title: The transcription factor SP1 regulates centriole function and chromosomal stability through a functional interaction with the mammalian target of rapamycin/raptor complex.
abstract: Specificity protein 1 (SP1) is an essential transcription factor implicated in the regulation of genes that control multiple cellular processes, including cell cycle, apoptosis, and DNA damage. Very few nontranscriptional roles for SP1 have been reported thus far. Using confocal microscopy and centrosome fractionation, we identified SP1 as a centrosomal protein. Sp1-deficient mouse embryonic fibroblasts and cells depleted of SP1 by RNAi have increased centrosome number associated with centriole splitting, decreased microtubule nucleation, chromosome misalignment, formation of multipolar mitotic spindles and micronuclei, and increased incidence of aneuploidy. Using mass spectrometry, we identified P70S6K, an effector of the mTOR/raptor (mTORC1) kinase complex, as a novel interacting protein of SP1. We found that SP1-deficient cells have increased phosphorylation of the P70S6K effector ribosomal protein S6, suggesting that SP1 participates in the regulation of the mTORC1/P70S6K/S6 signaling pathway. We previously reported that aberrant mTORC1 activation leads to supernumerary centrosomes, a phenotype rescued by the mTORC1 inhibitor rapamycin. Similarly, treatment with rapamycin rescued the multiple centrosome phenotype of SP1-deficient cells. Taken together, these data strongly support the hypothesis that SP1 is involved in the control of centrosome number via regulation of the mTORC1 pathway, and predict that loss of SP1 function can lead to aberrant centriole splitting, deregulated mTORC1 signaling, and aneuploidy, thereby contributing to malignant transformation.
authors.affiliation: Department of Biochemistry and Molecular Biology, Drexel University College of Medicine, Philadelphia, PA 19102, USA.
authors.forename: Aristotelis
authors.initials: A
authors.lastname: Astrinidis
authors.forename: Jiyoon
authors.initials: J
authors.lastname: Kim
authors.forename: Crystal M
authors.initials: CM
authors.lastname: Kelly
authors.forename: Beatrix A
authors.initials: BA
authors.lastname: Olofsson
authors.forename: Behzad
authors.initials: B
authors.lastname: Torabi
authors.forename: Elena M
authors.initials: EM
authors.lastname: Sorokina
authors.forename: Jane
authors.initials: J
authors.lastname: Azizkhan-Clifford
mesh_terms: D016475:3T3 Cells; D000818:Animals; D017209:Apoptosis; D002453:Cell Cycle; D002460:Cell Line; D002502:Centrioles / Q000502:physiology*; D018385:Centrosome / Q000502:physiology / Q000648:ultrastructure; D043171:Chromosomal Instability; D004249:DNA Damage; D005786:Gene Expression Regulation; D020868:Gene Silencing; D006367:HeLa Cells; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism*; D051379:Mice; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D034622:RNA Interference / Q000502:physiology; D016329:Sp1 Transcription Factor / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D058570:TOR Serine-Threonine Kinases
chemical_list: D047908:Intracellular Signaling Peptides and Proteins; D016329:Sp1 Transcription Factor; C546842:MTOR protein, human; C546843:mTOR protein, mouse; D017346:Protein Serine-Threonine Kinases; D058570:TOR Serine-Threonine Kinases