288 Signaling Response to Cyclophilin A and Stimulation of HIV-1 Infection are Independent Functions of CD147 M. Bukrinsky1, T. Pushkarsky1, V. Yurchenko2, B. Sherry3, B. Brichacek*1 1George Washington Univ Med Ctr, Washington, DC; 2Albert Einstein Coll of Med, Bronx, NY; and 3North Shore Long Island Jewish Res Inst, Manhasset, NY
Background: Cyclophilin A (CypA) is a ubiquitously distributed intracellular protein possessing peptidyl-prolyl cis-trans isomerase activity. In addition to its intracellular functions, CypA can be secreted into the extracellular environment and has been shown to induce chemotaxis of monocytes, neutrophils, and T lymphocytes.
Methods: We have demonstrated recently that this chemotactic activity of CypA is mediated by CD147, a signal-transducing receptor for extracellular cyclophilins. CypA is incorporated into HIV-1 particles through a specific interaction with the CA domain of the Gag precursor polyprotein and plays an essential role in the early steps of HIV-1 life cycle. Our recent studies demonstrated that virus-associated CypA interacts with CD147 on target cells and facilitates formation of the reverse transcription complex, thus increasing viral infectivity. However, the mechanism of the enhancing effect of this interaction is not understood. In particular, it is not clear whether signaling capacity of CD147 is required for its activity in HIV-1 entry. In this report, we demonstrate that the stimulating activity of CD147 on HIV-1 entry into target cells can be dissociated from its ability to initiate signaling response to CypA. Cells expressing CD147 carrying a mutation of Pro180Gly181 in the extracellular domain did not exhibit ERK1/2 activation after CypA stimulation, but retained CD147-specific enhanced susceptibility to HIV-1 infection. Consistent with this result, PD 98059, a specific inhibitor of mitogen-activated protein kinase kinase, did not reduce HIV-1 infection. Surprisingly, truncation of the cytoplasmic tail of CD147 did not abolish signaling response to CypA, but reduced infection by HIV-1 to the level observed in control cells.
Results: These results indicate that the cytoplasmic domain of CD147 is critical for enhancing HIV-1 infection, however, the role of this domain appears to be unrelated to signaling. The job of the CD147 cytoplasmic tail might be to tightly fix the protein in its position to prevent its displacement during virus entry. One of possible signaling-independent mechanisms by which CD147 may facilitate HIV-1 entering into target cells and virus uncoating is by anchoring the viral core shell (through p24-bound CypA) and subsequent mechanistic peeling of p24 from the core, thus revealing the capsid-less reverse transcription complex.
