Two membrane glycoproteins acting as energy‐dependent efflux pumps, mdr‐encoded P‐glycoprotein (P‐gp) and the more recently described multidrug resistance‐associated protein (MRP), are known to confer cellular resistance to many cytotoxic hydrophobic drugs. In the brain, P‐gp has been shown to be expressed specifically in the capillary endothelial cells forming the blood‐brain barrier, but localization of MRP has not been well characterized yet. Using RT‐PCR and immunoblot analysis, we have compared the expression of P‐gp and Mrp1 in homogenates, isolated capillaries, primary cultured endothelial cells, and RBE4 immortalized endothelial cells from rat brain. Whereas the mdr1a P‐gp‐encoding mRNA was specifically detected in brain microvessels and mdr1b mRNA in brain parenchyma, mrp1 mRNA was present both in microvessels and in parenchyma. However, Mrp1 was weakly expressed in microvessels. Mrp1 expression was higher in brain parenchyma, as well as in primary cultured brain endothelial cells and in immortalized RBE4 cells. This Mrp1 overexpression in cultured brain endothelial cells was less pronounced when the cells were cocultured with astrocytes. A low Mrp activity could be demonstrated in the endothelial cell primary monocultures, because the intracellular [3H]vincristine accumulation was increased by several MRP modulators. No Mrp activity was found in the cocultures or in the RBE4 cells. We suggest that in rat brain, Mrp1, unlike P‐gp, is not predominantly expressed in the blood‐brain barrier endothelial cells and that Mrp1 and the mdr1b P‐gp isoform may be present in other cerebral cells.

Insulin and insulin-like growth factors belong to a family of polypeptides involved in essential physiological processes. Placentin, a new member of the insulin family, was recently identified as a 139-amino acid open reading frame from a cDNA clone isolated from a subtracted library of first trimester human placenta. Tris/ Tricine/SDS-polyacrylamide gel electrophoresis and immunoblot analyses of histidine-tagged recombinant placentin indicate that it is composed of two peptide chains of apparent molecular masses of 4 and 13 kDa. Conditioned media produced by recombinant expression of placentin cDNA in the placental 3AsubE cell line were assayed for biological activity and found to stimulate tyrosine phosphorylation and DNA synthesis. While these effects closely mimicked those of insulin, they were not mediated by the insulin receptor as shown by the lack of tyrosine phosphorylation of this receptor upon placentin treatment. Moreover, in cytotrophoblast primary culture, production of chorionic gonadotropin, a marker of trophoblast differentiation, was increased upon treatment with placentin-conditioned media, while unaffected by insulin. These results suggest that placentin might participate in the cellular proliferation and/or differentiation processes during placental development.Insulin and insulin-like growth factors belong to a family of polypeptides essential for proper regulation of physiological processes such as energy metabolism, cell proliferation, development, and differentiation (1, 2). These polypeptides exert their effects through membrane receptors belonging to the superfamily of polypeptide growth factor receptor tyrosine kinases and their oncogenic analogs (3-5). The intracellular signal transduction pathway for these receptors is characterized by a tyrosine kinase activity that initiates a chain of phosphorylation-related events. The insulin family consists of insulin, IGF 1 I and II, relaxin (6), and LEY I-L (7). The consensus elements defining their relationship are the positions of six half-cystine residues essential for proper tertiary structure formation (8). While receptors mediating the effects of relaxin and LEY I-L have not yet been described, insulin and IGF I act through distinct tyrosine kinase subclass II receptors (3), and the actions of IGF II appear to be mediated through several receptors, including those for insulin and IGF I (1).

No abstract

A massive activation of T cells takes place during the early stages of a Trypanosoma cruzi infection in mice. We present data indicating that substantial amounts of interleukin 2 (IL-2) are secreted and IL-2 receptors are expressed during the period of increased proliferation (4-7 days post infection). Both concanavalin A-induced proliferation and IL-2 production are markedly decreased later in the acute infection (around 3 weeks post infection). This proliferation cannot be restored by externally added IL-2. Simultaneously, there is a drastic reduction in the number of both high- and low-affinity IL-2 receptors. The reduction is not attributable to the elimination of a particular T-cell population. In vivo administration of recombinant IL-2 failed to improve resistance to T. cruzi parasites as measured by parasitaemia and mortality.