A mechanism for the stimulation by inorganic mercury of [3H] thymidine incorporation into DNA in cultured Molt-4F cells.

Mercuric chloride at a narrow range of concentration (2 to 2.5 X 10(-5)M) facilitated [3H]thymidine incorporation into acid-insoluble material (DNA fraction) of cultured human T lymphoid cells, Molt-4F, after 72-hr culture with the metal. This effect by mercury was observed in spite of the decrease in growth rate and DNA contents of the cells. Thymidine kinase activity in Molt-4F cells treated with 2 X 10(-5)M mercury decreased to 50 to 60% of the control activity. The stimulation of [3H]thymidine incorporation into the cells by mercury, therefore, might be independent of the increase in thymidine kinase activity. 3H-Thymidine incorporation by the control cells decreased as culture time passed. In contrast to the control, [3H]thymidine incorporation by mercury-treated cells increased until 72-hr culture. [3H]Thymidine uptake by the control cells after 24, 48, or 72-hr culture increased until 20 min of incubation period, but thereafter no increase in the uptake was observed until 60 min. On the other hand, [3H]thymidine uptake by the cells treated with mercury for 24 to 72 hr increased linearly until 60 min of incubation period. These results seemed to indicate that the mercury stimulation of [3H]thymidine incorporation might be attributable not to the actual increase of DNA synthesis but to the suppression of the culture time-dependent decrease in the incorporation by the control cells.