Molecular mechanisms underlying cellular effects of human MEK1 mutations

Abstract

Terminal regions of Drosophila embryos are patterned by signaling through ERK, which is genetically deregulated in multiple human diseases. Quantitative studies of terminal patterning have been recently used to investigate gain-of-function variants of human MEK1, encoding the MEK kinase that directly activates ERK by dual phosphorylation. Unexpectedly, several mutations reduced ERK activation by extracellular signals, possibly through a negative feedback triggered by signal-independent activity of the mutant variants. Here we present experimental evidence supporting this model. Using a MEK variant that combines a mutation within the negative regulatory region with alanine substitutions in the activation loop, we prove that pathogenic variants indeed acquire signal-independent kinase activity. We also demonstrate that signal-dependent activation of these variants is independent of KSR, a conserved adaptor that is indispensable for activation of normal MEK. Finally, we show that attenuation of ERK activation by extracellular signals stems from transcriptional induction of Mkp3, a dual specificity phosphatase that deactivates ERK by dephosphorylation. These findings in the Drosophila embryo highlight its power for investigating diverse effects of human disease mutations.

Evolutionary history of MEK1 illuminates the nature of cancer and RASopathy mutations

“…6B bottom, D-F). The same phenotype was previously reported for other gain-of function MEK1 mutants (60, 61). Notably, ∼60% of embryos expressing Q56P MEK1 failed to form any cuticle.…”

“…Previously, we found that mutations that cause lethality of Drosophila embryos belong to the gain-of-function type mutations (52). Gain-of-function mutations allow for signaling, even in the absence of upstream pathway activation, as well as a more rapid response to activation by RAF even in the absence of necessary adapter proteins (60-62). All three mutations significantly increased embryonic lethality (Fig.…”

“…The utilized mutagenic primers are as follows: F53S-ATCAAGATGTaCCTCAGCCAGAAGG, G128D-CACATTGTCGaTTTCTACGGC, and Q56P-TTCCTCAGCCcGAAGGAGAAG. The UAS-MEK variants were cloned into pTIGER and integrated into attP40 site using the ΦC31-based integration system as described previously (60).…”

Qualitative differences in disease-associated MEK mutants reveal molecular signatures and aberrant signaling-crosstalk in cancer

“…Furthermore, MEK1 mutations, which are more frequent than those in MEK2, are also observed in many tumors such as melanoma, colorectal, lung, thyroid, and ovarian cancers 7 . These oncogenes ultimately hyperactivate ERK signaling and generate aberrant gene expression patterns that provoke cell overgrowth and/or a differentiation abnormality, thereby inducing cancer development and progression 8 , 9 . Targeting of these oncogenes for cancer therapy is therefore of particular interest, and their specific inhibitors (e.g., erlotinib, vemurafenib, and trametinib, inhibitors of EGFR, BRaf, and MEK, respectively) are currently in clinical use 10 .…”

Clinical activity of Mitogen-Activated Protein Kinase (MAPK) inhibitors in patients with MAP2K1 (MEK1)-mutated metastatic cancers

“…These mutations were identified in treatment naïve tumors as well as in those resistant to MAPK targeted therapies 7,[9][10][11][12][13][14][15] . A number of MAP2K1 mutations have been demonstrated to be oncogenic via their ability to transform non-cancerous cells, or by increasing the phosphorylation of downstream ERK 10,11,13,[16][17][18][19][20][21][22][23][24][25][26][27][28] . In 2018, Gao et al proposed a classification system for MAP2K1 mutations 2,13 .…”