Dual roles for lysine 490 of promyelocytic leukemia protein in the transactivation of glucocorticoid receptor-interacting protein 1

Glucocorticoid receptor-interacting protein 1 (GRIP1), a p160 family nuclear receptor co-activator protein, has three activation domains that recruit at least three secondary co-activators: CBP/p300, co-activator-associated arginine methyltransferase 1, and coiled-coil co-activator, which exhibits histone acetyltransferase and/or arginine methyltransferase activities. The regulatory mechanisms underlying the co-activation functions of GRIP1, which associates with promyelocytic leukemia protein (PML) in PML-nuclear bodies, are not well-understood. This study showed that PML specifically and dramatically enhanced the C-terminal transactivation activity of GRIP1 by directly binding to GRIP1 but only when it was sumoylated. Most of the transactivation activity resided in the N-terminal PML regions that are conserved among isoforms. Three N-terminal sumoylation residues (Lys 65, 160, and 490) exhibited differential roles in the regulation of GRIP1 activity, and the sumoylation of Lys 490 acted as the primary nuclear localization signal of PML. While GRIP1 transactivation was stimulated to a similar degree by PML (K490R), located in the nucleus, and wild-type PML, PML (K490D) and the C-truncated mutant PML1-489 both displayed an epinuclear localization and were mostly inactive in stimulating GRIP. Based on these data, nuclear foci, nuclear localization, and the sumoylation status of Lys 490 were not essential for the enhancement of GRIP1 activity by PML, but the charge status of Lys 490 was important for subcellular localization of PML and cross-talk between its N- and C-terminal regions to modulate transcriptional activation. Taken together, these results provide insight into the regulatory mechanisms of PML that control the functional activities of GRIP1.