A Study of the Protein Phosphatase 2A Involved in the Induction of NB4 and MR2 Cell Differentiation by ATRA.

Objective: To study whether protein phosphatases type 2A (PP2A) plays an important role in signal transduction of differentiation of NB4 induced by all-trans retinoic acid, furthermore, to evaluate whether PP2A plays an important role in MR2 resistance to ATRA.

Methods: ATRA, Okadaic acid (OKA) and both chemicals were incubated with NB4 and MR2 cells respectively. Wright’ staining and NBT reduction test were employed to evaluate the changes of cell phenotype. The expression of CD11b was measured by flow cytometer, and the proliferation of cells was measured by MTT method. At last the activity of PP2A was evaluated by Serine/Threonine phosphatase assay system.

Results: Results showed ATRA induced differentiation of NB4 significantly, but no effect on MR2 cell through Wright’ staining and NBT reduction test. OKA, the specific inhibitor of PP2A, could augment the differentiation induced by ATRA, and it combined with ATRA showed the slight induction of differentiation of MR2 cell. MTT showed the inhibitory rate of proliferation of ATRA, OKA and ATRA combined with OKA to NB4 were 25.1%, 10.1% and 38.4% respectively, and to MR2 were 4.8%, 7.2% and 19.3%. When ATRA, and ATRA combined with OKA were incubated with NB4 and MR2 respectively, the expression of CD11b on the surface of NB4 cell were 43.1% and 65.4% and on the surface of MR2 were from 0 to 9.3%. When OKA combined with ATRA were incubated with MR2, MR2 have showed the decreased activity of PPA. Conclusion PP2A plays an important role in the mechanism of differentiation of NB4 induced by ATRA and of resistance of MR2 to ATRA.