title: Induced expression of nucleolin phosphorylation-deficient mutant confers dominant-negative effect on cell proliferation.
abstract: Nucleolin (NCL) is a major nucleolar phosphoprotein that has pleiotropic effects on cell proliferation and is elevated in a variety of tumors. NCL is highly phosphorylated at the N-terminus by two major kinases: interphase casein kinase 2 (CK2) and mitotic cyclin-dependent kinase 1 (CDK1). Earlier we demonstrated that a NCL-mutant that is partly defective in undergoing phosphorylation by CK2 inhibits chromosomal replication through its interactions with Replication Protein A, mimicking the cellular response to DNA damage. We further delineated that the N-terminus of NCL associates with Hdm2, the most common E3 ubiquitin ligase of p53. We reported that NCL antagonizes Hdm2 to stabilize p53 and stimulates p53 transcriptional activity. Although NCL-phosphorylation by CK2 and ribosomal DNA transcription are closely coordinated during interphase, the role of NCL phosphorylation in regulating cell proliferation remains unexplored. We have therefore engineered unique human cells that specifically induce expression of NCL-wild type (WT) or a phosphorylation-deficient NCL-mutant, 6/S*A where all the six CK2 consensus serine sites residing in the N-terminus NCL were mutated to alanine. Here we show that this NCL-mutant is defective in undergoing phosphorylation by CK2. We also demonstrate that NCL-phosphorylation by CK2 is required through the S-phase progression in cell cycle and hence proliferation. Induced expression of NCL with mutated CK2 phosphorylation sites stabilizes p53, results in higher expression of Bcl2 (B-cell lymphoma 2) homology 3 (BH3)-only apoptotic markers and causes a dominant-negative effect on cell viability. Our unique cellular system thus provides the first evidential support to delineate phospho-specific functions of NCL on cell proliferation.
authors.affiliation: Biology Department, Brooklyn College, Brooklyn, New York, United States of America; City University of New York, Graduate Center, New York, New York, United States of America.
authors.forename: Shu
authors.initials: S
authors.lastname: Xiao
authors.affiliation: Biology Department, Brooklyn College, Brooklyn, New York, United States of America.
authors.forename: Elif
authors.initials: E
authors.lastname: Caglar
authors.affiliation: New York University School of Medicine, New York, New York, United States of America.
authors.forename: Priscilla
authors.initials: P
authors.lastname: Maldonado
authors.affiliation: Biology Department, Brooklyn College, Brooklyn, New York, United States of America; City University of New York, Graduate Center, New York, New York, United States of America.
authors.forename: Dibash
authors.initials: D
authors.lastname: Das
authors.affiliation: Biology Department, Brooklyn College, Brooklyn, New York, United States of America.
authors.forename: Zaineb
authors.initials: Z
authors.lastname: Nadeem
authors.affiliation: Great Neck South High School, Great Neck, New York, United States of America.
authors.forename: Angela
authors.initials: A
authors.lastname: Chi
authors.affiliation: New York University College of Dentistry, New York, New York, United States of America.
authors.forename: Benjamin
authors.initials: B
authors.lastname: Trinité
authors.affiliation: New York University College of Dentistry, New York, New York, United States of America.
authors.forename: Xin
authors.initials: X
authors.lastname: Li
authors.affiliation: Biology Department, Brooklyn College, Brooklyn, New York, United States of America; City University of New York, Graduate Center, New York, New York, United States of America.
authors.forename: Anjana
authors.initials: A
authors.lastname: Saxena
mesh_terms: D019943:Amino Acid Substitution; D017209:Apoptosis; D051017:Apoptosis Regulatory Proteins / Q000235:genetics / Q000378:metabolism; D047390:Casein Kinase II / Q000378:metabolism; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D015870:Gene Expression; D005799:Genes, Dominant; D006207:Half-Life; D006801:Humans; D010750:Phosphoproteins / Q000235:genetics* / Q000378:metabolism; D010766:Phosphorylation; D011499:Protein Processing, Post-Translational; D055550:Protein Stability; D016601:RNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D015533:Transcriptional Activation; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism; D000097796:Nucleolin
chemical_list: D051017:Apoptosis Regulatory Proteins; D047390:Casein Kinase II; D010750:Phosphoproteins; D016601:RNA-Binding Proteins; D016159:Tumor Suppressor Protein p53; D000097796:Nucleolin; C495901:TP53 protein, human