p21-activated kinase signalling in pancreatic cancer: New insights into tumour biology and immune modulation

Pancreatic cancer is one of the most aggressive and lethal malignancies worldwide, with a very poor prognosis and a five-year survival rate less than 8%. This dismal outcome is largely due to delayed diagnosis, early distant dissemination and resistance to conventional chemotherapies. Kras mutation is a well-defined hallmark of pancreatic cancer, with over 95% of cases harbouring Kras mutations that give rise to constitutively active forms of Kras. As important down-stream effectors of Kras, p21-activated kinases(PAKs) are involved in regulating cell proliferation, apoptosis, invasion/migration and chemo-resistance. Immunotherapy is now emerging as a promising treatment modality in the era of personalized anti-cancer therapeutics. In this review, basic knowledge of PAK structure and regulation is briefly summarised and the pivotal role of PAKs in Kras-driven pancreatic cancer is highlighted in terms of tumour biology and chemoresistance. Finally, the involvement of PAKs in immune modulation in the tumour microenvironment is discussed and the potential advantages of targeting PAKs are explored.

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 smallmolecule inhibitors of group Ⅱ PAKs for the treatment of cancer.

Targeting P21-activated kinase suppresses proliferation and enhances chemosensitivity in T-cell lymphoblastic lymphoma

T-cell lymphoblastic lymphoma(T-LBL)is a highly aggressive non-Hodgkin lymphoma with a poor prognosis.P21-activated kinase(PAK)is a component of the gene expression-based classifier that can predict the prognosis of T-LBL.However,the role of PAK in T-LBL progression and survival remains poorly understood.Herein,we found that the expression of PAK1 was significantly higher in T-LBL cell lines(Jurkat,SUP-T1,and CCRF-CEM)compared to the human T-lymphoid cell line.Moreover,PAK2 mRNA level of 32 relapsed T-LBL patients was significantly higher than that of 37 cases without relapse(P=.012).T-LBL patients with high PAK1 and PAK2 expression had significantly shorter median RFS than those with low PAK1 and PAK2 expression(PAK1,P=.028;PAK2,P=.027;PAK1/2,P=.032).PAK inhibitors,PF3758309(PF)and FRAX597,could suppress the proliferation of T-LBL cells by blocking the G1/S cell cycle phase transition.Besides,PF could enhance the chemosensitivity to doxorubicin in vitro and in vivo.Mechanistically,through western blotting and RNA sequencing,we identified that PF could inhibit the phosphorylation of PAK1/2 and downregulate the expression of cyclin D1,NF-κB and cell adhesion signaling pathways in T-LBL cell lines.These findings suggest that PAK might be associated with T-LBL recurrence and further found that PAK inhibitors could suppress proliferation and enhance chemosensitivity of T-LBL cells treated with doxorubicin.Collectively,our present study underscores the potential therapeutic effect of inhibiting PAK in T-LBL therapy.

PAK1基因对大肠癌细胞体外侵袭能力的影响

目的研究p21-activated kinase-1(PAK1)基因对大肠癌细胞系体外侵袭能力的影响。方法把重组p21活化蛋白激酶1质粒用脂质体转染大肠癌SW480细胞,同时设立空白对照组和空载体对照组。于转染后48h采用免疫印迹方法检测PAK1的蛋白表达水平,Boyden小室模型检测大肠癌细胞SW480在转染重组PAK1基因质粒后侵袭能力的变化。结果SW480细胞转染p21活化蛋白激酶1重组质粒后,与空白对照和空载体对照相比,PAK1蛋白水平明显增加,细胞的体外侵袭能力增强。结论转染pPAK1重组质粒能够有效上调PAK1基因,增强大肠癌细胞系体外侵袭潜能,提示PAK1基因高表达可能与大肠癌细胞的侵袭和转移等生物学行为相关。

The p21-activated kinases in neural cytoskeletal remodeling and related neurological disorders

The serine/threonine p21-activated kinases(PAKs),as main effectors of the Rho GTPases Cdc42 and Rac,represent a group of important molecular switches linking the complex cytoskeletal networks to broad neural activity.PAKs show wide expression in the brain,but they differ in specific cell types,brain regions,and developmental stages.PAKs play an essential and differential role in controlling neural cytoskeletal remodeling and are related to the development and fate of neurons as well as the structural and functional plasticity of dendritic spines.PAK-mediated actin signaling and interacting functional networks represent a common pathway frequently affected in multiple neurodevelopmental and neurodegenerative disorders.Considering specific small-molecule agonists and inhibitors for PAKs have been developed in cancer treatment,comprehensive knowledge about the role of PAKs in neural cytoskeletal remodeling will promote our understanding of the complex mechanisms underlying neurological diseases,which may also represent potential therapeutic targets of these diseases.

真核绿色荧光蛋白表达载体pEGFP-C1/PAK-1的构建及其在结直肠癌SW480细胞内的表达

目的:构建重组p21-activated kinase-1(PAK1)基因绿色荧光蛋白表达载体pEGFP-C1/PAK1,并转染入结直肠癌细胞SW480中表达.方法:在南方医科大学附属南方医院消化研究所实验室,从人类结直肠癌细胞株SW620细胞提取总RNA,经逆转录聚合酶链式反应获得人PAK1 cDNA片段,经过限制性内切酶进行酶切,T4连接酶进行连接,将目的基因克隆至真核绿色荧光蛋白表达载体pEGFP-C1上,然后转染结直肠癌细胞株SW480,观察其在细胞中表达.结果:重组载体经限制性内切酶酶切鉴定和DNA序列分析验证,显示插入载体的序列与目的基因一致,而且该重组载体能够在SW480细胞中表达.结论:成功构建了真核绿色荧光蛋白表达载体pEGFP-C1/PAK1,为研究PAK1在结直肠癌中的生物学功能奠定了基础.

Molecular determinants of the antitumor effects of trichostatin A in pancreatic cancer cells

AIM:To gain molecular insights into the action of the histone deacetylase inhibitor(HDACI) trichostatin-A(TSA) in pancreatic cancer(PC) cells.METHODS:Three PC cell lines,BxPC-3,AsPC-1 and CAPAN-1,were treated with various concentrations of TSA for def ined periods of time.DNA synthesis was assessed by measuring the incorporation of 5-bromo-2'deoxyuridine.Gene expression at the level of mRNA was quantif ied by real-time polymerase chain reaction.Expression and phosphorylation of proteins was monitored by immunoblotting,applying an infrared imaging technology.To study the role of p38 MAP kinase,the specif ic enzyme inhibitor SB202190 and an inactive control substance,SB202474,were employed.RESULTS:TSA most eff iciently inhibited BrdU incorporation in BxPC-3 cells,while CAPAN-1 cells displayed the lowest and AsPC-1 cells an intermediate sensitivity.The biological response of the cell lines correlated with the increase of histone H3 acetylation after TSA application.In BxPC-3 cells(which are wild-type for KRAS),TSA strongly inhibited phosphorylation of ERK 1/2 and AKT.In contrast,activities of ERK and AKT in AsPC-1 and CAPAN-1 cells(both expressing oncogenic KRAS) were not or were only modestly affected by TSA treatment.In all three cell lines,but most pronounced in BxPC-3 cells,TSA exposure induced an activation of the MAP kinase p38.Inhibition of p38 by SB202190 slightly but signif icantly diminished the antiproliferative effect of TSA in BxPC-3 cells.Interestingly,only BxPC-3 cells responded to TSA treatment by a signif icant increase of the mRNA levels of bax,a pro-apoptotic member of the BCL gene family.Finally,in BxPC-3 and AsPC-1 cells,but not in the cell line CAPAN-1,signif icantly higher levels of the cell cycle inhibitor protein p21Waf1 were observed after TSA application.CONCLUSION:The biological effect of TSA in PC cells correlates with the increase of acetyl-H3,p21Waf1,phospho-p38 and bax levels,and the decrease of phosphoERK 1/2 and phospho-AKT.

MiR-32-5p aggravates intestinal epithelial cell injury in pediatric enteritis induced by Helicobacter pylori

BACKGROUND Pediatric enteritis is one of the infectious diseases in the digestive system that causes a variety of digestive problems,including diarrhea,vomiting,and bellyache in children.Clinically,Helicobacter pylori(H.pylori)infection is one of the common factors to cause pediatric enteritis.It has been demonstrated that aberrant expression of microRNAs(miRNAs)is found in gastrointestinal diseases caused by H.pylori,and we discovered a significant increase of miR-32-5p in H.pylori-related pediatric enteritis.However,the exact role of miR-32-5p in it is still unknown.AIM To investigate the role of aberrant miR-32-5p in pediatric enteritis induced by H.pylori.METHODS MiR-32-5p expression was detected by quantitative real time-polymerase chain reaction.The biological role of miR-32-5p in H.pylori-treated intestinal epithelial cells was evaluated by Cell Counting Kit-8 assay and flow cytometry.The potential target of miR-32-5p was predicted with TargetScanHuman and verified by luciferase assay.The downstream mechanism of miR-32-5p was explored by using molecular biology methods.RESULTS We found that miR-32-5p was overexpressed in serum of H.pylori-induced pediatric enteritis.Further investigation revealed that H.pylori infection promoted the death of intestinal epithelial cells,and increased miR-32-5p expression.Moreover,miR-32-5p mimic further facilitated apoptosis and inflammatory cytokine secretion of intestinal epithelial cells.Further exploration revealed that SMAD family member 6(SMAD6)was the direct target of miR-32-5p,and SMAD6 overexpression partially rescued cell damage induced by H.pylori.The following experiments showed that miR-32-5p/SMAD6 participated in the apoptosis of intestinal epithelial cells induced by transforming growth factor-β-activated kinase 1(TAK1)-p38 activation under H.pylori infection.CONCLUSION Our work uncovered the crucial role of aberrant expression of miR-32-5p in H.pylori–related pediatric enteritis,and suggested that the TAK1-p38 pathway is involved in it.

Ⅰ类PAKs在神经退行性疾病的研究进展

P21活化的蛋白激酶(p21-activated kinases,PAKs)是Rho家族中GTP酶重要效应物,已证实对细胞繁殖和生存有重要意义。研究发现PAKs与神经元树突发育、细胞骨架的形成以及在细胞信号转导等方面起重要作用。本研究对Ⅰ类PAKs在神经退行性疾病中作用研究进展作一综述。

p-21活化激酶-1、Snail在结直肠癌侵袭与转移中的作用

目的观察p-21活化激酶-1（PAK1）、Snail在结直肠癌侵袭与转移中的作用。方法采用荧光原位杂交和免疫组织化学方法分别检测60例结直肠癌患者的正常结直肠黏膜与结直肠癌组织中PAK1和Snail的表达，分析两者在结卣肠癌中表达的意义以及相关性。结果PAK1mRNA、SnailmRNA存结随肠癌中的表达率分别为70．00％（42／60）和73．33％（44／60），均显著高于正常对照组（P〈0．05）；PAK1mRNA在Dukes不同分期中表达差异有统计学意义（x2=6．0708，P〈0．05），在有淋巴结转移的结直肠癌中表达显著高于无淋巴结转移的结直肠癌（x2=5．8764，P〈0．05）；SnailmRNA存Dukes不同分期中表达差异有统计学意义（x2=6．7930，P〈0．05），在有淋巴结转移的结直肠癌中表达显著高于无淋巴结转移的结直肠癌（x2=6．2130，P〈0．05）；PAK1和Snail蛋白在结直肠癌组织巾的表达呈正相关（r=0．31924，P〈0．05）。结论PAK1和Snail的高表达与结直肠癌的侵袭和转移有关；PAK1和Snail在结直肠癌侵袭和转移过程中可能存在相互促进作用。

Antitumor synergism between PAK4 silencing and immunogenic phototherapy of engineered extracellular vesicles

Immunotherapy has revolutionized the landscape of cancer treatment.However,single immunotherapy only works well in a small subset of patients.Combined immunotherapy with antitumor synergism holds considerable potential to boost the therapeutic outcome.Nevertheless,the synergistic,additive or antagonistic antitumor effects of combined immunotherapies have been rarely explored.Herein,we established a novel combined cancer treatment modality by synergizing p21-activated kinase 4(PAK4)silencing with immunogenic phototherapy in engineered extracellular vesicles(EVs)that were fabricated by coating M1 macrophage-derived EVs on the surface of the nano-complex cores assembled with si RNA against PAK4 and a photoactivatable polyethyleneimine.The engineered EVs induced potent PAK4 silencing and robust immunogenic phototherapy,thus contributing to effective antitumor effects in vitro and in vivo.Moreover,the antitumor synergism of the combined treatment was quantitatively determined by the Compu Syn method.The combination index(CI)and isobologram results confirmed that there was an antitumor synergism for the combined treatment.Furthermore,the dose reduction index(DRI)showed favorable dose reduction,revealing lower toxicity and higher biocompatibility of the engineered EVs.Collectively,the study presents a synergistically potentiated cancer treatment modality by combining PAK4 silencing with immunogenic phototherapy in engineered EVs,which is promising for boosting the therapeutic outcome of cancer immunotherapy.

Negative regulation of caspase 3-cleaved PAK2 activity by protein phosphatase 1

The p21-activated kinase 2 (PAK2) is activated by binding of small G proteins, Cdc42 and Rac, or through proteolytic cleavage by caspases or caspase-like proteases. Activation by both small G protein and caspase requires autophosphorylation at Thr-402 of PAK2. Although activation of PAK2 has been investigated for nearly a decade, the mechanism of PAK2 downregulation is unclear. In this study, we have applied the kinetic theory of substrate reaction during modification of enzyme activity to study the regulation mechanism of PAK2 activity by the catalytic subunit of protein phosphatase 1 (PP1α). On the basis of the kinetic equation of the substrate reaction during the reversible phosphorylation of PAK2, all microscopic kinetic constants for the free enzyme and enzyme-substrate(s) complexes have been determined. The results indicate that (1) PP1α can act directly on phosphorylated Thr-402 in the acti-vation loop of PAK2 and down-regulate its kinase activity; (2) binding of the exogenous protein/peptide substrates at the active site of PAK2 decreases both the rates of PAK2 autoactivation and inactivation. The present method provides a novel approach for studying reversible phosphorylation reactions. The advantage of this method is not only its usefulness in study of substrate effects on enzyme modifica-tion but also its convenience in study of modification reaction directly involved in regulation of enzyme activity. This initial study should provide a foundation for future structural and mechanistic work of protein kinases and phosphatases.

Exosomal miR-485-3p derived from pancreatic ductal epithelial cells inhibits pancreatic cancer metastasis through targeting PAK1

Background:Cell competition is an important feature in pancreatic cancer(PC)progression,but the underlying mechanism remains elusive.This study aims to explore the role of exosomes derived from normal pancreatic ductal epithelial cells involved in PC progression.Methods:PC cells and pancreatic stellate cells(PSCs)were treated with exosomes isolated from pancreatic ductal epithelial cells.Cell proliferation was assessed by CCK8 assays.Cell migration and invasion were assessed by Transwell assays.PC and matched adjacent non-tumor tissue specimens were obtained from 46 patients pathologically diagnosed with PC at Peking University First Hospital from 2013 to 2017.Tissue miR-485-3p and p21-activated kinase-1(PAK1)expression was examined by real-time polymerase chain reaction(RT-PCR),and the relationship of the two was analyzed using Pearman’s product-moment correlation.The clinical significance of miR-485-3p was analyzed using the Chi-square test,Wilcoxon rank-sum test,and Fisher exact probability,respectively.The binding of miR-485-3p to PAK15’-untranslated region(5’-UTR)was examined by luciferase assay.PC cells were xenografted into nude mice as a PC metastasis model.Results:Exosomes from pancreatic ductal epithelial cells suppressed PC cell migration and invasion as well as the secretion and migration of PSCs.MiR-485-3p was enriched in the exosomes of pancreatic ductal epithelial cells but deficient in those of PC cells and PSCs,in accordance with the lower level in PSCs and PC cells than that in pancreatic ductal cells.And the mature miR-485-3p could be delivered into these cells by the exosomes secreted by normal pancreatic duct cells,to inhibit PC cell migration and invasion.Clinical data analysis showed that miR-485-3p was significantly decreased in PC tissues(P<0.05)and was negatively associated with lymphovascular invasion(P=0.044).As a direct target of miR-485-3p,PAK1 was found to exert an inhibitory effect on PC cells,and there was a significantly negative correlation between the expression levels of miR-485-3p and PAK1(r=-0.6525,P<0.0001)in PC tissues.Moreover,miR-485-3p could suppress PC metastasisin vivo by targeting p21-activated kinase-1.Conclusions:Exosomal miR-485-3p delivered by normal pancreatic ductal epithelial cells into PC cells inhibits PC metastasis by directly targeting PAK1.The restoration of miR-485-3p by exosomes or some other vehicle might be a novel approach for PC treatment.

PAK GroupⅠ的异常表达与非小细胞肺癌的恶性程度相关

目的探讨P21活化激酶(p21-activated kinase,PAK)group Ⅰ在非小细胞肺癌中的表达模式和意义。方法应用免疫组化及Western Blot方法,分析检测了肺癌组织中PAK Group Ⅰ的表达情况及其与临床病理因素的关系。结果与正常肺组织相比,PAK Group Ⅰ在肺癌组织中出现明显的胞浆过表达67.31%(105/156),并且其异常表达模式与肺癌组织的组织学类型(P=0.027)、高分期(P=0.007)、淋巴结转移(P=0.035)及患者的不良预后(P<0.001)相关。结论肺癌组织中PAK Group Ⅰ蛋白过表达是非小细胞肺癌的恶性程度的重要标志之一。