Reversible cAMP-dependent change in nuclear localization of microtubule-associated protein-1 analogues.

Intranuclear immunofluorescent staining by monoclonal and polyclonal antibodies against microtubule-associated protein-1 (MAP-1) on SV-3Y1 cells disappeared when the cells were treated with 1 mM db-cAMP and 1 mM theophylline for 20-30 min at 37 degrees C. The nuclear dots of immunofluorescence disappeared and reappeared repeatedly on successive incubation of the cells with and without these drugs. The same phenomenon was induced by treatment of the cells with 6 mM theophylline or 6 mM papaverine which inhibits the cAMP-hydrolysing enzyme. The following results seem to support the hypothesis that cAMP-induced transfer of antigenic molecules from the nucleus to the cytoplasm is mediated by microtubules: Partial staining of the nucleus during the transitional period. Bright staining of the cytoplasm on treated cells in contrast to nuclear staining on control cells. Disappearance of the nuclear staining not only by the monoclonal antibody but also by the polyclonal antibody. Complete prevention of disappearance of nuclear dots induced by these drugs by pretreatment of the cells with colchicine (1 microgram/ml) or colcemid (1 microgram/ml).