rats (250–280 g) were used for behavioral tests. One hundred ninety four were used in MWM test and the other 106 rats in the NOD test. Following one week of habituation to the vivarium, rats were bilaterally implanted under deep anesthesia with cannulas aimed at the CA1 area of the hippocampus (CA1 coordinates in mm from Bregma: AP -3.14; lateral +/-2; DV -3.0). Through implanted cannulas artificial cerebrospinal fluid (ACSF), the group1 mGluR antagonist 6-Methyl-2-(phenylethynyl)pyridine (MPEP), the dynamin-dependent internalization inhibitor Dynasore, or the PKD1 inhibitor CID755673 were infused into the bilateral hippocampal CA1 areas (2 μL per side, over 5 min). The effects of these infusions and the effects of PKD1 knockdown were examined in MWM or NOD test.

Results

DHPG infusion increased the latency to reach the platform in the MWM test and reduced the preference for the novel object in the NOD task. We found that the DHPG effects were dose-dependent and could be maintained for up to 2 days. Notably, these effects could be prevented by pre-infusion of the group1 mGluR antagonist MPEP, the dynamin-dependent internalization inhibitor Dynasore, the PKD1 inhibitor CID755673, or by PKD1 knockdown in the hippocampal CA1 area.

Conclusion

Altogether, these findings provide direct evidence that PKD1-mediated signaling may play a critical role in the induction of learning and memory impairments by DHPG infusion into the hippocampal CA1 area.

Protein kinase D-dependent CXCR4 down-regulation upon BCR triggering is linked to lymphadenopathy in chronic lymphocytic leukaemia

In Chronic Lymphocytic Leukemia (CLL), infiltration of lymph nodes by leukemic cells is observed in patients with progressive disease and adverse outcome. We have previously demonstrated that B-cell receptor (BCR) engagement resulted in CXCR4 down-regulation in CLL cells, correlating with a shorter progression-free survival in patients. In this study, we show a simultaneous down-regulation of CXCR4, CXCR5 and CD62L upon BCR triggering. While concomitant CXCR4 and CXCR5 down-regulation involves PKDs, CD62L release relies on PKC activation. BCR engagement induces PI3K-δ-dependent phosphorylation of PKD2 and 3, which in turn phosphorylate CXCR4 Ser^324/325. Moreover, upon BCR triggering, PKD phosphorylation levels correlate with the extent of membrane CXCR4 decrease. Inhibition of PKD activity restores membrane expression of CXCR4 and migration towards CXCL12 in BCR-responsive cells in vitro. In terms of pathophysiology, BCR-dependent CXCR4 down-regulation is observed in leukemic cells from patients with enlarged lymph nodes, irrespective of their IGHV mutational status. Taken together, our results demonstrate that PKD-mediated CXCR4 internalization induced by BCR engagement in B-CLL is associated with lymph node enlargement and suggest PKD as a potential druggable target for CLL therapeutics.

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.

Novel Small Molecule Inhibitors of Protein Kinase D Suppress NF-kappaB Activation and Attenuate the Severity of Rat Cerulein Pancreatitis

Nuclear factor-kappa B (NF-κB) activation is a key early signal regulating inflammatory and cell death responses in acute pancreatitis. Our previous in vitro studies with molecular approaches on AR42J cell showed that protein kinase D (PKD/PKD1) activation was required in NF-κB activation induced by cholecystokinin 8 (CCK) or carbachol (CCh) in pancreatic acinar cells. Recently developed small molecule PKD inhibitors, CID755673 and CRT0066101, provide potentially important pharmacological approaches to further investigate the effect of PKD in pancreatitis therapy. The aim of this study was to explore whether CID755673 and CRT0066101 block NF-κB activation with in vitro and in vivo models of experimental pancreatitis and whether the small molecule PKD inhibitors have therapeutic effects when given before or after the initiation of experimental pancreatitis. Freshly prepared pancreatic acini were incubated with CID755673 or CRT006101, followed by hyperstimulation with CCK or CCh. For in vivo experimental pancreatitis, rats were treated with intraperitoneal injection of CID755673 or CRT0066101 prior to or after administering cerulein or saline. PKD activation and NF-κB-DNA binding activity in nuclear extracts from pancreatic acini and tissue were measured. The effects of PKD inhibitors on pancreatitis responses were evaluated. Our results showed that both CID755673 or CRT0066101 selectively and specifically inhibited PKD without effects on related protein kinase Cs. Inhibition of PKD resulted in significantly attenuation of NF-κB activation in both in vitro and in vivo models of experimental pancreatitis. NF-κB inhibition by CID755673 was associated with decreased inflammatory responses and attenuated severity of the disease, which were indicated by less inflammatory cell infiltration, reduced pancreatic interleukin-6 (IL-6) and monocyte chemoattractant protein-1 (MCP-1), decreased intrapancreatic trypsin activation, and alleviation in pancreatic necrosis, edema and vacuolization. Furthermore, PKD inhibitor CID755673, given after the initiation of pancreatitis in experimental rat model, significantly attenuated the severity of acute pancreatitis. Therapies for acute pancreatitis are limited. Our results indicate that small chemical PKD inhibitors have significant potential as therapeutic interventions by suppressing NF-κB activation.

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.

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.

Molecular mechanisms underlying protective effects of quercetin against mitochondrial dysfunction and progressive dopaminergic neurodegeneration in cell culture and MitoPark transgenic mouse models of Parkinson's Disease

Quercetin, one of the major flavonoids in plants, has been recently reported to have neuroprotective effects against neurodegenerative processes. However, since the molecular signaling mechanisms governing these effects are not well clarified, we evaluated quercetin's effect on the neuroprotective signaling events in dopaminergic neuronal models and further tested its efficacy in the MitoPark transgenic mouse model of Parkinson's disease (PD). Western blot analysis revealed that quercetin significantly induced the activation of two major cell survival kinases, protein kinase D1 (PKD1) and Akt in MN9D dopaminergic neuronal cells. Furthermore, pharmacological inhibition or siRNA knockdown of PKD1 blocked the activation of Akt, suggesting that PKD1 acts as an upstream regulator of Akt in quercetin-mediated neuroprotective signaling. Quercetin also enhanced cAMP response-element binding protein phosphorylation and expression of the cAMP response-element binding protein target gene brain-derived neurotrophic factor. Results from qRT-PCR, Western blot analysis, mtDNA content analysis, and MitoTracker assay experiments revealed that quercetin augmented mitochondrial biogenesis. Quercetin also increased mitochondrial bioenergetics capacity and protected MN9D cells against 6-hydroxydopamine-induced neurotoxicity. To further evaluate the neuroprotective efficacy of quercetin against the mitochondrial dysfunction underlying PD, we used the progressive dopaminergic neurodegenerative MitoPark transgenic mouse model of PD. Oral administration of quercetin significantly reversed behavioral deficits, striatal dopamine depletion, and TH neuronal cell loss in MitoPark mice. Together, our findings demonstrate that quercetin activates the PKD1-Akt cell survival signaling axis and suggest that further exploration of quercetin as a promising neuroprotective agent for treating PD may offer clinical benefits.

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.

Protein Kinase D: A Potential Therapeutic Target in Prostate Cancer

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

Inducible Inhibition of Gβγ Reveals Localization-dependent Functions at the Plasma Membrane and Golgi

Heterotrimeric G proteins signal at a variety of endomembrane locations, in addition to their canonical function at the cytoplasmic surface of the plasma membrane (PM), where they are activated by cell surface G protein-coupled receptors. Here we focus on βγ signaling at the Golgi, where βγ activates a signaling cascade, ultimately resulting in vesicle fission from the trans-Golgi network (TGN). To develop a novel molecular tool for inhibiting endogenous βγ in a spatial-temporal manner, we take advantage of a lipid association mutant of the widely used βγ inhibitor GRK2ct (GRK2ct-KERE) and the FRB/FKBP heterodimerization system. We show that GRK2ct-KERE cannot inhibit βγ function when expressed in cells, but recruitment to a specific membrane location recovers the ability of GRK2ct-KERE to inhibit βγ signaling. PM-recruited GRK2ct-KERE inhibits lysophosphatidic acid-induced phosphorylation of Akt, whereas Golgi-recruited GRK2ct-KERE inhibits cargo transport from the TGN to the PM. Moreover, we show that Golgi-recruited GRK2ct-KERE inhibits model basolaterally targeted but not apically targeted cargo delivery, for both PM-destined and secretory cargo, providing the first evidence of selectivity in terms of cargo transport regulated by βγ. Last, we show that Golgi fragmentation induced by ilimaquinone and nocodazole is blocked by βγ inhibition, demonstrating that βγ is a key regulator of multiple pathways that impact Golgi morphology. Thus, we have developed a new molecular tool, recruitable GRK2ct-KERE, to modulate βγ signaling at specific subcellular locations, and we demonstrate novel cargo selectivity for βγ regulation of TGN to PM transport and a novel role for βγ in mediating Golgi fragmentation.

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.

PKD signaling and pancreatitis

BACKGROUND

Acute pancreatitis is a serious medical disorder with no current therapies directed to the molecular pathogenesis of the disorder. Inflammation, inappropriate intracellular activation of digestive enzymes, and parenchymal acinar cell death by necrosis are the critical pathophysiologic processes of acute pancreatitis. Thus, it is necessary to elucidate the key molecular signals that mediate these pathobiologic processes and develop new therapeutic strategies to attenuate the appropriate signaling pathways in order to improve outcomes for this disease. A novel serine/threonine protein kinase D (PKD) family has emerged as key participants in signal transduction, and this family is increasingly being implicated in the regulation of multiple cellular functions and diseases.

METHODS

This review summarizes recent findings of our group and others regarding the signaling pathway and the biological roles of the PKD family in pancreatic acinar cells. In particular, we highlight our studies of the functions of PKD in several key pathobiologic processes associated with acute pancreatitis in experimental models.

RESULTS

Our findings reveal that PKD signaling is required for NF-κB activation/inflammation, intracellular zymogen activation, and acinar cell necrosis in rodent experimental pancreatitis. Novel small-molecule PKD inhibitors attenuate the severity of pancreatitis in both in vitro and in vivo experimental models. Further, this review emphasizes our latest advances in the therapeutic application of PKD inhibitors to experimental pancreatitis after the initiation of pancreatitis.

CONCLUSIONS

These novel findings suggest that PKD signaling is a necessary modulator in key initiating pathobiologic processes of pancreatitis, and that it constitutes a novel therapeutic target for treatments of this disorder.

Regulation of membrane KCNQ1/KCNE1 channel density by sphingomyelin synthase 1

Sphingomyelin synthase (SMS) catalyzes the conversion of phosphatidylcholine and ceramide to sphingomyelin and diacylglycerol. We previously showed that SMS1 deficiency leads to a reduction in expression of the K(+) channel KCNQ1 in the inner ear (Lu MH, Takemoto M, Watanabe K, Luo H, Nishimura M, Yano M, Tomimoto H, Okazaki T, Oike Y, and Song WJ. J Physiol 590: 4029-4044, 2012), causing hearing loss. However, it remains unknown whether this change in expression is attributable to a cellular process or a systemic effect in the knockout animal. Here, we examined whether manipulation of SMS1 activity affects KCNQ1/KCNE1 currents in individual cells. To this end, we expressed the KCNQ1/KCNE1 channel in human embryonic kidney 293T cells and evaluated the effect of SMS1 manipulations on the channel using whole cell recording. Application of tricyclodecan-9-yl-xanthogenate, a nonspecific inhibitor of SMSs, significantly reduced current density and altered channel voltage dependence. Knockdown of SMS1 by a short hairpin RNA, however, reduced current density alone. Consistent with this, overexpression of SMS1 increased the current density without changing channel properties. Furthermore, application of protein kinase D inhibitors also suppressed current density without changing channel properties; this effect was nonadditive with that of SMS1 short hairpin RNA. These results suggest that SMS1 positively regulates KCNQ1/KCNE1 channel density in a protein kinase D-dependent manner.

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

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

Inhibition of Receptor Dimerization as a Novel Negative Feedback Mechanism of EGFR Signaling

Dimerization of the epidermal growth factor receptor (EGFR) is crucial for initiating signal transduction. We employed raster image correlation spectroscopy to continuously monitor the EGFR monomer-dimer equilibrium in living cells. EGFR dimer formation upon addition of EGF showed oscillatory behavior with a periodicity of about 2.5 min, suggesting the presence of a negative feedback loop to monomerize the receptor. We demonstrated that monomerization of EGFR relies on phospholipase Cγ, protein kinase C, and protein kinase D (PKD), while being independent of Ca2+ signaling and endocytosis. Phosphorylation of the juxtamembrane threonine residues of EGFR (T654/T669) by PKD was identified as the factor that shifts the monomer-dimer equilibrium of ligand bound EGFR towards the monomeric state. The dimerization state of the receptor correlated with the activity of an extracellular signal-regulated kinase, downstream of the EGFR. Based on these observations, we propose a novel, negative feedback mechanism that regulates EGFR signaling via receptor monomerization.

Phrenic long-term facilitation requires PKCθ activity within phrenic motor neurons

Acute intermittent hypoxia (AIH) induces a form of spinal motor plasticity known as phrenic long-term facilitation (pLTF); pLTF is a prolonged increase in phrenic motor output after AIH has ended. In anesthetized rats, we demonstrate that pLTF requires activity of the novel PKC isoform, PKCθ, and that the relevant PKCθ is within phrenic motor neurons. Whereas spinal PKCθ inhibitors block pLTF, inhibitors targeting other PKC isoforms do not. PKCθ is highly expressed in phrenic motor neurons, and PKCθ knockdown with intrapleural siRNAs abolishes pLTF. Intrapleural siRNAs targeting PKCζ, an atypical PKC isoform expressed in phrenic motor neurons that underlies a distinct form of phrenic motor plasticity, does not affect pLTF. Thus, PKCθ plays a critical role in spinal AIH-induced respiratory motor plasticity, and the relevant PKCθ is localized within phrenic motor neurons. Intrapleural siRNA delivery has considerable potential as a therapeutic tool to selectively manipulate plasticity in vital respiratory motor neurons.

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.