Modulation of serum-stimulated DNA synthesis in cultured human fibroblasts by cAMP

Rechler, M.M.; Bruni, C.B.; Podskalny, J.M.; Warner, W.; Carchman, R.A.

Experimental Cell Research 104(2): 411-422


ISSN/ISBN: 0014-4827
PMID: 190022
DOI: 10.1016/0014-4827(77)90106-9
Accession: 068523421

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Density-dependent inhibition of growth of cultured human fibroblasts was associated with a 3- to 4-fold rise in the intracellular concentration of cyclic AMP (cAMP). Serum lowered cAMP levels in 2-5 min, with the low levels persisting for several hours. When quiescent fibroblast cultures were treated with 10% serum, the incorporation of TdR incorporation at the peak to the same extent as db-cAMP added together with serum. The inhibition decreased progressively when db-cAMP was added more than 8 h after serum. A cAMP-sensitive step may have occurred approx. 8 h after the addition of serum in mid-G1 of the cell cycle. Results obtained using fibroblasts synchronized at the G1/S boundary with hydroxyurea or exposed to db-cAMP for 24 h suggested that db-cAMP also inhibited TdR incorporation at the G1/S interphase or during S phase. Thus, whereas reduced cAMP concentrations did not appear to serve as an initial trigger for serum-stimulated DNA synthesis in human fibroblasts, db-cAMP and SC-2964, presumably by elevating cAMP levels, appeared to act in mid-G1 and possibly at the G1/S boundary or within S phase to inhibit thymidine incorporation.