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Biomedical subjects

V Kumar

Publications and source records attributed to V Kumar.

At least 181 records · Page 10Linked to original sources
PubMed1989

Clinical pharmacology of tetrahydroaminoacridine: a possible therapeutic agent Alzheimer's disease.

Tetrahydroaminoacridine (THA) was administered to a small number of patients with Alzheimer's disease. A minority of patients received the drug for longer than one week. Only one investigator [Summers et al. 1986] has reported dramatic palliative effects from the administration of THA. All investigators other than Summers reported side effects, especially troublesome is the frequent appearance of indications of hepatotoxicity. The efficacy and safety of THA are unknown. There is evidence that THA may have complex modes of action in addition to the inhibition of cholinesterases. There is a need for careful clinical assessment of THA and for further investigation of possible mechanisms of action.

Alzheimer Disease↗
PubMed1988

The estrogen receptor binds tightly to its responsive element as a ligand-induced homodimer.

Extracts containing wild-type or mutant human estrogen receptor (ER) have been used to study the binding of ER to its responsive element (ERE). Estradiol (E2) or the antiestrogen hydroxytamoxifen is required for ER binding as assayed by gel retardation. The DNA binding domain (DBD) encompasses the highly conserved region C. Both intact ER-E2 complexes and ER mutants truncated for the hormone binding domain (HBD) bind as dimers to an ERE. However, an HBD-truncated ER binds less tightly to an ERE than an intact ER-E2 complex. The DBD and HBD contain a constitutive and a stronger ER-induced dimerization function, respectively. Thus, in addition to inducing the activation function associated with the HBD, estrogen plays a crucial role in the formation of stable ER dimers that bind tightly to ERE.

Binding Sites↗
PubMed1988

Bone marrow cell transplants involving intra-H-2 recombinant inbred mouse strains. Evidence that hemopoietic histocompatibility-1 (Hh-1) genes are distinct from H-2D or H-2L.

Hemopoietic histocompatibility (Hh) Ag are noncodominantly expressed on bone marrow stem cells and other normal and neoplastic cells of hemopoietic origin. H-2/Hh-1 allogeneic or parental-strain bone marrow grafts are eliminated in a determinant specific manner by NK cells. In inbred mouse strains, seven Hh-1 alleles representing combinations of five different Hh-1 antigenic determinants are described. Each Hh-1 allele maps in the vicinity of H-2D, and the genes that map to Hh-1 are transacting regulatory genes. The expression of a particular determinant depends on the absence of the regulatory gene and the presence of the appropriate structural gene. The primary focus of this study is to ascertain whether the Hh-1 phenotype and the serologic H-2DL typing are always correlated or whether recombinant can separate the two. To achieve this, we used a panel of irradiated hosts that are able to recognize the different Hh-1 determinants on the bone marrow cells of congenic intra-H-2 recombinant donors. We report: 1) the majority of strains show a correlation between Hh-1 and H-2DL: 2) B10.RQDB and B10.WB strains dissociate Hh-1 from Lb: 3) nine H-2S/D interval recombinant strains exhibit no correlation between the H-2DL type and Hh-1 phenotype; and 4) in two strains from this group, B10.D2 (R106) and B10.RSF5, H-2S/D crossovers occurred within Hh-1r, (Hh-1 regulatory). We conclude that Hh-1r is a distinct regulatory locus mapping telomeric of H-2S and centromeric of, although probably closer to, H-2D.

Animals↗
PubMed1988

Dynamic state of site-specific DNA methylation concurrent to altered prolactin and growth hormone gene expression in the pituitary gland of pregnant and lactating rats.

The regulatory mechanism for the hormonal control of prolactin (PRL) and growth hormone (GH) gene expression in rat pituitary gland during gestation and lactation is verified in this study. The level of PRL-specific mRNA (mRNAPRL) sequences in the pituitary gland is elevated in the later part of gestation and more prominently so in lactation. In contrast the expression of GH gene is inhibited in the same tissue during gestation and lactation resulting in the dramatic decrease in the level of GH-specific mRNA (mRNAGH) sequences. We now demonstrate the influence of a tissue-specific altered DNA methylation pattern on the temporal modulation of expression of PRL and GH genes in the pituitary gland during alternate physiological states. An altered methylation pattern of specific "-C-" residues only in the coding region of PRL and GH gene can be detected concurrently with the altered level of expression of these genes in the pituitary gland during gestation and lactation. These results also demonstrate the dynamic state of methylation of specific -C- residues during the transition of these two genes from one state of expression to another in the same tissue. A correlation between site-specific DNA methylation and tissue-specific expression of PRL and GH gene in pituitary gland is reported. Thus a role of DNA methylation in the hormonal control of PRL and GH gene expression in physiological states such as pregnancy and lactation is proposed.

Albumins↗
PubMed1988

Restricted use of T cell receptor V genes in murine autoimmune encephalomyelitis raises possibilities for antibody therapy.

Experimental allergic encephalomyelitis (EAE) is a paralytic autoimmune disease induced in susceptible animals by active immunization with myelin basic protein (MBP) or by passive transfer of MBP-specific T helper (TH) lymphocytes. We have analyzed the T cell receptor genes of 33 clonally distinct TH cells specific for a nonapeptide of MBP inducing EAE in B10.PL (H-2u) mice. All 33 TH cells used two alpha variable gene segments (V alpha 2.3, 61%; V alpha 4.2, 39%), the same alpha joining gene segment (J alpha 39), and two V beta and J beta gene segments (V beta 8.2-J beta 2.6, 79%; V beta 13-J beta 2.2, 21%). The anti-V beta 8 monoclonal antibody F23.1 was found to block completely recognition of the nonapeptide by V beta 8 TH cells in vitro and to reduce significantly the susceptibility of B10.PL mice to peptide-induced EAE.

Animals↗
PubMed1988

Distribution of membrane cofactor protein of complement on human peripheral blood cells. An altered form is found on granulocytes.

Membrane cofactor protein (MCP) of human complement is an iC3/C3b-binding glycoprotein with a characteristic two-band (63 kDa and 55 kDa) pattern on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Using affinity chromatography, it has been found on human mononuclear cells and platelets. MCP has been purified and shown to be a cofactor for the I-mediated cleavage of C3b. A rabbit polyclonal antibody was produced to the purified protein and this reagent employed to analyze the distribution of MCP on human peripheral blood cells. Flow cytometric analysis indicated that MCP is unimodally present on all platelets, granulocytes, T helper lymphocytes, T suppressor/cytotoxic lymphocytes, B lymphocytes, natural killer cells and monocytes but not erythrocytes. The presence of MCP on granulocytes was unexpected. To evaluate this, MCP was isolated by immunoprecipitation and analyzed by SDS-PAGE followed by autoradiography. The Mr of granulocyte MCP was that of a single broad band in which the typical two-band pattern could not be distinguished. Alterations in the conditions of the affinity column procedure increased the efficiency of the isolation of monocyte MCP and led to the reproducible isolation of granulocyte MCP. These results indicate that MCP of granulocytes has both structural and functional differences compared to MCP of plateletes and mononuclear cells. The wide distribution of MCP among peripheral blood cells supports the concept that MCP is important in the protection of host cells from complement-mediated damage.

Antigens, CD↗
PubMed1988

Expression of human estrogen receptor mutants in Xenopus oocytes: correlation between transcriptional activity and ability to form protein-DNA complexes.

The human estrogen receptor (hER) is a trans-acting regulatory protein composed of a series of discrete functional domains. We have microinjected an hER expression vector (HEO) into Xenopus oocyte nuclei and demonstrate, using Western blot assay, that the hER is synthesized. When nuclear extracts from oocytes were prepared and incubated in the presence of a 2.7 kb DNA fragment comprising the 5' end of the vitellogenin gene B2, formation of estrogen-dependent complexes could be visualized by electron microscopy over the estrogen responsive element (ERE). Of crucial importance is the observation that the complex formation is inhibited by the estrogen antagonist tamoxifen, is restored by the addition of the hormone and does not take place with extracts from control oocytes injected with the expression vector lacking the sequences encoding the receptor. The presence of the biologically active hER is confirmed in co-injection experiments, in which HEO is co-introduced with a CAT reporter gene under the control of a vitellogenin promoter containing or lacking the ERE. CAT assays and primer extensions analyses reveal that both the receptor and the ERE are essential for estrogen induced stimulation of transcription. The same approach was used to analyze selective hER mutants. We find that the DNA binding domain (region C) is essential for protein--DNA complex formation at the ERE but is not sufficient by itself to activate transcription from the reporter gene. In addition to region C, both the hormone binding (region E) and amino terminal (region A/B) domains are needed for an efficient transcription activation.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

The N-terminal DNA-binding 'zinc finger' of the oestrogen and glucocorticoid receptors determines target gene specificity.

Steroid hormone receptors activate specific gene transcription by binding as hormone-receptor complexes to short DNA enhancer-like elements termed hormone response elements (HREs). We have shown previously that a highly conserved 66 amino acid region of the oestrogen (ER) and glucocorticoid (GR) receptors, which corresponds to part of the receptor DNA binding domain (region C) is responsible for determining the specificity of target gene activation. This region contains two sub-regions (CI and CII) analogous to the 'zinc-fingers' of the transcription factor TFIIIA. We show here that CI and CII appear to be separate domains both involved in DNA binding. Furthermore, using chimaeric ERs in which either the first (N-terminal) (CI) or second (CII) 'zinc finger' region has been exchanged with that of the GR, indicates that it is the first 'zinc finger' which largely determines target gene specificity. We suggest that receptor recognition of the HRE is analogous to that of the helix-turn-helix DNA binding motif in that the receptor binds to DNA as a dimer with the first 'zinc finger' lying in the major groove recognizing one half of the palindromic HRE, and that protein-DNA interaction is stabilized through non-specific DNA binding and dimer interactions contributed by the second 'zinc finger'.

Amino Acid Sequence↗
PubMed1988

Structure and function of the pS2 gene and estrogen receptor in human breast cancer cells.

The role of estrogen in the growth of human breast cancers has been investigated at two levels. First, we have studied the pS2 gene, whose transcription is stimulated by estrogen in the human breast cancer cell line, MCF-7. The pS2 gene product is a small, secreted polypeptide currently of unknown function, but with structural features similar to some growth factors. The expression of the pS2 gene has so far been detected only in MCF-7 cells and some breast cancer biopsies. Preliminary studies indicate that pS2 is a potential marker for hormone-dependent breast cancer. Ongoing studies will continue to focus on the implicated role of pS2 in the estrogen-mediated growth of breast cancers and its possible use as a marker for estrogen-dependent tumors. Second, we have analyzed the structure and function of the human ER. The receptor stimulates pS2 gene transcription by interacting with an ERE in the 5'-flanking region of that gene. A mutational analysis of the receptor protein has localized a DNA-binding domain, which determines target gene specificity, and a hormone-binding domain. These domains appear to be the only two regions of the receptor which are absolutely required for the transcription-activating function of the ER in transfection assays with reporter plasmids. The N-terminal region of the protein (regions A and B), which is necessary for increasing the efficiency of gene expression using the pS2 ERE, but not a vitellogenin ERE, may also play a role in transcription activation. Further progress in the characterization of the ER functional domains will require studies on target genes in a more physiological chromatin environment, as well as detailed physical analyses of receptor structure.

Amino Acid Sequence↗
PubMed1988

Effects of a subanesthetic concentration of nitrous oxide on overt and covert assessments of memory and associative processes.

Drug effects on human memory are usually assessed by overt recall or recognition tests. Covert tests which do not explicitly assess memory but which indirectly elicit previously presented information may be more sensitive to low levels of learning than overt tests. Three covert tests and corresponding overt recall tests were given to 16 men and 16 women breathing 30% nitrous oxide in oxygen or 100% oxygen to see if the covert tests resisted the memory-impairing effects of nitrous oxide. Nitrous oxide impaired performance on the overt tests. Performance in two covert tests, Constrained Associations and Word Completion, showed resistance to memory impairment. In the least resistant covert test, Free Associations, nitrous oxide altered associative processes. Performance in an additional test involving recognition and preferences for nonsense words repeated with varying frequencies also showed some resistance to memory impairment. The results support the distinction between declarative and procedural memory. Constrained Associations, Word Completion, and Nonsense Words tests may be useful for assessing low levels of learning during drug states.

Adolescent↗
PubMed1988

Polymorphism of Hh-1, the mouse hemopoietic histocompatibility locus.

The major goal of these studies is to more fully assess the polymorphism of the hemopoietic histocompatibility (Hh) genetic system. H-2 homozygosity is required for optimal immunogenicity of bone marrow cell (BMC) grafts, and "hybrid resistance" to grafts of parental strain BMC by irradiated H-2 heterozygous F1 hybrid mice suggests that Hh-1 antigens are inherited recessively. The Hh-1 antigens are also expressed on other normal hematopoietic cells and lymphoid tumors, and natural killer cells are the effectors which mediate the elimination of BMC grafts in an Hh-specific manner. Previous studies have demonstrated three different antigens mapping to the Hh-1 locus near H-2D. We test the expression of Hh-1 on BMC of all nonrecombinant H-2 haplotypes of independent origin and H-2j, a presumed natural recombinant. Hh-1 typing is based on the pattern of growth and rejection in a panel of hosts. F1 hybrids with H-2b, H-2d, and H-2k are produced and used as donors and hosts to confirm the phenotype. Grafts of b, d-, and j-haplotype marrow serve as prototypical examples of determinants that are provisionally designated as 1, 2, and 3, respectively. We describe a new determinant, 4, in the k haplotype. It is non-codominantly expressed, maps to H-2D, and is also expressed on H-2b BMC. NZW, H-2z grafts exhibit a phenotype similar to k, but express a unique determinant 5 which can be distinguished from determinant 4. This additional determinant is also expressed by the b haplotype. The d, f, and p haplotypes all express determinant 2, and grafts of j-haplotype marrow are found to express determinants 2 and 5 in addition to determinant 3. The q and r haplotypes are null for all known determinants. Finally, we describe a phenotype which is a new combination of previously described determinants: s-haplotype grafts express determinants 1, 2, and 4. The polymorphism of Hh-1 detected thus far consists of seven alleles which are combinations of five distinct determinants.

Animals↗