OBJECTIVETo investigate pig7 expression level in acute leukemia (AL) and its clinical significance and explore the possible mechanisms for pig7 silence in terms of methylation control.

METHODSExpression levels of pig7 mRNA in bone marrow samples from 138 patients with de novo AL and 21 normal controls and in 6 leukemic cell lines were detected by quantitative real-time reverse transcription PCR (RT-PCR). Differentiation induction effect by all-trans retinoic acid (ATRA) and concomitant change in pig7 expression were also monitored in NB4 cells. Endonuclease analysis was employed to determined the identity of pig7 transcript present in AL samples. Methylation specific PCR (MSP) was used to elucidate if hypermethylation was responsible for pig7 silence in AL.

RESULTSCompared with that in normal control, pig7 expression was markedly decreased (0.62 vs 18.30, median, P < 0.01) in AL patients on progression (at diagnosis, relapse or refractory). No significant difference was observed between acute myeloid leukemia (AML) and acute lymphoblastic leukemia (ALL). AL at diagnosis had a higher pig7 level than those with relapsed or refractory disease (1.43 vs 0.16, median, P < 0.05). The complete remission (CR) rate after chemotherapy was found to be significantly correlated with pig7 expression levels (P < 0.05). Differentiated NB4 cells showed an increased level of pig7 expression (from 1.61 +/- 0.72 to 44.75 +/- 3.93, P < 0.01). Only one form of pig7 transcripts i.e., Small integral membrane protein of late endosome (SIMPLE), was detected in AL patients. Hypermethylation of pig7 promoter was identified in K562 and HL-60 cells, in contrast to non-methylation predominant in U937 cells.

CONCLUSIONAberrant down-regulation of pig7 provides novel insights into leukemogenesis and therapy response prediction in AL.