Excess nitric oxide (NO) induces apoptosis in some cell types, including ma
crophages, Heat shock protein of 70 kDa (hsp70) has been reported to protec
t cells from various stresses, including apoptosis-inducing stimuli. Severa
l mammalian cytosolic DnaJ homologs, partner chaperones of hsp70 family mem
bers, have been identified. We asked if a DnaJ homolog is required to preve
nt NO-mediated apoptosis. When mouse macrophage-like RAW 264.7 cells were t
reated with an NO donor, SNAP, apoptosis occurred. This apoptosis could be
prevented by pretreatment of the cells with heat or a low dose of SNAP. Und
er these conditions, levels of hsc70 (an hsp70 member) remained unchanged,
whereas hsp70 was markedly induced. Of the DnaJ homologs dj1 (hsp40/hdj-1)
was strongly induced and dj2 (HSDJ/hdj-2) was moderately induced. In transf
ection experiments, hsp70, hsc70, di1 or dj2 alone was ineffective in preve
nting NO-mediated apoptosis, In contrast, both dj1 and dj2, in combination
with hsc70 or hsp70, prevented the cells from apoptosis, The hsp70-DnaJ cha
perone pairs exerted their anti-apoptotic effects upstream of caspase 3 act
ivation, and apparently upstream of cytochrome c release from mitochondria.