PLACEMENT OF THE BCL2 FAMILY MEMBER BAX IN THE DEATH PATHWAY OF SYMPATHETIC NEURONS ACTIVATED BY TROPHIC FACTOR DEPRIVATION

The BCL2 family member BAX is required for the induction of apoptosis in neonatal sympathetic neurons after NGF withdrawal. Bax-deficient sy mpathetic neurons are NGF-independent for survival. To characterize th e physiological state of neurons protected by BAX deficiency and to pl ace BAX within the death pathway, we determine which of the molecular changes induced by NGF deprivation depend on BAX and compare the resul ts with those for neurons protected by caspase inhibition. We find tha t neurons deficient in both Bax: and Bcl2 resist NGF-deprivation simil ar to Bax-deficient neurons discounting a role for BCL2 in the mechani sm by which Bar deficiency causes trophic factor independence. We iden tify two new molecular changes, phosphorylation of c-Jun on Ser(63) an d alpha-spectrin proteolysis, which precede and accompany apoptosis, r espectively. Early reversible changes induced by NGF withdrawal, such as decreased protein synthesis and glucose uptake, increased c-Jun pho sphorylation, increased steady state c-jun mRNA levels, and cellular a trophy, occur both in wild type and Bax-deficient neurons and thus are BAX-independent. In contrast to neurons protected by caspase inhibiti on, no c-fos induction occurs in Bax-deficient neurons. Terminal irrev ersible events of apoptosis such as caspase-mediated ol-spectrin prote olysis are prevented by both Bax-deficiency and caspase inhibition. Th is places BAX downstream or in a different pathway of the early change s and upstream of the terminal events such as those leading to c-fos i nduction and caspase activation. This order indicates that the physiol ogical state of NGF-deprived neurons protected by Bax deficiency may b e less perturbed than that of caspase inhibitor-saved neurons. (C) 199 8 Academic Press.