Involvement of ras activation in toxic hair cell damage of the mammalian cochlea.
To identify possible intracellular mediators of hair cell (HC) death due to ototoxins, we treated basal-turn, neonatal, rat HCs in vitro with several intracellular signaling inhibitors, prior to and during gentamicin exposure. The general guanine nucleotide-binding protein (G-protein) inhibitor, GDP-betaS (1 mM), provided potent HC protection, suggesting involvement of G-proteins in the intracellular pathway linking gentamicin exposure to HC death. ADP-betaS had minimal effect, indicating that the protection is specific to guanosine diphosphate (GDP)-binding, rather than a general reaction to nucleotides. Azido-GTP(32) photolabeling and gel electrophoresis indicated activation of an approximately 21 kDa G-protein in HCs after exposure to gentamicin. Spectroscopic analysis of peptide fragments from this band matched its sequence with H-Ras. The Ras inhibitors B581 (50 microM) and FTI-277 (10 microM) provided potent protection against damage and reduced c-Jun activation in HC nuclei, suggesting that activation of Ras is functionally involved in damage to these cells due to gentamicin.
Battaglia
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Department of Surgery, University of California, San Diego, School of Medicine, 9500 Gilman Drive 0666, La Jolla, CA 92093-0666, USA.
Pak
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Brors
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Bodmer
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Frangos
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Ryan
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D000818:Animals; D003051:Cochlea / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005839:Gentamicins / Q000633:toxicity*; D006131:Growth Inhibitors / Q000494:pharmacology; D006198:Hair Cells, Auditory / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D018631:ras Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*
D004791:Enzyme Inhibitors; D005839:Gentamicins; D006131:Growth Inhibitors; D018631:ras Proteins