1,721,004 research outputs found
Inhibition of T-cell proliferation by a MYB antisense oligomer is accompanied by selective down-regulation of DNA polymerase alpha expression.
No full textWe 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
Regulation of the proliferating cell nuclear antigen cyclin and thymidine kinase mRNA levels by growth factors.
Full text linkThe enzymes of the DNA synthesizing machinery constitute a group of gene products that are generally expressed co-ordinately at the G1/S boundary of the cell cycle. We have investigated how growth factors regulate the steady-state mRNA levels of two of these genes, the PCNA (proliferating cell nuclear antigen)/cyclin and the thymidine kinase genes. To detect the PCNA/cyclin mRNA, we isolated a cDNA clone from a human library. Two different cell lines were used for these studies: BALB/c3T3 cells, which are exquisitely sensitive to growth factors, and ts13 cells, a temperature-sensitive (ts) mutant of the cell cycle, which arrests in G1 at the restrictive temperature. The steady-state levels of the RNAs for these two genes under different growth conditions were also compared with the levels of histone H3 RNA which are good indicators of the fraction of cells in S phase. Both PCNA/cyclin and thymidine kinase genes share two fundamental characteristics, i.e. they are not inducible in a G1-specific ts mutant of the cell cycle at the restrictive temperature and their expression is inhibited by cycloheximide, indicating that unlike early growth-regulated genes, they require the previous expression of other growth-regulated genes. However, the two genes also show differences, the most notable being that PCNA/cyclin is inducible by epidermal growth factor alone, while thymidine kinase is not
Growth regulated expression of B-myb in fibroblasts and hematopoietic cells.
No full textThe B-myb cDNA has extensive sequence similarities to the c-myb proto-oncogene, but, at variance with c-myb, it is expressed in cells other than hematopoietic cells. In this paper, we show that (1) B-myb is expressed in mouse, human, and hamster fibroblasts; (2) B-myb mRNA levels are growth-regulated in both fibroblasts and peripheral blood mononuclear cells; (3) by its mode of growth regulation (peak of expression, behavior in G1-specific temperature sensitive (ts) mutants and in the presence of cycloheximide), B-myb can be classified, like c-myb, thymidine kinase, PCNA, and others, as a late growth-regulated gene; (4) B-myb mRNA levels decrease when HL-60 cells are induced to differentiate; and (5) the increase in mRNA levels in serum-stimulated cells is only partially explained by an increase in rate of transcription. The possibility that the B-myb gene may be the equivalent in fibroblasts and epithelial cells of the c-myb proto-oncogene of hematopoietic cells is discussed
Human gene for proliferating cell nuclear antigen has pseudogenes and localizes to chromosome 20.
No full textWe have isolated from a human genomic library a pseudogene of the proliferating cell nuclear antigen (PCNA) gene. Its sequence shows a 78% similarity with the human PCNA/cDNA. The PCNA gene is located on human chromosome 20, while the pseudogene maps to chromosome region Xpter in equilibrium Xq13. An additional locus detected by the full-length PCNA cDNA, but not by intron probes, segregates concordantly with chromosome region 6p12 in equilibrium 6pter and probably represents a second pseudogene
Differentiation induces pituitary adenylate cyclase-activating polypeptide receptor expression in PC-12 cells
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Matrix metalloproteinases as diagnostic (MMP-13) and prognostic (MMP-2, MMP-9) markers of prostate cancer.
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Effect of the myb gene product on expression of the PCNA gene in fibroblasts.
No full textTk-ts13 cells are BHK-derived fibroblasts that have a G1-specific temperature sensitive (ts) mutation so that the cells arrest in the G1 phase of the cell cycle at the restrictive temperature of 39.6 degrees. We have introduced into these cells a plasmid carrying the human c-myb cDNA under the control of the early SV40 promoter. The resulting cell line, ts13 myb cells, express the c-myb RNA and protein and, when serum-stimulated, they undergo one round of DNA replication even at the restrictive temperature. Under the same conditions, the parent cell line (tk-ts13 cells) are blocked in G1 and fail to replicate DNA. We have investigated the expression of two late growth-regulated genes, PCNA and histone H3, in tk-ts13 and in ts 13 myb cells, both at permissive and restrictive temperature. At the permissive temperature of 34 degrees, the mRNA levels for PCNA and histone H3 increase markedly after serum stimulation in both cell lines, reaching a peak at the time of DNA synthesis. At the restrictive temperature of 39.6 degrees, the mRNA's for PCNA, and histone H3 are detectable in serum-stimulated ts13 myb cells while they are not detectable in the parent tk-ts13 cell line. Run-on transcription assays indicate that these 2 genes are transcribed in tk-ts13 cells equally well at permissive and nonpermissive temperatures, and that the presence of the myb product does not significantly increase their rates of transcription. The stability of the respective mRNA's is roughly the same at either temperature and in both types of cells. These results indicate: (1) a constitutively expressed c-myb gene product confers to fibroblasts the ability of temporarily by-passing a ts block in the G1 phase of the cell cycle and (2) the myb product, under these conditions, regulates the mRNA levels of PCNA and histone H3 either directly or indirectly by a post-transcriptional mechanism
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