Secretory Leukocyte Protease Inhibitor Binds to Annexin II, a Cofactor for Macrophage HIV-1 Infection

Ma, Ge; Greenwell-Wild, Teresa; Lei, Kejian; Jin, Wenwen; Swisher, Jennifer; Hardegen, Neil; Wild, Carl T.; Wahl, Sharon M.

Annexin II Interacts with PS. How annexin II might support HIV-1 infection of macrophages was a mystery, but a recent study reporting that HIV-1 membranes contain PS (14) provided a potential clue. Although no binding partner for HIV-PS had been identified, we surmised that annexin II, a phospholipid-binding protein, might be a candidate. In this regard, direct binding of HIV-1 to platebound annexin II, but not irrelevant proteins, was demonstrated (Fig. 5 A) . Moreover, to verify an HIV-PS-macrophage annexin II connection, we exposed HIV-1 to excess soluble annexin II to bind/coat viral PS before addition to macrophages, and this markedly suppressed subsequent in- By RT-PCR, annexin II mRNA expression was higher in macrophages than freshly isolated blood monocytes (representative RT-PCR shown; graph represents mean Ϯ SD; n ϭ 3; *, P Ͻ 0.002). (B and C) By flow cytometry, purified CD4 ϩ CD14 ϩ monocytes expressed surface annexin II, with minimal expression on CD4 ϩ T cells. Shaded histograms represent annexin II fluorescence and white histograms represent cells stained with the isotype control antibody. (D) By coimmunoprecipitation and Western analysis, annexin II was detected in macrophage, but not T cell, membrane preparations. fection (Fig. 5 B) , compatible with inhibition of infection by soluble annexin V and/or PS vesicles (14) .