title: Ribosomal protein S6 phosphorylation is a determinant of cell size and glucose homeostasis.
abstract: The regulated phosphorylation of ribosomal protein (rp) S6 has attracted much attention since its discovery in 1974, yet its physiological role has remained obscure. To directly address this issue, we have established viable and fertile knock-in mice, whose rpS6 contains alanine substitutions at all five phosphorylatable serine residues (rpS6(P-/-)). Here we show that contrary to the widely accepted model, this mutation does not affect the translational control of TOP mRNAs. rpS6(P-/-) mouse embryo fibroblasts (MEFs) display an increased rate of protein synthesis and accelerated cell division, and they are significantly smaller than rpS6(P+/+) MEFs. This small size reflects a growth defect, rather than a by-product of their faster cell division. Moreover, the size of rpS6(P-/-) MEFs, unlike wild-type MEFs, is not further decreased upon rapamycin treatment, implying that the rpS6 is a critical downstream effector of mTOR in regulation of cell size. The small cell phenotype is not confined to embryonal cells, as it also selectively characterizes pancreatic beta-cells in adult rpS6(P-/-) mice. These mice suffer from diminished levels of pancreatic insulin, hypoinsulinemia, and impaired glucose tolerance.
authors.affiliation: Department of Biochemistry, The Hebrew University-Hadassah Medical School, Jerusalem 91120, Israel.
authors.forename: Igor
authors.initials: I
authors.lastname: Ruvinsky
authors.forename: Nitzan
authors.initials: N
authors.lastname: Sharon
authors.forename: Tal
authors.initials: T
authors.lastname: Lerer
authors.forename: Hannah
authors.initials: H
authors.lastname: Cohen
authors.forename: Miri
authors.initials: M
authors.lastname: Stolovich-Rain
authors.forename: Tomer
authors.initials: T
authors.lastname: Nir
authors.forename: Yuval
authors.initials: Y
authors.lastname: Dor
authors.forename: Philip
authors.initials: P
authors.lastname: Zisman
authors.forename: Oded
authors.initials: O
authors.lastname: Meyuhas
mesh_terms: D000409:Alanine / Q000378:metabolism; D019943:Amino Acid Substitution; D000818:Animals; D001786:Blood Glucose / Q000378:metabolism*; D018929:Cell Culture Techniques; D002455:Cell Division; D048429:Cell Size; D002472:Cell Transformation, Viral; D002478:Cells, Cultured; D047108:Embryonic Development; D005347:Fibroblasts / Q000166:cytology / Q000378:metabolism; D005455:Fluorescent Antibody Technique; D005456:Fluorescent Dyes; D005951:Glucose Tolerance Test; D006706:Homeostasis; D006720:Homozygote; D007211:Indoles; D007328:Insulin / Q000032:analysis; D007515:Islets of Langerhans / Q000166:cytology / Q000378:metabolism; D007700:Kinetics; D051379:Mice; D018345:Mice, Knockout; D008856:Microscopy, Fluorescence; D010179:Pancreas / Q000166:cytology; D010766:Phosphorylation; D014176:Protein Biosynthesis; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D038601:Ribosomal Protein S6 / Q000235:genetics / Q000378:metabolism*; D020123:Sirolimus / Q000494:pharmacology
chemical_list: D001786:Blood Glucose; D005456:Fluorescent Dyes; D007211:Indoles; D007328:Insulin; D012333:RNA, Messenger; D038601:Ribosomal Protein S6; C007293:DAPI; D000409:Alanine; D020123:Sirolimus