INHIBITION OF HUMAN-IMMUNODEFICIENCY-VIRUS REV AND HUMAN T-CELL LEUKEMIA-VIRUS REX FUNCTION, BUT NOT MASON-PFIZER MONKEY VIRUS CONSTITUTIVETRANSPORT ELEMENT ACTIVITY, BY A MUTANT HUMAN NUCLEOPORIN TARGETED TOCRM1

The hypothesis that the cellular protein Crm1 mediates human immunodef iciency virus type 1 (HTV-1) Rev-dependent nuclear export posits that Crm1 can directly interact both with the Rev nuclear export signal (NE S) and with cellular nucleoporins. Here, we demonstrate that Crm1 is i ndeed able to interact with active but not defective forms of the HTV- 1 Rev NES and of NESs found in other retroviral nuclear export factors . In addition, we demonstrate that Crm1 can bind the Rev NES when Rev is assembled onto the Rev response element RNA target and that Crm1, l ike Rev, is a nucleocytoplasmic shuttle protein. Crm1 also specificall y binds the Rev NES in vitro, although this latter interaction is dete ctable only in the presence of added Ran GTP. Overexpression of a trun cated, defective form of the nucleoporin Nup214/CAN, termed Delta CAN, that retains Crm1 binding ability resulted in the effective inhibitio n of HIV-1 Rev or human T-cell leukemia virus Rex-dependent gene expre ssion. In contrast, Delta CAN had no significant affect on Mason-Pfize r monkey virus constitutive transport element (MPMV CTE)-dependent nuc lear RNA export or on the expression of RNAs dependent on the cellular mRNA export pathway. As a result, Delta CAN specifically blocked late , but not early, HTV-1 gene expression in HIV-l-infected cells. These data strongly validate Crm1 as a cellular cofactor for HIV-1 Rev and d emonstrate that the MPMV CTE nuclear RNA export pathway uses a distinc t, Crm1-independent mechanism. In addition, these data identify a nove l and highly potent inhibitor of leucine rich NES-dependent nuclear ex port.