ABSTRACT
1. The regulation of large conductance calcium- and voltage-activated potassium (BK) currents by activation of the protein kinase C (PKC) and glucocorticoid signalling pathways was investigated in AtT20 D16:16 clonal mouse anterior pituitary corticotroph cells. 2. Maximal activation of PKC using the phorbol esters, 4beta-phorbol 12-myristate, 13-acetate (PMA), phorbol 12, 13 dibutyrate (PDBu) and 12-deoxyphorbol 13-phenylacetate (dPPA) elicited a rapid, and sustained, inhibition of the outward steady-state voltage- and calcium- dependent potassium current predominantly carried through BK channels. 3. The effect of PMA was blocked by the PKC inhibitors bisindolylmaleimide I (BIS; 100 nM) and chelerythrine chloride (CHE; 25 microM) and was not mimicked by the inactive phorbol ester analogue 4alpha-PMA. 4. PMA had no significant effect on the 1 mM tetraethylammonium (TEA)-insensitive outward current or pharmacologically isolated, high voltage-activated calcium current. 5. PMA had no significant effect on steady-state outward current in cells pre-treated for 2 h with 1 microM of the glucocorticoid agonist dexamethasone. Dexamethasone had no significant effect on steady-state outward current amplitude or sensitivity to 1 mM TEA and did not block PMA-induced translocation of the phorbol ester-sensitive PKC isoforms, PKCalpha and PKCepsilon, to membrane fractions. 6. Taken together these data suggest that in AtT20 D16:16 corticotroph cells BK channels are important targets for PKC action and that glucocorticoids inhibit PKC signalling downstream of PKC activation.
Subject(s)
Glucocorticoids/pharmacology , Pituitary Gland, Anterior/physiology , Potassium Channels, Calcium-Activated , Protein Kinase C/physiology , Signal Transduction/drug effects , Animals , Blotting, Western , Cells, Cultured , Electrophysiology , Enzyme Activation/drug effects , Enzyme Activation/physiology , Large-Conductance Calcium-Activated Potassium Channels , Mice , Patch-Clamp Techniques , Phorbol Esters/pharmacology , Pituitary Gland, Anterior/cytology , Pituitary Gland, Anterior/drug effects , Potassium Channel Blockers , Potassium Channels/agonists , Potassium Channels/metabolism , Protein Kinase C/metabolismABSTRACT
We have investigated the activity of STAT family members throughout a mammary developmental cycle. Transcripts for Stat 5 were upregulated during pregnancy whilst STAT1 and STAT3 mRNAs were expressed at constant levels. DNA binding complexes containing both STAT5a and 5b showed differing affinities for two naturally occurring STAT5 binding sites. In the involuting mammary gland STAT5 activity decreased whereas STAT3 was specifically activated. These observations reveal a complex pattern of activation of STAT factors during mammary growth, differentiation and remodelling and provide the first evidence for the involvement of STAT3 in development of the mammary gland.
