CHARACTERIZATION OF PHORBOL ESTERS BINDING TO K 562-CELLS

Abstract

Binding of 20-[3H]-phorbol 2, 13-dibutyrate ([3H]PDB) to intact human [leukemia] K 562 cells was characterized. Specific binding of [3H]PDB to K 562 cells at 20.degree. or 37.degree. C reached a maximum within 15-20 min. Maximal specific [3H]PDB binding to K 562 cells was followed by a decline (down regulation) of radioactivity. This down regulation was temperature dependent; no loss of radioactivity occurred by 1 h at 4.degree. C. When [3H]PDB binding was carried out at 4.degree. C, [3H]PDB bound to K 562 cells in a rapid, specific, and reversible manner. Phorbol esters which lack tumor-promoting activity, did not inhibit [3H]PDB binding. A Scatchard analysis was compatible with one class of binding sites, Kd = 50 nM and about 2 .times. 105 binding sites per cell. Human serum inhibited specific binding of [3H]PDB. The effect of several chemical compounds on [3H]PDB binding was also investigated. Most of the compounds tested such as butyrate, hemin, .gamma.-globulins, transferrin, insulin, EGF [epidermal growth factor], and albumin failed to significantly affect the binding of [3H]PDB. Retinoic acid and quinacrine significantly affected the binding of [3H]PDB; retinoic acid induced a marked increase of [3H]PDB binding which was dose dependent; quinacrine induced a decrease of [3H]PDB binding, even at low concentration.