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UBC Theses and Dissertations

Hyperactivation of ERK1/2 by DUSP6 inhibition leads to lethality in lung adenocarcinoma Oh, Min Hee


Mutations in the Epidermal Growth Factor Receptor (EGFR) and Kirsten Rat Sarcoma (KRAS) genes occur in a mutually exclusive manner in ~15% and ~30% of all lung adenocarcinomas (LACs), respectively. Using Doxycycline (Dox)-regulated gene expression vectors, we have previously demonstrated that the forced co-expression of EGFR and KRAS mutants in LAC cells induces lethality through the hyperactivation of the RAS-mitogen-activated protein kinase (MAPK) pathway. A subsequent phosphoproteomic assay using Tet-O-KRASG12V-PC9 cells, which carry an endogenous EGFR mutation and was engineered to express KRASG12V upon Dox treatment, revealed that phosphorylation of extracellular signal-regulated kinases (ERKs) increased acutely and dramatically compared to the Tet-O-GFP-PC9 control. This suggested that early activation of ERK1/2 is a crucial event in mediating the observed lethality. Additionally, genetic and pharmacological inhibition of ERK1/2 rescued multiple co-expression LAC cells, confirming that ERK is the main mediator of this phenomena. Here, I aim to investigate whether KRAS- or EGFR-driven LAC cells exploit any existing negative regulatory mechanisms of the ERK to maintain its levels below its upper signalling threshold. Because MAPK signalling is typically regulated by phosphatases, our group performed an analysis of the MAPK phosphatase expression data comparing two LAC TCGA tumor subsets – tumors with (n=107) and without (n=123) either EGFR or KRAS mutation. This analysis revealed that Dual-specificity phosphatase 6 (DUSP6) is the only phosphatase that is up-regulated in tumors with a mutation in either two genes in comparison to their wildtype counterparts, suggesting that these tumors may be dependent on a robust DUSP6 activity to moderate the P-ERK1/2 levels and prevent ERK hyperactivation. Furthermore, when DUSP6 was inhibited in mutant KRAS or mutant EGFR bearing LAC cells using DUSP6 small-interfering RNAs (siRNAs) or a DUSP6 inhibitor called (E)-2-benzylidene-3-(cyclohexylamino)-2,3-dihydro-1H-inden-1-one (BCI), we observed that only the mutant bearing LAC cells were more sensitive to DUSP6 inhibition than the KRAS and EGFR wildtype cells. Such findings suggest a potential therapeutic scenario in EGFR or KRAS mutant LACs can be targeting through inhibiting DUSP6, a key negative feedback regulator that prevents the hyperactivation of ERK.

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