title: The protein activator of protein kinase R, PACT/RAX, negatively regulates protein kinase R during mouse anterior pituitary development.
abstract: The murine double-stranded RNA-binding protein termed protein kinase R (PKR)-associated protein X (RAX) and the human homolog, protein activator of PKR (PACT), were originally characterized as activators of PKR. Mice deficient in RAX show reproductive and developmental defects, including reduced body size, craniofacial defects and anterior pituitary hypoplasia. As these defects are not observed in PKR-deficient mice, the phenotype has been attributed to PKR-independent activities of RAX. Here we further investigated the involvement of PKR in the physiological function of RAX, by generating rax(-/-) mice deficient in PKR, or carrying a kinase-inactive mutant of PKR (K271R) or an unphosphorylatable mutant of the PKR substrate eukaryotic translation initiation factor 2 α subunit (eIF2α) (S51A). Ablating PKR expression rescued the developmental and reproductive deficiencies in rax(-/-) mice. Generating rax(-/-) mice with a kinase-inactive mutant of PKR resulted in similar rescue, confirming that the rax(-/-) defects are PKR dependent; specifically that the kinase activity of PKR was required for these defects. Moreover, generating rax(-/-) mice that were heterozygous for an unphosphorylatable mutant eIF2α provides partial rescue of the rax(-/-) defect, consistent with mutation of one copy of the Eif2s1 gene. These observations were further investigated in vitro by reducing RAX expression in anterior pituitary cells, resulting in increased PKR activity and induction of the PKR-regulated cyclin-dependent kinase inhibitor p21(WAF1/CIP1). These results demonstrate that PKR kinase activity is required for onset of the rax(-/-) phenotype, implying an unexpected function for RAX as a negative regulator of PKR in the context of postnatal anterior pituitary tissue, and identify a critical role for the regulation of PKR activity for normal development.
authors.affiliation: Department of Molecular Genetics, Lerner Research Institute, Cleveland Clinic, OH, USA.|Graduate Program in Molecular Virology, Case Western Reserve University, Cleveland, OH, USA.
authors.forename: Benjamin K
authors.initials: BK
authors.lastname: Dickerman
authors.affiliation: Department of Molecular Genetics, Lerner Research Institute, Cleveland Clinic, OH, USA.
authors.forename: Christine L
authors.initials: CL
authors.lastname: White
authors.affiliation: Department of Molecular Genetics, Lerner Research Institute, Cleveland Clinic, OH, USA.
authors.forename: Patricia M
authors.initials: PM
authors.lastname: Kessler
authors.affiliation: Centre for Cancer Research, Hudson Institute of Medical Research, Clayton, Victoria, Australia.|Department of Molecular and Translational Science, Monash University, Clayton, Victoria, Australia.
authors.forename: Anthony J
authors.initials: AJ
authors.lastname: Sadler
authors.affiliation: Centre for Cancer Research, Hudson Institute of Medical Research, Clayton, Victoria, Australia.|Department of Molecular and Translational Science, Monash University, Clayton, Victoria, Australia.
authors.forename: Bryan R G
authors.initials: BR
authors.lastname: Williams
authors.affiliation: Department of Molecular Genetics, Lerner Research Institute, Cleveland Clinic, OH, USA.|Graduate Program in Molecular Virology, Case Western Reserve University, Cleveland, OH, USA.
authors.forename: Ganes C
authors.initials: GC
authors.lastname: Sen
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D002453:Cell Cycle; D002460:Cell Line; D049109:Cell Proliferation; D003433:Crosses, Genetic; D004789:Enzyme Activation; D015852:Eukaryotic Initiation Factor-2 / Q000235:genetics / Q000378:metabolism; D005260:Female; D006801:Humans; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D008822:Mice, Transgenic; D009154:Mutation; D009929:Organ Size; D010766:Phosphorylation; D010903:Pituitary Gland, Anterior / Q000166:cytology / Q000201:enzymology / Q000254:growth & development / Q000378:metabolism*; D011499:Protein Processing, Post-Translational; D034622:RNA Interference; D016601:RNA-Binding Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D019892:eIF-2 Kinase / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism
chemical_list: D015852:Eukaryotic Initiation Factor-2; C119610:Prkra protein, mouse; D016601:RNA-Binding Proteins; D019892:eIF-2 Kinase; C000605978:protein kinase R, mouse
keywords: Eif2ak2; Prkra; cell cycle; development; hypoplasia