Weiwen Long, Ph.D. (Advisor); Hongmei Ren, Ph.D. (Committee Member); Yong-jie Xu, M.D., Ph.D. (Committee Member); Paula A. Bubulya, Ph.D. (Committee Member); Michael Leffak, Ph.D. (Committee Member)
Doctor of Philosophy (PhD)
Extracellular-regulated kinase 3 (ERK3) is overexpressed in a variety of cancers, including lung cancer. This atypical mitogen-activated protein kinase (MAPK) has a unique structure which includes a C34 domain and C-terminus and about which relatively little is known. ERK3 has been demonstrated to promote cell migration and metastasis in multiple cancer types. A yeast two-hybrid assay using ERK3 as bait indicated Diacylglycerol kinase ζ (DGKζ) is a binding partner. DGKζ is an isoform in the DGK family, all the members of which phosphorylate the lipid diacylglycerol (DAG) to generate phosphatidic acid (PA). DGKζ was shown to promote migration in mouse embryonic fibroblasts (MEFs) and enhance invasion in some types of cancer cells, but its role in lung cancer has yet to be described. The interaction of these two proteins was confirmed by immunoprecipitation in both endogenous and overexpression conditions in cells as well as by in vitro assays. Further, as observed by immunofluorescence, these proteins colocalize in cells primarily near the cell periphery. Interestingly, DGKζ interacts with ERK3 via the C34 domain of ERK3 and deletion of this domain drastically reduces the ability of these proteins to form a stable complex. ERK3 interacts with DGKζ though the N-terminal and the C1 regions of DGKζ. Lipid mass spectrometry analysis revealed that knockdown of ERK3 reduced phosphatidic acid levels but promoted diacylglycerol and triacylglycerol levels. Changes to triacylglycerol and phosphatidic acid levels following ERK3 knockdown were confirmed in additional lung cancer cell lines. Despite these exciting findings, ERK3 had no effect on DGKζ localization or enzymatic activity, suggesting the effect of ERK3 on lipids may be independent of DGKζ. In lung cancer cells, DGKζ surprisingly decreased cell motility with DGKζ overexpression reducing cell migration and DGKζ knockdown increasing cell migration. With co-overexpression, DGKζ entirely inhibited the ability of ERK3 to promote cell migration. Interestingly, DGKζ could not alter migration in cells with stable ERK3 knockdown. Further, DGKζ had little effect on ERK3 ΔC34 promotion of cell migration, which is in line with DGKζ binding the C34 domain of ERK3 and suggests DGKζ requires this domain to prevent ERK3 from promoting migration. Together, this study has identified DGKζ as a new binding partner and negative regulator of ERK3 in controlling lung cancer cell migration and found important insights into a role for ERK3 in the regulation of lipid metabolism.
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