Regulation of annexin II by cytokine-initiated signaling pathways and E2A-HLF oncoprotein.
ABSTRACT In pro-B cell acute lymphoblastic leukemia (ALL), expression of the E2A-HLF fusion gene as a result of t(17;19)(q22;p13) is associated with poor prognosis, hypercalcemia, and hemorrhagic complications. We previously reported that the E2A-HLF fusion protein protects interleukin-3 (IL-3)-dependent lymphoid cells from apoptosis caused by cytokine starvation. Here, we report that annexin II, a surface phospholipid-binding protein and one of the proposed causes of the hemorrhagic complications of acute promyelocytic leukemia (APL), is also implicated in t(17;19)+ ALL. Annexin II was expressed at high levels in APL cells and in each of 4 t(17;19)+ leukemia cell lines, and annexin II expression was induced by enforced expression of E2A-HLF in leukemia cells. In IL-3-dependent cells, we found that annexin II expression was regulated by IL-3 mainly by Ras pathways, including Ras/phosphatidylinositol 3-kinase pathways. Moreover, E2A-HLF increased annexin II expression in IL-3-dependent cells in the absence of the cytokine. These findings indicate that E2A-HLF induces annexin II by substituting for cytokines that activate downstream pathways of Ras.