553 EFFECT OF POKEWEED MITOGEN AND RICIN ON PROTEIN SYNTHESIS IN CULTURED HUMAN LYMPHOID LINES

Abstract

Pokeweed mitogen (PWM) and ricin are both lectins derived from plant seeds. They are glycoproteins and share the ability to agglutinate a variety of animal cells particularly erythrocytes. Preliminary to development of a system to screen for the effect of environmental mutagens on the frequency of lectin resistant mutants we studied the effect of these 2 lectins on protein synthesis in long-term lymphoid lines. Ricin, a highly toxic compound is a known inhibitor of protein synthesis in other cell systems. PWM has primarily been evaluated for its mitogenic effect. Four lymphoid lines were studied: 8866 and GM1531 which are B cell lines, and CCRC/CEM and MOLT 4 which are considered to be T cell lines. Ricin (50 ug/ml) completely inhibited protein synthesis by 2 hours in all 4 lines as measured by the uptake of 3H leucine. PWM appeared more specific and at a concentration of 500 ug/ml inhibited protein synthesis only in the B lines (8866 and GM1531). This effect was maximal at 5 hours. To investigate the reason for the differential effect of PWM on T & B cells, 125I labeled PWM was incubated with 8866 and MOLT 4 to see if an increased binding to B cells could be demonstrated. A significantly greater number of counts bound to 8866 compared to MOLT 4. As lectins bind to cell surface carbohydrates, the possibility that this may represent a difference in the composition or arrangement of the surface glycoproteins is being investigated.