Cloning of senescent cell-derived inhibitors of DNA synthesis using an expression screen.
We here describe a rapid and simple expression screen method that has allowed us to isolate cDNAs coding for inhibitors of DNA synthesis from senescent human diploid fibroblasts. The assay involved transient transcriptional overexpression of a gene product encoded by a cDNA in a proliferating cell, on the assumption that this would be sufficient to block DNA synthesis in a short-term assay using tritiated thymidine autoradiography. Three cDNAs, referred to as senescent cell-derived inhibitors (sdi), that exhibit DNA synthesis-inhibitory activity when introduced into young cycling cells, were successfully identified. Expression of one of the cDNAs, sdi1, increased 10- to 20-fold in senescent compared with young cells and the increase in RNA closely paralleled the onset of the senescent phenotype and loss of cell proliferation. sdi1 expression was also increased in young cells made nondividing (quiescent) by deprivation of growth factors or contact inhibition. Following serum stimulation, RNA levels of sdi1 in quiescent cells were initially increased, but then declined to low levels just prior to the entry of the cells into S phase. In contrast, RNA levels of sdi1 in senescent cells failed to decline, suggesting a role for this gene in maintaining the senescent phenotype. The sdi1 gene has been mapped to the p arm of chromosome 6.
Noda
A
A
Roy M. and Phyllis Gough Huffington Center on Aging, Baylor College of Medicine, Houston, Texas 77030.
Ning
Y
Y
Venable
S F
SF
Pereira-Smith
O M
OM
Smith
J R
JR
D000595:Amino Acid Sequence; D001345:Autoradiography; D001483:Base Sequence; D015152:Blotting, Northern; D002455:Cell Division; D002478:Cells, Cultured; D016922:Cellular Senescence / Q000235:genetics; D002874:Chromosome Mapping; D002896:Chromosomes, Human, Pair 6; D003001:Cloning, Molecular; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins / Q000032:analysis / Q000235:genetics*; D004247:DNA / Q000032:analysis / Q000096:biosynthesis* / Q000235:genetics*; D005347:Fibroblasts / Q000737:chemistry / Q000166:cytology / Q000502:physiology; D006801:Humans; D008297:Male; D008722:Methods; D008969:Molecular Sequence Data; D010641:Phenotype; D011401:Promoter Regions, Genetic / Q000235:genetics; D012333:RNA, Messenger / Q000032:analysis / Q000235:genetics; D016192:Resting Phase, Cell Cycle; D016196:S Phase; D014162:Transfection
C493956:CDKN1A protein, human; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D012333:RNA, Messenger; D004247:DNA