Stimulation of NFkappa B activity by multiple signaling pathways requires PAK1

PAK1 and Therapy Resistance in Melanoma

Malignant melanoma claims more lives than any other skin malignancy. While primary melanomas are usually cured via surgical excision, the metastatic form of the disease portents a poor prognosis. Decades of intense research has yielded an extensive armamentarium of anti-melanoma therapies, ranging from genotoxic chemo- and radiotherapies to targeted interventions in specific signaling pathways and immune functions. Unfortunately, even the most up-to-date embodiments of these therapies are not curative for the majority of metastatic melanoma patients, and the need to improve their efficacy is widely recognized. Here, we review the reports that implicate p21-regulated kinase 1 (PAK1) and PAK1-related pathways in the response of melanoma to various therapeutic modalities. Ample data suggest that PAK1 may decrease cell sensitivity to programmed cell death, provide additional stimulation to growth-promoting molecular pathways, and contribute to the creation of an immunosuppressive tumor microenvironment. Accordingly, there is mounting evidence that the concomitant inhibition of PAK1 enhances the potency of various anti-melanoma regimens. Overall, the available information suggests that a safe and effective inhibition of PAK1-dependent molecular processes would enhance the potency of the currently available anti-melanoma treatments, although considerable challenges in implementing such strategies still exist.

PLPP/CIN-mediated NF2 S10 dephosphorylation distinctly regulates kainate-induced seizure susceptibility and neuronal death through PAK1-NF-κB-COX-2-PTGES2 signaling pathway

BACKGROUND

Pyridoxal-5'-phosphate phosphatase/chronophin (PLPP/CIN) selectively dephosphorylates serine (S) 10 site on neurofibromin 2 (NF2, also known as merlin (moesin-ezrin-radixin-like protein) or schwannomin). p21-activated kinase 1 (PAK1) is a serine/threonine protein kinase, which is involved in synaptic activity and plasticity in neurons. NF2 and PAK1 reciprocally regulate each other in a positive feedback manner. Thus, the aim of the present study is to investigate the effects of PLPP/CIN-mediated NF2 S10 dephosphorylation on PAK1-related signaling pathways under physiological and neuroinflammatory conditions, which are largely unknown.

METHODS

After kainate (KA) injection in wild-type, PLPP/CIN^-/- and PLPP/CIN^Tg mice, seizure susceptibility, PAK1 S204 autophosphorylation, nuclear factor-κB (NF-κB) p65 S276 phosphorylation, cyclooxygenase-2 (COX-2) upregulation, prostaglandin E synthase 2 (PTGES2) induction and neuronal damage were measured. The effects of 1,1'-dithiodi-2-naphthtol (IPA-3, a selective inhibitor of PAK1) pretreatment on these responses to KA were also validated.

RESULTS

PLPP/CIN overexpression increased PAK1 S204 autophosphorylation concomitant with the enhanced NF2 S10 dephosphorylation in hippocampal neurons under physiological condition. Following KA treatment, PLPP/CIN overexpression delayed the seizure on-set and accelerated PAK1 S204 phosphorylation, NF-κB p65 S276 phosphorylation, COX-2 upregulation and PTGES2 induction, which were ameliorated by PLPP/CIN deletion or IPA-3. Furthermore, IPA-3 pretreatment shortened the latency of seizure on-set without affecting seizure severity (intensity) and ameliorated CA3 neuronal death induced by KA.

CONCLUSIONS

These findings indicate that PLPP/CIN may regulate seizure susceptibility (the latency of seizure on-set) and CA3 neuronal death in response to KA through NF2-PAK1-NF-κB-COX-2-PTGES2 signaling pathway.

P-21 Activated Kinases in Liver Disorders

The p21 Activated Kinases (PAKs) are serine threonine kinases and play important roles in many biological processes, including cell growth, survival, cytoskeletal organization, migration, and morphology. Recently, PAKs have emerged in the process of liver disorders, including liver cancer, hepatic ischemia-reperfusion injury, hepatitis, and liver fibrosis, owing to their effects in multiple signaling pathways in various cell types. Activation of PAKs promotes liver cancer growth and metastasis and contributes to the resistance of liver cancer to radiotherapy and chemotherapy, leading to poor survival of patients. PAKs also play important roles in the development and progression of hepatitis and other pathological processes of the liver such as fibrosis and ischemia-reperfusion injury. In this review, we have summarized the currently available studies about the role of PAKs in liver disorders and the mechanisms involved, and further explored the potential therapeutic application of PAK inhibitors in liver disorders, with the aim to provide a comprehensive overview on current progress and perspectives of PAKs in liver disorders.

The molecular basis of p21-activated kinase-associated neurodevelopmental disorders: From genotype to phenotype

Although the identification of numerous genes involved in neurodevelopmental disorders (NDDs) has reshaped our understanding of their etiology, there are still major obstacles in the way of developing therapeutic solutions for intellectual disability (ID) and other NDDs. These include extensive clinical and genetic heterogeneity, rarity of recurrent pathogenic variants, and comorbidity with other psychiatric traits. Moreover, a large intragenic mutational landscape is at play in some NDDs, leading to a broad range of clinical symptoms. Such diversity of symptoms is due to the different effects DNA variations have on protein functions and their impacts on downstream biological processes. The type of functional alterations, such as loss or gain of function, and interference with signaling pathways, has yet to be correlated with clinical symptoms for most genes. This review aims at discussing our current understanding of how the molecular changes of group I p21-activated kinases (PAK1, 2 and 3), which are essential actors of brain development and function; contribute to a broad clinical spectrum of NDDs. Identifying differences in PAK structure, regulation and spatio-temporal expression may help understanding the specific functions of each group I PAK. Deciphering how each variation type affects these parameters will help uncover the mechanisms underlying mutation pathogenicity. This is a prerequisite for the development of personalized therapeutic approaches.

p21-Activated Kinase: Role in Gastrointestinal Cancer and Beyond

Simple Summary

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

Abstract

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

Small Molecule Inhibitors for Hepatocellular Carcinoma: Advances and Challenges

According to data provided by World Health Organization, hepatocellular carcinoma (HCC) is the sixth most common cause of deaths due to cancer worldwide. Tremendous progress has been achieved over the last 10 years developing novel agents for HCC treatment, including small-molecule kinase inhibitors. Several small molecule inhibitors currently form the core of HCC treatment due to their versatility since they would be more easily absorbed and have higher oral bioavailability, thus easier to formulate and administer to patients. In addition, they can be altered structurally to have greater volumes of distribution, allowing them to block extravascular molecular targets and to accumulate in a high concentration in the tumor microenvironment. Moreover, they can be designed to have shortened half-lives to control for immune-related adverse events. Most importantly, they would spare patients, healthcare institutions, and society as a whole from the burden of high drug costs. The present review provides an overview of the pharmaceutical compounds that are licensed for HCC treatment and other emerging compounds that are still investigated in preclinical and clinical trials. These molecules are targeting different molecular targets and pathways that are proven to be involved in the pathogenesis of the disease.

Molecular Pathways Involved in the Anti-Cancer Activity of Flavonols: A Focus on Myricetin and Kaempferol

Natural compounds have always represented valuable allies in the battle against several illnesses, particularly cancer. In this field, flavonoids are known to modulate a wide panel of mechanisms involved in tumorigenesis, thus rendering them worthy candidates for both cancer prevention and treatment. In particular, it was reported that flavonoids regulate apoptosis, as well as hamper migration and proliferation, crucial events for the progression of cancer. In this review, we collect recent evidence concerning the anti-cancer properties of the flavonols myricetin and kaempferol, discussing their mechanisms of action to give a thorough overview of their noteworthy capabilities, which are comparable to those of their most famous analogue, namely quercetin. On the whole, these flavonols possess great potential, and hence further study is highly advised to allow a proper definition of their pharmaco-toxicological profile and assess their potential use in protocols of chemoprevention and adjuvant therapies.

A Pseudorabies Virus Serine/Threonine Kinase, US3, Promotes Retrograde Transport in Axons via Akt/mToRC1

Infection of peripheral axons by alpha herpesviruses (AHVs) is a critical stage in establishing a lifelong infection in the host. Upon entering the cytoplasm of axons, AHV nucleocapsids and associated inner-tegument proteins must engage the cellular retrograde transport machinery to promote the long-distance movement of virion components to the nucleus. The current model outlining this process is incomplete, and further investigation is required to discover all viral and cellular determinants involved as well as the temporality of the events. Using a modified trichamber system, we have discovered a novel role of the pseudorabies virus (PRV) serine/threonine kinase US3 in promoting efficient retrograde transport of nucleocapsids. We discovered that transporting nucleocapsids move at similar velocities in both the presence and absence of a functional US3 kinase; however, fewer nucleocapsids are moving when US3 is absent, and they move for shorter periods of time before stopping, suggesting that US3 is required for efficient nucleocapsid engagement with the retrograde transport machinery. This led to fewer nucleocapsids reaching the cell bodies to produce a productive infection 12 h later. Furthermore, US3 was responsible for the induction of local translation in axons as early as 1 h postinfection (hpi) through the stimulation of a phosphatidylinositol 3-kinase (PI3K)/Akt-mToRC1 pathway. These data describe a novel role for US3 in the induction of local translation in axons during AHV infection, a critical step in transport of nucleocapsids to the cell body. IMPORTANCE Neurons are highly polarized cells with axons that can reach centimeters in length. Communication between axons at the periphery and the distant cell body is a relatively slow process involving the active transport of chemical messengers. There is a need for axons to respond rapidly to extracellular stimuli. Translation of repressed mRNAs present within the axon occurs to enable rapid, localized responses independently of the cell body. AHVs have evolved a way to hijack local translation in the axons to promote their transport to the nucleus. We have determined the cellular mechanism and viral components involved in the induction of axonal translation. The US3 serine/threonine kinase of PRV activates Akt-mToRC1 signaling pathways early during infection to promote axonal translation. When US3 is not present, the number of moving nucleocapsids and their processivity are reduced, suggesting that US3 activity is required for efficient engagement of nucleocapsids with the retrograde transport machinery.

Knockdown of PAK1 Inhibits the Proliferation and Invasion of Non-Small Cell Lung Cancer Cells Through the ERK Pathway

The p21-activated kinase (PAK) family of serine/threonine kinases plays a pivotal role in various human tumors, as supported by our previous report on the overexpressed PAK isoforms in non-small cell lung cancer (NSCLC). To better understand the role of PAKs in tumorigenesis, the authors examined PAK1 expression patterns and its significance in NSCLC. It was demonstrated by immunohistochemical staining that PAK1 was increased and localized in the cytoplasm in 151 of 207 cases. High levels of PAK1 expression correlated with a histologic type of tumor (squamous cell carcinoma), tumor node metastasis stage, and lymph nodal status. We also examined the biological role of PAK1 in lung cancer cell lines transfected with PAK1-small interfering RNA. Decreased expression of PAK1 inhibited lung cancer cell proliferation and invasion, which is the major cause of lung cancer malignancy. Downregulated expression of PAK1 hampered rapidly accelerated fibrosarcoma/mitogen-activated extracellular signal-regulated kinase/extracellular signal-regulated kinase pathway activity but did not affect Wnt/β-catenin signaling. Our findings suggest that PAK1 is an important oncogene in NSCLC, as decreased expression of PAK1 inhibited the proliferation and invasion of NSCLC cells by blocking the ERK pathway. These results provide evidence for using PAK1 inhibition as potential anticancer therapy.

RAB7A Regulates Vimentin Phosphorylation through AKT and PAK

Simple Summary

RAB7A (RAs-related in Brain 7A) is a master regulator of intracellular traffic controlling transport to late endosomes and lysosomes, two organelles of the endocytic pathway important for degradation. Thanks to this function, RAB7A is also involved in cellular processes linked to cancer, such as apoptosis, cytoskeletal reorganization, and cell migration. Therefore, the interest in the role of RAB7A in cancer progression is increasing. Previously, we demonstrated that RAB7A regulates phosphorylation and assembly of vimentin, a cytoskeletal intermediate filament protein, which is also an important mesenchymal marker of cancer cells. The aim of the present study is the identification of the kinases responsible for vimentin phosphorylation whose activity is affected by the modulation of RAB7A expression. We found that RAB7A is able to regulate AKT (also called protein kinase B or PKB) and PAK1 (P21-Activated Kinase 1) and several of their downstream effectors, which control proliferation, apoptosis, survival, migration, and invasion. These data suggest that RAB7A could have a key role in cancer development.

Abstract

RAB7A is a small GTPase that controls the late endocytic pathway but also cell migration through RAC1 (Ras-related C3 botulinum toxin substrate 1) and vimentin. In fact, RAB7A regulates vimentin phosphorylation at different sites and vimentin assembly, and, in this study, we identified vimentin domains interacting with RAB7A. As several kinases could be responsible for vimentin phosphorylation, we investigated whether modulation of RAB7A expression affects the activity of these kinases. We discovered that RAB7A regulates AKT and PAK1, and we demonstrated that increased vimentin phosphorylation at Ser38 (Serine 38), observed upon RAB7A overexpression, is due to AKT activity. As AKT and PAK1 are key regulators of several cellular events, we investigated if RAB7A could have a role in these processes by modulating AKT and PAK1 activity. We found that RAB7A protein levels affected beta-catenin and caspase 9 expression. We also observed the downregulation of cofilin-1 and decreased matrix metalloproteinase 2 (MMP2) activity upon RAB7A silencing. Altogether these results demonstrate that RAB7A regulates AKT and PAK1 kinases, affecting their downstream effectors and the processes they regulate, suggesting that RAB7A could have a role in a number of cancer hallmarks.

p21-Activated Kinases in Thyroid Cancer

The family of p21-activated kinases (PAKs) are oncogenic proteins that regulate critical cellular functions. PAKs play central signaling roles in the integrin/CDC42/Rho, ERK/MAPK, PI3K/AKT, NF-κB, and Wnt/β-catenin pathways, functioning both as kinases and scaffolds to regulate cell motility, mitosis and proliferation, cytoskeletal rearrangement, and other cellular activities. PAKs have been implicated in both the development and progression of a wide range of cancers, including breast cancer, pancreatic melanoma, thyroid cancer, and others. Here we will discuss the current knowledge on the structure and biological functions of both group I and group II PAKs, as well as the roles that PAKs play in oncogenesis and progression, with a focus on thyroid cancer and emerging data regarding BRAF/PAK signaling.

New Insights on the Effect of TNF Alpha Blockade by Gene Silencing in Noise-Induced Hearing Loss

Noise exposure represents the second most common cause of acquired sensorineural hearing loss and we observed that tumor necrosis factor α (TNFα) was involved in this context. The effect of Tnfα gene silencing on the expression profile related to the TNFα metabolic pathway in an experimental model of noise-induced hearing loss had not previously been studied. Methods: Single ears of Wistar rats were pretreated with Tnfα small interfering RNA (siRNA) by trans-tympanic administration 24 h before they were exposed to white noise (120 dBSPL for three hours). After 24 h of noise exposure, we analyzed the electrophysiological threshold and the amplitude of waves I, II, III, and IV in the auditory brain response click. In addition, qRT-PCR was performed to evaluate the TNFα metabolic pathway in the ears submitted or not to gene silencing. Results: Preservation of the electrophysiological threshold and the amplitude of waves was observed in the ears submitted to gene silencing compared to the ears not treated. Increased anti-apoptotic gene expression and decreased pro-apoptotic gene expression were found in the treated ears. Conclusion: Our results allow us to suggest that the blockade of TNFα by gene silencing was useful to prevent noise-induced hearing loss.

Tumor Necrosis Factor-Induced miR-146a Upregulation Promotes Human Lung Adenocarcinoma Metastasis by Targeting Merlin

Inflammation plays a key role in carcinogenesis and metastasis. This process involves the inactivation of tumor suppressor molecules, yet the molecular mechanisms by which inflammation impairs tumor suppressors are not completely understood. In this study, we show that proinflammatory signals such as tumor necrosis factor (TNF) support lung cancer metastasis by reducing the levels of the tumor suppressor Merlin through regulation of miR-146a. Immunodeficient mice inoculated with A549 cells expressing high miR-146a levels and low Merlin protein levels exhibited reduced survival, which correlated with the number of metastatic nodes formed. Accordingly, restoring Merlin protein levels inhibited metastasis and increased survival of the mice. Consistent with these results, we found that elevated miR-146a expression levels correlated with low Merlin protein levels in human lung adenocarcinoma. Furthermore, human invasive and metastatic tumors showed higher TNF and miR-146a levels, but lower Merlin protein levels than noninvasive tumors. These findings indicate that upregulation of miR-146a by TNF in lung adenocarcinoma promotes Merlin protein inhibition and metastasis. Thus, we suggest that the ratio between miR-146a and Merlin protein levels could be a relevant molecular biomarker that can predict lung cancer progression and that the TNF/miR-146a/Merlin pathway is a promising new therapeutic target to inhibit lung adenocarcinoma progression.

MicroRNA-7-5p induces cell growth inhibition, cell cycle arrest and apoptosis by targeting PAK2 in non-small cell lung cancer

MicroRNAs (miR) are known to be critical regulators in tumor progression. miR-7-5p was reported to be involved in several cancers, including glioblastoma, cervical cancer, and melanoma, but its prognostic value and biological function in non-small-cell lung cancer (NSCLC) remain unclear. In this study, using quantitative real-time PCR analysis, we found that miR-7-5p was significantly downregulated in NSCLC tissues and cell lines. Lower miR-7-5p expression was associated with tumor-node-metastasis stage and tumor size by chi-squared test. Deceased miR-7-5p expression was associated with a worse prognosis in patients with NSCLC using Kaplan-Meier survival analysis and multivariate Cox regression analysis. Experiments in NSCLC cell lines (A549 and H1299) demonstrated that upregulation of miR-7-5p significantly suppressed cell proliferation, but induced cell cycle G0/G1 phase arrest and apoptosis using Cell Counting Kit-8, colony formation, and flow cytometry analysis. Through loss-of-function assays, we further demonstrated that downregulation of miR-7-5p promoted cell proliferation and cell cycle G1/S transition, but decreased cell apoptosis in SPC-A1 cells. Furthermore, P21-activated kinase 2 (PAK2) was predicted and confirmed as a direct target gene of miR-7-5p in NSCLC cells by luciferase reporter assay. In addition, we found PAK2 overexpression could partially reverse the effects of miR-7-5p on cell proliferation, cell cycle distribution, and apoptosis. We thus concluded that lower expression of miR-7-5p was associated with poor prognosis and NSCLC progression by directly targeting PAK2.

TUFT1 promotes metastasis and chemoresistance in triple negative breast cancer through the TUFT1/Rab5/Rac1 pathway

Background

Triple negative breast cancer (TNBC) is a breast cancer (BC) subtype that is characterized by its strong invasion and a high risk of metastasis. However, the specific mechanisms underlying these phenotypes are unclear. TUFT1 plays an important role in BC and impacts the proliferation and survival of BC cells. Recent studies have shown that TUFT1 mediates intracellular lysosome localization and vesicle transport by regulating Rab GTPase, but the relevance of this activity in TNBC is unknown. Therefore, our aim was to systematically study the role of TUFT1 in the metastasis and chemoresistance of TNBC.

Methods

We measured TUFT1, Rab5-GTP, and Rac1-GTP expression levels in samples of human TNBC by immunohistochemistry (IHC) and conducted univariate and multivariate analyses. shRNA-mediated knockdown and overexpression, combined with transwell assays, co-immunoprecipitation, a nude mouse xenograft tumor model, and GTP activity assays were used for further mechanistic studies.

Results

TUFT1 expression was positively correlated with Rab5-GTP and Rac1-GTP in the TNBC samples, and co-expression of TUFT1 and Rab5-GTP predicted poor prognosis in TNBC patients who were treated with chemotherapy. Mechanism studies showed that TUFT1 could activate Rab5 by binding to p85α, leading to activation of Rac1 through recruitment of Tiam1, and concurrent down-regulation of the NF-κB pathway and proapoptotic factors, ultimately promoting metastasis and chemoresistance in TNBC cells.

Conclusions

Our findings suggest that the TUFT1/Rab5/Rac1 pathway may be a potential target for the effective treatment of TNBC.

Mixed lineage kinase 3 promotes breast tumorigenesis via phosphorylation and activation of p21-activated kinase 1

Mixed lineage kinase 3 (MLK3), a MAP3K member has been envisioned as a viable drug target in cancer, yet its detailed function and signaling is not fully elucidated. We identified that MLK3 tightly associates with an oncogene, PAK1. Mammalian PAK1 being a Ste20 (MAP4K) member, we tested whether it is an upstream regulator of MLK3. In contrast to our hypothesis, MLK3 activated PAK1 kinase activity directly, as well as in the cells. Although, MLK3 can phosphorylate PAK1 on Ser133 and Ser204 sites, PAK1S133A mutant is constitutively active, whereas, PAK1S204A is not activated by MLK3. Stable overexpression of PAK1S204A in breast cancer cells, impedes migration, invasion, and NFĸB activity. In vivo breast cancer cell tumorigenesis is significantly reduced in tumors expressing PAK1S204A mutant. These results suggest that mammalian PAK1 does not act as a MAP4K and MLK3-induced direct activation of PAK1 plays a key role in breast cancer tumorigenesis.

Inhibition of PAK1 alleviates cerulein-induced acute pancreatitis via p38 and NF-κB pathways

Acute pancreatitis is a life-threatening disease accompanied by systemic inflammatory response. NF-κB and p38 signal pathways are activated in AP induced by cerulein. And PAKs are multifunctional effectors of Rho GTPases with kinase activity. In the present study, the function of P21-activated kinase 1 (PAK1) in AP was investigated, and found that PAK1 was up-regulated in pancreas of AP mice model, and led to NF-κB and p38 pathway activation. PAK1 inhibition by shRNA or small molecule inhibitor FRAX597 decreased NF-κB and p38 activity, also alleviated the pathological damage in the pancreas of AP mice model, including decreasing the amylase and lipase levels in serum, decreasing the levels of tumor necrosis factor-α, interleukin-6, and interleukin-1β in AP. These results suggested that PAK1 inhibition protects against AP by inhibiting NF-κB and p38 pathways, and indicated that PAK1 is a potential therapy to alleviate AP patients in clinic, and these need to be explored further.

Focus on Cdc42 in Breast Cancer: New Insights, Target Therapy Development and Non-Coding RNAs

Breast cancer is the most common malignant tumors in females. Although the conventional treatment has demonstrated a certain effect, some limitations still exist. The Rho guanosine triphosphatase (GTPase) Cdc42 (Cell division control protein 42 homolog) is often upregulated by some cell surface receptors and oncogenes in breast cancer. Cdc42 switches from inactive guanosine diphosphate (GDP)-bound to active GTP-bound though guanine-nucleotide-exchange factors (GEFs), results in activation of signaling cascades that regulate various cellular processes such as cytoskeletal changes, proliferation and polarity establishment. Targeting Cdc42 also provides a strategy for precise breast cancer therapy. In addition, Cdc42 is a potential target for several types of non-coding RNAs including microRNAs and lncRNAs. These non-coding RNAs is extensively involved in Cdc42-induced tumor processes, while many of them are aberrantly expressed. Here, we focus on the role of Cdc42 in cell morphogenesis, proliferation, motility, angiogenesis and survival, introduce the Cdc42-targeted non-coding RNAs, as well as present current development of effective Cdc42-targeted inhibitors in breast cancer.

Salmonella stimulates pro-inflammatory signalling through p21-activated kinases bypassing innate immune receptors

Microbial infections are most often countered by inflammatory responses that are initiated through the recognition of conserved microbial products by innate immune receptors and result in pathogen expulsion^1-6. However, inflammation can also lead to pathology. Tissues such as the intestinal epithelium, which are exposed to microbial products, are therefore subject to stringent negative regulatory mechanisms to prevent signalling through innate immune receptors^6-11. This presents a challenge to the enteric pathogen Salmonella Typhimurium, which requires intestinal inflammation to compete against the resident microbiota and to acquire the nutrients and electron acceptors that sustain its replication^12,13. We show here that S. Typhimurium stimulates pro-inflammatory signalling by a unique mechanism initiated by effector proteins that are delivered by its type III protein secretion system. These effectors activate Cdc42 and the p21-activated kinase 1 (PAK1) leading to the recruitment of TNF receptor-associated factor 6 (TRAF6) and mitogen-activated protein kinase kinase kinase 7 (TAK1), and the stimulation of nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) inflammatory signalling. The removal of Cdc42, PAK1, TRAF6 or TAK1 prevented S. Typhimurium from stimulating NF-κB signalling in cultured cells. In addition, oral administration of a highly specific PAK inhibitor blocked Salmonella-induced intestinal inflammation and bacterial replication in the mouse intestine, although it resulted in a significant increase in the bacterial loads in systemic tissues. Thus, S. Typhimurium stimulates inflammatory signalling in the intestinal tract by engaging critical downstream signalling components of innate immune receptors. These findings illustrate the unique balance that emerges from host-pathogen co-evolution, in that pathogen-initiated responses that help pathogen replication are also important to prevent pathogen spread to deeper tissues.

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 chemo-therapies. 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 chemo-resistance. Finally, the involvement of PAKs in immune modulation in the tumour microenvironment is discussed and the potential advantages of targeting PAKs are explored.

G908R NOD2 variant in a family with sarcoidosis

Background

Sarcoidosis is a systemic disease characterized by the formation of immune granulomas in various organs, mainly the lungs and the lymphatic system. Exaggerated granulomatous reaction might be triggered in response to unidentified antigens in individuals with genetic susceptibility. The present study aimed to determine the genetic variants implicated in a familial case of sarcoidosis.

Methods

Sarcoidosis presentation and history, NOD2 profile, NF-κB and cytokine production in blood monocytes/macrophages were evaluated in individuals from a family with late appearance of sarcoidosis.

Results

In the present study, we report a case of familial sarcoidosis with typical thoracic sarcoidosis and carrying the NOD2 2722G > C variant. This variant is associated with the presence of three additional SNPs for the IL17RA, KALRN and EPHA2 genes, which discriminate patients expressing the disease from others. Despite a decrease in NF-κB activity, IL-8 and TNF-A mRNA levels were increased at baseline and in stimulated conditions.

Conclusions

Combination of polymorphisms in the NOD2, IL17RA, EPHA2 and KALRN genes could play a significant role in the development of sarcoidosis by maintaining a chronic pro-inflammatory status in macrophages.

Electronic supplementary material

The online version of this article (10.1186/s12931-018-0748-5) contains supplementary material, which is available to authorized users.

Breast cancer-associated gene 3 interacts with Rac1 and augments NF-κB signaling in vitro, but has no effect on RANKL-induced bone resorption in vivo

Breast cancer-associated gene 3 (BCA3) is a recently identified adaptor protein whose functions are still being defined. BCA3 has been reported to be an important regulator of nuclear factor-κB (NF-κB) signaling. It has also been reported to interact with the small GTPase, Rac1. Consistent with that observation, in the present study, BCA3 was found to interact with nuclear Rac1 in 293 cells and influence NF-κB signaling. Additional experiments revealed that depending on cell type, BCA3 augmented, attenuated or had no effect on NF-κB signaling in vitro. Since canonical NF-κB signaling is a critical downstream target from activated receptor activator of nuclear factor κB (RANK) that is required for mature osteoclast formation and function, BCA3 was selectively overexpressed in osteoclasts in vivo using the cathepsin K promoter and the response to exogenous receptor activator of nuclear factor κB ligand (RANKL) administration was examined. Despite its ability to augment NF-κB signaling in other cells, transgenic animals injected with high-dose RANKL had the same hypercalcemic response as their wild-type littermates. Furthermore, the degree of bone loss induced by a 2-week infusion of low-dose RANKL was the same in both groups. Combined with earlier studies, the data from our study data indicate that BCA3 can affect NF-κB signaling and that BCA3 plays a cell-type dependent role in this process. The significance of the BCA3/NF-κB interaction in vivo in bone remains to be determined.

Epidermal activation of the small GTPase Rac1 in psoriasis pathogenesis

The small GTPase Ras-related C3 botulinum toxin substrate 1 (RAC1) plays a central role in skin homeostasis, including barrier function, wound healing and inflammatory responses. Psoriasis is a common skin disease characterized by deregulation of these functions, and affected skin exhibit keratinocyte hyperproliferation, inflammation and immune cell infiltration. Although psoriasis is often triggered by environmental stimulus, there is a strong genetic association with genes expressed in both immune cells and keratinocytes, of which several are linked to Rac1 signaling. Rac1 is highly active in human psoriatic lesional skin and keratinocytes, and keratinocyte-specific overexpression of an activated mutant of Rac1, Rac1^V12, in a transgenic mouse model closely mimics the presentation of human psoriasis. Both Rac1 activation in keratinocytes and immune derived stimulus are required to drive psoriasiform signaling in transgenic mouse and human xenograft models of psoriasis. Therefore, understanding how increased Rac1 activation in psoriatic epidermis is regulated is central to understanding how the abnormal crosstalk between keratinocytes and immune cells is maintained.

Subverting Host Cell P21-Activated Kinase: A Case of Convergent Evolution across Pathogens

Intracellular pathogens have evolved a wide range of strategies to not only escape from the immune systems of their hosts, but also to directly exploit a variety of host factors to facilitate the infection process. One such strategy is to subvert host cell signalling pathways to the advantage of the pathogen. Recent research has highlighted that the human serine/threonine kinase PAK, or p21-activated kinase, is a central component of host-pathogen interactions in many infection systems involving viruses, bacteria, and eukaryotic pathogens. PAK paralogues are found in most mammalian tissues, where they play vital roles in a wide range of functions. The role of PAKs in cell proliferation and survival, and their involvement in a number of cancers, is of great interest in the context of drug discovery. In this review we discuss the latest insights into the surprisingly central role human PAK1 plays for the infection by such different infectious disease agents as viruses, bacteria, and parasitic protists. It is our intention to open serious discussion on the applicability of PAK inhibitors for the treatment, not only of neoplastic diseases, which is currently the primary objective of drug discovery research targeting these enzymes, but also of a wide range of infectious diseases.

Activity of caffeic acid phenethyl ester in Caenorhabditis elegans

AIM

Caffeic acid (3,4-dihydroxycinnamic acid) phenethyl ester (CAPE), the major constituent of propolis, is able to increase the survival of the nematode Caenorhabditis elegans after infection with the fungal pathogen Candida albicans.

RESULTS

CAPE increases the expression of several antimicrobial proteins involved in the immune response to C. albicans. Structural derivatives of CAPE were synthesized to identify structure-activity relationships and decrease metabolic liability, ultimately leading to a compound that has similar efficacy, but increased in vivo stability. The CED-10(Rac-1)/PAK1 pathway was essential for immunomodulation by CAPE and was a critical component involved in the immune response to fungal pathogens.

CONCLUSION

Caenorhabditis elegans is an efficient heterologous host to evaluate immunomodulatory compounds and identify components of the pathway(s) involved in the mode of action of compounds.

Suppression of FoxO6 by lipopolysaccharide in aged rat liver

The beneficial role of FoxO during aging has been proposed for its promotion of resistance to oxidative stress and inhibition of pro-inflammatory mediators. On the other hand, NF-κB is a pro-inflammatory transcription factor which is a key mediator of inflammatory cytokine generation. However, the correlation between FoxO6 and NF-κB during aging has not fully been explored.

The main purpose of the present study was to elucidate mechanisms underlying the protective role of FoxO6 in the maintenance of cellular homeostasis under potent pro-inflammatory conditions induced by LPS. Initial experimentation revealed that reduced FoxO6 activity during aging was caused by its phosphorylation, which suppressed its transcriptional activity in aged livers. Transfection with FoxO6-wt virus and FoxO6-siRNA in HepG2 cells revealed that FoxO6 phosphorylation by LPS leads to NF-κB activation via Akt and Pak1 pathways. Furthermore, Pak1 activity was increased in a phosphatidylinositol 3-kinase independent manner, and LPS-induced FoxO6 phosphorylation and FoxO6 inactivation were Pak1-dependent in nuclear fractions of cells. Further revealed Pak1 phosphorylation by LPS permitted interaction between FoxO6 and Akt.

Current study suggests FoxO6 phosphorylation facilitates the nuclear translocation of NF-κB via Akt and Pak1 pathways induced by LPS in aged rats.

RAC1 activation drives pathologic interactions between the epidermis and immune cells

Interactions between the epidermis and the immune system govern epidermal tissue homeostasis. These epidermis-immune interactions are altered in the inflammatory disease psoriasis; however, the pathways that underlie this aberrant immune response are not well understood. Here, we determined that Ras-related C3 botulinum toxin substrate 1 (RAC1) is a key mediator of epidermal dysfunction. RAC1 activation was consistently elevated in psoriatic epidermis and primary psoriatic human keratinocytes (PHKCs) exposed to psoriasis-related stimuli, but not in skin from patients with basal or squamous cell carcinoma. Expression of a constitutively active form of RAC1 (RACV12) in mice resulted in the development of lesions similar to those of human psoriasis that required the presence of an intact immune system. RAC1V12-expressing mice and human psoriatic skin showed similar RAC1-dependent signaling as well as transcriptional overlap of differentially expressed epidermal and immune pathways. Coculture of PHKCs with immunocytes resulted in the upregulation of RAC1-dependent proinflammatory cytokines, an effect that was reproduced by overexpressing RAC1 in normal human keratinocytes. In keratinocytes, modulating RAC1 activity altered differentiation, proliferation, and inflammatory pathways, including STAT3, NFκB, and zinc finger protein 750 (ZNF750). Finally, RAC1 inhibition in xenografts composed of human PHKCs and immunocytes abolished psoriasiform hyperplasia and inflammation in vivo. These studies implicate RAC1 as a potential therapeutic target for psoriasis and as a key orchestrator of pathologic epidermis-immune interactions.

Inhibition of p21-Activated Kinase 1 by IPA-3 Promotes Locomotor Recovery After Spinal Cord Injury in Mice

STUDY DESIGN

Ninety-six male adult CD-1 mice were randomly divided into sham, spinal cord injury (SCI) + vehicle, and SCI + IPA-3 groups. Expression of matrix metalloproteinase (MMP)-2 and MMP-9, production of tumor necrosis factors (TNF)-α and interleukin (IL)-1β, tissue edema, blood-spinal cord barrier penetrability, neural cell apoptosis, and neurological function recovery were measured.

OBJECTIVE

The aim of the study was to evaluate the effect of specific inhibition of p21-activated kinase 1 (PAK1) by IPA-3 on SCI and the underlying mechanisms thereof.

SUMMARY OF BACKGROUND DATA

SCI is a devastating clinical condition that may result in long-lasting and deteriorating functional deficits. The major goal of SCI treatment is to limit the development of secondary injury. IPA-3, a PAK1 inhibitor, exhibited neuroprotection against secondary damage after traumatic brain injury and subarachnoid hemorrhage (SAH).

METHODS

MMP-2, MMP-9, and cleaved caspase-3 expression were assessed by Western blot. Inflammatory cytokines TNF-α and IL-1β were detected by enzyme-linked immunosorbent assay (ELISA). The blood-spinal cord barrier disruption was measured by water content and Evans blue extravasation of the spinal cord. Neuronal apoptosis was evaluated by Nissl staining and Terminal-deoxynucleoitidyl Transferase Mediated Nick End Labeling (TUNEL) assay. The locomotor behavior of hind limb was evaluated by Basso Mouse Scale (BMS) at 1, 3, 7, 14, and 28 days post-injury.

RESULTS

Compared with SCI + vehicle mice, IPA-3 treatment showed decreased p-PAK1, MMP-2, MMP-9, cleaved caspase-3, TNF-α, and IL-1β expression. Moreover, inhibition of PAK1 by IPA-3 reduced spinal cord water content and Evans blue extravasation, increased neuronal survival, and reduced TUNEL-positive cells at 24 hours after SCI. Furthermore, IPA-3 improved spinal cord functional recovery 7 days after SCI.

CONCLUSION

Inhibition of PAK1 by IPA-3 promoted recovery of neurological function, possibly by downregulating the expression of MMP-2, MMP-9, TNF-α, and IL-1β. Our data suggest that PAK1 may be a potential therapeutic target in patients with SCI.

LEVEL OF EVIDENCE

1.

PAK1 modulates a PPARγ/NF-κB cascade in intestinal inflammation

P21-activated kinases (PAKs) are multifunctional effectors of Rho GTPases with both kinase and scaffolding activity. Here, we investigated the effects of inflammation on PAK1 signaling and its role in colitis-driven carcinogenesis. PAK1 and p-PAK1 (Thr423) were assessed by immunohistochemistry, immunofluorescence, and Western blot. C57BL6/J wildtype mice were treated with a single intraperitoneal TNFα injection. Small intestinal organoids from these mice and from PAK1-KO mice were cultured with TNFα. NF-κB and PPARγ were analyzed upon PAK1 overexpression and silencing for transcriptional/translational regulation. PAK1 expression and activation was increased on the luminal intestinal epithelial surface in inflammatory bowel disease and colitis-associated cancer. PAK1 was phosphorylated upon treatment with IFNγ, IL-1β, and TNFα. In vivo, mice administered with TNFα showed increased p-PAK1 in intestinal villi, which was associated with nuclear p65 and NF-κB activation. p65 nuclear translocation downstream of TNFα was strongly inhibited in PAK1-KO small intestinal organoids. PAK1 overexpression induced a PAK1-p65 interaction as visualized by co-immunoprecipitation, nuclear translocation, and increased NF-κB transactivation, all of which were impeded by kinase-dead PAK1. Moreover, PAK1 overexpression downregulated PPARγ and mesalamine recovered PPARγ through PAK1 inhibition. On the other hand PAK1 silencing inhibited NF-κB, which was recovered using BADGE, a PPARγ antagonist. Altogether these data demonstrate that PAK1 overexpression and activation in inflammation and colitis-associated cancer promote NF-κB activity via suppression of PPARγ in intestinal epithelial cells.

PAK1 promotes intestinal tumor initiation

p21-activated kinase 1 (PAK1) is a serine/threonine kinase that is overexpressed in colorectal cancer. PAK1 is a target of mesalamine [5-aminosylicylic acid (5-ASA)], a common drug for the treatment of ulcerative colitis with prospective chemopreventive properties. Here, we investigated whether PAK1 deletion impedes tumorigenesis in murine intestinal cancer models. Ten-week-old APC(min) or APC(min)/PAK1(-/-) mice were monitored for 8 weeks, euthanized, and assessed for tumor number and size. Six- to 8-week-old PAK1(-/-) and wild-type (WT) mice received one 10 mg/kg intraperitoneal injection of azoxymethane (AOM) and four cycles of 1.7% dextran sodium sulfate (DSS) for 4 days followed by 14 days of regular water. Mice also received 5-ASA via diet. Tumor incidence and size was assessed via colonoscopy and pathology. Molecular targets of PAK1 and 5-ASA were evaluated via immunohistochemistry (IHC) in both models. PAK1 deletion reduced tumor multiplicity and tumor burden but did not alter average tumor size in APC(min) mice. IHC revealed that PAK1 deletion reduced p-AKT, β-catenin, and c-Myc expression in APC(min) adenomas. Colonoscopy and pathologic analysis revealed that PAK1 deletion reduced tumor multiplicity without affecting tumor size in AOM/DSS-treated mice. 5-ASA treatment and PAK1 deletion impeded tumor multiplicity and dysplastic lesions in AOM/DSS mice. IHC further revealed that 5-ASA blocked β-catenin signaling via inhibition of PAK1/p-AKT. These data indicate that PAK1 contributes to initiation of intestinal carcinogenesis.

Overexpression of PAK1 promotes cell survival in inflammatory bowel diseases and colitis-associated cancer

BACKGROUND

Chronic gut inflammation predisposes to the development of colorectal cancer and increased mortality. Use of mesalamine (5-ASA) in the treatment of ulcerative colitis modulates the risk of neoplastic progression. p21 activated kinase 1 (PAK1) mediates 5-ASA activity by orchestrating MAPK signaling, Wnt-β catenin pathway, and cell adhesion; all implicated in the colon carcinogenesis. We evaluated the role of PAK1 in IBD and in colitis-associated cancer (CAC).

METHODS AND RESULTS

PAK1 expression was scored by immunohistochemistry in human samples from IBD, CAC, and in normal mucosa. Compared with controls, a higher PAK1 expression was detected in IBD which further increased in CAC. The consequence of PAK1 overexpression was investigated using normal diploid colon epithelial cells (HCEC-1CT), which showed higher proliferation and decreased apoptosis on overexpression of PAK1. Analysis of IBD and CAC samples showed activation of AKT (p-AKT). However, mTOR pathway was activated in IBD but not in CAC. Treatment of cells with specific inhibitors (PD98059/LY294002/rapamycin) of growth signaling pathways (MEK/PI3K/mTOR) demonstrated that in HCEC-1CT, PAK1 expression is regulated by MEK, PI3K, and mTOR. In colorectal cancer cell lines, PAK1, and beta-catenin expression correlated and inhibition of PAK1 and addition of 5-ASA elicited similar molecular affects by reducing ERK and AKT activation. Moreover, 5-ASA disrupted PAK1 interaction and colocalization with β-catenin.

CONCLUSIONS

Our data indicate that (1) PAK1 is upregulated in IBD and CAC (2) PAK1 overexpression is associated with activation of PI3K-AKT/mTOR prosurvival pathways in IBD.

Polycomb-mediated loss of microRNA let-7c determines inflammatory macrophage polarization via PAK1-dependent NF-κB pathway

Serine/threonine kinase family members p21-activated kinases (PAKs) are important regulators of cytoskeletal remodeling and cell motility in mononuclear phagocytic system, but their role in macrophage differentiation and polarization remains obscure. We have shown here that inflammatory stimuli induced PAK1 overexpression in human and murine macrophages. Elevated expression of PAK1 contributed to macrophage M1 polarization and lipopolysaccharide (LPS)-induced endotoxin shock. We further observed that epigenetic loss of microRNA let-7c due to enhancer of zeste homolog 2 (EZH2) upregulation determined PAK1 elevation and inflammatory phenotype in M1 macrophages. EZH2/let-7c/PAK1 axis promotes macrophage M1 polarization via NIK-IKK-NF-κB signaling. Moreover, pharmacological and genetic ablation with EZH2/let-7c/PAK1 axis blunted inflammatory phenotype in M1 macrophages. Critically, either myeloid-restricted PAK1 deletion (PAK1(Lyz2cre)) or pharmacological and genetic ablation with EZH2/let-7c/PAK1 signal resulted in resistance to LPS-induced endotoxin shock via blunting macrophage M1 polarization. PAK1, therefore, is an essential controller of inflammatory macrophage polarization, regulating immune responses against pathogenic stimuli.

Republished: tracing PAKs from GI inflammation to cancer

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

PAK signaling in cancer

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

Inhibition of p21-activated kinase 1 by IPA-3 attenuates secondary injury after traumatic brain injury in mice

The p21-activated kinase 1 (PAK1) is up-regulated in the brain following traumatic brain injury (TBI). Inhibition of PAK1 has been found to alleviate brain edema in a rat model of subarachnoid hemorrhage. Suppressing PAK1 activity might represent a novel therapeutics of attenuating secondary injury following TBI. Here we confirmed that the mRNA and protein levels of PAK1 and the protein level of p-PAK1 were significantly increased after inducing TBI in mice via M.A. Flierl's weight-drop model. A single intraperitoneal administration of IPA-3, a specific PAK1 inhibitor, immediately after TBI significantly reduced the protein level of p-PAK1, cleaved caspase-3 level, the number of apoptotic cells at the lesion sites of TBI mice. It also reduced brain water content and the blood-brain barrier permeability in TBI mice. Furthermore, the administration of IPA-3 significantly reduced the neurological severity score and increased the grip test score in TBI mice. Taken together, we demonstrate that PAK1 inhibition by IPA-3 may attenuate the secondary injury following TBI, suggesting it might be a promising neuroprotective strategy for preventing the development of secondary injury after TBI.

The role of p21-activated kinases in hepatocellular carcinoma metastasis

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

Aberrant Rac1-mineralocorticoid receptor pathways in salt-sensitive hypertension

According to Guyton's model, impaired renal sodium excretion plays a key role in the increased salt sensitivity of blood pressure (BP). Several factors contribute to impaired renal sodium excretion, including the sympathetic nervous system, the renin-angiotensin system and aldosterone. Accumulating evidence suggests that abnormalities in aldosterone and its receptor (i.e. the mineralocorticoid receptor (MR)) are involved in the development of salt-sensitive (SS) hypertension. Patients with metabolic syndrome often exhibit hyperaldosteronism and are susceptible to SS hypertension. Aldosterone secretion from the adrenal glands is not suppressed in obese hypertensive rats fed a high-salt diet because of the abundant production of adipocyte-derived aldosterone-releasing factors, which are independent of the negative feedback regulation of aldosterone secretion by the renin-angiotensin-aldosterone system. Increased plasma aldosterone levels lead to SS hypertension via MR activation in the kidney. Renal MR activity is increased in Dahl salt-sensitive rats fed a high-salt diet, despite the appropriate suppression of plasma aldosterone levels. In this rat strain, activation of MR in the distal nephron causes salt-induced hypertension. This paradoxical response of the MR to salt loading can be attributed to activation of Rac1, a small GTPase. In the presence of aldosterone, activated Rac1 synergistically and directly activates MR in a ligand-independent manner. Thus, Rac1 activation in the kidney determines the salt sensitivity of BP. Together, the available evidence suggests that the aberrant Rac1-MR pathway plays a key role in the development of SS hypertension.

Tracing PAKs from GI inflammation to cancer

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

Regulated localization is sufficient for hormonal control of regulator of G protein signaling homology Rho guanine nucleotide exchange factors (RH-RhoGEFs)

The regulator of G protein signaling homology (RH) Rho guanine nucleotide exchange factors (RhoGEFs) (p115RhoGEF, leukemia-associated RhoGEF, and PDZ-RhoGEF) contain an RH domain and are specific GEFs for the monomeric GTPase RhoA. The RH domains interact specifically with the α subunits of G12 heterotrimeric GTPases. Activated Gα13 modestly stimulates the exchange activity of both p115RhoGEF and leukemia-associated RhoGEF but not PDZ-RhoGEF. Because all three RH-RhoGEFs can localize to the plasma membrane upon expression of activated Gα13, cellular localization of these RhoGEFs has been proposed as a mechanism for controlling their activity. We use a small molecule-regulated heterodimerization system to rapidly control the localization of RH-RhoGEFs. Acute localization of the proteins to the plasma membrane activates RhoA within minutes and to levels that are comparable with activation of RhoA by hormonal stimulation of G protein-coupled receptors. The catalytic activity of membrane-localized RhoGEFs is not dependent on activated Gα13. We further show that the conserved RH domains can rewire two different RacGEFs to activate Rac1 in response to a traditional activator of RhoA. Thus, RH domains act as independent detectors for activated Gα13 and are sufficient to modulate the activity of RhoGEFs by hormones via mediating their localization to substrate, membrane-associated RhoA.

p21-Activated protein kinases and their emerging roles in glucose homeostasis

p21-Activated protein kinases (PAKs) are centrally involved in a plethora of cellular processes and functions. Their function as effectors of small GTPases Rac1 and Cdc42 has been extensively studied during the past two decades, particularly in the realms of cell proliferation, apoptosis, and hence tumorigenesis, as well as cytoskeletal remodeling and related cellular events in health and disease. In recent years, a large number of studies have shed light onto the fundamental role of group I PAKs, most notably PAK1, in metabolic homeostasis. In skeletal muscle, PAK1 was shown to mediate the function of insulin on stimulating GLUT4 translocation and glucose uptake, while in pancreatic β-cells, PAK1 participates in insulin granule localization and vesicle release. Furthermore, we demonstrated that PAK1 mediates the cross talk between insulin and Wnt/β-catenin signaling pathways and hence regulates gut proglucagon gene expression and the production of the incretin hormone glucagon-like peptide-1 (GLP-1). The utilization of chemical inhibitors of PAK and the characterization of Pak1(-/-) mice enabled us to gain mechanistic insights as well as to assess the overall contribution of PAKs in metabolic homeostasis. This review summarizes our current understanding of PAKs, with an emphasis on the emerging roles of PAK1 in glucose homeostasis.

P21 activated kinases: structure, regulation, and functions

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

Transcriptional regulation of fibronectin by p21-activated kinase-1 modulates pancreatic tumorigenesis

Pancreatic ductal adenocarcinoma (PDAC) is the eighth largest cause of cancer-related mortality across the world, with a median 5-year survival rate of less than 3.5%. This is partly because the molecules and the molecular mechanisms that contribute to PDAC are not well understood. Our goal is to understand the role of p21-activated kinase 1 (Pak1) signaling axis in the progression of PDAC. Pak1, a serine/threonine kinase, is a well-known regulator of cytoskeletal remodeling, cell motility, cell proliferation and cell survival. Recent reports suggest that Pak1 by itself can have an oncogenic role in a wide variety of cancers. In this study, we analyzed the expression of Pak1 in human pancreatic cancer tissues and found that Pak1 levels are significantly upregulated in PDAC samples as compared with adjacent normals. Further, to study the functional role of Pak1 in pancreatic cancer model systems, we developed stable overexpression and lentiviral short hairpin RNA-mediated knockdown (KD) clones of Pak1 and studied the changes in transforming properties of the cells. We also observed that Pak1 KD clones failed to form tumors in nude mice. By adopting a quantitative PCR array-based approach, we identified fibronectin, a component of the extracellular matrix and a mesenchymal marker, as a transcriptional target of Pak1 signaling. The underlying molecular mechanism of Pak1-mediated transformation includes its nuclear import and recruitment to the fibronectin promoter via interaction with nuclear factor-κB (NF-κB)-p65 complex. To our knowledge, this is the first study illustrating Pak1-NF-κB-p65-mediated fibronectin regulation as a potent tumor-promoting mechanism in KRAS intact model.

The SmgGDS splice variant SmgGDS-558 is a key promoter of tumor growth and RhoA signaling in breast cancer

Breast cancer malignancy is promoted by the small GTPases RhoA and RhoC. SmgGDS is a guanine nucleotide exchange factor that activates RhoA and RhoC in vitro. We previously reported that two splice variants of SmgGDS, SmgGDS-607, and SmgGDS-558, have different characteristics in binding and transport of small GTPases. To define the role of SmgGDS in breast cancer, we tested the expression of SmgGDS in breast tumors, and the role of each splice variant in proliferation, tumor growth, Rho activation, and NF-κB transcriptional activity in breast cancer cells. We show upregulated SmgGDS protein expression in breast cancer samples compared with normal breast tissue. In addition, Kaplan-Meier survival curves indicated that patients with high SmgGDS expression in their tumors had worse clinical outcomes. Knockdown of SmgGDS-558, but not SmgGDS-607, in breast cancer cells decreased proliferation, in vivo tumor growth, and RhoA activity. Furthermore, we found that SmgGDS promoted a Rho-dependent activation of the transcription factor NF-κB, which provides a potential mechanism to define how SmgGDS-mediated activation of RhoA promotes breast cancer. This study demonstrates that elevated SmgGDS expression in breast tumors correlates with poor survival, and that SmgGDS-558 plays a functional role in breast cancer malignancy. Taken together, these findings define SmgGDS-558 as a unique promoter of RhoA and NF-κB activity and a novel therapeutic target in breast cancer.

IMPLICATIONS

This study defines a new mechanism to regulate the activities of RhoA and NF-κB in breast cancer cells, and identifies SmgGDS-558 as a novel promoter of breast cancer malignancy.

Identification of novel gene targets and functions of p21-activated kinase 1 during DNA damage by gene expression profiling

P21-activated kinase 1 (PAK1), a serine/threonine protein kinase, modulates many cellular processes by phosphorylating its downstream substrates. In addition to its role in the cytoplasm, PAK1 also affects gene transcription due to its nuclear localization and association with chromatin. It is now recognized that PAK1 kinase activity and its nuclear translocation are rapidly stimulated by ionizing radiation (IR), and that PAK1 activation is a component of the DNA damage response. Owing to the role of PAK1 in the cell survival, its association with the chromatin, and now, stimulation by ionizing radiation, we hypothesize that PAK1 may be contributing to modulation of genes with roles in cellular processes that might be important in the DNA damage response. The purpose of this study was to identify new PAK1 targets in response to ionizing radiation with putative role in the DNA damage response. We examined the effect of IR on the gene expression patterns in the murine embryonic fibroblasts with or without Pak1 using microarray technology. Differentially expressed transcripts were identified using Gene Spring GX 10.0.2. Pathway, network, functional analyses and gene family classification were carried out using Kyoto Encyclopedia of Genes and Genomes (KEGG), Ingenuity Pathway, Gene Ontology and PANTHER respectively. Selective targets of PAK1 were validated by RT-qPCR. For the first time, we provide a genome-wide analysis of PAK1 and identify its targets with potential roles in the DNA damage response. Gene Ontology analysis identified genes in the IR-stimulated cells that were involved in cell cycle arrest and cell death. Pathway analysis revealed p53 pathway being most influenced by IR responsive, PAK1 targets. Gene family of transcription factors was over represented and gene networks involved in DNA replication, repair and cellular signaling were identified. In brief, this study identifies novel PAK1 dependent IR responsive genes which reveal new aspects of PAK1 biology.

Oncogene-induced cellular senescence elicits an anti-Warburg effect

Cellular senescence, an irreversible cell cycle arrest induced by a diversity of stimuli, has been considered as an innate tumor suppressing mechanism with implications and applications in cancer therapy. Using a targeted proteomics approach, we show that fibroblasts induced into senescence by expression of oncogenic Ras exhibit a decrease of global acetylation on all core histones, consistent with formation of senescence-associated heterochromatic foci. We also detected clear increases in repressive markers (e.g. >50% elevation of H3K27me2/3) along with decreases in histone marks associated with increased transcriptional expression/elongation (e.g. H3K36me2/3). Despite the increases in repressive marks of chromatin, 179 loci (of 2206 total) were found to be upregulated by global quantitative proteomics. The changes in the cytosolic proteome indicated an upregulation of mitochondrial proteins and downregulation of proteins involved in glycolysis. These alterations in primary metabolism are opposite to the well-known Warburg effect observed in cancer cells. This study significantly improves our understanding of stress-induced senescence and provides a potential application for triggering it in antiproliferative strategies that target the primary metabolism in cancer cells.

IPA-3 inhibits the growth of liver cancer cells by suppressing PAK1 and NF-κB activation

Hepatocellular carcinoma (HCC) is one of the major malignancies worldwide and is associated with poor prognosis due to the high incidences of metastasis and tumor recurrence. Our previous study showed that overexpression of p21-activated protein kinase 1 (PAK1) is frequently observed in HCC and is associated with a more aggressive tumor behavior, suggesting that PAK1 is a potential therapeutic target in HCC. In the current study, an allosteric small molecule PAK1 inhibitor, IPA-3, was evaluated for the potential in suppressing hepatocarcinogenesis. Consistent with other reports, inhibition of PAK1 activity was observed in several human HCC cell lines treated with various dosages of IPA-3. Using cell proliferation, colony formation and BrdU incorporation assays, we demonstrated that IPA-3 treatment significantly inhibited the growth of HCC cells. The mechanisms through which IPA-3 treatment suppresses HCC cell growth are enhancement of apoptosis and blockage of activation of NF-κB. Furthermore, our data suggested that IPA-3 not only inhibits the HCC cell growth, but also suppresses the metastatic potential of HCC cells. Nude mouse xenograft assay demonstrated that IPA-3 treatment significantly reduced the tumor growth rate and decreased tumor volume, indicating that IPA-3 can suppress the in vivo tumor growth of HCC cells. Taken together, our demonstration of the potential preclinical efficacy of IPA-3 in HCC provides the rationale for cancer therapy.