Rac1 and RhoG promote cell survival by the activation of PI3K and Akt, independently of their ability to stimulate JNK and NF-kappaB

Unveiling the role of PIK3R1 in cancer: A comprehensive review of regulatory signaling and therapeutic implications

Phosphoinositide 3-kinase (PI3K) is responsible for phosphorylating phosphoinositides to generate secondary signaling molecules crucial for regulating various cellular processes, including cell growth, survival, and metabolism. The PI3K is a heterodimeric enzyme complex comprising of a catalytic subunit (p110α, p110β, or p110δ) and a regulatory subunit (p85). The binding of the regulatory subunit, p85, with the catalytic subunit, p110, forms an integral component of the PI3K enzyme. PIK3R1 (phosphoinositide-3-kinase regulatory subunit 1) belongs to class IA of the PI3K family. PIK3R1 exhibits structural complexity due to alternative splicing, giving rise to distinct isoforms, prominently p85α and p55α. While the primary p85α isoform comprises multiple domains, including Src homology 3 (SH3) domains, a Breakpoint Cluster Region Homology (BH) domain, and Src homology 2 (SH2) domains (iSH2 and nSH2), the shorter isoform, p55α, lacks certain domains present in p85α. In this review, we will highlight the intricate regulatory mechanisms governing PI3K signaling along with the impact of PIK3R1 alterations on cellular processes. We will further delve into the clinical significance of PIK3R1 mutations in various cancer types and their implications for prognosis and treatment outcomes. Additionally, we will discuss the evolving landscape of targeted therapies aimed at modulating PI3K-associated pathways. Overall, this review will provide insights into the dynamic interplay of PIK3R1 in cancer, fostering advancements in precision medicine and the development of targeted interventions.

C-X-C motif chemokine ligand 12-C-X-C chemokine receptor type 4 signaling axis in cancer and the development of chemotherapeutic molecules

Chemokines are small, secreted cytokines crucial in the regulation of a variety of cell functions. The binding of chemokine C-X-C motif chemokine ligand 12 (CXCL12) (stromal cell-derived factor 1) to a G-protein-coupled receptor C-X-C chemokine receptor type 4 (CXCR4) triggers downstream signaling pathways with effects on cell survival, proliferation, chemotaxis, migration, and gene expression. Intensive and extensive investigations have provided evidence suggesting that the CXCL12-CXCR4 axis plays a pivotal role in tumor development, survival, angiogenesis, metastasis, as well as in creating tumor microenvironment, thus implying that this axis is a potential target for the development of cancer therapies. The structures of CXCL12 and CXCR4 have been resolved with experimental methods such as X-ray crystallography, NMR, or cryo-EM. Therefore, it is possible to apply structure-based computational approaches to discover, design, and modify therapeutic molecules for cancer treatments. Here, we summarize the current understanding of the roles played by the CXCL12-CXCR4 signaling axis in cellular functions linking to cancer progression and metastasis. This review also provides an introduction to protein structures of CXCL12 and CXCR4 and the application of computer simulation and analysis in understanding CXCR4 activation and antagonist binding. Furthermore, examples of strategies and current progress in CXCL12-CXCR4 axis-targeted development of therapeutic anticancer inhibitors are discussed.

Let-7g Upregulation Attenuated the KRAS-PI3K-Rac1-Akt Axis-Mediated Bioenergetic Functions

The aberrant activation of signaling pathways contributes to cancer cells with metabolic reprogramming. Thus, targeting signaling modulators is considered a potential therapeutic strategy for cancer. Subcellular fractionation, coimmunoprecipitation, biochemical analysis, and gene manipulation experiments revealed that decreasing the interaction of kirsten rat sarcoma viral oncogene homolog (KRAS) with p110α in lipid rafts with the use of naringenin (NGN), a citrus flavonoid, causes lipid raft-associated phosphatidylinositol 3-kinase (PI3K)-GTP-ras-related C3 botulinum toxin substrate 1 (Rac1)-protein kinase B (Akt)-regulated metabolic dysfunction of glycolysis and mitochondrial oxidative phosphorylation (OXPHOS), leading to apoptosis in human nasopharyngeal carcinoma (NPC) cells. The use of lethal-7g (let-7g) mimic and let-7g inhibitor confirmed that elevated let-7g resulted in a decrease in KRAS expression, which attenuated the PI3K-Rac1-Akt-BCL-2/BCL-xL-modulated mitochondrial energy metabolic functions. Increased let-7g depends on the suppression of the RNA-specificity of monocyte chemoattractant protein-induced protein-1 (MCPIP1) ribonuclease since NGN specifically blocks the degradation of pre-let-7g by NPC cell-derived immunoprecipitated MCPIP1. Converging lines of evidence indicate that the inhibition of MCPIP1 by NGN leads to let-7g upregulation, suppressing oncogenic KRAS-modulated PI3K-Rac1-Akt signaling and thereby impeding the metabolic activities of aerobic glycolysis and mitochondrial OXPHOS.

Role of RhoG as a regulator of cellular functions: integrating insights on immune cell activation, migration, and functions

BACKGROUND

RhoG is a multifaceted member of the Rho family of small GTPases, sharing the highest sequence identity with the Rac subfamily members. It acts as a molecular switch, when activated, plays a central role in regulating the fundamental processes in immune cells, such as actin-cytoskeleton dynamics, transendothelial migration, survival, and proliferation, including immunological functions (e.g., phagocytosis and trogocytosis) during inflammatory responses.

METHOD

We have performed a literature review based on published original and review articles encompassing the significant effect of RhoG on immune cell functions from central databases, including PubMed and Google Scholar.

RESULTS AND CONCLUSIONS

Recently published data shows that the dynamic expression of different transcription factors, non-coding RNAs, and the spatiotemporal coordination of different GEFs with their downstream effector molecules regulates the cascade of Rho signaling in immune cells. Additionally, alterations in RhoG-specific signaling can lead to physiological, pathological, and developmental adversities. Several mutations and RhoG-modulating factors are also known to pre-dispose the downstream signaling with abnormal gene expression linked to multiple diseases. This review focuses on the cellular functions of RhoG, interconnecting different signaling pathways, and speculates the importance of this small GTPase as a prospective target against several pathological conditions.

CircSRSF4 Enhances Proliferation, Invasion, and Migration to Promote the Progression of Osteosarcoma via Rac1

(1) Background: At present, cancer cell metastasis is the main cause of death in patients with malignant tumors, and up to 23% of osteosarcoma patients have died due to lung and lymph node metastasis. Therefore, finding new molecules involved in tumor development can provide new strategies for the diagnosis and treatment of osteosarcoma patients. Circular RNAs (circRNAs) are a type of RNA molecule that are connected head-to-tail to form a closed ring. There is increasing evidence that circRNAs are RNA molecules with many biological functions in various diseases. However, the role and mechanism of circRNAs in osteosarcoma have rarely been reported. (2) Methods: The expression of circSRSF4 in osteosarcoma tissues and cell lines was detected by quantitative real-time PCR (RT-qPCR), and the result of high-throughput sequencing was verified. In order to explore the effect of circSRSF4 on tumor proliferation, invasion, and migration, a dual-luciferase reporter assay, RNA binding protein immunoprecipitation assay, cell counting kit-8 (CCK-8), transwell assay, scratch wound healing assay, Western blot analysis, and other experiments were carried out in vitro. Rescue experiments and a xenograft model confirmed that circSRSF4 directly acted on miR-224 to regulate Rac1 expression. (3) Results: The expression of circSRSF4 was significantly higher in osteosarcoma tissues and cell lines. Down-regulating the expression of circSRSF4 in vitro significantly inhibited the proliferation, invasion, and migration of cells, and also reduced the expression of Rac1, while the overexpression of Rac1 and miR-224 inhibition could reverse these effects. The inhibition of circSRSF4 expression in vivo also attenuated tumor growth. A mechanistic study showed that circSRSF4 can be used as an miR-224 sponge to up-regulate the expression of Rac1, thereby promoting the development of osteosarcoma. (4) Conclusions: CircSRSF4 acting as a ceRNA promotes the malignant behavior of osteosarcoma through the circSRSF4/miR-224/Rac1 axis, which provides a new theoretical basis for the clinical prevention and treatment of osteosarcoma and the study of related markers and intervention targets.

Cell Signaling Pathways That Promote Radioresistance of Cancer Cells

Radiation therapy (RT) is a standard treatment for solid tumors and about 50% of patients with cancer, including pediatric cancer, receive RT. While RT has significantly improved the overall survival and quality of life of cancer patients, its efficacy has still been markedly limited by radioresistance in a significant number of cancer patients (intrinsic or acquired), resulting in failure of the RT control of the disease. Radiation eradicates cancer cells mainly by causing DNA damage. However, radiation also concomitantly activates multiple prosurvival signaling pathways, which include those mediated by ATM, ATR, AKT, ERK, and NF-κB that promote DNA damage checkpoint activation/DNA repair, autophagy induction, and/or inhibition of apoptosis. Furthermore, emerging data support the role of YAP signaling in promoting the intrinsic radioresistance of cancer cells, which occurs through its activation of the transcription of many essential genes that support cell survival, DNA repair, proliferation, and the stemness of cancer stem cells. Together, these signaling pathways protect cancer cells by reducing the magnitude of radiation-induced cytotoxicity and promoting radioresistance. Thus, targeting these prosurvival signaling pathways could potentially improve the radiosensitivity of cancer cells. In this review, we summarize the contribution of these pathways to the radioresistance of cancer cells.

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.

Metabolic labeling with an alkyne probe reveals similarities and differences in the prenylomes of several brain-derived cell lines and primary cells

Protein prenylation involves the attachment of one or two isoprenoid group(s) onto cysteine residues positioned near the C-terminus. This modification is essential for many signal transduction processes. In this work, the use of the probe C15AlkOPP for metabolic labeling and identification of prenylated proteins in a variety of cell lines and primary cells is explored. Using a single isoprenoid analogue, 78 prenylated protein groups from the three classes of prenylation substrates were identified including three novel prenylation substrates in a single experiment. Applying this method to three brain-related cell lines including neurons, microglia, and astrocytes showed substantial overlap (25%) in the prenylated proteins identified. In addition, some unique prenylated proteins were identified in each type. Eight proteins were observed exclusively in neurons, five were observed exclusively in astrocytes and three were observed exclusively in microglia, suggesting their unique roles in these cells. Furthermore, inhibition of farnesylation in primary astrocytes revealed the differential responses of farnesylated proteins to an FTI. Importantly, these results provide a list of 19 prenylated proteins common to all the cell lines studied here that can be monitored using the C15AlkOPP probe as well as a number of proteins that were observed in only certain cell lines. Taken together, these results suggest that this chemical proteomic approach should be useful in monitoring the levels and exploring the underlying role(s) of prenylated proteins in various diseases.

EphA2 and EGFR: Friends in Life, Partners in Crime. Can EphA2 Be a Predictive Biomarker of Response to Anti-EGFR Agents?

The Eph receptors represent the largest group among Receptor Tyrosine kinase (RTK) families. The Eph/ephrin signaling axis plays center stage during development, and the deep perturbation of signaling consequent to its dysregulation in cancer reveals the multiplicity and complexity underlying its function. In the last decades, they have emerged as key players in solid tumors, including colorectal cancer (CRC); however, what causes EphA2 to switch between tumor-suppressive and tumor-promoting function is still an active theater of investigation. This review summarizes the recent advances in understanding EphA2 function in cancer, with detail on the molecular determinants of the oncogene-tumor suppressor switch function of EphA2. We describe tumor context-specific examples of EphA2 signaling and the emerging role EphA2 plays in supporting cancer-stem-cell-like populations and overcoming therapy-induced stress. In such a frame, we detail the interaction of the EphA2 and EGFR pathway in solid tumors, including colorectal cancer. We discuss the contribution of the EphA2 oncogenic signaling to the resistance to EGFR blocking agents, including cetuximab and TKIs.

The ZNF750-RAC1 axis as potential prognostic factor for breast cancer

The human zinc finger (C2H2-type) protein ZNF750 is a transcription factor regulated by p63 that plays a critical role in epithelial tissues homoeostasis, as well as being involved in the pathogenesis of cancer. Indeed, missense mutations, truncation and genomic deletion have been found in oesophageal squamous cell carcinoma. In keeping, we showed that ZNF750 negatively regulates cell migration and invasion in breast cancer cells; in particular, ZNF750 binds and recruits KDM1A and HDAC1 on the LAMB3 and CTNNAL1 promoters. This interaction, in turn, represses the transcription of LAMB3 and CTNNAL1 genes, which are involved in cell migration and invasion. Given that ZNF750 is emerging as a crucial transcription factor that acts as tumour suppressor gene, here, we show that ZNF750 represses the expression of the small GTPase, Ras-related C3 botulinum toxin substrate 1 (RAC1) in breast cancer cell lines, by directly binding its promoter region. In keeping with ZNF750 controlling RAC1 expression, we found an inverse correlation between ZNF750 and RAC1 in human breast cancer datasets. More importantly, we found a significant upregulation of RAC1 in human breast cancer datasets and we identified a direct correlation between RAC1 expression and the survival rate of breast cancer patient. Overall, our findings provide a novel molecular mechanism by which ZNF750 acts as tumour suppressor gene. Hence, we report a potential clinical relevance of ZNF750/RAC1 axis in breast cancer.

Vav2 catalysis-dependent pathways contribute to skeletal muscle growth and metabolic homeostasis

Skeletal muscle promotes metabolic balance by regulating glucose uptake and the stimulation of multiple interorgan crosstalk. We show here that the catalytic activity of Vav2, a Rho GTPase activator, modulates the signaling output of the IGF1- and insulin-stimulated phosphatidylinositol 3-kinase pathway in that tissue. Consistent with this, mice bearing a Vav2 protein with decreased catalytic activity exhibit reduced muscle mass, lack of proper insulin responsiveness and, at much later times, a metabolic syndrome-like condition. Conversely, mice expressing a catalytically hyperactive Vav2 develop muscle hypertrophy and increased insulin responsiveness. Of note, while hypoactive Vav2 predisposes to, hyperactive Vav2 protects against high fat diet-induced metabolic imbalance. These data unveil a regulatory layer affecting the signaling output of insulin family factors in muscle.

Skeletal muscle plays a key role in regulating systemic glucose and metabolic homeostasis. Here, the authors show that the catalytic activity of Vav2, an activator of Rho GTPases, modulates those processes by favoring the responsiveness of this tissue to insulin and related factors.

Bacteria as a double-action sword in cancer

Bacteria have long been known as one of the primary causative agents of cancer, however, recent studies suggest that they can be used as a promising agent in cancer therapy. Because of the limitations that conventional treatment faces due to the specific pathophysiology and the tumor environment, there is a great need for the new anticancer therapeutic agents. Bacteriotherapy utilizes live, attenuated strains or toxins, peptides, bacteriocins of the bacteria in the treatment of cancer. Moreover, they are widely used as a vector for delivering genes, peptides, or drugs to the tumor target. Interestingly, it was found that their combination with the conventional therapeutic approaches may enhance the treatment outcome. In the genome editing era, it is feasible to develop a novel generation of therapeutic bacteria with fewer side effects and more efficacy for cancer therapy. Here we review the current knowledge on the dual role of bacteria in the development of cancer as well as cancer therapy.

Molecular cloning and characterization of DjRac1, a novel small G protein gene from planarian Dugesia japonica

Rac proteins are classified as a subfamily of the Rho family of small G proteins. They are important molecular switches which act as key signal transducers regulating a wide variety of processes in the cell. DjRac1, a novel Rac gene from planarian Dugesia japonica was cloned by RACE method and characterized. This cDNA contains 851 bp with a putative open reading frame of 190 amino acids. It has a predicted molecular mass of 21.12 kDa and an isoelectric point of 8.42. Whole-mount in situ hybridization and relative quantitative real-time PCR were used to study the spatial and temporal expression pattern of DjRac1 from 1 to 7 days in the regenerating planarians. Results showed that the expression of DjRac1 was concentrated in the blastema and the transcription level of DjRac1 was significantly upregulated after amputation within three days, suggesting DjRac1 might participate in the process of regeneration in planarian.

Gain of function mutant p53 protein activates AKT through the Rac1 signaling to promote tumorigenesis

Tumor suppressor p53 is the most frequently mutated gene in human cancer. Mutant p53 (mutp53) not only loses the tumor suppressive activity of wild type p53, but often gains new oncogenic activities to promote tumorigenesis, defined as mutp53 gain of function (GOF). While the concept of mutp53 GOF is well-established, its underlying mechanism is not well-understood. AKT has been suggested to be activated by mutp53 and contribute to mutp53 GOF, but its underlying mechanism is unclear. In this study, we found that the activation of the Rac1 signaling by mutp53 mediates the promoting effect of mutp53 on AKT activation. Blocking Rac1 signaling by RNAi or a Rac1 inhibitor can inhibit AKT activation by mutp53. Importantly, targeting Rac1/AKT can greatly compromise mutp53 GOF in tumorigenesis. Results from this study uncover a new mechanism for AKT activation in tumors, and reveal that activation of AKT by mutp53 via the Rac1 signaling contributes to mutp53 GOF in tumorigenesis. More importantly, this study provides Rac1 and AKT as potential targets for therapy in tumors containing mutp53.

Signaling Determinants of Glioma Cell Invasion

Tumor cell invasiveness is a critical challenge in the clinical management of glioma patients. In addition, there is accumulating evidence that current therapeutic modalities, including anti-angiogenic therapy and radiotherapy, can enhance glioma invasiveness. Glioma cell invasion is stimulated by both autocrine and paracrine factors that act on a large array of cell surface-bound receptors. Key signaling elements that mediate receptor-initiated signaling in the regulation of glioblastoma invasion are Rho family GTPases, including Rac, RhoA and Cdc42. These GTPases regulate cell morphology and actin dynamics and stimulate cell squeezing through the narrow extracellular spaces that are typical of the brain parenchyma. Transient attachment of cells to the extracellular matrix is also necessary for glioblastoma cell invasion. Interactions with extracellular matrix components are mediated by integrins that initiate diverse intracellular signalling pathways. Key signaling elements stimulated by integrins include PI3K, Akt, mTOR and MAP kinases. In order to detach from the tumor mass, glioma cells secrete proteolytic enzymes that cleave cell surface adhesion molecules, including CD44 and L1. Key proteases produced by glioma cells include uPA, ADAMs and MMPs. Increased understanding of the molecular mechanisms that control glioma cell invasion has led to the identification of molecular targets for therapeutic intervention in this devastating disease.

Elmo1 function, linked to Rac1 activity, regulates peripheral neuronal numbers and myelination in zebrafish

Peripheral nervous system development involves a tight coordination of neuronal birth and death and a substantial remodelling of the myelinating glia cytoskeleton to achieve myelin wrapping of its projecting axons. However, how these processes are coordinated through time is still not understood. We have identified engulfment and cell motility 1, Elmo1, as a novel component that regulates (i) neuronal numbers within the Posterior Lateral Line ganglion and (ii) radial sorting of axons by Schwann cells (SC) and myelination in the PLL system in zebrafish. Our results show that neuronal and myelination defects observed in elmo1 mutant are rescued through small GTPase Rac1 activation. Inhibiting macrophage development leads to a decrease in neuronal numbers, while peripheral myelination is intact. However, elmo1 mutants do not show defective macrophage activity, suggesting a role for Elmo1 in PLLg neuronal development and SC myelination independent of macrophages. Forcing early Elmo1 and Rac1 expression specifically within SCs rescues elmo1-/- myelination defects, highlighting an autonomous role for Elmo1 and Rac1 in radial sorting of axons by SCs and myelination. This uncovers a previously unknown function of Elmo1 that regulates fundamental aspects of PNS development.

PODXL2 maintains cellular stemness and promotes breast cancer development through the Rac1/Akt pathway

The cluster of differentiation 34 (CD34) family, which includes CD34, podocalyxin-like protein 1 (PODXL), and PODXL2, are type-I transmembrane sialomucins and markers of hematopoietic stem cells (HSCs) and vascular-associated tissues. CD34 family proteins are expressed by endothelial cells and hematopoietic precursors. PODXL is well known to be associated with invadopodia formation and to promote the epithelial-mesenchymal transition, tumor migration and invasion. PODXL expression was correlated with poor survival of cancer patients. However, the role of PODXL2 in cancer has been less fully explored. To reveal the novel role of PODXL2 in breast cancer, the present study evaluated PODXL2 levels in relation to clinical outcomes of cancer patients by performing a bioinformatics analysis using the Oncomine database, Kaplan-Meier plots, and the CCLE database. Empirical validation of bioinformatics predictions was conducted utilizing the short hairpin (sh)-RNA silencing method for PODXL2 in the BT474 invasive ductal breast carcinoma cell line. The bioinformatics analysis revealed that PODXL2 overexpression was correlated with poor survival of breast cancer patients, suggesting an oncogenic role of PODXL2 in breast carcinoma. In a validation experiment, knockdown of PODXL2 in BT474 cells slightly influenced cell proliferation, suppressed migration, and inhibited expressions of downstream molecules, including Ras-related C3 botulinum toxin substrate 1 (Rac1), phosphorylated (p)-Akt (S473), and p-paxillin (Y31) proteins. In addition, knockdown of PODXL2 reduced expression levels of cancer stem cell (CSC) markers, including Oct-4 and Nanog, and the breast CSC marker aldehyde dehydrogenase 1 (ALDH1). Collectively, our present study demonstrated that PODXL2 plays a crucial role in cancer development and could serve as a potential prognostic biomarker in breast cancer patients.

Nanomechanical insights: Amyloid beta oligomer-induced senescent brain endothelial cells

Senescent cells accumulate in various peripheral tissues during aging and have been shown to exacerbate age-related inflammatory responses. We recently showed that exposure to neurotoxic amyloid β (Aβ1-42) oligomers can readily induce a senescence phenotype in human brain microvascular endothelial cells (HBMECs). In the present work, we used atomic force microscopy (AFM) to further characterize the morphological properties such as cell membrane roughness and cell height and nanomechanical properties such as Young's modulus of the membrane (membrane stiffness) and adhesion resulting from the interaction between AFM tip and cell membrane in Aβ1-42 oligomer-induced senescent human brain microvascular endothelial cells. Morphological imaging studies showed a flatter and spread-out nucleus in the senescent HBMECs, both characteristic features of a senescent phenotype. Furthermore, the mean cell body roughness and mean cell height were lower in senescent HBMECs compared to untreated normal HBMECs. We also observed increased stiffness and alterations in the adhesion properties in Aβ1-42 oligomer-induced senescent endothelial cells compared to the untreated normal HBMECs suggesting dynamic reorganization of cell membrane. We then show that vascular endothelial growth factor receptor 1 (VEGFR-1) knockdown or overexpression of Rho GTPase Rac 1 in the endothelial cells inhibited senescence and reversed these nanomechanical alterations, confirming a direct role of these pathways in the senescent brain endothelial cells. These results illustrate that nanoindentation and topographic analysis of live senescent brain endothelial cells can provide insights into cerebrovascular dysfunction in neurodegenerative diseases such as Alzheimer's disease.

Cho W, Soleimanpour S. Bacteriotherapy in Breast Cancer

Breast cancer is the second most common cause of cancer-related mortality among women around the world. Conventional treatments in the fight against breast cancer, such as chemotherapy, are being challenged regarding their effectiveness. Thus, strategies for the treatment of breast cancer need to be continuously refined to achieve a better patient outcome. We know that a number of bacteria are pathogenic and some are even associated with tumor development, however, recent studies have demonstrated interesting results suggesting some bacteria may have potential for cancer therapy. Therefore, the therapeutic role of bacteria has aroused attention in medical and pharmaceutical studies. Furthermore, genetic engineering has been used in bacterial therapy and may led to greater efficacy with few side effects. Some genetically modified non-pathogenic bacterial species are more successful due to their selectivity for cancer cells but with low toxicity for normal cells. Some live, attenuated, or genetically modified bacterias are capable to multiply in tumors and inhibit their growth. This article aims to review the role of bacteria and their products including bacterial peptides, bacteriocins, and toxins for the treatment of breast cancer.

Oxidized base 8-oxoguanine, a product of DNA repair processes, contributes to dendritic cell activation

A growing body of evidence suggests that elevated levels of reactive oxygen species (ROS) in the airways caused by exposure to gas phase pollutants or particulate matter are able to activate dendritic cells (DCs); however, the exact mechanisms are still unclear. When present in excess, ROS can modify macromolecules including DNA. One of the most abundant DNA base lesions is 7,8-dihydro-8-oxoguanine (8-oxoG), which is repaired by the 8-oxoguanine DNA glycosylase 1 (OGG1)-initiated base excision repair (BER) (OGG1-BER) pathway. Studies have also demonstrated that in addition to its role in repairing oxidized purines, OGG1 has guanine nucleotide exchange factor activity when bound to 8-oxoG. In the present study, we tested the hypothesis that exposure to 8-oxoG, the specific product of OGG1-BER, induces functional changes of DCs. Supporting our hypothesis, transcriptome analysis revealed that in mouse lungs, out of 95 genes associated with DCs' function, 22 or 42 were significantly upregulated after a single or multiple intranasal 8-oxoG challenges, respectively. In a murine model of allergic airway inflammation, significantly increased serum levels of ovalbumin (OVA)-specific IgE antibodies were detected in mice sensitized via nasal challenges with OVA+8-oxoG compared to those challenged with OVA alone. Furthermore, exposure of primary human monocyte-derived DCs (moDC) to 8-oxoG base resulted in significantly enhanced expression of cell surface molecules (CD40, CD86, CD83, HLA-DQ) and augmented the secretion of pro-inflammatory mediators IL-6, TNF and IL-8, whereas it did not considerably influence the production of the anti-inflammatory cytokine IL-10. The stimulatory effects of 8-oxoG on human moDCs were abolished upon siRNA-mediated OGG1 depletion. Collectively, these data suggest that OGG1-BER-generated 8-oxoG base-driven cell signaling activates DCs, which may contribute to initiation of both the innate and adaptive immune responses under conditions of oxidative stress.

PKN1 kinase-negative knock-in mice develop splenomegaly and leukopenia at advanced age without obvious autoimmune-like phenotypes

Protein kinase N1 (PKN1) knockout (KO) mice spontaneously form germinal centers (GCs) and develop an autoimmune-like disease with age. Here, we investigated the function of PKN1 kinase activity in vivo using aged mice deficient in kinase activity resulting from the introduction of a point mutation (T778A) in the activation loop of the enzyme. PKN1[T778A] mice reached adulthood without external abnormalities; however, the average spleen size and weight of aged PKN1[T778A] mice increased significantly compared to aged wild type (WT) mice. Histologic examination and Southern blot analyses of spleens showed extramedullary hematopoiesis and/or lymphomagenesis in some cases, although without significantly different incidences between PKN1[T778A] and WT mice. Additionally, flow cytometry revealed increased numbers in B220⁺, CD3⁺, Gr1⁺ and CD193⁺ leukocytes in the spleen of aged PKN1[T778A] mice, whereas the number of lymphocytes, neutrophils, eosinophils, and monocytes was reduced in the peripheral blood, suggesting an advanced impairment of leukocyte trafficking with age. Moreover, aged PKN1[T778A] mice showed no obvious GC formation nor autoimmune-like phenotypes, such as glomerulonephritis or increased anti-dsDNA antibody titer, in peripheral blood. Our results showing phenotypic differences between aged Pkn1-KO and PKN1[T778A] mice may provide insight into the importance of PKN1-specific kinase-independent functions in vivo.

Fluvastatin Inhibits HMG-CoA Reductase and Prevents Non-Small Cell Lung Carcinogenesis

Lung cancer is the leading cause of cancer-related death worldwide. However, promising agents for lung cancer prevention are still very limited. Identification of preventive targets and novel effective preventive agents is urgently needed for clinical applications. In this study, we found that fluvastatin targeted 3-Hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase (HMGCR), which a rate-limiting enzyme in the mevalonate pathway, and inhibited non-small cell lung cancer (NSCLC) tumorigenesis. Initially, we demonstrated that HMGCR is overexpressed in human lung adenocarcinoma tissues compared with normal tissues. Knockdown of HMGCR in NSCLC cells attenuated growth and induced apoptosis in vitro and in vivo Furthermore, we found that fluvastatin, an inhibitor of HMGCR, suppressed NSCLC cell growth and induced apoptosis. Intriguingly, fluvastastin functions by inhibiting the HMGCR-driven Braf/MEK/ERK1/2 and Akt signaling pathways. Notably, fluvastatin attenuated tumor growth in 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK)-induced lung tumorigenesis and in a patient-derived xenograft lung tumor model. Overall, our findings suggest that fluvastatin might be promising chemopreventive or potential therapeutic drug against NSCLC tumorigenesis, providing hope for rapid clinical translation.

RAC1 inhibition reverses cisplatin resistance in esophageal squamous cell carcinoma and induces downregulation of glycolytic enzymes

Development of chemoresistance remains a major challenge in treating esophageal squamous cell carcinoma (ESCC) patients despite treatment advances. However, the role of RAC1 in chemoresistance of ESCC and the underlying mechanisms remain largely unknown. In this study, we found that higher levels of RAC1 expression were associated with poorer prognosis in ESCC patients. Enhanced RAC1 expression increased cell proliferation, migration, and chemoresistance in vitro. Combination therapy using RAC1 inhibitor EHop-016 and cisplatin significantly promoted cell viability inhibition, G2/M phase cycle arrest, and apoptosis when compared to each monotherapy. Mechanistically, glycolysis was significantly downregulated in the RAC1 inhibitor monotherapy group and the combination group via inhibiting AKT/FOXO3a signaling when compared to the control group. Moreover, the silencing of RAC1 inhibited AKT/FOXO3a signaling and cell glycolysis while the upregulation of RAC1 produced an opposite effect. In murine xenograft models, the tumor volume and the expression of glycolytic enzymes were significantly reduced in combination therapy when compared to each monotherapy group. Overall, our study demonstrates that targeting RAC1 with an inhibitor overcomes cisplatin resistance in ESCC by suppressing glycolytic enzymes, which provides a promising strategy for treatment of ESCC in clinical practice.

Induction of entosis in prostate cancer cells by nintedanib and its therapeutic implications

Entosis is a homogeneous cell-in-cell phenomenon and a non-apoptotic cell death process. Tyrosine kinase inhibitors have been used in the treatment of prostate cancer and have already demonstrated efficacy in a clinical setting. The present study investigated the role of entosis in prostate cancer treated with the tyrosine kinase inhibitor nintedanib. Prostate cancer cells were treated with nintedanib in vitro and entosis was observed. Mice xenografts were created to evaluate whether nintedanib is able to induce entosis in vivo. The reverse transcription-quantitative polymerase chain reaction, western blotting and immunofluorescence were performed to investigate whether the entosis pathway is induced by nintedanib. It was also investigated whether entosis can contribute to cell survival and progression under nintedanib stress, and nintedanib was revealed to enhance prostate cancer cell entosis. Nintedanib-induced entosis in prostate cancer cells occurred through phosphoinositide 3-kinase/cell division cycle 42 (CDC42) inhibition, followed by the upregulation of epithelial (E-)cadherin and components of the Rho kinase (ROCK) signaling pathway. In addition, nintedanib-resistant cells exhibiting entosis had a higher invasive ability. In addition, in vivo treatment of mice xenografts with nintedanib also increased the expression of E-cadherin and components of the ROCK signaling pathway. Nintedanib can promote entosis during prostate cancer treatment by modulating the CDC42 pathway. Furthermore, prostate cancer cells acquired nintedanib resistance and survived by activating entosis.

Engineering of Human Corneal Endothelial Cells In Vitro

Human corneal endothelial cells are responsible for controlling corneal transparency, however they are notorious for their limited proliferative capability. Thus, damage to these cells may cause irreversible blindness. Currently, the only way to cure blindness caused by corneal endothelial dysfunction is via corneal transplantation of a cadaver donor cornea with healthy corneal endothelium. Due to severe shortage of donor corneas worldwide, it has become paramount to develop human corneal endothelial grafts in vitro that can subsequently be transplanted in humans. Recently, we have reported effective expansion of human corneal endothelial cells by reprogramming the cells into progenitor status through use of p120-Kaiso siRNA knockdown. This new reprogramming approach circumvents the need of using induced pluripotent stem cells or embryonic stem cells. Successful promotion of this technology will encourage scientists to re-think how "contact inhibition" can safely be perturbed to our benefit, i.e., effective engineering of an in vivo-like tissue while successful maintaining the normal phenotype. In this review, we present current advances in reprogramming corneal endothelial cells in vitro, detail the methods to successful engineer human corneal endothelial grafts, and discuss their future clinical applications to cure corneal blindness.

Kalirin-7 plays a neuroprotective role in Neuro-2A cells injured by oxygen-glucose deprivation and reperfusion through Rac1 activation

Objective(s):

The study explored the neuroprotective role of Kalirin-7 (Kal-7) in Neuro-2A cells after oxygen-glucose deprivation and reperfusion (OGD/R) treatment.

Materials and Methods:

The study used an OGD/R model of mouse Neuro-2A neuroblastoma cells in vitro. Cells were transfected with pCAGGS-Kal-7 to up-regulating kal-7. Then cell proliferation and apoptosis were respectively analyzed by Trypan blue exclusion method and flow cytometry. To examine the involvement of Rac1, cells were treated with Rac1-GTP inhibitor NSC23766 before treatment with OGD/R. Expressions of Bax, Bcl-2, Rac1, and down-stream targets of Rac1 were analyzed by Western blot.

Results:

Kal-7 significantly decreased OGD/R induced cell apoptosis (P<0.01), but no significant effects were observed on cell proliferation. Kal-7 increased the expressions of apoptosis-related protein of Bcl-2 and Rac1, but decreased the expression of Bax in Neuro-2A cells stimulated to OGD/R. Rac1 was activated by Kal-7 due to the increased levels of its down-stream targets, p-p38 and p-PAK1. NSC23766 reduced the anti-apoptotic effect of Kal-7 as the enhanced apoptotic cell rate and increased Bax/Bcl-2 ratio.

Conclusion:

These findings suggest that the protective effects of Kal-7 against OGD/R injury in Neuro-2A cells were dependent in a Rac1 activation signaling.

The Intermolecular Interaction of Ephexin4 Leads to Autoinhibition by Impeding Binding of RhoG

Ephexin4 is a guanine nucleotide-exchange factor (GEF) for RhoG and is involved in various RhoG-related cellular processes such as phagocytosis of apoptotic cells and migration of cancer cells. Ephexin4 forms an oligomer via an intermolecular interaction, and its GEF activity is increased in the presence of Elmo, an Ephexin4-interacting protein. However, it is uncertain if and how Ephexin4 is autoinhibited. Here, using an Ephexin4 mutant that abrogated the intermolecular interaction, we report that this interaction impeded binding of RhoG to Ephexin4 and thus inhibited RhoG activation. Mutation of the glutamate residue at position 295, which is a highly conserved residue located in the region of Ephexin4 required for the intermolecular interaction, to alanine (Ephexin4^E295A) disrupted the intermolecular interaction and increased binding of RhoG, resulting in augmented RhoG activation. In addition, phagocytosis of apoptotic cells and formation of membrane ruffles were increased more by expression of Ephexin4^E295A than by expression of wild-type Ephexin4. Taken together, our data suggest that Ephexin4 is autoinhibited through its intermolecular interaction, which impedes binding of RhoG.

Alterations of 63 hub genes during lingual carcinogenesis in C57BL/6J mice

To identify potential biomarkers of lingual cancer, 75 female C57BL/6J mice were subjected to 16-week oral delivery of 4-nitroquinoline-1-oxide (4NQO; 50 mg/L), with 10 mice used as controls. Lingual mucosa samples representative of normal tissue (week 0) and early (week 12) and advanced (week 28) tumorigenesis were harvested for microarray and methylated DNA immunoprecipitation sequencing (MeDIP-Seq). Combined analysis with Short Time-series Expression Miner (STEM), the Cytoscape plugin cytoHubba, and screening of differentially expressed genes enabled identification of 63 hub genes predominantly altered in the early stage rather than the advanced stage. Validation of microarray results was carried out using qRT-PCR. Of 63 human orthologous genes, 35 correlated with human oral squamous cell carcinoma. KEGG analysis showed "pathways in cancer", involving 13 hub genes, as the leading KEGG term. Significant alterations in promoter methylation were confirmed at Tbp, Smad1, Smad4, Pdpk1, Camk2, Atxn3, and Cdh2. HDAC2, TBP, and EP300 scored ≥10 on Maximal Clique Centrality (MCC) in STEM profile 11 and were overexpressed in human tongue cancer samples. However, expression did not correlate with smoking status, tumor differentiation, or overall survival. These results highlight potentially useful candidate biomarkers for lingual cancer prevention, diagnosis, and treatment.

TET1-Mediated Hypomethylation Activates Oncogenic Signaling in Triple-Negative Breast Cancer

Both gains and losses of DNA methylation are common in cancer, but the factors controlling this balance of methylation remain unclear. Triple-negative breast cancer (TNBC), a subtype that does not overexpress hormone receptors or HER2/NEU, is one of the most hypomethylated cancers observed. Here, we discovered that the TET1 DNA demethylase is specifically overexpressed in about 40% of patients with TNBC, where it is associated with hypomethylation of up to 10% of queried CpG sites and a worse overall survival. Through bioinformatic analyses in both breast and ovarian cancer cell line panels, we uncovered an intricate network connecting TET1 to hypomethylation and activation of cancer-specific oncogenic pathways, including PI3K, EGFR, and PDGF. TET1 expression correlated with sensitivity to drugs targeting the PI3K-mTOR pathway, and CRISPR-mediated deletion of TET1 in two independent TNBC cell lines resulted in reduced expression of PI3K pathway genes, upregulation of immune response genes, and substantially reduced cellular proliferation, suggesting dependence of oncogenic pathways on TET1 overexpression. Our work establishes TET1 as a potential oncogene that contributes to aberrant hypomethylation in cancer and suggests that TET1 could serve as a druggable target for therapeutic intervention.Significance: This study addresses a critical gap in knowledge of how and why methylation is prognostic in breast cancer and shows how this information can be used to stratify patients with TNBC for targeted therapy. Cancer Res; 78(15); 4126-37. ©2018 AACR.

Blockage of the mevalonate pathway overcomes the apoptotic resistance to MEK inhibitors with suppressing the activation of Akt in cancer cells

With increasing clinical demands for MEK inhibitors in cancer treatment, overcoming the resistance to MEK inhibitors is an urgent problem to be solved. Numerous reports have shown that MEK inhibition results in the activation of PI3K-Akt signaling, which may confer apoptotic resistance to MEK inhibitors. We here demonstrate that the blockade of the mevalonate pathway using the antilipidemic drug statins represses Akt activation following MEK inhibition and induces significant apoptosis when co-treated with CH5126766 or trametinib. These events were clearly negated by the addition of mevalonate or geranylgeranyl pyrophosphate, indicating that the protein geranylgeranylation is implicated in the apoptotic resistance to MEK inhibitors. Furthermore, mechanistically, the combined treatment of CH5126766 with statins upregulated TNF-related apoptosis-inducing ligand (TRAIL), which was dependent on inhibition of the mevalonate pathway and is involved in apoptosis induction in human breast cancer MDA-MB-231 cells. The present study not only revealed that the mevalonate pathway could be targetable to enhance the efficacy of MEK inhibitors, but also proposes that combinatorial treatment of MEK inhibitors with statins may be a promising therapeutic strategy to sensitize cancer cells to apoptosis.

RCC2 over-expression in tumor cells alters apoptosis and drug sensitivity by regulating Rac1 activation

Background

Small GTP binding protein Rac1 is a component of NADPH oxidases and is essential for superoxide-induced cell death. Rac1 is activated by guanine nucleotide exchange factors (GEFs), and this activation can be blocked by regulator of chromosome condensation 2 (RCC2), which binds the switch regions of Rac1 to prevent access from GEFs.

Methods

Three cancer cell lines with up- or down-regulation of RCC2 were used to evaluate cell proliferation, apoptosis, Rac1 signaling and sensitivity to a group of nine chemotherapeutic drugs. RCC2 expression in lung cancer and ovarian cancer were studied using immunochemistry stain of tumor tissue arrays.

Results

Forced RCC2 expression in tumor cells blocked spontaneous- or Staurosporine (STS)-induced apoptosis. In contrast, RCC2 knock down in these cells resulted in increased apoptosis to STS treatment. The protective activity of RCC2 on apoptosis was revoked by a constitutively activated Rac1, confirming a role of RCC2 in apoptosis by regulating Rac1. In an immunohistochemistry evaluation of tissue microarray, RCC2 was over-expressed in 88.3% of primary lung cancer and 65.2% of ovarian cancer as compared to non-neoplastic lung and ovarian tissues, respectively. Because chemotherapeutic drugs can kill tumor cells by activating Rac1/JNK pathway, we suspect that tumors with RCC2 overexpression would be more resistant to these drugs. Tumor cells with forced RCC2 expression indeed had significant difference in drug sensitivity compared to parental cells using a panel of common chemotherapeutic drugs.

Conclusions

RCC2 regulates apoptosis by blocking Rac1 signaling. RCC2 expression in tumor can be a useful marker for predicting chemotherapeutic response.

GTPases Rac1 and Ras Signaling from Endosomes

The endocytic compartment is not only the functional continuity of the plasma membrane but consists of a diverse collection of intracellular heterogeneous complex structures that transport, amplify, sustain, and/or sort signaling molecules. Over the years, it has become evident that early, late, and recycling endosomes represent an interconnected vesicular-tubular network able to form signaling platforms that dynamically and efficiently translate extracellular signals into biological outcome. Cell activation, differentiation, migration, death, and survival are some of the endpoints of endosomal signaling. Hence, to understand the role of the endosomal system in signal transduction in space and time, it is therefore necessary to dissect and identify the plethora of decoders that are operational in the different steps along the endocytic pathway. In this chapter, we focus on the regulation of spatiotemporal signaling in cells, considering endosomes as central platforms, in which several small GTPases proteins of the Ras superfamily, in particular Ras and Rac1, actively participate to control cellular processes like proliferation and cell mobility.

MicroRNA-373 Promotes Growth and Cellular Invasion in Osteosarcoma Cells by Activation of the PI3K/AKT-Rac1-JNK Pathway: The Potential Role in Spinal Osteosarcoma

Spinal osteosarcoma (OS) has been proven to be more difficult to treat owing to potently malignant metastasis. The present study aimed to explore the functional role of microRNA (miR)-373 in cell growth and invasion of OS cells, as well as its underlying mechanism. The expression of miR-373 was analyzed in spinal OS tissues and cell lines. MG-63 cells were transfected with the miR-373 mimic or inhibitor and/or treated with the phosphoinositide 3-kinase (PI3K) (LY294002) inhibitor or Ras-related C3 botulinum toxin substrate 1 (Rac) guanosine triphosphate (GTPase) (NSC23766) inhibitor, and then the impact of miR-373 aberrant expression on cell growth and invasion was measured, along with the impact of overexpressing miR-373 on the expression of p53 and PI3K/AKT pathway-related proteins. We found that miR-373 was specifically upregulated in spinal OS tissues (p < 0.01) and OS cell lines (p < 0.01 or p < 0.001). Moreover, miR-373 expression was significantly associated with TNM stage (p = 0.035) and tumor size (p = 0.002). Overexpression of miR-373 promoted MG-63 cell viability, migration, invasion, and colony formation (all p < 0.05), while silencing of miR-373 and LY294002 exerted the opposite effects. Additionally, miR-373 overexpression downregulated p53 as well as its downstream targeted genes and orderly activated the PI3K/AKT-Rac1-JNK signaling pathway. In conclusion, miR-373 promotes growth and cellular invasion in OS cells by activating the PI3K/AKT-Rac1-JNK pathway. Therefore, miR-373 might be a candidate for molecular targeted therapy of spinal OS.

Regulation of circular dorsal ruffles, macropinocytosis, and cell migration by RhoG and its exchange factor, Trio

The small GTPase RhoG and its exchange factor, Trio, regulate the formation and size of circular dorsal ruffles and associated functions, including macropinocytosis and cell migration.

Circular dorsal ruffles (CDRs) are actin-rich structures that form on the dorsal surface of many mammalian cells in response to growth factor stimulation. CDRs represent a unique type of structure that forms transiently and only once upon stimulation. The formation of CDRs involves a drastic rearrangement of the cytoskeleton, which is regulated by the Rho family of GTPases. So far, only Rac1 has been consistently associated with CDR formation, whereas the role of other GTPases in this process is either lacking or inconclusive. Here we show that RhoG and its exchange factor, Trio, play a role in the regulation of CDR dynamics, particularly by modulating their size. RhoG is activated by Trio downstream of PDGF in a PI3K- and Src-dependent manner. Silencing RhoG expression decreases the number of cells that form CDRs, as well as the area of the CDRs. The regulation of CDR area by RhoG is independent of Rac1 function. In addition, our results show the RhoG plays a role in the cellular functions associated with CDR formation, including macropinocytosis, receptor internalization, and cell migration. Taken together, our results reveal a novel role for RhoG in the regulation of CDRs and the cellular processes associated with their formation.

Epidermal Rac1 regulates the DNA damage response and protects from UV-light-induced keratinocyte apoptosis and skin carcinogenesis

Non-melanoma skin cancer (NMSC) is the most common type of cancer. Increased expression and activity of Rac1, a small Rho GTPase, has been shown previously in NMSC and other human cancers; suggesting that Rac1 may function as an oncogene in skin. DMBA/TPA skin carcinogenesis studies in mice have shown that Rac1 is required for chemically induced skin papilloma formation. However, UVB radiation by the sun, which causes DNA damage, is the most relevant cause for NMSC. A potential role of Rac1 in UV-light-induced skin carcinogenesis has not been investigated so far. To investigate this, we irradiated mice with epidermal Rac1 deficiency (Rac1-EKO) and their controls using a well-established protocol for long-term UV-irradiation. Most of the Rac1-EKO mice developed severe skin erosions upon long-term UV-irradiation, unlike their controls. These skin erosions in Rac1-EKO mice healed subsequently. Surprisingly, we observed development of squamous cell carcinomas (SCCs) within the UV-irradiation fields. This shows that the presence of Rac1 in the epidermis protects from UV-light-induced skin carcinogenesis. Short-term UV-irradiation experiments revealed increased UV-light-induced apoptosis of Rac1-deficient epidermal keratinocytes in vitro as well as in vivo. Further investigations using cyclobutane pyrimidine dimer photolyase transgenic mice revealed that the observed increase in UV-light-induced keratinocyte apoptosis in Rac1-EKO mice is DNA damage dependent and correlates with caspase-8 activation. Furthermore, Rac1-deficient keratinocytes showed reduced levels of p53, γ-H2AX and p-Chk1 suggesting an attenuated DNA damage response upon UV-irradiation. Taken together, our data provide direct evidence for a protective role of Rac1 in UV-light-induced skin carcinogenesis and keratinocyte apoptosis probably through regulating mechanisms of the DNA damage response and repair pathways.

Design of novel lead molecules against RhoG protein as cancer target - a computational study

Cancer is a class of diseases characterized by uncontrolled cell growth. Every year more than 2 million people are affected by the disease. Rho family proteins are actively involved in cytoskeleton regulation. Over-expression of Rho family proteins show oncogenic activity and promote cancer progression. In the present work RhoG protein is considered as novel target of cancer. It is a member of Rho family and Rac subfamily protein, which plays pivotal role in regulation of microtubule formation, cell migration and contributes in cancer progression. In order to understand the binding interaction between RhoG protein and the DH domain of Ephexin-4 protein, the 3D structure of RhoG was evaluated and Molecular Dynamic Simulations was performed to stabilize the structure. The 3D structure of RhoG protein was validated and active site identified using standard computational protocols. Protein-protein docking of RhoG with Ephexin-4 was done to understand binding interactions and the active site structure. Virtual screening was carried out with ligand databases against the active site of RhoG protein. The efficiency of virtual screening is analysed with enrichment factor and area under curve values. The binding free energy of docked complexes was calculated using prime MM-GBSA module. The SASA, FOSA, FISA, PISA and PSA values of ligands were carried out. New ligands with high docking score, glide energy and acceptable ADME properties were prioritized as potential inhibitors of RhoG protein.

RHOG-DOCK1-RAC1 Signaling Axis Is Perturbed in DHEA-Induced Polycystic Ovary in Rat Model

The function of RHOG, a RAC1 activator, was explored in the ovary during ovarian follicular development and pathological conditions. With the help of immunoblotting and immunolocalization, we determined the expression and localization of RHOG in normal (estrous cycle) and polycystic ovaries using Sprague Dawley (SD) rat model. Employing polymerase chain reaction and flow cytometry, we analyzed the transcript and expression levels of downstream molecules of RHOG, DOCK1, and RAC1 in the polycystic ovarian syndrome (PCOS) ovary along with normal antral follicular theca and granulosa cells after dehydroepiandrosterone (DHEA) supplementation. The effect of RHOG knockdown on DOCK1, VAV, and RAC1 expression was evaluated in the human ovarian cells (SKOV3), theca cells, and granulosa cells from SD rats with the help of flow cytometry. Oocyte at secondary follicles along with stromal cells showed optimal expression of RHOG. Immunoblotting of RHOG revealed its maximum expression at diestrus and proestrus, which was downregulated at estrus stage. Mild immunostaining of RHOG was also present in the theca and granulosa cells of the secondary and antral follicles. Polycystic ovary exhibited weak immunostaining for RHOG and that was corroborated by immunoblotting-based investigations. RHOG effectors DOCK1 and ELMO1 were found reduced in the ovary in PCOS condition/DHEA. RHOG silencing reduced the expression of DOCK1 and RAC1 in the theca and granulosa cells from SD rat antral follicles and that was mirrored in the human ovarian cells. Collectively, RHOG can mediate signaling through downstream effectors DOCK1 and RAC1 during ovarian follicular development (theca and granulosa cells and oocyte), but DHEA downregulated them in the PCOS ovary.

Tyrosine Phosphorylation of SGEF Regulates RhoG Activity and Cell Migration

SGEF and Ephexin4 are members of the Ephexin subfamily of RhoGEFs that specifically activate the small GTPase RhoG. It is reported that Ephexin1 and Ephexin5, two well-characterized Ephexin subfamily RhoGEFs, are tyrosine-phosphorylated by Src, and that their phosphorylation affect their activities and functions. In this study, we show that SGEF, but not Ephexin4, is tyrosine-phosphorylated by Src. Tyrosine phosphorylation of SGEF suppresses its interaction with RhoG, the elevation of RhoG activity, and SGEF-mediated promotion of cell migration. We identified tyrosine 530 (Y530), which is located within the Dbl homology domain, as a major phosphorylation site of SGEF by Src, and Y530F mutation blocked the inhibitory effect of Src on SGEF. Taken together, these results suggest that the activity of SGEF is negatively regulated by tyrosine phosphorylation of the DH domain.

Computational Identification of Novel Stage-Specific Biomarkers in Colorectal Cancer Progression

It is well-known that the conversion of normal colon epithelium to adenoma and then to carcinoma stems from acquired molecular changes in the genome. The genetic basis of colorectal cancer has been elucidated to a certain extent, and much remains to be known about the identity of specific cancer genes that are associated with the advancement of colorectal cancer from one stage to the next. Here in this study we attempted to identify novel cancer genes that could underlie the stage-specific progression and metastasis of colorectal cancer. We conducted a stage-based meta-analysis of the voluminous tumor genome-sequencing data and mined using multiple approaches for novel genes driving the progression to stage-II, stage-III and stage-IV colorectal cancer. The consensus of these driver genes seeded the construction of stage-specific networks, which were then analyzed for the centrality of genes, clustering of subnetworks, and enrichment of gene-ontology processes. Our study identified three novel driver genes as hubs for stage-II progression: DYNC1H1, GRIN2A, GRM1. Four novel driver genes were identified as hubs for stage-III progression: IGF1R, CPS1, SPTA1, DSP. Three novel driver genes were identified as hubs for stage-IV progression: GSK3B, GGT1, EIF2B5. We also identified several non-driver genes that appeared to underscore the progression of colorectal cancer. Our study yielded potential diagnostic biomarkers for colorectal cancer as well as novel stage-specific drug targets for rational intervention. Our methodology is extendable to the analysis of other types of cancer to fill the gaps in our knowledge.

RAC1 GTPase promotes the survival of breast cancer cells in response to hyper-fractionated radiation treatment

Radiation therapy is a staple approach for cancer treatment, whereas radioresistance of cancer cells remains a substantial clinical problem. In response to ionizing radiation (IR) induced DNA-damage, cancer cells can sustain/activate pro-survival signaling pathways, leading to apoptotic resistance and induction of cell cycle checkpoint/DNA repair. Previous studies show that Rac1 GTPase is overexpressed/hyperactivated in breast cancer cells and is associated with poor prognosis. Studies from our laboratory reveal that Rac1 activity is necessary for G2/M checkpoint activation and cell survival in response to IR exposure of breast and pancreatic cancer cells. In the present study, we investigated the effect of Rac1 on the survival of breast cancer cells treated with hyper-fractionated radiation (HFR), which is used clinically for cancer treatment. Results in this report indicate that Rac1 protein expression is increased in the breast cancer cells that survived HFR compared to parental cells. Furthermore, this increase of Rac1 is associated with enhanced activities of ERK1/2 and NF-κB signaling pathways and increased levels of anti-apoptotic protein Bcl-xL and Mcl-1, which are downstream targets of ERK1/2 and NF-κB signaling pathways. Using Rac1 specific inhibitor and dominant negative mutant N17Rac1, here we demonstrate that Rac1 inhibition decreases the phosphorylation of ERK1/2 and IκBα, as well as the levels of Bcl-xL and Mcl-1 protein in the HFR-selected breast cancer cells. Moreover, inhibition of Rac1 using either small molecule inhibitor or dominant negative N17Rac1 abrogates clonogenic survival of HFR-selected breast cancer cells and decreases the level of intact PARP, which is indicative of apoptosis induction. Collectively, results in this report suggest that Rac1 signaling is essential for the survival of breast cancer cells subjected to HFR and implicate Rac1 in radioresistance of breast cancer cells. These studies also provide the basis to explore Rac1 as a therapeutic target for radioresistant breast cancer cells.

Targeting therapeutic liabilities engendered by PIK3R1 mutations for cancer treatment

The regulatory subunit of PI3K, p85α (encoded by PIK3R1), binds, stabilizes and inhibits the PI3K p110 catalytic subunit. Functional characterization of PIK3R1 mutations has identified not only hypomorphs with reduced inhibition of p110, but also hypomorphs and dominant negative mutants that disrupt a novel regulatory role of p85α on PTEN or neomorphs that activate unexpected signaling pathways. The diverse phenotypic spectrum of these PIK3R1 driver mutations underscores the need for different treatment strategies targeting tumors harboring these mutations. This article describes the functional consequences of the spectrum of PIK3R1 driver mutations and therapeutic liabilities they may engender.

Suppression of phospho-p85α-GTP-Rac1 lipid raft interaction by bichalcone analog attenuates cancer cell invasion

The p85α subunit of phosphatidylinositol 3-kinase (PI3K) acts as a key regulator of cell proliferation and motility, which mediates signals that confer chemoresistance to many human cancer cells. Using small interfering RNAs against matrix metalloproteinase-2 (MMP-2) and the MMP-2 promoter-driven luciferase assay, we showed that the new synthetic bichalcone analog TSWU-CD4 inhibits the invasion of human cancer cells by down-regulating MMP-2 expression. Treatment with TSWU-CD4 inhibited MMP-2 expression and cell invasion, which were restored by ectopic wild type (wt) p85α or a constitutively active form of MAPK kinase 3 (CA MKK3), CA MKK6, or CA p38α mitogen-activated protein kinase (MAPK). The attenuated formation of lipid raft-associated phospho (p)-p85α-GTP-Rac1 complexes, protein kinase B (Akt) Ser 473 phosphorylation, and cell invasion by TSWU-CD4 was reversed by overexpression of wt p85α or the p85α Brc-homology (BH) domain. The ectopic expression of CA Rac1^L61 (but not wt Rac1) could overcome the suppression of Ser 473 phosphorylation, lipid raft association of Akt, the interaction between GTP-bound Rac1 and p85α in lipid rafts, and cell invasion by TSWU-CD4. The involvement of Akt activity in the functions of NF-κB-mediated MMP-2 was further confirmed through the attenuation of Akt phosphorylation signaling using the Akt-specific inhibitor MK-2206 and ectopic expression of NF-κB p65. Collectively, the inhibitory effect of TSWU-CD4 on cancer cell invasion was likely to suppress the p-p85α-GTP-Rac1 interaction in lipid rafts by targeting the p85α BH domain, which resulted in the suppression of MMP-2 expression via the PI3K-Akt-mediated ERK-MKK3/MKK6-p38 MAPK-NF-κB signaling pathway. © 2016 Wiley Periodicals, Inc.

Rac1 augments Wnt signaling by stimulating β-catenin-lymphoid enhancer factor-1 complex assembly independent of β-catenin nuclear import

β-Catenin transduces the Wnt signaling pathway and its nuclear accumulation leads to gene transactivation and cancer. Rac1 GTPase is known to stimulate β-catenin-dependent transcription of Wnt target genes and we confirmed this activity. Here we tested the recent hypothesis that Rac1 augments Wnt signaling by enhancing β-catenin nuclear import; however, we found that silencing/inhibition or up-regulation of Rac1 had no influence on nuclear accumulation of β-catenin. To better define the role of Rac1, we employed proximity ligation assays (PLA) and discovered that a significant pool of Rac1-β-catenin protein complexes redistribute from the plasma membrane to the nucleus upon Wnt or Rac1 activation. More importantly, active Rac1 was shown to stimulate the formation of nuclear β-catenin-lymphoid enhancer factor 1 (LEF-1) complexes. This regulation required Rac1-dependent phosphorylation of β-catenin at specific serines, which when mutated (S191A and S605A) reduced β-catenin binding to LEF-1 by up to 50%, as revealed by PLA and immunoprecipitation experiments. We propose that Rac1-mediated phosphorylation of β-catenin stimulates Wnt-dependent gene transactivation by enhancing β-catenin-LEF-1 complex assembly, providing new insight into the mechanism of cross-talk between Rac1 and canonical Wnt/β-catenin signaling.

MicroRNA-542-3p Suppresses Tumor Cell Invasion via Targeting AKT Pathway in Human Astrocytoma

The molecular mechanism underlying constitutive activation of AKT signaling, which plays essential roles in astrocytoma progression, is not fully characterized. Increasing numbers of studies have reported that microRNAs are involved in the malignant behavior of astrocytoma cells via directly targeting multiple oncogenes or tumor suppressors. Here, we found that microRNA (miR)-542-3p expression was decreased in glioblastoma cell lines and astrocytoma tissues, and reduced levels of miR-542-3p expression correlated with high histopathological grades and poor prognosis of astrocytoma patients. Exogenous miR-542-3p suppressed glioblastoma cell invasion through not only targeting AKT1 itself but also directly down-regulating its two important upstream regulators, namely, integrin-linked kinase and PIK3R1. Notably, overexpressing miR-542-3p decreased AKT1 phosphorylation and directly and indirectly repressed nuclear translocation and transactivation activity of β-catenin to exert its anti-invasive effect. Furthermore, the miR-542-3p expression level negatively correlated with AKT activity as well as levels of integrin-linked kinase and PIK3R1 in human astrocytoma specimens. These findings suggest that miR-542-3p acts as a negative regulator in astrocytoma progression and that miR-542-3p down-regulation contributes to aberrant activation of AKT signaling, leaving open the possibility that miR-542-3p may be a potential therapeutic target for high grade astrocytoma.