A brain serine/threonine protein kinase activated by Cdc42 and Rac1

Dual-targeted NAMPT inhibitors as a progressive strategy for cancer therapy

In mammals, nicotinamide phosphoribosyltransferase (NAMPT) is a crucial enzyme in the nicotinamide adenine dinucleotide (NAD+) synthesis pathway catalyzing the condensation of nicotinamide (NAM) with 5-phosphoribosyl-1-pyrophosphate (PRPP) to produce nicotinamide mononucleotide (NMN). Given the pivotal role of NAD+ in a range of cellular functions, including DNA synthesis, redox reactions, cytokine generation, metabolism, and aging, NAMPT has become a promising target for many diseases, notably cancer. Therefore, various NAMPT inhibitors have been reported and classified as first and second-generation based on their chemical structures and design strategies, dual-targeted being one. However, most NAMPT inhibitors suffer from several limitations, such as dose-dependent toxicity and poor pharmacokinetic properties. Consequently, there is no clinically approved NAMPT inhibitor. Hence, research on discovering more effective and less toxic dual-targeted NAMPT inhibitors with desirable pharmacokinetic properties has drawn attention recently. This review summarizes the previously reported dual-targeted NAMPT inhibitors, focusing on their design strategies and advantages over the single-targeted therapies.

Aloesin-loaded chitosan/cellulose-based scaffold promotes skin tissue regeneration

Skin wound healing and regeneration is very challenging across the world as simple or acute wounds can be transformed into chronic wounds or ulcers due to foreign body invasion, or diseases like diabetes or cancer. The study was designed to develop a novel bioactive scaffold, by loading aloesin to chitosan-coated cellulose scaffold, to cure full-thickness skin wounds. The physiochemical characterization of the scaffold was carried out using scanning electron microscopy (SEM) facilitated by energy-dispersive spectrophotometer (EDS), atomic force microscopy (AFM), and Fourier transform infrared spectroscopy (FTIR). The results indicated the successful coating of chitosan and aloesin on cellulose without any physical damage. The drug release kinetics confirmed the sustained release of aloesin by showing a cumulative release of up to 88 % over 24 h. The biocompatibility of the aloesin-loaded chitosan/cellulose (AlCsCFp) scaffold was evaluated by the WST-8 assay that confirmed the significantly increased adherence and proliferation of fibroblasts on the AlCsCFp scaffold. The in vivo wound healing study showed that both 0.05 % and 0.025 % AlCsCFp scaffolds have significantly higher wound closure rates (i.e. 88.2 % and 95.6 % approximately) as compared to other groups. This showed that novel composite scaffold has a wound healing ability. Furthermore, histological and gene expression analysis demonstrated that the scaffold also induced cell migration, angiogenesis, re-epithelialization, collagen deposition, and tissue granulation formation. Thus, it is concluded that the aloesin-loaded chitosan/cellulose-based scaffold has great therapeutic potential for being used in wound healing applications in the clinical setting in the future.

Rapamycin vs TORin-1 or Gleevec vs Nilotinib: Simple chemical evolution that converts PAK1-blockers to TOR-blockers or vice versa?

Both PAK1 (RAC/CDC42-activating kinase 1) and TOR (Target of Rapamycin) are among the major oncogenic/ageing kinases. However, they play the opposite role in our immune system, namely immune system is suppressed by PAK1, while it requires TOR. Thus, PAK1-blockers, would be more effective for therapy of cancers, than TOR-blockers. Since 2015 when we discovered genetically that PDGF-induced melanogenesis depends on "PAK1", we are able to screening a series of PAK1-blockers as melanogenesis-inhibitors which could eventually promote longevity. Interestingly, rapamycin, the first TOR-inhibitor, promotes melanogenesis, clearly indicating that TOR suppresses melanogenesis. However, a new TOR-inhibitor called TORin-1 no longer suppresses immune system, and blocks melanogenesis in cell culture. These observations strongly indicate that TORin-1 acts as PAK1-blockers, instead of TOR-blockers, in vivo. Thus, it is most likely that melanogenesis in cell culture could enable us to discriminate PAK1-blockers from TORblockers.

HIF2α-dependent Dock4/Rac1-signaling regulates formation of adherens junctions and cell polarity in normoxia

Hypoxia-inducible factors (HIF) 1 and 2 regulate similar but distinct sets of target genes. Although HIFs are best known for their roles in mediating the hypoxia response accumulating evidence suggests that under certain conditions HIFs, particularly HIF2, may function also under normoxic conditions. Here we report that HIF2α functions under normoxic conditions in kidney epithelial cells to regulate formation of adherens junctions. HIF2α expression was required to induce Dock4/Rac1/Pak1-signaling mediating stability and compaction of E-cadherin at nascent adherens junctions. Impaired adherens junction formation in HIF2α- or Dock4-deficient cells led to aberrant cyst morphogenesis in 3D kidney epithelial cell cultures. Taken together, we show that HIF2α functions in normoxia to regulate epithelial morphogenesis.

Inhibition of P21-activated kinases 1 and 4 synergistically suppresses the growth of pancreatic cancer by stimulating anti-tumour immunity

BACKGROUND

Pancreatic ductal adenocarcinoma (PDA) is one of the most lethal types of cancer, and KRAS oncogene occurs in over 90% of cases. P21-activated kinases (PAK), containing six members (PAK1 to 6), function downstream of KRAS. PAK1 and PAK4 play important roles in carcinogenesis, but their combinational effect remains unknown. In this study, we have determined the effect of dual inhibition of PAK1 and PAK4 in PDA progression using knockout (KO) cancer cell lines.

METHODS

Murine wild-type (WT) and PAK1KO pancreatic cancer cell lines were isolated from PAK1+/+ and PAK1-/- KPC (LSL-KrasG12D/+; LSL-Trp53 R172H/+; Pdx-1-Cre) mice. KPC PAK4KO and KPC PAK1&4 KO cell lines were generated from KPC WT and KPC PAK1KO cell lines respectively using the CRISPR-CAS9 gene knockout technique. PAK WT and KO cell lines were used in mouse models of pancreatic tumours. Cells and tumour tissue were also used in flow cytometry and proteomic studies. A human PDA tissue microarray was stained by immunohistochemistry.

RESULTS

Double knock out of PAK1 and PAK4 caused complete regression of tumour in a syngeneic mouse model. PAK4KO inhibited tumour growth by stimulating a rapid increase of cytotoxic CD8+ T cell infiltration. PAK1KO synergistically with PAK4KO increased cytotoxic CD8+ T cell infiltration and stimulated a sustained infiltration of CD8+ T cells at a later phase to overcome the immune evasion in the PAK4KO tumour. The human PDA tissue microarray study showed the important role of PAK1 and PAK4 in intra-tumoral T-cell function.

CONCLUSION

Our results demonstrated that dual inhibition of PAK1 and PAK4 synergistically suppressed PDA progression by stimulating cytotoxic CD8 + T cell response.

ATG9B regulates bacterial internalization via actin rearrangement

Invasive bacterial pathogens are internalized by host cells through endocytosis, which is regulated by a cascade of actin rearrangement signals triggered by host cell receptors or bacterial proteins delivered into host cells. However, the molecular mechanisms that mediate actin rearrangement to promote bacterial invasion are not fully understood. Here, we show that the autophagy-related (ATG) protein ATG9B regulates the internalization of various bacteria by controlling actin rearrangement. ATG knockout screening and knockdown experiments in HeLa cells identified ATG9B as a critical factor for bacterial internalization. In particular, cells with ATG9B knockdown exhibited an accumulation of actin filaments and phosphorylated LIM kinase and cofilin, suggesting that ATG9B is involved in actin depolymerization. Furthermore, the kinase activity of Unc-51-like autophagy-activating kinase 1 was found to regulate ATG9B localization and actin remodeling. These findings revealed a newly discovered function of ATG proteins in bacterial infection rather than autophagy-mediated immunity.

Presynaptic Rac1 in the hippocampus selectively regulates working memory

One of the most extensively studied members of the Ras superfamily of small GTPases, Rac1 is an intracellular signal transducer that remodels actin and phosphorylation signaling networks. Previous studies have shown that Rac1-mediated signaling is associated with hippocampal-dependent working memory and longer-term forms of learning and memory and that Rac1 can modulate forms of both pre- and postsynaptic plasticity. How these different cognitive functions and forms of plasticity mediated by Rac1 are linked, however, is unclear. Here, we show that spatial working memory is selectively impaired following the expression of a genetically encoded Rac1-inhibitor at presynaptic terminals, while longer-term cognitive processes are affected by Rac1 inhibition at postsynaptic sites. To investigate the regulatory mechanisms of this presynaptic process, we leveraged new advances in mass spectrometry to identify the proteomic and post-translational landscape of presynaptic Rac1 signaling. We identified serine/threonine kinases and phosphorylated cytoskeletal signaling and synaptic vesicle proteins enriched with active Rac1. The phosphorylated sites in these proteins are at positions likely to have regulatory effects on synaptic vesicles. Consistent with this, we also report changes in the distribution and morphology of synaptic vesicles and in postsynaptic ultrastructure following presynaptic Rac1 inhibition. Overall, this study reveals a previously unrecognized presynaptic role of Rac1 signaling in cognitive processes and provides insights into its potential regulatory mechanisms.

Dendritic spines and their role in the pathogenesis of neurodevelopmental and neurological disorders

Since Cajal introduced dendritic spines in the 19th century, they have attained considerable attention, especially in neuropsychiatric and neurologic disorders. Multiple roles of dendritic spine malfunction and pathology in the progression of various diseases have been reported. Thus, it is inevitable to consider these structures as new therapeutic targets for treating neuropsychiatric and neurologic disorders such as autism spectrum disorders, schizophrenia, dementia, Down syndrome, etc. Therefore, we attempted to prepare a narrative review of the literature regarding the role of dendritic spines in the pathogenesis of aforementioned diseases and to shed new light on their pathophysiology.

Pulses of RhoA signaling stimulate actin polymerization and flow in protrusions to drive collective cell migration

In animals, cells often move as collectives to shape organs, close wounds, or-in the case of disease-metastasize. To accomplish this, cells need to generate force to propel themselves forward. The motility of singly migrating cells is driven largely by an interplay between Rho GTPase signaling and the actin network. Whether cells migrating as collectives use the same machinery for motility is unclear. Using the zebrafish posterior lateral line primordium as a model for collective cell migration, we find that active RhoA and myosin II cluster on the basal sides of the primordium cells and are required for primordium motility. Positive and negative feedbacks cause RhoA and myosin II activities to pulse. These pulses of RhoA signaling stimulate actin polymerization at the tip of the protrusions and myosin-II-dependent actin flow and protrusion retraction at the base of the protrusions and deform the basement membrane underneath the migrating primordium. This suggests that RhoA-induced actin flow on the basal sides of the cells constitutes the motor that pulls the primordium forward, a scenario that likely underlies collective migration in other contexts.

PAK in Pancreatic Cancer-Associated Vasculature: Implications for Therapeutic Response

Angiogenesis has been associated with numbers of solid tumours. Anti-angiogenesis drugs starve tumours of nutrients and oxygen but also make it difficult for a chemo reagent to distribute into a tumour, leading to aggressive tumour growth. Anti-angiogenesis drugs do not appear to improve the overall survival rate of pancreatic cancer. Vessel normalisation is merging as one of the new approaches for halting tumour progression by facilitating the tumour infiltration of immune cells and the delivery of chemo reagents. Targeting p21-activated kinases (PAKs) in cancer has been shown to inhibit cancer cell growth and improve the efficacy of chemotherapy. Inhibition of PAK enhances anti-tumour immunity and stimulates the efficacy of immune checkpoint blockades. Inhibition of PAK also improves Car-T immunotherapy by reprogramming the vascular microenvironment. This review summarizes current research on PAK's role in tumour vasculature and therapeutical response, with a focus on pancreatic cancer.

The Arp2/3 complex promotes periodic removal of Pak1-mediated negative feedback to facilitate anticorrelated Cdc42 oscillations

The conserved GTPase Cdc42 is a major regulator of polarized growth in most eukaryotes. Cdc42 periodically cycles between active and inactive states at sites of polarized growth. These periodic cycles are caused by positive feedback and time-delayed negative feedback loops. In the bipolar yeast S. pombe, both growing ends must regulate Cdc42 activity. At each cell end, Cdc42 activity recruits the Pak1 kinase which prevents further Cdc42 activation thus establishing negative feedback. It is unclear how Cdc42 activation returns to the end after Pak1-dependent negative feedback. Using genetic and chemical perturbations, we find that disrupting branched actin-mediated endocytosis disables Cdc42 reactivation at the cell ends. With our experimental data and mathematical models, we show that endocytosis-dependent Pak1 removal from the cell ends allows the Cdc42 activator Scd1 to return to that end to enable reactivation of Cdc42. Moreover, we show that Pak1 elicits its own removal via activation of endocytosis. In agreement with these observations, our model and experimental data show that in each oscillatory cycle, Cdc42 activation increases followed by an increase in Pak1 recruitment at that end. These findings provide a deeper insight into the self-organization of Cdc42 regulation and reveal previously unknown feedback with endocytosis in the establishment of cell polarity.

A Protein-Protein Interaction Analysis Suggests a Wide Range of New Functions for the p21-Activated Kinase (PAK) Ste20

The p21-activated kinases (PAKs) are important signaling proteins. They contribute to a surprisingly wide range of cellular processes and play critical roles in a number of human diseases including cancer, neurological disorders and cardiac diseases. To get a better understanding of PAK functions, mechanisms and integration of various cellular activities, we screened for proteins that bind to the budding yeast PAK Ste20 as an example, using the split-ubiquitin technique. We identified 56 proteins, most of them not described previously as Ste20 interactors. The proteins fall into a small number of functional categories such as vesicle transport and translation. We analyzed the roles of Ste20 in glucose metabolism and gene expression further. Ste20 has a well-established role in the adaptation to changing environmental conditions through the stimulation of mitogen-activated protein kinase (MAPK) pathways which eventually leads to transcription factor activation. This includes filamentous growth, an adaptation to nutrient depletion. Here we show that Ste20 also induces filamentous growth through interaction with nuclear proteins such as Sac3, Ctk1 and Hmt1, key regulators of gene expression. Combining our observations and the data published by others, we suggest that Ste20 has several new and unexpected functions.

Clinicopathological significance and the associated signaling pathway of p21-activated kinase 1 (PAK1) in colorectal cancer

The aim of this study was to evaluate the clinicopathological significance and associated signaling pathways of p21-activated kinase 1 (PAK1) in colorectal cancer (CRC). PAK1 immunohistochemical expression was investigated in 246 human CRC tissues to evaluate its clinicopathological significance and prognostic role. Correlations between PAK1 and the immunoscore, HIF-1α, and pFOXO1 were also evaluated. PAK1 was expressed in 169 of 246 CRC tissues (68.7%). PAK1 expression significantly correlated with the metastatic lymph node ratio (P = 0.023). However, PAK1 expression did not correlate with tumor size, tumor location, tumor differentiation, lymphovascular and perineural invasion, or distant metastasis. PAK1 expression was significantly higher in CRC with a low immunoscore than in CRC with a high immunoscore (P = 0.017). In addition, there were significant correlations between PAK1, HIF-1α, and pFOXO1 expression (P = 0.001 and P = 0.024, respectively). Patients with PAK1 expression had worse overall and recurrence-free survival than those without PAK1 expression (P 0.001 and P = 0.001, respectively). PAK1 expression was significantly correlated with worse prognosis in CRCs patients. In addition, PAK1 expression was significantly correlated with a low immunoscore and high expression of HIF-1α and pFOXO1 in CRCs.

PAK2/beta-catenin/c-Myc/PKM2 signal transduction suppresses ovarian granulosa cell apoptosis in polycystic ovary syndrome

Polycystic ovary syndrome (PCOS) exhibits the highest morbidity among endocrine diseases in women ranging from age 18 to 44. However, its pathogenesis remains unclear. The imbalance between systemic and ovarian oxidative stress (OS) is a key characteristic of PCOS, and accumulating evidence indicates that the antioxidative protein nuclear factor erythroid-2-related factor 2 (Nrf2) is implicated in cell apoptosis and inflammation caused by OS. The activated kinase 2 (PAK2)/-catenin/c-Myc/pyruvate kinase M2 (PKM2) axis is a newly identified signaling pathway that may regulate Nrf2 expression and thereby influence OS. In this study, we sought to identify PAK2 expression and function in PCOS cells. PAK2 and downstream PKM2 expression in KGN cells and tissues were detected by microarray and qPCR. Cell viability was determined using CCK-8 and colony formation assays (CFAs). Apoptosis was examined by flow cytometry. qPCR and ELISA were used to examine cell inflammation. Oxidant and OS-related enzymes were examined by ELISA. We found that PAK2 and PKM2 expression levels were reduced in KGN cells and PCOS ovarian cortex tissues. PAK2 overexpression activated β-catenin/c-Myc/PKM2 while PAK2 silencing deactivated it. PAK2 overexpression was reduced, whereas PAK2 silencing promoted, KGN cell proliferation and colony formation. Cell apoptosis and inflammation were also induced by PAK2 overexpression but were alleviated by its silencing. Furthermore, increased peroxidation product levels decreased antioxidative protein activities, and deactivated antioxidative Nrf2/HO-1 pathway were detected in PAK2-overexpressing KGN cells, whereas these effects were counteracted in PAK2 silenced cells. Our data suggest that PAK2 and its associated β-catenin/c-Myc/PKM2 inhibited cell viability and induced apoptosis and inflammation by triggering OS by deactivating the Nrf2/HO-1 pathway, suggesting the potential of PAK2 as a therapeutic PCOS treatment target.

Pulses of RhoA Signaling Stimulate Actin Polymerization and Flow in Protrusions to Drive Collective Cell Migration

In animals, cells often move as collectives to shape organs, close wounds, or-in the case of disease-metastasize. To accomplish this, cells need to generate force to propel themselves forward. The motility of singly migrating cells is driven largely by an interplay between Rho GTPase signaling and the actin network (Yamada and Sixt, 2019). Whether cells migrating as collectives use the same machinery for motility is unclear. Using the zebrafish posterior lateral line primordium as a model for collective cell migration, we find that active RhoA and myosin II cluster on the basal sides of the primordium cells and are required for primordium motility. Positive and negative feedbacks cause RhoA and myosin II activities to pulse. These pulses of RhoA signaling stimulate actin polymerization at the tip of the protrusions and myosin II-dependent actin flow and protrusion retraction at the base of the protrusions, and deform the basement membrane underneath the migrating primordium. This suggests that RhoA-induced actin flow on the basal sides of the cells constitutes the motor that pulls the primordium forward, a scenario that likely underlies collective migration in other-but not all (Bastock and Strutt, 2007; Lebreton and Casanova, 2013; Matthews et al., 2008)-contexts.

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.

A ubiquitin-based effector-to-inhibitor switch coordinates early brain, craniofacial, and skin development

The molecular mechanisms that coordinate patterning of the embryonic ectoderm into spatially distinct lineages to form the nervous system, epidermis, and neural crest-derived craniofacial structures are unclear. Here, biochemical disease-variant profiling reveals a posttranslational pathway that drives early ectodermal differentiation in the vertebrate head. The anteriorly expressed ubiquitin ligase CRL3-KLHL4 restricts signaling of the ubiquitous cytoskeletal regulator CDC42. This regulation relies on the CDC42-activating complex GIT1-βPIX, which CRL3-KLHL4 exploits as a substrate-specific co-adaptor to recognize and monoubiquitylate PAK1. Surprisingly, we find that ubiquitylation converts the canonical CDC42 effector PAK1 into a CDC42 inhibitor. Loss of CRL3-KLHL4 or a disease-associated KLHL4 variant reduce PAK1 ubiquitylation causing overactivation of CDC42 signaling and defective ectodermal patterning and neurulation. Thus, tissue-specific restriction of CDC42 signaling by a ubiquitin-based effector-to-inhibitor is essential for early face, brain, and skin formation, revealing how cell-fate and morphometric changes are coordinated to ensure faithful organ development.

The Evaluation of Rac1 Signaling as a Potential Therapeutic Target of Alzheimer's Disease

The Small GTPase Rac1 is critical for various fundamental cellular processes, including cognitive functions. The cyclical activation and inactivation of Rac1, mediated by Rac guanine nucleotide exchange factors (RacGEFs) and Rac GTPase-activating proteins (RacGAPs), respectively, are essential for activating intracellular signaling pathways and controlling cellular processes. We have recently shown that the Alzheimer's disease (AD) therapeutic drug donepezil activates the Rac1-PAK pathway in the nucleus accumbens (NAc) for enhanced aversive learning. Also, PAK activation itself in the NAc enhances aversive learning. As aversive learning allows short-term preliminary AD drug screening, here we tested whether sustained Rac1 activation by RacGAP inhibition can be used as an AD therapeutic strategy for improving AD-learning deficits based on aversive learning. We found that the RacGAP domain of breakpoint cluster region protein (Bcr) (Bcr-GAP) efficiently inhibited Rac1 activity in a membrane ruffling assay. We also found that, in striatal/accumbal primary neurons, Bcr knockdown by microRNA mimic-expressing adeno-associated virus (AAV-miRNA mimic) activated Rac1-PAK signaling, while Bcr-GAP-expressing AAV inactivated it. Furthermore, conditional knockdown of Bcr in the NAc of wild-type adult mice enhanced aversive learning, while Bcr-GAP expression in the NAc inhibited it. The findings indicate that Rac1 activation by RacGAP inhibition enhances aversive learning, implying the AD therapeutic potential of Rac1 signaling.

The Rho guanine dissociation inhibitor α inhibits skeletal muscle Rac1 activity and insulin action

The molecular events governing skeletal muscle glucose uptake have pharmacological potential for managing insulin resistance in conditions such as obesity, diabetes, and cancer. With no current pharmacological treatments to target skeletal muscle insulin sensitivity, there is an unmet need to identify the molecular mechanisms that control insulin sensitivity in skeletal muscle. Here, the Rho guanine dissociation inhibitor α (RhoGDIα) is identified as a point of control in the regulation of insulin sensitivity. In skeletal muscle cells, RhoGDIα interacted with, and thereby inhibited, the Rho GTPase Rac1. In response to insulin, RhoGDIα was phosphorylated at S101 and Rac1 dissociated from RhoGDIα to facilitate skeletal muscle GLUT4 translocation. Accordingly, siRNA-mediated RhoGDIα depletion increased Rac1 activity and elevated GLUT4 translocation. Consistent with RhoGDIα's inhibitory effect, rAAV-mediated RhoGDIα overexpression in mouse muscle decreased insulin-stimulated glucose uptake and was detrimental to whole-body glucose tolerance. Aligning with RhoGDIα's negative role in insulin sensitivity, RhoGDIα protein content was elevated in skeletal muscle from insulin-resistant patients with type 2 diabetes. These data identify RhoGDIα as a clinically relevant controller of skeletal muscle insulin sensitivity and whole-body glucose homeostasis, mechanistically by modulating Rac1 activity.

Roles of Rac1-Dependent Intrinsic Forgetting in Memory-Related Brain Disorders: Demon or Angel

Animals are required to handle daily massive amounts of information in an ever-changing environment, and the resulting memories and experiences determine their survival and development, which is critical for adaptive evolution. However, intrinsic forgetting, which actively deletes irrelevant information, is equally important for memory acquisition and consolidation. Recently, it has been shown that Rac1 activity plays a key role in intrinsic forgetting, maintaining the balance of the brain's memory management system in a controlled manner. In addition, dysfunctions of Rac1-dependent intrinsic forgetting may contribute to memory deficits in neurological and neurodegenerative diseases. Here, these new findings will provide insights into the neurobiology of memory and forgetting, pathological mechanisms and potential therapies for brain disorders that alter intrinsic forgetting mechanisms.

Pak1 pathway hyper-activation mediates resistance to endocrine therapy and CDK4/6 inhibitors in ER+ breast cancer

Cyclin-dependent kinase 4 and 6 inhibitors (CDK4/6i) have been approved in combination with endocrine therapy (ET) to treat estrogen receptor-positive (ER+) metastatic breast cancer (BC). However, drug resistance represents the leading cause of breast cancer patients mortality. This study aimed to identify novel resistance mechanisms to ER antagonists in combination with CDK4/6 inhibitors. We generated two ER+ BC cell lines, T47D and MCF7, resistant to the combination of the ER antagonist fulvestrant and CDK4/6i abemaciclib, named T47D-FAR and MCF7-FAR. Transcriptomic analysis revealed common up-regulation of genes involved in MAPK and epithelial to mesenchymal transition (EMT) pathways in FAR cells, sustaining their hyper-invasive phenotype and increased anchorage-independent growth, compared to sensitive cells. FAR cells showed higher p21-activated kinase 1 (Pak1) expression and phosphorylation levels than parental cells. PAK1 knockdown by siRNAs hampered cell proliferation, reduced anchorage-independent growth and invasive properties of T47D-FAR and MCF7-FAR, re-sensitizing them to fulvestrant and abemaciclib. Conversely, over-expression of PAK1 in MCF7 and T47D cells increased tumor spheroids' growth and invasion and reduced sensitivity to fulvestrant and abemaciclib, confirming its role in inducing drug resistance. Finally, treatment with Pak1 inhibitors, PF-3758309 (PF309) and NVS-PAK1-1, restored cell sensitivity to fulvestrant and abemaciclib of MCF7-FAR and T47D-FAR cells, both in vitro and in vivo. In conclusion, our data suggested a pivotal role for Pak1 in resistance to ET and CDK4/6i in ER+ breast cancers. These data might promote the rationale for the development of novel Pak1 inhibitors for treatment of patients with ER+ BC progressing on ET plus CDK4/6i.

Cell-based optimization and characterization of genetically encoded location-based biosensors for Cdc42 or Rac activity

Rac (herein referring to the Rac family) and Cdc42 are Rho GTPases that regulate the formation of lamellipoda and filopodia, and are therefore crucial in processes such as cell migration. Relocation-based biosensors for Rac and Cdc42 have not been characterized well in terms of their specificity or affinity. In this study, we identify relocation sensor candidates for both Rac and Cdc42. We compared their (1) ability to bind the constitutively active Rho GTPases, (2) specificity for Rac and Cdc42, and (3) relocation efficiency in cell-based assays. Subsequently, the relocation efficiency was improved by a multi-domain approach. For Rac1, we found a sensor candidate with low relocation efficiency. For Cdc42, we found several sensors with sufficient relocation efficiency and specificity. These optimized sensors enable the wider application of Rho GTPase relocation sensors, which was showcased by the detection of local endogenous Cdc42 activity at assembling invadopodia. Moreover, we tested several fluorescent proteins and HaloTag for their influence on the recruitment efficiency of the Rho location sensor, to find optimal conditions for a multiplexing experiment. This characterization and optimization of relocation sensors will broaden their application and acceptance.

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.

Targeting P21-Activated Kinase-1 for Metastatic Prostate Cancer

Metastatic prostate cancer (mPCa) has limited therapeutic options and a high mortality rate. The p21-activated kinase (PAK) family of proteins is important in cell survival, proliferation, and motility in physiology, and pathologies such as infectious, inflammatory, vascular, and neurological diseases as well as cancers. Group-I PAKs (PAK1, PAK2, and PAK3) are involved in the regulation of actin dynamics and thus are integral for cell morphology, adhesion to the extracellular matrix, and cell motility. They also play prominent roles in cell survival and proliferation. These properties make group-I PAKs a potentially important target for cancer therapy. In contrast to normal prostate and prostatic epithelial cells, group-I PAKs are highly expressed in mPCA and PCa tissue. Importantly, the expression of group-I PAKs is proportional to the Gleason score of the patients. While several compounds have been identified that target group-I PAKs and these are active in cells and mice, and while some inhibitors have entered human trials, as of yet, none have been FDA-approved. Probable reasons for this lack of translation include issues related to selectivity, specificity, stability, and efficacy resulting in side effects and/or lack of efficacy. In the current review, we describe the pathophysiology and current treatment guidelines of PCa, present group-I PAKs as a potential druggable target to treat mPCa patients, and discuss the various ATP-competitive and allosteric inhibitors of PAKs. We also discuss the development and testing of a nanotechnology-based therapeutic formulation of group-I PAK inhibitors and its significant potential advantages as a novel, selective, stable, and efficacious mPCa therapeutic over other PCa therapeutics in the pipeline.

Expression Patterns of PAK4 and PHF8 Are Associated with the Survival of Gallbladder Carcinoma Patients

Background: PAK4 and PHF8 are involved in cancer progression and are under evaluation as targets for cancer therapy. However, despite extensive studies in human cancers, there are limited reports on the roles of PAK4 and PHF8 in gallbladder cancers. Methods: Immunohistochemical expression of PAK4 and PHF8 and their prognostic significance were evaluated in 148 human gallbladder carcinomas. Results: PAK4 expression was significantly associated with PHF8 expression in gallbladder carcinomas. Positive expression of nuclear PAK4, cytoplasmic PAK4, nuclear PHF8, and cytoplasmic PHF8 were significantly associated with shorter overall survival and relapse-free survival in univariate analysis. Multivariate analysis showed that nuclear PAK4 expression and nuclear PHF8 expression were independent predictors of overall survival and relapse-free survival in gallbladder carcinomas. Furthermore, coexpression of nuclear PAK4 and nuclear PHF8 predicted shorter overall survival (p < 0.001) and relapse-free survival (p < 0.001) of gallbladder carcinoma in multivariate analysis. Conclusions: This study suggests that the individual and coexpression patterns of PAK4 and PHF8 as the prognostic indicators for gallbladder carcinoma patients.

Domain Architecture of the Nonreceptor Tyrosine Kinase Ack1

The nonreceptor tyrosine kinase (NRTK) Ack1 comprises a distinct arrangement of non-catalytic modules. Its SH3 domain has a C-terminal to the kinase domain (SH1), in contrast to the typical SH3-SH2-SH1 layout in NRTKs. The Ack1 is the only protein that shares a region of high homology to the tumor suppressor protein Mig6, a modulator of EGFR. The vertebrate Acks make up the only tyrosine kinase (TK) family known to carry a UBA domain. The GTPase binding and SAM domains are also uncommon in the NRTKs. In addition to being a downstream effector of receptor tyrosine kinases (RTKs) and integrins, Ack1 can act as an epigenetic regulator, modulate the degradation of the epidermal growth factor receptor (EGFR), confer drug resistance, and mediate the progression of hormone-sensitive tumors. In this review, we discuss the domain architecture of Ack1 in relation to other protein kinases that possess such defined regulatory domains.

Pharmacological Inhibition of p-21 Activated Kinase (PAK) Restores Impaired Neurite Outgrowth and Remodeling in a Cellular Model of Down Syndrome

Down syndrome (DS) is characterized by the trisomy of chromosome 21 and by cognitive deficits that have been related to neuronal morphological alterations in humans, as well as in animal models. The gene encoding for amyloid precursor protein (APP) is present in autosome 21, and its overexpression in DS has been linked to neuronal dysfunction, cognitive deficit, and Alzheimer's disease-like dementia. In particular, the neuronal ability to extend processes and branching is affected. Current evidence suggests that APP could also regulate neurite growth through its role in the actin cytoskeleton, in part by influencing p21-activated kinase (PAK) activity. The latter effect is carried out by an increased abundance of the caspase cleavage-released carboxy-terminal C31 fragment. In this work, using a neuronal cell line named CTb, which derived from the cerebral cortex of a trisomy 16 mouse, an animal model of human DS, we observed an overexpression of APP, elevated caspase activity, augmented cleavage of the C-terminal fragment of APP, and increased PAK1 phosphorylation. Morphometric analyses showed that inhibition of PAK1 activity with FRAX486 increased the average length of the neurites, the number of crossings per Sholl ring, the formation of new processes, and stimulated the loss of processes. Considering our results, we propose that PAK hyperphosphorylation impairs neurite outgrowth and remodeling in the cellular model of DS, and therefore we suggest that PAK1 may be a potential pharmacological target.

Proximity proteomics identifies septins and PAK2 as decisive regulators of actomyosin-mediated expulsion of von Willebrand factor

In response to tissue injury, within seconds the ultra-large glycoprotein von Willebrand factor (VWF) is released from endothelial storage organelles (Weibel-Palade bodies) into the lumen of the blood vasculature, where it leads to the recruitment of platelets. The marked size of VWF multimers represents an unprecedented burden on the secretory machinery of endothelial cells (ECs). ECs have evolved mechanisms to overcome this, most notably an actomyosin ring that forms, contracts, and squeezes out its unwieldy cargo. Inhibiting the formation or function of these structures represents a novel therapeutic target for thrombotic pathologies, although characterizing proteins associated with such a dynamic process has been challenging. We have combined APEX2 proximity labeling with an innovative dual loss-of-function screen to identify proteins associated with actomyosin ring function. We show that p21 activated kinase 2 (PAK2) recruits septin hetero-oligomers, a molecular interaction that forms a ring around exocytic sites. This cascade of events controls actomyosin ring function, aiding efficient exocytic release. Genetic or pharmacological inhibition of PAK2 or septins led to inefficient release of VWF and a failure to form platelet-catching strings. This new molecular mechanism offers additional therapeutic targets for the control of thrombotic disease and is highly relevant to other secretory systems that employ exocytic actomyosin machinery.

Cdc42 signaling regulated by dopamine D2 receptor correlatively links specific brain regions of hippocampus to cocaine addiction

BACKGROUND

Hippocampus plays critical roles in drug addiction. Cocaine-induced modifications in dopamine receptor function and the downstream signaling are important regulation mechanisms in cocaine addiction. Rac regulates actin filament accumulation while Cdc42 stimulates the formation of filopodia and neurite outgrowth. Based on the region specific roles of small GTPases in brain, we focused on the hippocampal subregions to detect the regulation of Cdc42 signaling in long-term morphological and behavioral adaptations to cocaine.

METHODS

Genetically modified mouse models of Cdc42, dopamine receptor D1 (D1R) and D2 (D2R) and expressed Cdc42 point mutants that are defective in binding to and activation of its downstream effector molecules PAK and N-WASP were generated, respectively, in CA1 or dentate gyrus (DG) subregion.

RESULTS

Cocaine induced upregulation of Cdc42 signaling activity. Cdc42 knockout or mutants blocked cocaine-induced increase in spine plasticity in hippocampal CA1 pyramidal neurons, leading to a decreased conditional place preference (CPP)-associated memories and spatial learning and memory in water maze. Cdc42 knockout or mutants promoted cocaine-induced loss of neurogenesis in DG, leading to a decreased CPP-associated memories and spatial learning and memory in water maze. Furthermore, by using D1R knockout, D2R knockout, and D2R/Cdc42 double knockout mice, we found that D2R, but not D1R, regulated Cdc42 signaling in cocaine-induced neural plasticity and behavioral changes.

CONCLUSIONS

Cdc42 acts downstream of D2R in the hippocampus and plays an important role in cocaine-induced neural plasticity through N-WASP and PAK-LIMK-Cofilin, and Cdc42 signaling pathway correlatively links specific brain regions (CA1, dentate gyrus) to cocaine-induced CPP behavior.

PAK and PI3K pathway activation confers resistance to KRASG12C inhibitor sotorasib

BACKGROUND

KRAS is a frequently mutated oncogene in human cancer. Clinical studies on the covalent inhibitors of the KRASG12C mutant have reported promising results. However, primary and acquired resistance may limit their clinical use.

METHODS

Sotorasib-resistant cell lines were established. We explored the signalling pathways activated in these resistant cell lines and their roles in sotorasib resistance.

RESULTS

The resistant cells exhibited increased cell-matrix adhesion with increased levels of stress fibres and focal adherens. p21-activated kinases (PAKs) were activated in resistant cells, which phosphorylate MEK at serine 298 of MEK and serine 338 of c-Raf to activate the mitogen-activated protein kinase pathway. The PAK inhibitors FRAX597 and FRAX486 in synergy with sotorasib reduced the viability of KRASG12C mutant cancer cells. Furthermore, the PI3K/AKT pathway was constitutively active in sotorasib-resistant cells. The overexpression of constitutively activated PI3K or the knockdown of PTEN resulted in resistance to sotorasib. PI3K inhibitor alpelisib was synergistic with sotorasib in compromising the viability of KRASG12C mutant cancer cells. Moreover, PI3K and PAK pathways formed a mutual positive regulatory loop that mediated sotorasib resistance.

CONCLUSIONS

Our results indicate that the cell-matrix interaction-dependent activation of PAK mediates resistance to sotorasib through the activation of MAPK and PI3K pathways.

Rho family GTPase signaling through type II p21-activated kinases

Signaling from the Rho family small GTPases controls a wide range of signaling outcomes. Key among the downstream effectors for many of the Rho GTPases are the p21-activated kinases, or PAK group. The PAK family comprises two types, the type I PAKs (PAK1, 2 and 3) and the type II PAKs (PAK4, 5 and 6), which have distinct structures and mechanisms of regulation. In this review, we discuss signal transduction from Rho GTPases with a focus on the type II PAKs. We discuss the role of PAKs in signal transduction pathways and selectivity of Rho GTPases for PAK family members. We consider the less well studied of the Rho GTPases and their PAK-related signaling. We then discuss the molecular basis for kinase domain recognition of substrates and for regulation of signaling. We conclude with a discussion of the role of PAKs in cross talk between Rho family small GTPases and the roles of PAKs in disease.

Minor Kinases with Major Roles in Cytokinesis Regulation

Cytokinesis, the conclusive act of cell division, allows cytoplasmic organelles and chromosomes to be faithfully partitioned between two daughter cells. In animal organisms, its accurate regulation is a fundamental task for normal development and for preventing aneuploidy. Cytokinesis failures produce genetically unstable tetraploid cells and ultimately result in chromosome instability, a hallmark of cancer cells. In animal cells, the assembly and constriction of an actomyosin ring drive cleavage furrow ingression, resulting in the formation of a cytoplasmic intercellular bridge, which is severed during abscission, the final event of cytokinesis. Kinase-mediated phosphorylation is a crucial process to orchestrate the spatio-temporal regulation of the different stages of cytokinesis. Several kinases have been described in the literature, such as cyclin-dependent kinase, polo-like kinase 1, and Aurora B, regulating both furrow ingression and/or abscission. However, others exist, with well-established roles in cell-cycle progression but whose specific role in cytokinesis has been poorly investigated, leading to considering these kinases as "minor" actors in this process. Yet, they deserve additional attention, as they might disclose unexpected routes of cell division regulation. Here, we summarize the role of multifunctional kinases in cytokinesis with a special focus on those with a still scarcely defined function during cell cleavage. Moreover, we discuss their implication in cancer.

A meta-analysis indicates that the regulation of cell motility is a non-intrinsic function of chemoattractant receptors that is governed independently of directional sensing

Chemoattraction, defined as the migration of a cell toward a source of a chemical gradient, is controlled by chemoattractant receptors. Chemoattraction involves two basic activities, namely, directional sensing, a molecular mechanism that detects the direction of a source of chemoattractant, and actin-based motility, which allows the migration of a cell towards it. Current models assume first, that chemoattractant receptors govern both directional sensing and motility (most commonly inducing an increase in the migratory speed of the cells, i.e. chemokinesis), and, second, that the signaling pathways controlling both activities are intertwined. We performed a meta-analysis to reassess these two points. From this study emerge two main findings. First, although many chemoattractant receptors govern directional sensing, there are also receptors that do not regulate cell motility, suggesting that is the ability to control directional sensing, not motility, that best defines a chemoattractant receptor. Second, multiple experimental data suggest that receptor-controlled directional sensing and motility can be controlled independently. We hypothesize that this independence may be based on the existence of separated signalling modules that selectively govern directional sensing and motility in chemotactic cells. Together, the information gathered can be useful to update current models representing the signalling from chemoattractant receptors. The new models may facilitate the development of strategies for a more effective pharmacological modulation of chemoattractant receptor-controlled chemoattraction in health and disease.

Expression of Marker PAK1 in Sinonasal Polyposis

Introduction Chronic rhinosinusitis with nasal polyposis involves mucosal lining of nose and paranasal sinuses. Numerous studies studied the mechanism leading to sinonasal polyposis. We attempted study the inflammatory mechanisms responsible for the recruitment and activation of leukocytes. Aim To study and compare the expression of the immunohistochemistry marker PAK1 in sinonasal polyposis and normal nasal mucosa. Material and Methods Prospective observational study done by comparing two groups of 30 each with Group A comprises Sinonasal polyposis and Group B comprises normal nasal mucosa. The specimens were subjected to PAK1 immunohistochemical staining. Results Immunihistrochemical staining showed higher intensity stain in sinonasal polyp when compared to normal nasal mucosa. Conclusion The upregulation of PAK1 in sinonasal polyposis when compared to normal nasal mucosa may indicate an increased cellular proliferation and turnover in the background of chronic inflammation.

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.

A perspective on molecular signalling dysfunction, its clinical relevance and therapeutics in autism spectrum disorder

Intellectual disability (ID) and autism spectrum disorder (ASD) are neurodevelopmental disorders that have become a primary clinical and social concern, with a prevalence of 2-3% in the population. Neuronal function and behaviour undergo significant malleability during the critical period of development that is found to be impaired in ID/ASD. Human genome sequencing studies have revealed many genetic variations associated with ASD/ID that are further verified by many approaches, including many mouse and other models. These models have facilitated the identification of fundamental mechanisms underlying the pathogenesis of ASD/ID, and several studies have proposed converging molecular pathways in ASD/ID. However, linking the mechanisms of the pathogenic genes and their molecular characteristics that lead to ID/ASD has progressed slowly, hampering the development of potential therapeutic strategies. This review discusses the possibility of recognising the common molecular causes for most ASD/ID based on studies from the available models that may enable a better therapeutic strategy to treat ID/ASD. We also reviewed the potential biomarkers to detect ASD/ID at early stages that may aid in diagnosis and initiating medical treatment, the concerns with drug failure in clinical trials, and developing therapeutic strategies that can be applied beyond a particular mutation associated with ASD/ID.

Stimulation of Neurite Outgrowth in Cerebrocortical Neurons by Sodium Channel Activator Brevetoxin-2 Requires Both N-Methyl-D-aspartate Receptor 2B (GluN2B) and p21 Protein (Cdc42/Rac)-Activated Kinase 1 (PAK1)

N-methyl-D-aspartate (NMDA) receptors play a critical role in activity-dependent dendritic arborization, spinogenesis, and synapse formation by stimulating calcium-dependent signaling pathways. Previously, we have shown that brevetoxin 2 (PbTx-2), a voltage-gated sodium channel (VGSC) activator, produces a concentration-dependent increase in intracellular sodium [Na⁺]_I and increases NMDA receptor (NMDAR) open probabilities and NMDA-induced calcium (Ca²⁺) influxes. The objective of this study is to elucidate the downstream signaling mechanisms by which the sodium channel activator PbTx-2 influences neuronal morphology in murine cerebrocortical neurons. PbTx-2 and NMDA triggered distinct Ca²⁺-influx pathways, both of which involved the NMDA receptor 2B (GluN2B). PbTx-2-induced neurite outgrowth in day in vitro 1 (DIV-1) neurons required the small Rho GTPase Rac1 and was inhibited by both a PAK1 inhibitor and a PAK1 siRNA. PbTx-2 exposure increased the phosphorylation of PAK1 at Thr-212. At DIV-5, PbTx-2 induced increases in dendritic protrusion density, p-cofilin levels, and F-actin throughout the dendritic arbor and soma. Moreover, PbTx-2 increased miniature excitatory post-synaptic currents (mEPSCs). These data suggest that the stimulation of neurite outgrowth, spinogenesis, and synapse formation produced by PbTx-2 are mediated by GluN2B and PAK1 signaling.

Recent advances on development of p21-activated kinase 4 inhibitors as anti-tumor agents

The p21-activated kinase 4 (PAK4) is a member of the PAKs family. It is overexpressed in multiple tumor tissues. Pharmacological inhibition of PAK4 attenuates proliferation, migration, and invasion of cancer cells. Recent studies revealed that inhibition of PAK4 sensitizes immunotherapy which has been extensively exploited as a new strategy to treat cancer. In the past few years, a large number of PAK4 inhibitors have been reported. Of note, the allosteric inhibitor KPT-9274 has been tested in phase Ⅰ clinic trials. Herein, we provide an update on recent research progress on the PAK4 mediated signaling pathway and highlight the development of the PAK4 small molecular inhibitors in recent 5 years. Meanwhile, challenges, limitations, and future developmental directions will be discussed as well.

The trilogy of P21 activated kinase, autophagy and immune evasion in pancreatic ductal adenocarcinoma

Pancreatic Ductal Adenocarcinoma (PDA) is one of the most lethal types of cancer with a dismal prognosis. KRAS mutation is a commonly identified oncogene in PDA tumorigenesis and P21-activated kinases (PAKs) are its downstream mediator. While PAK1 is more well-studied, PAK4 also attracted increasing interest. In PDA, PAK inhibition not only reduces cancer cell viability but also sensitises it to chemotherapy. While PDA remains resistant to existing immunotherapies, PAK inhibition has been shown to increase cancer immunogenicity of melanoma, glioblastoma and PDA. Furthermore, autophagy plays an important role in PDA immune evasion, and accumulating evidence has pointed to a connection between PAK and cancer cell autophagy. In this literature review, we aim to summarize currently available studies that have assessed the potential connection between PAK, autophagy and immune evasion in PDA biology to guide future research.

p21-activated kinase 4 inhibition protects against liver ischemia/reperfusion injury: Role of nuclear factor erythroid 2-related factor 2 phosphorylation

BACKGROUND AND AIMS

p21-activated kinase 4 (PAK4), an oncogenic protein, has emerged as a promising target for anticancer drug development. Its role in oxidative stress conditions, however, remains elusive. We investigated the effects of PAK4 signaling on hepatic ischemia/reperfusion (I/R) injury.

APPROACH AND RESULTS

Hepatocyte- and myeloid-specific Pak4 knockout (KO) mice and their littermate controls were subjected to a partial hepatic I/R (HIR) injury. We manipulated the catalytic activity of PAK4, either through genetic engineering (gene knockout, overexpression of wild-type [WT] or dominant-negative kinase) or pharmacological inhibitor, coupled with a readout of nuclear factor erythroid 2-related factor 2 (Nrf2) activity, to test the potential function of PAK4 on HIR injury. PAK4 expression was markedly up-regulated in liver during HIR injury in mice and humans. Deletion of PAK4 in hepatocytes, but not in myeloid cells, ameliorated liver damages, as demonstrated in the decrease in hepatocellular necrosis and inflammatory responses. Conversely, the forced expression of WT PAK4 aggravated the pathological changes. PAK4 directly phosphorylated Nrf2 at T369, and it led to its nuclear export and proteasomal degradation, all of which impaired antioxidant responses in hepatocytes. Nrf2 silencing in liver abolished the protective effects of PAK4 deficiency. A PAK4 inhibitor protected mice from HIR injury.

CONCLUSIONS

PAK4 phosphorylates Nrf2 and suppresses its transcriptional activity. Genetic or pharmacological suppression of PAK4 alleviates HIR injury. Thus, PAK4 inhibition may represent a promising intervention against I/R-induced liver injury.

Pinch2 regulates myelination in the mouse central nervous system

The extensive morphological changes of oligodendrocytes during axon ensheathment and myelination involve assembly of the Ilk-Parvin-Pinch (IPP) heterotrimeric complex of proteins to relay essential mechanical and biochemical signals between integrins and the actin cytoskeleton. Binding of Pinch1 and Pinch2 isoforms to Ilk is mutually exclusive and allows the formation of distinct IPP complexes with specific signaling properties. Using tissue-specific conditional gene ablation in mice, we reveal an essential role for Pinch2 during central nervous system myelination. Unlike Pinch1 gene ablation, loss of Pinch2 in oligodendrocytes results in hypermyelination and in the formation of pathological myelin outfoldings in white matter regions. These structural changes concur with inhibition of Rho GTPase RhoA and Cdc42 activities and phenocopy aspects of myelin pathology observed in corresponding mouse mutants. We propose a dual role for Pinch2 in preventing an excess of myelin wraps through RhoA-dependent control of membrane growth and in fostering myelin stability via Cdc42-dependent organization of cytoskeletal septins. Together, these findings indicate that IPP complexes containing Pinch2 act as a crucial cell-autonomous molecular hub ensuring synchronous control of key signaling networks during developmental myelination.

Molecular dynamics simulations reveal the activation mechanism of mutations G12V and Q61L of Cdc42

Cell division control protein 42 homolog (Cdc42), which contributes to multiple cellular processes including cell proliferation and migration, is a potential target for cancer therapy, especially in the intervention of tumor migration. Cdc42's mutants G12V and Q61L are discovered constitutively active, and the overexpression of them exhibits oncogenic activities. Here, using molecular dynamics (MD) simulations and dynamic analysis, we illustrated the activation mechanism of Cdc42^G12V and Cdc42^Q61L . Without GAP, the two mutations differently elicited state transition from the wild-type's open "inactive" state 1 to the closed "active" state 2, induced by the introduction of a newly formed water-mediated T35-γ-phosphate hydrogen bond in G12V system and the additional hydrophobic interactions between L61 and T35 together with the direct T35-γ-phosphate hydrogen bond in Q61L system. When binding with GAP, both mutations weakened the hydrogen bond interactions between Cdc42-GTP and GAP's finger loop, and disturbed the catalytically competent organizations of GAP's catalytic R305/R306 and Cdc42's Q61, thereby impairing the GAP-mediated GTP hydrolysis. Our findings first reveal the activation mechanism of Cdc42's G12V and Q61L mutants on a molecular basis, which provide new insights into the structural and dynamical characteristics of Cdc42 and its mutants and can be exploited in the further development of novel therapies targeting Cdc42-related cancers.

Statin Treatment as a Targeted Therapy for APC-Mutated Colorectal Cancer

Background

Mutations in the tumor suppressor gene Adenomatous Polyposis Coli (APC) are found in 80% of sporadic colorectal cancer (CRC) tumors and are also responsible for the inherited form of CRC, Familial adenomatous polyposis (FAP).

Methods

To identify novel therapeutic strategies for the treatment of APC mutated CRC, we generated a drug screening platform that incorporates a human cellular model of APC mutant CRC using CRISPR-cas9 gene editing and performed an FDA-approved drug screen targeting over 1000 compounds.

Results

We have identified the group of HMG-CoA Reductase (HMGCR) inhibitors known as statins, which cause a significantly greater loss in cell viability in the APC mutated cell lines and in in vivo APC mutated patient derived xenograft (PDX) models, compared to wild-type APC cells. Mechanistically, our data reveals this new synthetic lethal relationship is a consequence of decreased Wnt signalling and, ultimately, a reduction in the level of expression of the anti-apoptotic protein Survivin, upon statin treatment in the APC-mutant cells only. This mechanism acts via a Rac1 mediated control of beta-catenin.

Conclusion

Significantly, we have identified a novel synthetic lethal dependence between APC mutations and statin treatment, which could potentially be exploited for the treatment of APC mutated cancers.

The Giardia ventrolateral flange is a lamellar membrane protrusion that supports attachment

Attachment to the intestinal epithelium is critical to the lifestyle of the ubiquitous parasite Giardia lamblia. The ventrolateral flange is a sheet-like membrane protrusion at the interface between parasites and attached surfaces. This structure has been implicated in attachment, but its role has been poorly defined. Here, we identified a novel actin associated protein with putative WH2-like actin binding domains we named Flangin. Flangin complexes with Giardia actin (GlActin) and is enriched in the ventrolateral flange making it a valuable marker for studying the flanges' role in Giardia biology. Live imaging revealed that the flange grows to around 1 μm in width after cytokinesis, then remains uniform in size during interphase, grows in mitosis, and is resorbed during cytokinesis. A flangin truncation mutant stabilizes the flange and blocks cytokinesis, indicating that flange disassembly is necessary for rapid myosin-independent cytokinesis in Giardia. Rho family GTPases are important regulators of membrane protrusions and GlRac, the sole Rho family GTPase in Giardia, was localized to the flange. Knockdown of Flangin, GlActin, and GlRac result in flange formation defects. This indicates a conserved role for GlRac and GlActin in forming membrane protrusions, despite the absence of canonical actin binding proteins that link Rho GTPase signaling to lamellipodia formation. Flangin-depleted parasites had reduced surface contact and when challenged with fluid shear force in flow chambers they had a reduced ability to remain attached, confirming a role for the flange in attachment. This secondary attachment mechanism complements the microtubule based adhesive ventral disc, a feature that may be particularly important during mitosis when the parental ventral disc disassembles in preparation for cytokinesis. This work supports the emerging view that Giardia's unconventional actin cytoskeleton has an important role in supporting parasite attachment.

Cdc42/Rac Interactive Binding Containing Effector Proteins in Unicellular Protozoans With Reference to Human Host: Locks of the Rho Signaling

Small GTPases are the key to actin cytoskeleton signaling, which opens the lock of effector proteins to forward the signal downstream in several cellular pathways. Actin cytoskeleton assembly is associated with cell polarity, adhesion, movement and other functions in eukaryotic cells. Rho proteins, specifically Cdc42 and Rac, are the primary regulators of actin cytoskeleton dynamics in higher and lower eukaryotes. Effector proteins, present in an inactive state gets activated after binding to the GTP bound Cdc42/Rac to relay a signal downstream. Cdc42/Rac interactive binding (CRIB) motif is an essential conserved sequence found in effector proteins to interact with Cdc42 or Rac. A diverse range of Cdc42/Rac and their effector proteins have evolved from lower to higher eukaryotes. The present study has identified and further classified CRIB containing effector proteins in lower eukaryotes, focusing on parasitic protozoans causing neglected tropical diseases and taking human proteins as a reference point to the highest evolved organism in the evolutionary trait. Lower eukaryotes’ CRIB containing proteins fall into conventional effector molecules, PAKs (p21 activated kinase), Wiskoit-Aldrich Syndrome proteins family, and some have unique domain combinations unlike any known proteins. We also highlight the correlation between the effector protein isoforms and their selective specificity for Cdc42 or Rac proteins during evolution. Here, we report CRIB containing effector proteins; ten in Dictyostelium and Entamoeba, fourteen in Acanthamoeba, one in Trypanosoma and Giardia. CRIB containing effector proteins that have been studied so far in humans are potential candidates for drug targets in cancer, neurological disorders, and others. Conventional CRIB containing proteins from protozoan parasites remain largely elusive and our data provides their identification and classification for further in-depth functional validations. The tropical diseases caused by protozoan parasites lack combinatorial drug targets as effective paradigms. Targeting signaling mechanisms operative in these pathogens can provide greater molecules in combatting their infections.

p21-Activated kinases as promising therapeutic targets in hematological malignancies

The p21-Activated Kinases (PAKs) are a family of six serine/threonine kinases that were originally identified as downstream effectors of the Rho GTPases Cdc42 and Rac. Since the first PAK was discovered in 1994, studies have revealed their fundamental and biological importance in the development of physiological systems. Within the cell, PAKs also play significant roles in regulating essential cellular processes such as cytoskeletal dynamics, gene expression, cell survival, and cell cycle progression. These processes are often deregulated in numerous cancers when different PAKs are overexpressed or amplified at the chromosomal level. Furthermore, PAKs modulate multiple oncogenic signaling pathways which facilitate apoptosis escape, uncontrolled proliferation, and drug resistance. There is growing insight into the critical roles of PAKs in regulating steady-state hematopoiesis, including the properties of hematopoietic stem cells (HSC), and the initiation and progression of hematological malignancies. This review will focus on the most recent studies that provide experimental evidence showing how specific PAKs regulate the properties of leukemic stem cells (LSCs) and drug-resistant cells to initiate and maintain hematological malignancies. The current understanding of the molecular and cellular mechanisms by which the PAKs operate in specific human leukemia or lymphomas will be discussed. From a translational point of view, PAKs have been suggested to be critical therapeutic targets and potential prognosis markers; thus, this review will also discuss current therapeutic strategies against hematological malignancies using existing small-molecule PAK inhibitors, as well as promising combination treatments, to sensitize drug-resistant cells to conventional therapies. The challenges of toxicity and non-specific targeting associated with some PAK inhibitors, as well as how future approaches for PAK inhibition to overcome these limitations, will also be addressed.

TLK1-mediated MK5-S354 phosphorylation drives prostate cancer cell motility and may signify distinct pathologies

Metastases account for the majority of prostate cancer (PCa) deaths, and targeting them is a major goal of systemic therapy. We identified a novel interaction between two kinases: tousled‐like kinase 1 (TLK1) and MAP kinase‐activated protein kinase 5 (MK5) that promotes PCa spread. In PCa progression, TLK1–MK5 signalling appears to increase following antiandrogen treatment and in metastatic castration‐resistant prostate cancer (mCRPC) patients. Determinations of motility rates (2D and 3D) of different TLK1‐ and MK5‐perturbed cells, including knockout (KO) and knockdown (KD), as well as the use of specific inhibitors, showed the importance of these two proteins for in vitro dissemination. We established that TLK1 phosphorylates MK5 on three residues (S160, S354 and S386), resulting in MK5 activation, and additionally, mobility shifts of MK5 also supported its phosphorylation by TLK1 in transfected HEK 293 cells. Expression of MK5‐S354A or kinase‐dead MK5 in MK5‐depleted mouse embryonic fibroblast (MEF) cells failed to restore their motility compared with that of wild‐type (WT) MK5‐rescued MK5^−/− MEF cells. A pMK5‐S354 antiserum was used to establish this site as an authentic TLK1 target in androgen‐sensitive human prostate adenocarcinoma (LNCaP) cells, and was used in immunohistochemistry (IHC) studies of age‐related PCa sections from TRAMP (transgenic adenocarcinoma of the mouse prostate) mice and to probe a human tissue microarray (TMA), which revealed pMK5‐S354 level is correlated with disease progression (Gleason score and nodal metastases). In addition, The Cancer Genome Atlas (TCGA) analyses of PCa expression and genome‐wide association study (GWAS) relations identify TLK1 and MK5 as potential drivers of advanced PCa and as markers of mCRPC. Our work suggests that TLK1–MK5 signalling is functionally involved in driving PCa cell motility and clinical features of aggressiveness; hence, disruption of this axis may inhibit the metastatic spread of PCa.

Spatiotemporally Orchestrated Interactions between Viral and Cellular Proteins Involved in the Entry of African Swine Fever Virus

African swine fever (ASF) is a highly contagious hemorrhagic disease in domestic pigs and wild boars with a mortality of up to 100%. The causative agent, African swine fever virus (ASFV), is a member of the Asfarviridae family of the nucleocytoplasmic large DNA viruses. The genome size of ASFV ranges from 170 to 194 kb, encoding more than 50 structural and 100 nonstructural proteins. ASFV virions are 260–300 nm in diameter and composed of complex multilayered structures, leading to an intricate internalization pathway to enter host cells. Currently, no commercial vaccines or antivirals are available, due to the insufficient knowledge of the viral receptor(s), the molecular events of ASFV entry into host cells, and the functions of virulence-associated genes. During the early stage of ASFV infection, the fundamental aspects of virus-host interactions, including virus internalization, intracellular transport through the endolysosomal system, and membrane fusion with endosome, are precisely regulated and orchestrated via a series of molecular events. In this review, we summarize the currently available knowledge on the pathways of ASFV entry into host cells and the functions of viral proteins involved in virus entry. Furthermore, we conclude with future perspectives and highlight areas that require further investigation. This review is expected to provide unique insights for further understanding ASFV entry and facilitate the development of vaccines and antivirals.