Objective       To determine the alteration of human stem cell marker Musashi2 (Msi2) in the differentiation of human myelomonocytic leukemia cell line THP-1 induced by phorbol myristoyl acetate (PMA).       Methods      After THP-1 cells were incubated with PMA for 0

6

12 and 24 h respectively

the cell morphological changes were observed under an inverted microscope. The proportion of differentiated cells was calculated. The expression of CD11b

which is a THP-1 cell differential surface marker

was assayed using flow cytometry (FCM). Real-time PCR and Western blotting were applied to detect the mRNA and protein expression of Msi2 respectively. The expression of Msi2 downstream signal molecule Numb was detected by real-time PCR. The mRNA and protein expression of Numb downstream signal molecule Notch1 were detected by real-time PCR and Western blotting respectively.       Results      The THP-1 cells treated by PMA for 24 h showed differential phenotype of macrophages. The proportion of differentiated cells in the experimental group was significantly higher than that in the untreated group (P0.05)

and the expression of CD11b significantly increased in the 24 h treatment group (59.30±8.70) compared with that in the untreated group (0.32±0.08) (P0.05). The mRNA and protein relative expression of Msi2 were (0.33±0.08) and (0.50±0.01) in the THP-1 cells treated by PMA for 24 h

respectively

and were significantly lower than that in the untreated group (P0.05). Numb mRNA relative expression was 2.92±0.33 after PMA treatment for 12 h

and was significantly higher than that in the untreated group (P0.05). However

when THP-1 cells were treated by PMA for 24 h

the mRNA and protein relative expression of Notch1 were 0.31±0.03 and 0.23±0.01

respectively

which decreased significantly compared with that in the untreated group (P0.05).       Conclusion      The expression of stem cell marker Msi2 reduces significantly during THP-1 cell differentiation

indicating Msi2-Numb-Notch1 pathway may regulate the differentiation of leukemia cells.