Presence of the β(II) isotype of tubulin in the nuclei of cultured mesangial cells from rat kidney

Consuelo Walss, Jeffrey I. Kreisberg, Richard F. Ludueña

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38 Scopus citations

Abstract

Tubulin has generally been considered to be a cytosolic protein whose only function is to form microtubules. This assumption is supported by a great deal of evidence derived from immunohistochemical studies using antibodies directed against whole tubulin or its component polypeptides α and β-tubulin. We have re-examined the intracellular distribution of tubulin using monoclonal antibodies specific for the β(I), β(II), β(III), and β(IV) isotypes of β-tubulin. Our test system is the cultured rat kidney mesangial cell. We have found that β(III) is absent from these cells and that β(I) and β(IV) are present in microtubules throughout the cytosol. In contrast, β(II) is present largely in the nuclei. Immunoblotting of purified nuclear extracts shows that the β(II)-reactive antigen co-migrates with β- tubulin. Extraction of the cytosol and chromatin suggests that β(II) is concentrated in the nucleoli and also in a reticulated network in the rest of the nucleoplasm. An antibody to tyrosinated α-tubulin shows that α is also present in the nucleoli. Treatment of the cells with fluorescent colchicine shows an accumulation of colchicine in the nucleoli. Finally, fluorescently labeled αβ(II)-tubulin dimers, when microinjected into the cells, enter the nuclei and are concentrated in the nucleoli. These results suggest that the β(II) isotype of tubulin is present as an αβ(II) dimer in the nuclei of cultured mesangial cells and suggest the possibility that different tubulin isotypes may have specific functions within the cell.

Original languageEnglish (US)
Pages (from-to)274-284
Number of pages11
JournalCell Motility and the Cytoskeleton
Volume42
Issue number4
DOIs
StatePublished - 1999

Keywords

  • Microtubules
  • Nuclear matrix
  • Nucleolus
  • Tubulin isotypes

ASJC Scopus subject areas

  • Structural Biology
  • Cell Biology

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