The very different effects of Cholera Toxin (CT) on cell growth and proliferation may depend on the type of ganglio-side receptors in cell membranes and different signal transduction mechanisms triggered,but other functions relatedto the drug resistance mechanisms can not be excluded.The effect of CT treatment on the "in vitro" clonogenicity,thePopulation Doubling Time (PDT),apoptosis,PKA activation and Bax and Bcl-2 expression was evaluated in WEHI-3Bcell line and its CT-resistant subclone (WEHI-3B/CTRES).In WEHI-3B parental cells the dramatic accumulation ofcAMP induced by CT correlated well with PKA activation,increased PDT value,inhibition of clonogenicity and apop-tosis.H-89 treatment inhibited PKA activation by CT but did not protect the cells from apoptosis and growth inhibition.In WEHI-3B/CTRES no significant CT-dependent accumulation of cAMP occurred with any increase of PKA activityand PDT.In CT resistant cells (WEHI-3B/CTRES),Bcl-2 expression was down regulated by both CT or drug treatment(eg.,ciprofloxacin,CPX) although these cells were protected from CT-dependent apoptosis but not from drug-inducedapoptosis.Differently from other cell models described,down regulation of Bcl-2 is proved to be independent on cAMPaccumulation and PKA activation.Our observations support the implication of cAMP dependent kinase (PKA) in theinhibition of WEHI-3B cells growth and suggest that,in WEHI-3B/CTRES,Bcl-2 expression could be modulated byCT in the absence of cAMP accumulation.Also in consideration of many contradictory data reported in literature,ourcell models(of one sensitive parental cell strain and two clones with different uncrossed specific resistance to CT andCPX)provides a new and interesting tool for better investigating the relationship between the CT signal transductionmechanisms and Bcl-2 expression and function.
