P21-activated Kinase 4 Knockdown Research Articles

AB042. Combined anti-PD-L1 and anti-VEGFR2 therapy promotes the antitumor immune response in glioblastoma multiforme by reprogramming tumor microenvironment.

Inhibitors of programmed cell death ligand 1 (PD-L1) and vascular endothelial growth factor receptor 2 (VEGFR2) are commonly used in the clinic, but they are beneficial for only a minority of glioblastoma multiforme (GBM) patients. GBM has significant immunosuppressive properties, and there are many immunosuppressive cells and dysfunctional effector T-cell in the tumor microenvironment (TME), which is one of the important reasons for the failure of clinical treatment of GBM. P21-activated kinase 4 (PAK4) is a threonine protein kinase, and as a pivotal immune suppressor in the TME. PAK4 knockdown attenuates vascular abnormalities and promotes T-cell infiltration. Using RNA sequencing (RNA-seq) technology, western blotting, and immunofluorescence, we identified changes in genes expression following VEGFR2 knockdown. The impact of anti-PD-L1 and anti-VEGFR2 on GBM cells apoptosis was assessed using coculture assays, western blotting, and flow cytometry. Additionally, the therapeutic efficacy of anti-PD-L1 and anti-VEGFR2 therapy was evaluated through in vivo experiments, immunohistochemistry, and immunofluorescence. Our studies revealed that VEGFR2 binds and phosphorylates signal transducer and activator of transcription 3 (p-STAT3), thereby regulating the expression of PAK4. Anti-PD-L1 and anti-VEGFR2 therapy can increase the secretion of interferon-gamma (IFN-γ), granzyme B, and perforin by immune cells and promoting the cytotoxic effects of cytotoxic cluster of differentiation 8 (CD8)+ T cells, and overexpression of PAK4 could reverse this effect. We also demonstrated that combination therapy with anti-PD-L1 and anti-VEGFR2 agents prevents tumor growth in an intracranial tumor model. Our results support that anti-VEGFR2 therapy can downregulate PAK4, reprogram the TME by increasing CD8+ T cells infiltration and activation, and enhance the therapeutic effect of anti-PD-L1 therapy on GBM cells.

Targeting PAK4 reverses cisplatin resistance in NSCLC by modulating ER stress

Chemoresistance poses a significant impediment to effective treatments for non-small-cell lung cancer (NSCLC). P21-activated kinase 4 (PAK4) has been implicated in NSCLC progression by invasion and migration. However, the involvement of PAK4 in cisplatin resistance is not clear. Here, we presented a comprehensive investigation into the involvement of PAK4 in cisplatin resistance within NSCLC. Our study revealed enhanced PAK4 expression in both cisplatin-resistant NSCLC tumors and cell lines. Notably, PAK4 silencing led to a remarkable enhancement in the chemosensitivity of cisplatin-resistant NSCLC cells. Cisplatin evoked endoplasmic reticulum stress in NSCLC. Furthermore, inhibition of PAK4 demonstrated the potential to sensitize resistant tumor cells through modulating endoplasmic reticulum stress. Mechanistically, we unveiled that the suppression of the MEK1-GRP78 signaling pathway results in the sensitization of NSCLC cells to cisplatin after PAK4 knockdown. Our findings establish PAK4 as a promising therapeutic target for addressing chemoresistance in NSCLC, potentially opening new avenues for enhancing treatment efficacy and patient outcomes.

MiR-199a/b-3p inhibits colorectal cancer cell proliferation, migration and invasion through targeting PAK4 and BCAR3

BackgroundColorectal cancer (CRC) is one of the leading causes of cancer-related death worldwide. P21 activated kinase 4 (PAK4) and Breast cancer anti-estrogen resistance 3 (BCAR3) have been reported to be involved in numerous aspects in tumorous progression. In this study, we propose to screen multi-targeted microRNAs. (miRNAs), which simultaneously inhibit neoplastic evolution through suppressing the transcription of target genes.MethodsMTT and Colony formation assays measured cell’s viability and proliferation. Scratch wound and Transwell assays detected the ability in migration and invasion for SW116 cells. The multi-targeted microRNAs of PAK4 and BCAR3 were predicted using bioinformatics analysis and verified by conducting dual luciferase reporter assay, western blot and qRT-PCR that could detect the expression levels of miR-199a/b-3p.ResultsThe knockdown of PAK4 significantly impeded proliferation and colony formation of SW1116 cells when the knockdown of BCAR3 hindered migration and invasion of SW1116 cells. MiR-199a/b-3p directly targeted the 3'-UTR of PAK4 and BCAR3, further effected proliferation, colony formation, migration, and invasion of SW1116 cells. PAK4 or BCAR3 overexpression could partially reversed inhibitory effects of miR-199a/b-3p.ConclusionsThese results provided a new multi-targeted cite for cancerous suppressant to improve the prognosis of CRC inpatients.

Exosome-mediated RNAi of PAK4 prolongs survival of pancreatic cancer mouse model after loco-regional treatment

With a dismal survival rate, pancreatic cancer (PC) remains one of the most aggressive and devastating malignancies, predominantly due to the absence of a valid biomarker for diagnosis and limited therapeutic options for advanced diseases. Exosomes (Exo) as cell-derived vesicles, are widely used as natural nanocarriers for drug delivery. P21-activated kinase 4 (PAK4) is oncogenic when overexpressed, promoting cell survival, migration and anchorage-independent growth. Herein we validated PAK4 as a therapeutic target in an in vivo PC tumour mouse model using Exo-mediated RNAi following intra-tumoural administration. PC derived Exo were firstly isolated by ultracentrifugation on sucrose cushion and characterised for their surface marker expression, size, number, purity and morphology. SiRNA was encapsulated into Exo via electroporation and dual uptake of Exo and siRNA was investigated by flow cytometry and confocal microscopy. In vitro siPAK4 silencing in PC cells following uptake was assessed by flow cytometry, western blotting, and in vitro scratch assay. In vivo efficacy (tumour growth delay and mouse survival) of siPAK4 was evaluated in PC bearing NSG mouse model. Ex vivo tumours were examined using Haematoxylin and eosin (H&E) staining and immunohistochemistry. Results showed high quality PC-derived PANC-1 Exo were obtained. SiRNA was incorporated in Exo with 16.5% encapsulation efficiency. In vitro imaging confirmed Exo and siRNA co-localisation in cells. PAK4 knockdown was successful with 30 nM Exo-siPAK4 at 24 h post incubation in vitro. Intra-tumoural administration of Exo-siPAK4 (0.03 mg/kg siPAK4 and 6.1 × 1011 Exo, each dose, two doses) reduced PC tumour growth in vivo and enhanced mice survival (p < 0.001), with minimal toxicity observed compared to polyethylenimine (PEI) used as a commercial transfection reagent. H&E staining of tumours showed significant tissue apoptosis in siPAK4 treated groups. PAK4 knockdown prolongs survival of PC-bearing mice suggesting its potential as a new therapeutic target for PC. PANC-1 Exo demonstrated comparable efficacy but safer profile than PEI as in vivo RNAi transfection reagent.

MicroRNA-140-5p inhibits the tumorigenesis of oral squamous cell carcinoma by targeting p21-activated kinase 4.

Oral squamous cell carcinoma (OSCC) is a serious global health problem. Recently, accumulating microRNA (miRNA) has emerged as crucial players in the development and progression of carcinomas including OSCC. Our study aimed to further investigate the roles of miR-140-5p in OSCC tumorigenesis and related molecular basis. In this study, OSCC tissues and adjacent normal tissues were isolated from 34 OSCC patients who suffered from surgical resection at our hospital. MiR-140-5p level was measured by reverse-transcription quantitative polymerase chain reaction assay. p21-activated kinase 4 (PAK4) protein level was determined by western blot assay in OSCC cells at 48 h posttransfection or OSCC xenograft tumors at day 35 after OSCC cell injection. The cell proliferative ability was assessed by cell counting kit-8 assay in OSCC cells at 0, 24, 48, 72 h after transfection. Cell apoptosis and cell-cycle analysis was conducted using a flow cytometry in OSCC cells at 48 h after transfection. The interaction between miR-140-5p and PAK4 3'-untranslated region was tested by bioinformatics analysis and luciferase reporter assay in OSCC cells at 48 h after transfection. Mouse xenograft models of OSCC were established to examine the influence of miR-140-5p on OSCC tumorigenesis in vivo during 35 days after OSCC cell injection. Our data showed that miR-140-5p expression was notably downregulated in OSCC tissues and cell lines. MiR-140-5p inhibited the expression of PAK4 by direct interaction in OSCC cells. Functional analysis disclosed that miR-140-5p overexpression or PAK4 knockdown suppressed cell proliferation, promoted cell apoptosis, and induced cell-cycle arrest in OSCC. Moreover, PAK4 upregulation rescued the detrimental effects of miR-140-5p on cell proliferation and cell-cycle progression and hampered cell apoptosis induced by miR-140-5p in OSCC. In vivo experiments demonstrated that miR-140-5p overexpression suppressed the growth of OSCC xenograft tumors by downregulating PAK4. In conclusion, our data revealed miR-140-5p suppressed OSCC tumorigenesis by targeting PAK4 in vitro and in vivo, deepening our understanding on the function and molecular basis of miR-140-5p in the development of OSCC.

A novel PAK4-CEBPB-CLDN4 axis involving in breast cancer cell migration and invasion

Claudin-4 (CLDN4), a crucial member of tight junction proteins, is aberrantly expressed in breast cancer cells and contributes to cell migration and invasion. However, the mechanisms controlling CLDN4 expression in breast cancer are poorly understood. Here, we reported that CLDN4 expression correlated positively with p21-activated kinase 4 (PAK4) expression in human breast cancer tissues. Knockdown of PAK4 in MDA-MB-231 and ZR-75-30 cells suppressed CLDN4 expression and significantly inhibited cell migration and invasion. Conversely, restoration of CLDN4 expression in PAK4-knockdown cells reversed the inhibition of migration and invasion. We identified CCAAT/enhancer-binding protein β (CEBPB) as a novel transcriptional regulator of CLDN4 and confirmed that CEBPB bound to the −1093 to −991 bp region of the CLDN4 promoter. Importantly, we found that PAK4 enhanced CEBPB phosphorylation on Thr-235. In summary, we showed that PAK4-mediated CEBPB activation upregulated CLDN4 expression to promote breast cancer cell migration and invasion. Our results might contribute to understanding the mechanisms of CLDN4 regulation and suggest PAK4-CEBPB-CLDN4 axis as a potential therapeutic target for breast cancer.

The p21-activated kinase 4-Slug transcription factor axis promotes epithelial-mesenchymal transition and worsens prognosis in prostate cancer.

Epithelial-mesenchymal transition (EMT) facilitates cancer invasion and metastasis and thus accelerates cancer progression. p21-activated kinase 4 (PAK4) is a critical regulator of prostate cancer (PC) progression. Here, we report that PAK4 activation promotes PC progression through the EMT regulator Slug. We find that phosphorylated PAK4S474 (pPAK4) levels, an index of PAK4 activation, were tightly associated with Gleason score (p < 0.001), a clinical indicator of PC progression, but not with prostate serum antigen levels or tumor stage. Stable silencing of PAK4 in PC cells reduced their potential for EMT, cellular invasion, and metastasis in vivo. PAK4 bound and directly phosphorylated Slug at two previously unknown sites, S158 and S254, which resulted in its stabilization. The non-phosphorylatable form SlugS158A/S254A upregulated transcription of CDH1, which encodes E-cadherin, and thus suppressed EMT and invasion, to a greater extent than did wild-type Slug. The strong EMT inducer TGF-β elevated pPAK4 and pSlugS158 levels; PAK4 knockdown or introduction of a dominant-negative form of PAK4 inhibited both TGF-β-stimulated EMT and an increase in pSlugS158 levels. Finally, immunohistochemistry revealed a positive correlation between pPAK4 and pSlugS158 but an inverse correlation between pSlugS158 and E-cadherin. The results suggest that the PAK4-Slug axis represents a novel pathway that promotes PC progression.

MicroRNA-485 inhibits malignant biological behaviour of glioblastoma cells by directly targeting PAK4.

Glioblastoma (GBM), which is characterised by rapid growth, cellular heterogeneity, angiogenesis, extensive invasion, hypoxia and necrosis, is the most common histological subtype of glioma in adults. MicroRNA(miRNA) dysregulation is a common feature of human cancers, including GBM. Previous studies have suggested that miRNAs are a novel class of regulatory molecules in various human cancers. Therefore, miRNAs may be investigated as a novel candidate and screening tool in the clinical diagnosis, therapy and prognosis of GBM. Recent accumulating evidence has demonstrated that miRNA‑485(miR‑485) is involved in the development and progression of several types of human cancers. However, the expression level, exact role and underlying mechanisms of miR‑485 in GBM remain unclear. In this study, miR‑485 was downregulated in both GBM tissue specimens and cell lines. miR‑485 overexpression inhibited GBM cell proliferation, colony formation, migration and invasion; increased apoptosis invitro; and reduced tumour growth invivo. In addition, p21‑activated kinase4 (PAK4) was demonstrated to be a direct and functional target of miR‑485 in GBM. Furthermore, PAK4 was upregulated in GBM tissues and negatively correlated with miR‑485 expression. Moreover, PAK4 knockdown exhibited a similar effect to miR‑485 overexpression in GBM cells. Enforced expression of PAK4 rescued miR‑485 tumour‑suppressor functions in GBM cells. miR‑485 inhibited the activation of the AKT and ERK signalling pathways in GBM. These results indicate that miR‑485 acts as a tumour suppressor in GBM by, at least partially, directly targeting PAK4 and regulating the AKT and ERK signalling pathways. Thus, miR‑485 may be a potential target for the treatment of patients with GBM.

P21-Activated Kinase 4 Signaling Promotes Japanese Encephalitis Virus-Mediated Inflammation in Astrocytes.

Japanese encephalitis virus (JEV) targets central nervous system, resulting in neuroinflammation with typical features of neuronal death along with hyper activation of glial cells. Exploring the mechanisms responsible for the JEV-caused inflammatory response remains a pivotal area of research. In the present study, we have explored the function of p21-activated kinase 4 (PAK4) in JEV-mediated inflammatory response in human astrocytes. The results showed that JEV infection enhances the phosphorylation of PAK4 in U251 cells and mouse brain. Knockdown of PAK4 resulted in decreased expression of inflammatory cytokines that include tumor necrosis factor alpha, interleukin-6, interleukin-1β, and chemokine (C-C motif) ligand 5 and interferon β upon JEV infection, suggesting that PAK4 signaling promotes JEV-mediated inflammation. In addition, we found that knockdown of PAK4 led to the inhibition of MAPK signaling including ERK, p38 MAPK and JNK, and also resulted in the reduced nuclear translocation of NF-κB and phosphorylation of AP-1. These results demonstrate that PAK4 signaling actively promotes JEV-mediated inflammation in human astrocytes via MAPK-NF-κB/AP-1 pathway, which will provide a new insight into the molecular mechanism of the JEV-induced inflammatory response.

P21-activated kinase 4 involves TSH induced papillary thyroid cancer cell proliferation.

Papillary thyroid cancer is a common endocrine malignancy. Although p21-activated kinase 4 (PAK4) is involved in the development of different types of tumor, its function has not been investigated in papillary thyroid cancer. Here, we identified a role for PAK4 in papillary thyroid cancer progression. Levels of PAK4 and PAK4 phosphorylated at serine 474 correlated significantly with tumor size and TNM stage. Furthermore, stable knockdown of PAK4 retarded cellular proliferation, migration, and invasion. Moreover, thyroid stimulating hormone-induced cellular proliferation in papillary thyroid cancer was found to be dependent on TSHR/cAMP/PKA/PAK4 signaling, with levels of phosphorylated PAK4 correlating positively with serum thyroid stimulating hormone and PKA Cα levels in patients with papillary thyroid cancer. These findings revealed a novel function of PAK4 in thyroid stimulating hormone-induced papillary thyroid cancer progression and suggest that PAK4 may become a promising diagnostic and therapeutic target for this disease.

The P21-activated kinase PAK4 is implicated in fatty-acid potentiation of insulin secretion downstream of free fatty acid receptor 1

ABSTRACTFree fatty acid receptor 1 (FFA1/GPR40) plays a key role in the potentiation of glucose-stimulated insulin secretion by fatty acids in pancreatic β cells. We previously demonstrated that GPR40 signaling leads to cortical actin remodeling and potentiates the second phase of insulin secretion. In this study, we examined the role of p21 activated kinase 4 (PAK4), a known regulator of cytoskeletal dynamics, in GPR40-dependent potentiation of insulin secretion. The fatty acid oleate induced PAK4 phosphorylation in human islets, in isolated mouse islets and in the insulin secreting cell line INS832/13. However, oleate-induced PAK4 phosphorylation was not observed in GPR40-null mouse islets. siRNA-mediated knockdown of PAK4 in INS832/13 cells abrogated the potentiation of insulin secretion by oleate, whereas PAK7 knockdown had no effect. Our results indicate that PAK4 plays an important role in the potentiation of insulin secretion by fatty acids downstream of GPR40.

Overexpression of P21-activated kinase 4 is associated with poor prognosis in non-small cell lung cancer and promotes migration and invasion.

BackgroundP21-activated kinase 4 (PAK4), an effector of the Rho family protein Cdc42, is an important oncogene whose expression is increased in many human cancers and is generally positively correlated with advanced disease and decreased survival. However, little is known about the expression and biological function of PAK4 in human non-small cell lung cancer (NSCLC).MethodsPAK4 expression in NSCLC tissues and adjacent non-tumor tissues were assessed by immunohistochemistry, real-time PCR, and western blotting. Prognostic value of PAK4 expression was evaluated by Kaplan-Meier analysis and Cox regression. siRNA-mediated gene silencing and protein kinase assay was applied to demonstrate the role and the mechanism of PAK4 in lung cancer cell migration, invasion.ResultsThe results showed that PAK4 was overexpressed in NSCLC cell lines and human NSCLC tissues. PAK4 expression was detected both in the membranes and cytoplasm of NSCLC cancer cells in vivo. Moreover, increased expression of PAK4 was associated with metastasis, shorter overall survival, advanced stage of NSCLC. Furthermore, PAK4 expression was positively correlated with phosphorylation of LIMK1 expression levels. Knockdown of PAK4 in NSCLC cell lines led to reduce the phosphorylation of LIMK1, which resulted in decrease of the cell migration and invasion. In addition, PAK4 bound to LIMK1 directly and activated it via phosphorylation.ConclusionsThese data demonstrate that PAK4 mediated LIMK1 phosphorylation regulates the migration and invasion in NSCLC. Therefore, PAK4 might be a significant prognostic marker and potential therapeutic molecular target in NSCLC.

P21-Activated Kinase 4 Critically Regulates Melanogenesis via Activation of the CREB/MITF and β-Catenin/MITF Pathways

p21-activated kinase 4 (PAK4) regulates a wide range of cellular events, including cytoskeletal remodeling, cell growth, and survival. Our previous study identified PAK4 as a key regulator of cAMP-response element-binding protein (CREB) that acts upstream of microphthalmia-associated transcription factor (MITF), a master transcription factor in melanogenesis. We therefore investigated the role of PAK4 in melanogenesis. Melanocytes express both PAK2 and PAK4 isoforms, but only RNA interference knockdown of PAK4 significantly influenced α-melanocyte-stimulating hormone (α-MSH)-induced melanogenesis in B16 melanoma cells. Consistent with this result, PAK4 inhibition by PF3758309, a potent ATP-competitive inhibitor of PAKs, suppressed not only α-MSH-induced melanogenesis in B16 melanoma and human epithelial melanocyte cells but also UVB-induced melanogenesis in the skin of melanin-possessing hairless mice (HRM-2) in a dose-dependent manner. Inhibition of PAK4 over several days markedly decreased the levels of CREB, MITF, and tyrosinase in both HRM-2 mice and B16 melanoma cells. Moreover, PAK4 knockdown and inhibition suppressed α-MSH-stimulated β-catenin phosphorylation at serine 675 (S675) but enhanced phosphorylation at S33/37, an indicator for ubiquitination-dependent proteolysis. Together, our results provide evidence that PAK4 promotes α-MSH/UVB-induced melanogenesis via the CREB and Wnt/β-catenin signaling pathways and suggest that PAK4 may be a potential therapeutic target in pigmentation disorders.

P21-Activated Kinase 4 (PAK4) as a Predictive Marker of Gemcitabine Sensitivity in Pancreatic Cancer Cell Lines.

Purposep21-activated kinases (PAKs) are involved in cytoskeletal reorganization, gene transcription, cell proliferation and survival, and oncogenic transformation. Therefore, we hypothesized that PAK expression levels could predict the sensitivity of pancreatic cancer cells to gemcitabine treatment, and PAKs could be therapeutic targets.Materials and MethodsCell viability inhibition by gemcitabine was evaluated in human pancreatic cancer cell lines (Capan-1, Capan-2, MIA PaCa-2, PANC-1, Aspc-1, SNU-213, and SNU-410). Protein expression and mRNA of molecules was detected by immunoblot analysis and reverse transcription polymerase chain reaction. To define the function of PAK4, PAK4 was controlled using PAK4 siRNA.ResultsCapan-2, PANC-1, and SNU-410 cells were resistant to gemcitabine treatment. Immunoblot analysis of signaling molecules reported to indicate gemcitabine sensitivity showed higher expression of PAK4 and lower expression of human equilibrative nucleoside transporter 1 (hENT1), a well-known predictive marker for gemcitabine activity, in the resistant cell lines. Knockdown of PAK4 using siRNA induced the upregulation of hENT1. In resistant cell lines (Capan-2, PANC-1, and SNU-410), knockdown of PAK4 by siRNA resulted in restoration of sensitivity to gemcitabine.ConclusionPAK4 could be a predictive marker of gemcitabine sensitivity and a potential therapeutic target to increase gemcitabine sensitivity in pancreatic cancer.

P21‐Activated Kinase 4 Regulates the Cyclin‐Dependent Kinase Inhibitor P57Kip2 in Human Breast Cancer

The p21-activated kinases have been implicated in the control of cell cycle progression. However, the biological mechanism underlying the role of p21-activated kinase 4 (PAK4) in cell cycle control remains unknown. Here, by using quantitative RT-PCR and immunoblot analyses, we discovered that over-expression of PAK4 could suppress cyclin-dependent kinase inhibitor 1C (p57(Kip2) ) expression in the MCF-7 human breast cancer cell line, whereas lentiviral vector-mediated small interfering RNA (siRNA) knockdown of PAK4 markedly promoted p57(Kip2) expression in MCF-7 cells. Furthermore, PAK4-mediated down-regulation of p57(Kip2) was reversed by MG132, a specific proteasome inhibitor. The ubiquitination assay confirmed that the activity of PAK4 attenuated p57(Kip2) protein stability through the ubiquitin-proteasome pathway in MCF-7 cells. Moreover, a significant inverse correlation between PAK4 and p57(Kip2) protein levels was observed in breast cancer tissues by immunohistochemical analysis. Taken together, our data demonstrate a novel function for PAK4 in regulating the stability of p57(Kip2) , possibly through the ubiquitin-proteasome pathway, leading to increased proliferation of breast cancer cells. Thus, PAK4 may be used as a potential diagnostic and therapeutic target for human breast cancer.

Functional cooperativity by direct interaction between PAK4 and MMP-2 in the regulation of anoikis resistance, migration and invasion in glioma

Gliomas display anoikis resistance, enhanced invasion in to the adjacent brain parenchyma and eventually recur despite using the standard therapies. Our studies on increased anoikis sensitization in matrix metalloproteinase-2 (MMP-2)-knockdown 4910 and 5310 human glioma xenograft cells were interestingly correlated with p21-activated kinase 4 (PAK4) inhibition, prompting us to further investigate the role of PAK4 in glioma. Here, we report the PAK4 upregulation in positive correlation with increasing glioma pathological grades. The siRNA-mediated PAK4 knockdown elevated anoikis, and inhibited invasion and migration by downregulating MMP-2, αvβ3-integrin and phospho-epidermal growth factor receptor (phospho-EGFR). The cDNA-PCR arrays revealed a transcriptional suppression of essential proteins involved in cell proliferation and adhesion in PAK4-knockdown cells. Most importantly, glutathione S-transferase pull-down assays demonstrated the MMP-2 as a new PAK4-interacting protein which binds to PAK4 kinase domain. Individual EGFR/ErbB2 inhibitor and αvβ3 antibody treatments in PAK4si-treated cells indicated the regulation of αvβ3/EGFR survival signaling by PAK4. Overexpression of PAK4 significantly reversed the MMP2si-induced cell death in both cell lines. Codepletion of PAK4 and MMP-2 resulted in robust anoikis-mediated cell death, and severely inhibited invasive and migratory properties in these cells. PAK4si inhibited in vivo tumor growth in nude mice by inhibiting MMP-2, β3-integrin and phospho-EGFR levels in tumors. Our findings indicate a physical association between PAK4 and MMP-2, and suggest the future therapeutic potential of PAK4/MMP-2 dual targeting in glioma treatment.

P21-Activated kinase 4 promotes prostate cancer progression through CREB

Prostate cancer is initially androgen-dependent but, over time, usually develops hormone- and chemo-resistance. The present study investigated a role for p21-activated kinase 4 (PAK4) in prostate cancer progression. PAK4 activation was markedly inhibited by H89, a specific protein kinase A (PKA) inhibitor, and PAK4 was activated by the elevation of cAMP. The catalytic subunit of PKA interacted with the regulatory domain of PAK4, and directly phosphorylated PAK4 at serine 474 (S474). Catalytically active PAK4 enhanced the transcriptional activity of CREB independent of S133 phosphorylation. Stable knockdown of PAK4 in PC-3 and DU145 prostate cancer cells inhibited tumor formation in nude mice. Decreased tumorigenicity correlated with decreased expression of CREB and its targets, including Bcl-2 and cyclin A1. Additionally, in androgen-dependent LNCap-FGC cells, PAK4 regulated cAMP-induced neuroendocrine differentiation, which is known to promote tumor progression. Finally, PAK4 enhanced survival and decreased apoptosis following chemotherapy. These results suggested that PAK4 regulates progression toward hormone- and chemo-resistance in prostate cancer, and this study identified both a novel activation mechanism and potential downstream effector pathways. Therefore, PAK4 may be a promising therapeutic target in prostate cancer.