title: Critical roles of LGN/GPSM2 phosphorylation by PBK/TOPK in cell division of breast cancer cells.
abstract: To investigate the molecular mechanism of mammary carcinogenesis and identify novel molecular targets for breast cancer therapy, we analyzed genome-wide gene expression profiles of 81 clinical breast cancer samples. Here, we report the critical role of LGN/GPSM2 (Leu-Gly-Asn repeat-enriched protein/G-protein signaling modulator 2) in the growth of breast cancer cells. Semiquantitative RT-PCR and Northern blot analyses confirmed upregulation of LGN/GPSM2 in a large proportion of breast cancers. Immunocytochemical staining identified LGN/GPSM2 at the spindle in cells at metaphase, and at midzone and midbody in cytokinetic cells. Western blot analysis indicated the highest expression and the phosphorylated form of LGN/GPSM2 protein in G2/M phase. Treatment with small-interfering RNAs (siRNAs) targeting LGN/GPSM2 caused incompletion of cell division and resulted in significant growth suppression of breast cancer cells. We found that the 450th threonine (Thr450) of LGN/GPSM2 was phosphorylated by the serine/threonine kinase PBK/TOPK during mitosis. Overexpression of LGN/GPSM2-T450A in which Thr450 was substituted with alanine induced growth suppression and aberrant chromosomal segregation. These findings imply an important role of LGN/GPSM2 in cell division of breast cancer cells and suggest that the PBK/TOPK-LGN/GPSM2 pathway might be a promising molecular target for treatment of breast cancer.
authors.affiliation: Laboratory of Molecular Medicine, Human Genome Center, Institute of Medical Science, The University of Tokyo, Tokyo, Japan.
authors.forename: Chikako
authors.initials: C
authors.lastname: Fukukawa
authors.forename: Koji
authors.initials: K
authors.lastname: Ueda
authors.forename: Toshihiko
authors.initials: T
authors.lastname: Nishidate
authors.forename: Toyomasa
authors.initials: T
authors.lastname: Katagiri
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Nakamura
mesh_terms: D015152:Blotting, Northern; D015153:Blotting, Western; D001943:Breast Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000473:pathology*; D002455:Cell Division / Q000502:physiology; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D005260:Female; D006801:Humans; D007124:Immunoenzyme Techniques; D047468:Immunoprecipitation; D047908:Intracellular Signaling Peptides and Proteins / Q000502:physiology*; D020929:Mitogen-Activated Protein Kinase Kinases; D008938:Mitosis; D016297:Mutagenesis, Site-Directed; D009154:Mutation / Q000235:genetics; D010749:Phosphoprotein Phosphatases / Q000378:metabolism; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics; D034741:RNA, Small Interfering / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction
chemical_list: C102754:GPSM2 protein, human; D047908:Intracellular Signaling Peptides and Proteins; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D017346:Protein Serine-Threonine Kinases; D020929:Mitogen-Activated Protein Kinase Kinases; C409022:PDZ-binding kinase; D010749:Phosphoprotein Phosphatases