Anti-proliferative effects of 8-chloro-cAMP and other cAMP analogs are unrelated to their effects on protein kinase A regulatory subunit expression.
Conflicting reports have attributed 8-chloro-cAMP (Cl-cAMP)-mediated inhibition of tumor cell growth to either a toxic 8-chloro-adenosine (Cl-AdR) breakdown product or a Cl-cAMP-mediated decrease in ratio of Type I to Type II regulatory (R) subunits of protein kinase A (PKA). Using the MCF-7 human breast cancer and S49 mouse lymphoma cell lines as models, we show that the effects of Cl-cAMP and other cAMP analogs on growth and R subunit expression are unrelated. MCF-7 cell growth was insensitive to most analogs and inducers of cAMP, but was potently inhibited by Cl-cAMP acting through uptake and phosphorylation of its Cl-AdR breakdown product. Possible roles of adenosine receptors or P(2) purinoceptors in these Cl-cAMP-mediated growth effects were ruled out by studies with agonists and antagonists. Cholera toxin markedly decreased the ratio of Type I to Type II R subunits in MCF-7 cells without affecting growth, while growth inhibitory concentrations of Cl-cAMP or Cl-AdR had insignificant effects on this ratio. In S49 cells, where PKA activation is known to inhibit cell growth, PKA-deficient mutants retained sensitivity to both Cl-cAMP and the related 8-bromo-cAMP. Adenosine kinase (AK)-deficient S49 cells were inhibited only by higher concentrations of these 8-halogenated cAMP analogs. Of the commonly used cAMP analogs, only 8-(4-chlorophenylthio)-cAMP acted purely as a cyclic nucleotide-having no effect on PKA-deficient cells, but strongly inhibiting both wild-type and AK-deficient cells. Where growth inhibitory concentrations of most cAMP analogs reduced RI expression in the AK-deficient mutant, a functionally equivalent concentration of (N(6), O(2'))dibutyryl-cAMP maintained or increased this expression.
Lamb
Darija
D
Department of Biochemistry and Molecular Biology, The University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma 73190, USA.
Steinberg
Robert A
RA
D015762:2-Chloroadenosine / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology*; D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology*; D000248:Adenosine Kinase / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D002455:Cell Division / Q000187:drug effects; D054746:Cyclic AMP-Dependent Protein Kinase Type II; D017868:Cyclic AMP-Dependent Protein Kinases / Q000172:deficiency / Q000187:drug effects / Q000378:metabolism*; D015870:Gene Expression / Q000187:drug effects; D006801:Humans; D051379:Mice; D009154:Mutation; D021122:Protein Subunits; D014407:Tumor Cells, Cultured
D000970:Antineoplastic Agents; D021122:Protein Subunits; D015762:2-Chloroadenosine; D015124:8-Bromo Cyclic Adenosine Monophosphate; C044258:8-chloro-cyclic adenosine monophosphate; D000248:Adenosine Kinase; D054746:Cyclic AMP-Dependent Protein Kinase Type II; D017868:Cyclic AMP-Dependent Protein Kinases; C075440:8-chloroadenosine