Purpuric drug eruptions induced by EGFR tyrosine kinase inhibitors are associated with IQGAP1-mediated increase in vascular permeability.

Epidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKIs) are used as a treatment for non-small-cell lung cancer. There have been some reports of EGFR-TKIs being associated with vascular adverse events. We found that EGFR-TKIs decreased the proliferation of HMEC-1s (immortalized human dermal microvascular endothelial cells) and HMVECs (human dermal microvascular endothelial cells), and also inhibited the phosphorylation of EGFR and ERK. We examined the mRNA expression profile of erlotinib-treated HMEC-1s and identified IQ motif containing GTPase activating protein 1 (IQGAP1) as the most consistently up-regulated transcript and protein. IQGAP1 was also overexpressed and co-localized with endothelial cells in the lesional skin. Notably, increased IQGAP1 expression was associated with decreased transendothelial electrical resistance and increased vascular permeability in vitro. Erlotinib treatment enriched the staining of IQGAP1 and reduced the intensities of α-catenin at the sites of cell-cell contact. In conclusion, erlotinib induces adherens junction dysfunction by modulating the expression of IQGAP1 in dermal endothelial cells. © 2020 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

IQGAP1 Mediates Hcp1-Promoted Escherichia coli Meningitis by Stimulating the MAPK Pathway.

Escherichia coli-induced meningitis remains a life-threatening disease despite recent advances in the field of antibiotics-based therapeutics, necessitating continued research on its pathogenesis. The current study aims to elucidate the mechanism through which hemolysin-coregulated protein 1 (Hcp1) induces the apoptosis of human brain microvascular endothelial cells (HBMEC). Co-immunoprecipitation coupled with mass spectrometric (MS) characterization led to the identification of IQ motif containing GTPase activating protein 1 (IQGAP1) as a downstream target of Hcp1. IQGAP1 was found to be up-regulated by Hcp1 treatment and mediate the stimulation of HBMEC apoptosis. It was shown that Hcp1 could compete against Smurf1 for binding to IQGAP1, thereby rescuing the latter from ubiquitin-dependent degradation. Subsequent study suggested that IQGAP1 could stimulate the MAPK signaling pathway by promoting the phosphorylation of ERK1/2, an effect that was blocked by U0126, an MAPK inhibitor. Furthermore, U0126 also demonstrated therapeutic potential against E. coli meningitis in a mouse model. Taken together, our results suggested the feasibility of targeting the MAPK pathway as a putative therapeutic strategy against bacterial meningitis.

Angiopoietin-1 requires IQ domain GTPase-activating protein 1 to activate Rac1 and promote endothelial barrier defense.

OBJECTIVE: IQ domain GTPase-activating protein 1 (IQGAP1) contributes to cytoskeletal network regulation in epithelial cells by its scaffolding properties and by binding the Rho GTPase Rac1 to maintain its activity. The functions of IQGAP1 in endothelial cells beyond angiogenesis remain unclear. We hypothesized that IQGAP1 participates in the regulation of endothelial barrier function. METHODS AND RESULTS: Silencing IQGAP1 in human microvascular endothelial cells resulted in a disruption of adherens junctions, formation of interendothelial gaps, and a reduction in barrier function. Furthermore, silencing of IQGAP1 abrogated the barrier enhancement effect of angiopoietin-1 (Angpt-1) and abolished the barrier-stabilizing effect of Angpt-1 on thrombin-stimulated cells. Coimmunoprecipitation detected binding of endogenous IQGAP1 with Rac1 at baseline that was stronger when Rac1 was activated and weaker when it was deactivated. Measurement of GTP-bound Rac1 revealed that Angpt-1 failed to activate Rac1 not only if IQGAP1 was silenced but also if cells were transfected with a mutant disabled in Rac1 binding (T1050AX2). Furthermore, a dominant-active Rac1 was sufficient to completely reverse the morphological and functional changes induced by reduction in IQGAP1. CONCLUSION: These experiments are the first demonstration of IQGAP1 regulating barrier function in any cell type. Further, our data show that Angpt-1 requires IQGAP1 as an indispensable activator of Rac1.

TNFalpha induced oxidative stress dependent Akt signaling affects actin cytoskeletal organization in glioma cells.

Inflammation which is an indispensable participant in tumor progression is intricately linked with redox modulation. The pro-inflammatory cytokine Tumor Necrosis Factor (TNFalpha) elevates reactive oxygen species (ROS) in glioblastoma multiforme (GBM). As both TNFalpha and oxidative stress independently play role in regulating cytoskeletal organization and cell survival pathways we investigated whether TNFalpha mediated oxidative stress regulates responses that offer survival advantages to glioblastoma cells. Treatment with TNFalpha elevated Akt phosphorylation in glioma cells. Increased in Akt phosphorylation was concurrent with the decrease in ROS scavenger SOD-1 levels. TNFalpha mediated increase in Akt phosphorylation was dependent on oxidative stress as Akt phosphorylation was abrogated in the presence of ROS inhibitor and elevated in cells transfected with SOD-1 siRNA. TNFalpha altered actin cytoskeletal organization and increased Cdc42 levels. This increase in Cdc42 was concomitant with its increased interaction with scaffold protein IQGAP-1. Also, we report for the first time a ROS dependent interaction between pAkt and IQGAP-1 in TNFalpha treated cells. Importantly, Akt inhibition not only reversed TNFalpha mediated changes in actin cytoskeletal organization but also abrogated anchorage independent growth. Together, these results suggest that TNFalpha induced oxidative stress affects Akt activation to regulate actin organization and growth of glioma cells.

Anti-proliferative and proapoptotic effects of benzyl isothiocyanate on human pancreatic cancer cells is linked to death receptor activation and RasGAP/Rac1 down-modulation.

Benzyl isothiocyanate can exert anti-tumor effect by arrest of cell cycle progression and induction of apoptosis in human pancreatic cancer cells. Among them, the dissection of the molecular mechanism of induction of apoptosis is important because the knowledge may be exploited for both cancer prevention and treatment. Our studies reported here indicate that BITC-mediated apoptosis involves the disappearance of intact 21-kDa Bid protein, cytochrome c release and predominant procaspase-3 cleavage. Using adenocarcinoma and metastatic pancreatic cancer cells, we investigated whether this dietary isothiocyanate induces apoptosis by converging two major pathways: the death receptor-mediated extrinsic and the mitochondrial intrinsic pathway. Indeed, cell surface receptor analysis by flow cytometry demonstrates the up-regulation of DR4, a member of death receptor family in BITC exposed pancreatic cancer cells. Since BITC is able to trigger death receptor signaling, we were interested in examining the effects of BITC and death receptor ligand TRAIL together on pancreatic cancer cell death. Interestingly, BITC augments TRAIL-induced apoptosis in both metastatic and adenocarcinoma cells. Moreover, we report for the first time that the sensitivity of metastatic pancreatic cancer cells to this isothiocyanate might be due to down-modulation of the proangiogenic molecule small GTPase Rac1 and caspase-3 substrate RasGAP, a regulator of Rho GTPase family.

Inhibition of tubule-cell proliferation to prevent cyst formation: a new avenue to treat ADPKD?

Tubule-cell hyperproliferation precedes cyst development in autosomal dominant polycystic kidney disease (ADPKD). Parker et al. report that insulin-like growth factor-1 stimulates ADPKD cell proliferation by activating Ras and Raf; inhibition of Ras or Raf abolished this effect. Inhibiting tubule-cell proliferation could halt cyst formation and prolong survival of functional tubules, offering a new treatment for ADPKD patients.

Hyperproliferation of PKD1 cystic cells is induced by insulin-like growth factor-1 activation of the Ras/Raf signalling system.

Autosomal dominant polycystic kidney disease (ADPKD) largely results from mutations in the PKD1 gene leading to hyperproliferation of renal tubular epithelial cells and consequent cyst formation. Rodent models of PKD suggest that the multifunctional hormone insulin-like growth factor-1 (IGF-1) could play a pathogenic role in renal cyst formation. In order to test this possibility, conditionally immortalized renal epithelial cells were prepared from normal individuals and from ADPKD patients with known germline mutations in PKD1. All patient cell lines had a decreased or absence of polycystin-1 but not polycystin-2. These cells had an increased sensitivity to IGF-1 and to cyclic AMP, which required phosphatidylinositol-3 (PI3)-kinase and the mitogen-activated protein kinase, extracellular signal-regulated protein kinase (ERK) for enhanced growth. Inhibition of Ras or Raf abolished the stimulated cell proliferation. Our results suggest that haploinsufficiency of polycystin-1 lowers the activation threshold of the Ras/Raf signalling system leading to growth factor-induced hyperproliferation. Inhibition of Ras or Raf activity may be a therapeutic option for decreasing tubular cell proliferation in ADPKD.

PI3K-dependent lysosome exocytosis in nitric oxide-preconditioned hepatocytes.

We investigated the signal mediators and the cellular events involved in the nitric oxide (NO)-induced hepatocyte resistance to oxygen deprivation in isolated hepatocytes treated with the NO donor (Z)-1-(N-methyl-N-[6-(N-methylammoniohexyl)amino])diazen-1-ium-1,2-diolate (NOC-9). NOC-9 greatly induced PI3K activation, as tested by phosphorylation of PKB/Akt. This effect was prevented by either 1H-(1,2,4)-oxadiazolo-(4,3)-quinoxalin-1-one, an inhibitor of the soluble guanylate cyclase (sGC), or KT5823, an inhibitor of cGMP-dependent kinase (cGK), as well as by farnesyl protein transferase inhibitor, which blocks the function of Ras GTPase. Bafilomycin A, an inhibitor of the lysosome-type vacuolar H+-ATPase, cytochalasin D, which disrupts the cytoskeleton-dependent organelle traffic, and wortmannin, which inhibits the PI3K-dependent traffic of lysosomes, all abolished the NOC-9-induced hepatocyte protection. The treatment with NOC-9 was associated with the PI3K-dependent peripheral translocation and fusion with the plasma membrane of lysosomes and the appearance at the cell surface of the vacuolar H+-ATPase. Inhibition of sGC, cGK, and Ras, as well as the inhibition of PI3K by wortmannin, prevented the exocytosis of lysosomes and concomitantly abolished the protective effect of NOC-9 on hypoxia-induced pHi and [Na+]i alterations and cell death. These data indicate that NO increases hepatocyte resistance to hypoxic injury by activating a pathway involving Ras, sGC, and cGK that determines PI3K-dependent exocytosis of lysosomes.

HMG-CoA reductase inhibitors (statins) as anticancer drugs (review).

Apart from their lipid lowering activity, HMG-CoA reductase inhibitors (statins) impair numerous cellular functions associated with metastasis, e.g. gene expression, angiogenesis, cell adhesion, cell motility and invasiveness. Furthermore, statins have impact on apoptotic cell death and modulate cellular susceptibility to cell killing by anticancer drugs and ionizing radiation. Part of the effects provoked by statins are due to the inhibition of the prenylation of low molecular weight GTPases, in particular Ras and Rho, which play key roles in signaling evoked by stimulation of cell surface receptors. C-terminal lipid modification of Ras/Rho GTPases is essential for their correct intracellular localization and function. By depletion of the cellular pool of isoprene precursor molecules, statins reduce the level of membrane-bound active Ras/Rho proteins, thereby impairing corresponding functions. Since broad clinical experience already exists for statins, their incorporation into established tumor-therapeutic regimens would be realizable in a rather short period of time. Here, data available at present arguing for the usefulness of statins in anticancer therapy are summarized and discussed.

Galpha and Gbeta gamma require distinct Src-dependent pathways to activate Rap1 and Ras.

The Src tyrosine kinase is necessary for activation of extracellular signal-regulated kinases (ERKs) by the beta-adrenergic receptor agonist, isoproterenol. In this study, we examined the role of Src in the stimulation of two small G proteins, Ras and Rap1, that have been implicated in isoproterenol's signaling to ERKs. We demonstrate that the activation of isoproterenol of both Rap1 and Ras requires Src. In HEK293 cells, isoproterenol activates Rap1, stimulates Rap1 association with B-Raf, and activates ERKs, all via PKA. In contrast, the activation by isoproterenol of Ras requires Gbetagamma subunits, is independent of PKA, and results in the phosphoinositol 3-kinase-dependent activation of AKT. Interestingly, beta-adrenergic stimulation of both Rap1 and ERKs, but not Ras and AKT, can be blocked by a Src mutant (SrcS17A) that is incapable of being phosphorylated and activated by PKA. Furthermore, a Src mutant (SrcS17D), which mimics PKA phosphorylation at serine 17, stimulates Rap1 activation, Rap1/B-Raf association, and ERK activation but does not stimulate Ras or AKT. These data suggest that Rap1 activation, but not that of Ras, is mediated through the direct phosphorylation of Src by PKA. We propose that the beta(2)-adrenergic receptor activates Src via two independent mechanisms to mediate distinct signaling pathways, one through Galpha(s) to Rap1 and ERKs and the other through Gbetagamma to Ras and AKT.