IQGAP1 Regulates Actin Polymerization and Contributes to Bleomycin-Induced Lung Fibrosis.

We previously found IQ motif containing GTPase activating protein (IQGAP1) to be consistently elevated in lung fibroblasts (LF) isolated from patients with scleroderma (systemic sclerosis, SSc)-associated interstitial lung disease (ILD) and reported that IQGAP1 contributed to SSc by regulating expression and organization of α-smooth muscle actin (SMA) in LF. The aim of this study was to compare the development of ILD in the presence and absence of IQGAP1. Pulmonary fibrosis was induced in IQGAP1 knockout (KO) and wild-type (WT) mice by a single-intratracheal instillation of bleomycin. Two and three weeks later, mice were euthanized and investigated. We observed that the IQGAP1 KO mouse was characterized by a reduced rate of actin polymerization with reduced accumulation of actin in the lung compared to the WT mouse. After exposure to bleomycin, the IQGAP1 KO mouse demonstrated decreased contractile activity of LF, reduced expression of SMA, TGFß, and collagen, and lowered overall fibrosis scores compared to the WT mouse. The numbers of inflammatory cells and expression of pro-inflammatory cytokines in lung tissue were not significantly different between IQGAP1 KO and WT mice. We conclude that IQGAP1 plays an important role in the development of lung fibrosis induced by bleomycin, and the absence of IQGAP1 reduces the contractile activity of lung fibroblast and bleomycin-induced pulmonary fibrosis. Thus, IQGAP1 may be a potential target for novel anti-fibrotic therapies for lung fibrosis.

Coordination of actin plus-end dynamics by IQGAP1, formin, and capping protein.

Cell processes require precise regulation of actin polymerization that is mediated by plus-end regulatory proteins. Detailed mechanisms that explain plus-end dynamics involve regulators with opposing roles, including factors that enhance assembly, e.g., the formin mDia1, and others that stop growth (capping protein, CP). We explore IQGAP1's roles in regulating actin filament plus-ends and the consequences of perturbing its activity in cells. We confirm that IQGAP1 pauses elongation and interacts with plus ends through two residues (C756 and C781). We directly visualize the dynamic interplay between IQGAP1 and mDia1, revealing that IQGAP1 displaces the formin to influence actin assembly. Using four-color TIRF, we show that IQGAP1's displacement activity extends to formin-CP "decision complexes," promoting end-binding protein turnover at plus-ends. Loss of IQGAP1 or its plus-end activities disrupts morphology and migration, emphasizing its essential role. These results reveal a new role for IQGAP1 in promoting protein turnover on filament ends and provide new insights into how plus-end actin assembly is regulated in cells.

IQGAP3 Is an Important Mediator of Skin Inflammatory Diseases.

IQGAP3 (IQ Motif Containing GTPase Activating Protein 3) is member of the IQGAP family of scaffold proteins, which are essential for assembling multiprotein complexes that coordinate various intracellular signaling pathways. Previous research has shown that IQGAP3 is overexpressed in psoriatic skin lesions. Given its involvement in processes like cell proliferation and chemokine signaling, we sought to explore its molecular role in driving the psoriatic phenotype of keratinocytes. By conducting transcriptome profiling of HaCaT keratinocytes, we identified numerous psoriasis-associated pathways that were affected when IQGAP3 was knocked down. These included alterations in NFkB signaling, EGFR signaling, activation of p38/MAPK and ERK1/ERK2, lipid metabolism, cytokine production, and the response to inflammatory cytokine stimulation. Real-time analysis further revealed changes in cell growth dynamics, including proliferation and wound healing. The balance between cell proliferation and apoptosis was altered, as were skin barrier functions and the production of IL-6 and IFNγ. Despite these significant findings, the diversity of the alterations observed in the knockdown cells led us to conclude that IQGAP3 may not be the best target for the therapeutic inhibition to normalize the phenotype of keratinocytes in psoriasis.

Real-Time Monitoring of RAS Activity Using In Vitro and In-Cell NMR Spectroscopy.

The activation level of RAS can be determined by GTP hydrolysis rate (khy) and GDP-GTP exchange rates (kex). Either impaired GTP hydrolysis or enhanced GDP-GTP exchange causes the aberrant activation of RAS in oncogenic mutants. Therefore, it is important to quantify the khy and kex for understanding the mechanisms of RAS oncogenesis and drug development. Conventional methods have individually measured the kex and khy of RAS. However, within the intracellular environment, GTP hydrolysis and GDP-GTP exchange reactions occur simultaneously under conditions where GTP concentration is kept constant. In addition, the intracellular activity of RAS is influenced by endogenous regulatory proteins, such as RAS GTPase activating proteins (GAPs) and the guanine-nucleotide exchange factors (GEFs). Here, we describe the in vitro and in-cell NMR methods to estimate the khy and kex simultaneously by measuring the time-dependent changes of the fraction of GTP-bound ratio under the condition of constant GTP concentration.

IQGAP1 and NWASP promote human cancer cell dissemination and metastasis by regulating ß1-integrin via FAK and MRTF/SRF.

Attachment of circulating tumor cells to the endothelial cells (ECs) lining blood vessels is a critical step in cancer metastatic colonization, which leads to metastatic outgrowth. Breast and prostate cancers are common malignancies in women and men, respectively. Here, we observe that ß1-integrin is required for human prostate and breast cancer cell adhesion to ECs under shear-stress conditions in vitro and to lung blood vessel ECs in vivo. We identify IQGAP1 and neural Wiskott-Aldrich syndrome protein (NWASP) as regulators of ß1-integrin transcription and protein expression in prostate and breast cancer cells. IQGAP1 and NWASP depletion in cancer cells decreases adhesion to ECs in vitro and retention in the lung vasculature and metastatic lung nodule formation in vivo. Mechanistically, NWASP and IQGAP1 act downstream of Cdc42 to increase ß1-integrin expression both via extracellular signal-regulated kinase (ERK)/focal adhesion kinase signaling at the protein level and by myocardin-related transcription factor/serum response factor (SRF) transcriptionally. Our results identify IQGAP1 and NWASP as potential therapeutic targets to reduce early metastatic dissemination.

Identification of a novel disulfideptosis-related gene signature for prognostic implication in lower-grade gliomas.

Lower-grade gliomas (GBMLGG) are common, fatal, and difficult-to-treat cancers. The current treatment choices have impressive efficacy constraints. As a result, the development of effective treatments and the identification of new therapeutic targets are urgent requirements. Disulfide metabolism is the cause of the non-apoptotic programmed cell death known as disulfideptosis, which was only recently discovered. The mRNA expression data and related clinical information of GBMLGG patients downloaded from public databases were used in this study to investigate the prognostic significance of genes involved in disulfideptosis. In the Cancer Genome Atlas (TCGA) and Gene Expression Omnibus (GEO) cohort, our findings showed that many disulfidptosis-related genes were expressed differently in normal and GBMLGG tissues. It was discovered that IQ motif-containing GTPase-activating protein 1 (IQGAP1) is a key gene that influences the outcome of GBMLGG. Besides, a nomogram model was built to foresee the visualization of GBMLGG patients. In addition, in vivo and in vitro validation of IQGAP1's cancer-promoting function was done. In conclusion, we discovered a gene signature associated with disulfideptosis that can effectively predict OS in GBMLGG patients. As a result, treating disulfideptosis may be a viable alternative for GBMLGG patients.

Infiltrative Vessel Co-optive Growth Pattern Induced by IQGAP3 Overexpression Promotes Microvascular Invasion in Hepatocellular Carcinoma.

PURPOSE: Microvascular invasion (MVI) is a major unfavorable prognostic factor for intrahepatic metastasis and postoperative recurrence of hepatocellular carcinoma (HCC). However, the intervention and preoperative prediction for MVI remain clinical challenges due to the absent precise mechanism and molecular marker(s). Herein, we aimed to investigate the mechanisms underlying vascular invasion that can be applied to clinical intervention for MVI in HCC. EXPERIMENTAL DESIGN: The histopathologic characteristics of clinical MVI+/HCC specimens were analyzed using multiplex immunofluorescence staining. The liver orthotopic xenograft mouse model and mechanistic experiments on human patient-derived HCC cell lines, including coculture modeling, RNA-sequencing, and proteomic analysis, were used to investigate MVI-related genes and mechanisms. RESULTS: IQGAP3 overexpression was correlated significantly with MVI status and reduced survival in HCC. Upregulation of IQGAP3 promoted MVI+-HCC cells to adopt an infiltrative vessel co-optive growth pattern and accessed blood capillaries by inducing detachment of activated hepatic stellate cells (HSC) from the endothelium. Mechanically, IQGAP3 overexpression contributed to HCC vascular invasion via a dual mechanism, in which IQGAP3 induced HSC activation and disruption of the HSC-endothelial interaction via upregulation of multiple cytokines and enhanced the trans-endothelial migration of MVI+-HCC cells by remodeling the cytoskeleton by sustaining GTPase Rac1 activity. Importantly, systemic delivery of IQGAP3-targeting small-interfering RNA nanoparticles disrupted the infiltrative vessel co-optive growth pattern and reduced the MVI of HCC. CONCLUSIONS: Our results revealed a plausible mechanism underlying IQGAP3-mediated microvascular invasion in HCC, and provided a potential target to develop therapeutic strategies to treat HCC with MVI.

The GTPase activating protein Gyp7 regulates Rab7/Ypt7 activity on late endosomes.

Organelles of the endomembrane system contain Rab GTPases as identity markers. Their localization is determined by guanine nucleotide exchange factors (GEFs) and GTPase activating proteins (GAPs). It remains largely unclear how these regulators are specifically targeted to organelles and how their activity is regulated. Here, we focus on the GAP Gyp7, which acts on the Rab7-like Ypt7 protein in yeast, and surprisingly observe the protein exclusively in puncta proximal to the vacuole. Mistargeting of Gyp7 to the vacuole strongly affects vacuole morphology, suggesting that endosomal localization is needed for function. In agreement, efficient endolysosomal transport requires Gyp7. In vitro assays reveal that Gyp7 requires a distinct lipid environment for membrane binding and activity. Overexpression of Gyp7 concentrates Ypt7 in late endosomes and results in resistance to rapamycin, an inhibitor of the target of rapamycin complex 1 (TORC1), suggesting that these late endosomes are signaling endosomes. We postulate that Gyp7 is part of regulatory machinery involved in late endosome function.

SynGAP regulates synaptic plasticity and cognition independently of its catalytic activity.

SynGAP is an abundant synaptic GTPase-activating protein (GAP) critical for synaptic plasticity, learning, memory, and cognition. Mutations in SYNGAP1 in humans result in intellectual disability, autistic-like behaviors, and epilepsy. Heterozygous Syngap1-knockout mice display deficits in synaptic plasticity, learning, and memory and exhibit seizures. It is unclear whether SynGAP imparts structural properties at synapses independently of its GAP activity. Here, we report that inactivating mutations within the GAP domain do not inhibit synaptic plasticity or cause behavioral deficits. Instead, SynGAP modulates synaptic strength by physically competing with the AMPA-receptor-TARP excitatory receptor complex in the formation of molecular condensates with synaptic scaffolding proteins. These results have major implications for developing therapeutic treatments for SYNGAP1-related neurodevelopmental disorders.

BGLF4 kinase regulates the formation of the EBV cytoplasmic assembly compartment and the recruitment of cellular IQGAP1 for virion release.

After Epstein-Barr virus (EBV) genome replication and encapsidation in the nucleus, nucleocapsids are translocated into the cytoplasm for subsequent tegumentation and maturation. The EBV BGLF4 kinase, which induces partial disassembly of the nuclear lamina, and the nuclear egress complex BFRF1/BFLF2 coordinately facilitate the nuclear egress of nucleocapsids. Here, we demonstrate that within EBV reactivated epithelial cells, viral capsids, tegument proteins, and glycoproteins are clustered in the juxtanuclear concave region, accompanied by redistributed cytoplasmic organelles and the cytoskeleton regulator IQ-domain GTPase-activation protein 1 (IQGAP1), close to the microtubule-organizing center (MTOC). The assembly compartment (AC) structure was diminished in BGLF4-knockdown TW01-EBV cells and BGLF4-knockout bacmid-carrying TW01 cells, suggesting that the formation of AC structure is BGLF4-dependent. Notably, glycoprotein gp350/220 was observed by confocal imaging to be distributed in the perinuclear concave region and surrounded by the endoplasmic reticulum (ER) membrane marker calnexin, indicating that the AC may be located within a globular structure derived from ER membranes, adjacent to the outer nuclear membrane. Moreover, the viral capsid protein BcLF1 and tegument protein BBLF1 were co-localized with IQGAP1 near the cytoplasmic membrane in the late stage of replication. Knockdown of IQGAP1 did not affect the AC formation but decreased virion release from both TW01-EBV and Akata+ cells, suggesting IQGAP1-mediated trafficking regulates EBV virion release. The data presented here show that BGLF4 is required for cytoskeletal rearrangement, coordination with the redistribution of cytoplasmic organelles and IQGAP1 for virus maturation, and subsequent IQGAP1-dependent virion release.IMPORTANCEEBV genome is replicated and encapsidated in the nucleus, and the resultant nucleocapsids are translocated to the cytoplasm for subsequent virion maturation. We show that a cytoplasmic AC, containing viral proteins, markers of the endoplasmic reticulum, Golgi, and endosomes, is formed in the juxtanuclear region of epithelial and B cells during EBV reactivation. The viral BGLF4 kinase contributes to the formation of the AC. The cellular protein IQGAP1 is also recruited to the AC and partially co-localizes with the virus capsid protein BcLF1 and tegument protein BBLF1 in EBV-reactivated cells, dependent on the BGLF4-induced cytoskeletal rearrangement. In addition, virion release was attenuated in IQGAP1-knockdown epithelial and B cells after reactivation, suggesting that IQGAP1-mediated trafficking may regulate the efficiency of virus maturation and release.

Neurofibromin 1 mediates sleep depth in Drosophila.

Neural regulation of sleep and metabolic homeostasis are critical in many aspects of human health. Despite extensive epidemiological evidence linking sleep dysregulation with obesity, diabetes, and metabolic syndrome, little is known about the neural and molecular basis for the integration of sleep and metabolic function. The RAS GTPase-activating gene Neurofibromin (Nf1) has been implicated in the regulation of sleep and metabolic rate, raising the possibility that it serves to integrate these processes, but the effects on sleep consolidation and physiology remain poorly understood. A key hallmark of sleep depth in mammals and flies is a reduction in metabolic rate during sleep. Here, we examine multiple measures of sleep quality to determine the effects of Nf1 on sleep-dependent changes in arousal threshold and metabolic rate. Flies lacking Nf1 fail to suppress metabolic rate during sleep, raising the possibility that loss of Nf1 prevents flies from integrating sleep and metabolic state. Sleep of Nf1 mutant flies is fragmented with a reduced arousal threshold in Nf1 mutants, suggesting Nf1 flies fail to enter deep sleep. The effects of Nf1 on sleep can be localized to a subset of neurons expressing the GABAA receptor Rdl. Sleep loss has been associated with changes in gut homeostasis in flies and mammals. Selective knockdown of Nf1 in Rdl-expressing neurons within the nervous system increases gut permeability and reactive oxygen species (ROS) in the gut, raising the possibility that loss of sleep quality contributes to gut dysregulation. Together, these findings suggest Nf1 acts in GABA-sensitive neurons to modulate sleep depth in Drosophila.

circSLCO1B7 suppresses the malignant progression of hepatocellular carcinoma via the miR-556-3p/DAB2IP axis.

Circular RNAs (circRNAs) are noncoding RNAs with a circular colsed structure that play an important role in the occurrence and development of cancers. The functional mechanism of circRNAs as ceRNAs in hepatocellular carcinoma (HCC) and its effect on the invasion and metastasis of HCC need to be further studied. Five pairs of HCC tissues were selected for high-throughput sequencing, and 19 circRNAs with differential expression were obtained. The expression of circSLCO1B7 was obviously downregulated in 50 pairs of tumor tissues and plasma of HCC patients, which was closely related to the TNM stage, lymph node metastasis and tumor size. Cell functional experiments showed that circSLCO1B7 could inhibit cell growth, migration, invasion and promote cell apoptosis. In the regulatory mechanism, circSLCO1B7 sponged miR-556-3p to regulate the expression of the downstream target gene DAB2IP and induced the Epithelial-mesenchymal transition (EMT) progression. Our results indicated that circSLCO1B7 significantly inhibits the metastasis of HCC via the miR-556-3p/DAB2IP axis. Thus, circSLCO1B7 is a good candidate as a therapeutic target.

DAB2IP stabilizes p27Kip1 via suppressing PI3K/AKT signaling in clear cell renal cell carcinoma.

Renal cell carcinoma (RCC) is the most lethal of the urologic malignancies. We previously discovered that DAB2IP, a novel Ras GTPase-activating protein, was frequently epigenetically silenced in RCC, and DAB2IP loss was correlated with the overall survival of RCC patients. In this study, we determined the biological functions of DAB2IP in clear cell RCC (ccRCC) and its potential mechanisms of action. Correlations between DAB2IP expression level and ccRCC tumor size and patient survival were analyzed, and the results showed that ccRCC patients with high DAB2IP mRNA level exhibited smaller tumor size and better survival than the patients with low DAB2IP. Compared to control, DAB2IP knockdown significantly increased cell proliferation, promoted cell cycle progression in G1/S phase, and decreased p27 expression. Mechanism studies demonstrated that loss of DAB2IP promoted p27 protein phosphorylation, cytosolic sequestration, and subsequently ubiquitination-mediated degradation in ccRCC cells. Further studies confirmed that the proline-rich domain in C terminal (CPR) of DAB2IP suppressed AKT phosphorylation and p27 phosphorylation on S10. Hence, DAB2IP is essential for p27 protein stabilization in ccRCC, which is at less partly mediated by PI3K/AKT signaling pathway.

Interneuron-Targeted Disruption of SYNGAP1 Alters Sensory Representations in the Neocortex and Impairs Sensory Learning.

SYNGAP1 haploinsufficiency in humans leads to severe neurodevelopmental disorders characterized by intellectual disability, autism, epilepsy, and sensory processing deficits. However, the circuit mechanisms underlying these disorders are not well understood. In mice, a decrease of SynGAP levels results in cognitive deficits by interfering with the development of excitatory glutamatergic connections. Recent evidence suggests that SynGAP also plays a crucial role in the development and function of GABAergic inhibitory interneurons. Nevertheless, it remains uncertain whether and to what extent the expression of SYNGAP1 in inhibitory interneurons contributes to cortical circuit function and related behaviors. The activity of cortical neurons has not been measured simultaneously with behavior. To address these gaps, we recorded from layer 2/3 neurons in the primary whisker somatosensory cortex (wS1) of mice while they learned to perform a whisker tactile detection task. Our results demonstrate that mice with interneuron-specific SYNGAP1 haploinsufficiency exhibit learning deficits characterized by heightened behavioral responses in the absence of relevant sensory input and premature responses to unrelated sensory stimuli not associated with reward acquisition. These behavioral deficits are accompanied by specific circuit abnormalities within wS1. Interneuron-specific SYNGAP1 haploinsufficiency increases detrimental neuronal correlations directly related to task performance and enhances responses to irrelevant sensory stimuli unrelated to the reward acquisition. In summary, our findings indicate that a reduction of SynGAP in inhibitory interneurons impairs sensory representation in the primary sensory cortex by disrupting neuronal correlations, which likely contributes to the observed cognitive deficits in mice with pan-neuronal SYNGAP1 haploinsufficiency.SIGNIFICANCE STATEMENT SYNGAP1 haploinsufficiency leads to severe neurodevelopmental disorders. The exact nature of neural circuit dysfunction caused by SYNGAP1 haploinsufficiency remains poorly understood. SynGAP plays a critical role in the function of GABAergic inhibitory interneurons as well as glutamatergic pyramidal neurons in the neocortex. Whether and how decreasing SYNGAP1 level in inhibitory interneurons disrupts a behaviorally relevant circuit remains unclear. We measure neural activity and behavior in mice learning a perceptual task. Mice with interneuron-targeted disruption of SYNGAP1 display increased detrimental neuronal correlations and elevated responses to irrelevant sensory inputs, which are related to impaired task performance. These results show that cortical interneuron dysfunction contributes to sensory deficits in SYNGAP1 haploinsufficiency with important implications for identifying therapeutic targets.

Upregulation of IQGAP2 by EBV transactivator Rta and its influence on EBV life cycle.

Epstein-Barr virus (EBV) is a human oncogenic γ-herpesvirus that establishes persistent infection in more than 90% of the world's population. EBV has two life cycles, latency and lytic replication. Reactivation of EBV from latency to the lytic cycle is initiated and controlled by two viral immediate-early transcription factors, Zta and Rta, encoded by BZLF1 and BRLF1, respectively. In this study, we found that IQGAP2 expression was elevated in EBV-infected B cells and identified Rta as a viral gene responsible for the IQGAP2 upregulation in both B cells and nasopharyngeal carcinoma cell lines. Mechanistically, we showed that Rta increases IQGAP2 expression through direct binding to the Rta-responsive element in the IQGAP2 promoter. We also demonstrated the direct interaction between Rta and IQGAP2 as well as their colocalization in the nucleus. Functionally, we showed that the induced IQGAP2 is required for the Rta-mediated Rta promoter activation in the EBV lytic cycle progression and may influence lymphoblastoid cell line clumping morphology through regulating E-cadherin expression. IMPORTANCE Elevated levels of antibodies against EBV lytic proteins and increased EBV DNA copy numbers in the sera have been reported in patients suffering from Burkitt's lymphoma, Hodgkin's lymphoma, and nasopharyngeal carcinoma, indicating that EBV lytic cycle progression may play an important role in the pathogenesis of EBV-associated diseases and highlighting the need for a more complete mechanistic understanding of the EBV lytic cycle. Rta acts as an essential transcriptional activator to induce lytic gene expression and thus trigger EBV reactivation. In this study, scaffolding protein IQGAP2 was found to be upregulated prominently following EBV infection via the direct binding of Rta to the RRE in the IQGAP2 promoter but not in response to other biological stimuli. Importantly, IQGAP2 was demonstrated to interact with Rta and promote the EBV lytic cycle progression. Suppression of IQGAP2 was also found to decrease E-cadherin expression and affect the clumping morphology of lymphoblastoid cell lines.

Diverse p120RasGAP interactions with doubly phosphorylated partners EphB4, p190RhoGAP, and Dok1.

RasGAP (p120RasGAP), the founding member of the GTPase-activating protein (GAP) family, is one of only nine human proteins to contain two SH2 domains and is essential for proper vascular development. Despite its importance, its interactions with key binding partners remains unclear. In this study we provide a detailed viewpoint of RasGAP recruitment to various binding partners and assess their impact on RasGAP activity. We reveal the RasGAP SH2 domains generate distinct binding interactions with three well-known doubly phosphorylated binding partners: p190RhoGAP, Dok1, and EphB4. Affinity measurements demonstrate a 100-fold weakened affinity for RasGAP-EphB4 binding compared to RasGAP-p190RhoGAP or RasGAP-Dok1 binding, possibly driven by single versus dual SH2 domain engagement with a dominant N-terminal SH2 interaction. Small-angle X-ray scattering reveals conformational differences between RasGAP-EphB4 binding and RasGAP-p190RhoGAP binding. Importantly, these interactions do not impact catalytic activity, implying RasGAP utilizes its SH2 domains to achieve diverse spatial-temporal regulation of Ras signaling in a previously unrecognized fashion.

Targeting Wnt/ß-catenin-mediated upregulation of oncogenic NLGN3 suppresses cancer stem cells in glioblastoma.

Glioblastoma (GBM) is the most malignant tumor in brain and is highly resistant to therapy. Clinical evidence suggests increased number of cancer stem cells (CSCs) may contribute to the failure of conventional therapies, but the mechanisms associated with acquisition of CSC properties in GBM are not fully understood. We found that DAB2IP suppresses CSC properties by targeting the synaptic proteins neuroligin 3 (NLGN3) in GBM. Furthermore, we showed that GBM-derived NLGN3 has an oncogenic function by inducing CSC properties within GBM. Moreover, elevated NLGN3 transcription mediated by Wnt/ß-catenin signaling pathway resulted in increased secretion of NLGN3 into the surrounding tumor microenvironment. Both condition media containing NLGN3 and recombinant NLGN3 transformed neighboring cells to CSCs, suggesting NLGN3 as a critical component inducing CSC properties. Furthermore, targeting NLGN3-bearing CSCs using upstream Wnt/ß-catenin inhibitors synergistically enhances the efficacy of conventional treatment. Hence, we unveiled the series of regulatory mechanisms for acquisition of CSC properties in GBM progression by Wnt/ß-catenin-mediated NLGN3. These results may provide a new targeting strategy to improve the therapeutic efficacy of GBM treatments.

7-Ketocholesterol Promotes Retinal Pigment Epithelium Senescence and Fibrosis of Choroidal Neovascularization via IQGAP1 Phosphorylation-Dependent Signaling.

Accumulation of 7-ketocholesterol (7KC) occurs in age-related macular degeneration (AMD) and was found previously to promote fibrosis, an untreatable cause of vision loss, partly through induction of endothelial-mesenchymal transition. To address the hypothesis that 7KC causes mesenchymal transition of retinal pigment epithelial cells (RPE), we exposed human primary RPE (hRPE) to 7KC or a control. 7KC-treated hRPE did not manifest increased mesenchymal markers, but instead maintained RPE-specific proteins and exhibited signs of senescence with increased serine phosphorylation of histone H3, serine/threonine phosphorylation of mammalian target of rapamycin (p-mTOR), p16 and p21, ß-galactosidase labeling, and reduced LaminB1, suggesting senescence. The cells also developed senescence-associated secretory phenotype (SASP) determined by increased IL-1ß, IL-6, and VEGF through mTOR-mediated NF-κB signaling, and reduced barrier integrity that was restored by the mTOR inhibitor, rapamycin. 7KC-induced p21, VEGF, and IL-1ß were inhibited by an inhibitor of protein kinase C. The kinase regulates IQGAP1 serine phosphorylation. Furthermore, after 7KC injection and laser-induced injury, mice with an IQGAP1 serine 1441-point mutation had significantly reduced fibrosis compared to littermate control mice. Our results provide evidence that age-related accumulation of 7KC in drusen mediates senescence and SASP in RPE, and IQGAP1 serine phosphorylation is important in causing fibrosis in AMD.

Multi-omics data integration reveals the molecular network of dysregulation IQGAP2-mTOR promotes cell proliferation.

IQGAP2 as a tumor suppressor gene can influence cell proliferation in multiple tumor cell lines. However, the regulation network of cell proliferation resulting solely from the deficiency of IQGAP2 in cells was still unclear. Here, we integrated transcriptome, proteome, and phosphoproteome analyses to investigate the regulatory network of cell proliferation in IQGAP2 knockdown HaCaT and HEK293 cells. Our findings revealed that the dysregulation of the IQGAP2-mTOR molecular network led to increased cell proliferation. We demonstrated that IQGAP2 knockdown enhanced the phosphorylation levels of AKT and S6K, leading to increased cell proliferation. Additionally, we found that AKT and mTOR inhibitors partially rescued abnormal cell proliferation by reducing hyperphosphorylation. Our data suggest a potential connection between the mTOR signaling pathway and aberrant cell proliferation in IQGAP2 knockdown cells. These findings offer a new therapeutic strategy for patients with IQGAP2 deficiency.

The IQGAP scaffolds: Critical nodes bridging receptor activation to cellular signaling.

The scaffold protein IQGAP1 assembles multiprotein signaling complexes to influence biological functions. Cell surface receptors, particularly receptor tyrosine kinases and G-protein coupled receptors, are common IQGAP1 binding partners. Interactions with IQGAP1 modulate receptor expression, activation, and/or trafficking. Moreover, IQGAP1 couples extracellular stimuli to intracellular outcomes via scaffolding of signaling proteins downstream of activated receptors, including mitogen-activated protein kinases, constituents of the phosphatidylinositol 3-kinase pathway, small GTPases, and ß-arrestins. Reciprocally, some receptors influence IQGAP1 expression, subcellular localization, binding properties, and post-translational modifications. Importantly, the receptor:IQGAP1 crosstalk has pathological implications ranging from diabetes and macular degeneration to carcinogenesis. Here, we describe the interactions of IQGAP1 with receptors, summarize how they modulate signaling, and discuss their contribution to pathology. We also address the emerging functions in receptor signaling of IQGAP2 and IQGAP3, the other human IQGAP proteins. Overall, this review emphasizes the fundamental roles of IQGAPs in coupling activated receptors to cellular homeostasis.