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.

Gene polymorphisms of interleukin-28, p21-activated protein kinases 4, and response to interferon-α based therapy in Chinese patients with chronic hepatitis B

Background Peg-lnterferon-a treatment is expensive and associated with considerable adverse effects, selection of patients with the highest probability of response is essential for clinical practice. The objective of this study was to assess the relationship between the gene polymorphisms of interleukin-28 （IL-28）, p21-activated protein kinase 4 （PAK4） and the response to interferon treatment in chronic hepatitis B patients. Methods Two hundred and forty interferon-naive treatment HBeAg seropositive chronic hepatitis B patients were enrolled in the present prospective nested case-control study. Peripheral blood samples were collected, including 92 with favorable response and 148 without response to the interferon treatment. Rs8099917, rs12980602, and rs9676717 SNP was genotyped using matrix assisted laser desorption/ionization time of flight mass spectrometry （MALDI-TOF MS）. Results IL-28 genotype was not associated with response to interferon treatment （OR for GT/GG vs. TT, 0.881 （95% CI 0.388-2.002）; P=0.762; OR for CT/CC vs. TT, 0.902 （95% CI 0.458-1.778）; P=-0.766）. Rs9676717 in PAK4 genotype was independently associated with the response （OR for CT/CC vs. TT, 0.524 （95% CI 0.310-0.888）; P=0.016）. When adjusting for age, gender, smoking, drinking, levels of hepatitis B virus DNA, and alanine aminotransferase （ALT）, rs9676717 genotype TT appeared to be associated with a higher probability of response for interferon treatment （OR, 0.155 （95% CI 0.034-0.700）; P=0.015）. Conclusion Genotype TTfor rs9676717 in PAK4 gene and no drinking may be predictive of the interferon-a treatment success.

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.

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.

Activation of Rac1-PI3K/Akt is required for epidermal growth factorinduced PAK1 activation and cell migration in MDA-MB-231 breast cancer cells

Epidermal growth factor （EGF） may increase cell motility, an event implicated in cancer cell invasion and metastasis. However, the underlying mechanisms for EGF-induced cell motility remain elusive. In this study, we found that EGF treatment could activate Ras-related C3 botulinum toxin substrate 1 （Racl）, PI3K/Akt and p21- actived kinase （PAK1） along with cell migration. Ectopic expression of PAK1 K299R, a dominant negative PAK1 mutant, could largely abolish EGF-induced cell migration. Blocking PI3K/Akt signalling with LY294002 or Akt siRNA remarkably inhibited both EGF-induced PAK1 activation and cell migration. Furthermore, expression of dominant-negative Racl （T17N） could largely block EGF-induced PI3K/Akt-PAK1 activation and cell migration. Interestingly, EGF could induce a significant production of ROS, and N-acetyl-L-cysteine, a scavenger of ROS which abolished the EGF-induced ROS generation, cell migration, as well as activation of PI3K/Akt and PAK, but not Racl. Our study demonstrated that EGF-induced cell migration involves a cascade of signalling events, including activation of Racl, generation of ROS and subsequent activation of PI3K/Akt and PAK1.

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。

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.

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。

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.

PAK1 is a novel cardiac protective signaling molecule

We review here the novel cardiac protective effects of the multifunctional enzyme, p21-aetivated kinase 1 （PAK1）, a member of a serine/threonine protein kinase family. Despite the large body of evidence from studies in noncardiac tissue indicating that PAK1 activity is key in the regulation of a number of cellular functions, the role of PAK1 in the heart has only been revealed over the past few years. In this review, we assemble an overview of the recent findings on PAKI signaling in the heart, particularly its cardiac protective effects. We present a model for PAK1 signaling that provides a mechanism for specifically affecting cardiac cellular processes in which regulation of protein phosphorylation states by protein phosphatase 2A （PP2A） predominates. We discuss the anti-adrenergic and antihypertrophic cardiac protective effects of PAK1, as well as its role in maintaining ventricular Ca2＋ homeostasis and electrophysiological stability under physiological, β-adrenergic and hypertrophic stress conditions.