Messenger RNAs coding for enzymes of polyamine biosynthesis are induced during the G0-G1 transition but not during traverse of the normal G1 phase
✍ Scribed by Eva Stimac; David R. Morris
- Publisher
- John Wiley and Sons
- Year
- 1987
- Tongue
- English
- Weight
- 562 KB
- Volume
- 133
- Category
- Article
- ISSN
- 0021-9541
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✦ Synopsis
The events occurring during emergence of cells from quiescence ("Go") are not necessarily identical to those in the G, phase of continuously dividing cells. Cellular levels of t h e mRNAs coding for ornithine decarboxylase (ODC) and S-adenosyl-methionine decarboxylase (SDC), key enzymes in polyamine synthesis, increased maximally within 5 h after addition of serum to resting 3T3 cells, following a kinetic course similar to that of c-myc mRNA. In a pure early G, population of cells, prepared by centrifugal elutriation of growing fibroblasts, the levels of ODC and SDC mRNAs were not significantly lower than in other phases of the cell cycle and approximated serum-induced levels rather than t h e reduced values found in serum-starved cells. Thus, we conclude that the mRNAs coding for t h e polyamine biosynthetic enzymes, like cmyc, are growth controlled, but not regulated during traverse of a normal cell cycle.
Ornithine decarboxylase (ODC) and S-adenosylme-have presented evidence indicating that, although the thionine decarboxylase (SDC) catalyze sequential reac-synthesis of c-myc is regulated strongly during the Gotions in the pathway of polyamine biosynthesis. The G1 transition, neither the rate of synthesis of the protein polyamines are essential for cell proliferation and, al-nor the level of its mRNA vary significantly during the though the precise functions of these compounds are not transit of a normal cell cycle (Hann et al., 1985; Lachyet understood, they are clearly required to maintain man et al., 1985;Persson et al., 1985;Rabbitts et al., the rate of DNA synthesis through the S phase of the 1985; Thompson et al., 1985). Because of the prominent cell cycle (reviewed in Marton and Morris, 1987). The regulation of polyamine biosynthesis in response to celintracellular levels of the polyamines, as well as the lular growth stimuli, we measured the levels of the activities of the enzymes involved in their synthesis, are mRNAs coding for ODC and SDC during serum-stimuregulated in response to growth factors, hormones, tu-lation of quiescent Swiss 3T3 mouse fibroblasts and mor promoters, and other stimuli (reviewed in Heby, compared these to a homogeneous population of early 1981; Pegg and McCann, 1982;Pegg, 1984). Thus, cellu-G1 cells obtained from random growing cultures. As lar ODC and SDC activities are generally related to the may be the case with all competence genes, the enzymes rate of cell proliferation. Induction of ODC activity in of polyamine biosynthesis are growth controlled, but we response to a variety of stimuli is accompanied by cor-found no evidence that they are cell cycle regulated.