Herbimycin A and geldanamycin inhibit okadaic acid-induced apoptosis and p38 activation in NRK-52E renal epithelial cells

It is important to understand the mechanisms by which phosphorylation-depen dent events play a role in regulation of apoptosis in toxicant-metabolizing organs such as the kidney. Our previous work demonstrated that the toxican t and phosphatase inhibitor okadaic acid induces apoptosis of renal epithel ial cells via a mechanism that appears to involve the modulation of c-raf-1 , p38 kinase, and extracellular regulatory kinase (ERK) cascades, Using the benzoquinone ansamycins and tyrosine kinase inhibitors geldanamycin and he rbimycin A, we examined the contribution of tyrosine phosphorylation and c- raf-1 activities to okadaic acid-induced apoptosis, In this report we show that both geldanamycin and herbimycin A protected NRK-52E cells from okadai c acid-induced apoptosis, abrogated the overall okadaic acid-induced kinase activation, and specifically inhibited activation of p38 kinase by okadaic acid. Herbimycin A and geldanamycin also abrogated okadaic-acid induced mo rphologic changes such as cell rounding and cell membrane blebbing. Herbimy cin A and geldanamycin caused pronounced cell spreading, cell flattening, a nd a decrease in okadaic acid-induced loss of actin filaments. Interestingl y, herbimycin A showed more potent inhibitory effect than geldanamycin, and herbimycin A alone inhibited okadaic acid-induced movement of p38 kinase i nto the cytosol. These results imply that decreased p38 activity and its cy tosolic translocation together with cellular resistance to cytoskeletal dis organization may play a significant role in resistance to phosphorylation-d ependent apoptosis. Furthermore, the results imply that changes in cell sha pe may partially modulate the observed alterations in signal transduction i nduced by okadaic acid. (C) 1999 Academic Press.