SAMHD1-induced endosomal FAK signaling promotes human renal clear cell carcinoma metastasis by activating Rac1-mediated lamellipodia protrusion.

Human sterile α motif and HD domain-containing protein 1 (SAMHD1) has deoxyribonucleoside triphosphohydrolase (dNTPase) activity that allows it to defend against human immunodeficiency virus type I (HIV-1) infections and regulate the cell cycle. Although SAMHD1 mutations have been identified in various cancer types, their role in cancer is unclear. Here, we aimed to investigate the oncogenic role of SAMHD1 in human clear cell renal cell carcinoma (ccRCC), particularly as a core molecule promoting cancer cell migration. We found that SAMHD1 participated in endocytosis and lamellipodia formation. Mechanistically, SAMHD1 contributed to the formation of the endosomal complex by binding to cortactin. Thereafter, SAMHD1-stimulated endosomal focal adhesion kinase (FAK) signaling activated Rac1, which promoted lamellipodia formation on the plasma membrane and enhanced the motility of ccRCC cells. Finally, we observed a strong correlation between SAMHD1 expression and the activation of FAK and cortactin in tumor tissues obtained from patients with ccRCC. In brief, these findings reveal that SAMHD1 is an oncogene that plays a pivotal role in ccRCC cell migration through the endosomal FAK-Rac1 signaling pathway.

Ninjurin1 deficiency aggravates colitis development by promoting M1 macrophage polarization and inducing microbial imbalance.

Disruption of colonic homeostasis caused by aberrant M1/M2 macrophage polarization and dysbiosis contributes to inflammatory bowel disease (IBD) pathogenesis. However, the molecular factors mediating colonic homeostasis are not well characterized. Here, we found that Ninjurin1 (Ninj1) limits colon inflammation by regulating macrophage polarization and microbiota composition under homeostatic conditions and during colitis development. Ninj1 deletion in mice induced hypersusceptibility to colitis, with increased prevalence of colitogenic Prevotellaceae strains and decreased immunoregulatory Lachnospiraceae strains. Upon co-housing (CoH) with WT mice, Ninj1-/- mice showed increased Lachnospiraceae and decreased Prevotellaceae abundance, with subsequent improvement of colitis. Under homeostatic conditions, M1 macrophage frequency was higher in the Ninj1-/- mouse colons than wild-type (WT) mouse colons, which may contribute to increased basal colonic inflammation and microbial imbalance. Following colitis induction, Ninj1 expression was increased in macrophages; meanwhile Ninj1-/- mice showed severe colitis development and impaired recovery, associated with decreased M2 macrophages and escalated microbial imbalance. In vitro, Ninj1 knockdown in mouse and human macrophages activated M1 polarization and restricted M2 polarization. Finally, the transfer of WT macrophages ameliorated severe colitis in Ninj1-/- mice. These findings suggest that Ninj1 mediates colonic homeostasis by modulating M1/M2 macrophage balance and preventing extensive dysbiosis, with implications for IBD prevention and therapy.

Dabigatran reduces endothelial permeability through inhibition of thrombin-induced cytoskeleton reorganization.

Dabigatran etexilate (DE), a new oral anti-coagulant, is a direct thrombin inhibitor. Clinical trials showed the favorable benefit-to-risk profile of DE compared to warfarin for the prevention of ischemic stroke in patients with atrial fibrillation. Remarkably, patients treated with dabigatran showed reduced rates of intracerebral hemorrhage compared to warfarin. As the breakdown of endothelial barrier integrity is associated with hemorrhagic events and as thrombin increases endothelial permeability, we hypothesized that dabigatran preserves the endothelial barrier by inhibiting thrombin-induced permeability. We assessed leakage of fluorescein isothiocyanate (FITC)-dextran through the endothelial monolayer and measured trans-endothelial electrical resistance of the endothelial monolayer after treatment of thrombin or thrombin pre-incubated with dabigatran. Thrombin increased the permeability of endothelial cells. Dabigatran effectively blocked the ability of thrombin to increase permeability. Dabigatran inhibited the formation of actin stress fibers induced by thrombin and inhibited consequent destabilization of junctional protein complexes and intercellular gap formation. The interaction of thrombin with protease activated receptor-1 activates the Rho A guanosine triphosphate (GTP)ase-myosin light chain (MLC) phosphorylation signaling axis, leading to actin cytoskeleton changes. This signaling pathway was effectively inhibited by dabigatran in endothelial cells. Consistently, the number of phosphorylated MLC-positive cells was significantly decreased in ischemic tissue of rat brains. These results indicate dabigatran blocks the ability of thrombin to induce vascular permeability and the resulting underlying signaling cascade in endothelial cells. Our findings provide evidence that dabigatran may confer a lower risk of intracerebral hemorrhage by preserving endothelial barrier integrity.

SAMHD1 acetylation enhances its deoxynucleotide triphosphohydrolase activity and promotes cancer cell proliferation.

SAM domain and HD domain containing protein 1 (SAMHD1) is a deoxynucleotide triphosphohydrolase (dNTPase) that inhibits retroviruses by depleting intracellular deoxynucleotide triphosphates (dNTPs) in non-cycling myeloid cells. Although SAMHD1 is expressed ubiquitously throughout the human body, the molecular mechanisms regulating its enzymatic activity and function in non-immune cells are relatively unexplored. Here, we demonstrate that the dNTPase activity of SAMHD1 is regulated by acetylation, which promotes cell cycle progression in cancer cells. SAMHD1 is acetylated at residue lysine 405 (K405) in vitro and in vivo by an acetylatransferase, arrest defective protein 1 (ARD1). Acetylated SAMHD1 wildtype proteins have enhanced dNTPase activity in vitro, whereas non-acetylated arginine substituted mutants (K405R) do not. K405R mutant expressing cancer cells have reduced G1/S transition and slower proliferation compared to wildtype. SAMHD1 acetylation levels are strongest during the G1 phase, indicating a role during G1 phase. Collectively, these findings suggest that SAMHD1 acetylation enhances its dNTPase activity and promotes cancer cell proliferation. Therefore, SAMHD1 acetylation may be a potent therapeutic target for cancer treatment.

Hemorrhagic Transformation After Large Cerebral Infarction in Rats Pretreated With Dabigatran or Warfarin.

BACKGROUND AND PURPOSE: It is uncertain whether hemorrhagic transformation (HT) after large cerebral infarction is less frequent in dabigatran users than warfarin users. We compared the occurrence of HT after large cerebral infarction among rats pretreated with dabigatran, warfarin, or placebo. METHODS: This was a triple-blind, randomized, and placebo-controlled experiment. After treatment with warfarin (0.2 mg/kg), dabigatran (20 mg/kg), or saline for 7 days, Wistar rats were subjected to transient middle cerebral artery occlusion. As the primary outcome, HT was determined by gradient-recalled echo imaging. For the secondary outcome, intracranial hemorrhage was assessed via gradient-recalled echo imaging in surviving rats and via autopsy for dead rats. RESULTS: Of 62 rats, there were 33 deaths (53.2%, 17 technical reasons). Of the intention-to-treat population, 33 rats underwent brain imaging. HT was less frequent in the dabigatran group than the warfarin group (placebo 2/14 [14%], dabigatran 0/10 [0%], and warfarin 9/9 [100%]; dabigatran versus warfarin; P<0.001). In all 62 rats, compared with the placebo (2/14 [14.3%]), the incidence of intracranial hemorrhage was significantly higher in the warfarin group (19/29 [65.5%]; P=0.003), but not in the dabigatran group (6/19 [31.6%]; P=0.420). Mortality was significantly higher in the warfarin group than the dabigatran group (79.3% versus 47.4%; P=0.022), but not related to the hemorrhage frequency. CONCLUSIONS: The risk of HT after a large cerebral infarction was significantly increased in rats pretreated with warfarin than those with dabigatran. However, the results here may not have an exact clinical translation.

ARD1-mediated aurora kinase A acetylation promotes cell proliferation and migration.

Aurora kinase A (AuA) is a prerequisite for centrosome maturation, separation, and mitotic spindle assembly, thus, it is essential for cell cycle regulation. Overexpression of AuA is implicated in poor prognosis of many types of cancer. However, the regulatory mechanisms underlying the functions of AuA are still not fully understood. Here, we report that AuA colocalizes with arrest defective protein 1 (ARD1) acetyltransferase during cell division and cell migration. Additionally, AuA is acetylated by ARD1 at lysine residues at positions 75 and 125. The double mutations at K75/K125 abolished the kinase activity of AuA. Moreover, the double mutant AuA exhibited diminished ability to promote cell proliferation and cell migration. Mechanistic studies revealed that AuA acetylation at K75/K125 promoted cell proliferation via activation of cyclin E/CDK2 and cyclin B1. In addition, AuA acetylation stimulated cell migration by activating the p38/AKT/MMP-2 pathway. Our findings indicate that ARD1-mediated acetylation of AuA enhances cell proliferation and migration, and probably contributes to cancer development.

Fc-saxatilin suppresses hypoxia-induced vascular leakage by regulating endothelial occludin expression.

Vascular leakage due to compromised integrity of the endothelial barrier is closely associated with brain damage in several neurological disorders, including ischaemic stroke. Saxatilin, a snake venom disintegrin containing the Arg-Gly-Asp (RGD) motif, exerts thrombolytic and antiplatelet effects by interacting with multiple integrins on platelets. Integrin signalling is indispensable for regulation of endothelial permeability. Saxatilin may play a role in vascular leakage after ischaemia because it has high affinity for endothelial integrins. Here, we determined whether Fc-saxatilin, an Fc-fusion protein of saxatilin, could prevent vascular leakage under hypoxic or ischaemic conditions. In mouse brain microvascular endothelial cells, hypoxia increased the permeability to FITC-dextran, and this effect was attenuated by Fc-saxatilin treatment. Fc-saxatilin also blocked vascular leakage of Evans Blue in the ischaemic brain induced by middle cerebral artery occlusion in mice. Furthermore, the expression of occludin, a tight junction protein, was reduced by hypoxia in endothelial cells. This downregulation of occludin was attenuated by Fc-saxatilin treatment. We also determined the activity of matrix metalloproteinases (MMPs) 2 and 9 because they are implicated in the degradation of occludin and of the microvascular basal lamina. Hypoxia increased MMP-9 activity, and this increase was attenuated by Fc-saxatilin treatment. Fc-saxatilin specifically bound to integrin αvß3 of the endothelial cells and inhibited hypoxia-induced activation of FAK, a downstream signalling molecule in integrin-dependent signal transduction. Taken together, these results provide new insights into the mechanism via which Fc-saxatilin, as an integrin antagonist, prevents vascular leakage under ischemic conditions by regulating occludin expression in endothelial tight junctions.

Effects of Mesenchymal Stem Cell Treatment on the Expression of Matrix Metalloproteinases and Angiogenesis during Ischemic Stroke Recovery.

BACKGROUND: The efficacy of mesenchymal stem cell (MSC) transplantation in ischemic stroke might depend on the timing of administration. We investigated the optimal time point of MSC transplantation. After MSC treatment, we also investigated the expression of matrix metalloproteinases (MMPs), which play a role in vascular and tissue remodeling. METHODS: Human bone marrow-derived MSCs (2 × 10(6), passage 5) were administrated intravenously after permanent middle cerebral artery occlusion (MCAO) was induced in male Sprague-Dawley rats. First, we determined the time point of MSC transplantation that led to maximal neurological recovery at 1 h, 1 day, and 3 days after MCAO. Next, we measured activity of MMP-2 and MMP-9, neurological recovery, infarction volume, and vascular density after transplanting MSCs at the time that led to maximal neurological recovery. RESULTS: Among the MSC-transplanted rats, those of the MSC 1-hour group showed maximal recovery in the rotarod test (P = 0.023) and the Longa score (P = 0.018). MMP-2 activity at 1 day after MCAO in the MSC 1-hour group was significantly higher than that in the control group (P = 0.002), but MMP-9 activity was not distinct. The MSC 1-hour group also showed smaller infarction volume and higher vascular density than did the control group. CONCLUSIONS: In a permanent model of rodent MCAO, very early transplantation of human MSCs (1 h after MCAO) produced greater neurological recovery and decreased infraction volume. The elevation of MMP-2 activity and the increase in vascular density after MSC treatment suggest that MSCs might help promote angiogenesis and lead to neurological improvement during the recovery phase after ischemic stroke.