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Initiation of DNA synthesis by microtubule disruption in quiescent rat 3Y1 cells
Y Shinohara1, E Nishida, H Sakai
1Department of Biophysics and Biochemistry, Faculty of Science, University of Tokyo, Japan.
Abstract:
Disruption of cytoplasmic microtubules by colchicine, colcemid or vinblastine induced the initiation of DNA synthesis and cell division in quiescent cultures of rat embryo fibroblast cell line, 3Y1, in the absence of growth factors. The microtubule-disruption-induced DNA synthesis was so marked that we could initiate analysis of the mechanism. Incubation of quiescent 3Y1 cells with high concentrations of vinblastine or those of vinblastine plus colcemid, which formed large tubulin paracrystals concomitant with the depolymerization of cytoplasmic microtubules, initiated DNA synthesis in the cells. Because these treatments did not increase the free tubulin level in the cells, but rather decreased it, an increase in the free tubulin level may not be required for initiation of DNA synthesis induced by microtubule-disrupting agents. Culture fluid of the 3Y1 cells incubated with colchicine did not stimulate the initiation of DNA synthesis when added to other quiescent 3Y1 cells after conversion of the colchicine in the culture fluid to lumicolchicine by ultraviolet irradiation. This suggested that colchicine treatment did not induce secretion of any mitogenic factors from 3Y1 cells. These results suggest that disruption of normal microtubules may elicit intracellular signals leading to cell proliferation.
Insights
Disrupting cytoplasmic microtubules with agents like colchicine initiates DNA synthesis and cell division in quiescent rat embryo fibroblasts (3Y1 cells) without growth factors. This suggests microtubule disruption triggers intracellular signals for cell proliferation.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- Cytoplasmic microtubules play crucial roles in cell structure and division.
- Quiescent cells typically require external growth factors to initiate DNA synthesis and proliferation.
Purpose of the Study:
- To investigate the effect of microtubule-disrupting agents on DNA synthesis and cell division in quiescent rat embryo fibroblasts (3Y1 cells).
- To elucidate the underlying mechanism of microtubule-disruption-induced cell proliferation.
Main Methods:
- Treatment of quiescent 3Y1 cells with microtubule-disrupting agents (colchicine, colcemid, vinblastine).
- Analysis of DNA synthesis and cell division.
- Measurement of free tubulin levels.
- Testing for secreted mitogenic factors in culture supernatant.
Main Results:
- Colchicine, colcemid, and vinblastine induced DNA synthesis and cell division in quiescent 3Y1 cells without growth factors.
- Microtubule disruption led to the formation of tubulin paracrystals and decreased free tubulin levels.
- Colchicine treatment did not induce the secretion of mitogenic factors from 3Y1 cells.
Conclusions:
- Disruption of cytoplasmic microtubules can initiate DNA synthesis and cell proliferation in quiescent cells.
- The initiation of DNA synthesis by microtubule-disrupting agents may not require an increase in free tubulin levels.
- Microtubule disruption appears to elicit intracellular signals that promote cell proliferation.