[Establishment and characterization of rat myelomonocytic leukemia clones undergoing differentiation or apoptosis]

It has not clearly been elucidated how differently differentiation-inducing drugs act on tumor cells, whether they promote differentiation or apoptosis. To elucidate the mechanisms whether leukemic cells responding to ONO-4007, a lipid A derivative, undergo differentiation or apoptosis, we established two cell clones from a rat myelomonocytic leukemia c-WRT-7/P2 clone which undergoes differentiation followed by apoptosis by ONO-4007-treatment. One of the clones (1D6) showed the features of differentiation, such as phagocytosis when treated with ONO-4007 more than 24 hrs. The other clone (3B1) clearly showed the features of apoptosis, such as DNA ladder formation within 24 hrs after incubation with ONO-4007. We then examined expression of CD14, p21, p38MAPK, JNK/SAPK, and bcl-2, functional p53 statuses and cell cycle in these two clones, and revealed the following: Without treatment with ONO-4007; 1) CD14, p21, and bcl-2 proteins were equally expressed in both clones; 2) wild-type and non-functional mutated-type p53 were present in both clones and the p53 in 3B1 clone was recessive whereas that in 1D6 clone was dominant negative; 3) p38MAPK in 3B1 clone was already phospholyrated whereas that in 1D6 clone was not. After treatment with ONO-4007; 1) neither expressions of CD14 nor that of p21 protein was changed in any of the clones; 2) p38MAPK in 3B1 clone was dephospholyrated at 1 and 2 hrs after treatment whereas that in 1D6 clone was phospholyrated at 4 and 8 hrs after treatment; 3) the expression of bcl-2 protein in 3B1 clone was reduced. These findings suggest that p53 may be one of the key factors in leading these cells to differentiation or apoptosis, and that bcl-2 may suppress the apoptosis.