Human SGT interacts with Bag-6/Bat-3/Scythe and cells with reduced levels of either protein display persistence of few misaligned chromosomes and mitotic arrest.
The human small glutamine-rich TPR-containing protein (hSGT) is essential for cell division since RNA-interference-mediated strong reduction of hSGT protein levels causes mitotic arrest (M. Winnefeld, J. Rommelaere, and C. Cziepluch, The human small glutamine-rich TPR-containing protein is required for progress through cell division, Exp. Cell Res. 293 (2004), 43-57). Analysis of HeLa cells expressing a histone 2A-YFP fusion protein revealed the continuous presence of few mislocalized chromosomes close to the spindle poles as possible cause for hSGT depletion-dependent prometaphase arrest. Cells unable to rescue these mislocalized chromosomes into the metaphase plate died at this stage through apoptosis. In order to address hSGT function at the molecular level, mass spectrometry analysis of proteins which co-immunoprecipitated with Flag-tagged hSGT was performed. Thereby, Hsp70 and Bag-6/Bat-3/Scythe were identified as novel hSGT interaction partners while interaction with Hsc70 was confirmed. Results obtained with truncated versions of the hSGT protein revealed that Bag-6/Bat-3/Scythe and Hsp70 or Hsc70 were independently able to form complexes with hSGT. Interaction of hSGT with Hsc70, Hsp70 or Bag-6/Bat-3/Scythe was demonstrated in prometaphase, thereby suggesting a possible role for complexes containing hSGT and distinct (co)-chaperones during mitosis. Finally, cells from populations with reduced levels of Bag-6/Bat-3/Scythe also displayed persistence of mislocalized chromosomes and mitotic arrest, which strongly indicated that hSGT-Bag-6/Bat-3/Scythe complexes could be directly or indirectly required for complete chromosome congression.
Winnefeld
Marc
M
Infection and Cancer Department, Abteilung F010 and Institut National de la Santé et de la Recherche Médicale U 701, Deutsches Krebsforschungszentrum, Postfach 101949, D-69120 Heidelberg, Germany.
Grewenig
Annabel
A
Schnölzer
Martina
M
Spring
Herbert
H
Knoch
Tobias A
TA
Gan
Eugene C
EC
Rommelaere
Jean
J
Cziepluch
Celina
C
D017209:Apoptosis; D001665:Binding Sites / Q000235:genetics; D002352:Carrier Proteins / Q000737:chemistry / Q000378:metabolism*; D023902:Chromosome Pairing; D002877:Chromosomes, Human / Q000378:metabolism*; D004847:Epithelial Cells / Q000166:cytology; D050883:HSC70 Heat-Shock Proteins / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D008938:Mitosis; D018832:Molecular Chaperones; D011485:Protein Binding; D011506:Proteins / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D008941:Spindle Apparatus / Q000378:metabolism; D014407:Tumor Cells, Cultured
C092009:BAG6 protein, human; D002352:Carrier Proteins; D050883:HSC70 Heat-Shock Proteins; D018832:Molecular Chaperones; D011506:Proteins; D011993:Recombinant Fusion Proteins; C114575:SGTA protein, human