ERK activation increases nitroprusside induced apoptosis in  human melanoma  cells  irrespective of p53 status: Role of  superoxide dismutases

Abstract

Constitutive ERK activation, superoxide dismutases   (SOD)  and  p53 mutations     are

implicated in modulating  tumor apoptotic response. We now investigated whether

human melanoma survival  in response to sodium nitroprusside (SNP) is modulated by:

a) stable introduction of  a DN- mutant p53 ; b) pharmacologically  inhibiting ERK

activation with UO126 ; c)  addition of exogenous SOD.  Nitroprusside     releases nitric

oxide   (NO) when intact , or acts  in a NO-independent manner  via   iron and residual

cyanide after  light exposure (lex-SNP) . When tested  at 300 µM in 72 hour treatments

by cytometric  live-dead assays   , intact  SNP  caused a 50 % lethality  versus a 30 %

lethality  induced by lex-SNP. No  protection from SNP toxicity was seen  when  

inhibiting  the  PI3-kinase  pathway  with  LY294002  or c-Jun NH(2) kinase  signaling

with  SP600125. However   , pretreatment with UO126 protected from   SNP –mediated 

cell death including  counteracting apoptosis-associated  Bax expression and PARP

cleavage, plus  reversing   loss of  Cu,Zn-SOD.   Moreover ,  addition of exogenous

SOD also protected cells from SNP toxicity.    In spite of the  greater earlier effects of 

intact SNP, cells treated with  single doses of either  intact or lex-SNP, revealed  about a 

90 % mortality  in longer 120 hour treatments, and  these were also counteracted   by

UO126 or  exogenous SOD.  This report   is   the   first to show   that:   constitutive

ERK activation characteristic of cancer cells,   increases a nitroprusside-induced 

apoptosis  modulated by SOD.