title: The nuclear pool of tetraspanin CD9 contributes to mitotic processes in human breast carcinoma.
abstract: Tetraspanin-29 (CD9) is an integral membrane protein involved in several fundamental cell processes and in cancer metastasis. Here, characterization of a panel of breast cancer cells revealed a nuclear pool of CD9, not present in normal human mammary epithelial cells. Antibody binding to surface CD9 of breast cancer cells resulted in increased nuclear CD9 fluorescence. CD9 was also found, along with a plasma membrane-associated pool, in the nuclei of all primary ductal breast carcinoma patient specimens analyzed. In all patients, about 40% of the total CD9 cellular fluorescence was nuclear. CD9 colocalized at the nuclear level with CEP97, a protein implicated in centrosome function, and with the IGSF8, an established CD9 partner in the plasma membrane. Co-immunoprecipitation of CEP97 and IGSF8 with CD9 was shown in nuclear extracts from breast cancer cells expressing a CD9-GFP fusion protein. However, by fluorescence resonance energy transfer (FRET) analysis, no direct binding of CD9 with either protein was observed, suggesting that CD9 is part of a larger nuclear protein complex. CD9 depletion or exposure of parental breast cancer cells to anti-CD9 mAb resulted in polynucleation and multipolar mitoses. These data indicate that the nuclear CD9 pool has an important role in the mitotic process.
  
  
  CONCLUSIONS
  The discovery of a nuclear pool of CD9 has prognostic and/or therapeutic potential for patients with ductal carcinoma of the breast.
authors.affiliation: Cancer Research Center, Roseman University of Health Sciences, Las Vegas, Nevada.
authors.forename: Germana
authors.initials: G
authors.lastname: Rappa
authors.affiliation: Cancer Research Center, Roseman University of Health Sciences, Las Vegas, Nevada.
authors.forename: Toni M
authors.initials: TM
authors.lastname: Green
authors.affiliation: Cancer Research Center, Roseman University of Health Sciences, Las Vegas, Nevada. alorico@roseman.edu.
authors.forename: Aurelio
authors.initials: A
authors.lastname: Lorico
mesh_terms: D015703:Antigens, CD / Q000378:metabolism; D001943:Breast Neoplasms / Q000378:metabolism* / Q000473:pathology; D018270:Carcinoma, Ductal, Breast / Q000378:metabolism* / Q000473:pathology; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000378:metabolism; D002467:Cell Nucleus / Q000502:physiology; D005260:Female; D031541:Fluorescence Resonance Energy Transfer; D006801:Humans; D061986:MCF-7 Cells; D008565:Membrane Proteins / Q000378:metabolism; D008869:Microtubule-Associated Proteins / Q000378:metabolism; D008938:Mitosis; D060245:Tetraspanin 29 / Q000378:metabolism*
chemical_list: D015703:Antigens, CD; C554869:CD9 protein, human; C523555:CEP97 protein, human; C440028:IGSF8 protein, human; D008565:Membrane Proteins; D008869:Microtubule-Associated Proteins; D060245:Tetraspanin 29