Augmentation of postconfluence growth arrest of 10T1/2 fibroblasts by endogenous cyclic adenosine 3':5'-monophosphate.
We have previously demonstrated that, by elevating intracellular adenosine 3':5'-cyclic monophosphate (cAMP) levels by inhibition of cAMP phosphodiesterase with Ro 20-1724 or by forskolin stimulation of adenylcyclase, the growth of neoplastically transformed 10T1/2 fibroblasts could be inhibited when these cells were in contact with growth-inhibited nontransformed 10T1/2 cells (J. S. Bertram and M. B. Faletto, Cancer Res., 45: 1946-1952, 1985) and furthermore that the extent of this growth inhibition correlated strongly with the degree of junctional communication between the two cell types (P.P. Mehta et al., Cell, 44: 187-196, 1986). To determine if these treatments enhance the degree of growth control of the nontransformed 10T1/2 cells, cultures were exposed to varying concentrations of Ro 20-1724 and/or forskolin. Drug treatment caused no significant effects on growth rate or cell spreading when cells were treated during logarithmic growth phase; however, major reductions of up to 70% in confluent saturation density and concomitant increases in cell spreading occurred in cultures making extensive cell/cell contacts. Decreases in saturation density correlated strongly with induced elevations of both intra- and extracellular cAMP concentrations. These effects could not be duplicated by the addition of exogenous cAMP agonists 8-bromo-cAMP and/or dibutyryl-cAMP. Two-dimensional electrophoresis of phosphate-labeled proteins revealed that forskolin treatment induced a quantitatively and qualitatively different phosphorylation profile than did 8-bromo-cAMP. Both basal and drug-induced intracellular cAMP levels fell as cells progressed from logarithmic to confluent growth state, implying that cells become sensitized to cAMP by the attainment of extensive cell/cell contacts. It is suggested that the drug-induced elevations of endogenously synthesized cAMP are accentuating a physiological role of cAMP on the postconfluent growth arrest of murine fibroblasts. The requirements for cell/cell contact and the known increased junctional communication induced by cAMP furthermore suggest that cAMP is enhancing the junctional transfer of a growth-inhibiting regulatory molecule. A likely candidate is cAMP itself.
Matsukawa
T
T
Cancer Research Center of Hawaii, University of Hawaii, Honolulu 96813.
Bertram
J S
JS
D015105:3',5'-Cyclic-AMP Phosphodiesterases / Q000037:antagonists & inhibitors; D012368:4-(3-Butoxy-4-methoxybenzyl)-2-imidazolidinone / Q000494:pharmacology; D000262:Adenylyl Cyclases / Q000378:metabolism; D000818:Animals; D002455:Cell Division / Q000187:drug effects*; D002460:Cell Line; D005576:Colforsin / Q000494:pharmacology; D003260:Contact Inhibition / Q000187:drug effects*; D000242:Cyclic AMP / Q000494:pharmacology / Q000502:physiology*; D003593:Cytoplasm / Q000502:physiology; D066298:In Vitro Techniques; D051379:Mice; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D010750:Phosphoproteins / Q000378:metabolism; D013997:Time Factors
D010726:Phosphodiesterase Inhibitors; D010750:Phosphoproteins; D005576:Colforsin; D012368:4-(3-Butoxy-4-methoxybenzyl)-2-imidazolidinone; D000242:Cyclic AMP; D015105:3',5'-Cyclic-AMP Phosphodiesterases; D000262:Adenylyl Cyclases