title: Arrested cell proliferation through cysteine protease activity of eukaryotic ribosomal protein S4.
abstract: S4 is an integral protein of the smaller subunit of cytosolic ribosome. In prokaryotes, it regulates the synthesis of ribosomal proteins by feedback inhibition of the α-operon gene expression, and it facilitates ribosomal RNA synthesis by direct binding to RNA polymerase. However, functional roles of S4 in eukaryotes are poorly understood, although its deficiency in humans is thought to produce Turner syndrome. We report here that wheat S4 is a cysteine protease capable of abrogating total protein synthesis in an actively translating cell-free system of rabbit reticulocytes. The translation-blocked medium, imaged by atomic force microscopy, scanning electron microscopy, and transmission electron microscopy, shows dispersed polysomes, and the disbanded polyribosome elements aggregate to form larger bodies. We also show that human embryonic kidney cells transfected with recombinant wheat S4 are unable to grow and proliferate. The mutant S4 protein, where the putative active site residue Cys 41 is replaced by a phenylalanine, can neither suppress protein synthesis nor arrest cell proliferation, suggesting that the observed phenomenon arises from the cysteine protease attribute of S4. The results also inspire many questions concerning in vivo significance of extraribosomal roles of eukaryotic S4 performed through its protease activity.
authors.affiliation: School of Chemistry, University of Hyderabad, Hyderabad, India.
authors.forename: Madasu
authors.initials: M
authors.lastname: Yadaiah
authors.forename: Babu
authors.initials: B
authors.lastname: Sudhamalla
authors.forename: P Nageswara
authors.initials: PN
authors.lastname: Rao
authors.forename: Karnati R
authors.initials: KR
authors.lastname: Roy
authors.forename: Dasari
authors.initials: D
authors.lastname: Ramakrishna
authors.forename: Gulam
authors.initials: G
authors.lastname: Hussain Syed
authors.forename: Kolluru V A
authors.initials: KV
authors.lastname: Ramaiah
authors.forename: Abani K
authors.initials: AK
authors.lastname: Bhuyan
mesh_terms: D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000818:Animals; D001483:Base Sequence; D049109:Cell Proliferation; D002474:Cell-Free System; D057056:Cysteine Proteases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D018744:DNA, Plant / Q000235:genetics; D057809:HEK293 Cells; D006801:Humans; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011132:Polyribosomes / Q000378:metabolism / Q000648:ultrastructure; D011487:Protein Conformation; D011817:Rabbits; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D012156:Reticulocytes / Q000378:metabolism; D012269:Ribosomal Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D014908:Triticum / Q000235:genetics / Q000378:metabolism*; D051020:bcl-X Protein / Q000378:metabolism; D019892:eIF-2 Kinase / Q000378:metabolism
chemical_list: D018744:DNA, Plant; D010940:Plant Proteins; D011994:Recombinant Proteins; D012269:Ribosomal Proteins; D051020:bcl-X Protein; C031798:ribosomal protein S4; D019892:eIF-2 Kinase; D057056:Cysteine Proteases