1,25-DIHYDROXYVITAMIN D-3 ALTERS THE EFFECT OF CAMP IN THYROID-CELLS BY INCREASING THE REGULATORY SUBUNIT TYPE II-BETA OF THE CAMP-DEPENDENT PROTEIN-KINASE

1,25-Dihydroxyvitamin D-3 (1,25-(OH)(2)D-3) attenuates the stimulatory effects of cAMP on proliferation and iodide uptake in rat thyroid FRT L-5 cells. This study examines the effects of 1,25-(OH)(2)D-3 on the c AMP-dependent protein kinase (PKA). Cytosol proteins separated by anio n exchange chromatography showed increased [H-3]cAMP binding activity as well as increased kinase activity in the fractions containing PKA t ype II in 1,25(OH)(2)D-3 (10 nM)-treated cells compared to the control cells, Western blot analysis of 1,25-(OH)(2)D-3-treated cells reveale d a 4-fold increase in the cytosolic amount of the PKA regulatory subu nit RII beta, whereas no changes were detected in the regulatory subun its RI alpha and RII alpha or the catalytic (C) subunit. Northern blot analyses showed a similar increase in RII beta mRNA in cells treated for 12 h with 1,25-(OH)(2)D-3 (10 nM), and RII beta mRNA increased fur ther to 10-fold above control cell level after 96 h of incubation. Iod ide uptake was synergistically stimulated with both PKAI- and PKAII-di rected pairs of cAMP analogs, The PKAI synergism was, however, inhibit ed by 1,25-(OH)(2)D-3 treatment of the cells, whereas the PKAII synerg ism was unaffected. In conclusion, 1,25-(OH)(2)D-3 attenuates both PKA I formation and PKAI-stimulated iodide uptake in rat thyroid FRTL-5 ce lls by increasing the level of RII beta without altering the other PKA subunit levels.