The Necrotic Signal Induced by Mycophenolic Acid Overcomes Apoptosis-Resistance in Tumor Cells

The amount of inosine monophosphate dehydrogenase (IMPDH), a pivotal enzyme for the biosynthesis of the guanosine tri-phosphate (GTP), is frequently increased in tumor cells. The anti-viral agent ribavirin and the immunosuppressant mycophenolic acid (MPA) are potent inhibitors of IMPDH. We recently showed that IMPDH inhibition led to a necrotic signal requiring the activation of Cdc42.Herein, we strengthened the essential role played by this small GTPase in the necrotic signal by silencing Cdc42 and by the ectopic expression of a constitutive active mutant of Cdc42. Since resistance to apoptosis is an essential step for the tumorigenesis process, we next examined the effect of the MPA–mediated necrotic signal on different tumor cells demonstrating various mechanisms of resistance to apoptosis (Bcl2-, HSP70-, Lyn-, BCR-ABL–overexpressing cells). All tested cells remained sensitive to MPA–mediated necrotic signal. Furthermore, inhibition of IMPDH activity in Chronic Lymphocytic Leukemia cells was significantly more efficient at eliminating malignant cells than apoptotic inducers.These findings indicate that necrosis and apoptosis are split signals that share few if any common hub of signaling. In addition, the necrotic signaling pathway induced by depletion of the cellular amount of GTP/GDP would be of great interest to eliminate apoptotic-resistant tumor cells

Exposed Hydrophobic Residues in Human Immunodeficiency Virus Type 1 Vpr Helix-1 Are Important for Cell Cycle Arrest and Cell Death

The human immunodeficiency virus type 1 (HIV-1) accessory protein viral protein R (Vpr) is a major determinant for virus-induced G2/M cell cycle arrest and cytopathicity. Vpr is thought to perform these functions through the interaction with partner proteins. The NMR structure of Vpr revealed solvent exposed hydrophobic amino acids along helices 1 and 3 of Vpr, which could be putative protein binding domains. We previously showed that the hydrophobic patch along helix-3 was important for G2/M blockade and cytopathicity. Mutations of the exposed hydrophobic residues along helix-1 were found to reduce Vpr-induced cell cycle arrest and cell death as well. The levels of toxicity during virion delivery of Vpr correlated with G2/M arrest. Thus, the exposed hydrophobic amino acids in the amino-terminal helix-1 are important for the cell cycle arrest and cytopathicity functions of Vpr

Importance of the difference in surface pressures of the cell membrane in doxorubicin resistant cells that do not express Pgp and ABCG2

P-glycoprotein (Pgp) represents the archetypal mechanism of drug resistance. But Pgp alone cannot expel drugs. A small but growing body of works has demonstrated that the membrane biophysical properties are central to Pgp-mediated drug resistance. For example, a change in the membrane surface pressure is expected to support drug–Pgp interaction. An interesting aspect from these models is that under specific conditions, the membrane is predicted to take over Pgp concerning the mechanism of drug resistance especially when the surface pressure is high enough, at which point drugs remain physically blocked at the membrane level. However it remains to be determined experimentally whether the membrane itself could, on its own, affect drug entry into cells that have been selected by a low concentration of drug and that do not express transporters. We demonstrate here that in the case of the drug doxorubicin, alteration of the surface pressure of membrane leaflets drive drug resistance

The Naturally Processed CD95L Elicits a c-Yes/Calcium/PI3K-Driven Cell Migration Pathway

Patients affected by chronic inflammatory disorders display high amounts of soluble CD95L. This homotrimeric ligand arises from the cleavage by metalloproteases of its membrane-bound counterpart, a strong apoptotic inducer. In contrast, the naturally processed CD95L is viewed as an apoptotic antagonist competing with its membrane counterpart for binding to CD95. Recent reports pinpointed that activation of CD95 may attract myeloid and tumoral cells, which display resistance to the CD95-mediated apoptotic signal. However, all these studies were performed using chimeric CD95Ls (oligomerized forms), which behave as the membrane-bound ligand and not as the naturally processed CD95L. Herein, we examine the biological effects of the metalloprotease-cleaved CD95L on CD95-sensitive activated T-lymphocytes. We demonstrate that cleaved CD95L (cl-CD95L), found increased in sera of systemic lupus erythematosus (SLE) patients as compared to that of healthy individuals, promotes the formation of migrating pseudopods at the leading edge of which the death receptor CD95 is capped (confocal microscopy). Using different migration assays (wound healing/Boyden Chamber/endothelial transmigration), we uncover that cl-CD95L promotes cell migration through a c-yes/Ca2+/PI3K-driven signaling pathway, which relies on the formation of a CD95-containing complex designated the MISC for Motility-Inducing Signaling Complex. These findings revisit the role of the metalloprotease-cleaved CD95L and emphasize that the increase in cl-CD95L observed in patients affected by chronic inflammatory disorders may fuel the local or systemic tissue damage by promoting tissue-filtration of immune cells

Production of the Non-apoptotic Metalloprotease-Cleaved CD95L and Its Cytotoxic Recombinant Counterpart Designed Ig-CD95L

International audienceThe ligand of CD95, CD95L (also known as FasL or CD178), is a type II transmembrane protein that belongs to the Tumor Necrosis factor (TNF) family (Fig. 1a). This membrane-bound cytokine is mainly expressed at the surface of activated T lymphocytes and natural killer cells, where it is used as an apoptotic factor to eliminate infected and transformed cells (Strasser et al., Immunity 30:180-192, 2009)

Identification of a Novel Mutation in MAGT1 and Progressive Multifocal Leucoencephalopathy in a 58-Year-Old Man with XMEN Disease.

XMEN disease (X-linked immunodeficiency with Magnesium defect, Epstein-Barr virus infection and Neoplasia) is a novel primary immune deficiency caused by mutations in MAGT1 and characterised by chronic infection with Epstein-Barr virus (EBV), EBV-driven lymphoma, CD4 T-cell lymphopenia, and dysgammaglobulinemia [1]. Functional studies have demonstrated roles for magnesium as a second messenger in T-cell receptor signalling [1], and for NKG2D expression and consequently NK- and CD8 T-cell cytotoxicity [2]. 7 patients have been described in the literature; the oldest died at 45 years and was diagnosed posthumously [1-3]. We present the case of a 58-year-old Caucasian gentleman with a novel mutation in MAGT1 with the aim of adding to the phenotype of this newly described disease by detailing his clinical course over more than 20 years

Immunology and Microbiology Elevated CD1c þ Myeloid Dendritic Cell Proportions Associate With Clinical Activity and Predict Disease Reactivation in Noninfectious Uveitis

Citation: Chen P, Urzua CA, Knickelbein JE, et al. Elevated CD1c þ myeloid dendritic cell proportions associate with clinical activity and predict disease reactivation in noninfectious uveitis

Elevated CD1c(+) Myeloid Dendritic Cell Proportions Associate With Clinical Activity and Predict Disease Reactivation in Noninfectious Uveitis

PURPOSE. To test the association between elevated proportions of CD1c(+) myeloid dendritic cells (mDCs) and disease activation/reactivation in noninfectious uveitis. METHODS. Noninfectious uveitis patients (n = 89) and healthy controls (n = 111) were recruited. The proportion of CD1c(+) mDCs in the total dendritic cell (DC) population of peripheral blood was measured by flow cytometry (CD1c(+) mDCs gated on Lineage 1(+)HLADR(+) DCs). Disease activity was assessed per Standardization of Uveitis Nomenclature criteria. Uveitis reactivation was ascribed to clinically quiescent patients who developed reactivation of intraocular inflammation within 6 months. RESULTS. The proportions of CD1c(+) mDCs were increased in noninfectious uveitis patients, especially in active disease, compared to healthy controls. This CD1c(+) mDC elevation was not associated with underlying systemic diseases, anatomic locations of uveitis, medications, or demographic factors. Longitudinal data showed that the dynamics of CD1c(+) mDC levels were correlated with disease activity. The average proportion of CD1c(+) mDCs in active uveitis patients was 60% so we set this as the cutoff between high and low CD1c(+) mDC levels. Although 74% of quiescent patients had low proportions of CD1c(+) mDCs, 26% still had high proportions. Quiescent patients with high CD1c(+) mDC proportions showed increased risk of disease reactivation, compared to quiescent patients with low CD1c(+) mDC proportions. CONCLUSIONS. Increased proportions of CD1c(+) mDCs were associated with clinical activity, and quiescent patients with elevated CD1c(+) mDCs were more likely to undergo reactivation. This suggests that CD1c(+) mDC proportion may be a potential biomarker for assessing clinical activation and reactivation in noninfectious uveitis.National Institutes of Health (NIH)/National Eye Institute (NEI) NIH Medical Research Scholars Program Pan-American Ophthalmological Foundation/Retina Research Foundation CONICY