Retinoids, all-trans-retinoic acid (ATRA) and 9-cis-retinoic acid (9-cis-RA
), induced morphological changes and apoptosis-like cell death characterize
d by cell shrinkage, chromatin condensation and nuclear disintegration in t
hree canine osteosarcoma cells, OOS, HOS and POS, at a concentration of 10(
-5) M. Both retinoid receptors, RARs and RXRs, were identified in these cel
ls. 9-cis-RA bound to both the RXRs and the RARs, whereas ATRA bound to onl
y the RARs in these cells. Those results indicate that the induction of apo
ptosis in canine osteosarcoma cells may be mediated by the specific control
of RARs and RXRs.