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R T Radulescu

Publications and source records attributed to R T Radulescu.

15 recordsLinked to original sources
PubMed1997

Nuclear localization of insulin-like growth factor binding protein 3 in a lung cancer cell line.

Considerable evidence exists that lung cancer cell lines produce large amounts of insulin-like growth factor-binding proteins (IGFBPs). In addition, these cells are subject to an autocrine or paracrine growth control by insulin-like growth factors (IGFs). We now demonstrate by immunocytochemistry with IGFBP-3 antibodies that nuclei of a lung cancer cell line distinctly immunostain for IGFBP-3. This finding led us to investigate in more detail the localization of this protein that, to date, had only been known to occur extracellularly. Ligand blotting revealed that purified nuclear extracts contain a 43,000-Da IGFBP which can bind [I125]IGF-I. By Western blot this protein was identified as IGFBP-3. Thus, our data are consistent with the results of a previous structural study predicting a nuclear localization for IGFBP-3. Moreover, our findings raise the possibility that nuclear IGFBP-3 is functional and involved in the pathogenesis of lung cancer.

Blotting, Western↗
PubMed1996

Prion function and dysfunction: a structure-based scenario.

Prion diseases are transmissible, neurodegenerative disorders associated with as yet incompletely defined isoforms of a cellular protein termed prion protein (PrP). We have now identified in PrP structural information compatible with nucleotide- and nucleic acid-binding. As such, PrP contains a putative nicotinamide adenine dinucleotide (NADH)-binding site. Moreover, the PrP octarepeats reveal homology to the nucleic acid-binding and strand-annealing octarepeats of mammalian heterogeneous ribonucleoprotein (RNP) A1. Therefore, PrP may have NADH-dependent oxidoreductase activity as well as A1-like functions such as nucleic acid annealing and splicing. Moreover, we propose that infectious prions are propagated through a dynamic molecular symbiosis between a ribozyme-like nucleic acid and a conformational isomer of the RNP-like prion protein. Thus, our model has important implications for the understanding and treatment of prion diseases.

Amino Acid Sequence↗
PubMed1995

Binding of the LXCXE insulin motif to a hexapeptide derived from retinoblastoma protein.

Peptides corresponding to retinoblastoma protein (RB) fragment 649-654 (LFYKKV) were tested for their ability to recognize the LXCXE sequence motif in human papilloma virus type 16E7 protein (HPV-16E7) encompassing E7 residues 21-26 (DLYCYE) and an identical motif in human insulin comprising insulin B-chain residues 16-21 (YLVCGE), respectively. Interaction between these complementary peptide sequences was observed by several approaches, including direct and competitive ELISA as well as affinity chromatography. Moreover, we demonstrated that immobilized RB649-654 displays specific recognition properties towards full-length insulin. Hence, this study provides a first experimental support for the previously anticipated complex formation between insulin and RB.

Amino Acid Sequence↗
PubMed1995

Insulin receptor alpha-subunit: a putative gene regulatory molecule.

Previous studies have demonstrated the presence of the insulin receptor in the cell nucleus. Recently, it was shown that the insulin receptor also exhibits nuclear tyrosine kinase activity. In the present investigation, I have searched for structural correlates to a nuclear localization of the insulin receptor as well as to other potential nuclear actions of this molecule. Interestingly, this analysis yielded that the insulin receptor (alpha-subunit) contains a bipartite nuclear localization signal (consistent with the preceding experimental data), several zinc finger-like motifs and an RGG box. These findings have intriguing implications with regard to a presumable role of the insulin receptor (alpha-subunit) as a gene regulatory molecule.

Amino Acid Sequence↗
PubMed1995

Antibody constant region: potential to bind metal and nucleic acid.

Environmental challenges appear to elicit similar patterns of cellular responses such as positive autoregulation and autoamplification whether one considers the generation of antibodies with identical antigen specificity or the accumulation of host-protective transcription factors. Therefore, I analyzed the structure of immunoglobulins (Ig) for motifs commonly found in transcription factors. Specifically, the well-known abundance and periodic location of cysteine residues in immunoglobulin chains prompted me to check antibody constant regions for the presence of putative metal-binding domains and zinc finger-like sequences. The constant regions of Ig light and heavy chains were found to harbor one or several copies, respectively, of a short cysteine- and histidine-containing sequence. Moreover, all four IgG subclasses were detected to comprise zinc finger-like motifs in their heavy chain constant and hinge domains. Yet another finding is the occurrence of several sequences of the form serine-proline-X-X and/or threonine-proline-X-X in the hinge sections of IgA and IgG3. These results suggest that antibody constant regions, as a fragment and/or embedded in a full-length immunoglobulin chain, may complex metal, thus acquiring conformations conducive to dimerization and nucleic acid binding. As such, my study provides a putative structural basis for the known requirement of divalent metal cations, particularly of zinc ions, for a normal immune response, and warrants further investigations, both theoretical and experimental, into the potential of antibody constant regions for metal binding and gene regulation. Moreover, future testing of the proposed zinc finger peptides from Ig constant domains should yield information relevant to zinc finger design with potentially wide applications in research and clinical medicine.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1995

The 'LXCXE' hydropathic superfamily of ligands for retinoblastoma protein: a proposal.

The present study reports structural similarities between viral oncoproteins, growth factors belonging to the insulin family, members of the steroid/thyroid receptor superfamily, a D-type cyclin, the Elf-1 transcription factor and Bcl oncoproteins in regions that have been shown or proposed to mediate complex formation of these proteins with the tumor suppressor retinoblastoma protein (RB). This relationship predicts a common intracellular pathway for mitogenic signals and molecules promoting cell survival. Conversely, the structural evidence described here suggests that RB may play a central role both at the boundary between negative and positive cell growth regulation as well as in developmental decisions between cell death and cell survival.

Amino Acid Sequence↗
PubMed1995

Synthetic inducible biological response amplifiers (SIBRAs): rational peptides at the crossroads between molecular evolution and structure-based drug design.

The present study proposes a novel type of synthetic chimaeric polypeptides potentially useful in the therapy of various diseases. The prototype peptide termed 'synthetic inducible biological response amplifier' (SIBRA) would comprise a ligand-binding site, a DNA-binding region, a trans-activating domain as well as strings of residues ensuring bioavailability and targeting to specific compartments such as the cell nucleus. These domains would be selected from cellular proteins, artificially tailored to a SIBRA and further modified towards a molecule with both in vivo and intracellular activity. Since proposed to resemble a host molecule with autoregulatory properties, a SIBRA would be activated upon exposure to a defined environmental stimulus and amplify host responses appropriate for this stimulus. Proteins would accumulate that share functional domains with the administered SIBRA and have a positive autoregulatory capacity. The latter may involve the interaction of the induced protein with the promoter of its gene resulting in a direct positive autoregulatory loop or require the induction of intermediary proteins that eventually upregulate the production of SIBRA-like host proteins. Since the ligand-binding site of a SIBRA is rationally designed to target a pathogenic protein, SIBRAs could be regarded as the product of an artificial acceleration and refinement of strategies intrinsic to the immune system.

Biological Availability↗
PubMed1992

Prediction of homologous binding sites on RB and p107 common for viral oncoproteins and cellular ligands.

Hydropathic anticomplementarity of amino acids specifies that peptides translated from complementary DNA strands may acquire amphiphilic conformations and bind to each other. This concept has been coined 'Molecular Recognition Theory' (MRT) or 'complementary peptide theory'. Inactivation of retinoblastoma protein (RB), a tumor suppressor gene product, has been shown to be involved in the pathogenesis of many tumors and to be due to either mutation of the RB gene, hyperphosphorylation or complex formation with viral oncoproteins. The viral oncoproteins share a common RB binding motif with cellular ligands. The exact site on RB associating with this common RB binding motif of viral oncoproteins and cellular ligands has not been identified yet. This study is the first to predict putative binding sites on RB and p107, a cellular protein with RB sequence homology, respectively, by using the hydropathic complementarity approach. These sites are residues 649-654 of RB and 657-662 of p107. Moreover, this paper proposes a structure for a potential antineoplastic agent based on the amino acid sequence of the predicted RB binding site. The data presented herein should have important implications both for the understanding of cancer pathophysiology and for the drug design of antineoplastic compounds.

Amino Acid Sequence↗
PubMed1992

Proposed interaction between insulin and retinoblastoma protein.

Retinoblastoma protein (RB) is a tumor suppressor gene product involved in embryogenesis and cell cycle progression. One of the major mechanisms leading to RB dysfunction is complex formation with viral oncoproteins using the common RB binding motif Leu X Cys X Glu (LXCXE) which has also been identified in cellular ligands, e.g., RBP-1 and RBP-2. p107, a cellular protein with RB sequence homology, has been shown to bind to the same viral oncoproteins associating with RB and is therefore thought to contribute to cell cycle regulation. It has recently been suggested that insulin stimulates gene transcription through direct association with an, as yet, unidentified intracellular transcription factor. Due to the central roles of RB and p107 in coupling external growth signals with the progression of the cell cycle clock, we have hypothesized that these two proteins might be candidates for mediating the effects of insulin on DNA. We report here the identification of a region in the B-chain of human insulin that has the sequence LXCXE. Based on this finding we predict that the insulin B-chain may interact with RB and/or p107. Since we have also identified sequences hydropathically related to LXCXE in insulin-like growth factor I (IGF-I) and II (IGF-II), but not in relaxin, nerve growth factor, epidermal growth factor, glucagon or beta-endorphin, we further propose that both IGF-I and -II may assemble with RB and/or p107, too. Moreover, binding sites on RB and p107 identical with those suggested for viral oncoproteins and cellular ligands are predicted for insulin/IGF-I/IGF-II by using the hydropathic complementarity approach.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1990

Differential effect of opioids on immunoglobulin production by lymphocytes isolated from Peyer's patches and spleen.

The mucosal immune system plays an important role in blocking the penetration of invasive organisms into various mucosal surfaces. Evidence now suggests neuroendocrine peptide hormones have immunomodulatory properties, including the ability to alter mucosal immunity. The potential for opioid compounds and corticotropic hormone (ACTH) to modulate mucosal immune function was investigated. We have found beta-endorphin, ACTH, and naltrindole (delta-class opioid receptor antagonist) to significantly suppress concanavalin A-stimulated Peyer's patch lymphocyte immunoglobulin production of IgA, IgG, and IgM isotypes. Oxymorphindole, a delta class opioid receptor agonist, significantly decreased IgM but not IgA or IgG production by the mitogen-stimulated Peyer's patch lymphocytes. Both oxymorphindole and naltrindole modestly reduced interleukin-2 receptor expression of concanavalin A- (Con A)-stimulated splenic and Peyer's patch lymphocytes. Neither compound appreciably affected immunoglobulin production by lipopolysaccharide-stimulated Peyer's patch lymphocytes. Collectively, these results indicate stress-related peptides such as ACTH and opioids may be involved in the regulation of immunoglobulin synthesis by Peyer's patch lymphocytes.

Adrenocorticotropic Hormone↗