PAK signalling during the development and progression of cancer

p21-Activated kinases (PAKs) are positioned at the nexus of several oncogenic signalling pathways. Overexpression or mutational activation of PAK isoforms frequently occurs in various human tumours, and recent data suggest that excessive PAK activity drives many of the cellular processes that are the hallmarks of cancer. In this Review, we discuss the mechanisms of PAK activation in cancer, the key substrates that mediate the developmental and oncogenic effects of this family of kinases, and how small-molecule inhibitors of these enzymes might be best developed and deployed for the treatment of cancer.

Cellular entry of ebola virus involves uptake by a macropinocytosis-like mechanism and subsequent trafficking through early and late endosomes

Zaire ebolavirus (ZEBOV), a highly pathogenic zoonotic virus, poses serious public health, ecological and potential bioterrorism threats. Currently no specific therapy or vaccine is available. Virus entry is an attractive target for therapeutic intervention. However, current knowledge of the ZEBOV entry mechanism is limited. While it is known that ZEBOV enters cells through endocytosis, which of the cellular endocytic mechanisms used remains unclear. Previous studies have produced differing outcomes, indicating potential involvement of multiple routes but many of these studies were performed using noninfectious surrogate systems such as pseudotyped retroviral particles, which may not accurately recapitulate the entry characteristics of the morphologically distinct wild type virus. Here we used replication-competent infectious ZEBOV as well as morphologically similar virus-like particles in specific infection and entry assays to demonstrate that in HEK293T and Vero cells internalization of ZEBOV is independent of clathrin, caveolae, and dynamin. Instead the uptake mechanism has features of macropinocytosis. The binding of virus to cells appears to directly stimulate fluid phase uptake as well as localized actin polymerization. Inhibition of key regulators of macropinocytosis including Pak1 and CtBP/BARS as well as treatment with the drug EIPA, which affects macropinosome formation, resulted in significant reduction in ZEBOV entry and infection. It is also shown that following internalization, the virus enters the endolysosomal pathway and is trafficked through early and late endosomes, but the exact site of membrane fusion and nucleocapsid penetration in the cytoplasm remains unclear. This study identifies the route for ZEBOV entry and identifies the key cellular factors required for the uptake of this filamentous virus. The findings greatly expand our understanding of the ZEBOV entry mechanism that can be applied to development of new therapeutics as well as provide potential insight into the trafficking and entry mechanism of other filoviruses.

Filoviruses, including Zaire ebolavirus (ZEBOV), are among the most pathogenic viruses known. Our understanding of how these viruses enter into host cells is very limited. A deeper understanding of this process would enable the design of better targeted antiviral therapies. This study defines in detail, key steps of ZEBOV cellular uptake and trafficking into cells using wild type virus as well as the host factors that are responsible for permitting virus entry into cells. Our data indicated that the primary mechanism of ZEBOV uptake is a macropinocytosis-like process that delivers the virus to early endosomes and subsequently to late endosomes. These findings aid in our understanding of how filoviruses infect cells and suggest that disruption of macropinocytosis may be useful in treatment of infection.

MicroRNA-7, a homeobox D10 target, inhibits p21-activated kinase 1 and regulates its functions

MicroRNAs are noncoding RNAs that inhibit the expression of their targets in a sequence-specific manner and play crucial roles during oncogenesis. Here we show that microRNA-7 (miR-7) inhibits p21-activated kinase 1 (Pak1) expression, a widely up-regulated signaling kinase in multiple human cancers, by targeting the 3'-untranslated region (UTR) of Pak1 mRNA. We noticed an inverse correlation between the levels of endogenous miR-7 and Pak1 expression in human cancer cells. We discovered that endogenous miR-7 expression is positively regulated by a homeodomain transcription factor, HoxD10, the loss of which leads to an increased invasiveness. HoxD10 directly interacts with the miR-7 chromatin. Accordingly, the levels of Pak1 protein are progressively up-regulated whereas those of miR-7 and its upstream activator HoxD10 are progressively down-regulated in a cellular model of breast cancer progression from low to highly invasive phenotypes. Furthermore, HoxD10 expression in highly invasive breast cancer cells resulted in an increased miR-7 expression but reduced Pak1 3'-UTR-luciferase activity and reduced Pak1 protein. Finally, we show that miR-7 introduction inhibits the motility, invasiveness, anchorage-independent growth, and tumorigenic potential of highly invasive breast cancer cells. Collectively, these findings establish for the first time that Pak1 is a target of miR-7 and that HoxD10 plays a regulatory role in modifying the expression of miR-7 and, consequently, the functions of the miR-7-Pak1 pathway in human cancer cells.

PAK signaling in oncogenesis

The p21-activated kinase (PAK) family of serine/threonine kinases is important in physiological processes including motility, survival, mitosis, transcription and translation. PAKs are evolutionally conserved and widely expressed in a variety of tissues and are often overexpressed in multiple cancer types. Depending on structural and functional similarities, the six members of PAK family are divided into two groups with three members in each group. Group I PAKs are activated by extracellular signals through GTPase-dependent and GTPase-independent mechanisms. In contrast, group II PAKs are constitutively active. Over the years, accumulating data from tissue culture models and human tumors has increased our understanding about the biology of PAK family members. In this review, we have summarized the complex regulation of PAK and its downstream diverse myriads of effectors, which in turn are responsible for the biological effects of PAK family of kinases in cancer cells.

Targeting super-enhancer-associated oncogenes in oesophageal squamous cell carcinoma

OBJECTIVES

Oesophageal squamous cell carcinoma (OSCC) is an aggressive malignancy and the major histological subtype of oesophageal cancer. Although recent large-scale genomic analysis has improved the description of the genetic abnormalities of OSCC, few targetable genomic lesions have been identified, and no molecular therapy is available. This study aims to identify druggable candidates in this tumour.

DESIGN

High-throughput small-molecule inhibitor screening was performed to identify potent anti-OSCC compounds. Whole-transcriptome sequencing (RNA-Seq) and chromatin immunoprecipitation sequencing (ChIP-Seq) were conducted to decipher the mechanisms of action of CDK7 inhibition in OSCC. A variety of in vitro and in vivo cellular assays were performed to determine the effects of candidate genes on OSCC malignant phenotypes.

RESULTS

The unbiased high-throughput small-molecule inhibitor screening led us to discover a highly potent anti-OSCC compound, THZ1, a specific CDK7 inhibitor. RNA-Seq revealed that low-dose THZ1 treatment caused selective inhibition of a number of oncogenic transcripts. Notably, further characterisation of the genomic features of these THZ1-sensitive transcripts demonstrated that they were frequently associated with super-enhancer (SE). Moreover, SE analysis alone uncovered many OSCC lineage-specific master regulators. Finally, integrative analysis of both THZ1-sensitive and SE-associated transcripts identified a number of novel OSCC oncogenes, including PAK4, RUNX1, DNAJB1, SREBF2 and YAP1, with PAK4 being a potential druggable kinase.

CONCLUSIONS

Our integrative approaches led to a catalogue of SE-associated master regulators and oncogenic transcripts, which may significantly promote both the understanding of OSCC biology and the development of more innovative therapies.

PAK signalling drives acquired drug resistance to MAPK inhibitors in BRAF-mutant melanomas

Targeted BRAF inhibition (BRAFi) and combined BRAF and MEK inhibition (BRAFi and MEKi) therapies have markedly improved the clinical outcomes of patients with metastatic melanoma. Unfortunately, the efficacy of these treatments is often countered by the acquisition of drug resistance. Here we investigated the molecular mechanisms that underlie acquired resistance to BRAFi and to the combined therapy. Consistent with previous studies, we show that resistance to BRAFi is mediated by ERK pathway reactivation. Resistance to the combined therapy, however, is mediated by mechanisms independent of reactivation of ERK in many resistant cell lines and clinical samples. p21-activated kinases (PAKs) become activated in cells with acquired drug resistance and have a pivotal role in mediating resistance. Our screening, using a reverse-phase protein array, revealed distinct mechanisms by which PAKs mediate resistance to BRAFi and the combined therapy. In BRAFi-resistant cells, PAKs phosphorylate CRAF and MEK to reactivate ERK. In cells that are resistant to the combined therapy, PAKs regulate JNK and β-catenin phosphorylation and mTOR pathway activation, and inhibit apoptosis, thereby bypassing ERK. Together, our results provide insights into the molecular mechanisms underlying acquired drug resistance to current targeted therapies, and may help to direct novel drug development efforts to overcome acquired drug resistance.

Genomic alterations link Rho family of GTPases to the highly invasive phenotype of pancreas cancer

Pancreas ductal adenocarcinoma (PDAC) is a highly lethal cancer that typically presents as advanced, unresectable disease. This invasive tendency, coupled with intrinsic resistance to standard therapies and genome instability, are major contributors to poor long-term survival. The genetic elements governing the invasive propensity of PDAC have not been well elucidated. Here, in the course of validating resident genes in highly recurrent and focal amplifications in PDAC, we have identified Rio Kinase 3 (RIOK3) as an amplified gene that alters cytoskeletal architecture as well as promotes pancreatic ductal cell migration and invasion. We determined that RIOK3 promotes its invasive activities through activation of the small G protein, Rac. This genomic and functional link to Rac signaling prompted a genome wide survey of other components of the Rho family network, revealing p21 Activated Kinase 4 (PAK4) as another amplified gene in PDAC tumors and cell lines. Like RIOK3, PAK4 promotes pancreas ductal cell motility and invasion. Together, the genomic and functional profiles establish the Rho family GTP-binding proteins as integral to the hallmark invasive nature of this lethal disease.

Dual and Specific Inhibition of NAMPT and PAK4 By KPT-9274 Decreases Kidney Cancer Growth

Kidney cancer (or renal cell carcinoma, RCC) is the sixth most common malignancy in the United States and one of the relatively few whose incidence is increasing. Because of the near universal resistance which occurs with the use of current treatment regimens, reprogrammed metabolic pathways are being investigated as potential targets for novel therapies of this disease. Borrowing from studies on other malignancies, we have identified the PAK4 and NAD biosynthetic pathways as being essential for RCC growth. We now show, using the dual PAK4/NAMPT inhibitor KPT-9274, that interference with these signaling pathways results in reduction of G2-M transit as well as induction of apoptosis and decrease in cell invasion and migration in several human RCC cell lines. Mechanistic studies demonstrate that inhibition of the PAK4 pathway by KPT-9274 attenuates nuclear β-catenin as well as the Wnt/β-catenin targets cyclin D1 and c-Myc. Furthermore, NAPRT1 downregulation, which we show occurs in all RCC cell lines tested, makes this tumor highly dependent on NAMPT for its NAD requirements, such that inhibition of NAMPT by KPT-9274 leads to decreased survival of these rapidly proliferating cells. When KPT-9274 was administered in vivo to a 786-O (VHL-mut) human RCC xenograft model, there was dose-dependent inhibition of tumor growth with no apparent toxicity; KPT-9274 demonstrated the expected on-target effects in this mouse model. KPT-9274 is being evaluated in a phase I human clinical trial in solid tumors and lymphomas, which will allow this data to be rapidly translated into the clinic for the treatment of RCC. Mol Cancer Ther; 15(9); 2119-29. ©2016 AACR.

Amplification of CCND1 and PAK1 as predictors of recurrence and tamoxifen resistance in postmenopausal breast cancer

The 11q13 region is amplified in approximately 15% of all breast tumors. Situated in this region are the cyclin D1 gene (CCND1) and the p-21-activated kinase 1 (PAK1) gene. Both genes encode proteins shown to activate the estrogen receptor (ER), leading to transcription of CCND1 and other ER-responsive genes. Here, we investigate the prognostic and treatment predictive role of CCND1 and PAK1 gene amplification in postmenopausal breast cancer patients randomized to tamoxifen treatment or no adjuvant treatment. Amplification of CCND1 and PAK1, assessed by real-time PCR, was observed in 12.5 and 9.3%, respectively. Amplification of PAK1 was seen in 37% of the CCND1-amplified tumors, indicating coamplification (P<0.001). In ER-positive patients, amplification of at least one of the genes indicated a reduced recurrence-free survival (P=0.025). When response to tamoxifen treatment was analysed, patients with PAK1 amplification showed decreased benefit from the drug (ER+; relative risk ratio (RR)=1.62; 95% confidence interval (CI), 0.47-5.55) compared to patients without amplification (ER+; RR=0.53; 95% CI, 0.32-0.88). This was not evident for CCND1 amplification. We show that PAK1 may be a predictor of tamoxifen resistance and furthermore, we do not discard PAK1 as a potential candidate oncogene in the 11q13 amplicon. In addition, we show that high pak1 protein levels may predict tamoxifen insensitivity.

Nucleo-cytoplasmic shuttling of PAK4 modulates β-catenin intracellular translocation and signaling

The canonical Wnt/β-catenin signaling pathway plays a central role in development and cancer. The p21-activated kinase 4 (PAK4) involves in a wide range of cellular processes, including cytoskeletal reorganization, cell proliferation, gene transcription and oncogenic transformation. However, the cross talk between the Wnt and PAK4 signaling pathways is poorly understood. Here, we show that PAK4 is a nucleo-cytoplasmic shuttling protein, containing three nuclear export signals (NESs) and two nuclear localization signals (NLSs). PAK4 is exported by the chromosome region maintenance-1 (CRM-1)-dependent pathway and is imported into the nucleus in an importin α5-dependent manner. PAK4 interacts with and phosphorylates β-catenin on Ser675, which promotes the TCF/LEF transcriptional activity and stabilizes β-catenin through inhibition of its degradation. Moreover, nuclear import of PAK4 accompanies with the nuclear import of β-catenin and increased TCF/LEF transcriptional activity. We further demonstrated that PAK4 associates with the TCF/LEF transcriptional complex by ChIP assays. These findings uncover a novel role for PAK4 in modulating intracellular translocation and signaling of β-catenin.

Amplification of 11q13 in ovarian carcinoma

Amplification at the 11q13 locus is commonly observed in breast, ovarian, head and neck, oral, and esophageal cancer. Studies of this region led to the identification of multiple amplicons containing several potential oncogenes including EMSY, PAK1, RSF1, and GAB2. Here, we investigate the amplification of the above four genes and their prognostic significance in histologically and clinically defined subsets of ovarian cancer. Amplification of all four genes was assessed by fluorescent in situ hybridization in tissue microarrays containing 538 clinically annotated ovarian carcinomas with 12 years of follow-up data. Overall, for the entire cohort, EMSY was amplified in 44 (16%) of 269 cases, PAK1 was amplified in 38 (15%) of 255 cases, RSF1 was amplified in 37 (12%) of 310 cases, and GAB2 was amplified in 41 (16%) of 255 cases. Amplification of EMSY, PAK1, RSF1, and GAB2 were all highly correlated with each other and with a serous histology. Univariate survival analysis showed that tumors with EMSY and RSF1 amplification were associated with a significantly worse outcome. A molecular inversion probe array was then used to study the 11q13 amplicon in 33 high grade serous carcinomas. The core of the amplicon mapped to a 6-Mb region encompassing EMSY, PAK1, RSF1, and GAB2. However, a second more telomeric amplicon was also observed for which no candidate genes have been identified. In summary, amplification of these four putative oncogenes from 11q13 in early ovarian cancer is associated with a serous histology and in the case of EMSY and RSF1 a poor outcome. These findings support the hypothesis that the11q13 amplicon in ovarian cancer is likely driven by a cassette of genes rather than by a single oncogene. This article contains Supplementary Material available at http://www.interscience.wiley.com/jpages/1045-2257/suppmat.

PAK1 as a therapeutic target

IMPORTANCE OF THE FIELD

P21-activated kinases (PAKs) are involved in multiple signal transduction pathways in mammalian cells. PAKs, and PAK1 in particular, play a role in such disorders as cancer, mental retardation and allergy. Cell motility, survival and proliferation, the organization and function of cytoskeleton and extracellular matrix, transcription and translation are among the processes affected by PAK1.

AREAS COVERED IN THIS REVIEW

We discuss the mechanisms that control PAK1 activity, its involvement in physiological and pathophysiological processes, the benefits and the drawbacks of the current tools to regulate PAK1 activity, the evidence that suggests PAK1 as a therapeutic target and the likely directions of future research.

WHAT THE READER WILL GAIN

The reader will gain a better knowledge and understanding of the areas described above.

TAKE HOME MESSAGE

PAK1 is a promising therapeutic target in cancer and allergen-induced disorders. Its suitability as a target in vascular, neurological and infectious diseases remains ambiguous. Further advancement of this field requires progress on such issues as the development of specific and clinically acceptable inhibitors, the choice between targeting one or multiple PAK isoforms, elucidation of the individual roles of PAK1 targets and the mechanisms that may circumvent inhibition of PAK1.

PAK4 inhibition improves PD-1 blockade immunotherapy

Lack of tumor infiltration by immune cells is the main mechanism of primary resistance to programmed cell death protein 1 (PD-1) blockade therapies for cancer. It has been postulated that cancer cell-intrinsic mechanisms may actively exclude T cells from tumors, suggesting that the finding of actionable molecules that could be inhibited to increase T cell infiltration may synergize with checkpoint inhibitor immunotherapy. Here, we show that p21-activated kinase 4 (PAK4) is enriched in non-responding tumor biopsies with low T cell and dendritic cell infiltration. In mouse models, genetic deletion of PAK4 increased T cell infiltration and reversed resistance to PD-1 blockade in a CD8 T cell-dependent manner. Furthermore, combination of anti-PD-1 with the PAK4 inhibitor KPT-9274 improved anti-tumor response compared with anti-PD-1 alone. Therefore, high PAK4 expression is correlated with low T cell and dendritic cell infiltration and a lack of response to PD-1 blockade, which could be reversed with PAK4 inhibition.

A Rac-Pak signaling pathway is essential for ErbB2-mediated transformation of human breast epithelial cancer cells

The activation of receptor tyrosine kinases, particularly ErbB2, has an important role in the genesis of breast cancer. ErbB2 kinase activity promotes Ras-mediated stimulation of downstream protein kinase cascades, including the Ras/Raf-1/MAPK/ERK kinase (Mek)/extracellular signal-regulated kinase (Erk) pathway, leading to tumor cell growth and migration. Signaling through the Ras-Erk pathway can be influenced by p21-activated kinase-1 (Pak1), an effector of the Rho family GTPases Rac and Cdc42. In this study, we asked if ErbB2 expression correlates with Pak1 and Erk activity in human breast cancer specimens, and if Pak1 signaling is required for ErbB2 transformation in a three-dimensional (3D) in vitro setting and in xenografts. We found a correlation between ErbB2 expression and activation of Pak in estrogen receptor-positive human breast tumor samples and observed that in 3D cultures, activation of Rac-Pak1 pathway by ErbB2 homodimers induced growth factor-independent proliferation and promoted disruption of 3D mammary acinar-like structures through activation of the Erk and Akt pathways. Further, we found that inhibition of Pak1 by small molecules compromised activation of Erk and Akt, resulting in reversion of the malignant phenotype and restoration of normal acinar architecture. Finally, ErbB2-amplified breast cancer cells expressing a specific Pak inhibitor showed delayed tumor formation and downregulation of Erk and Akt signaling in vivo. These data imply that the Rac-Pak pathway is vital to ErbB2-mediated transformation and that Pak inhibitors represent plausible drug targets in breast cancers in which ErbB2 signaling is activated.

Targeting PAK4 to reprogram the vascular microenvironment and improve CAR-T immunotherapy for glioblastoma

Malignant solid tumors are characterized by aberrant vascularity that fuels the formation of an immune-hostile microenvironment and induces resistance to immunotherapy. Vascular abnormalities may be driven by pro-angiogenic pathway activation and genetic reprogramming in tumor endothelial cells (ECs). Here, our kinome-wide screening of mesenchymal-like transcriptional activation in human glioblastoma (GBM)-derived ECs identifies p21-activated kinase 4 (PAK4) as a selective regulator of genetic reprogramming and aberrant vascularization. PAK4 knockout induces adhesion protein re-expression in ECs, reduces vascular abnormalities, improves T cell infiltration and inhibits GBM growth in mice. Moreover, PAK4 inhibition normalizes the tumor vascular microenvironment and sensitizes GBM to chimeric antigen receptor-T cell immunotherapy. Finally, we reveal a MEF2D/ZEB1- and SLUG-mediated mechanism by which PAK4 reprograms the EC transcriptome and downregulates claudin-14 and VCAM-1 expression, enhancing vessel permeability and reducing T cell adhesion to the endothelium. Thus, targeting PAK4-mediated EC plasticity may offer a unique opportunity to recondition the vascular microenvironment and strengthen cancer immunotherapy.

Prolactin-stimulated activation of ERK1/2 mitogen-activated protein kinases is controlled by PI3-kinase/Rac/PAK signaling pathway in breast cancer cells

There is strong evidence that deregulation of prolactin (PRL) signaling contributes to pathogenesis and chemoresistance of breast cancer. Therefore, understanding cross-talk between distinct signal transduction pathways triggered by activation of the prolactin receptor (PRL-R), is essential for elucidating the pathogenesis of metastatic breast cancer. In this study, we applied a sequential inhibitory analysis of various signaling intermediates to examine the hierarchy of protein interactions within the PRL signaling network and to evaluate the relative contributions of multiple signaling branches downstream of PRL-R to the activation of the extracellular signal-regulated kinases ERK1 and ERK2 in T47D and MCF-7 human breast cancer cells. Quantitative measurements of the phosphorylation/activation patterns of proteins showed that PRL simultaneously activated Src family kinases (SFKs) and the JAK/STAT, phosphoinositide-3 (PI3)-kinase/Akt and MAPK signaling pathways. The specific blockade or siRNA-mediated suppression of SFK/FAK, JAK2/STAT5, PI3-kinase/PDK1/Akt, Rac/PAK or Ras regulatory circuits revealed that (1) the PI3-kinase/Akt pathway is required for activation of the MAPK/ERK signaling cascade upon PRL stimulation; (2) PI3-kinase-mediated activation of the c-Raf-MEK1/2-ERK1/2 cascade occurs independent of signaling dowstream of STATs, Akt and PKC, but requires JAK2, SFKs and FAK activities; (3) activated PRL-R mainly utilizes the PI3-kinase-dependent Rac/PAK pathway rather than the canonical Shc/Grb2/SOS/Ras route to initiate and sustain ERK1/2 signaling. By interconnecting diverse signaling pathways PLR may enhance proliferation, survival, migration and invasiveness of breast cancer cells.

Rho GTPase signaling at the synapse: implications for intellectual disability

Intellectual disability (ID) imposes a major medical and social-economical problem in our society. It is defined as a global reduction in cognitive and intellectual abilities, associated with impaired social adaptation. The causes of ID are extremely heterogeneous and include non-genetic and genetic changes. Great progress has been made over recent years towards the identification of ID-related genes, resulting in a list of approximately 450 genes. A prominent neuropathological feature of patients with ID is altered dendritic spine morphogenesis. These structural abnormalities, in part, reflect impaired cytoskeleton remodeling and are associated with synaptic dysfunction. The dynamic, actin-rich nature of dendritic spines points to the Rho GTPase family as a central contributor, since they are key regulators of actin dynamics and organization. It is therefore not surprising that mutations in genes encoding regulators and effectors of the Rho GTPases have been associated with ID. This review will focus on the role of Rho GTPase signaling in synaptic structure/function and ID.

Activation of Pak1/Akt/eNOS signaling following sphingosine-1-phosphate release as part of a mechanism protecting cardiomyocytes against ischemic cell injury

We investigated whether plasma long-chain sphingoid base (LCSB) concentrations are altered by transient cardiac ischemia during percutaneous coronary intervention (PCI) in humans and examined the signaling through the sphingosine-1-phosphate (S1P) cascade as a mechanism underlying the S1P cardioprotective effect in cardiac myocytes. Venous samples were collected from either the coronary sinus (n = 7) or femoral vein (n = 24) of 31 patients at 1 and 5 min and 12 h, following induction of transient myocardial ischemia during elective PCI. Coronary sinus levels of LCSB were increased by 1,072% at 1 min and 941% at 5 min (n = 7), while peripheral blood levels of LCSB were increased by 579% at 1 min, 617% at 5 min, and 436% at 12 h (n = 24). In cultured cardiac myocytes, S1P, sphingosine (SPH), and FTY720, a sphingolipid drug candidate, showed protective effects against CoCl induced hypoxia/ischemic cell injury by reducing lactate dehydrogenase activity. Twenty-five nanomolars of FTY720 significantly increased phospho-Pak1 and phospho-Akt levels by 56 and 65.6% in cells treated with this drug for 15 min. Further experiments demonstrated that FTY720 triggered nitric oxide release from cardiac myocytes is through pertussis toxin-sensitive phosphatidylinositol 3-kinase/Akt/endothelial nitric oxide synthase signaling. In ex vivo hearts, ischemic preconditioning was cardioprotective in wild-type control mice (Pak1(f/f)), but this protection appeared to be ineffective in cardiomyocyte-specific Pak1 knockout (Pak1(cko)) hearts. The present study provides the first direct evidence of the behavior of plasma sphingolipids following transient cardiac ischemia with dramatic and early increases in LCSB in humans. We also demonstrated that S1P, SPH, and FTY720 have protective effects against hypoxic/ischemic cell injury, likely a Pak1/Akt1 signaling cascade and nitric oxide release. Further study on a mouse model of cardiac specific deletion of Pak1 demonstrates a crucial role of Pak1 in cardiac protection against ischemia/reperfusion injury.

siRNA and pharmacological inhibition of endocytic pathways to characterize the differential role of macropinocytosis and the actin cytoskeleton on cellular uptake of dextran and cationic cell penetrating peptides octaarginine (R8) and HIV-Tat

Cell penetrating peptides (CPPs) have been extensively studied as vectors for cellular delivery of therapeutic macromolecules. It is widely accepted that they can enter cells directly across the plasma membrane but also gain access through endocytic pathways that are yet to be fully defined. Here we developed siRNA methods in epithelial cell lines, HeLa and A431, to inhibit endocytic pathways regulated by clathrin heavy chain, flotillin-1, caveolin-1, dynamin-2 and Pak-1. In each case, functional uptake assays were developed to characterize the requirement for these proteins, and the pathways they regulate, in the internalisation of defined endocytic probes and also the CPPs octaarginine and HIV-Tat. Peptide uptake was only inhibited in A431 cells depleted of the macropinocytosis regulator Pak-1, but experimental variables including choice of cell line, pharmacological inhibitor, macropinocytic probe and serum starvation significantly influence our ability to assess and assign this pathway as an important route for CPP uptake. Actin disruption with Cytochalasin D inhibited peptide entry in both cell lines but the effects of this agent on dextran uptake was cell line dependent, reducing uptake in HeLa cells and increasing uptake in A431 cells. This was further supported in experiments inducing actin stabilisation by Jasplakinolide, emphasising that the actin cytoskeleton can both promote and hinder endocytosis. Overall the data identify important aspects regarding the comparative mechanisms of CPP uptake and macropinocytosis, and accentuate the significant methodological challenges of studying this pathway as an endocytic portal and an entry route for drug delivery vectors.

Polycomb-mediated loss of microRNA let-7c determines inflammatory macrophage polarization via PAK1-dependent NF-κB pathway

Serine/threonine kinase family members p21-activated kinases (PAKs) are important regulators of cytoskeletal remodeling and cell motility in mononuclear phagocytic system, but their role in macrophage differentiation and polarization remains obscure. We have shown here that inflammatory stimuli induced PAK1 overexpression in human and murine macrophages. Elevated expression of PAK1 contributed to macrophage M1 polarization and lipopolysaccharide (LPS)-induced endotoxin shock. We further observed that epigenetic loss of microRNA let-7c due to enhancer of zeste homolog 2 (EZH2) upregulation determined PAK1 elevation and inflammatory phenotype in M1 macrophages. EZH2/let-7c/PAK1 axis promotes macrophage M1 polarization via NIK-IKK-NF-κB signaling. Moreover, pharmacological and genetic ablation with EZH2/let-7c/PAK1 axis blunted inflammatory phenotype in M1 macrophages. Critically, either myeloid-restricted PAK1 deletion (PAK1(Lyz2cre)) or pharmacological and genetic ablation with EZH2/let-7c/PAK1 signal resulted in resistance to LPS-induced endotoxin shock via blunting macrophage M1 polarization. PAK1, therefore, is an essential controller of inflammatory macrophage polarization, regulating immune responses against pathogenic stimuli.

MiR-145 inhibits human colorectal cancer cell migration and invasion via PAK4-dependent pathway

MicroRNA-145 (miR-145), as a tumor-suppressive miRNA, has been demonstrated down-regulated in colorectal cancer (CRC) cells, and could inhibit CRC cells growth. However, the molecular pathway in which miR-145 modulates CRC malignant transformation has not been fully revealed. Here, we reported an intense correlation between the expressions of PAK4 and miR-145 in human CRC cell lines. Transwell assay verified overexpression of miR-145, as well as knockdown of PAK4, significantly suppressed cell migration and invasion ability. The impaired migration and invasion ability of SW1116 cells was affected through the down-regulation of phosphorylation level of LIMK1 and cofilin in a PAK4-dependent manner. Collectively, we have demonstrated that miR-145 suppressed CRC migration and invasion through PAK4 pathway, which provides an attractive microRNA-based therapeutic target for CRC.

PAK1-mediated activation of ERK1/2 regulates lamellipodial dynamics

PAK1 is a member of the p21-activated kinase (PAK) family of serine/threonine kinases that are activated by the Rho GTPases Rac and Cdc42, and are implicated in regulating morphological polarity, cell migration and adhesion. Here we investigate the function of PAK1 in cell motility using macrophages derived from PAK1-null mice. We show that CSF1, a macrophage chemoattractant, transiently stimulates PAK1 and MAPK activation, and that MAPK activation is reduced in PAK1-/- macrophages. PAK1 regulates the dynamics of lamellipodium extension as cells spread in response to adhesion but is not essential for macrophage migration or chemotaxis towards CSF1. Following adhesion, PAK1-/- macrophages spread more rapidly and have more lamellipodia than wild-type cells; however, these lamellipodia were less stable than those in wild-type macrophages. ERK1/2 activity was reduced in PAK1-/- macrophages during adhesion, and inhibition of ERK1/2 activation in wild-type macrophages was sufficient to increase the spread area and mimic the lamellipodial dynamics of PAK1-/- macrophages. Together, these data indicate that PAK1 signals via ERK1/2 to regulate lamellipodial stability.

Pak1 kinase links ErbB2 to β-catenin in transformation of breast epithelial cells

p21-Activated kinase-1 (Pak1) is frequently upregulated in human breast cancer and is required for transformation of mammary epithelial cells by ErbB2. Here, we show that loss of Pak1, but not the closely related Pak2, leads to diminished expression of β-catenin and its target genes. In MMTV-ErbB2 transgenic mice, loss of Pak1 prolonged survival, and mammary tissues of such mice showed loss of β-catenin. Expression of a β-catenin mutant bearing a phospho-mimetic mutation at Ser 675, a specific Pak1 phosphorylation site, restored transformation to ErbB2-positive, Pak1-deficient mammary epithelial cells. Mice bearing xenografts of ErbB2-positive breast cancer cells showed tumor regression when treated with small-molecule inhibitors of Pak or β-catenin, and combined inhibition by both agents was synergistic. These data delineate a signaling pathway from ErbB2 to Pak to β-catenin that is required for efficient transformation of mammary epithelial cells, and suggest new therapeutic strategies in ErbB2-positive breast cancer.

LncRNA-H19 activates CDC42/PAK1 pathway to promote cell proliferation, migration and invasion by targeting miR-15b in hepatocellular carcinoma

BACKGROUND

Hepatocellular carcinoma (HCC) is one of the main causes of cancer-related death. This study aims to explore the role and underlying mechanism of H19 in HCC.

METHODS

qRT-PCR detected miR-15b-5p and H19 expression, as well as the mRNA level of EMT-associated genes. Western blotting detected protein level of EMT-associated genes. Immunohistochemistry (IHC) examined CDC42 in HCC tissues. Dual luciferase reporter assay verified the regulatory mechanism among H19, miR-15b and CDC42. Colony formation, wound healing assay, transwell, flow cytometry measured proliferation, migration, invasion and apoptosis, respectively.

RESULTS

H19 and CDC42 were up-regulated while miR-15b was down-regulated in HCC cells and tissues. miR-15b interacted with H19 and CDC42 3'-UTR. H19 knockdown inhibited proliferation, migration and invasion, and increased apoptosis, which was rescued by miR-15b inhibitor. H19 knockdown suppressed CDC42/PAK1 pathway and EMT progress.

CONCLUSION

H19 knockdown inhibited proliferation, migration and invasion, and promoted apoptosis of HCC cells via targeting miR-15b/CDC42/PAK1 axis.