Kinase P21-activated Kinase 1 Research Articles

Activation of oncogenic signaling kinase PAK1 by ionising radiation confers an aggressive phenotype in head and neck squamous cell carcinoma

Head and neck squamous cancers are very aggressive tumors often diagnosed in late stages with poor prognosis. HNSCCs are usually treated by a course of radiation (IR) therapy and followed by surgery. These treatment regimens fail to bring a complete response. Molecular signatures in tumors are attributed to this response and an improved understanding of the signaling events could offer new avenues for therapy. Here, we show that P21 activated kinase-1 (PAK1) - an oncogenic signaling serine/threonine kinase, is activated upon exposure to IR and this leads to an accelerated tumorigenic character in HNSCC cells. Our results show that PAK1 is highly expressed in HNSCC cell lines, as compared to normal buccal mucosa cells and when HNSCC cells were exposed to IR, they show activated PAK1 and an aggressive phenotype as determined by in vitro functional assays. PAK1 levels were elevated in HNSCC as compared to adjacent normal oral tissues and our results also show convincing evidence of activated PAK1 in patient tumor samples of post- IR treatment as compared to pre-IR treatment and is associated with poor survival. Pak1 Knockout (KO) clones in HNSCC cells showed that they were more sensitive to IR as compared to wild type (wt) cells. This altered sensitivity to IR was attributed to enhanced DNA damage response modulated by PAK1 in cells. Overall, our results suggest that PAK1 expression in HNSCC could be a critical determinant in IR therapy response and silencing PAK1 is likely to be a treatment modality to improve clinical outcomes.

PAK4 kinase as a potential therapeutic target of the transcription factor p63-meditated squamous cell carcinomas of the pancreas.

This study was undertaken to better understand the pathogenesis of squamous cell carcinoma (SCC) of the pancreas and to determine if inhibiting the p21-activated kinase 4 (PAK4) activity could be used for treating pancreatic SCCs. Here are the context of the research and preliminary results: Although significant research has been done on adenocarcinoma of the pancreas, the current understanding of pancreatic SCCs remains limited, and there is no known cure for it. We established a mouse model of pancreatic SCCs by over-expressing the transcription factor p63 in the pancreatic ductal epithelial-specific manner. Our working hypothesis was that dysregulation of p63-mediate transcriptional networks can lead to the development of pancreatic SCCs. As the stability of p63 is regulated at the protein level by phosphorylation, we searched for kinase that stabilizes p63 and identified PAK4 kinase. Although previous studies have shown that PAK4 is frequently overexpressed in ductal adenocarcinoma of the pancreas, the involvement of PAK4 in the pathogenesis of pancreatic SCCs remained unclear. We have demonstrated that suppression of the PAK4 kinase activity by a small molecule inhibitor reduced p63 levels in cellular models of pancreatic SCCs, leading to the complete suppression of their proliferation in vitro. These results indicate that PAK4 kinase can serve as a novel therapeutic target for some pancreatic SCCs and that PAK4-mediated stabilization/upregulation of the transcription factor p63 can be the key molecular event underlying the pathogenesis of pancreatic SCCs. We will use our mouse models in future studies to determine if administration of the PAK4 inhibitor in vivo can be used as an effective therapy for the treatment and prevention of the development of this most dangerous cancer subtype in human cancers.

Blocking PAK1 kinase activity promotes the differentiation of acute megakaryocytic leukemia cells and induces their apoptosis

Objective: To investigate the effect of blocking P21 activated kinase 1 (PAK1) activity on the proliferation, differentiation, and apoptosis of acute megakaryocytic leukemia (AMKL) cell lines (CHRF and CMK) . Methods: Cell counts were used to detect the effects of PAK1 inhibitors (IPA-3 and G5555) on AMKL cell proliferation inhibition and colony formation, and flow cytometry was used to detect its effects on AMKL cell cycle. The effect of PAK1 inhibitor on the expression of cyclin D1 and apoptosis-related protein Cleaved caspase 3 was detected using Western blot, while interference with the protein expression level of PAK1 in AMKL cells was assessed using lentivirus-mediated shRNA transfection technology. Flow cytometry was used to detect the effects of knockdown of PAK1 kinase activity on the ability of polyploid DNA formation and cell apoptosis in AMKL cells. Results: PAK1 inhibitors inhibited the proliferation of AMKL cells in a dose-dependent manner and reduced the ability of cell colony formation, and the difference was statistically significant when compared with the control group (P<0.05) . Moreover, they also reduced the percentage of AMKL cells in S phase, and Western blot detection showed that the expression levels of phosphorylated PAK1 and cyclin D1 decreased significantly. Finally, PAK1 inhibitors induced AMKL cell apoptosis by up-regulating Cleaved caspase 3 and showed different abilities to increase the content of polyploid DNA in megakaryocytes. Only high concentrations of IPA-3 and low doses of G5555 increased the number of polyploid megakaryocytes, while knockdown of PAK1 kinase activity promoted AMKL cell differentiation and increased the apoptosis rate. Conclusion: PAK1 inhibitor significantly arrests AMKL cell growth and promotes cell apoptosis. Knocking down the expression of PAK1 promotes the formation of polyploid DNA and induces AMKL cell apoptosis. The above findings indicate that inhibiting the activity of PAK1 may control AMKL effectively.

Lights, Camera, PAKtion: Design and Engineering of a Subcellular Targeting Optogenetic PAK1 Kinase and Sensor

p21‐activated kinase 1 (PAK1) is a major ‘pathogenic kinase’ that directs cell motility, cytoskeletal remodeling and has been shown to function as a downstream regulator for various cancer signaling cascades. Such biological roles require a tight spatial and kinetic control of its localization and activity. Unfortunately, the spatiotemporal nature of these pathways renders the application of conventional tools inadequate for studying localized PAK1 induced cell behavior. Therefore, we have designed and engineered an optogenetic analog of PAK1 to address the difficulties in assessing PAK1 intracellular activity.Optogenetics is a powerful light‐triggered technology that, via control of protein biochemical activity, allows for the spatial and temporal control over a variety of biological processes. We developed an engineering strategy to construct a genetically expressed, light‐responsive optogenetic analog of PAK1 (optoPAK1) and demonstrated that, upon illumination, optoPAK1 migrates to specified intracellular sites. OptoPAK1 was designed to function independently of endogenous biochemical regulation in a constitutively active manner with minimal activity in the dark state. We employed the improved light‐induced dimer (iLid) system as a means to recruit and photoactivate the protein analog at discrete subcellular domains. Furthermore, we designed intracellular spatially segregated reporters of optoPAK1 activity and preliminary data displayed that optoPAK1 phosphorylates these reporters in a light‐dependent fashion. Taken together, optoPAK1 and its corresponding biosensor offer the opportunity to appropriately study the relationship between PAK1 compartmentalized biochemical activity and cell behavior.

Natural Compound Shikonin Is a Novel PAK1 Inhibitor and Enhances Efficacy of Chemotherapy against Pancreatic Cancer Cells.

Shikonin is the main component of root extracts from the Chinese herbal medicine Lithospermum erythrorhizon, which is commonly used for the treatment of various diseases including cancer. Previous research showed that shikonin suppressed pancreatic cancer growth; nevertheless, its molecular targets and mechanisms have not been elucidated. This study aimed to investigate the interaction and regulatory mechanisms of shikonin on its potential target p21-activated kinase 1 (PAK1). Through a labchip-based screening method, shikonin was identified as a potential bioactive PAK1 inhibitor. Molecular docking technology was used to detect the interaction sites of shikonin and PAK1 kinase. Western blot was performed to validate the mechanism. MTT and flow cytometry were practiced to investigate the effect of shikonin against pancreatic cancer cells. The results show that shikonin significantly inhibited the activity of PAK1 kinase with IC50 value of 7.252 ± 0.054 μM. Molecular docking studies showed that shikonin binds to the ATP-binding pocket of the PAK1 kinase domain. Moreover, shikonin inhibited PAK1 activation and its downstream signaling pathway proteins, while reducing proliferation and inducing apoptosis of pancreatic cancer cells. Further studies showed that the treatment of shikonin sensitized pancreatic cancer cells to chemotherapeutic drugs. These results suggest that shikonin, a potential natural inhibitor targeting PAK1 kinase, has promising potent applications in the treatment of pancreatic cancer and chemotherapy sensitization.

Nuplazid suppresses esophageal squamous cell carcinoma growth in vitro and in vivo by targeting PAK4

BackgroundDue to the high recurrence and low 5-year survival rates of esophageal squamous cell carcinoma (ESCC) after treatment, the discovery of novel drugs for recurrence chemoprevention is of particular importance.MethodsWe screened the FDA-approved drug library and found that Nuplazid, an atypical antipsychotic that acts as an effective 5-HT 2 A receptor inverse agonist, could potentially exert anticancer effects in vitro and in vivo on ESCC.ResultsPull-down results indicated that Nuplazid binds with p21-activated kinase 4 (PAK4), and a kinase assay showed that Nuplazid strongly suppressed PAK4 kinase activity. Moreover, Nuplazid exhibited inhibitory effects on ESCC in vivo.ConclusionsOur findings indicate that Nuplazid can suppress ESCC progression through targeting PAK4.

Theoretical Evaluation of 5, 6-Diaroylisoindoline-1,3-dione as Potential Carcinogenic Kinase PAK1 Inhibitor: DFT Calculation, Molecular Docking Study and ADMET Prediction

Background: The carcinogenic kinase PAK1 (p21-activated kinase 1) is associated with the progression of many disorders, including Alzheimer's disease, various cancers, type-2 diabetes and hypertension. Although few synthetic PAK1 inhibitors and herbal therapeutics, such as propolis and curcumin, are available in the market, a comprehensive remedy of PAK1 related ailments is still not studied in detail. Recently, several phthalimide-metal complexes (viz. Λ-FL172, Λ-FL411, called optically active octahedral ruthenium phthalimide complex) were shown as poor inhibition potency toward PAK1. However, for a full understanding of the inhibition of PAK1 about phthalimide analogues, this study has been designed. Methods: This manuscript presents density functional theory (DFT) based computational approaches of aryl derivatives of phthalimide. The DFT was used to calculate the equilibrium geometries, thermodynamic analysis, dipole moment, polarizability, electrostatic potential map, Mulliken, Hirshfeld, NBO population analysis, frontier molecular orbital contribution, reactivity descriptor, Fukui function analysis of phthalimide derivatives. Molecular docking and ADMET prediction were also performed. Result: The phthalimide derivatives were subjected to molecular docking studies, and binding affinities ranging from -7.3 to -7.7 kcal/mol against PAK1 kinase were determined. The docked ligands demonstrated stronger hydrogen bonding, electrostatic interactions, and hydrophobic interactions with PAK1 kinase. The magnitude of these contacts usually related with bond lengths and attraction forces. The derivatives with an elevated docking score were chosen against ADMET in silico, and they have an excellent oral bioavailability without observed carcinogenesis or mutagenicity affect. Conclusion: These results reveal that these phthalimide derivatives might be potential inhibitors for the protein kinase PAK1.

A computational approach to explore and identify potential herbal inhibitors for the p21-activated kinase 1 (PAK1)

The oncogenic kinase PAK1 (p21-activated kinase 1) is involved in developing many diseases including cancers, neurofibromatosis, Alzheimer's disease, diabetes (type 2), and hypertension. Thus, it is thought to be a prominent therapeutic target, and its selective inhibitors have a huge market potential. Recently, herbal PAK1 inhibitors have gained immense interest over synthetic ones mainly due to their non-toxic effects. Till date, many herbal compounds have been suggested to inhibit PAK1, but their information on selectivity, bioavailability, ADMET (absorption, distribution, metabolism, excretion, and toxicity) properties, and molecular interactions with PAK1 has not been explored. Hence, this study was designed with computational approaches to explore and identify the best herbal PAK1-blockers showing good ADMET properties, druggable features and binding affinity with PAK1. Herbal inhibitors reported here were initially filtered with Lipinski’s rule of five (RO5). Then, molecular docking between these inhibitors and PAK1 catalytic sites was performed using AutoDock Vina and GOLD suite to determine the binding affinity and interactions. Finally, 200 ns molecular dynamics (MD) simulations on three top-ranked inhibitors including cucurbitacin I (C-I), nymphaeol A (NA), and staurosporine (SPN) were carried out. The binding free energies and interactions revealed that NA can strongly bind with the PAK1 catalytic cleft. PASS prediction and ADMET profiling supported that NA is appeared to be a more selective and safer inhibitor than C-I and SPN. These results conform to the previous experimental evidences, and therefore, NA from Okinawa propolis could be a promising inhibitor for treating PAK1-dependent illnesses.Communicated by Ramaswamy H. Sarma

Strategy and validation of a structure-based method for the discovery of selective inhibitors of PAK isoforms and the evaluation of their anti-cancer activity

p21 activated kinase 4 (PAK4), which belongs to the serine/threonine (Ser/Thr) protein kinase family, is a representative member of the PAK family and plays a significant role in multiple processes associated with cancer development. In this study, structure-based virtual screening was performed to discover novel and selective small molecule scaffolds, and a 6-hydroxy-2-mercapto-3-phenylpyrimidin-4(3H)-one-based compound (SPU-106, 14#) was identified as an effective PAK4 inhibitor. By combining both a molecular docking study and molecular dynamics (MD) simulation strategies, the binding mode was determined in the PAK4 site. The SPU-106 compound could efficiently and selectively bind to the PAK4 kinase domain at an IC50 of 21.36 μM according to the kinase analysis. The designed molecular probe demonstrated that SPU-106 binds to the kinase domain in the C-terminus of PAK4. Further investigation revealed that the SPU-106 had a strong inhibitory effect on the invasion of SGC7901 cells but without any cytotoxicity. The western blot analysis indicated that the compound potently inhibited the PAK4/LIMK1/cofilin and PAK4/SCG10 signaling pathways. Thus, our work shows the successful application of computational strategies for the discovery of selective hits, and SPU-106 may be an effective PAK4 inhibitor for further development as an antitumor agent.

Cytotoxic Desulfated Saponin from Holothuria atra Predicted to Have High Binding Affinity to the Oncogenic Kinase PAK1: A Combined In Vitro and In Silico Study.

Sea cucumbers have long been utilized in foods and Asiatic folk medicines for their nutritive and health benefits. Herein, three sea cucumber species were investigated and Holothuria atra showed the highest cytotoxicity among these. Next, a desulfated saponin, desulfated echinoside B (DEB), was purified from H. atra through bioassay-guided fractionation. LC-ESI-MS (Liquid chromatography-electrospray ionization mass spectrometry) analysis also showed H. atra to be a rich source of saponins. DEB showed cytotoxicity on cancer cells with IC50 values of 0.5⁻2.5 µM, and on brine shrimps with an IC50 value of 9.2 µM. In molecular docking studies, DEB was found to bind strongly with the catalytic domain of PAK1 (p21-activated kinase 1) and it showed binding energy of -8.2 kcal/mol compared to binding energy of -7.7 kcal/mol for frondoside A (FRA). Both of them bind to the novel allosteric site close to the ATP-binding cleft. Molecular dynamics (MD) simulation demonstrated that DEB can form a more stable complex with PAK1, remaining inside the allosteric binding pocket and forming the maximum number of hydrogen bonds with the surrounding residues. Moreover, important ligand binding residues were found to be less fluctuating in the DEB-PAK1 complex than in the FRA-PAK1 complex throughout MD simulation. Our experimental and computational studies showed that both DEB and FRA can act as natural allosteric PAK1 inhibitors and DEB appeared to be more promising than FRA.

Anti-cancer effect of novel PAK1 inhibitor via induction of PUMA-mediated cell death and p21-mediated cell cycle arrest

Hyper-activation of PAK1 (p21-activated kinase 1) is frequently observed in human cancer and speculated as a target of novel anti-tumor drug. In previous, we also showed that PAK1 is highly activated in the Smad4-deficient condition and suppresses PUMA (p53 upregulated modulator of apoptosis) through direct binding and phosphorylation. On the basis of this result, we have tried to find novel PAK1-PUMA binding inhibitors. Through ELISA-based blind chemical library screening, we isolated single compound, IPP-14 (IPP; Inhibitor of PAK1-PUMA), which selectively blocks the PAK1-PUMA binding and also suppresses cell proliferation via PUMA-dependent manner. Indeed, in PUMA-deficient cells, this chemical did not show anti-proliferating effect. This chemical possessed very strong PAK1 inhibition activity that it suppressed BAD (Bcl-2-asoociated death promoter) phosphorylation and meta-phase arrest via Aurora kinase inactivation in lower concentration than that of previous PAK1 kinase, FRAX486 and AG879. Moreover, our chemical obviously induced p21/WAF1/CIP1 (Cyclin-dependent kinase inhibitor 1A) expression by releasing from Bcl-2 (B-cell lymphoma-2) and by inhibition of AKT-mediated p21 suppression. Considering our result, IPP-14 and its derivatives would be possible candidates for PAK1 and p21 induction targeted anti-cancer drug.

Hair Growth Promoting and Anticancer Effects of p21-activated kinase 1 (PAK1) Inhibitors Isolated from Different Parts of Alpinia zerumbet.

PAK1 (p21-activated kinase 1) is an emerging target for the treatment of hair loss (alopecia) and cancer; therefore, the search for PAK1 blockers to treat these PAK1-dependent disorders has received much attention. In this study, we evaluated the anti-alopecia and anticancer effects of PAK1 inhibitors isolated from Alpinia zerumbet (alpinia) in cell culture. The bioactive compounds isolated from alpinia were found to markedly promote hair cell growth. Kaempferol-3-O-β-d-glucuronide (KOG) and labdadiene, two of the isolated compounds, increased the proliferation of human follicle dermal papilla cells by approximately 117%–180% and 132%–226%, respectively, at 10–100 μM. MTD (2,5-bis(1E,3E,5E)-6-methoxyhexa-1,3,5-trien-1-yl)-2,5-dihydrofuran) and TMOQ ((E)-2,2,3,3-tetramethyl-8-methylene-7-(oct-6-en-1-yl)octahydro-1H-quinolizine) showed growth-promoting activity around 164% and 139% at 10 μM, respectively. The hair cell proliferation induced by these compounds was significantly higher than that of minoxidil, a commercially available treatment for hair loss. Furthermore, the isolated compounds from alpinia exhibited anticancer activity against A549 lung cancer cells with IC50 in the range of 67–99 μM. Regarding the mechanism underlying their action, we hypothesized that the anti-alopecia and anticancer activities of these compounds could be attributed to the inhibition of the oncogenic/aging kinase PAK1.

Activated-PAK4 predicts worse prognosis in breast cancer and promotes tumorigenesis through activation of PI3K/AKT signaling.

The p21-activated kinase 4 (PAK4) is sufficient to transform noncancerous mammary epithelial cells and to form tumors in the mammary glands of mice. The accumulated information suggests that PAK4 might be an oncogenic protein in breast cancer. In this study, we sought to identify the role for PAK4 in breast cancer progression. Immunohistochemical study revealed that high PAK4 expression is associated with larger tumor size, lymph node metastasis, and advanced stage cancer in 93 invasive breast carcinoma patients. Moreover, high PAK4 expression was significantly associated with poor overall and disease-free survival. PAK4 remained an independent adverse prognosticator after univariate and multivariate analysis. Ectopic expression of wild-type PAK4 in MDA-MB-231 cells activated PI3K/AKT signaling and resulted in the enhancement of the cell proliferation, migration, and invasion, whereas PAK4-induced effects were blocked by the PAK4 kinase inhibitor PF- 3758309, PAK4 siRNAs or the PI3K inhibitor LY294002. Furthermore, a kinase-active PAK4 (S474E) strongly induced PI3K/AKT activation, and promoted proliferation, migration and invasion in breast cancer cells. A kinase-inactive PAK4 KD (K350A/K351A) did partially upregulate PI3K/AKT, and promoted invasive phenotype. Taken together, these findings suggest that PAK4-activated PI3K/AKT signaling is both kinase-dependent and -independent, which contributes to breast cancer progression. Thus, our results imply that dual inhibition of PAK4 and PI3K/AKT signaling might be a potential therapeutic approach for breast cancer therapy.

Abstract PD3-04: PAK-1 amplified breast cancer cell lines are preferentially sensitive to PAK inhibition with G-5555

Abstract The small GTP-binding proteins Rac1 and Cdc42 stimulate activity of the serine/threonine kinase p21-activated kinase-1 (PAK-1) to drive growth factor signaling networks and Ras-driven tumorigenesis. Genomic amplification and over-expression of PAK1 are prevalent in luminal breast cancer and correlate with poor clinical outcome. Here we use a novel and selective small molecule inhibitor, G-5555, of the group I PAKs (PAK1, 2, and 3) to evaluate the importance of PAK1 in promoting growth of PAK1 amplified breast cancer cells. Cell lines with amplification of PAK1 were found to be more sensitive to PAK1 inhibition than non-amplified cell lines. Additionally, reverse phase protein array (RPPA) was used to assess the effects of PAK1 inhibition on a wide range of signaling pathways in both amplified and non-amplified cell lines. Reduced levels of phosphorylation of MEK S298 was observed in all cell lines exposed to G-5555 irrespective of amplification status, consistent with PAK1 inhibition in these cell lines. However, modulation of this downstream PAK1 substrate did not correlate with inhibition of cell proliferation or induction of cell death. Cell lines that showed inhibition of proliferation in response to G-5555 also showed enhanced levels of cell death along with apoptosis. Moreover, G-5555 reduced tumor growth in the PAK1 amplified MDA-MB-175 xenograft tumor model. Finally, we compared the in vitro activity of G-5555 with palbociclib, a recently approved inhibitor of the cyclin-dependent kinases CDK4 and CDK6, in PAK1 amplified luminal breast cancer cell lines. Our data supports PAK1 as an attractive target in PAK1 amplified cells and tumors and suggests that inhibiting PAK1 rather than CDK4/6 in this context may be a more attractive therapeutic strategy. Citation Format: Ong CC, Blackwood E, Jakubiak D, Daemen A, Ramaswamy S, Heise C, Schmidt M, Sanders L, Wilson TR, Huw L, Ndubaku C, Rudolph J, Hoeflich KP, Friedman L, O'Brien T. PAK-1 amplified breast cancer cell lines are preferentially sensitive to PAK inhibition with G-5555. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr PD3-04.

(-)-β-hydrastine suppresses the proliferation and invasion of human lung adenocarcinoma cells by inhibiting PAK4 kinase activity.

(-)-β-hydrastine is one of the main active components of the medicinal plant, Hydrastis canadensis, which is used in many dietary supplements intended to enhance the immune system. However, whether (-)-β-hydrastine affects the tumor signaling pathway remains unexplored. In the present study, we found that (-)-β-hydrastine inhibited the kinase activity of p21-activated kinase 4 (PAK4), which is involved in the regulation of cytoskeletal reorganization, cell proliferation, gene transcription, oncogenic transformation and cell invasion. In the present study, (-)-β-hydrastine suppressed lung adenocarcinoma cell proliferation by inhibiting expression of cyclin D1/D3 and CDK2/4/6, leading to cell cycle arrest at the G1 phase, in a PAK4 kinase-dependent manner. Moreover, inhibition of PAK4 kinase activity by (-)-β-hydrastine also promoted the early apoptosis of lung adenocarcinoma cells through the mitochondrial apoptosis pathway. In addition, (-)-β-hydrastine significantly suppressed the migration and invasion of human lung adenocarcinoma cells in conjunction with concomitant blockage of the PAK4/LIMK1/cofilin, PAK4/SCG10 and PAK4/MMP2 pathways. All of these data indicate that (-)-β-hydrastine, as a novel PAK4 inhibitor, suppresses the proliferation and invasion of lung adenocarcinoma cells. Taken together, these results provide novel insight into the development of a PAK4 kinase inhibitor and a potential therapeutic strategy for lung cancer.

P21-activated kinase 1 determines stem-like phenotype and sunitinib resistance via NF-κB/IL-6 activation in renal cell carcinoma.

The p21-activated kinase 1 (PAK1), a serine/threonine kinase that orchestrates cytoskeletal remodeling and cell motility, has been shown to function as downstream node for various oncogenic signaling pathways to promote cell proliferation, regulate apoptosis and accelerate mitotic abnormalities, resulting in tumor formation and invasiveness. Although alterations in PAK1 expression and activity have been detected in various human malignancies, its potential biological and clinical significance in renal cell carcinoma (RCC) remains obscure. In this study, we found increased PAK1 and phosphorylated PAK1 levels in tumor tissues according to TNM stage progression. Elevated phosphorylated PAK1 levels associated with progressive features and indicated unfavorable overall survival (OS) as an independent adverse prognosticator for patients with RCC. Moreover, PAK1 kinase activation with constitutive active PAK1 mutant T423E promoted growth, colony formation, migration, invasion and stem-like phenotype of RCC cells, and vice versa, in PAK1 inhibition by PAK1 kinase inactivation with specific PAK1 shRNA, dead kinase PAK1 mutant K299R or allosteric inhibitor IPA3. Stem-like phenotype due to sunitinib administration via increased PAK1 kinase activation could be ameliorated by PAK1 shRNA, PAK1 mutant K299R and IPA3. Furthermore, nuclear factor-κB (NF-κB)/interleukin-6 (IL-6) activation was found to be responsible for PAK1-mediated stem-like phenotype following sunitinib treatment. Both IL-6 neutralizing antibody and IPA3 administration enhanced tumor growth inhibition effect of sunitinib treatment on RCC cells in vitro and in vivo. Our results unraveled that oncogenic activation of PAK1 defines an important mechanism for maintaining stem-like phenotype and sunitinib resistance through NF-κB/IL-6 activation in RCC, lending PAK1-mediated NF-κB/IL-6 activation considerable appeal as novel pharmacological therapeutic targets against sunitinib resistance.

Hispidin and related herbal compounds from Alpinia zerumbet inhibit both PAK1-dependent melanogenesis in melanocytes and reactive oxygen species (ROS) production in adipocytes.

Recently several compounds from Okinawa plants including Alpinia zerumbet (alpinia) were shown to inhibit directly the oncogenic/ageing kinase PAK1 (p21-activated kinase 1). Furthermore, it was recently revealed that both PAK1 and PAK4 (p21-activated kinase 4) are equally essential for the melanogenesis in melanoma cells. Thus, in this study, we tested if several alpinia compounds inhibit the melanogenesis in melanoma (B16F10) cells, as well as the PAK1-dependent up-regulation of both reactive oxygen species (ROS) and nitric oxide (NO) in cultured adipocytes (3T3-L1) without any cytotoxicity. The effect of alpinia compounds on the melanogenesis was measured by both the melanin content and intracellular tyrosinase activity in melanoma cells treated with 3-isobutyl-1-methylxanthine (IBMX), a melanogenesis stimulating hormone. We found that (1E,3E,5E)-6-methoxyhexa-1,3,5-trien-1-yl)-2,5-dihydrofuran (MTD), 5,6-dehydrokawain (DK), labdadiene, hispidin and dihydro-5,6-dehydrokawain (DDK) at 50 μg/mL reduced the melanin content by 63-79%. The MTD, DK and hispidin, at 50 μg/mL, inhibited tyrosinase activity by 70-83% in melanoma cells. Among these compounds, labdadiene, MTD, (E)-2,2,3,3-Tetramethyl8-methylene-7-(oct-6-en-1-yl)octahydro-1H-quinolizine (TMOQ) and hispidin strongly inhibited the ROS production. Hispidin, labdadiene and MTD at 20 μg/mL inhibited NO production by over 70%. These findings altogether suggest that some of these alpinia compounds could be potentially useful for the prevention or treatment of hyperpigmentation and obesity.

Tyrosyl phosphorylated serine-threonine kinase PAK1 is a novel regulator of prolactin-dependent breast cancer cell motility and invasion.

Despite efforts to discover the cellular pathways regulating breast cancer metastasis, little is known as to how prolactin (PRL) cooperates with extracellular environment and cytoskeletal proteins to regulate breast cancer cell motility and invasion. We implicated serine-threonine kinase p21-activated kinase 1 (PAK1) as a novel target for PRL-activated Janus-kinase 2 (JAK2). JAK2-dependent PAK1 tyrosyl phosphorylation plays a critical role in regulation of both PAK1 kinase activity and scaffolding properties of PAK1. Tyrosyl phosphorylated PAK1 facilitates PRL-dependent motility via at least two mechanisms: formation of paxillin/GIT1/βPIX/pTyr-PAK1 complexes resulting in increased adhesion turnover and phosphorylation of actin-binding protein filamin A. Increased adhesion turnover is the basis for cell migration and phosphorylated filamin A stimulates the kinase activity of PAK1 and increases actin-regulating activity to facilitate cell motility. Tyrosyl phosphorylated PAK1 also stimulates invasion of breast cancer cells in response to PRL and three-dimensional (3D) collagen IV via transcription and secretion of MMP-1 and MMP-3 in a MAPK-dependent manner. These data illustrate the complex interaction between PRL and the cell microenvironment in breast cancer cells and suggest a pivotal role for PRL/PAK1 signaling in breast cancer metastasis.

Several herbal compounds in Okinawa plants directly inhibit the oncogenic/aging kinase PAK1.

The p21-activated kinase 1 (PAK1) is emerging as a promising therapeutic target, and the search for blockers of this oncogenic/aging kinase would be potentially useful for the treatment of various diseases/disorders in the future. Here, we report for the first time the anti-PAK1 activity of compounds derived from three distinct Okinawa plants. 5,6-Dehydrokawain (DK) and dihydro-5,6-dehydrokawain (DDK) from alpinia inhibited directly PAK1 more strongly than mimosine and mimosinol from leucaena. Cucurbitacin I isolated from bitter gourd/melon also exhibited a moderate anti-PAK1 activity. Hispidin, a metabolite of DK, strongly inhibited PAK1 with the IC50 = 5.7 μM. The IC50 of three hispidin derivatives (H1-3) for PAK1 inhibition ranges from 1.2 to 2.0 μM, while mimosine tetrapeptides [mimosine-Phe-Phe-Tyr (MFFY) and mimosine-Phe-Trp-Tyr (MFWY)] inhibit PAK1 at nanomolar level (IC50 of 0.13 and 0.60 μM, respectively). Thus, we hope these derivatives of hispidin and mimosine could be used as potential leading compounds for developing far more potent anti-PAK1 drugs which would be useful for clinical application in the future.

The role of protein kinase PAK1 in the regulation of estrogen-independent growth of breast cancer

The main goal of this work was to study the intracellular signaling pathways responsible for the development of hormone resistance and maintaining the autonomous growth of breast cancer cells. In particular, the role of PAK1 (p21-activated kinase 1), the key mitogenic signaling protein, in the development of cell resistance to estrogens was analyzed. In vitro studies were performed on cultured breast cancer cell lines: estrogen-dependent estrogen receptor (ER)-positive MCF-7 cells and estrogen-resistant ER-negative HBL-100 cells. We found that the resistant HBL-100 cells were characterized by a higher level of PAK1 and demonstrated PAK1 involvement in the maintaining of estrogen-independent cell growth. We have also shown PAK1 ability to up-regulate Snail1, one of the epithelial-mesenchymal transition proteins, and obtained experimental evidence for Snail1 importance in the regulation of cell proliferation. In general, the results obtained in this study demonstrate involvement of PAK1 and Snail1 in the formation of estrogen-independent phenotype of breast cancer cells showing the potential role of both proteins as markers of hormone resistance of breast tumors.