title: Characterization of a human placental factor which inhibits specific binding of phorbol esters to cultured cells.
abstract: Phorbol ester receptors have been demonstrated in a variety of cells and tissues using [3H]phorbol-12,13-dibutyrate (PDBu) as a ligand. In a search for possible endogenous ligand(s) for the receptor, we used the human placenta as a source. A factor that can inhibit the binding of [3H]PDBu on different types of cells was purified (133-fold) from an extract of human placenta. This factor, PEBIF ('phorbol ester binding inhibitory factor'), is sensitive to pepsin and resistant to trypsin treatment. It is heat- and acid (pH3)-stable and can be precipitated by 80% ethanol with no loss of activity. PEBIF inhibits binding whether it is added before or after incubation of [3H]PDBu with human amniotic membrane cells (FL). Inhibition occurs at both 37 degrees C and 4 degrees C and is rapid and reversible; it does not require intact cells, since it also occurs with membrane fractions. PEBIF does not act like a binding protein for PDBu, and the kinetics of the inhibition on FL cells is non-competitive. Inhibition was also observed in rat liver cells (IAR 6) and Friend erythroleukaemia cells (FELC). Differentiation of FELC induced by hexamethylene bisacetamide can be inhibited by 12-O-tetradecanoyl-phorbol-13-acetate (TPA) only if TPA-sensitive cells (TS 19-101) are used; no inhibition is observed with TPA-resistant cells (TR 19-9). The same is true of PEBIF. It has been shown that these two clones have about the same number of receptors, with no change of affinity; and the extent of inhibition of PDBu binding by PEBIF was similar in the two clones. Like TPA, PEBIF can increase 2-deoxyglucose uptake in mouse fibroblasts (BALB/3T3 cells). These data suggest that this physiological factor may play a role in the regulation of cell differentiation and/or in the modulation of carcinogenesis.
mesh_terms: D001692:Biological Transport / Q000187:drug effects; D029742:Caenorhabditis elegans Proteins; D002352:Carrier Proteins; D002454:Cell Differentiation / Q000187:drug effects; D002460:Cell Line; D003847:Deoxyglucose / Q000378:metabolism; D005260:Female; D006801:Humans; D007700:Kinetics; D004915:Leukemia, Erythroblastic, Acute; D008024:Ligands; D010703:Phorbol Esters / Q000037:antagonists & inhibitors*; D010704:Phorbols / Q000037:antagonists & inhibitors*; D010920:Placenta / Q000032:analysis*; D011247:Pregnancy; D011493:Protein Kinase C; D011956:Receptors, Cell Surface / Q000187:drug effects*; D011955:Receptors, Drug
chemical_list: D029742:Caenorhabditis elegans Proteins; D002352:Carrier Proteins; D008024:Ligands; D010703:Phorbol Esters; D010704:Phorbols; D011956:Receptors, Cell Surface; D011955:Receptors, Drug; C083141:phorbol ester binding protein; C027776:phorbol ester receptor; D003847:Deoxyglucose; D011493:Protein Kinase C