We report the molecular identification of a sialic acid-independent host–parasite interaction in the Plasmodium falciparum malaria parasite invasion of RBCs. Two nonglycosylated exofacial regions of human band 3 in the RBC membrane were identified as a crucial host receptor binding the C-terminal processing products of merozoite surface protein 1 (MSP1). Peptides derived from the receptor region of band 3 inhibited the invasion of RBCs by P. falciparum. A major segment of the band 3 receptor (5ABC) bound to native MSP142 and blocked the interaction of native MSP142 with intact RBCs in vitro. Recombinant MSP119 (the C-terminal domain of MSP142) bound to 5ABC as well as RBCs. The binding of both native MSP142 and recombinant MSP119 was not affected by the neuraminidase treatment of RBCs, but sensitive to chymotrypsin treatment. In addition, recombinant MSP138 showed similar interactions with the band 3 receptor and RBCs, although the interaction was relatively weak. These findings suggest that the chymotrypsin-sensitive MSP1–band 3 interaction plays a role in a sialic acid-independent invasion pathway and reveal the function of MSP1 in the Plasmodium invasion of RBCs

In Plasmodium falciparum malaria, erythrocyte invasion by circulating merozoites may occur via two distinct pathways involving either a sialic acid-dependent or -independent mechanism. Earlier, we identified two nonglycosylated exofacial regions of erythrocyte band 3 termed 5ABC and 6A as an important host receptor in the sialic acid-independent invasion pathway. 5ABC, a major segment of this receptor, interacts with the 42-kDa processing product of merozoite surface protein 1 (MSP1 42 ) through its 19-kDa C-terminal domain. Here, we show that two regions of merozoite surface protein 9 (MSP9), also known as acidic basic repeat antigen, interact directly with 5ABC during erythrocyte invasion by P. falciparum. Native MSP9 as well as recombinant polypeptides derived from two regions of MSP9 (MSP9/⌬1 and MSP9/⌬2) interacted with both 5ABC and intact erythrocytes. Soluble 5ABC added to the assay mixture drastically diminished the binding of MSP9 to erythrocytes. Recombinant MSP9/⌬1 and MSP9/⌬2 present in the culture medium blocked P. falciparum reinvasion into erythrocytes in vitro. Native MSP9 and MSP1 42 , the two ligands binding to the 5ABC receptor, existed as a stable complex. Our results establish a novel concept wherein the merozoite exploits a specific complex of co-ligands on its surface to target a single erythrocyte receptor during invasion. This new paradigm poses a new challenge in the development of a vaccine for blood stage malaria.

ABSTRACT:Oral clearance of lamotrigine, an antiepileptic drug commonly used in pregnant women, is increased in pregnancy by unknown mechanisms. In this study, we show that 17␤-estradiol (E 2 ) upregulates expression of UDP glucuronosyltransferase (UGT) 1A4, the major enzyme responsible for elimination of lamotrigine. Endogenous mRNA expression levels of UGT1A4 in estrogen receptor (ER) ␣-negative HepG2 cells were induced 2.3-fold by E 2 treatment in the presence of ER␣ expression. E 2 enhanced transcriptional activity of UGT1A4 in a concentration-dependent manner in HepG2 cells when ER␣ was cotransfected. Induction of UGT1A4 transcriptional activity by E 2 was also observed in ER␣-positive MCF7 cells, which was abrogated by pretreatment with the antiestrogen fulvestrant (ICI 182,780). Analysis of UGT1A4 upstream regions using luciferase reporter assays identified a putative specificity protein-1 (Sp1) binding site (؊1906 to ؊1901 base pairs) that is critical for the induction of UGT1A4 transcriptional activity by E 2 . Deletion of the Sp1 binding sequence abolished the UGT1A4 up-regulation by E 2 , and Sp1 bound to the putative Sp1 binding site as determined by a electrophoretic mobility shift assay. Analysis of ER␣ domains using ER␣ mutants revealed that the activation function (AF) 1 and AF2 domains but not the DNA binding domain of ER␣ are required for UGT1A4 induction by E 2 in HepG2 cells. Finally, E 2 treatment increased lamotrigine glucuronidation in ER␣-transfected HepG2 cells. Together, our data indicate that up-regulation of UGT1A4 expression by E 2 is mediated by both ER␣ and Sp1 and is a potential mechanism contributing to the enhanced elimination of lamotrigine in pregnancy.Human pregnancy is accompanied by various physiological changes, including a dramatic increase in the production of female hormones, i.e., estrogen and progesterone. Blood levels of these hormones rise up to 100-fold by term (Cunningham, 2005). At this high concentration, female hormones manifest functions different from those of their conventional role as gonadal hormones. As a result, various clinical symptoms associated with pregnancy occur, e.g., delayed gastric emptying or intrahepatic cholestasis. Clinical evidence suggests that pregnancy also alters the rate and extent of hepatic drug metabolism (Anderson, 2005;Hodge and Tracy, 2007). Hepatic metabolism is a major elimination route of drugs, and altered drug metabolism during pregnancy can lead to increased drug toxicity or decreased drug efficacy, adversely affecting both the mother and fetus. However, mechanisms underlying altered hepatic drug metabolism in pregnancy are poorly understood.Lamotrigine is widely prescribed for seizure control in women with child-bearing potential (Sabers et al., 2004;EURAP Study Group, 2006). Of clinical importance to its use during pregnancy, the apparent clearance of lamotrigine increases by 50 to 90% in pregnancy, requiring dosage adjustment to prevent exacerbation of seizures (de Haan et al., 2004;Harden, 2007;Pennell et al., 2008). La...