PKD1 mediates negative feedback of PI3K/Akt activation in response to G protein-coupled receptors

Protein Kinase D1 Correlates with Less Lymph Node Metastasis Risk, Enhanced 5-FU Sensitivity, and Better Prognosis in Colorectal Cancer

Protein kinase D1 (PKD1) controls tumor growth and invasion of gastrointestinal tract-related cancers, but its prognostic role in colorectal cancer (CRC) is not clear yet. Therefore, this research intended to assess the potential of PKD1 as a marker for CRC patients' management, also to evaluate its effect on 5-fluorouracil (5-FU) chemosensitivity in CRC cell lines. PKD1 protein and mRNA expressions were measured by immunohistochemistry and reverse transcription-quantitative polymerase chain reaction assays in 214 CRC patients, respectively. The PKD1 overexpression plasmids and negative control (NC) plasmids were transfected into the HCT-116 and LoVo cell lines followed by 0-16 μM 5-FU treatment. PKD1 protein (P < 0.001) and mRNA expressions (P < 0.001) were both descended in tumor tissues compared to tumor-adjacent tissues. Meanwhile, tumor PKD1 protein and mRNA expressions were both negatively related to lymph node metastasis, N stage, and tumor-node-metastasis (TNM) stage (all P < 0.05). Prognostically, high expressions of PKD1 protein and mRNA were linked with prolonged disease-free survival (DFS) and overall survival (OS) (all P < 0.05). After adjustment by multivariate Cox analyses, PKD1 mRNA high expression independently forecasted longer DFS [hazard ratio (HR) = 0.199, P = 0.002] and OS (HR = 0.212, P = 0.022). In vitro experiments revealed that PKD1 overexpression decreased the half maximal inhibitory concentration value of 5-FU in the HCT-116 (P = 0.016) and LoVo (P = 0.007) cell lines. PKD1 expression links with less lymph node metastasis risk and satisfied prognosis in CRC patients, which promotes CRC cell chemosensitivity to 5-FU chemosensitivity as well.

Protein kinase D1 overexpression potentiates epidermal growth factor signaling pathway in MCF-7 cells

BACKGROUND

Protein kinase D1, PKD1, is a serine-threonine kinase implicated in cell proliferation, migration, invasion, and/or apoptosis and its activation by several growth factors sets this enzyme as a key regulator of tumorigenesis and tumor progression. Despite many studies, its role in the regulation of intracellular signaling pathways remains widely disparate and needs to be clarified.

METHODS AND RESULTS

By using human breast cancer cells MCF-7, overexpressing or not PKD1, we demonstrated that PKD1 expression level modulated the tumor growth-promoting epidermal growth factor (EGF) signaling pathway. We also showed that EGF acutely stimulated PKD1 phosphorylation with similar time courses both in control and PKD1-overexpressing cells. However, PKD1 overexpression specifically and markedly increased EGF-induced phosphorylation of Akt (onto T308 and S473 residues) and extracellular-regulated protein kinase (ERK1/2). Finally, pharmacological inhibition of PKD1 activity or lowering its expression level using specific siRNAs drastically reduced EGF-stimulated Akt and ERK phosphorylation in PKD1overexpressing cells, but not in control cells.

CONCLUSIONS

Overall, these results identified the level of PKD1 expression as a key determinant in the regulation of the EGF signaling pathway highlighting its crucial role in a tumorigenic setting.

Induction of Apoptosis via Inactivating PI3K/AKT Pathway in Colorectal Cancer Cells Using Aged Chinese Hakka Stir-Fried Green Tea Extract

Food extract supplements, with high functional activity and low side effects, play a recognized role in the adjunctive therapy of human colorectal cancer. The present study reported a new functional beverage, which is a type of Chinese Hakka stir-fried green tea (HSGT) aged for several years. The extracts of the lyophilized powder of five HSGT samples with different aging periods were analyzed with high-performance liquid chromatography. The major components of the extract were found to include polyphenols, catechins, amino acids, catechins, gallic acid and caffeine. The tea extracts were also investigated for their therapeutic activity against human colorectal cancer cells, HT-29, an epithelial cell isolated from the primary tumor. The effect of different aging time of the tea on the anticancer potency was compared. Our results showed that, at the cellular level, all the extracts of the aged teas significantly inhibited the proliferation of HT-29 in a concentration-dependent manner. In particular, two samples prepared in 2015 (15Y, aged for 6 years) and 2019 (19Y, aged for 2 years) exhibited the highest inhibition rate for 48 h treatment (cell viability was 50% at 0.2 mg/mL). Further, all the aged tea extracts examined were able to enhance the apoptosis of HT-29 cells (apoptosis rate > 25%) and block the transition of G1/S phase (cell-cycle distribution (CSD) from <20% to >30%) population to G2/M phase (CSD from nearly 30% to nearly 10%) at 0.2 mg/mL for 24 h or 48 h. Western blotting results also showed that the tea extracts inhibited cyclin-dependent kinases 2/4 (CDK2, CDK4) and CylinB1 protein expression, as well as increased poly ADP-ribose polymerase (PRAP) expression and Bcl2-associated X (Bax)/B-cell lymphoma-2 (Bcl2) ratio. In addition, an upstream signal of one of the above proteins, phosphatidylinositol 3-kinase (PI3K)/protein kinase B (AKT) signalling, was found to be involved in the regulation, as evidenced by the inhibition of phosphorylated PI3K and AKT by the extracts of the aged tea. Therefore, our study reveals that traditional Chinese aged tea (HSGT) may inhibit colon cancer cell proliferation, cell-cycle progression and promoted apoptosis of colon cancer cells by inactivating PI3K/AKT signalling.

Gα15 in early onset of pancreatic ductal adenocarcinoma

The GNA15 gene is ectopically expressed in human pancreatic ductal adenocarcinoma cancer cells. The encoded Gα15 protein can promiscuously redirect GPCR signaling toward pathways with oncogenic potential. We sought to describe the distribution of GNA15 in adenocarcinoma from human pancreatic specimens and to analyze the mechanism driving abnormal expression and the consequences on signaling and clinical follow-up. We detected GNA15 expression in pre-neoplastic pancreatic lesions and throughout progression. The analysis of biological data sets, primary and xenografted human tumor samples, and clinical follow-up shows that elevated expression is associated with poor prognosis for GNA15, but not any other GNA gene. Demethylation of the 5′ GNA15 promoter region was associated with ectopic expression of Gα15 in pancreatic neoplastic cells, but not in adjacent dysplastic or non-transformed tissue. Down-modulation of Gα15 by shRNA or CRISPR/Cas9 affected oncogenic signaling, and reduced adenocarcimoma cell motility and invasiveness. We conclude that de novo expression of wild-type GNA15 characterizes transformed pancreatic cells. The methylation pattern of GNA15 changes in preneoplastic lesions coincident with the release a transcriptional blockade that allows ectopic expression to persist throughout PDAC progression. Elevated GNA15 mRNA correlates with poor prognosis. In addition, ectopic Gα15 signaling provides an unprecedented mechanism in the early steps of pancreas carcinogenesis distinct from classical G protein oncogenic mutations described previously in GNAS and GNAQ/GNA11.

Interaction between Mas1 and AT1RA contributes to enhancement of skeletal muscle angiogenesis by angiotensin-(1-7) in Dahl salt-sensitive rats

The heptapeptide angiotensin-(1-7) (Ang-(1-7)) is protective in the cardiovascular system through its induction of vasodilator production and angiogenesis. Despite acting antagonistically to the effects of elevated, pathophysiological levels of angiotensin II (AngII), recent evidence has identified convergent and beneficial effects of low levels of both Ang-(1-7) and AngII. Previous work identified the AngII receptor type I (AT1R) as a component of the protein complex formed when Ang-(1-7) binds its receptor, Mas1. Importantly, pharmacological blockade of AT1R did not alter the effects of Ang-(1-7). Here, we use a novel mutation of AT1RA in the Dahl salt-sensitive (SS) rat to test the hypothesis that interaction between Mas1 and AT1R contributes to proangiogenic Ang-(1-7) signaling. In a model of hind limb angiogenesis induced by electrical stimulation, we find that the restoration of skeletal muscle angiogenesis in SS rats by Ang-(1-7) infusion is impaired in AT1RA knockout rats. Enhancement of endothelial cell (EC) tube formation capacity by Ang-(1-7) is similarly blunted in AT1RA mutant ECs. Transcriptional changes elicited by Ang-(1-7) in SS rat ECs are altered in AT1RA mutant ECs, and tandem mass spectrometry-based proteomics demonstrate that the protein complex formed upon binding of Ang-(1-7) to Mas1 is altered in AT1RA mutant ECs. Together, these data support the hypothesis that interaction between AT1R and Mas1 contributes to proangiogenic Ang-(1-7) signaling.

Regulation of Osteoclast Differentiation at Multiple Stages by Protein Kinase D Family Kinases

Balanced osteoclast and osteoblast activity is necessary for skeletal health, whereas unbalanced osteoclast activity causes bone loss in many skeletal conditions. A better understanding of pathways that regulate osteoclast differentiation and activity is necessary for the development of new therapies to better manage bone resorption. The roles of Protein Kinase D (PKD) family of serine/threonine kinases in osteoclasts have not been well characterized. In this study we use immunofluorescence analysis to reveal that PKD2 and PKD3, the isoforms expressed in osteoclasts, are found in the nucleus and cytoplasm, the mitotic spindle and midbody, and in association with the actin belt. We show that PKD inhibitors CRT0066101 and CID755673 inhibit several distinct aspects of osteoclast formation. Treating bone marrow macrophages with lower doses of the PKD inhibitors had little effect on M-CSF + RANKL-dependent induction into committed osteoclast precursors, but inhibited their motility and subsequent differentiation into multinucleated mature osteoclasts, whereas higher doses of the PKD inhibitors induced apoptosis of the preosteoclasts. Treating post-fusion multinucleated osteoclasts with the inhibitors disrupted the osteoclast actin belts and impaired their resorptive activity. In conclusion, these data implicate PKD kinases as positive regulators of osteoclasts, which are essential for multiple distinct processes throughout their formation and function.

Regulation of platelet-activating factor-mediated interleukin-6 promoter activation by the 48 kDa but not the 45 kDa isoform of protein tyrosine phosphatase non-receptor type 2

Background

An underlying state of inflammation is thought to be an important cause of cardiovascular disease. Among cells involved in the early steps of atherosclerosis, monocyte-derived dendritic cells (Mo-DCs) respond to inflammatory stimuli, including platelet-activating factor (PAF), by the induction of various cytokines, such as interleukin 6 (IL-6). PAF is a potent phospholipid mediator involved in both the onset and progression of atherosclerosis. It mediates its effects by binding to its cognate G-protein coupled receptor, PAFR. Activation of PAFR-induced signaling pathways is tightly coordinated to ensure specific cell responses.

Results

Here, we report that PAF stimulated the phosphatase activity of both the 45 and 48 kDa isoforms of the protein tyrosine phosphatase non-receptor type 2 (PTPN2). However, we found that only the 48 kDa PTPN2 isoform has a role in PAFR-induced signal transduction, leading to activation of the IL-6 promoter. In luciferase reporter assays, expression of the 48 kDa, but not the 45 kDa, PTPN2 isoform increased human IL-6 (hIL-6) promoter activity by 40% after PAF stimulation of HEK-293 cells, stably transfected with PAFR (HEK-PAFR). Our results suggest that the differential localization of the PTPN2 isoforms and the differences in PAF-induced phosphatase activation may contribute to the divergent modulation of PAF-induced IL-6 promoter activation. The involvement of PTPN2 in PAF-induced IL-6 expression was confirmed in immature Mo-DCs (iMo-DCs), using siRNAs targeting the two isoforms of PTPN2, where siRNAs against the 48 kDa PTPN2 significantly inhibited PAF-stimulated IL-6 mRNA expression. Pharmacological inhibition of several signaling pathways suggested a role for PTPN2 in early signaling events. Results obtained by Western blot confirmed that PTPN2 increased the activation of the PI3K/Akt pathway via the modulation of protein kinase D (PKD) activity. WT PKD expression counteracted the effect of PTPN2 on PAF-induced IL-6 promoter transactivation and phosphorylation of Akt. Using siRNAs targeting the individual isoforms of PTPN2, we confirmed that these pathways were also active in iMo-DCs.

Conclusion

Taken together, our data suggest that PTPN2, in an isoform-specific manner, could be involved in the positive regulation of PI3K/Akt activation, via the modulation of PKD activity, allowing for the maximal induction of PAF-stimulated IL-6 mRNA expression.

Protein kinase D1 inhibition interferes with mitosis progression

Protein kinase D1 (PKD1) plays a vital role in signal transduction, cell proliferation, membrane trafficking, and cancer; however, the majority of the studies up to date had centered primarily on PKD1 functions in interphase, very little is known about its role during cell division. We previously demonstrated that during mitosis PKD1 is activated and associated with centrosomes, spindles, and midbodies. However, these observations did not address whether PKD1 was associated with mitosis regulation. Accordingly, we used rapidly acting PKD-specific inhibitors to examine the contribution of PKD1 the sequence of events in mitosis. We found that although PKD1 overexpression did not affect mitosis progression, suppression of its catalytic activity by two structurally unrelated inhibitors (kb NB 142-70 and CRT 0066101) induced a significant delay in metaphase to anaphase transition time. PKD1 inhibition during mitosis also produced the appearance of abnormal spindles, defects in chromosome alignment, and segregation as well as apoptosis. Thus, these observations indicate that PKD1 activity is associated with mitosis regulation.

Measuring GPCR-Induced Activation of Protein Tyrosine Phosphatases (PTP) Using In-Gel and Colorimetric PTP Assays

Given the increasing amount of data showing the importance of protein tyrosine phosphatases (PTPs) in G protein-coupled receptor (GPCR) signaling pathways, the modulation of this enzyme family by that type of receptor can become an important experimental question. Here, we describe two different methods, an in-gel and a colorimetric PTP assay, to evaluate the modulation of PTP activity after stimulation with GPCR agonists.

HLA Class II-Triggered Signaling Cascades Cause Endothelial Cell Proliferation and Migration: Relevance to Antibody-Mediated Transplant Rejection

Transplant recipients developing donor-specific HLA class II (HLA-II) Abs are at higher risk for Ab-mediated rejection (AMR) and transplant vasculopathy. To understand how HLA-II Abs cause AMR and transplant vasculopathy, we determined the signaling events triggered in vascular endothelial cells (EC) following Ab ligation of HLA-II molecules. HLA-II expression in EC was induced by adenoviral vector expression of CIITA or by pretreatment with TNF-α/IFN-γ. Ab ligation of class II stimulated EC proliferation and migration. Class II Ab also induced activation of key signaling nodes Src, focal adhesion kinase, PI3K, and ERK that regulated downstream targets of the mammalian target of rapamycin (mTOR) pathway Akt, p70 ribosomal S6 kinase, and S6 ribosomal protein. Pharmacological inhibitors and small interfering RNA showed the protein kinases Src, focal adhesion kinase, PI3K/Akt, and MEK/ERK regulate class II Ab-stimulated cell proliferation and migration. Treatment with rapalogs for 2 h did not affect HLA-II Ab-induced phosphorylation of ERK; instead, mTOR complex (mTORC)1 targets were dependent on activation of ERK. Importantly, suppression of mTORC2 for 24 h with rapamycin or everolimus or treatment with mTOR active-site inhibitors enhanced HLA-II Ab-stimulated phosphorylation of ERK. Furthermore, knockdown of Rictor with small interfering RNA caused overactivation of ERK while abolishing phosphorylation of Akt Ser⁴⁷³ induced by class II Ab. These data are different from HLA class I Ab-induced activation of ERK, which is mTORC2-dependent. Our results identify a complex signaling network triggered by HLA-II Ab in EC and indicate that combined ERK and mTORC2 inhibitors may be required to achieve optimal efficacy in controlling HLA-II Ab-mediated AMR.

Protein kinase D1 (PKD1) phosphorylation on Ser203 by type I p21-activated kinase (PAK) regulates PKD1 localization

Although PKC-mediated phosphorylation of protein kinase D1 (PKD1) has been extensively characterized, little is known about PKD1 regulation by other upstream kinases. Here we report that stimulation of epithelial or fibroblastic cells with G protein-coupled receptor agonists, including angiotensin II or bombesin, induced rapid and persistent PKD1 phosphorylation at Ser²⁰³, a highly conserved residue located within the PKD1 N-terminal domain. Exposure to PKD or PKC family inhibitors did not prevent PKD1 phosphorylation at Ser²⁰³, indicating that it is not mediated by autophosphorylation. In contrast, several lines of evidence indicated that the phosphorylation of PKD1 at Ser²⁰³ is mediated by kinases of the class I PAK subfamily, specifically 1) exposing cells to four structurally unrelated PAK inhibitors (PF-3758309, FRAX486, FRAX597, and IPA-3) that act via different mechanisms abrogated PKD1 phosphorylation at Ser²⁰³, 2) siRNA-mediated knockdown of PAK1 and PAK2 in IEC-18 and Swiss 3T3 cells blunted PKD1 phosphorylation at Ser²⁰³, 3) phosphorylation of Ser²⁰³ markedly increased in vitro when recombinant PKD1 was incubated with either PAK1 or PAK2 in the presence of ATP. PAK inhibitors did not interfere with G protein-coupled receptor activation-induced rapid translocation of PKD1 to the plasma membrane but strikingly prevented the dissociation of PKD1 from the plasma membrane and blunted the phosphorylation of nuclear targets, including class IIa histone deacetylases. We conclude that PAK-mediated phosphorylation of PKD1 at Ser²⁰³ triggers its membrane dissociation and subsequent entry into the nucleus, thereby regulating the phosphorylation of PKD1 nuclear targets, including class IIa histone deacetylases.

Role of phosphatidylinositol-4,5-bisphosphate 3-kinase signaling in vesicular trafficking

Phosphatidylinositol-4,5-bisphosphate 3-kinases (PI3Ks) are regulatory enzymes involved in the generation of lipid species that modulate cellular signaling pathways through downstream effectors to influence a variety of cellular functions. Years of intensive study of PI3Ks have produced a significant body of literature in many areas, including that PI3K can mediate intracellular vesicular trafficking and through these actions contribute to a number of important physiological functions. This review focuses on the crucial roles that PI3K and AKT, a major downstream partner of PI3K, play in the regulation of vesicle trafficking during various forms of vesicular endocytosis and exocytosis.

G-protein-coupled receptor kinase 2 terminates G-protein-coupled receptor function in steroid hormone 20-hydroxyecdysone signaling

G-protein-coupled receptors (GPCRs) transmit extracellular signals across the cell membrane. GPCR kinases (GRKs) desensitize GPCR signals in the cell membrane. However, the role and mechanism of GRKs in the desensitization of steroid hormone signaling are unclear. In this study, we propose that GRK2 is phosphorylated by protein kinase C (PKC) in response to induction by the steroid hormone 20-hydroxyecdysone (20E), which determines its translocation to the cell membrane of the lepidopteran Helicoverpa armigera. GRK2 protein expression is increased during the metamorphic stage because of induction by 20E. Knockdown of GRK2 in larvae causes accelerated pupation, an increase in 20E-response gene expression, and advanced apoptosis and metamorphosis. 20E induces translocation of GRK2 from the cytoplasm to the cell membrane via steroid hormone ecdysone-responsive GPCR (ErGPCR-2). GRK2 is phosphorylated by PKC on serine 680 after induction by 20E, which leads to the translocation of GRK2 to the cell membrane. GRK2 interacts with ErGPCR-2. These data indicate that GRK2 terminates the ErGPCR-2 function in 20E signaling in the cell membrane by a negative feedback mechanism.

Biphasic Regulation of Yes-associated Protein (YAP) Cellular Localization, Phosphorylation, and Activity by G Protein-coupled Receptor Agonists in Intestinal Epithelial Cells: A NOVEL ROLE FOR PROTEIN KINASE D (PKD)

We examined the regulation of Yes-associated protein (YAP) localization, phosphorylation, and transcriptional activity in intestinal epithelial cells. Our results show that stimulation of intestinal epithelial IEC-18 cells with the G protein-coupled receptor (GPCR) agonist angiotensin II, a potent mitogen for these cells, induced rapid translocation of YAP from the nucleus to the cytoplasm (within 15 min) and a concomitant increase in YAP phosphorylation at Ser(127) and Ser(397) Angiotensin II elicited YAP phosphorylation and cytoplasmic accumulation in a dose-dependent manner (ED50 = 0.3 nm). Similar YAP responses were provoked by stimulation with vasopressin or serum. Treatment of the cells with the protein kinase D (PKD) family inhibitors CRT0066101 and kb NB 142-70 prevented the increase in YAP phosphorylation on Ser(127) and Ser(397) via Lats2, YAP cytoplasmic accumulation, and increase in the mRNA levels of YAP/TEAD-regulated genes (Ctgf and Areg). Furthermore, siRNA-mediated knockdown of PKD1, PKD2, and PKD3 markedly attenuated YAP nuclear-cytoplasmic shuttling, phosphorylation at Ser(127), and induction of Ctgf and Areg expression in response to GPCR activation. These results identify a novel role for the PKD family in the control of biphasic localization, phosphorylation, and transcriptional activity of YAP in intestinal epithelial cells. In turn, YAP and TAZ are necessary for the stimulation of the proliferative response of intestinal epithelial cells to GPCR agonists that act via PKD. The discovery of interaction between YAP and PKD pathways identifies a novel cross-talk in signal transduction and demonstrates, for the first time, that the PKDs feed into the YAP pathway.

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.

CARMA3 regulates the invasion, migration, and apoptosis of non-small cell lung cancer cells by activating NF-кB and suppressing the P38 MAPK signaling pathway

In our previous study, CARMA3 overexpression in lung cancer cells promoted cell proliferation and invasion; however, the mechanism underlying the role of CARMA3 in cancer cell invasion remained unclear. In the present study, knockdown of CARMA3 in A549 and H1299 cells suppressed cell invasion and migration, and downregulated matrix metalloprotease 9 expression at the protein and mRNA levels, as shown by Western blotting and real-time PCR. CARMA3 knockdown increased cell apoptosis, as shown by flow cytometry, increased the mRNA and protein expression levels of Bax and Caspase3, and downregulated Bcl-2 in A549 and H1299 cells. Phosphorylated P38 levels increased and NF-кB activation decreased following knockdown of CARMA3. SB203580, a P38 MAPK inhibitor, activated NF-кB, increased cell migration, and inhibited cell apoptosis after knockdown of CARMA3 compared to knockdown of CARMA3 without SB203580. These findings indicate that CARMA3 may suppress the activation of the P38 MAPK signaling pathway to regulate invasion, migration and apoptosis of lung cancer cells by activating NF-кB (P65) in the nucleus.

Impaired PI3K/Akt Signaling as a Potential Cause of Failure to Precondition Rat Hearts Under Conditions of Simulated Hyperglycemia

The aim of the study was to evaluate the impact of simulated acute hyperglycemia (HG) on PI3K/Akt signaling in preconditioned and non-preconditioned isolated rat hearts perfused with Krebs-Henseleit solution containing normal (11 mmol/l) or elevated (22 mmol/l) glucose subjected to ischemia-reperfusion. Ischemic preconditioning (IP) was induced by two 5-min cycles of coronary occlusion followed by 5-min reperfusion. Protein levels of Akt, phosphorylated (activated) Akt (P-Akt), as well as contents of BAX protein were assayed (Western blotting) in cytosolic fraction of myocardial tissue samples taken prior to and after 30-min global ischemia and 40-min reperfusion. In “normoglycemic” conditions (NG), IP significantly increased P-Akt at the end of long-term ischemia, while reperfusion led to its decrease together with the decline of BAX levels as compared to non-preconditioned hearts. On the contrary, under HG conditions, P-Akt tended to decline in IP-hearts after long-term ischemia, and it was significantly higher after reperfusion than in non-preconditioned controls. No significant influence of IP on BAX levels at the end of I/R was observed under HG conditions. It seems that high glucose may influence IP-induced activation of Akt and its downstream targets, as well as maintain persistent Akt activity that may be detrimental for the heart under above conditions.

Mitotic Golgi translocation of ERK1c is mediated by a PI4KIIIβ-14-3-3γ shuttling complex

Golgi fragmentation is a highly regulated process that allows division of the Golgi complex between the two daughter cells. The mitotic reorganization of the Golgi is accompanied by a temporary block in Golgi functioning, as protein transport in and out of the Golgi stops. Our group has previously demonstrated the involvement of the alternatively spliced variants ERK1c and MEK1b (ERK1 is also known as MAPK3, and MEK1 as MAP2K1) in mitotic Golgi fragmentation. We had also found that ERK1c translocates to the Golgi at the G2 to M phase transition, but the molecular mechanism underlying this recruitment remains unknown. In this study, we narrowed the translocation timing to prophase and prometaphase, and elucidated its molecular mechanism. We found that CDK1 phosphorylates Ser343 of ERK1c, thereby allowing the binding of phosphorylated ERK1c to a complex that consists of PI4KIIIβ (also known as PI4KB) and the 14-3-3γ dimer (encoded by YWHAB). The stability of the complex is regulated by protein kinase D (PKD)-mediated phosphorylation of PI4KIIIβ. The complex assembly induces the Golgi shuttling of ERK1c, where it is activated by MEK1b, and induces Golgi fragmentation. Our work shows that protein shuttling to the Golgi is not completely abolished at the G2 to M phase transition, thus integrating several independent Golgi-regulating processes into one coherent pathway.

Protein kinase D promotes plasticity-induced F-actin stabilization in dendritic spines and regulates memory formation

PKD regulates the stabilization of the F-actin network within dendritic spines upon chemically induced plasticity changes and is needed for proper hippocampal LTP and spatial memory formation.

Actin turnover in dendritic spines influences spine development, morphology, and plasticity, with functional consequences on learning and memory formation. In nonneuronal cells, protein kinase D (PKD) has an important role in stabilizing F-actin via multiple molecular pathways. Using in vitro models of neuronal plasticity, such as glycine-induced chemical long-term potentiation (LTP), known to evoke synaptic plasticity, or long-term depolarization block by KCl, leading to homeostatic morphological changes, we show that actin stabilization needed for the enlargement of dendritic spines is dependent on PKD activity. Consequently, impaired PKD functions attenuate activity-dependent changes in hippocampal dendritic spines, including LTP formation, cause morphological alterations in vivo, and have deleterious consequences on spatial memory formation. We thus provide compelling evidence that PKD controls synaptic plasticity and learning by regulating actin stability in dendritic spines.

Targeting vascular endothelial growth factor receptor 2 and protein kinase D1 related pathways by a multiple kinase inhibitor in angiogenesis and inflammation related processes in vitro

Emerging evidence suggests that the vascular endothelial growth factor receptor 2 (VEGFR2) and protein kinase D1 (PKD1) signaling axis plays a critical role in normal and pathological angiogenesis and inflammation related processes. Despite all efforts, the currently available therapeutic interventions are limited. Prior studies have also proved that a multiple target inhibitor can be more efficient compared to a single target one. Therefore, development of novel inflammatory pathway-specific inhibitors would be of great value. To test this possibility, we screened our molecular library using recombinant kinase assays and identified the previously described compound VCC251801 with strong inhibitory effect on both VEGFR2 and PKD1. We further analyzed the effect of VCC251801 in the endothelium-derived EA.hy926 cell line and in different inflammatory cell types. In EA.hy926 cells, VCC251801 potently inhibited the intracellular activation and signaling of VEGFR2 and PKD1 which inhibition eventually resulted in diminished cell proliferation. In this model, our compound was also an efficient inhibitor of in vitro angiogenesis by interfering with endothelial cell migration and tube formation processes. Our results from functional assays in inflammatory cellular models such as neutrophils and mast cells suggested an anti-inflammatory effect of VCC251801. The neutrophil study showed that VCC251801 specifically blocked the immobilized immune-complex and the adhesion dependent TNF-α -fibrinogen stimulated neutrophil activation. Furthermore, similar results were found in mast cell degranulation assay where VCC251801 caused significant reduction of mast cell response. In summary, we described a novel function of a multiple kinase inhibitor which strongly inhibits the VEGFR2-PKD1 signaling and might be a novel inhibitor of pathological inflammatory pathways.

Dual PI3K/mTOR Inhibitors Induce Rapid Overactivation of the MEK/ERK Pathway in Human Pancreatic Cancer Cells through Suppression of mTORC2

The PI3K/AKT/mTOR pathway, which is aberrantly stimulated in many cancer cells, has emerged as a target for therapy. However, mTORC1/S6K also mediates negative feedback loops that attenuate upstream signaling. Suppression of these feedback loops opposes the growth-suppressive effects of mTOR inhibitors and leads to drug resistance. Here, we demonstrate that treatment of PANC-1 or MiaPaCa-2 pancreatic ductal adenocarcinoma (PDAC) cells with the dual PI3K/mTOR kinase inhibitor (PI3K/TOR-KI) BEZ235 blocked mTORC1/S6K activation (scored by S6 phosphorylation at Ser(240/244)), mTORC1/4E-BP1 (assayed by 4E-BP1 phosphorylation at Thr(37/46)), and mTORC2-mediated AKT phosphorylation at Ser(473), in a concentration-dependent manner. Strikingly, BEZ235 markedly enhanced the MEK/ERK pathway in a dose-dependent manner. Maximal ERK overactivation coincided with complete inhibition of phosphorylation of AKT and 4E-BP1. ERK overactivation was induced by other PI3K/TOR-KIs, including PKI-587 and GDC-0980. The MEK inhibitors U126 or PD0325901 prevented ERK overactivation induced by PI3K/TOR-KIs. The combination of BEZ235 and PD0325901 caused a more pronounced inhibition of cell growth than that produced by each inhibitor individually. Mechanistic studies assessing PI3K activity in single PDAC cells indicate that PI3K/TOR-KIs act through a PI3K-independent pathway. Doses of PI3K/TOR-KIs that enhanced MEK/ERK activation coincided with those that inhibited mTORC2-mediated AKT phosphorylation on Ser(473), suggesting a role of mTORC2. Knockdown of RICTOR via transfection of siRNA markedly attenuated the enhancing effect of BEZ235 on ERK phosphorylation. We propose that dual PI3K/mTOR inhibitors suppress a novel negative feedback loop mediated by mTORC2, thereby leading to enhanced MEK/ERK pathway activity in pancreatic cancer cells.

PKD1 is downregulated in non-small cell lung cancer and mediates the feedback inhibition of mTORC1-S6K1 axis in response to phorbol ester

Protein kinase D1 (PKD1) is increasingly implicated in multiple biological and molecular events that regulate the proliferation or invasiveness in several cancers. However, little is known about the expression and functions of PKD1 in non-small cell lung cancer (NSCLC). In the present study, 34 pairs of human NSCLC and matched normal bronchiolar epitheliums were enrolled and evaluated for PKD1 expression by quantitative real-time PCR. We showed that PKD1 was downregulated in 26 of 34 cancer tissues in comparison with matched normal epitheliums. Moreover, patients with venous invasion or lymph node metastasis showed significant lower expression of PKD1. Exposure of NSCLC A549 and H520 cells to the PKD family inhibitor kb NB 142-70(Kb), at concentrations that inhibited PKD1 activation, strikingly potentiated S6K1 phosphorylation at Thr(389) and S6 phosphorylation at Ser(235/236) in response to phorbol ester (PMA). Knockdown of PKD1 with siRNAs strikingly enhanced S6K1 phosphorylation whereas constitutively active PKD1 resulted in the S6K1 activity inhibition. Furthermore, the PI3K inhibitors LY294002, BKM120 and MEK inhibitors U0126, PD0325901 blocked the enhanced S6K1 activity induced by Kb. Collectively, our results identify decreased expression of the PKD1 as a marker for NSCLC and the loss of PKD1 expression increases the malignant potential of NSCLC cells. This may be due to the function of PKD1 as a negative regulator of mTORC1-S6K1. Our results suggest that re-expression or activation of PKD1 might serve as a potential therapeutic target for NSCLC treatment.

Protein kinase D1 mediates class IIa histone deacetylase phosphorylation and nuclear extrusion in intestinal epithelial cells: role in mitogenic signaling

We examined whether class IIa histone deacetylases (HDACs) play a role in mitogenic signaling mediated by protein kinase D1 (PKD1) in IEC-18 intestinal epithelial cells. Our results show that class IIa HDAC4, HDAC5, and HDAC7 are prominently expressed in these cells. Stimulation with ANG II, a potent mitogen for IEC-18 cells, induced a striking increase in phosphorylation of HDAC4 at Ser(246) and Ser(632), HDAC5 at Ser(259) and Ser(498), and HDAC7 at Ser(155). Treatment with the PKD family inhibitors kb NB 142-70 and CRT0066101 or small interfering RNA-mediated knockdown of PKD1 prevented ANG II-induced phosphorylation of HDAC4, HDAC5, and HDAC7. A variety of PKD1 activators in IEC-18 cells, including vasopressin, lysophosphatidic acid, and phorbol esters, also induced HDAC4, HDAC5, and HDAC7 phosphorylation. Using endogenously and ectopically expressed HDAC5, we show that PKD1-mediated phosphorylation of HDAC5 induces its nuclear extrusion into the cytoplasm. In contrast, HDAC5 with Ser(259) and Ser(498) mutated to Ala was localized to the nucleus in unstimulated and stimulated cells. Treatment of IEC-18 cells with specific inhibitors of class IIa HDACs, including MC1568 and TMP269, prevented cell cycle progression, DNA synthesis, and proliferation induced in response to G protein-coupled receptor/PKD1 activation. The PKD1-class IIa HDAC axis also functions in intestinal epithelial cells in vivo, since an increase in phosphorylation of HDAC4/5 and HDAC7 was demonstrated in lysates of crypt cells from PKD1 transgenic mice compared with matched nontransgenic littermates. Collectively, our results reveal a PKD1-class IIa HDAC axis in intestinal epithelial cells leading to mitogenic signaling.