Reevaluation of the Role of ERK3 in Perinatal Survival and Post-Natal Growth Using New Genetically-Engineered Mouse Models

Abstract

38The physiological functions of the atypical MAP kinase ERK3 remain poorly characterized. 39Previous analysis of mice with a targeted insertion of the lacZ reporter in the Mapk6 locus 40 (Mapk6 lacZ ) showed that inactivation of ERK3 in Mapk6 lacZ mice leads to perinatal lethality 41 associated with intrauterine growth restriction, defective lung maturation, and neuromuscular 42 anomalies. To further explore the role of ERK3 in physiology and disease, we generated novel 43 mouse models expressing a catalytically-inactive (Mapk6 KD ) or conditional (Mapk6  ) allele of 44 ERK3. Surprisingly, we found that mice devoid of ERK3 kinase activity or expression survive 45 the perinatal period without any observable lung or neuromuscular phenotype. ERK3 mutant 46 mice reached adulthood, were fertile and showed no apparent health problem. However, analysis 47 56 57 Extracellular signal-regulated kinase 3 (ERK3) and ERK4 are atypical members of the mitogen-58 activated protein (MAP) kinase family (1). Despite their identification more than 25 years ago, 59 very little is known about their physiological functions. The ERK3 gene (MAPK6 in human) is 60 expressed ubiquitously in adult mammalian tissues, while ERK4 gene (MAPK4) shows a 61 restricted expression profile being detected mainly in brain tissue (2-4) 62 (www.gtexportal.org/home). During mouse embryogenesis, ERK3 mRNA and protein levels 63 peak around embryonic day 11, after the onset of organogenesis, and then decline thereafter (5). 64Expression of ERK3 is also up-regulated during in vitro differentiation of cell line models along 65 the neuronal or muscle lineage (2, 6). These early observations have suggested a potential role 66 for ERK3 signaling in cell differentiation and tissue development. 67 68 Analogous to classical MAP kinases, ERK3 is activated by phosphorylation of the activation 69 loop, which stimulates its intrinsic catalytic activity and affinity for the substrate MK5 (7). 70Activation loop phosphorylation is mediated by Group I p21-activated kinases (8, 9), and is 71 reversed by the action of the MAP kinase phosphatase DUSP2 (10). Of note, it has been 72 previously proposed that ERK3 enzymatic activity is dispensable for MK5 activation and that 73 ERK3 may exert a scaffolding function (11). However, other experiments using coupled in vitro 74 kinase assays did not suppport this hypothesis (7). A more recent study reported that 75 overexpression of ERK3 induces rounding of MDA-MB-231 breast cancer cells by an unknown 76 mechanism independent of its kinase activity (12). The physiological importance of catalytic and 77 non-catalytic functions of ERK3 remains an open question. 78 * Mixed C57Bl/6J-129/Sv genetic background

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

“…The physiological roles of the atypical MAP kinase ERK3 remain to be fully investigated. Recently, we reported that ERK3-deficient mice or mice expressing a catalytically-inactive allele of ERK3 show a reduced growth rate postnatally (Soulez et al, 2019). A similar growth retardation phenotype was described in another mouse model of ERK3 deficiency (Ronkina et al, 2019).…”

“…We have shown previously that mice expressing a kinase-dead (KD) allele of ERK3 (Mapk6 KD/KD ) have a reduced postnatal growth rate as compared to WT control mice (Soulez et al, 2019). This growth phenotype affected both female and male mice.…”

“…Mapk6 KD/KD and Mapkakpk5 −/− mutant mice have been described (Shi et al, 2003;Soulez et al, 2019). Mice were housed under specific pathogen-free conditions at the Institute for Research in Immunology and Cancer.…”

“…This growth phenotype affected both female and male mice. No difference in body weight was observed between the two genotypes at birth (Soulez et al, 2019). Given the close correlation between the increase in body mass and muscle mass during the first weeks of postnatal life (White et al, 2010), we measured the CSA of individual myofibers from the entire TA muscle of littermate WT and Mapk6 KD/KD mice at postnatal 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 (Ronkina et al, 2019;Soulez et al, 2019). However, ERK3 kinase activity is required for optimal post-natal growth of newborn mice (Soulez et al, 2019).…”