Inhibition of erythroid differentiation in MEL cells by UV irradiation. Cell cycle and DNA repair activity

Effect of bacitracin on erythroid differentiation of MEL cells

“…Cells were allowed to differentiate and the percentage of benzidine-positive cells (%B +) was measured at the indicated day. Individual cell clones were obtained from the 250 pg/ml bacitracin-treated cells by plating the treated population in 0.4% agar in nonselective conditions (Foresti et al, 1993).…”

“…The lowvalues of variance indicate that the positive correlations between time and number of differentiated cells are no longer found To explore more extensively the unexpected dramatic effect of lower doses of bacitracin on erythropoiesis, the possible involvement of DNA repair mechanisms was investigated. Hydroxyurea, an inhibitor of DNA repair (Cress and Gerner, 1977), was added to two treated cultures at concentration (lmM) not interfering with MEL cell differentiation (Foresti et al, 1993). Concentrations of 25 ng/ml and 250 pg/ml bacitracin were chosen as representative of the two main effects reported in Figures 2 and 3.…”

“…It has been previously reported that the ability of MEL cells to undergo erythroid differentiation can be permanently blocked by exposing the cells for a few hours at a sublethal dose of any of the several chemical mutagens (Foresti et al, 1990a,b), or UV irradiation (Foresti et al, 1992). However, it was shown that the period of sensitivity to mutagens corresponds to the start of the S phase in MEL cell cultures parasynchronized in G1/S by induction with DMSO (Foresti et al, 1986) or synchronized in G1/S by thymidine and hydroxyurea blocks (Foresti et al, 1990a;Foresti et al, 1992). A strict correlation has been observed between the ability of a tested compound to damage the DNA and the inhibition of erythroid differentiation in MEL cells, as many chemicals that do not interact with DNA are without effect (Foresti et al, 1990a,b).…”

“…A strict correlation has been observed between the ability of a tested compound to damage the DNA and the inhibition of erythroid differentiation in MEL cells, as many chemicals that do not interact with DNA are without effect (Foresti et al, 1990a,b). The inhibition of differentiation, or of any other cellular function tested, such as G6PD or 6PGD or HPRT, caused by mutagenic agents is the result of a genetic damage, as a very high frequency (30-50%) of cellular mutant clones can easily be isolated from the treated cultures (Foresti et al, 1990a(Foresti et al, ,b, 1992. Studies on DNA repair activity during the cell cycle of MEL cells indicate that the DNA repair in the early S phase is less efficient than in the remaining periods of the cell cycle (Foresti et al, 1990a;Foresti et al, 1992).…”

“…The inhibition of differentiation, or of any other cellular function tested, such as G6PD or 6PGD or HPRT, caused by mutagenic agents is the result of a genetic damage, as a very high frequency (30-50%) of cellular mutant clones can easily be isolated from the treated cultures (Foresti et al, 1990a(Foresti et al, ,b, 1992. Studies on DNA repair activity during the cell cycle of MEL cells indicate that the DNA repair in the early S phase is less efficient than in the remaining periods of the cell cycle (Foresti et al, 1990a;Foresti et al, 1992). The fixation of a mutation into the cellular genome is the result of several causes, all acting at the same time: (1) ability of the tested compound to damage DNA; (2) efficiency of DNA repair; (3) the period of the cell cycle when the cells are treated.…”