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Two periods of sensitivity to mutagens in induced Mel cells with different outcomes
M Foresti1, I Paoletti, F Mele
1Dipartimento di Genetica, Biologia Generale e Molecolare, Università degli Studi di Napoli Federico II, Italy.
Abstract:
Mouse erythroleukemia (Mel) cells are particularly sensitive to mutagenic agents between 18 and 24 h from the start of induction (Foresti, M.L. Gaudio, G. Geraci and P. Manduca (1986) Inhibition of dimethyl sulfoxide induced erythropoietic differentiation of murine erythroleukemia cells in culture. Cancer Res., 46, 6260-6263). We show here the occurrence of another period of sensitivity during the initial 5 h after the addition of the inducer dimethyl sulfoxide (DMSO) to the culture medium. The sensitivity to the mutagenic action of a sublethal 3-s pulse of UV light (13.5 J/m2) was monitored on the progeny of the irradiated cells at day 5 after the start of induction. The effects were analysed on functions strictly linked to the final expression of the differentiated phenotype: hemoglobin concentration, percent cells producing hemoglobin (%B+), activity of delta-amino levulinic acid dehydrase (ALA-DH) and presence of globins. Each function appeared differently and selectively affected in the progeny of the cells depending on the exact time of irradiation during the period of sensitivity Specifically, cells irradiated at hour 3 after induction show both hemoglobin concentration and ALA-DH activity values increased by a factor 3 over controls. Cells irradiated at hour 5 show an almost complete halt in cell induction and the other tested functions show minimal values. Cells are nearly insensitive to irradiation at later times, until hour 20, after which a second period of sensitivity with peak value at hour 22 occurs at which time hemoglobin concentration in the progeny of irradiated cells is increased by a factor 3 over controls, ALA-DH activity is increased by a factor 15 while percent B+ value is at its minimum. The differential effects of UV irradiation on Mel cell functions in the first and in the second period of sensitivity to mutagens confirm the hypothesis that the consequences of a mutational event are strictly dependent on the functional state of the cell. The 1-5 h period of sensitivity in which Mel cells fix the effects of the mutagen in their genome corresponds to increased thymidine incorporation not correlated with cell duplication.
Insights
Murine erythroleukemia (Mel) cells exhibit two distinct periods of mutagen sensitivity. Early UV irradiation (1-5h) impacts differentiation functions differently than later irradiation (18-24h), confirming cell state dependence.
Area of Science:
- Cell Biology
- Molecular Biology
- Genetics
Background:
- Murine erythroleukemia (Mel) cells are a model for studying erythropoiesis.
- Mel cells are known to be sensitive to mutagens during specific induction phases.
Purpose of the Study:
- To identify and characterize a novel period of mutagen sensitivity in early-induced Mel cells.
- To investigate the differential effects of UV irradiation on Mel cell differentiation markers at distinct sensitivity periods.
Main Methods:
- Mel cells were induced with dimethyl sulfoxide (DMSO).
- Cells were exposed to a sublethal UV pulse at various time points (0-5h and 18-24h).
- Progeny cells were analyzed at day 5 for hemoglobin concentration, %B+, delta-amino levulinic acid dehydrase (ALA-DH) activity, and globin presence.
Main Results:
- A new sensitivity period was identified within the first 5 hours of DMSO induction.
- UV irradiation at 3h increased hemoglobin and ALA-DH activity, while irradiation at 5h nearly halted differentiation.
- A second sensitivity period (18-24h) showed distinct effects, with peak sensitivity at 22h, significantly increasing hemoglobin and ALA-DH but decreasing %B+.
- Differential effects confirmed the dependence of mutational consequences on cellular functional state.
Conclusions:
- Mel cells exhibit at least two distinct periods of sensitivity to UV mutagens during DMSO-induced differentiation.
- The timing of mutagen exposure critically influences the outcome on differentiation markers.
- These findings support the hypothesis that the cellular functional state dictates the consequences of genetic damage.