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Cyclic adenosine monophosphate acts synergistically with dexamethasone to inhibit the entrance of cultured adult rat hepatocytes into S‐phase: With a note on the use of nucleolar and extranucleolar [ 3 H]‐thymidine labelling patterns to determine rapid changes in the rate of onset of DNA replication
Author(s) -
Vintermyr Olav Karsten,
Mellgren Gunnar,
Bøe Roald,
Døskeland Stein Ove
Publication year - 1989
Publication title -
journal of cellular physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.529
H-Index - 174
eISSN - 1097-4652
pISSN - 0021-9541
DOI - 10.1002/jcp.1041410219
Subject(s) - adenosine , dna synthesis , ibmx , medicine , thymidine , cell cycle , endocrinology , biology , dexamethasone , hepatocyte , microbiology and biotechnology , intracellular , cell , dna , chemistry , biochemistry , in vitro , forskolin , stimulation
Analogs of cyclic adenosine monophosphate (cAMP) (N 6 benzoyl cAMP and N 6 monobutyryl cAMP) as well as agents that increased the intracellular level of cAMP (glucagon and isobutylmethylxanthine) inhibited the EGF‐stimulated DNA replication of adult rat hepatocytes in primary culture independently of cell density. This inhibition was strongly potentiated by the glucocorticoid dexamethasone. The effect of cAMP (and dexamethasone) was not due to toxicity, because the inhibition was reversible and the cell ultrastructure preserved. cAMP acted by decreasing the rate of transition from G 1 ‐ to S‐phase, the duration of G 2 ‐ and S‐phase of the hepatocyte cell cycle being unaffected. DNA replication started in the extranucleolar compartment of the nucleus and ended in the nucleolar compartment as described earlier for cells grown in the absence of cAMP (O.K. Vintermyr and S.O. Døskeland, J. Cell. Physiol., 1987, 132:12‐21). The action of cAMP was very rapid: significant inhibition of the transition was noted 2 hr after the addition of glucagon/IBMX and half‐maximal inhibition after 4 hours. The determination of extranucleolarly labelled nuclei in cells pulse‐labelled with [ 3 H]thymidine allowed precise analysis of rapid changes in the probability of transition from G 1 ‐ to S‐phase. The extranucleolar labelling index could also be determined in cells continuously exposed to [ 3 H]thymidine.