A dominant-negative mutant of raf blocks mitogen-activated protein kinase activation by growth factors and oncogenic p21ras

p74raf-1, a serine/threonine kinase, is structurally related to the protein kinase C (PKC) family and contains a cysteine motif in its N-terminal domain, which is essential for its regulation. It has been shown that p74raf-1 functions upstream of mitogen-activated protein (MAP) kinase kinase. We have constructed a p74raf-1 mutant (N delta raf) that only contains the N-terminal regulatory domain. When transiently expressed in COS-M6 cells, N delta raf efficiently blocked the activation of the MAP extracellular signal regulated kinase (ERK2), induced by either epidermal growth factor, phorbol ester, serum, or oncogenic p21ras. Similar constructs with the cysteine motifs from either PKC-alpha or diacylglycerol kinase did not inhibit activation of ERK2. Overexpression of full-length p74raf-1 rescued the inhibition of ERK2 by N delta raf in a stimulus dependent manner, indicating that N delta raf acts as a competitive inhibitor of wild-type p74raf-1. In contrast, overexpression of either PKC-alpha, -epsilon, or -zeta in N delta raf-containing cells could not rescue the inhibition of ERK2. We conclude that p74raf-1 is an essential mediator of epidermal growth factor- and phorbol ester-induced ERK2 activation and that the MAP kinase kinase activity of p74raf-1 cannot be substituted with either PKC-alpha, -epsilon or -zeta.     

Detection of multiple conformations of the E-domain of 5S rRNA from Escherichia coli in solution and in crystals by NMR spectroscopy

NMR spectroscopy of the E-domain fragment of Escherichia coli 5S rRNA indicates that this molecule exists in solution as either a stem-loop or as a duplex with two U-U base pairs in the bulge region. At temperatures below 27 degrees C, interconversion between the monomeric and dimeric forms in solution occurs on a time scale of weeks and allows the preparation of samples on which NMR structure determinations can be carried out on predominantly monomeric or dimeric species. The NMR results obtained provide comparison data for the distinction between A- and B-form E.coli 5S rRNA and for the possible kinetics of conversion between these forms. NMR evidence is presented that the duplex form also exists in crystals and suggestions are made for means to obtain stem-loop conformations of E-domain and other small RNA stem-loop sequences in crystals.     

The behavior of the coiled body in cells infected with adenovirus in vitro

The coiled body is a phylogenetically conserved nuclear organelle whose function is not known. Probes for detection of p80-coilin, an 80 kDa protein enriched in the coiled body, have made possible studies determining the behavior of the coiled body during the cell cycle, in proliferating cells, as well as reports suggesting some relationship of the coiled body to mRNA splicing and to the nucleolus. The objective of this study is to examine the distribution of p80-coilin and nucleolar proteins in cells infected with adenovirus in vitro. HeLa cells grown as monolayers were infected with successive dilutions of type 5 human adenovirus culture and fixed in methanol/acetone at different time points. Single and double indirect immunofluorescence was performed with human autoantibodies to p80-coilin, fibrillarin, NOR-90/hUBF, RNA polymerase I, PM-Scl, and To, as well as rabbit polyclonal serum to p80-coilin (R288) and mouse monoclonal antibody to adenovirus 72-kDa DNA-binding protein. Indirect immunofluorescence (IIF) with anti-p80-coilin antibodies showed that the usual bright dot-like coiled body staining pattern was replaced in infected cells by 1-5 clusters of tiny dots at the periphery of the nucleus. This phenomenon was first detected within 12 h of infection and affected more severely cells with increased length and load of infection. Cells subjected to heat shock presented no such alteration. Double IIF showed cells with abnormal coiled body appearance expressed the viral 72-kDa DNA-binding protein. Nucleolar proteins RNA polymerase I and NOR-90/hUBF became associated with the p80-coilin-enriched clusters and were no longer detected in the nucleolus. Other nucleolar proteins, like PM-Scl and To, remained associated to the nucleolus and were not detected in the newly formed clusters. Fibrillarin had a heterogeneous behavior, being restricted to the nucleolus in some infected cells while in some others it was associated with the p80-coilin-enriched clusters. Thus our results showed that in vitro adenovirus infection induced radical redistribution of nucleolar and coiled body constituents into newly formed structures characterized by clusters of tiny dots in the periphery of the nucleus. The fact that three major proteins involved in rRNA synthesis and processing colocalized with p80-coilin in these clusters may bring additional support to the idea that the coiled body and p80-coilin may be implicated in functions related to the nucleolus.     

Do patients with antiphospholipid syndrome have autoantibodies to beta 2-glycoprotein I?

High positive anticardiolipin antibody tests have been associated with recurrent thrombosis and pregnancy loss. Although these antibodies were believed to bind negatively charged phospholipids, recent reports have suggested that a serum protein, beta 2-glycoprotein I (beta 2-GPI), may be the true antigen for these antibodies. To resolve this issue, we compared binding of 75 anticardiolipin-positive and 71 anticardiolipin-negative serum samples from patients with rheumatic diseases to beta 2-GPI by using an enzyme-linked immunosorbent assay (ELISA). Serum samples from 30 healthy blood donors and 10 laboratory personnel were used as normal controls. We found no difference in binding between the three groups of serum samples. In addition, when binding to beta 2-GPI coated plates was compared with binding to ELISA plates without beta 2-GPI (blank), no difference was observed. Finally, binding of anticardiolipin-positive serum samples to plates coated with cardiolipin-beta 2-GPI mixture varied directly with the cardiolipin concentrations. Based on these findings, we conclude that anticardiolipin-positive serum samples do not bind beta 2-GPI.