Alan Engelman, Ph.D.

Associate Professor of Pathology

Dana-Farber Cancer Institute
44 Binney Street
JFB-815
Boston, MA 02115
Tel: 617-632-4361
Fax: 617-632-3113
e-mail:alan_engelman@dfci.harvard.edu
5 postdoctoral fellows, 2 graduate students

Research in my laboratory focuses on the integration step in the retroviral life cycle. In order to replicate, retroviruses must integrate the cDNA product of reverse transcription into a host cell chromosome. In addition to the viral integrase (IN) protein, host cell proteins play essential roles in integration. IN functions in the context of preintegration complexes (PICs) that contain the cDNA, host cell, and other viral proteins.

PICs isolated from infected cells catalyze cDNA integration in vitro. Although work with purified IN proteins has revealed details of IN structure and function, little is known about the organization and structure of PICs. We previously defined the HIV-1 intasome as the nucleoprotein complex within PICs that mediates integration. Current projects focus on defining the stoichiometries and folding topologies of viral and cell proteins in purified PICs. In vivo roles of host cell factors in HIV-1 integration are evaluated using RNAi and gene knockout strategies.

One cell protein that directly binds to HIV-1 IN, lens epithelium-derived growth factor (LEDGF), greatly stimulates recombinant IN catalytic activity in vitro. LEDGF was knocked out in mice to generate a clean ex vivo model system. HIV-1 titer was reduced approximately 80-fold on LEDGF knockout cells, revealing a crucial role for the host factor in infection. Different retroviruses differentially target genomic features like genes and promoter regions during integration - lentiviruses like HIV-1 preferentially target active genes fairly equally along their lengths. The frequency and distribution of HIV-1 integration were severely disrupted in LEDGF knockout cells: global integration was reduced approximately tenfold, with significant redistributions of residual proviruses to gene-poor regions and transcriptional start sites, mimicking the natural distributions of other retroviruses. The results highlighted a critical role for LEDGF at the genomic targeting step of lentiviral integration.

References:

Shun MC, Daigle JE, Vandegraaff N, Engelman A. Wild-type levels of HIV-1 infectivity in the absence of cellular emerin protein. J Virol 2007;81:166-72.

Daelemans D, Lu R, De Clercq E, Engelman A. Characterization of a replication-competent, integrase defective HIV/simian virus 40 chimera as a powerful tool for the discovery and validation of HIV integrase inhibitors. J Virol 2007;81:4381-5.

Shun MC, Raghavendra NK, Vandegraaff N, Daigle JE, Hughes S, Kellam P, Cherepanov P, Engelman A. LEDGF/p75 functions downstream from preintegration complex formation to effect gene-specific HIV-1 integration. Genes Dev 2007;21:1767-78.          

Brass AL, Dykxhoorn DM, Benita Y, Yan N, Engelman A, Xavier RJ, Lieberman J, Elledge SJ. Identification of host proteins required for HIV infection through a functional genomic screen. Science 2008;319:921-6.

Engelman A, Cherepanov P. The lentivirus integrase binding protein LEDGF/p75 and HIV-1 replication. PLoS Pathog 2008;4:e1000046.