Glial Cell Adhesion Molecule (GlialCAM) Determines Proliferative versus Invasive Cell States in Glioblastoma.

The malignant brain cancer glioblastoma (GBM) contains groups of highly invasive cells that drive tumor progression as well as recurrence after surgery and chemotherapy. The molecular mechanisms that enable these GBM cells to exit the primary mass and disperse throughout the brain remain largely unknown. Here we report using human tumor specimens and primary spheroids from male and female patients that glial cell adhesion molecule (GlialCAM), which has normal roles in brain astrocytes and is mutated in the developmental brain disorder megalencephalic leukoencephalopathy with subcortical cysts (MLC), is differentially expressed in subpopulations of GBM cells. High levels of GlialCAM promote cell-cell adhesion and a proliferative GBM cell state in the tumor core. In contrast, GBM cells with low levels of GlialCAM display diminished proliferation and enhanced invasion into the surrounding brain parenchyma. RNAi-mediated inhibition of GlialCAM expression leads to activation of proinvasive extracellular matrix adhesion and signaling pathways. Profiling GlialCAM-regulated genes combined with cross-referencing to single-cell transcriptomic datasets validates functional links among GlialCAM, Mlc1, and aquaporin-4 in the invasive cell state. Collectively, these results reveal an important adhesion and signaling axis comprised of GlialCAM and associated proteins including Mlc1 and aquaporin-4 that is critical for control of GBM cell proliferation and invasion status in the brain cancer microenvironment.SIGNIFICANCE STATEMENT Glioblastoma (GBM) contains heterogeneous populations of cells that coordinately drive proliferation and invasion. We have discovered that glial cell adhesion molecule (GlialCAM)/hepatocyte cell adhesion molecule (HepaCAM) is highly expressed in proliferative GBM cells within the tumor core. In contrast, GBM cells with low levels of GlialCAM robustly invade into surrounding brain tissue along blood vessels and white matter. Quantitative RNA sequencing identifies various GlialCAM-regulated genes with functions in cell-cell adhesion and signaling. These data reveal that GlialCAM and associated signaling partners, including Mlc1 and aquaporin-4, are key factors that determine proliferative and invasive cell states in GBM.

Combinatorial phosphorylation modulates the structure and function of the G protein γ subunit in yeast.

Intrinsically disordered regions (IDRs) in proteins are often targets of combinatorial posttranslational modifications, which serve to regulate protein structure and function. Emerging evidence suggests that the N-terminal tails of G protein γ subunits, which are essential components of heterotrimeric G proteins, are intrinsically disordered, phosphorylation-dependent determinants of G protein signaling. Here, we found that the yeast Gγ subunit Ste18 underwent combinatorial, multisite phosphorylation events within its N-terminal IDR. G protein-coupled receptor (GPCR) activation and osmotic stress induced phosphorylation at Ser7, whereas glucose and acid stress induced phosphorylation at Ser3, which was a quantitative indicator of intracellular pH. Each site was phosphorylated by a distinct set of kinases, and phosphorylation of one site affected phosphorylation of the other, as determined through exposure to serial stimuli and through phosphosite mutagenesis. Last, we showed that phosphorylation resulted in changes in IDR structure and that different combinations of phosphorylation events modulated the activation rate and amplitude of the downstream mitogen-activated protein kinase Fus3. These data place Gγ subunits among intrinsically disordered proteins that undergo combinatorial posttranslational modifications that govern signaling pathway output.

CD40 in Endothelial Cells Restricts Neural Tissue Invasion by Toxoplasma gondii.

Little is known about whether pathogen invasion of neural tissue is affected by immune-based mechanisms in endothelial cells. We examined the effects of endothelial cell CD40 on Toxoplasma gondii invasion of the retina and brain, organs seeded hematogenously. T. gondii circulates in the bloodstream within infected leukocytes (including monocytes and dendritic cells) and as extracellular tachyzoites. After T. gondii infection, mice that expressed CD40 restricted to endothelial cells exhibited diminished parasite loads and histopathology in the retina and brain. These mice also had lower parasite loads in the retina and brain after intravenous (i.v.) injection of infected monocytes or dendritic cells. The protective effect of endothelial cell CD40 was not explained by changes in cellular or humoral immunity, reduced transmigration of leukocytes into neural tissue, or reduced invasion by extracellular parasites. Circulating T. gondii-infected leukocytes (dendritic cells used as a model) led to infection of neural endothelial cells. The number of foci of infection in these cells were reduced if endothelial cells expressed CD40. Infected dendritic cells and macrophages expressed membrane-associated inducible Hsp70. Infected leukocytes triggered Hsp70-dependent autophagy in CD40+ endothelial cells and anti-T. gondii activity dependent on ULK1 and beclin 1. Reduced parasite load in the retina and brain not only required CD40 expression in endothelial cells but was also dependent on beclin 1 and the expression of inducible Hsp70 in dendritic cells. These studies suggest that during endothelial cell-leukocyte interaction, CD40 restricts T. gondii invasion of neural tissue through a mechanism that appears mediated by endothelial cell anti-parasitic activity stimulated by Hsp70.

Stalk-dependent and Stalk-independent Signaling by the Adhesion G Protein-coupled Receptors GPR56 (ADGRG1) and BAI1 (ADGRB1).

The adhesion G protein-coupled receptors (aGPCRs) are a large yet poorly understood family of seven-transmembrane proteins. A defining characteristic of the aGPCR family is the conserved GAIN domain, which has autoproteolytic activity and can cleave the receptors near the first transmembrane domain. Several aGPCRs, including ADGRB1 (BAI1 or B1) and ADGRG1 (GPR56 or G1), have been found to exhibit significantly increased constitutive activity when truncated to mimic GAIN domain cleavage (ΔNT). Recent reports have suggested that the new N-terminal stalk, which is revealed by GAIN domain cleavage, can directly activate aGPCRs as a tethered agonist. We tested this hypothesis in studies on two distinct aGPCRs, B1 and G1, by engineering mutant receptors lacking the entire NT including the stalk (B1- and G1-SL, with "SL" indicating "stalkless"). These receptors were evaluated in a battery of signaling assays and compared with full-length wild-type and cleavage-mimicking (ΔNT) forms of the two receptors. We found that B1-SL, in multiple assays, exhibited robust signaling activity, suggesting that the membrane-proximal stalk region is not necessary for its activation. For G1, however, the results were mixed, with the SL mutant exhibiting robust activity in several signaling assays (including TGFα shedding, activation of NFAT luciferase, and ß-arrestin recruitment) but reduced activity relative to ΔNT in a distinct assay (activation of SRF luciferase). These data support a model in which the activation of certain pathways downstream of aGPCRs is stalk-dependent, whereas signaling to other pathways is stalk-independent.

Clinical pharmacokinetics of tacrolimus in Iranian liver transplant recipients.

Tacrolimus, a cornerstone of immunosuppressive therapy in solid organ transplantation, has a narrow therapeutic range with considerable inter-individual and intra-individual pharmacokinetic variability. To date, there is no information on the pharmacokinetics of tacrolimus in Iranian liver transplant recipients. This study was designed to determine pharmacokinetic properties of orally administered tacrolimus in Iranian adult liver transplant recipients. Tacrolimus doses and steady state whole blood trough concentrations as well as patient demographic and clinical data were obtained retrospectively using the 30 included patients' medical records. Pharmacokinetic parameters were estimated by using a nonlinear mixed effect model program (Monolix version 3.1). Absorption rate constant was fixed at two hours(-1). Drug apparent clearance (CL/F), apparent volume of distribution (Vd/F), and elimination half life (t½ß) were calculated. The administered dose of tacrolimus to the patients ranged from 0.02 to 0.14 mg/Kg/day. Tacrolimus blood trough concentrations varied widely within the range of 1.8 to 30 ng/mL. The mean values of CL/F, Vd/F, and t½ß were found to be 9.3 ± 0.96 L/h, 101 ± 29 L, and 7.5 hours, respectively. The pharmacokinetics of tacrolimus was highly variable among our patients. CL/F, Vd/F, and t½ß of tacrolimus in this study were comparable to reported values from Italian heart transplant patients but somewhat different from reported ones from other solid organ transplant populations.

A review of the potential protective effects of pentoxifylline against drug-induced nephrotoxicity.

PURPOSE: Drug-induced nephrotoxicity is one of the most common side effects of medications and accounts for about 20 % of hospital admissions for acute kidney injury (AKI). Some possible pharmacologic mechanisms of pentoxifylline (PTX) that suggest it as a candidate to ameliorate AKI include interaction at the level of the adenosine receptors, increase in erythrocyte deformability, stimulation of vasodilatory prostaglandins production and prevention of vascular congestion, and suppression of tumor necrosis factor alpha (TNF-α) and apoptosis. This manuscript reviews all clinical and animal studies on the use of PTX as a renoprotective agent against a number of nephrotoxic drugs. METHODS: Data were collected by searching MEDLINE, PubMed, Scopus, Cochrane central register of controlled trials, and Cochrane database systematic reviews. Key words used as search terms were pentoxifylline, nephroprotective, renoprotective, drug-induced renal diseases, drug-induced nephrotoxicity, drug-induced renal toxicity, and drug-induced nephropathy. This search was performed without time limitation. RESULTS AND CONCLUSION: Most greatest number of studies and human clinical trials on the renoprotective effect of PTX against drug-induced nephrotoxicity involves cyclosporine (Cyc). It seems that despite encouraging results from animal studies, there is insufficient evidence to support the renoprotective effect of PTX against Cyc-induced nephrotoxicity in humans. Although some available animal studies show protective effects of PTX against renal toxicity of some antimicrobial and cytotoxic agents, designing clinical trials to approve these nephroprotective effects requires prior confirmation of no reducing antimicrobial or antitumor action of these medications by PTX.

Clinical pharmacokinetics of oral versus sublingual administration of tacrolimus in adult liver transplant recipients.

OBJECTIVES: Oral tacrolimus administration is the common route of drug delivery. Recent studies suggest sublingual administration of tacrolimus as an alternative route may produce comparable drug trough levels with similar or even lower doses than the oral route, especially in lung transplant recipients; however, most of this research does not encompass intraindividual variations compared between the 2 routes. This study sought to compare the bioavailability and blood trough concentrations of orally and sublingually administered tacrolimus in adult liver transplant recipients by considering intraindividual variations in tacrolimus pharmacokinetics properties. MATERIALS AND METHODS: Six adult liver transplant recipients received their tacrolimus either orally or sublingually within 2 consecutive days. Blood samples to determine tacrolimus concentrations were gathered at 0, 0.5, 1, 2, 4, 6, and 12 hours after oral and sublingual tacrolimus administration. Mean data values were used to calculate the pharmacokinetics parameters via the feathering or residual method, using the 1-compartment, first-order elimination pharmacokinetics model. Compared pharmacokinetics parameters included drug bioavailability, maximum blood concentration (C(max)), time to reach maximum blood level (T(max)), and trough blood concentrations. RESULTS: Trough whole blood levels, area under the concentration-time curve, T(max), and C(max) after oral and sublingual administration of tacrolimus were not significantly different (10.4 ± 7.4 vs 11.2 ± 11.3 ng/mL for trough blood concentration, 181.5 ± 114.1 vs 160.8 ± 115.9 ng.h/mL for AUC, 1.9 ± 1.2 vs 1.4 ± 0.7 h for T(max), and 19.9 ± 10.8 vs 17.2 ± 11.7 ng/mL for C(max)). A double-peak phenomenon was observed in some concentration-time profiles. CONCLUSIONS: Sublingual tacrolimus administration does provide therapeutic drug concentrations in adult liver transplant recipients. Therefore, sublingual tacrolimus may confidently be considered as an alternative route to oral administration in patients who are unable to swallow their drugs.