Figure 17.4 Translocation of MEK1 and ERK1 regulated by MEK1 SUMOylation. (A)
MEK1 is concentrated in the nucleus, and ERK1 localizes in cytoplasm rather than the
nucleus in resting cells. (B) Stimulation of GPCR by cAMP causes activation of putative
MEKK and phosphorylation/SUMOylation of MEK1, which activates MEK1 and
phosphorylates ERK1. (C) Recruitment of MEK1 and ERK1 to the membrane with the
same kinetics as SUMOylation of MEK1. (D) MEK1 is released from the membrane by de-
SUMOylation and ubiquitinated by MIP1
A small ubiquitin-related modifier, SUMO, is structurally similar to
ubiquitin and covalently attached to a lysine residue on the substrate protein.
Modification of the substrate by SUMO (SUMOylation) can control
subcellular localization of the substrate protein and protect it from
ubiquitination and proteasomal degradation by competitive attachment to
the same lysine residues (Buschmann et al., 2000; Muller et al., 2001).