The RNA-binding protein HuD binds to a regulatory element in the 3Ј untranslated region (3Ј UTR) of the GAP-43 mRNA. To investigate the functional significance of this interaction, we generated PC12 cell lines in which HuD levels were controlled by transfection with either antisense (pDuH) or sense (pcHuD) constructs. pDuH-transfected cells contained reduced amounts of GAP-43 protein and mRNA, and these levels remained low even after nerve growth factor (NGF) stimulation, a treatment that is normally associated with protein kinase C (PKC)-dependent stabilization of the GAP-43 mRNA and neuronal differentiation. Analysis of GAP-43 mRNA stability demonstrated that the mRNA had a shorter half-life in these cells. In agreement with their deficient GAP-43 expression, pDuH cells failed to grow neurites in the presence of NGF or phorbol esters. These cells, however, exhibited normal neurite outgrowth when exposed to dibutyryl-cAMP, an agent that induces outgrowth independently from GAP-43. We observed opposite effects in pcHuD-transfected cells. The GAP-43 mRNA was stabilized in these cells, leading to an increase in the levels of the GAP-43 mRNA and protein. pcHuD cells were also found to grow short spontaneous neurites, a process that required the presence of GAP-43. In conclusion, our results suggest that HuD plays a critical role in PKC-mediated neurite outgrowth in PC12 cells and that this protein does so primarily by promoting the stabilization of the GAP-43 mRNA. INTRODUCTIONIn addition to transcriptional factors, RNA-binding proteins play a critical role in the developmental control of gene expression. Among these is ELAV (embryonic lethal abnormal vision), an RNA-binding protein identified in Drosophila, where the gene is required for normal development and maintenance of the nervous system (Campos et al., 1985;Robinow et al., 1988). In higher vertebrates and mammals, four members of the ELAV-like family have been identified. These are also referred to as Hu proteins, namely HuR (also known as HuA), HuB (Hel-N1), HuC, and HuD, because these are targets of anti-Hu antibodies present in the sera of patients with paraneoplastic encephalomyelitis (Dalmau et al., 1992). HuR is ubiquitously expressed (Ma et al., 1996), while HuB, HuC, and HuD are expressed uniquely in the nervous system. Recent studies indicate that overexpression of neural ELAV-like proteins is sufficient to induce neuronal differentiation in vitro and in vivo (Wakamatsu and Weston, 1997; Akamatsu et al., 1999;Antic et al., 1999;Kasashima et al., 1999). While the exact function and targets of ELAV/Hu proteins remain to be fully elucidated, it seems likely that this family of RNA-binding proteins controls neuronal differentiation by selectively modulating the expression of neural-specific, growth-associated genes.The growth-associated protein GAP-43 is expressed in neurons primarily during the initial establishment and regeneration of neural connections (Skene, 1989;Benowitz and Routtenberg, 1997 Eggen et al., 1995;Chiaramello et al., 1996;Kinney et ...
Metnase is a human SET and transposase domain protein that methylates histone H3 and promotes DNA double-strand break repair. We now show that Metnase physically interacts and co-localizes with Topoisomerase IIα (Topo IIα), the key chromosome decatenating enzyme. Metnase promotes progression through decatenation and increases resistance to the Topo IIα inhibitors ICRF-193 and VP-16. Purified Metnase greatly enhanced Topo IIα decatenation of kinetoplast DNA to relaxed circular forms. Nuclear extracts containing Metnase decatenated kDNA more rapidly than those without Metnase, and neutralizing anti-sera against Metnase reversed that enhancement of decatenation. Metnase automethylates at K485, and the presence of a methyl donor blocked the enhancement of Topo IIα decatenation by Metnase, implying an internal regulatory inhibition. Thus, Metnase enhances Topo IIα decatenation, and this activity is repressed by automethylation. These results suggest that cancer cells could subvert Metnase to mediate clinically relevant resistance to Topo IIα inhibitors.
Abstract:We have previously shown that the RNA-binding protein HuD binds to a regulatory element in the growth-associated protein (GAP)-43 mRNA and that this interaction involves its first two RNA recognition motifs (RRMs). In this study, we investigated the functional significance of this interaction by overexpression of human HuD protein (pcHuD) or its truncated form lacking the third RRM (pcHuD IϩII) in PC12 cells. Morphological analysis revealed that pcHuD cells extended short neurites containing GAP-43-positive growth cones in the absence of nerve growth factor (NGF). These processes also contained tubulin and F-actin filaments but were not stained with antibodies against neurofilament M protein.In correlation with this phenotype, pcHuD cells contained higher levels of GAP-43 without changes in levels of other NGF-induced proteins, such as SNAP-25 and tau. In mRNA decay studies, HuD stabilized the GAP-43 mRNA, whereas HuD IϩII did not have any effect either on GAP-43 mRNA stability or on the levels of GAP-43 protein. Likewise, pcHuD IϩII cells showed no spontaneous neurite outgrowth and deficient outgrowth in response to NGF. Our results indicate that HuD is sufficient to increase GAP-43 gene expression and neurite outgrowth in the absence of NGF and that the third RRM in the protein is critical for this function. Key Words: Growth-associated protein-43-Neurite outgrowth-Hu proteins-PC12 cells-mRNA stability.
The macromolecules contributed by the freshwater gastropod Biomphalaria glabrata, intermediate host of Schistosoma mansoni, to developing offspring inside egg masses are poorly known. SDS-PAGE fractionated egg mass fluids (EMF) of M line and BB02 B. glabrata were analyzed by MALDI-TOF (MS and tandem MS). A MASCOT database was assembled with EST data from B. glabrata and other molluscs to aid in sequence characterization. Of approximately 20 major EMF polypeptides, 16 were identified as defense-related, including protease inhibitors, a hemocyanin-like factor and tyrosinase (each with possible phenoloxidase activity), extracellular Cu-Zn SOD, two categories of C-type lectins, Gram negative bacteria-binding protein (GNBP), aplysianin/achacinlike protein, as well as versions of lipopolysaccharide binding protein/bacterial permeability increasing proteins (LBP/BPI) that differed from those previously described from hemocytes. Along with two sequences that were encoded by "unknown" ESTs, EMF also yielded a compound containing a vWF domain that is likely involved in defense and a polypeptide with homology to the Aplysia pheromone temptin. Further study of B. glabrata pheromones is warranted as these could be useful in efforts to control these schistosome-transmitting snails. Several of the EMF polypeptides were contained in the albumen gland, the organ that produces most EMF. Thus parental investment of B. glabrata in immunoprotection of its offspring is indicated to be considerable.
Arsenic is an environmental toxin that enhances the carcinogenic effect of DNA-damaging agents, such as ultraviolet radiation and benzo[a]pyrene. Interaction with zinc finger proteins has been shown to be an important molecular mechanism for arsenic toxicity and cocarcinogenesis. Arsenicals such as arsenite, arsenic trioxide (ATO), and monomethylarsonous acid (MMA(III)) have been reported to interact with cysteine residues of zinc finger domains, but little is known about potential differences in their selectivity of interaction. Herein we analyzed the interaction of arsenite, MMA(III), and ATO with C2H2, C3H1, and C4 configurations of zinc fingers using UV–vis, cobalt, fluorescence, and mass spectrometry. We observed that arsenite and ATO both selectively bound to C3H1 and C4 zinc fingers, while MMA(III) interacted with all three configurations of zinc finger peptides. Structurally and functionally, arsenite and ATO caused conformational changes and zinc loss on C3H1 and C4 zinc finger peptide and protein, respectively, whereas MMA(III) changed conformation and displaced zinc on all three types of zinc fingers. The differential selectivity was also demonstrated in zinc finger proteins isolated from cells treated with these arsenicals. Our results show that trivalent inorganic arsenic compounds, arsenite and ATO, have the same selectivity and behavior when interacting with zinc finger proteins, while methylation removes the selectivity. These findings provide insights on the molecular mechanisms underlying the differential effects of inorganic versus methylated arsenicals, as well as the role of in vivo arsenic methylation in arsenic toxicity and carcinogenesis.
OBJECTIVES-To determine whether cross-talk occurs between ER and NF-κB, to assess the functional consequences of such an ER/NF-κB interaction, and to identify other unknown regulatory proteins that may participate in the NF-κB transcriptional complex.STUDY DESIGN-Electromobility gel shifts, reporter gene assays, and mass spectrometry were used to identify proteins interacting with the NF-κB DNA response element.RESULTS-ER and the p65 subunit of NF-κB co-localized on DNA. This interaction was inhibitory for ER transcriptional activity. Sequencing of proteins bound to the NF-κB/DNA complex identified DNA modifying enzymes, scaffolding proteins, chaperones, and elements of the nuclear matrix.CONCLUSION-These studies have identified an inhibitory interaction between estrogen receptors and the p65 subunit of NF-κB with implications for estrogen action in pregnancy and in cancer. New accessory proteins have also been identified that bind to protein complexes on the NF-κB DNA response element.
The mammalian 70K protein, a component of the U1 small nuclear ribonucleoprotein involved in pre-mRNA splicing, interacts with a number of proteins important for regulating constitutive and alternative splicing. Similar proteins that interact with the yeast homolog of the 70K protein, Snp1p, have yet to be identified. We used the two-hybrid system to find four U1-Snp1 associating (Usa) proteins. Two of these proteins physically associate with Snp1p as assayed by coimmunoprecipitation. One is Prp8p, a known, essential spliceosomal component. This interaction suggests some novel functions for Snp1p and the U1 small nuclear ribonucleoprotein late in spliceosome development. The other, Exo84p, is a conserved subunit of the exocyst, an eight-protein complex functioning in secretion. We show here that Exo84p is also involved in pre-mRNA splicing. A temperaturesensitive exo84 mutation caused increased ratios of pre-mRNA to mRNA for the Rpl30 and actin transcripts in cells incubated at the non-permissive temperature. The mutation also led to a defect in splicing and prespliceosome formation in vitro; an indication that Exo84p has a direct role in splicing. The results elucidate a surprising link between splicing and secretion.The U1 snRNP 1 has an early, hierarchic role in pre-mRNA splicing in the yeast Saccharomyces cerevisiae (1-3). It must be bound to pre-mRNA for subsequent stable association of the other four spliceosomal snRNPs with the pre-mRNA. Once U1 snRNP is bound, U2 snRNP binds, and the prespliceosome is formed. The tri-snRNP complex, U4/U6.U5, then binds to form the spliceosome. The spliceosome next undergoes a number of coordinated rearrangements (4). The duplexes between the U4 and U6 snRNAs and between U1 snRNA and the 5Ј-splice site (SS) of the pre-mRNA are disrupted, whereas new pairings between U2 and U6 snRNAs, U6 snRNA and the 5Ј-SS, and U5 snRNA and the pre-mRNA exons 1 and 2 are formed. These rearrangements lead to the formation of the active catalytic site of the spliceosome. Splicing of the pre-mRNA then ensues by two transesterification reactions.The yeast U1 snRNP recognizes both the 5Ј-SS and the branchpoint region of the pre-mRNA (3, 5). From 5 to 7 nucleotides of the 5Ј end of the U1 snRNA base pair with the
Heat shock proteins (HSPs), which are important for a number of different intracellular functions, are occasionally found on the surface of cells. The function of heat shock protein on the cell surface is not understood, although it has been shown to be greater in some tumor cells and some virally infected cells. Surface expression of both glycoprotein 96 (gp96) and Hsp70 occurs on tumor cells, and this expression correlates with natural killer cell killing of the cells. We examined the surface expression of gp96 and Hsp70 on human breast cell lines MCF7, MCF10A, AU565, and HS578, and in primary human mammary epithelial cells by immunofluorescence microscopy and flow cytometry. The nonmalignant cell lines HS578, MCF10A, and HMEC showed no surface expression of gp96, whereas malignant cell lines MCF7 and AU565 were positive for gp96 surface expression. All of the breast cell lines examined showed Hsp70 surface expression. These results also confirm previous studies, demonstrating that Hsp70 is on the plasma membrane of tumor cell lines. Given the involvement of heat shock proteins, gp96 and Hsp70, in innate and adaptive immunity, these observations may be important in the immune response to tumor cells.
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