Publication Date


Document Type


Committee Members

Weiwen Long, Ph.D. (Advisor); Michael P. Markey, Ph.D. (Committee Member); Michael Craig, Ph.D. (Committee Member)

Degree Name

Master of Science (MS)


Extracellular signal-regulated kinase 3 (ERK3) is a member of the atypical mitogen-activated protein kinase (MAPK) subfamily, whose members have been shown to play important roles in a number of cellular processes including proliferation, differentiation, migration, and apoptosis. While signals regulating ERK3 kinase activity remain unclear, ERK3 is known to be an unstable protein with function tightly regulated via ubiquitination and proteasomal turnover. The deubiquitinating enzyme USP20 has been shown to regulate ERK3 by stabilizing the kinase, but presently, no destabilizing ubiquitin ligases have been identified. The SKP1-CUL1-F-box protein (SCF) E3 ligases are a subfamily of ubiquitin E3 ligases composed of the adaptor protein SKP1, the scaffold protein Cullin1 (CUL1) and a specific F-box protein. As a component of the SCF-E3 ligase complex, the F-box protein recruits specific substrates to the E3 complex via its substrate interaction domain. Many substrates of SCF-E3 ligases contain a so-called phospho-degron, a phosphorylated S/TXXXS/T consensus motif recognized by F-box proteins such as FBW7 and β-TRCP. Remarkably, the ERK3 protein sequence contains a number of these potential phosphorylated S/TXXXS/T motifs. As such, an siRNA screening was performed to identify potential F-box protein(s) capable of regulating ERK3 protein level. Knockdown of FBW7 resulted in a remarkable increase in ERK3 protein level, suggesting FBW7 negatively regulates ERK3 protein. This was confirmed upon overexpression of FBW7, which led to a significant decrease in ERK3 protein level. Furthermore, we have demonstrated FBW7 downregulates ERK3 protein stability in a manner dependent on its F-box domain. To determine which domain of ERK3 is central to regulation by FBW7, several ERK3 deletion mutants were generated. Using these mutants, we found the ERK3 C34 domain is required for FBW7 regulation of ERK3 and is itself sufficient for FBW7-ERK3 interaction. Taken together, these results demonstrate that FBW7 negatively regulates ERK3 protein stability in a manner dependent on the FBW7 F-box and ERK3 C34 domains.

Page Count


Department or Program

Department of Biochemistry and Molecular Biology

Year Degree Awarded