Cellular Role of the HIV-1 Integration Factor, LEDGF

Katherine Jones, The Salk Institute for Biological Studies, La Jolla
Basic Biomedical Sciences
Innovative, Developmental, Exploratory Award (IDEA)

The Lens Epithelium-Derived Growth Factor (LEDGF/p75), a member of the hepatoma-derived growth factor family, is a transcriptional co-activator for stress-induced genes and a survival factor that protects cells from various environmental stresses. LEDGF/p75 plays a critical role in early HIV-1 replication, where it interacts directly with the HIV-1 integrase protein and directs viral preintegration complexes to the body of actively-transcribed cellular genes. In LEDGF-depleted cells, HIV-1 loses its strong bias for integrating into active transcription units, and instead targets host cell promoter regions and CpG islands. We have recently discovered that LEDGF/p75 interacts directly with a co-transcriptional regulatory factor, Iws1 (“interacts with Spt6”). We find that Iws1 functions as an assembly factor to recruit various factors to the RNAPII elongation complex. In turn, Iws1 is recruited to the elongation complex through binding of the Spt6 transcription elongation factor and histone H3 chaperone to the P-TEFb/Ser2P C-terminal domain (CTD) of the RNAPII Rpb1 subunit. The Spt6:Iws1:CTD complex recruits mRNA export factors (REF1/Aly, Rrp6) as well as histone modifying enzymes (such as HYPB/Setd2), and is required for elongation-coupled H3K36 methylation, a signature chromatin mark of active transcription. Our preliminary data indicate that LEDGF/p75 is present at the HIV-1 genome, and that Iws1 and HYPB/Setd2 direct LEDGF/p75 to viral chromatin in vivo. These findings suggest that Iws1 may recruit LEDGF and HIV-1 integrase to the RNAPII elongation complex, or to newly-transcribed chromatin. Here we will examine the association of Iws1 with LEDGF and the HIV-1 integrase protein and address whether Iws1 recruits HIV-IN to the RNAPII elongation complex and/or to H3K36 methylated chromatin, and to assess the possible role of Iws1 in activating transcription from LEDGF/p75-regulated genes under conditions of oxidative stress.