Molecular Mechanism Of Regulation Of Extramedullary Infiltration In AML1/ETO Positive Acute Myeloid Leukemia By APP/ERK/MMP-2

Amyloid precursor protein (APP) has been reported to be highly expressed in AML1/ETO positive acute myeloid leukemia (AML1/ETO+ AML), and we found it express even higher in those with extramedullary infiltration in our previous study. But it’s still unknown what role APP plays and how it works in AML1/ETO+ AML. This study was designed to investigate the effect of APP gene on the prognosis and its molecular mechanism of extramedullary infiltration in the patients with AML1/ETO+ AML.

44 cases of AML1/ETO+ AML patients with median age of 29 years old, who were admitted to our hospital from February, 2006 to February, 2012 and made the diagnosis according to WHO2008 diagnosis standard, and had completed conventional induction, consolidation and intensive therapy, were investigated in this study. They were divided into high expression group (n=22) and low one (n=22) according to APP mRNA median expression level from bone marrow cells before the first chemotherapy by QRT-PCR. Some of bone marrow samples were checked by Western Blot, and 5 biopsy specimens from extramedullary infiltration were tested by APP antibody immunohistochemistry staining. Incidence of extramedullary leukemia (EML), complete response (CR), overall survival (OS), and recurrence free survival (RFS) was differentiated between the two groups. Differences of cell ultrastructure, migration, proliferation, apoptosis and expression of ERK, MMP-2, MMP-9 and CXCR4 were studied on Kasumi-1 cell line between wild, negative control (NC) and si-APP group in which the expression levels of APP gene were down regulated with application of siRNA technology.Çå

The incidence of EML was significantly different (45.5% versus 9.1%) in the two groups (P=0.007) and it was positively correlative with the expression levels of APP mRNA (r_p=0.435, P=0.004). Extramedullary infiltration site also showed high expression of APP by immunohistochemistry, while the control group was negative. Not only CR rate after two courses of chemotherapy, but also OS and RFS with median follow-up of 28(4-70) months, of high expression group was all significantly lower than that of low expression group (Table 1). Compared with the wild and NC group, cell apoptosis of si-APP group was significantly increased (12.33 ± 0.75 vs 19.80 ± 1.51, P=0.000); the number of microvilli on the surface of the cell membrane significantly reduced; the ability of the cell migration by Tanswell chamber migration assay significantly decreased (P=0.004); and expression of P-ERK, c-MYC, MMP-2 decreased significantly which was confirmed by ERK and c-MYC blocker treatment (Figure 1).

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In sum, incidence of EML is significantly higher and the prognosis is poor in the patients with AML1/ETO+ AML with high expression of APP gene. We first describe that APP gene may mediate AML1/ETO+ leukemia cells in the development of extramedullary infiltration by up-regulation of the ERK/MMP-2 pathway.