The Receptor Binding of Insulin and Poly(Adpribose)-Synthesis during the Cell Cycle
Hormones can influence the poly(ADP-ribose)-synthesis in the nuclei of cells. But ADP-ribosylation of a component of the receptor adenylate cyclase system influences also cell functions via the cAMP level. In our investigations Chang liver cells, which are target cells for insulin, and HeLa cells were treated with insulin, 3-methoxybenzamide or both agents together and the insulin receptor sites determined with FITC-labeled insulin. In HeLa cells insulin as well as methoxybenzamide decreased the FITC-insulin binding to cytoplasmic and nuclear receptor sites. In contrast to this result, both compounds generates higher receptor binding sites in Chang liver cells. Both cell lines were synchronized by thymidine and N20 treatment. HeLa cells had after pretreatment with insulin, especially during the S-phase, decreased insulin receptor sites. These investigations were done at different times after starting the cell cycle progression after the release of the mitotic block. The highest binding values were obtained at the end of the S-phase and beginning of G2. The poly(ADP-ribose)-synthesis in untreated HeLa cells showed 3 peaks. The first peak was at the beginning of G1, the second at the first part of the S-phase and the third near the end of the DNA synthesis. In insulin pretreated HeLa cells only the 1st and 2nd peak appeared, not the third. The poly(ADP-ribose)-synthesis in the 1st part of S-phase was strongly increased. In Chang liver cells, insulin pretreatment changes the PAR-synthesis pattern strongly. From nucleoid sedimentation studies we could show that poly(ADP-ribose)-synthesis on DNA-nuclear cage binding sites is reduced after insulin treatment, which is possibly connected to increased transcription activity.
KeywordsEDTA Cage Tyrosine Sedimentation Adenosine
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