Apoptosis induction associated with cell cycle dysregulation by rice bran agglutinin

Effects of rice bran agglutinin (RBA) on human monoblastic leukemia U937 ce lls were examined in comparison with those of wheat germ agglutinin (WGA) a nd Viscum album agglutinin (VAA). These lectins inhibit cell growth, and se veral lines of evidence indicate that the growth inhibition is caused by th e induction of apoptosis. We observed that RBA induces chromatin condensati on, externalization of membrane phosphatidylserine, and DNA ladder formatio n, features of apoptosis. DNA ladder formation was inhibited by a general i nhibitor against caspases, which are known to play essential roles in apopt osis. Flow cytometric analysis revealed that RBA and WGA cause G2/M phase c ell cycle arrest with increased expression of Waf1/p2l, while cell cycle ar rest was not observed for VAA. These data indicate that RBA induces apoptos is associated with cell cycle arrest in U937 cells, and suggest that the in duction mechanism for RBA is similar to that for WGA, but different from th at for VAA.