P21-activated kinase 5 is overexpressed during colorectal cancer progression and regulates colorectal carcinoma cell adhesion and migration

Smad4 and TGFβ1 dependent gene expression signatures in conditional intestinal adenoma, organoids and colorectal cancer

TGF-β ligands suppress growth yet can paradoxically and potently promote cancer invasion and metastasis depending on downstream pathway mutational context, such as loss of Mothers against decapentaplegic homolog 4 (Smad4). Here, we characterised phenotypes and associated gene expression signatures in conditional murine intestinal adenoma with and without Smad4. Conditional Lgr5-CreERT2 activation in Apcfl/flSmad4fl/fl mice resulted in homozygote floxed alleles (ApcΔ/ΔSmad4Δ/Δ) and adenoma formation. The adenoma phenotype was discordant, with reduced small intestinal adenoma burden yet development of large non-metastatic caecal adenoma with nuclear localisation of phospho-Smad2/3. Derived ApcΔ/ΔSmad4Δ/Δ adenoma organoids resisted TGF-β1 dose dependent growth arrest and cell death (IC50 534 pM) compared to ApcΔ/ΔSmad4+/+ (IC50 24 pM). TGF-β1 (390 pM) altered adenoma bulk mRNA expression most significantly for Id1low and Spp1high in ApcΔ/ΔSmad4Δ/Δ. Single cell RNAseq of caecal adenoma identified expansion of Lgr5low, Pak3high and Id1low progenitor populations in ApcΔ/ΔSmad4Δ/Δ. Of the 76 Smad4 and TGF-β1 dependent genes identified in Apcfl/flSmad4fl/fl adenoma organoids, only 7 human equivalent genes were differentially expressed in SMAD4 mutated colorectal cancer (TCGA cohorts), including ID1low. SMAD4low, ID1low SPP1high and PAK3high all correlated with poorer survival. Murine adenoma identified Smad4 dependent gene expression signatures that require further evaluation as functional biomarker classifiers of SMAD4 mutated cancer subtypes.

Expression and Purification of Recombinant Bowman-Birk Trypsin Inhibitor from Foxtail Millet Bran and Its Anticolorectal Cancer Effect In Vitro and In Vivo

Trypsin inhibitors derived from plants have various pharmacological activities and promising clinical applications. In our previous study, a Bowman-Birk-type major trypsin inhibitor from foxtail millet bran (FMB-BBTI) was extracted with antiatherosclerotic activity. Currently, we found that FMB-BBTI possesses a prominent anticolorectal cancer (anti-CRC) activity. Further, a recombinant FMB-BBTI (rFMB-BBTI) was successfully expressed in a soluble manner in host strain Escherichia coli. BL21 (DE3) was induced by isopropyl-β-d-thiogalactoside (0.1 mM) at 37 °C for 3.5 h by the pET28a vector system. Fortunately, a purity greater than 93% of rFMB-BBTI with anti-CRC activity was purified by nickel-nitrilotriacetic acid affinity chromatography. Subsequently, we found that rFMB-BBTI displays a strikingly anti-CRC effect, characterized by the inhibition of cell proliferation and clone formation ability, cell cycle arrest at the G2/M phase, and induction of cell apoptosis. It is interesting that the rFMB-BBTI treatment had no obvious effect on normal colorectal cells in the same concentration range. Importantly, the anti-CRC activity of rFMB-BBTI was further confirmed in the xenografted nude mice model. Taken together, our study highlights the anti-CRC activity of rFMB-BBTI in vitro and in vivo, uncovering the clinical potential of rFMB-BBTI as a targeted agent for CRC in the future.

Implication of Rac1 GTPase in molecular and cellular mitochondrial functions

Rac1 is a member of the Rho GTPase family which plays major roles in cell mobility, polarity and migration, as a fundamental regulator of actin cytoskeleton. Signal transduction by Rac1 occurs through interaction with multiple effector proteins, and its activity is regulated by guanine nucleotide exchange factors (GEFs) and GTPase-activating proteins (GAPs). The small protein is mainly anchored to the inner side of the plasma membrane but it can be found in endocellular compartments, notably endosomes and cell nuclei. The protein localizes also into mitochondria where it contributes to the regulation of mitochondrial dynamics, including both mitobiogenesis and mitophagy, in addition to signaling processes via different protein partners, such as the proapoptotic protein Bcl-2 and chaperone sigma-1 receptor (σ-1R). The mitochondrial form of Rac1 (mtRac1) has been understudied thus far, but it is as essential as the nuclear or plasma membrane forms, via its implication in regulation of oxidative stress and DNA damages. Rac1 is subject to diverse post-translational modifications, notably to a geranylgeranylation which contributes importantly to its mitochondrial import and its anchorage to mitochondrial membranes. In addition, Rac1 contributes to the mitochondrial translocation of other proteins, such as p53. The mitochondrial localization and functions of Rac1 are discussed here, notably in the context of human diseases such as cancers. Inhibitors of Rac1 have been identified (NSC-23766, EHT-1864) and some are being developed for the treatment of cancer (MBQ-167) or central nervous system diseases (JK-50561). Their effects on mtRac1 warrant further investigations. An overview of mtRac1 is provided here.

Hyperactivation of p21-Activated Kinases in Human Cancer and Therapeutic Sensitivity

Over the last three decades, p21-activated kinases (PAKs) have emerged as prominent intracellular nodular signaling molecules in cancer cells with a spectrum of cancer-promoting functions ranging from cell survival to anchorage-independent growth to cellular invasiveness. As PAK family members are widely overexpressed and/or hyperactivated in a variety of human tumors, over the years PAKs have also emerged as therapeutic targets, resulting in the development of clinically relevant PAK inhibitors. Over the last two decades, this has been a promising area of active investigation for several academic and pharmaceutical groups. Similar to other kinases, blocking the activity of one PAK family member leads to compensatory activity on the part of other family members. Because PAKs are also activated by stress-causing anticancer drugs, PAKs are components in the rewiring of survival pathways in the action of several therapeutic agents; in turn, they contribute to the development of therapeutic resistance. This, in turn, creates an opportunity to co-target the PAKs to achieve a superior anticancer cellular effect. Here we discuss the role of PAKs and their effector pathways in the modulation of cellular susceptibility to cancer therapeutic agents and therapeutic resistance.

Combination of PAKs inhibitors IPA-3 and PF-3758309 effectively suppresses colon carcinoma cell growth by perturbing DNA damage response

PURPOSE

PAKs proteins are speculated as new promising targets for cancer therapy due to their central role in many oncogenic pathways. Because PAKs proteins are very significant during carcinogenesis, we aimed to investigate the hypothesis that inhibition of PAKs with IPA-3 and PF-3758309 treatment could synergistically reduce colon carcinoma cell growth.

MATERIALS AND METHODS

The cytotoxic effects of both drugs were determined by a cell viability assay. Cell cycle and apoptosis were analyzed by flow cytometry. The effects of inhibitor drugs on marker genes of apoptosis, autophagy, cell cycle, and DNA damage were tested via immunoblotting.

RESULTS AND CONCLUSIONS

We found out the synergistic effect of these drugs in pair on five colon cancer cell lines. Combined treatment with IPA-3+PF-3758309 in SW620 and Colo 205 cells markedly suppressed colon formation and induced apoptosis, cell cycle arrest, and autophagy compared with treatment with each drug alone. Additionally, this combination sensitized colon cancer cells to ionizing radiation that resulted in inhibition of cell growth.

SIGNIFICANCE

Collectively, our findings show for the first time that cotreatment of IPA-3 with PF-3758309 exhibits superior inhibitory effects on colon carcinoma cell growth via inducing DNA damage-related cell death and also enforces a cell cycle arrest.

p21-Activated Kinase: Role in Gastrointestinal Cancer and Beyond

Simple Summary

Gastrointestinal tumors are the most common tumors with a high mortality rate worldwide. Numerous protein kinases have been studied in anticipation of finding viable tumor therapeutic targets, including PAK. PAK is a serine/threonine kinase that plays an important role in the malignant phenotype of tumors. The function of PAK in tumors is highlighted in cell proliferation, survival, motility, tumor cell plasticity and the tumor microenvironment, therefore providing a new possible target for clinical tumor therapy. Based on the current research works of PAK, we summarize and analyze the PAK features and signaling pathways in cells, especially the role of PAK in gastrointestinal tumors, thereby hoping to provide a theoretical basis for both the future studies of PAK and potential tumor therapeutic targets.

Abstract

Gastrointestinal tumors are the most common tumors, and they are leading cause of cancer deaths worldwide, but their mechanisms are still unclear, which need to be clarified to discover therapeutic targets. p21-activating kinase (PAK), a serine/threonine kinase that is downstream of Rho GTPase, plays an important role in cellular signaling networks. According to the structural characteristics and activation mechanisms of them, PAKs are divided into two groups, both of which are involved in the biological processes that are critical to cells, including proliferation, migration, survival, transformation and metabolism. The biological functions of PAKs depend on a large number of interacting proteins and the signaling pathways they participate in. The role of PAKs in tumors is manifested in their abnormality and the consequential changes in the signaling pathways. Once they are overexpressed or overactivated, PAKs lead to tumorigenesis or a malignant phenotype, especially in tumor invasion and metastasis. Recently, the involvement of PAKs in cellular plasticity, stemness and the tumor microenvironment have attracted attention. Here, we summarize the biological characteristics and key signaling pathways of PAKs, and further analyze their mechanisms in gastrointestinal tumors and others, which will reveal new therapeutic targets and a theoretical basis for the clinical treatment of gastrointestinal cancer.

A zebrafish embryo screen utilizing gastrulation identifies the HTR2C inhibitor pizotifen as a suppressor of EMT-mediated metastasis

Metastasis is responsible for approximately 90% of cancer-associated mortality but few models exist that allow for rapid and effective screening of anti-metastasis drugs. Current mouse models of metastasis are too expensive and time consuming to use for rapid and high-throughput screening. Therefore, we created a unique screening concept utilizing conserved mechanisms between zebrafish gastrulation and cancer metastasis for identification of potential anti-metastatic drugs. We hypothesized that small chemicals that interrupt zebrafish gastrulation might also suppress metastatic progression of cancer cells and developed a phenotype-based chemical screen to test the hypothesis. The screen used epiboly, the first morphogenetic movement in gastrulation, as a marker and enabled 100 chemicals to be tested in 5 hr. The screen tested 1280 FDA-approved drugs and identified pizotifen, an antagonist for serotonin receptor 2C (HTR2C) as an epiboly-interrupting drug. Pharmacological and genetic inhibition of HTR2C suppressed metastatic progression in a mouse model. Blocking HTR2C with pizotifen restored epithelial properties to metastatic cells through inhibition of Wnt signaling. In contrast, HTR2C induced epithelial-to-mesenchymal transition through activation of Wnt signaling and promoted metastatic dissemination of human cancer cells in a zebrafish xenotransplantation model. Taken together, our concept offers a novel platform for discovery of anti-metastasis drugs.

Coordinated dysregulation of cancer progression by the HER family and p21-activated kinases

Most epithelial cancer types are polygenic in nature and are driven by coordinated dysregulation of multiple regulatory pathways, genes, and protein modifications. The process of coordinated regulation of cancer promoting pathways in response to extrinsic and intrinsic signals facilitates the dysregulation of several pathways with complementary functions, contributing to the hallmarks of cancer. Dysregulation and hyperactivation of cell surface human epidermal growth factor receptors (HERs) and cytoskeleton remodeling by p21-activated kinases (PAKs) are two prominent interconnected aspects of oncogenesis. We briefly discuss the discoveries and significant advances in the area of coordinated regulation of HERs and PAKs in the development and progression of breast and other epithelial cancers. We also discuss how initial studies involving heregulin signaling via HER3-HER2 axis and HER2-overexpressing breast cancer cells not only discovered a mechanistic role of PAK1 in breast cancer pathobiology but also acted as a bridge in generating a broader cancer research interest in other PAK family members and cancer types and catalyzed establishing the role of PAKs in human cancer, at-large. In addition, growth factor stimulation of the PAK pathway also helped to recognize new facets of PAKs, connecting the PAK pathway to oncogenesis, nuclear signaling, gene expression, mitotic progression, DNA damage response, among other phenotypic responses, and shaped the field of PAK cancer research. Finally, we recount some of the current limitations of HER- and PAK-directed therapeutics in counteracting acquired therapeutic resistance and discuss how cancer's as a polygenic disease may be best targeted with a polygenic approach.

PAK5 promotes the cell stemness ability by phosphorylating SOX2 in lung squamous cell carcinomas

Growing evidences suggest that the overexpression of p21-activated kinase 5 (PAK5) plays an important role in various tumor progression. However, the role of PAK5 and its downstream target gene(s) in lung squamous cell carcinomas (LUSC) are waiting to be elucidated. TCGA data were utilized to evaluate the expression levels of PAK5 in LUSC. We then explored the role of PAK5 in maintaining the stem-like phenotype of lung squamous cancer cells through RT-PCR, flow cytometry, oncosphere-forming assay. In addition, co-immunoprecipitation, western blotting and immunofluorescence assays were used to determine SOX2 as a novel effector of PAK5. Xenograft models in nude mice were established to explore the roles of PAK5 in lung cancer growth. In this study, we have shown that PAK5 is overexpressed in LUSC tissues. The absence of PAK5 abolishes self-renewal ability of LUSC cells by decreasing the expression and phosphorylation of SOX2 in vitro and in vivo. In xenograft models, knockdown or pharmacological inhibition of PAK5 suppressed the tumor growth and metastasis of lung squamous cancer cells in vivo. Taken together, our findings suggest that the PAK5-mediated SOX2 phosphorylation promoted the cancer stem cell-like phenotype of LUSC cells. PAK5 inhibition may be a promising target in the treatment of SOX2 positive lung squamous cell cancer.

PAK5 facilitates the proliferation, invasion and migration in colorectal cancer cells

Colorectal cancer (CRC) is the third-most common cancer around the world, accounting for approximately 10% of cancer-related mortality. Deeper molecular understanding of colorectal carcinogenesis will provide evidences for identification of early diagnostic indicators and novel therapeutic strategies for CRC treatment. The p21cdc42/rac1 -activated kinase 5 (PAK5) has been reported to be involved in a variety of tumor-promoting behaviors, whereas the underlying mechanisms of PAK5 in CRC progression are still obscure. Our current study revealed an upregulated expression of PAK5 in human CRC tissues as compared with normal adjacent biopsies, which was associated with tumor progression and metastasis. We further unraveled that inhibition of PAK5 was correlated with restrained proliferation, migration, and invasion of CRC cells in vitro and in vivo. Moreover, we showed an indispensable role of PAK5 in interacting with Cdc42 and Integrin β1, β3, thus, to facilitate the migration and invasion of CRC cells. Collectively, we pointed out a potential of PAK5 to serve as a novel therapeutic target in restricting CRC proliferation and metastasis. The uncovered mechanisms will deepen the comprehension with regard to the mechanisms of CRC progression, as well as providing new insights for therapeutic intervention in colorectal cancer.

Rac1 Signaling: From Intestinal Homeostasis to Colorectal Cancer Metastasis

The small GTPase Rac1 has been implicated in a variety of dynamic cell biological processes, including cell proliferation, cell survival, cell-cell contacts, epithelial mesenchymal transition (EMT), cell motility, and invasiveness. These processes are orchestrated through the fine tuning of Rac1 activity by upstream cell surface receptors and effectors that regulate the cycling Rac1-GDP (off state)/Rac1-GTP (on state), but also through the tuning of Rac1 accumulation, activity, and subcellular localization by post translational modifications or recruitment into molecular scaffolds. Another level of regulation involves Rac1 transcripts stability and splicing. Downstream, Rac1 initiates a series of signaling networks, including regulatory complex of actin cytoskeleton remodeling, activation of protein kinases (PAKs, MAPKs) and transcription factors (NFkB, Wnt/β-catenin/TCF, STAT3, Snail), production of reactive oxygen species (NADPH oxidase holoenzymes, mitochondrial ROS). Thus, this GTPase, its regulators, and effector systems might be involved at different steps of the neoplastic progression from dysplasia to the metastatic cascade. After briefly placing Rac1 and its effector systems in the more general context of intestinal homeostasis and in wound healing after intestinal injury, the present review mainly focuses on the several levels of Rac1 signaling pathway dysregulation in colorectal carcinogenesis, their biological significance, and their clinical impact.

Systemic analysis of the expression and prognostic significance of PAKs in breast cancer

PAKs (p21-activated kinases) are reported to play crucial roles in a variety of cellular processes and participate in the progression of human cancers. However, the expression and prognostic values of PAKs remain poorly explored in breast cancers. In our study, we examined the mRNA and protein expression levels of PAKs and the prognostic value. We also analyzed the interaction network, genetic alteration, and functional enrichment of PAKs. The results showed that the mRNA levels of PAK1, PAK2, PAK4 and PAK6 were significantly up-regulated in breast cancer compared with normal tissues, while the reverse trend for PAK3 and PAK5 was found, furthermore, the proteins expression of PAK1, PAK2 and PAK4 in breast cancer tissues were higher than that in normal breast tissues. Survival analysis revealed breast cancer patients with low mRNA expression of PAK3 and PAK5 showed worse RFS, conversely, elevated PAK4 levels predicted worse RFS. In addition, the breast cancer patients with PAKs genetic alterations correlated with worse OS. These results indicated that PAKs might be promising potential biomarkers for breast cancer.

Human p21-activated kinase 5 (PAK5) expression and potential mechanisms in relevant cancers: Basic and clinical perspectives for molecular cancer therapeutics

An oncogenic role, p21-activated kinase 5 (PAK5), has proven as a significant mediator for many cellular progression, which is expressed highly in human organs such as lung, liver, kidney, blood vessels endothelial cells and inflammatory cells. PAK5 was primitively detected in the cerebrum and accelerated the filopodia formation in neurocytes. It can reverse the effect of Rho and adjust its activity to mediate maintenance and development of nerve axon by binding with Cdc42-GTP. Moreover, PAK5 has been suggested to mediate protean, multitudinous and inscrutable functions in cancer. Currently, many researches indicated that PAK5 was dysregulated in ovarian cancer, cervical cancer, melanoma, osteosarcoma, renal carcinoma, breast cancer, gastric cancer and so on, which was involved in cell proliferation, apoptosis, migration and invasion. This review focuses the latest knowledge on the structure, expression, signalling pathway of PAK5, emphasizing its function in cancer.

A PAK5-DNPEP-USP4 axis dictates breast cancer growth and metastasis

Although clinically associated with the progression of multiple cancers, the biological function of p21-activated kinase 5 (PAK5) in breast cancer remains largely unknown. Here, we reveal that the PAK5-aspartyl aminopeptidase (DNPEP)-ubiquitin-specific protease 4 (USP4) axis is involved in breast cancer progression. We show that PAK5 interacts with and phosphorylates DNPEP at serine 119. Functionally, we demonstrate that DNPEP overexpression suppresses breast cancer cell proliferation and invasion and restricts breast cancer growth and metastasis in mice. Furthermore, we identify USP4 as a downstream target of the PAK5-DNPEP pathway; DNPEP mediates USP4 downregulation. Importantly, we verify that DNPEP expression is frequently downregulated in breast cancer tissues and is negatively correlated with PAK5 and USP4 expression. PAK5 decreases DNPEP abundance via the ubiquitin-proteasome pathway. Consistently, analyses of clinical breast cancer specimens revealed significantly increased PAK5 and USP4 levels and an association between higher PAK5 and USP4 expression and worse breast cancer patient survival. These findings suggest a pivotal role for PAK5-elicited signaling in breast cancer progression.

Prognostic significance of PAK family kinases in acute myeloid leukemia

Acute myeloid leukemia (AML) is a clonal and heterogeneous disease characterized by a myriad of genetic defects. Genetic abnormalities are powerful prognostic factors. P21-activated kinases (PAKs) are a kind of serine/threonine protein kinases, which is regulator of plenty of oncogenic signaling pathways. The clinical and prognostic value of PAKs in AML is unclear. A total of 155 AML patients with PAK expression data from The Cancer Genome Atlas database were enrolled in this study. Eighty-four patients underwent chemotherapy only, 71 also underwent allogeneic hematopoietic stem cell transplantation (allo-HSCT). In the chemotherapy-only group, high PAK3 and PAK7 expression were both bound up with poor EFS and OS (all P < 0.05). However, high PAK2 expressers had better EFS and OS (all P < 0.05). Multivariate analysis demonstrated that high PAK7 expression was an adverse independent prognostic factor in patients who received chemotherapy only. PAKs have no influence in EFS and OS in patients who underwent allo-HSCT. In conclusion, high PAK2 expression is a favorable prognostic factor, as to the high expression of PAK3 and PAK7, they are poor prognostic factors, and PAK7 has better prognostic value, but their prognostic effects can be offset by allo-HSCT.

PAK5 Induces EMT and Promotes Cell Migration and Invasion by Activating the PI3K/AKT Pathway in Ovarian Cancer

Ovarian cancer is the most lethal gynecologic cancer and currently ranks fifth in causing cancer-related deaths among women. P21^cdc42/rac1-activated kinase 5 (PAK5) is a newly identified protein that has been indicated to have oncogenic potential. The present study investigated the expression level of PAK5 in clinical ovarian cancer and the functional roles of PAK5 in ovarian cancer progression. It was initially found that PAK5 was highly expressed in ovarian cancer tissues, particularly in patients with distant metastasis. Higher expression of PAK5 predicted poor survival fates in patients with ovarian cancer (p = 0.008). Knockdown of PAK5 in SKOV3 cells caused epithelial cell phenotypes, whereas overexpression of PAK5 led to remarkable mesenchymal cell phenotypes in A2780 cells. When PAK5 was depleted from SKOV3 cells, cells exhibited impaired wound recovery abilities. Cell migration and invasion abilities were also significantly inhibited. On the contrary, when PAK5 was overexpressed in A2780 cells, the wound recovery ability was enhanced by 68%. Cell migration and invasion abilities were consistently increased to approximately 2-fold. After knockdown of PAK5, the phosphorylation levels of PI3K p85 at Tyr458 and its downstream AKT at Ser473 were both decreased. The total protein of PI3K and AKT as well as the phosphorylation level of AKT at Thr308 remained unaffected. These data suggested that PI3K induced epithelial-to-mesenchymal transition and promoted cell migration and invasion by activating the PI3K/AKT pathway in ovarian cancer. The oncogenic potential of PAK5 in ovarian cancer might suggest that any therapeutic strategies targeting PAK5 had the promising value for ovarian cancer treatment.

PAK5 promotes the migration and invasion of cervical cancer cells by phosphorylating SATB1

p21-activated kinase 5 (PAK5) is involved in several oncogenic signaling pathways and its amplification or overexpression has been found in various types of cancer; however, the pathophysiologic role of PAK5 in cervical cancer (CC) remains elusive. This study aims to elucidate the effects of PAK5 on CC metastasis and its specific regulation mechanism. We performed western blotting and immunohistochemistry (IHC) analysis and found that the expression levels of PAK5 were significantly upregulated in CC cells and tissues. In addition, statistical analysis via IHC showed that increased PAK5 significantly correlated with CC progression. Mn²⁺-Phos-tag SDS-PAGE, western blotting, immunofluorescence and dual luciferase reporter assays were utilized to determine the involvement of SATB1 in PAK5-mediated epithelial-mesenchymal transition (EMT). We found that PAK5-mediated special AT-rich binding protein-1 (SATB1) phosphorylation on Ser47 initiated EMT cascade and promoted migration and invasion of CC cells. Furthermore, overexpression of PAK5 induced lung metastasis of CC cells in xenograft modes. Taken together, we conclude that PAK5 is a novel prognostic indicator and plays an important role in the CC metastasis.

Reconstruction of the genome-scale co-expression network for the Hippo signaling pathway in colorectal cancer

The Hippo signaling pathway (HSP) has been identified as an essential and complex signaling pathway for tumor suppression that coordinates proliferation, differentiation, cell death, cell growth and stemness. In the present study, we conducted a genome-scale co-expression analysis to reconstruct the HSP in colorectal cancer (CRC). Five key modules were detected through network clustering, and a detailed discussion of two modules containing respectively 18 and 13 over and down-regulated members of HSP was provided. Our results suggest new potential regulatory factors in the HSP. The detected modules also suggest novel genes contributing to CRC. Moreover, differential expression analysis confirmed the differential expression pattern of HSP members and new suggested regulatory factors between tumor and normal samples. These findings can further reveal the importance of HSP in CRC.

P21-activated kinase 7 (PAK7) interacts with and activates Wnt/β-catenin signaling pathway in breast cancer

Background: Breast cancer is the highest incidence of tumor in women, which seriously threaten women's health. The occurrence and progression of breast cancer is linked to inactivation or downregulation of tumor suppressors, and activation or upregulation of oncogenes. However, the mechanism of PAK7 involving in the occurrence and progression of breast cancer is not yet fully understood. Methods: PAK7 expression was analyzed by RT-qPCR and immunohistochemistry and correlated with clinicopatholgical parameters in breast cancer tissue microarray. The effects of PAK7 on breast cancer cells were detected by CCK-8 assay, colon formation assay, wound healing and transwell assays, and flow cytometry. The relationship between PAK7 and Wnt/β-catenin signaling pathway was determined by western blotting, TOP/FOP flash, co-Immunoprecipitation and co-localization assays. Results: PAK7 expression was significantly increased in breast cancer tissues and positively correlated with pathological differentiation and TNM stage of breast cancer. Overexpression of PAK7 could significantly promote proliferation and migration of breast cancer cells, and inhibit apoptosis. In contrast, PAK7 knockdown significantly inhibited the proliferation and migration of breast cancer cells and promoted apoptosis. In addition, PAK7 could activate Wnt/β-catenin signaling pathway in breast cancer cells. Further study found that PAK7 could directly bind to GSK3β and β-catenin, and regulate β-catenin degradation by phosphorylating GSK3β. Conclusions: Our study demonstrated that PAK7, as an oncogene, involved in breast cancer progression by activating the Wnt/β-catenin signaling pathway, suggesting that the potential applicability of PAK7 as a target for breast cancer treatment.

Chronic exposure to cigarette smoke leads to activation of p21 (RAC1)-activated kinase 6 (PAK6) in non-small cell lung cancer cells

Epidemiological data clearly establishes cigarette smoking as one of the major cause for lung cancer worldwide. Recently, targeted therapy has become one of the most preferred modes of treatment for cancer. Though certain targeted therapies such as anti-EGFR are in clinical practice, they have shown limited success in lung cancer patients who are smokers. This demands discovery of alternative drug targets through systematic investigation of cigarette smoke-induced signaling mechanisms. To study the signaling events activated in response to cigarette smoke, we carried out SILAC-based phosphoproteomic analysis of H358 lung cancer cells chronically exposed to cigarette smoke. We identified 1,812 phosphosites, of which 278 phosphosites were hyperphosphorylated (≥ 3-fold) in H358 cells chronically exposed to cigarette smoke. Our data revealed hyperphosphorylation of S560 within the conserved kinase domain of PAK6. Activation of PAK6 is associated with various processes in cancer including metastasis. Mechanistic studies revealed that inhibition of PAK6 led to reduction in cell proliferation, migration and invasion of the cigarette smoke treated cells. Further, siRNA mediated silencing of PAK6 resulted in decreased invasive abilities in a panel of non-small cell lung cancer (NSCLC) cells. Consistently, mice bearing tumor xenograft showed reduced tumor growth upon treatment with PF-3758309 (group II PAK inhibitor). Immunohistochemical analysis revealed overexpression of PAK6 in 66.6% (52/78) of NSCLC cases in tissue microarrays. Taken together, our study indicates that PAK6 is a promising novel therapeutic target for NSCLC, especially in smokers.

PAK5 overexpression is associated with lung metastasis in osteosarcoma

p21-activated kinases (PAKs) are multifunctional effectors of Rho GTPases, which are associated with cytoskeletal organization, cellular morphogenesis, migration and survival. PAKs are overactive in a number of tumor tissues and have attracted attention as a potential target for cancer therapy. In the present study, PAK5 levels were analyzed in primary osteosarcoma (OS) samples (n=65) using reverse transcription-quantitative polymerase chain reaction (RT-qPCR) and immunohistochemistry (IHC) methods. In the primary OS tissue, increased PAK5 expression (IHC score >2, n=37) was associated with significantly decreased overall survival (P=0.036) compared with decreased PAK5 expression (IHC score ≤2, n=28). PAK5 expression was identified to be significantly associated with metastasis (P=0.010). The lung is the most common metastasis site for OS. In addition, the level of PAK5 in lung metastasis tissue (n=13) was detected using RT-qPCR and IHC methods. PAK5 expression was increased in lung metastasis tissue compared with in primary OS samples. PAK5 was silenced using short hairpin RNA in OS cell lines. Wound healing, migration and nude mice model assay results consistently demonstrated that PAK5 knockdown was able to significantly inhibit OS migration. In PAK5-knockdown cells, the alteration in the expression of a number of metastasis-associated factors, including epithelial cadherin, vimentin, fibronectin and matrix metalloproteinase 2 (MMP2), was analyzed. Only MMP2 expression was decreased significantly (P<0.05). The expression level of MMP2 was analyzed in primary OS tissue and lung metastasis tissue using RT-qPCR and IHC methods. Expression of MMP2 was identified to be associated with expression of PAK5. The results of the present study suggest that PAK5 promotes OS cell migration and that PAK5 expression may be used to predict lung metastasis.

High-level expression of P21-Cdc/Rac-activated kinase 7 is closely related to metastatic potential and poor prognosis of colon carcinoma

P21 protein (Cdc42/Rac)-activated kinase 7 (PAK7) can promote neurite outgrowth, induce microtubule stabilization, and activate cell survival signaling pathways. PAK7 expression was found to increase with colon carcinoma progression, but the prognostic value, clinical significance, and underlying mechanisms have not been explored. In my study, the expression of PAK7 was up-related at both the transcriptional and the translational levels in colon tumors compared to that in adjacent normal colon tissue. Patients with PAK7-positive tumors had a lower rate of overall survival (OS) and metastasis-free survival (MFS) (log-rank test, P < 0.001). A Cox proportional hazards model showed that PAK7 expression was an independent prognostic factor for OS (hazard ration [HR], 2.08; 95% confidence interval [CI], 1.16-3.73; P = 0.004) and MFS (HR, 2.88; 95% CI, 1.53-5.42; P < 0.001) in patients with colon cancer. Patients with tumors that were over-expressing PAK7 experienced metastasis, and died within a significantly shorter time after surgery (P < 0.001). Knockdown of PAK7 by a specific short hairpin RNA (shRNA) significantly suppressed the progression of epithelial to mesechymal transition (EMT), migration, and invasion of colon cancer cells in vitro and tumor growth in vivo. However, overexpression of PAK7 significantly promoted these processes. These findings indicate that aberrant PAK7 expression is associated with the occurrence of metastasis and poor clinical outcomes of human colon cancer by promoting the EMT, and the assessment of PAK7 expression might be helpful in predicting metastasis and prognostication for patients with colon cancer.

MiR-106a-5p inhibits the cell migration and invasion of renal cell carcinoma through targeting PAK5

MicroRNA-106a-5p (MiR-106a-5p), a small non-coding RNA, has been reported to be downregulated in astrocytoma, osteosarcoma and colorectal cancer. However, the expression levels and biological function in renal cell carcinoma (RCC) have not been studied yet. In this study, we found that the miR-106a-5p was significantly downregulated in RCC tissues and cell lines, and that overexpression of miR-106a-5p led to decreased cell metastasis ability in a xenograft model. Inhibition of miR-106a-5p in RCC cell lines altered the cell migration, invasion and wound healing abilities. Mechanistic studies demonstrated that miR-106a-5p directly bound to the 3'-UTR of the PAK5 mRNA and mediated a decrease in the protein expression of PAK5. We further proved that PAK5 protein levels were negatively correlated with the miR-106a-5p expression in both patient samples and xenograft model. In epigenetics, methylation specific PCR experiments indicated that the upstream gene promoter of miR-106a-5p was hypermethylated in RCC, which might be responsible for its downregulation. Our findings suggested that miR-106a-5p might be a potential gene therapy target for the treatment of RCC metastasis.

PAK5-mediated phosphorylation and nuclear translocation of NF-κB-p65 promotes breast cancer cell proliferation in vitro and in vivo

Background

Abnormal proliferation is significantly associated with the promotion of malignant tumor. Growing evidence suggest that the signal pathways of p21^cdc42/rac1-activated kinase 5 (PAK5) have been found in various tumor progression, however, the role of PAK5 in breast cancer remains largely unclear.

Methods

We evaluated PAK5 and p65 staining in breast cancer tissues (BCTs) and paired non-cancerous tissues (NTs) using tissue microarray (TMA) technology. The functions of PAK5 were studied in vitro and in vivo. Cell Counting Kit-8 (CCK-8) and flow cytometry were performed to determine proliferation of breast cancer cells. Phosphorylation assay and co-immunoprecipitation (co-IP) were employed to identify the regulation mechanism of p65 by PAK5. The activation of Cyclin D1 promoter was measured with luciferase reporter assay. Xenograft models in nude mice were established to explore the roles of PAK5 in breast cancer growth.

Results

In this study, we show that PAK5 is highly expressed in breast cancer tissues and the increased PAK5 is significantly associated with breast cancer progression. Overexpression of PAK5 promotes the proliferation and cell-cycle progression by increasing the expression of Cyclin D1 in vitro and in vivo. Mechanistic studies demonstrated that PAK5 can promote the phosphorylation and the nuclear translocation of p65 subunit of nuclear factor-kappaB (NF-κB). Furthermore, p65 can directly bind to the promoter of Cyclin D1 and mediate an increase in its protein expression.

Conclusions

Taken together, our findings suggest that PAK5 may serve as a potential prognosis marker and therapeutic target for human breast cancer.

High expression of P21-activated kinase 5 protein is associated with poor survival in gastric cancer

P21-activated kinase 5 (PAK5), also termed PAK7, is one of the six members of the PAK family of serine/threonine kinases, which are downstream effectors in several cancer signaling pathways. PAK5 promotes neural outgrowth, contributes to microtubule stability and induces resistance to apoptosis. However, the clinical importance of PAK5 in gastric cancer has not been comprehensively investigated. In the present study, PAK5 expression was evaluated in gastric cancer tissue samples. Furthermore, the associations between high expression of PAK5, and clinicopathological features and prognosis were examined. PAK5 expression in primary gastric cancer specimens resected from 279 patients who underwent gastrectomy at the Tokyo Medical and Dental University Hospital was evaluated using immunohistochemistry. Of the 279 patients, 44 (15.8%) exhibited high PAK5 expression, which was significantly associated with the differentiated pathological type (differentiated vs. undifferentiated; P<0.001), depth of tumor invasion (T1 vs. T2-T4; P<0.001), lymph node metastasis (N0 vs. N1-N3; P<0.001), presence of distant metastasis or recurrence (present vs. absent; P=0.038), advanced tumor stage (I vs. II-IV; P=0.001) and worse disease-specific survival (P=0.013). In stage I-III disease, 38/254 (15.0%) patients exhibited high PAK5 expression, and high expression of PAK5 was significantly associated with relapse-free interval (P=0.044). PAK5 may serve an important role in tumor progression and influence the outcome of patients with gastric cancer.

PAK5 mediates cell: cell adhesion integrity via interaction with E-cadherin in bladder cancer cells

Urothelial bladder cancer is a major cause of morbidity and mortality worldwide, causing an estimated 150 000 deaths per year. Whilst non-muscle-invasive bladder tumours can be effectively treated, with high survival rates, many tumours recur, and some will progress to muscle-invasive disease with a much poorer long-term prognosis. Thus, there is a pressing need to understand the molecular transitions occurring within the progression of bladder cancer to an invasive disease. Tumour invasion is often associated with a down-regulation of E-cadherin expression concomitant with a suppression of cell:cell junctions, and decreased levels of E-cadherin expression have been reported in higher grade urothelial bladder tumours. We find that expression of E-cadherin in a panel of bladder cancer cell lines correlated with the presence of cell:cell junctions and the level of PAK5 expression. Interestingly, exogenous PAK5 has recently been described to be associated with cell:cell junctions and we now find that endogenous PAK5 is localised to cell junctions and interacts with an E-cadherin complex. Moreover, depletion of PAK5 expression significantly reduced junctional integrity. These data suggest a role for PAK5 in maintaining junctional stability and we find that, in both our own patient samples and a commercially available dataset, PAK5mRNA levels are reduced in human bladder cancer compared with normal controls. Taken together, the present study proposes that PAK5 expression levels could be used as a novel prognostic marker for bladder cancer progression.

PAK5 is auto-activated by a central domain that promotes kinase oligomerization

The present study shows for the first time that self-association of PAK5 in vivo underlies its high basal activity, which contrasts with the inactive state of cellular PAK4. Such PAK5 self-association interferes with the engagement of the auto-inhibitory (AID) with the catalytic domain.

PAKs in Human Cancer Progression: From Inception to Cancer Therapeutic to Future Oncobiology

Since the initial recognition of a mechanistic role of p21-activated kinase 1 (PAK1) in breast cancer invasion, PAK1 has emerged as one of the widely overexpressed or hyperactivated kinases in human cancer at-large, allowing the PAK family to make in-roads in cancer biology, tumorigenesis, and cancer therapeutics. Much of our current understanding of the PAK family in cancer progression relates to a central role of the PAK family in the integration of cancer-promoting signals from cell membrane receptors as well as function as a key nexus-modifier of complex, cytoplasmic signaling network. Another core aspect of PAK signaling that highlights its importance in cancer progression is through PAK's central role in the cross talk with signaling and interacting proteins, as well as PAK's position as a key player in the phosphorylation of effector substrates to engage downstream components that ultimately leads to the development cancerous phenotypes. Here we provide a comprehensive review of the recent advances in PAK cancer research and its downstream substrates in the context of invasion, nuclear signaling and localization, gene expression, and DNA damage response. We discuss how a deeper understanding of PAK1's pathobiology over the years has widened research interest to the PAK family and human cancer, and positioning the PAK family as a promising cancer therapeutic target either alone or in combination with other therapies. With many landmark findings and leaps in the progress of PAK cancer research since the infancy of this field nearly 20 years ago, we also discuss postulated advances in the coming decade as the PAK family continues to shape the future of oncobiology.

Group II p21-activated kinases as therapeutic targets in gastrointestinal cancer

P21-activated kinases (PAKs) are central players in various oncogenic signaling pathways. The six PAK family members are classified into group I (PAK1-3) and group II (PAK4-6). Focus is currently shifting from group I PAKs to group II PAKs. Group II PAKs play important roles in many fundamental cellular processes, some of which have particular significance in the development and progression of cancer. Because of their important functions, group II PAKs have become popular potential drug target candidates. However, few group II PAKs inhibitors have been reported, and most do not exhibit satisfactory kinase selectivity and “drug-like” properties. Isoform- and kinase-selective PAK inhibitors remain to be developed. This review describes the biological activities of group II PAKs, the importance of group II PAKs in the development and progression of gastrointestinal cancer, and small-molecule inhibitors of group II PAKs for the treatment of cancer.

GATA1 induces epithelial-mesenchymal transition in breast cancer cells through PAK5 oncogenic signaling

Epithelial-mesenchymal transition (EMT) is a key process in tumor metastatic cascade that is characterized by the loss of cell-cell junctions, resulting in the acquisition of migratory and invasive properties. E-cadherin is a major component of intercellular junctions and the reduction or loss of its expression is a hallmark of EMT. Transcription factor GATA1 has a critical anti-apoptotic role in breast cancer, but its function for metastasis has not been investigated. Here, we found that GATA1, as a novel E-cadherin repressor, promotes EMT in breast cancer cells. GATA1 binds to E-cadherin promoter, down-regulates E-cadherin expression, disrupts intercellular junction and promotes metastasis of breast cancer cell in vivo. Moreover, GATA1 is a new substrate of p21-activated kinase 5 (PAK5), which is phosphorylated on serine 161 and 187 (S161 and S187). GATA1 recruits HDAC3/4 to E-cadherin promoter, which is reduced by GATA1 S161A S187A mutant. These data indicate that phosphorylated GATA1 recruits more HDAC3/4 to promote transcriptional repression of E-cadherin, leading to the EMT of breast cancer cells. Our findings provide insights into the novel function of GATA1, contributing to a better understanding of the EMT, indicating that GATA1 and its phosphorylation may play an important role in the metastasis of breast cancer.

PAK5-mediated E47 phosphorylation promotes epithelial-mesenchymal transition and metastasis of colon cancer

The p21-activated kinase 5 (PAK5) is overexpressed in advanced cancer and the transcription factor E47 is a direct repressor of E-cadherin and inducer of epithelial-mesenchymal transition (EMT). However, the relationship between PAK5 and E47 has not been explored. In this study, we found that PAK5-mediated E47 phosphorylation promoted EMT in advanced colon cancer. PAK5 interacted with E47 and phosphorylated E47 on Ser39 under hepatocyte growth factor (HGF) stimulation, which decreased cell-cell cohesion, increased cell migration and invasion in vitro and promoted metastasis in a xenograft model. Furthermore, phosphorylation of E47 facilitated its accumulating in nucleus in an importin α-dependent manner, and enhanced E47 binding to E-cadherin promoter directly, leading to inhibition of E-cadherin transcription. In contrast, PAK5-knockdown resulted in blockage of HGF-induced E47 phosphorylation, attenuated association of E47 with importin α and decreased E47 binding to E-cadherin promoter. In addition, we demonstrated a close correlation between PAK5 and phospho-Ser39 E47 expression in colon cancer specimens. More importantly, high expression of phospho-E47 was associated with an aggressive phenotype of colon cancer and nuclear phospho-E47 staining was found in certain cases of colon cancer with metastasis. Collectively, E47 is a novel substrate of PAK5, and PAK5-mediated phosphorylation of E47 promotes EMT and metastasis of colon cancer, suggesting that phosphorylated E47 on Ser39 may be a potential therapeutic target in progressive colon cancer.

Signaling, Regulation, and Specificity of the Type II p21-activated Kinases

The p21-activated kinases (PAKs) are a family of six serine/threonine kinases that act as key effectors of RHO family GTPases in mammalian cells. PAKs are subdivided into two groups: type I PAKs (PAK1, PAK2, and PAK3) and type II PAKs (PAK4, PAK5, and PAK6). Although these groups are involved in common signaling pathways, recent work indicates that the two groups have distinct modes of regulation and have both unique and common substrates. Here, we review recent insights into the molecular level details that govern regulation of type II PAK signaling. We also consider mechanisms by which signal transduction is regulated at the level of substrate specificity. Finally, we discuss the implications of these studies for clinical targeting of these kinases.

Efficient inhibition of human glioma development by RNA interference-mediated silencing of PAK5

Glioma is the most common type of primary intracranial tumor and is highly lethal due to its pathogenetic location, high invasiveness, and poor prognosis. Even combined surgery and chemoradiotherapy do not effectively rescue glioma patients. Molecular target therapy is considered a safe and promising therapy for glioma. The identification of a novel, effective target protein in gliomas is of great interest. We found that PAK5 was highly expressed in the tumor tissues of glioma patients and human glioma cell lines. We then used a lentivirus-delivered short hairpin RNA to stably silence PAK5 expression in glioma cells and explore its influence. The results showed that the inhibition of PAK5 reduced cell viability and delayed the cell cycle at the G0/G1 phase in the glioma cells with PAK5 high expression. In addition, silencing PAK5 expression in U87 cells weakened their colony formation ability and in vivo tumorigenesis ability. Further studies demonstrated that PAK5 inhibition led to an increase in cleaved caspase 3 and a decrease in β-catenin. In conclusion, our results suggest that the inhibition of PAK5 by RNA interference might efficiently suppress tumor development of glioma cells with PAK5 high expression. This finding provides a novel, promising therapeutic target for glioma treatment.

p21-Activated kinase 5 affects cisplatin-induced apoptosis and proliferation in hepatocellular carcinoma cells

p21-Activated kinase 5 (PAK5) is the last identified member of the PAK family. The PAKs are highly conserved serine/threonine and effector proteins for Cdc42 and Rac and are essential in regulating cell motility and survival. Previous studies have demonstrated that PAK5 played a pivotal role in apoptosis, proliferation, cancer migration, and invasion. However, the biological function of PAK5 in hepatocellular carcinoma, as well as its underlying mechanism, still remains to be fully elucidated. In the present study, we demonstrated that PAK5 markedly inhibited cisplatin-induced apoptosis and promoted cell proliferation in hepatocellular carcinoma cells. Moreover, our results showed that overexpression of PAK5 contributed to cell cycle regulation. In order to elucidate the underlying mechanism of PAK5 on cisplatin-induced apoptosis and cell cycle regulation, we also examined the protein expressions of chk2 and p-chk2. In summary, our study investigated the role of PAK5 in cisplatin-induced cellular processes and provided evidence of its underlying mechanism.

Targeted anti-colon cancer activities of a millet bran-derived peroxidase were mediated by elevated ROS generation

Foxtail millet (Setaria italica) is the sixth most important cereal in the world.

P21-activated kinase 7 mediates cisplatin-resistance of esophageal squamous carcinoma cells with Aurora-A overexpression

Aurora-A overexpression is common in various types of cancers and has been shown to be involved in tumorigenesis through different signaling pathways, yet how the deregulation affects cancer therapeutics remains elusive. Here we showed that overexpression of Aurora-A rendered esophageal cancer cells resistance to cisplatin (CDDP) by inhibiting apoptosis. By using an apoptosis array, we identified a downstream gene, p21-activated kinase 7 (PAK7). PAK7 was upregulated by Aurora-A overexpression at both mRNA and protein levels. Importantly, the expression levels of Aurora-A and PAK7 were correlated in ESCC primary samples. Chromatin immunoprecipitation (ChIP) assay revealed that binding of E2F1 to the promoter of PAK7 was significantly enhanced upon Aurora-A activation, and knockdown of transcription factor E2F1 decreased PAK7 expression, suggesting that Aurora-A regulated PAK7 through E2F1. Furthermore, we demonstrated that PAK7 knockdown led to increased apoptosis, and Aurora-A-induced resistance to CDDP was reversed by downregulation of PAK7, suggesting PAK7 was a downstream player of Aurora-A that mediated chemoresistance of ESCC cells to CDDP. Our data suggest that PAK7 may serve as an attractive candidate for therapeutics in ESCC patients with Aurora-A abnormality.

Establishment of a New Ovarian Cancer Cell Line CA5171

A new cell line, CA5171, derived from a chemotherapy-naive, high-grade undifferentiated ovarian carcinoma was established and characterized. The CA5171 cells presented with cobblestone morphology and a doubling time of 24 hours. Gene mutation analysis showed that the cells belonged to the type II ovarian cancer pathway with mutations of PIK3CA, PTEN, and TP53. Single-nucleotide polymorphism array analysis showed no homozygous gene deletion; however, several loci of gene copy number gains were noted in chromosome 1, 2, 5, 9, 10, 12, 15, 16, 20, and X. The in vitro and in vivo experiments showed that the cells were sensitive to paclitaxel and doxorubicin, but resistant to cisplatin. The cells also presented epithelial-mesenchymal transition properties that may have been related to their invasion and migration potential. The CA5171 cells show the potential as a new cell line for studies on epithelial ovarian carcinoma.

Republished: tracing PAKs from GI inflammation to cancer

P-21 activated kinases (PAKs) are effectors of Rac1/Cdc42 which coordinate signals from the cell membrane to the nucleus. Activation of PAKs drive important signalling pathways including mitogen activated protein kinase, phospoinositide 3-kinase (PI3K/AKT), NF-κB and Wnt/β-catenin. Intestinal PAK1 expression increases with inflammation and malignant transformation, although the biological relevance of PAKs in the development and progression of GI disease is only incompletely understood. This review highlights the importance of altered PAK activation within GI inflammation, emphasises its effect on oncogenic signalling and discusses PAKs as therapeutic targets of chemoprevention.

Aberrant methylation of ERBB pathway genes in sporadic colorectal cancer

The ErbB signalling network plays a crucial role in the growth and progression of several cancers, including colorectal cancer (CRC), and includes potentially drug-targetable genes. Oncogenic activation of the ErbB pathway by mutations and focal amplifications have emerged recently as an important predictive marker of the prognosis of CRC patients. However, in contrast to genetic events, little is known about epigenetic alternations of ErbB-associated genes and their impact on gene expression. Genome-wide methylation in sporadic CRCs (n = 12) paired with adjacent normal tissues have been previously analysed by Illumina Infinium HumanMethylation27 (HM27) at 27,578 CpG sites. For confirmation of our initial genome-wide analysis, we used a published HM27 dataset (GSE25062). Subsequently, CpG island methylation of selected ErbB pathway-associated genes was assessed on 233 CRC samples using methylation-sensitive polymerase chain reaction (MS-PCR) and analysed along with various genetic factors associated with CRC [epigenotype, BRAF and KRAS mutations, microsatellite instability (MSI)]. Methylation and expression integration was performed using published datasets including 25 pairs of CRC and normal colon tissues (GSE25062 and GSE25070), and confirmed with real-time PCR. Our previous microarray-based genome-wide DNA methylation analysis of 12 CRCs revealed that four ErbB-associated genes (PIK3CD, PKCΒ, ERBB4, ) were differentially methylated in CRCs. This was further confirmed by statistical re-analysis of an HM27 dataset (GSE25062). Frequent methylation at these loci in tumours was subsequently confirmed by MS-PCR (63 %, 43 %, 43 % and 92 %, respectively). Hypermethylation of PKCΒ associated with KRAS mutation (p = 0.04), whereas hypermethylation of ERBB4 associated with high-methylation epigenotypes (HME), BRAF mutation and MSI (p = 0.001, 0.002 and 0.0002, respectively). One of the four analysed genes (PKCΒ) was significantly downregulated in CRC tissue, as revealed by real-time PCR and re-analysis of the GSE25062 and GSE25070 datasets. After careful re-analysis of published methylation and expression data, we conclude that methylation of ERBB4, PAK7 and PIK3CD has no functional role in CRC carcinogenesis. In contrast, methylation seems to have a potential impact on the biology of colorectal tumours by negatively modulating the expression of PKCΒ. Importantly, the relationship between DNA methylation of PKCΒ and gene expression may warrant further attention in the context of colon cancer chemoprevention and anti-cancer therapy.

PAK signaling in cancer

Transformation of a normal cell to a cancer cell is caused by mutations in genes that regulate proliferation, apoptosis, and invasion. Small GTPases such as Ras, Rho, Rac and Cdc42 orchestrate many of the signals that are required for malignant transformation. The p21-activated kinases (PAKs) are effectors of Rac and Cdc42. PAKs are a family of serine/threonine protein kinases comprised of six isoforms (PAK1–6), and they play important roles in cytoskeletal dynamics, cell survival and proliferation. They act as key signal transducers in several cancer signaling pathways, including Ras, Raf, NFκB, Akt, Bad and p53. Although PAKs are not mutated in cancers, they are overexpressed, hyperactivated or amplified in several human tumors and their role in cell transformation make them attractive therapeutic targets. This review discusses the evidence that PAK is important for cell transformation and some key signaling pathways it regulates. This review primarily discusses Group I PAKs (PAK1, PAK2 and PAK3) as Group II PAKs (PAK4, PAK5 and PAK6) are discussed elsewhere in this issue (by Minden).

PAK4-6 in cancer and neuronal development

PAKs 4, 5 and 6 are members of the group B family of p21-activated kinases. Among this group, PAK4 has been most extensively studied. While it has essential roles in embryonic development, in adults high levels of PAK4 are frequently associated with cancer. PAK4 is overexpressed in a variety of cancers, and the Pak4 gene is amplified in some cancers. PAK4 overexpression is sufficient to cause oncogenic transformation in cells and in mouse models. The tight connection between PAK4 and cancer make it a promising diagnostic tool as well as a potential drug target. The group B PAKs also have important developmental functions. PAK4 is important for many early developmental processes, while PAK5 and PAK6 play roles in learning and memory in mice. This chapter provides an overview of the roles of the group B PAKs in cancer as well as development, and includes a discussion of PAK mediated signaling pathways and cellular functions.

p21-activated kinase 7 is an oncogene in human osteosarcoma

p21-activated kinase 7 (PAK7), also named as PAK5, is a member of Rac/Cdc42-associated Ser/Thr protein kinases. It is overexpressed in some types of cancer such as colorectal and pancreatic cancers. However, the expression status and biological function of PAK7 in osteosarcoma are still ambiguous. To evaluate the expression levels of PAK7 in osteosarcoma tissues and cell lines, immunohistochemistry was used. To investigate the role of PAK7 in cell proliferation, apoptosis and tumorigenicity in vitro and vivo, a recombinant lentivirus expressing PAK7 short hairpin RNA (Lv-shPAK7) was developed and transfected into Saos-2 cells. The silencing effect of PAK7 was confirmed by quantitative real-time PCR (qRT-PCR) and Western blot technique. PAK7 was overexpressed in osteosarcoma tissue and cell line. By knocking-down of PAK7, the proliferation and colony formation of Saos-2 cells were inhibited and apoptosis enhanced significantly. The in vivo tumorigenic ability in xenograft model of Saos-2 cells was also notably inhibited when PAK7 was knocked down. Our results imply that PAK7 promotes cell proliferation and tumorigenesis and may be an attractive candidate for the therapeutic target of osteosarcoma.

The role of p21-activated kinases in hepatocellular carcinoma metastasis

The p21-activated kinases (PAKs) are downstream effectors of the Rho family small GTPases as well as a wide variety of mitogenic factors and have been implicated in cancer formation, development and metastasis. PAKs phosphorylate a wide spectrum of substrates to mediate extracellular signals and regulate cytoskeletal remodeling, cell motility and survival. In this review, we aim to summarize the findings regarding the oncogenic role and the underlying mechanisms of PAKs signaling in various cancers, and in particular highlight the prime importance of PAKs in hepatocellular carcinoma (HCC) progression and metastasis. Recent studies exploring the potential therapeutic application of PAK inhibitors will also be discussed.

Tracing PAKs from GI inflammation to cancer

P-21 activated kinases (PAKs) are effectors of Rac1/Cdc42 which coordinate signals from the cell membrane to the nucleus. Activation of PAKs drive important signalling pathways including mitogen activated protein kinase, phospoinositide 3-kinase (PI3K/AKT), NF-κB and Wnt/β-catenin. Intestinal PAK1 expression increases with inflammation and malignant transformation, although the biological relevance of PAKs in the development and progression of GI disease is only incompletely understood. This review highlights the importance of altered PAK activation within GI inflammation, emphasises its effect on oncogenic signalling and discusses PAKs as therapeutic targets of chemoprevention.

An oncogenic kinase: putting PAK5 forward

INTRODUCTION

Overexpression of p21-activated kinase 5 (PAK5) is discovered in many tumors, probably due to its regulation in cytoskeleton, antiapoptosis and proliferation. A better understanding of the modulation mechanisms of PAK5 is needed for the development of tumor treatment where current therapeutics is inadequate.

AREAS COVERED

This review discusses the current understanding of PAK5 functions as an oncogenic kinase in tumor cellular regulation. Mechanisms of action and molecular pathways involved in cytoskeleton regulation, antiapoptosis and proliferation of tumors are discussed.

EXPERT OPINION

PAKs are serine/threonine kinases and downstream effectors for Cdc42 and Rac, the subfamilies of Rho small GTPases. PAK5 shares sequence identities in p21-GTPase-binding domain and kinase domain and is completely different in other regions compared with other PAKs. Overexpression of PAK5 has been found in several tumors, probably due to its contribution to proliferation, cytoskeleton and anti-apoptosis. Additional regulation mechanisms which are independent of Rho GTPases also indicate that PAK5 functions as a special signal molecule in cellular signaling pathways of tumor progression.

P21 activated kinases: structure, regulation, and functions

The p21 activated kinases (Paks) are well known effector proteins for the Rho GTPases Cdc42 and Rac. The Paks contain 6 members, which fall into 2 families of proteins. The first family consists of Paks 1, 2, and 3, and the second consists of Paks 4, 5, and 6. While some of the Paks are ubiquitously expressed, others have more restrictive tissue specificity. All of them are found in the nervous system. Studies using cell culture, transgenic mice, and knockout mice, have revealed important roles for the Paks in cytoskeletal organization and in many aspects of cell growth and development. This review discusses the basic structures of the Paks, and their roles in cell growth, development, and in cancer.

Expression and prognostic significance of p21-activated kinase 6 in hepatocellular carcinoma

BACKGROUND

p21-activated protein kinase (PAK) 6 is a serine-threonine kinase belonging to the PAK family. Previous studies have indicated that abnormal expressions of PAK1, PAK2, and PAK5 played critical roles in hepatocellular carcinoma (HCC). Recent studies suggested that deregulation of PAK6 expression played an important role in oncogenesis. To explore the potential roles of PAK6 in HCC, expression of PAK6 was detected in human HCC specimens.

METHODS

Immunohistochemistry and Western blot analysis were performed for PAK6 in 121 HCC samples. The data were correlated with clinicopathologic features. The univariate and multivariate survival analyses were also performed to determine their clinical prognostic significance.

RESULTS

PAK6 was overexpressed in HCC as compared with the adjacent noncancerous liver tissues. High expression of PAK6 was associated with Edmondson-Steiner grade (P = 0.006) and number of tumor nodules (P < 0.001), and PAK6 was positively correlated with proliferation marker Ki-67 (P < 0.01). Univariate analysis suggested that PAK6 expression was associated with poor prognosis (P < 0.001). Multivariate analysis indicated that PAK6 and Ki-67 protein expressions were independent prognostic markers for HCC (P = 0.0245 and 0.0331, respectively).

CONCLUSIONS

Our results suggest that PAK6 overexpression is involved in the pathogenesis of HCC; it may be an independent poor prognostic factor for HCC.

Role of p-21-activated kinases in cancer progression

The p-21-activated kinases (PAKs) are downstream effectors of Rho GTPases Rac and Cdc42. The PAK family consists of six members which are segregated into two subgroups (Group I and Group II) based on sequence homology. Group I PAKs (PAK1-3) are the most extensively studied but there is increasing interest in the functionality of Group II PAKs (PAK4-6). The PAK family proteins are thought to play an important role in many different cellular processes, some of which have particular significance in the context of cancer progression. This review explores established and more recent data, linking the PAK family kinases to cancer progression including expression profiles, evasion of apoptosis, promotion of cell survival, and regulation of cell invasion. Finally, we discuss attempts to therapeutically target the PAK family and outline the major obstacles that still need to be overcome.

P21-activated kinase 5 plays essential roles in the proliferation and tumorigenicity of human hepatocellular carcinoma

AIM

To investigate the roles of P21-activated kinase 5 (PAK5) in proliferation and tumorigenicity of human hepatocellular carcinoma (HCC).

METHODS

HCC and matched paraneoplastictis tissue samples were obtained from 30 patients. Human HCC cell lines SMMC7721, HepG2, Hep3B, SK-HEP-1, Huh-7, and liver cell line HL-7702 were examined. The expression of PAK5 gene was studied using real-time qPCR and Western blotting. Cell proliferation was quantified with the MTT assay. Cell cycle was analyzed with flow cytometry. The tumorigenicity of Lv-shRNA-transfected HepG2 cells was evaluated in BALB/cA nude mice.

RESULTS

The mRNA level of PAK5 was significantly higher in 25 out of 30 HCC samples compared to the matched paraneoplastic tissues. The HCC cell lines showed varying expression of PAK5 protein, and the highest level was found in the HepG2 cells. PAK5 gene silencing in HepG2 cells markedly reduced the cell proliferation and colony formation, and induced cell cycle arrest in the G1 phase. Furthermore, PAK5 gene silencing suppressed the tumor formation in nude mice, and significantly decreased the expression of HCC-related genes Cyclin D1 and beta-catenin.

CONCLUSION

PAK5 may play essential roles in the initiation and progression of human HCC. Thus, it may be an effective therapeutic target or perhaps serve as a clinical diagnostic or prognostic marker in human HCC.