Inhibition of redox/Fyn/c-Cbl pathway function by Cdc42 controls tumour initiation capacity and tamoxifen sensitivity in basal-like breast cancer cells

Cellular polarity pilots breast cancer progression and immunosuppression

Disrupted cellular polarity (DCP) is a hallmark of solid cancer, the malignant disease of epithelial tissues, which occupies ~90% of all human cancers. DCP has been identified to affect not only the cancer cell's aggressive behavior but also the migration and infiltration of immune cells, although the precise mechanism of DCP-affected tumor-immune cell interaction remains unclear. This review discusses immunosuppressive tumor microenvironments (TME) caused by DCP-driven tumor cell proliferation with DCP-impaired immune cell functions. We will revisit the fundamental roles of cell polarity (CP) proteins in sustaining mammary luminal homeostasis, epithelial transformation, and breast cancer progression. Then, the current data on CP involvement in immune cell activation, maturation, migration, and tumor infiltration are evaluated. The CP status on the immune effector cells and their targeted tumor cells are highlighted in tumor immune regulation, including the antigen presentation and the formation of immune synapses (IS). CP-regulated antigen presentation and delivery and the formation of IS between the immune cells, especially between the immune effectors and tumor cells, will be addressed. Alterations of CP on the tumor cells, infiltrated immune effector cells, or both are discussed with these aspects. We conclude that CP-mediated tumor aggressiveness coupled with DCP-impaired immune cell disability may decide the degree of immunosuppressive status and responsiveness to immune checkpoint blockade (ICB). Further elucidating the dynamics of CP- or DCP-mediated immune regulation in TME will provide more critical insights into tumor-immune cell dynamics, which is required to invent more effective approaches for cancer immunotherapy.

Mutation in CDC42 Gene Set as a Response Biomarker for Immune Checkpoint Inhibitor Therapy

BACKGROUND

Immune checkpoint inhibitors (ICIs) have achieved great success; however, a subset of patients exhibits no response. Consequently, there is a critical need for reliable predictive biomarkers. Our focus is on CDC42, which stimulates multiple signaling pathways promoting tumor growth. We hypothesize that an impaired function of CDC42 may serve as an indicator of a patient's response to ICI therapy.

METHODS

We consider CDC42 and its downstream binding and effector proteins as a gene set, as mutations in these components could lead to defective CDC42 function. To elucidate the biomarker function of mutations within the CDC42 gene set, we curated a comprehensive discovery dataset that included seven ICI treatment cohorts. And we curated two ICI treatment cohorts for validation. We explored the mechanism based on The Cancer Genome Atlas database. We also examined whether combining a CDC42 inhibitor with ICI could enhance ICI's efficacy.

RESULTS

Mutations in the CDC42 gene set were associated with improved overall survival and progression-free survival. Furthermore, our analysis of immune response landscapes among different statuses of the CDC42 gene set supports its role as a biomarker. Animal experiments also revealed that the combination of the CDC42 inhibitor (ML141) with anti-PD-1 blockade can additively reduce tumor growth.

CONCLUSIONS

Our study suggests that the CDC42 gene set mutations could potentially serve as a novel biomarker for the clinical response to ICI treatment. This finding also provides insights into the potential of combining ICI and CDC42 inhibitor use for more efficient patient treatment.

The role of CBL family ubiquitin ligases in cancer progression and therapeutic strategies

The CBL (Casitas B-lineage lymphoma) family, as a class of ubiquitin ligases, can regulate signal transduction and activate receptor tyrosine kinases through various tyrosine kinase-dependent pathways. There are three members of the family: c-CBL, CBL-b, and CBL-c. Numerous studies have demonstrated the important role of CBL in various cellular pathways, particularly those involved in the occurrence and progression of cancer, hematopoietic development, and regulation of T cell receptors. Therefore, the purpose of this review is to comprehensively summarize the function and regulatory role of CBL family proteins in different human tumors, as well as the progress of drug research targeting CBL family, so as to provide a broader clinical measurement strategy for the treatment of tumors.

Targeting small GTPases: emerging grasps on previously untamable targets, pioneered by KRAS

Small GTPases including Ras, Rho, Rab, Arf, and Ran are omnipresent molecular switches in regulating key cellular functions. Their dysregulation is a therapeutic target for tumors, neurodegeneration, cardiomyopathies, and infection. However, small GTPases have been historically recognized as "undruggable". Targeting KRAS, one of the most frequently mutated oncogenes, has only come into reality in the last decade due to the development of breakthrough strategies such as fragment-based screening, covalent ligands, macromolecule inhibitors, and PROTACs. Two KRAS^G12C covalent inhibitors have obtained accelerated approval for treating KRAS^G12C mutant lung cancer, and allele-specific hotspot mutations on G12D/S/R have been demonstrated as viable targets. New methods of targeting KRAS are quickly evolving, including transcription, immunogenic neoepitopes, and combinatory targeting with immunotherapy. Nevertheless, the vast majority of small GTPases and hotspot mutations remain elusive, and clinical resistance to G12C inhibitors poses new challenges. In this article, we summarize diversified biological functions, shared structural properties, and complex regulatory mechanisms of small GTPases and their relationships with human diseases. Furthermore, we review the status of drug discovery for targeting small GTPases and the most recent strategic progress focused on targeting KRAS. The discovery of new regulatory mechanisms and development of targeting approaches will together promote drug discovery for small GTPases.

The Role of Mitotic Slippage in Creating a "Female Pregnancy-like System" in a Single Polyploid Giant Cancer Cell

In our recent work, we observed that triple-negative breast cancer MDA-MB-231 cells respond to doxorubicin (DOX) via "mitotic slippage" (MS), discarding cytosolic damaged DNA during the process that provides their resistance to this genotoxic treatment. We also noted two populations of polyploid giant cells: those budding surviving offspring, versus those reaching huge ploidy by repeated MS and persisting for several weeks. Their separate roles in the recovery from treatment remained unclear. The current study was devoted to characterising the origin and relationship of these two sub-populations in the context of MS. MS was hallmarked by the emergence of nuclear YAP1/OCT4A/MOS/EMI2-positivity featuring a soma-germ transition to the meiotic-metaphase-arrested "maternal germ cell". In silico, the link between modules identified in the inflammatory innate immune response to cytosolic DNA and the reproductive module of female pregnancy (upregulating placenta developmental genes) was observed in polyploid giant cells. Asymmetry of the two subnuclei types, one repairing DNA and releasing buds enriched by CDC42/ACTIN/TUBULIN and the other persisting and degrading DNA in a polyploid giant cell, was revealed. We propose that when arrested in MS, a "maternal cancer germ cell" may be parthenogenetically stimulated by the placental proto-oncogene parathyroid-hormone-like-hormone, increasing calcium, thus creating a "female pregnancy-like" system within a single polyploid giant cancer cell.

Fyn deficiency inhibits oxidative stress by decreasing c-Cbl-mediated ubiquitination of Sirt1 to attenuate diabetic renal fibrosis

OBJECTIVE

Oxidative stress (OS) is the main cause leading to diabetic renal fibrosis. Recently, Fyn was paid much attention on OS and emerged as a pivotal player in acute kidney injury, while whether Fyn regulates oxidative stress in chronic diabetes nephropathy (DN) has not been clarified yet. The purpose of this study was to identify the role of Fyn in DN and elucidated its regulatory mechanism.

METHODS

The db/db mice and littermate control C57BKS/J mice were injected by tail vein with Fyn interfering adenovirus or Fyn overexpressing adenovirus to investigate the role of Fyn in vivo. Primary glomerular mesangial cells (GMCs) were used for in vitro studies.

RESULTS

Fyn was up-regulated in high glucose (HG)-induced GMCs and kidneys of diabetic mice. Additionally, Fyn knockdown reduced the level of OS in HG-induced GMCs and kidneys of diabetic mice, thereby ameliorating diabetic renal fibrosis. While overexpression of Fyn significantly increased the level of OS in GMCs and kidney tissues, resulting in renal damage. Moreover, Fyn deficiency exerted antioxidant effects by activating the Sirt1/Foxo3a pathway. Mechanistically, Fyn facilitated the combination of c-Cbl and Sirt1 by phosphorylating c-Cbl at Tyr⁷³¹, which triggered K48-linked polyubiquitination of Sirt1 at Lys³⁷⁷ and Lys⁵¹³ by c-Cbl and promoted Sirt1 degradation, impairing the antioxidant effects of Foxo3a.

CONCLUSIONS

Fyn deficiency promoted Foxo3a nuclear transcription via reducing the ubiquitination of Sirt1 by c-Cbl, thereby alleviating renal oxidative damage in diabetic mice. These results identified Fyn as a potential therapeutic target against DN.

Excessive ultraviolet C irradiation causes spore protein denaturation and prohibits the initiation of spore germination in Bacillus subtilis

Ultraviolet (UV) -C is widely used to kill bacteria as it damages chromosomal DNA. We analyzed the denaturation of the protein function of Bacillus subtilis spores after UV-C irradiation. Almost all of the B. subtilis spores germinated in Luria-Bertani (LB) liquid medium, but the colony-forming unit (CFU) of the spores on LB agar plates decreased to approximately 1/10³ by 100 mJ/cm² of UV-C irradiation. Some of the spores germinated in LB liquid medium under phase-contrast microscopy, but almost no colonies formed on the LB agar plates after 1 J/cm² of UV-C irradiation. The fluorescence of the green fluorescent protein (GFP) -fused spore proteins, YeeK-GFP, YeeK is a coat protein, decreased following UV-C irradiation of over 1 J/cm², while that of SspA-GFP, SspA is a core protein, decreased following UV-C irradiation of over 2 J/ cm², respectively. These results revealed that UV-C affected on coat proteins more than core proteins. We conclude that 25 to 100 mJ/cm² of UV-C irradiation can cause DNA damage, and more than 1 J/cm² of UV-C irradiation can cause the denaturation of spore proteins involved in germination. Our study would contribute to improve the technology to detect the bacterial spores, especially after UV sterilization.

Small molecule RAF265 as an antiviral therapy acts against HSV-1 by regulating cytoskeleton rearrangement and cellular translation machinery

Host-targeting antivirals (HTAs) have received increasing attention for their potential as broad-spectrum antivirals that pose relatively low risk of developing drug resistance. The repurposing of pharmaceutical drugs for use as antivirals is emerging as a cost- and time- efficient approach to developing HTAs for the treatment of a variety of viral infections. In this study, we used a virus titer method to screen 30 small molecules for antiviral activity against Herpes simplex virus-1 (HSV-1). We found that the small molecule RAF265, an anticancer drug that has been shown to be a potent inhibitor of B-RAF V600E, reduced viral loads of HSV-1 by 4 orders of magnitude in Vero cells and reduced virus proliferation in vivo. RAF265 mediated cytoskeleton rearrangement and targeted the host cell's translation machinery, which suggests that the antiviral activity of RAF265 may be attributed to a dual inhibition strategy. This study offers a starting point for further advances toward clinical development of antivirals against HSV-1.

Small-Molecule RAF265 as an Antiviral Therapy Acts against PEDV Infection

Porcine epidemic diarrhea virus (PEDV), a member of the family Coronaviridae, causes acute diarrhea, vomiting, dehydration, and high mortality in newborn piglets, and has caused significant economic losses in the pig industry. There are currently no specific drugs available to treat PEDV. Viruses depend exclusively on the cellular machinery to ensure an efficient replication cycle. In the present study, we found that small-molecule RAF265, an anticancer drug that has been shown to be a potent inhibitor of RAF, reduced viral loads of PEDV by 4 orders of magnitude in Vero cells, and protected piglets from virus challenge. RAF265 reduced PEDV production by mediating cytoskeleton arrangement and targeting the host cell’s translation machinery. Treatment with RAF265 inhibited viral entry of PEDV S-glycoprotein pseudotyped viral vector particle (PEDV-pp), at half maximal effective concentrations (EC₅₀) of 79.1 nM. RAF265 also presented potent inhibitory activity against viral infection by SARS-CoV-2-pp and SARS-CoV-pp. The present work may provide a starting point for further progress toward the development of antiviral strategies effective against coronavirus PEDV.

The role of E3 ubiquitin ligases in the development and progression of glioblastoma

Despite recent advances in our understanding of the disease, glioblastoma (GB) continues to have limited treatment options and carries a dismal prognosis for patients. Efforts to stratify this heterogeneous malignancy using molecular classifiers identified frequent alterations in targetable proteins belonging to several pathways including the receptor tyrosine kinase (RTK) and mitogen-activated protein kinase (MAPK) signalling pathways. However, these findings have failed to improve clinical outcomes for patients. In almost all cases, GB becomes refractory to standard-of-care therapy, and recent evidence suggests that disease recurrence may be associated with a subpopulation of cells known as glioma stem cells (GSCs). Therefore, there remains a significant unmet need for novel therapeutic strategies. E3 ubiquitin ligases are a family of >700 proteins that conjugate ubiquitin to target proteins, resulting in an array of cellular responses, including DNA repair, pro-survival signalling and protein degradation. Ubiquitin modifications on target proteins are diverse, ranging from mono-ubiquitination through to the formation of polyubiquitin chains and mixed chains. The specificity in substrate tagging and chain elongation is dictated by E3 ubiquitin ligases, which have essential regulatory roles in multiple aspects of brain cancer pathogenesis. In this review, we begin by briefly summarising the histological and molecular classification of GB. We comprehensively describe the roles of E3 ubiquitin ligases in RTK and MAPK, as well as other, commonly altered, oncogenic and tumour suppressive signalling pathways in GB. We also describe the role of E3 ligases in maintaining glioma stem cell populations and their function in promoting resistance to ionizing radiation (IR) and chemotherapy. Finally, we consider how our knowledge of E3 ligase biology may be used for future therapeutic interventions in GB, including the use of blood-brain barrier permeable proteolysis targeting chimeras (PROTACs).

An Overview of Potential Therapeutic Agents Targeting WNT/PCP Signaling

Since the discovery of the proto-oncogene Wnt1 (Int1) in 1982, WNT signaling has been identified as one of the most important pathways that regulates a wide range of fundamental developmental and physiological processes in multicellular organisms. The canonical WNT signaling pathway depends on the stabilization and translocation of β-catenin and plays important roles in development and homeostasis. The WNT/planar cell polarity (WNT/PCP) signaling, also known as one of the β-catenin-independent WNT pathways, conveys directional information to coordinate polarized cell behaviors. Similar to WNT/β-catenin signaling, disruption or aberrant activation of WNT/PCP signaling also underlies a variety of developmental defects and cancers. However, the pharmacological targeting of WNT/PCP signaling for therapeutic purposes remains largely unexplored. In this review, we briefly discuss WNT/PCP signaling in development and disease and summarize the known drugs/inhibitors targeting this pathway.

HACE1 blocks HIF1α accumulation under hypoxia in a RAC1 dependent manner

Uncovering the mechanisms that underpin how tumor cells adapt to microenvironmental stress is essential to better understand cancer progression. The HACE1 (HECT domain and ankyrin repeat-containing E3 ubiquitin-protein ligase) gene is a tumor suppressor that inhibits the growth, invasive capacity, and metastasis of cancer cells. However, the direct regulatory pathways whereby HACE1 confers this tumor-suppressive effect remain to be fully elucidated. In this report, we establish a link between HACE1 and the major stress factor, hypoxia-inducible factor 1 alpha (HIF1α). We find that HACE1 blocks the accumulation of HIF1α during cellular hypoxia through decreased protein stability. This property is dependent on HACE1 E3 ligase activity and loss of Ras-related C3 botulinum toxin substrate 1 (RAC1), an established target of HACE1 mediated ubiquitinylation and degradation. In vivo, genetic deletion of Rac1 reversed the increased HIF1α expression observed in Hace1^-/- mice in murine KRas^G12D-driven lung tumors. An inverse relationship was observed between HACE1 and HIF1α levels in tumors compared to patient-matched normal kidney tissues, highlighting the potential pathophysiological significance of our findings. Together, our data uncover a previously unrecognized function for the HACE1 tumor suppressor in blocking HIF1α accumulation under hypoxia in a RAC1-dependent manner.

Rho GTPases: Promising candidates for overcoming chemotherapeutic resistance

Despite therapeutic advances, resistance to chemotherapy remains a major challenge to patients with malignancies. Rho GTPases are essential for the development and progression of various diseases including cancer, and a vast number of studies have linked Rho GTPases to chemoresistance. Therefore, understanding the underlying mechanisms can expound the effects of Rho GTPases towards chemotherapeutic agents, and targeting Rho GTPases is a promising strategy to downregulate the chemo-protective pathways and overcome chemoresistance. Importantly, exceptions in certain biological conditions and interactions among the members of Rho GTPases should be noted. In this review, we focus on the role of Rho GTPases, particularly Rac1, in regulating chemoresistance and provide an overview of their related mechanisms and available inhibitors, which may offer novel options for future targeted cancer therapy.

Comprehensive Proteomic Characterization Reveals Subclass-Specific Molecular Aberrations within Triple-negative Breast Cancer

Triple-negative breast cancer (TNBC) is the most aggressive subtype of breast cancer lacking targeted therapies. This is attributed to its high heterogeneity that complicates elucidation of its molecular aberrations. Here, we report identification of specific proteome expression profiles pertaining to two TNBC subclasses, basal A and basal B, through in-depth proteomics analysis of breast cancer cells. We observed that kinases and proteases displayed unique expression patterns within the subclasses. Systematic analyses of protein-protein interaction and co-regulation networks of these kinases and proteases unraveled dysregulated pathways and plausible targets for each TNBC subclass. Among these, we identified kinases AXL, PEAK1, and TGFBR2 and proteases FAP, UCHL1, and MMP2/14 as specific targets for basal B subclass, which represents the more aggressive TNBC cell lines. Our study highlights intricate mechanisms and distinct targets within TNBC and emphasizes that these have to be exploited in a subclass-specific manner rather than a one-for-all TNBC therapy.

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Proteome profiling reveals functionally distinct subclasses within TNBC

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Kinases and proteases underlie unique functional signatures among the subclasses

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Kinase-protease-centric networks highlight subclass-specific molecular rewiring

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Protein association dysregulations reveal TNBC subclass-specific protein targets

An LTR Retrotransposon-Derived Long Noncoding RNA lncMER52A Promotes Hepatocellular Carcinoma Progression by Binding p120-Catenin

Long terminal repeat (LTR) retrotransposons are a major class of transposable elements, accounting for 8.67% of the human genome. LTRs can serve as regulatory sequences and drive transcription of tissue or cancer-specific transcripts. However, the role of these LTR-activated transcripts, especially long non-coding RNAs (lncRNA), in cancer development remains largely unexplored. Here, we identified a novel lncRNA derived from MER52A retrotransposons (lncMER52A) that was exclusively expressed in hepatocellular carcinoma (HCC). HCC patients with higher lncMER52A had advanced TNM stage, less differentiated tumors, and shorter overall survival. LncMER52A promoted invasion and metastasis of HCC cells in vitro and in vivo. Mechanistically, lncMER52A stabilized p120-catenin and triggered the activation of Rho GTPase downstream of p120-catenin. Furthermore, we found that chromatin accessibility was crucial for the expression of lncMER52A. In addition, YY1 transcription factor bound to the cryptic MER52A LTR promoter and drove lncMER52A transcription in HCC. In conclusion, we identified an LTR-activated lncMER52A, which promoted the progression of HCC cells via stabilizing p120-catenin and activating p120-ctn/Rac1/Cdc42 axis. LncMER52A could serve as biomarker and therapeutic target for patients with HCC. SIGNIFICANCE: A novel long noncoding RNA lncMER52 modulates cell migration and invasion via posttranslational control of p120-catenin protein stability. GRAPHICAL ABSTRACT: http://cancerres.aacrjournals.org/content/canres/80/5/976/F1.large.jpg.

CDC42 promotes vascular calcification in chronic kidney disease

Vascular calcification is prevalent in patients with chronic kidney disease (CKD) and a major risk factor of cardiovascular disease. Vascular calcification is now recognised as a biological process similar to bone formation involving osteogenic differentiation of vascular smooth muscle cells (VSMCs). Cell division cycle 42 (CDC42), a Rac1 family member GTPase, is essential for cartilage development during endochondral bone formation. However, whether CDC42 affects osteogenic differentiation of VSMCs and vascular calcification remains unknown. In the present study, we observed a significant increase in the expression of CDC42 both in rat VSMCs and in calcified arteries during vascular calcification. Alizarin red staining and calcium content assay revealed that adenovirus-mediated CDC42 overexpression led to an apparent VSMC calcification in the presence of calcifying medium, accompanied with up-regulation of bone-related molecules including RUNX2 and BMP2. By contrast, inhibition of CDC42 by ML141 significantly blocked calcification of VSMCs in vitro and aortic rings ex vivo. Moreover, ML141 markedly attenuated vascular calcification in rats with CKD. Furthermore, pharmacological inhibition of AKT signal was shown to block CDC42-induced VSMC calcification. These findings demonstrate for the first time that CDC42 contributes to vascular calcification through a mechanism involving AKT signalling; this uncovered a new function of CDC42 in regulating vascular calcification. This may provide a potential therapeutic target for the treatment of vascular calcification in the context of CKD. © 2019 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Control of antiviral innate immune response by protein geranylgeranylation

The mitochondrial antiviral signaling protein (MAVS) orchestrates host antiviral innate immune response to RNA virus infection. However, how MAVS signaling is controlled to eradicate virus while preventing self-destructive inflammation remains obscure. Here, we show that protein geranylgeranylation, a posttranslational lipid modification of proteins, limits MAVS-mediated immune signaling by targeting Rho family small guanosine triphosphatase Rac1 into the mitochondria-associated endoplasmic reticulum (ER) membranes (MAMs) at the mitochondria-ER junction. Protein geranylgeranylation and subsequent palmitoylation promote Rac1 translocation into MAMs upon viral infection. MAM-localized Rac1 limits MAVS' interaction with E3 ligase Trim31 and hence inhibits MAVS ubiquitination, aggregation, and activation. Rac1 also facilitates the recruitment of caspase-8 and cFLIPL to the MAVS signalosome and the subsequent cleavage of Ripk1 that terminates MAVS signaling. Consistently, mice with myeloid deficiency of protein geranylgeranylation showed improved survival upon influenza A virus infection. Our work revealed a critical role of protein geranylgeranylation in regulating antiviral innate immune response.

Cdc42 Promotes ADSC-Derived IPC Induction, Proliferation, And Insulin Secretion Via Wnt/β-Catenin Signaling

PURPOSE

Type 1 diabetes mellitus (T1DM) is characterized by irreversible islet β cell destruction. Accumulative evidence indicated that Cdc42 and Wnt/β-catenin signaling both play a critical role in the pathogenesis and development of T1DM. Further, bio-molecular mechanisms in adipose-derived mesenchymal stem cells (ADSCs)-derived insulin-producing cells (IPCs) remain largely unknown. Our aim was to investigate the underlying mechanism of Cdc42/Wnt/β-catenin pathway in ADSC-derived IPCs, which may provide new insights into the therapeutic strategy for T1DM patients.

METHODS

ADSC induction was accomplished with DMSO under high-glucose condition. ML141 (Cdc42 inhibitor) and Wnt-3a (Wnt signaling activator) were administered to ADSCs from day 2 until the induction finished. Morphological changes were determined by an inverted microscope. Dithizone staining was employed to evaluate the induction of ADSC-derived IPCs. qPCR and Western blotting were employed to measure the mRNA and protein expression level of islet cell development-related genes and Wnt signaling-related genes. The proliferation ability of ADSC-derived IPCs was also detected with a cell counting kit (CCK) assay. The expression and secretion of Insulin were detected with immunofluorescence test and enzyme-linked immunosorbent assay (ELISA) respectively.

RESULTS

During induction, morphological characters of ADSCs changed into spindle and round shape, and formed islet-line cell clusters, with brown dithizone-stained cytoplasm. Expression levels of islet cell development-related genes were up-regulated in ADSC-derived IPCs. Wnt-3a promoted Wnt signaling markers and islet cell development-related gene expression at mRNA and protein levels, while ML141 played a negative effect. Wnt-3a promoted ADSC-derived IPC proliferation and glucose-stimulated insulin secretion (GSIS), while ML141 played a negative effect.

CONCLUSION

Our research demonstrated that DMSO and high-glucose condition can induce ADSCs into IPCs, and Wnt signaling promotes the induction. Cdc42 may promote IPC induction, IPC proliferation and insulin secretion via Wnt/β-catenin pathway, meaning that Cdc42 may be regarded as a potential target in the treatment of T1DM.

Roles of Small GTPases in Acquired Tamoxifen Resistance in MCF-7 Cells Revealed by Targeted, Quantitative Proteomic Analysis

Development of tamoxifen resistance remains a tremendous challenge for the treatment of estrogen-receptor (ER)-positive breast cancer. Small GTPases of the Ras superfamily play crucial roles in intracellular trafficking and cell signaling, and aberrant small-GTPase signaling is implicated in many types of cancer. In this study, we employed a targeted, quantitative proteomic approach that relies on stable-isotope labeling by amino acids in cell culture (SILAC), gel fractionation, and scheduled multiple-reaction-monitoring (MRM) analysis, to assess the differential expression of small GTPases in MCF-7 and the paired tamoxifen-resistant breast cancer cells. The method displayed superior sensitivity and reproducibility over the shotgun-proteomic approach, and it facilitated the quantification of 96 small GTPases. Among them, 13 and 10 proteins were significantly down- and up-regulated (with >1.5-fold change), respectively, in the tamoxifen-resistant line relative to in the parental line. In particular, we observed a significant down-regulation of RAB31 in tamoxifen-resistant cells, which, in combination with bioinformatic analysis and downstream validation experiments, supported a role for RAB31 in tamoxifen resistance in ER-positive breast-cancer cells. Together, our results demonstrated that the targeted proteomic method constituted a powerful approach for revealing the role of small GTPases in therapeutic resistance.

Tamoxifen inhibits the proliferation of non‑melanoma skin cancer cells by increasing intracellular calcium concentration

Tamoxifen is an estrogen receptor (ER) antagonist used as first-line chemotherapy in breast cancer. Recent studies suggest that tamoxifen may be effective not only for ER‑positive but also for ER‑negative cancer cases. The aim of the present study was to investigate the antiproliferative effect of tamoxifen against human non‑melanoma skin cancer cells. Tamoxifen inhibited the proliferation of the skin squamous cell carcinoma (SCC) cell lines A431, DJM‑1 and HSC‑1. A431 cells did not express ER‑α or -β, suggesting that tamoxifen may exert antiproliferative effects on skin SCC cells via a non‑ER‑mediated pathway. Tamoxifen increased the intracellular calcium concentration of skin SCC cells, and this increase in intracellular calcium concentration by calcium ionophore A23187 suppressed the proliferation of skin SCC cells. These data indicate that tamoxifen inhibited the proliferation of human skin SCC cells via increasing intracellular calcium concentration. Voltage-gated calcium channels and non‑selective cation channels are involved in the increase in intracellular calcium concentration induced by tamoxifen. The broad-spectrum protein kinase C (PKC) inhibitor phloretin significantly attenuated the antiproliferative effect of tamoxifen on skin SCC cells. From these data, it may be concluded that tamoxifen inhibits the proliferation of skin SCC cells by induction of extracellular calcium influx via calcium channels in the plasma membrane and by subsequent activation of PKC.

Inhibition of the RhoGTPase Cdc42 by ML141 enhances hepatocyte differentiation from human adipose-derived mesenchymal stem cells via the Wnt5a/PI3K/miR-122 pathway: impact of the age of the donor

Background

Human adipose-derived mesenchymal stem cells (hADSCs) are promising cells that may promote hepatocyte differentiation (Hep-Dif) and improve liver function, but the involvement of Cdc42, a key small RhoGTPase which plays a crucial role in aging, is still not well established. We hypothesized that the inhibition of Cdc42 may rescue the hepatogenic potential of hADSCs derived from aged donors.

Methods

hADSCs isolated from 61 women of different ages were cultured for evaluation of the proliferation of cells, adherence, apoptosis, immunomodulation, immunophenotyping, multipotency, gene expression, and cell function during Hep-Dif. Inhibition of Cdc42 by ML141 was realized during two phases: initiation (days –2 to 14 (D–2/14)) from undifferentiated to hepatoblast-like cells, or maturation (days 14 to 28 (D14/28)) from undifferentiated to hepatocyte-like cells. Mechanistic insights of the Wnt(s)/MAPK/PI3K/miR-122 pathways were studied.

Results

Cdc42 activity in undifferentiated hADSCs showed an age-dependent significant increase in Cdc42-GTP correlated to a decrease in Cdc42GAP; the low potentials of cell proliferation, doubling, adherence, and immunomodulatory ability (proinflammatory over anti-inflammatory) contrary to the apoptotic index of the aged group were significantly reversed by ML141. Aged donor cells showed a decreased potential for Hep-Dif which was rescued by ML141 treatment, giving rise to mature and functional hepatocyte-like cells as assessed by hepatic gene expression, cytochrome activity, urea and albumin production, low-density lipoprotein (LDL) uptake, and glycogen storage. ML141-induced Hep-Dif showed an improvement in mesenchymal-epithelial transition, a switch from Wtn-3a/β-catenin to Wnt5a signaling, involvement of PI3K/PKB but not the MAPK (ERK/JNK/p38) pathway, induction of miR-122 expression, reinforcing the exosomes release and the production of albumin, and epigenetic changes. Inhibition of PI3K and miR-122 abolished completely the effects of ML141 indicating that inhibition of Cdc42 promotes the Hep-Dif through a Wnt5a/PI3K/miR-122/HNF4α/albumin/E-cadherin-positive action. The ML141(D–2/14) protocol had more pronounced effects when compared with ML141(D14/28); inhibition of DNA methylation in combination with ML141(D–2/14) showed more efficacy in rescuing the Hep-Dif of aged hADSCs. In addition to Hep-Dif, the multipotency of aged hADSC-treated ML141 was observed by rescuing the adipocyte and neural differentiation by inducing PPARγ/FABP4 and NeuN/O4 but inhibiting Pref-1 and GFAP, respectively.

Conclusion

ML141 has the potential to reverse the age-related aberrations in aged stem cells and promotes their hepatogenic differentiation. Selective inhibition of Cdc42 could be a potential target of drug therapy for aging and may give new insights on the improvement of Hep-Dif.

Electronic supplementary material

The online version of this article (10.1186/s13287-018-0910-5) contains supplementary material, which is available to authorized users.

Targeting Rac and Cdc42 GTPases in Cancer

Rac and Cdc42 are small GTPases that have been linked to multiple human cancers and are implicated in epithelial to mesenchymal transition, cell-cycle progression, migration/invasion, tumor growth, angiogenesis, and oncogenic transformation. With the exception of the P29S driver mutation in melanoma, Rac and Cdc42 are not generally mutated in cancer, but are overexpressed (gene amplification and mRNA upregulation) or hyperactivated. Rac and Cdc42 are hyperactivated via signaling through oncogenic cell surface receptors, such as growth factor receptors, which converge on the guanine nucleotide exchange factors that regulate their GDP/GTP exchange. Hence, targeting Rac and Cdc42 represents a promising strategy for precise cancer therapy, as well as for inhibition of bypass signaling that promotes resistance to cell surface receptor-targeted therapies. Therefore, an understanding of the regulatory mechanisms of these pivotal signaling intermediates is key for the development of effective inhibitors. In this review, we focus on the role of Rac and Cdc42 in cancer and summarize the regulatory mechanisms, inhibitory efficacy, and the anticancer potential of Rac- and Cdc42-targeting agents. Cancer Res; 78(12); 3101-11. ©2018 AACR.

A role for activated Cdc42 in glioblastoma multiforme invasion

Cdc42 is a Rho-GTPase which plays a major role in regulating cell polarity and migration by specifying the localization of filopodia. However, the role of Cdc42 in GBM invasion has not been thoroughly investigated. We generated stable doxycycline-inducible clones expressing wild type (WT)-, constitutively active (CA)-, and dominant negative (DN)-Cdc42 in three different human glioma cell lines. Expression of CA-Cdc42 significantly increased the migration and invasive properties of malignant glioma cells compared to WT and DN-Cdc42 cell clones, and this was accompanied by a greater number of filopodia and focal adhesion structures which co-localize with phosphorylated focal adhesion kinase (FAK). By mass spectrometry and immunoprecipitation studies, we demonstrated that activated Cdc42 binds to IQGAP1. When implanted orthotopically in mice, the CA-Cdc42 expressing glioma cells exhibited enhanced local migration and invasion, and led to larger tumors, which significantly reduced survival. Using the Cancer Genome Atlas dataset, we determined that high Cdc42 expression is associated with poorer progression free survival, and that Cdc42 expression is highest in the proneural and neural subgroups of GBM. In summary, our studies demonstrate that activated Cdc42 is a critical determinant of the migratory and invasive phenotype of malignant gliomas, and that its effect may be mediated, at least in part, through its interaction with IQGAP1 and phosphorylated FAK.

The R-Enantiomer of Ketorolac Delays Mammary Tumor Development in Mouse Mammary Tumor Virus-Polyoma Middle T Antigen (MMTV-PyMT) Mice

Epidemiologic studies report improved breast cancer survival in women who receive ketorolac (Toradol) for postoperative pain relief compared with other analgesic agents. Ketorolac is a racemic drug. The S-enantiomer inhibits cyclooxygenases; R-ketorolac is a selective inhibitor of the small GTPases Ras-related C3 botulinum toxin substrate 1 (Rac1) and cell division control protein 42 (Cdc42), which are signaling molecules up-regulated during breast cancer progression and metastasis. The goal of this study was to determine whether R-ketorolac altered breast cancer development in the mouse mammary tumor virus-polyoma middle T-antigen model. Mice were administered ketorolac orally at 1 mg/kg twice daily to approximate the typical human dose. Mammary glands were analyzed for tumor number and immunohistochemical markers of proliferation and differentiation. R-ketorolac treatment significantly reduced mammary epithelial proliferation, based on Ki67 staining, and suppressed tumor development. Proliferative mammary epithelium from R-ketorolac-treated mice displayed greater differentiation, based on significantly higher total E-cadherin and decreased keratin 5 staining than epithelium of placebo-treated mice. No differences were detected in estrogen receptor, progesterone receptor, β-catenin, or vimentin expression between placebo and R-ketorolac treatment groups. These findings indicate that R-ketorolac treatment slows tumor progression in an aggressive model of breast cancer. R-ketorolac may thus represent a novel therapeutic approach for breast cancer prevention or treatment based on its pharmacologic activity as a Rac1 and Cdc42 inhibitor.

Comparative Proteomics Analysis Identifies Cdc42-Cdc42BPA Signaling as Prognostic Biomarker and Therapeutic Target for Colon Cancer Invasion

Metastasis is one of the major causes of treatment failure in the patients with colon cancer. The aim of our study is to find key proteins and pathways that drive invasion and metastasis in colon cancer. Eight rounds of selection of cancer cells invading through matrigel-coated chamber were performed to obtain highly invasive colon cancer sublines HCT116-I8 and RKO-I8. Stable Isotope Labeling by Amino Acids in Cell Culture technology was used to identify the differently expressed proteins, and the proteomics data were analyzed by ingenuity pathway analysis. PAK1-PBD immunoprecipitation combined with Western blot were carried out to determine Cdc42 activity, and qRT-PCR and Western blot were used to determine gene expression. The functional role of Cdc42BPA and Cdc42 pathway in colon cancer invasion was studied by loss-of-function experiments including pharmacological blockade, siRNA knockdown, chamber invasion, and WST-1 assays. Human colon cancer tissue microarray was analyzed by immunohistochemistry for overexpression of Cdc42BPA and its correlation with clinicopathological parameters and patient survival outcomes. HCT116-I8 and RKO-I8 cells showed significantly stronger invasive potential as well as decreased E-cadherin and increased vimentin expressions compared with parental cells. The differently expressed proteins in I8 cells compared with parental cells were identified. Bioinformatics analysis of proteomics data suggested that Cdc42BPA protein and Cdc42 signaling pathway are important for colon cancer invasion, which was confirmed by experimental data showing upregulation of Cdc42BPA and higher expression of active GTP-bound form of Cdc42 in HCT116-I8 and RKO-I8 cells. Functionally, pharmacological and genetic blockade of Cdc42BPA and Cdc42 signaling markedly suppressed colon cancer cell invasion and reversed epithelial mesenchymal transition process. Furthermore, compared with adjacent normal tissues, Cdc42BPA expression was significantly higher in colon cancer tissues and further upregulated in metastatic tumors in lymph nodes. More importantly, Cdc42BPA expression was correlated with metastasis and poor survival of the patients with colon cancer. This study provides the first evidence that Cdc42BPA and Cdc42 signaling are important for colon cancer invasion, and Cdc42BPA has potential implications for colon cancer prognosis and treatment.

High glucose levels promote the proliferation of breast cancer cells through GTPases

Hyperglycemia or diabetes mellitus (DM), which is characterized by high blood glucose levels, has been linked to an increased risk of cancer for years. However, the underlying molecular mechanisms of the pathophysiological link are not yet fully understood. In this study, we demonstrate that high glucose levels promote the proliferation of breast cancer cells by stimulating epidermal growth factor receptor (EGFR) activation and the Rho family GTPase Rac1 and Cdc42 mediate the corresponding signaling induced by high glucose levels. We further show that Cdc42 promotes EGFR phosphorylation by blocking EGFR degradation, which may be mediated by the Cbl proteins, whereas the Rac1-mediated EGFR phosphorylation is independent of EGFR degradation. Our findings elucidate a part of the underlying molecular mechanism of the link between high glucose levels and tumorigenesis in breast cancer and may provide new insights on the therapeutic strategy for cancer patients with diabetes or hyperglycemia.

Leptin signaling and cancer chemoresistance: Perspectives

Obesity is a major health problem and currently is endemic around the world. Obesity is a risk factor for several different types of cancer, significantly promoting cancer incidence, progression, poor prognosis and resistance to anti-cancer therapies. The study of this resistance is critical as development of chemoresistance is a serious drawback for the successful and effective drug-based treatments of cancer. There is increasing evidence that augmented adiposity can impact on chemotherapeutic treatment of cancer and the development of resistance to these treatments, particularly through one of its signature mediators, the adipokine leptin. Leptin is a pro-inflammatory, pro-angiogenic and pro-tumorigenic adipokine that has been implicated in many cancers promoting processes such as angiogenesis, metastasis, tumorigenesis and survival/resistance to apoptosis. Several possible mechanisms that could potentially be developed by cancer cells to elicit drug resistance have been suggested in the literature. Here, we summarize and discuss the current state of the literature on the role of obesity and leptin on chemoresistance, particularly as it relates to breast and pancreatic cancers. We focus on the role of leptin and its significance in possibly driving these proposed chemoresistance mechanisms, and examine its effects on cancer cell survival signals and expansion of the cancer stem cell sub-populations.

Interaction of the Small GTPase Cdc42 with Arginine Kinase Restricts White Spot Syndrome Virus in Shrimp

Many types of small GTPases are widely expressed in eukaryotes and have different functions. As a crucial member of the Rho GTPase family, Cdc42 serves a number of functions, such as regulating cell growth, migration, and cell movement. Several RNA viruses employ Cdc42-hijacking tactics in their target cell entry processes. However, the function of Cdc42 in shrimp antiviral immunity is not clear. In this study, we identified a Cdc42 protein in the kuruma shrimp (Marsupenaeus japonicus) and named it MjCdc42. MjCdc42 was upregulated in shrimp challenged by white spot syndrome virus (WSSV). The knockdown of MjCdc42 and injection of Cdc42 inhibitors increased the proliferation of WSSV. Further experiments determined that MjCdc42 interacted with an arginine kinase (MjAK). By analyzing the binding activity and enzyme activity of MjAK and its mutant, ΔMjAK, we found that MjAK could enhance the replication of WSSV in shrimp. MjAK interacted with the envelope protein VP26 of WSSV. An inhibitor of AK activity, quercetin, could impair the function of MjAK in WSSV replication. Further study demonstrated that the binding of MjCdc42 and MjAK depends on Cys²⁷¹ of MjAK and suppresses the WSSV replication-promoting effect of MjAK. By interacting with the active site of MjAK and suppressing its enzyme activity, MjCdc42 inhibits WSSV replication in shrimp. Our results demonstrate a new function of Cdc42 in the cellular defense against viral infection in addition to the regulation of actin and phagocytosis, which has been reported in previous studies. IMPORTANCE The interaction of Cdc42 with arginine kinase plays a crucial role in the host defense against WSSV infection. This study identifies a new mechanism of Cdc42 in innate immunity and enriches the knowledge of the antiviral innate immunity of invertebrates.

Quantitative proteomic analyses of mammary organoids reveals distinct signatures after exposure to environmental chemicals

Common environmental contaminants such as bisphenols and phthalates and persistent contaminants such as polychlorinated biphenyls are thought to influence tissue homeostasis and carcinogenesis by acting as disrupters of endocrine function. In this study we investigated the direct effects of exposure to bisphenol A (BPA), mono-n-butyl phthalate (Pht), and polychlorinated biphenyl 153 (PCB153) on the proteome of primary organotypic cultures of the mouse mammary gland. At low-nanomolar doses each of these agents induced distinct effects on the proteomes of these cultures. Although BPA treatment produced effects that were similar to those induced by estradiol, there were some notable differences, including a reduction in the abundance of retinoblastoma-associated protein and increases in the Rho GTPases Ras-related C3 botulinum toxin substrate 1 (Rac1) and cell division cycle protein CDC42. Both Pht and PCB153 induced changes that were distinct from those induced by estrogen, including decreased levels of the transcriptional corepressor C-terminal binding protein 1. Interestingly, the three chemicals appeared to alter the abundance of distinct splice forms of many proteins as well as the abundance of several proteins that regulate RNA splicing. Our combined results indicate that the three classes of chemical have distinct effects on the proteome of normal mouse mammary cultures, some estrogen-like but most estrogen independent, that influence diverse biological processes including apoptosis, cell adhesion, and proliferation.

CDC42 Use in Viral Cell Entry Processes by RNA Viruses

The cellular actin cytoskeleton presents a barrier that must be overcome by many viruses, and it has become increasingly apparent many viral species have developed a diverse repertoire of mechanisms to hijack cellular actin-regulating signalling pathways as part of their cell entry processes. The Rho family GTPase Cdc42 is appreciated as a key moderator of cellular actin dynamics, and the development of specific Cdc42-inhibiting agents has given us an unprecedented ability to investigate its individual role in signalling pathways. However, investigative use of said agents, and the subsequent characterisation of the role Cdc42 plays in viral entry processes has been lacking. Here, we describe the current literature on the role of Cdc42 in human immunodeficiency virus (HIV)-1 cell entry, which represents the most investigated instance of Cdc42 function in viral cell entry processes, and also review evidence of Cdc42 use in other RNA virus cell entries, demonstrating prime areas for more extensive research using similar techniques.

Phytochemicals modulate carcinogenic signaling pathways in breast and hormone-related cancers

Over the years, nutrition and environmental factors have been demonstrated to influence human health, specifically cancer. Owing to the fact that cancer is a leading cause of death worldwide, efforts are being made to elucidate molecular mechanisms that trigger or delay carcinogenesis. Phytochemicals, in particular, have been shown to modulate oncogenic processes through their antioxidant and anti-inflammatory activities and their ability to mimic the chemical structure and activity of hormones. These compounds can act not only by influencing oncogenic proteins, but also by modulating noncoding RNAs such as microRNAs and long noncoding RNAs. Although we are only beginning to understand the complete effects of many natural compounds, such as phytochemicals, researchers are motivated to combine these agents with traditional, chemo-based, or hormone-based therapies to fight against cancer. Since ongoing studies continue to prove effective, herein we exalt the importance of improving dietary choices as a chemo-preventive strategy.

Involvement of the Cdc42 pathway in CFTR post-translational turnover and in its plasma membrane stability in airway epithelial cells

Cystic fibrosis transmembrane conductance regulator (CFTR) is a chloride channel that is expressed on the apical plasma membrane (PM) of epithelial cells. The most common deleterious allele encodes a trafficking-defective mutant protein undergoing endoplasmic reticulum-associated degradation (ERAD) and presenting lower PM stability. In this study, we investigated the involvement of the Cdc42 pathway in CFTR turnover and trafficking in a human bronchiolar epithelial cell line (CFBE41o-) expressing wild-type CFTR. Cdc42 is a small GTPase of the Rho family that fulfils numerous cell functions, one of which is endocytosis and recycling process via actin cytoskeleton remodelling. When we treated cells with chemical inhibitors such as ML141 against Cdc42 and wiskostatin against the downstream effector N-WASP, we observed that CFTR channel activity was inhibited, in correlation with a decrease in CFTR amount at the cell surface and an increase in dynamin-dependent CFTR endocytosis. Anchoring of CFTR to the cortical cytoskeleton was then presumably impaired by actin disorganization. When we performed siRNA-mediated depletion of Cdc42, actin polymerization was not impacted, but we observed actin-independent consequences upon CFTR. Total and PM CFTR amounts were increased, resulting in greater activation of CFTR. Pulse-chase experiments showed that while CFTR degradation was slowed, CFTR maturation through the Golgi apparatus remained unaffected. In addition, we observed increased stability of CFTR in PM and reduction of its endocytosis. This study highlights the involvement of the Cdc42 pathway at several levels of CFTR biogenesis and trafficking: (i) Cdc42 is implicated in the first steps of CFTR biosynthesis and processing; (ii) it contributes to the stability of CFTR in PM via its anchoring to cortical actin; (iii) it promotes CFTR endocytosis and presumably its sorting toward lysosomal degradation.

Distant polypharmacology among MLP chemical probes

Small molecules are essential tool compounds to probe the role of proteins in biology and advance toward more efficient therapeutics. However, they are used without a complete knowledge of their selectivity across the entire proteome, at risk of confounding their effects due to unknown off-target interactions. Current state-of-the-art computational approaches to predicting the affinity profile of small molecules offer a means to anticipate potential nonobvious selectivity liabilities of chemical probes. The application of in silico target profiling on the full set of chemical probes from the NIH Molecular Libraries Program (MLP) resulted in the identification of biologically relevant in vitro affinities for proteins distantly related to the primary targets of ML006, ML123, ML141, and ML204, helping to lower the risk of their further use in chemical biology.

Redox biology in normal cells and cancer: restoring function of the redox/Fyn/c-Cbl pathway in cancer cells offers new approaches to cancer treatment

This review discusses a unique discovery path starting with novel findings on redox regulation of precursor cell and signaling pathway function and identification of a new mechanism by which relatively small changes in redox status can control entire signaling networks that regulate self-renewal, differentiation, and survival. The pathway central to this work, the redox/Fyn/c-Cbl (RFC) pathway, converts small increases in oxidative status to pan-activation of the c-Cbl ubiquitin ligase, which controls multiple receptors and other proteins of central importance in precursor cell and cancer cell function. Integration of work on the RFC pathway with attempts to understand how treatment with systemic chemotherapy causes neurological problems led to the discovery that glioblastomas (GBMs) and basal-like breast cancers (BLBCs) inhibit c-Cbl function through altered utilization of the cytoskeletal regulators Cool-1/βpix and Cdc42, respectively. Inhibition of these proteins to restore normal c-Cbl function suppresses cancer cell division, increases sensitivity to chemotherapy, disrupts tumor-initiating cell (TIC) activity in GBMs and BLBCs, controls multiple critical TIC regulators, and also allows targeting of non-TICs. Moreover, these manipulations do not increase chemosensitivity or suppress division of nontransformed cells. Restoration of normal c-Cbl function also allows more effective harnessing of estrogen receptor-α (ERα)-independent activities of tamoxifen to activate the RFC pathway and target ERα-negative cancer cells. Our work thus provides a discovery strategy that reveals mechanisms and therapeutic targets that cannot be deduced by standard genetics analyses, which fail to reveal the metabolic information, isoform shifts, protein activation, protein complexes, and protein degradation critical to our discoveries.

Cool-1-mediated inhibition of c-Cbl modulates multiple critical properties of glioblastomas, including the ability to generate tumors in vivo

We discovered that glioblastoma (GBM) cells use Cool-1/β-pix to inhibit normal activation of the c-Cbl ubiquitin ligase via the redox/Fyn/c-Cbl pathway and that c-Cbl inhibition is critical for GBM cell function. Restoring normal c-Cbl activity by Cool-1 knockdown in vitro reduced GBM cell division, almost eliminated generation of adhesion-independent spheroids, reduced the representation of cells expressing antigens thought to identify tumor initiating cells (TICs), reduced levels of several proteins of critical importance in TIC function (such as Notch-1 and Sox2), and increased sensitivity to BCNU (carmustine) and temozolomide (TMZ). In vivo, Cool-1 knockdown greatly suppressed the ability of GBM cells to generate tumors, an outcome that was c-Cbl dependent. In contrast, Cool-1 knockdown did not reduce division or increase BCNU or TMZ sensitivity in primary glial progenitor cells and Cool-1/c-Cbl complexes were not found in normal brain tissue. Our studies provide the first evidence that Cool-1 may be critical in the biology of human tumors, that suppression of c-Cbl by Cool-1 may be critical for generation of at least a subset of GBMs and offer a novel target that appears to be selectively necessary for TIC function and modulates chemoresistance in GBM cells. Targeting such proteins that inhibit c-Cbl offers potentially attractive opportunities for therapeutic development.

miR-18a inhibits CDC42 and plays a tumour suppressor role in colorectal cancer cells

The miR-17-92 cluster of microRNAs is elevated in colorectal cancer, and has a causative role in cancer development. Of the six miR-17-92 cluster members, miR-19a and b in particular are key promoters of cancer development and cell proliferation, while preliminary evidence suggests that miR-18a may act in opposition to other cluster members to decrease cell proliferation. It was hypothesised that miR-18a may have a homeostatic function in helping to contain the oncogenic effect of the entire miR-17-92 cluster, and that elevated miR-17-92 cluster activity without a corresponding increase in miR-18a may promote colorectal tumour progression. In colorectal cancer samples and corresponding normal colorectal mucosa, miR-18a displayed lower overall expression than other miR-17-92 cluster members. miR-18a was shown to have an opposing role to other miR-17-92 cluster members, in particular the key oncogenic miRNAs, miR-19a and b. Transfection of HCT116 and LIM1215 colorectal cancer cell lines with miR-18a mimics decreased proliferation, while a miR-18a inhibitor increased proliferation. miR-18a was also responsible for decreasing cell migration, altering cell morphology, inducing G1/S phase cell cycle arrest, increasing apoptosis, and enhancing the action of a pro-apoptotic agent. CDC42, a mediator of the PI3K pathway, was identified as a novel miR-18a target. Overexpression of miR-18a reduced CDC42 expression, and a luciferase assay confirmed that miR-18a directly targets the 3′UTR of CDC42. miR-18a mimics had a similar effect on proliferation as a small molecule inhibitor of CDC42. Inhibition of CDC42 expression is likely to be a key mechanism by which miR-18a impairs cancer cell growth, with a target protector experiment revealing miR-18a influences proliferation via direct inhibition of CDC42. Inhibition of CCND1 by miR-18a may also assist in this growth-suppression effect. The homeostatic function of miR-18a within the miR-17-92 cluster in colorectal cancer cells may be achieved through suppression of CDC42 and the PI3K pathway.

Essential role of PH domain and leucine-rich repeat protein phosphatase 2 in Nrf2 suppression via modulation of Akt/GSK3β/Fyn kinase axis during oxidative hepatocellular toxicity

Instances of sustained oxidative activity have been shown to involve dysregulation of Nrf2-mediated transcriptional induction; however, mechanisms warranting Nrf2-repression remain unclear. In this study, using primary rat hepatocytes, we have attempted to identify factors that may negatively influence Nrf2 survival pathway. Though studies indicate a conspicuous association between Akt and Nrf2, a confirmatory link between the two is unaddressed. On inhibiting PI3K/Akt pathway, we observed compromised activities of antioxidant and detoxification enzymes culminating in oxidative cytotoxicity. This was accompanied by reduced nuclear retention of Nrf2 and its ARE binding affinity, increased Nrf2 ubiquitination and concurrent decline in its downstream targets. Moreover, Akt inhibition enhanced nuclear translocation as well as phosphorylation of Fyn kinase, an enzyme linked to Nrf2 degradation, by relieving GSK3β from phosphorylation-mediated repression. The involvement of Akt and Fyn kinase in influencing Nrf2 signaling was further confirmed in oxidatively stressed hepatocytes by using tert-butyl hydroperoxide (tBHP). tBHP-induced decrease in Nrf2 levels was associated with enhanced Fyn kinase phosphorylation, Fyn kinase nuclear translocation and decreased levels of phosphorylated GSK3β(Ser9) in a time-dependent manner. Interestingly, tBHP induced site-specific deactivation of Akt as only Akt(Ser473) phosphorylation was observed to be affected. Further, protein expression as well as nuclear localization of PHLPP2, a phosphatase specific for Akt(Ser473), was found to be significantly enhanced in tBHP-stressed hepatocytes. Silencing of PHLPP2 not only resulted in considerable restoration of Nrf2 signaling, enhanced Nrf2-ARE binding and reduced Nrf2 ubiquitination but also significantly suppressed tBHP-induced ROS generation and alterations in mitochondrial permeability. We infer that cellular PHLPP2 levels may aggravate oxidative toxicity by suppressing Nrf2/ARE transcriptional regulation via Akt(Se473)/GSK3β/Fyn kinase axis. The study indicates that PHLPP2 could serve as a new target for developing strategies to manage pathological conditions exacerbated due to oxidative stress.

MEK1/2 inhibition suppresses tamoxifen toxicity on CNS glial progenitor cells

It is increasingly apparent that treatment with a variety of anticancer agents often is associated with adverse neurological consequences. Clinical studies indicate that exposure even to tamoxifen (TMX), a putatively benign antihormonal agent widely used in breast cancer treatment, causes cognitive dysfunction and changes in CNS metabolism, hippocampal volume, and brain structure. We found that TMX is toxic for a variety of CNS cell populations in vitro and also increased cell death in the corpus callosum and reduced cell division in the mouse subventricular zone, the hippocampal dentate gyrus, and the corpus callosum. We further discovered that MEK1/2 inhibition selectively rescued primary glial progenitors from TMX toxicity in vitro while enhancing TMX effects on MCF7 luminal human breast cancer cells. In vivo, MEK1/2 inhibition prevented TMX-induced cell death in systemically treated mice. Our results demonstrate unexpected cytotoxicity of this putatively benign antihormonal agent and offer a potential strategy for rescuing CNS cells from adverse effects of TMX.

Transforming growth factor β-induced superficial zone protein accumulation in the surface zone of articular cartilage is dependent on the cytoskeleton

The phenotype of articular chondrocytes is dependent on the cytoskeleton, specifically the actin microfilament architecture. Articular chondrocytes in monolayer culture undergo dedifferentiation and assume a fibroblastic phenotype. This process can be reversed by altering the actin cytoskeleton by treatment with cytochalasin. Whereas dedifferentiation has been studied on chondrocytes isolated from the whole cartilage, the effects of cytoskeletal alteration on specific zones of cells such as superficial zone chondrocytes are not known. Chondrocytes from the superficial zone secrete superficial zone protein (SZP), a lubricating proteoglycan that reduces the coefficient of friction of articular cartilage. A better understanding of this phenomenon may be useful in elucidating chondrocyte dedifferentiation in monolayer and accumulation of the cartilage lubricant SZP, with an eye toward tissue engineering functional articular cartilage. In this investigation, the effects of cytoskeletal modulation on the ability of superficial zone chondrocytes to secrete SZP were examined. Primary superficial zone chondrocytes were cultured in monolayer and treated with a combination of cytoskeleton modifying reagents and transforming growth factor β (TGFβ) 1, a critical regulator of SZP production. Whereas cytochalasin D maintains the articular chondrocyte phenotype, the hallmark of the superficial zone chondrocyte, SZP, was inhibited in the presence of TGFβ1. A decrease in TGFβ1-induced SZP accumulation was also observed when the microtubule cytoskeleton was modified using paclitaxel. These effects of actin and microtubule alteration were confirmed through the application of jasplakinolide and colchicine, respectively. As Rho GTPases regulate actin organization and microtubule polymerization, we hypothesized that the cytoskeleton is critical for TGFβ-induced SZP accumulation. TGFβ-mediated SZP accumulation was inhibited by small molecule inhibitors ML141 (Cdc42), NSC23766 (Rac1), and Y27632 (Rho effector Rho Kinase). On the other hand, lysophosphatidic acid, an upstream activator of Rho, increased SZP synthesis in response to TGFβ1. These results suggest that SZP production is dependent on the functional cytoskeleton, and Rho GTPases contribute to SZP accumulation by modulating the actions of TGFβ.

PLEKHG2 promotes heterotrimeric G protein βγ-stimulated lymphocyte migration via Rac and Cdc42 activation and actin polymerization

PLEKHG2 is a Dbl family Rho guanine nucleotide exchange factor (RhoGEF) whose gene was originally identified as being upregulated in a leukemia mouse model and was later shown to be activated by heterotrimeric G protein βγ (Gβγ) subunits. However, its function and activation mechanisms remain elusive. Here we show that, compared to its expression in primary human T cells, its expression is upregulated in several leukemia cell lines, including Jurkat T cells. Downregulation of PLEKHG2 in Jurkat T cells by small interfering RNAs (siRNAs) specifically inhibited Gβγ-stimulated Rac and Cdc42, but not RhoA, activation. Consequently, suppressing PLEKHG2 expression blocked actin polymerization and SDF1α-stimulated lymphocyte migration. Additional studies indicate that Gβγ likely activates PLEKHG2, in part by binding the N terminus of PLEKHG2 to release an autoinhibition imposed by its C terminus, which interacts with a region encompassing the catalytic Dbl homology (DH) domain. As a result, overexpressing either the N terminus or the C terminus of PLEKHG2 blocked Gβγ-stimulated Rac and Cdc42 activation and prevented Jurkat T cells from forming membrane protrusions and migrating. Together, our studies have provided the first evidence for the endogenous function of PLEKHG2, which may serve as a key Gβγ-stimulated RhoGEF that regulates lymphocyte chemotaxis via Rac and Cdc42 activation and actin polymerization.