Received for publication February 15, 2007.
Revised June 9, 2007.
Accepted for publication July 3, 2007.

DISRUPTION OF OLIGOMERIZATION INDUCES NUCLEO-CYTOPLASMIC SHUTTLING OF LEUKEMIA-ASSOCIATED RHOGEF

Abstract

The rgsRhoGEFs comprise a subfamily of three guanine nucleotide exchange factors, which function in linking heterotrimeric G-proteins to the monomeric RhoGTPase. Here we reveal the novel finding that oligomerization of leukemia-associated RhoGEF (LARG) functions to prevent nucleo-cytoplasmic shuttling and to retain LARG in the cytoplasm. We establish that oligomerization is mediated by a predicted coiled-coil sequence (amino acids 1507-1520) in the extreme C-terminus of LARG and that substitution of isoleucinces 1507/1510 with alanines disrupts homo-oligomerization and leads to nucleo-cytoplasmic shuttling via the CRM1 nuclear transport pathway. Also, we demonstrate that induced dimerization of an otherwise nuclear monomeric LARG mutant promotes cytoplasmic localization. Furthermore, we establish that nuclear import of monomeric LARG is mediated by the nuclear localization sequence ²⁹PTDKKQK³⁵ in the extreme N-terminus. We propose that nucleo-cytoplasmic shuttling provides a mechanism for spatially regulating the activity of LARG towards its cytoplasmic targets as well as potentially new nuclear targets.

Key words: G12,13;other G's, RGS proteins, Cdc42, rho, rac, other small G proteins