Diversity of nuclear phorbol ester tumor promoter receptors in mouse liver: Evidence for two classes of binding sites

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Summary Two classes of phorbol ester binding sites have been demonstrated in the nuclear fraction of liver from female CD-1 mice. Equilibrium binding studies of 0.40 M NaCl nuclear extracts yielded a sigmoidal saturation curve which was resolved by Hill plot analysis into two components. However, when nuclei were extracted in 0.24 M NaCl, the 12-0-tetradecanoylphorbol-13-acetate saturation curve of the extract was biphasic in shape consisting of both high and low affinity binding sites termed Class I and II receptors. When the 0.24 M NaCl extracted nuclear pellet was extracted further in 0.40 M NaCl, saturation analysis of the extract revealed only the low affinity binding site (Class II). This is the first study to identify the existence of phorbol ester receptors in liver nuclei.