Latency-associated nuclear antigen encoded by Kaposi's sarcoma-associated herpesvirus interacts with tat and activates the long terminal repeat of human immunodeficiency virus type 1 in human cells

The latency-associated nuclear antigen (LANA) is constitutively expressed i n cells infected with the Kaposi's sarcoma (KS) herpesvirus (KSHV), also re ferred to as human herpesvirus 8. KSHV is tightly associated with body cavi ty-based lymphomas (BCBLs) in immunocompromised patients infected with huma n immunodeficiency virus (HIV). LANA, encoded by open reading frame 73 of K SHV, is one of a small subset of proteins expressed during latent infection and was shown to be important in tethering the viral episome to host chrom osomes. Additionally, it has been shown that LANA can function as a regulat or of transcription. However, its role in the progression of disease is sti ll being elucidated. Since KS is one of the most common AIDS-associated can cers in the United States and BCBLs appear predominantly in AIDS patients, we examined whether LANA is able to regulate the HIV type 1 (HIV-1) long te rminal repeat (LTR). Using luciferase-based transient transfection assays, we found that LANA was able to transactivate the HIV-1 LTR in the human B-c ell line BJAB, human monocytic cell line U937, and the human embryonic kidn ey fibroblast cell line 293T. Moreover, we observed that the virus-encoded HIV transactivator protein Tat cooperated with LANA in activation of the LT R in a dose-response fashion with increasing amounts of LANA. Surprisingly, LANA alone was sufficient to transactivate the HIV-1 LTR in BJAB cells. In similar assays using a HIV-1 LTR construct with the core enhancer elements deleted; the activity of LANA was diminished but not abolished, indicating a mechanism which involves the cooperation of the core enhancer elements a nd downstream elements which include Tat. Furthermore, transient transfecti on of an infectious clone of HIV with LANA demonstrated effects similar to those seen in the reporter assays based on Western blot analysis of HIV Gag polypeptide p24. Interestingly, we also demonstrated that the carboxy term inus of LANA associates with Tat in cells and in vitro. These experiments s uggest a role for LANA in activating the HIV-1 LTR through association with cellular molecules targeting the core enhancer elements and Tat and may ha ve important consequences in increasing the levels of HIV in infected indiv iduals and, hence, the disease state.