CHARACTERIZATION OF 2 PITUITARY GH(3) CELL SUBLINES PARTIALLY RESISTANT TO APOPTOSIS INDUCTION BY OKADAIC ACID

Pituitary GH(3) cells die by apoptosis when treated with okadaic acid, a specific inhibitor of ser/thr phosphatases. Incubations starting at concentrations of 5 and 12.5 nM followed by stepwise rises resulted i n two populations (the S-1 and S-2 sublines) that proliferated at init ially lethal 30 nM. Cells were partially resistant to higher concentra tions of okadaic acid and its derivative methyl okadaate. Toxicity of the structurally distinct inhibitors cantharidic acid and calyculin A was differently affected in the two resistant lines. The enhanced expr ession of the P-glycoprotein was one mechanism of resistance in S-1 an d S-2. Resistance was reversed completely (S-1) or partially (S-2) by the addition of verapamil. In addition, phosphatase activity, presumab ly PP2A, was increased in S-2. Therefore, pharmacokinetic and pharmaco dynamic mechanisms can protect pituitary GH(3) cells from apoptotic ce ll death by okadaic acid. (C) 1997 Elsevier Science Inc.