Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.7.1.21 (thymidine kinase)
 7,561 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Previously we have shown that bovine vascular smooth muscle cells (SMCs) express c-myb mRNA (Reilly, C. F., Kindy, M. S., Brown, K. E., Rosenberg, R. D., and Sonenshein, G. E. (1989) J. Biol. Chem. 264, 6990-6995). Here we have characterized changes in the low level of c-myb mRNA expressed in quiescent serum-deprived subconfluent SMCs upon entry into the cell cycle. After serum stimulation, levels of c-myb mRNA increased 3-4-fold during late G1 and remained at this level during S phase. A 1.5-kilobase partial c-myb cDNA clone, isolated from a bovine SMC library, was partially sequenced and found to be 89 and 85% homologous to the human and murine c-myb genes, respectively. Using bovine and murine c-myb clones, no change in the rate of c-myb gene transcription or mRNA stability was detected during the cell cycle. Thus, the regulation of changes in c-myb mRNA levels in SMCs appears distinct from mechanisms seen in hematopoietic or fibroblastic cells. Vectors containing myb binding sites linked to the thymidine kinase promoter and the chloramphenicol acetyltransferase reporter gene were transiently transfected into SMC cultures. KHK-CAT-dAX, which contains nine concatenated myb binding sites, exhibited 7-fold more activity than the parental dAX-TK-CAT vector in exponentially growing SMCs. The levels of chloramphenicol acetyltransferase activity in exponentially growing cells were approximately 2-fold higher than in cells that had been serum deprived for 24 h and were entering quiescence. Thus SMCs produce a functional c-myb protein that can activate transcription from a heterologous promoter. Furthermore, introduction of antisense c-myb oligonucleotides to quiescent serum-deprived SMC cultures severely inhibited entry of cells into S phase upon serum addition. Thus, expression of the c-myb oncogene plays an important role in cell cycle progression of SMCs.
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PMID:Expression of the c-myb proto-oncogene in bovine vascular smooth muscle cells. 153 45

We recently found that inhibition of MYB protein synthesis in human peripheral blood mononuclear cells (PBMC) exposed to human c-myb (designated MYB) antisense oligodeoxynucleotides prevents entry into S phase and cell proliferation. To determine the mechanism(s) by which down-regulation of human c-myb protein (MYB) synthesis interferes with DNA synthesis, we analyzed mRNA levels of DNA polymerase alpha and proliferating cell nuclear antigen (PCNA), transcripts of two genes required for DNA synthesis, in normal and leukemic T lymphocytes exposed to MYB antisense oligodeoxynucleotides. Expression of DNA polymerase alpha was inhibited both in normal T lymphocytes progressing from G0 to S phase and in exponentially growing CCRF-CEM leukemic cells, whereas expression of PCNA was inhibited only in mitogen-stimulated PBMC and remained essentially unaffected in the leukemia T-cell line. The functional link between expression of MYB and DNA polymerase alpha mRNAs was further demonstrated by analyzing DNA polymerase alpha mRNA levels in a temperature-sensitive (ts) fibroblast cell line (TK-ts13; TK is thymidine kinase) constitutively expressing human MYB mRNA driven by the simian virus 40 (SV40) promoter. In the MYB-expressing TK-ts13 cells, DNA polymerase alpha mRNA levels were unaffected following shift to the nonpermissive temperature of 39.6 degrees C, whereas in the parental line, DNA polymerase alpha mRNA levels were readily down-regulated. These findings indicate that the expression of MYB is related to that of DNA polymerase alpha in cells expressing MYB at high levels and suggest that there is a functional link between c-myb and DNA polymerase alpha mRNA expression during cell cycle progression of normal T lymphocytes.
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PMID:Inhibition of T-cell proliferation by a MYB antisense oligomer is accompanied by selective down-regulation of DNA polymerase alpha expression. 169 13