Plasmodium falciparum inhibitor-3 homolog increases protein phosphatase type 1 activity and is essential for parasitic survival.

Growing evidence indicates that the protein regulators governing protein phosphatase 1 (PP1) activity have crucial functions because their deletion drastically affects cell growth and division. PP1 has been found to be essential in Plasmodium falciparum, but little is known about its regulators. In this study, we have identified a homolog of Inhibitor-3 of PP1, named PfI3. NMR analysis shows that PfI3 belongs to the disordered protein family. High affinity interaction of PfI3 and PfPP1 is demonstrated in vitro using several methods, with an apparent dissociation constant K(D) of 100 nm. We further show that the conserved (41)KVVRW(45) motif is crucial for this interaction as the replacement of the Trp(45) by an Ala(45) severely decreases the binding to PfPP1. Surprisingly, PfI3 was unable to rescue a yeast strain deficient in I3 (Ypi1). This lack of functional orthology was supported as functional assays in vitro have revealed that PfI3, unlike yeast I3 and human I3, increases PfPP1 activity. Reverse genetic approaches suggest an essential role of PfI3 in the growth and/or survival of blood stage parasites because attempts to obtain knock-out parasites were unsuccessful, although the locus of PfI3 is accessible. The main localization of a GFP-tagged PfI3 in the nucleus of all blood stage parasites is compatible with a regulatory role of PfI3 on the activity of nuclear PfPP1.

Colonic inflammation in mice is improved by cigarette smoke through iNKT cells recruitment.

Cigarette smoke (CS) protects against intestinal inflammation during ulcerative colitis. Immunoregulatory mechanisms sustaining this effect remain unknown. The aim of this study was to assess the effects of CS on experimental colitis and to characterize the intestinal inflammatory response at the cellular and molecular levels. Using the InExpose® System, a smoking device accurately reproducing human smoking habit, we pre-exposed C57BL/6 mice for 2 weeks to CS, and then we induced colitis by administration of dextran sodium sulfate (DSS). This system allowed us to demonstrate that CS exposure improved colonic inflammation (significant decrease in clinical score, body weight loss and weight/length colonic ratio). This improvement was associated with a significant decrease in colonic proinflammatory Th1/Th17 cytokine expression, as compared to unexposed mice (TNF (p=0.0169), IFNγ (p<0.0001), and IL-17 (p=0.0008)). Smoke exposure also induced an increased expression of IL-10 mRNA (p=0.0035) and a marked recruitment of iNKT (invariant Natural Killer T; CD45+ TCRß+ CD1d tetramer+) cells in the colon of DSS-untreated mice. Demonstration of the role of iNKT cells in CS-dependent colitis improvement was performed using two different strains of NKT cells deficient mice. Indeed, in Jα18KO and CD1dKO animals, CS exposure failed to induce significant regulation of DSS-induced colitis both at the clinical and molecular levels. Thus, our study demonstrates that iNKT cells are pivotal actors in the CS-dependent protection of the colon. These results highlight the role of intestinal iNKT lymphocytes and their responsiveness to environmental stimuli. Targeting iNKT cells would represent a new therapeutic way for inflammatory bowel diseases.