Dynamics of the Ternary Complex Formed by c-Myc Interactor JPO2, Transcriptional Co-Activator LEDGF/p75 and Chromatin [Gene Regulation]

March 14th, 2014 by Hendrix, J., van Heertum, B., Vanstreels, E., Daelemans, D., De Rijck, J.

Lens epithelium-derived growth factor (LEDGF/p75) is a transcriptional co-activator involved in targeting human immunodeficiency virus (HIV) integration and the development of MLL fusion-mediated acute leukemia. A previous study revealed that LEDGF/p75 dynamically scans the chromatin, and upon interaction with HIV-1 integrase (IN), their complex is locked on chromatin. At present, it is not known whether LEDGF/p75-mediated chromatin locking is typical for interacting proteins. Here, we employed continuous photobleaching, fluorescence correlation and cross-correlation spectroscopy to investigate in vivo chromatin binding of JPO2, a LEDGF/p75- and c-Myc-interacting protein involved in transcriptional regulation. In the absence of LEDGF/p75, JPO2 performs chromatin scanning inherent to transcription factors. However, while the dynamics of JPO2 chromatin binding are decelerated upon interaction with LEDGF/p75, very strong locking of their complex onto chromatin is absent. Similar results were obtained with the domesticated transposase pogZ, another cellular interaction partner of LEDGF/p75. We furthermore show that diffusive JPO2 can oligomerize, that JPO2 and LEDGF/p75 interact directly and specifically in vivo through the specific interaction domain (SID) of JPO2 and the C-terminal domain of LEDGF/p75 comprising the integrase binding domain (IBD), and that modulation of JPO2 dynamics requires a functional PWWP domain in LEDGF/p75. Our results suggest that the dynamics of the LEDGF/p75-chromatin interaction depend on the specific partner and that strong chromatin locking is not a property of all LEDGF/p75 binding proteins.