Reevaluation of the Role of Extracellular Signal-Regulated Kinase 3 in Perinatal Survival and Postnatal Growth Using New Genetically Engineered Mouse Models

Abstract

The physiological functions of the atypical mitogen-activated protein kinase extracellular signal-regulated kinase 3 (ERK3) remain poorly characterized. Previous analysis of mice with a targeted insertion of the lacZ reporter in the Mapk6 locus (Mapk6 lacZ ) showed that inactivation of ERK3 in Mapk6 lacZ mice leads to perinatal lethality associated with intrauterine growth restriction, defective lung maturation, and neuromuscular anomalies. To further explore the role of ERK3 in physiology and disease, we generated novel mouse models expressing a catalytically inactive (Mapk6 KD ) or conditional (Mapk6 ⌬ ) allele of ERK3. Surprisingly, we found that mice devoid of ERK3 kinase activity or expression survive the perinatal period without any observable lung or neuromuscular phenotype. ERK3 mutant mice reached adulthood, were fertile, and showed no apparent health problem. However, analysis of growth curves revealed that ERK3 kinase activity is necessary for optimal postnatal growth. To gain insight into the genetic basis underlying the discrepancy in phenotypes of different Mapk6 mutant mouse models, we analyzed the regulation of genes flanking the Mapk6 locus by quantitative PCR. We found that the expression of several Mapk6 neighboring genes is deregulated in Mapk6 lacZ mice but not in Mapk6 KD or Mapk6 ⌬ mutant mice. Our genetic analysis suggests that off-target effects of the targeting construct on local gene expression are responsible for the perinatal lethality phenotype of Mapk6 lacZ mutant mice.

ERK3-MK5 signaling regulates myogenic differentiation and muscle regeneration by promoting FoxO3 degradation

“…Recently, we reported that ERK3-deficient mice or mice expressing a catalytically-inactive allele of ERK3 show a reduced growth rate postnatally (6). A similar growth retardation phenotype was described in another mouse model of ERK3 deficiency (5).…”

“…This growth phenotype affected both female and male mice. No difference in body weight was observed between the two genotypes at birth (6). Given the close correlation between the increase in body mass and muscle mass during the first weeks of post-natal life (20), we measured the crosssectional area (CSA) of individual myofibers from the entire tibialis anterior (TA) muscle of littermate WT and Mapk6 KD/KD mice at post-natal day (P) 15.…”

“…These observations point to a possible role of ERK3 signaling in cellular differentiation. Genetic invalidation studies have revealed that mice lacking ERK3 expression or activity are born at normal mendelian frequency and survive to adulthood without any apparent health problem (5,6).…”

ERK3/MAPK6 is required for KRAS-mediated NSCLC tumorigenesis

“…Phosphorylation at S189 is required for the activation of the kinase, and is therefore utilized as an activation marker. Recently, initial genetic knockout studies in mice suggesting an obligatory role for ERK3/MAPK6 in lung maturation and neonatal survival have been re-evaluated, and the previously observed phenotypical changes were primarily attributed to off-target effects [16][17][18]. ERK3 undergoes N-terminal ubiquitination, and is therefore an extremely unstable protein with a half-life of 30-45 min [19].…”

ERK3/MAPK6 controls IL-8 production and chemotaxis

“…ERK3 mRNA is ubiquitously expressed in all tissues with highest expression levels detected in brain, muscles and gastrointestinal tract (Coulombe and Meloche, 2007). It was reported that genetic deletion of ERK3 led to a respiratory failure, disturbed growth and neonatal lethality in mice within the first days of life, however, these observations were recently challenged by two publications that confirmed that the observed phenotype was probably attributed to off target effects (Klinger et al, 2009;Ronkina et al, 2019;Soulez et al, 2019). Unlike conventional MAPKs, ERK3 possesses a single phospho-acceptor site at serine 189 within its N-terminus domain, which is constitutively phosphorylated in resting cells.…”