Human Immunodeficiency Virus Type 1 Vpr Binds to the N Lobe of the Wee1 Kinase Domain and Enhances Kinase Activity for Cdc2

Abstract

Human immunodeficiency virus type 1 Vpr is a virion-associated accessory protein that has multiple activities within an infected cell. One of the most dramatic effects of Vpr is the induction of cell cycle arrest at the G ₂ /M boundary, followed by apoptosis. This effect has implications for CD4 ⁺ cell loss in AIDS. In normal cell cycle regulation, Wee1, a key regulator for G ₂ -M progression, phosphorylates Tyr15 on Cdc2 and thereby blocks the progression of cells into M phase. We demonstrate that Vpr physically interacts with Wee1 at the N lobe of the kinase domain analogous to that present in other kinases. This interaction with Vpr enhances Wee1 kinase activity for Cdc2. Overexpression of Wee1 kinase-deficient mutants competes for Vpr-mediated cell cycle arrest, and deletion of the region of Wee1 that binds Vpr abrogates that competition. However, the Vpr mutants I74P and I81P, which fail to induce G ₂ arrest, can bind to and increase the kinase activity of Wee1 to the same extent as wild-type Vpr. Therefore, we conclude that the binding of Vpr to Wee1 is not sufficient for Vpr to activate the G ₂ checkpoint, and it may reflect an independent function of Vpr.