title: IQGAP1 translocates to the nucleus in early S-phase and contributes to cell cycle progression after DNA replication arrest.
abstract: IQGAP1 is a plasma membrane-associated protein and an important regulator of the actin cytoskeleton, contributing to cell migration, polarity and adhesion. In this study, we demonstrate the nuclear translocation of IQGAP1 using confocal microscopy and cell fractionation. Moreover, we identify a specific pool of IQGAP1 that accumulates in the nucleus during late G1-early S phase of the cell cycle. The nuclear targeting of IQGAP1 was facilitated by N- and C-terminal sequences, and its ability to slowly shuttle between nucleus and cytoplasm/membrane was partly regulated by the CRM1 export receptor. The inhibition of GSK-3β also stimulated nuclear localization of IQGAP1. The dramatic nuclear accumulation of IQGAP1 observed when cells were arrested in G1/S phase suggested a possible role in cell cycle regulation. In support of this, we used immunoprecipitation assays to show that the nuclear pool of IQGAP1 in G1/S-arrested cells associates with DNA replication complex factors RPA32 and PCNA. More important, the siRNA-mediated silencing of IQGAP1 significantly delayed cell cycle progression through S phase and G2/M in NIH 3T3 cells released from thymidine block. Our findings reveal an unexpected regulatory pathway for IQGAP1, and show that a pool of this cytoskeletal regulator translocates into the nucleus in late G1/early S phase to stimulate DNA replication and progression of the cell cycle.
authors.affiliation: Westmead Institute for Cancer Research, The University of Sydney, Westmead, Millennium Institute at Westmead Hospital, Westmead, NSW 2145, Australia.
authors.forename: Michael
authors.initials: M
authors.lastname: Johnson
authors.forename: Manisha
authors.initials: M
authors.lastname: Sharma
authors.forename: Mariana G
authors.initials: MG
authors.lastname: Brocardo
authors.forename: Beric R
authors.initials: BR
authors.lastname: Henderson
mesh_terms: D021581:Active Transport, Cell Nucleus / Q000187:drug effects / Q000502:physiology; D000818:Animals; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000235:genetics / Q000378:metabolism; D003593:Cytoplasm / Q000235:genetics / Q000378:metabolism; D004261:DNA Replication / Q000187:drug effects*; D004847:Epithelial Cells / Q000166:cytology / Q000378:metabolism; D005347:Fibroblasts / Q000166:cytology / Q000378:metabolism; D016193:G1 Phase / Q000187:drug effects* / Q000235:genetics; D038362:Glycogen Synthase Kinase 3 / Q000378:metabolism; D000071679:Glycogen Synthase Kinase 3 beta; D006801:Humans; D006918:Hydroxyurea / Q000494:pharmacology*; D051379:Mice; D018613:Microscopy, Confocal; D012516:Osteosarcoma / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D054730:Protein Interaction Domains and Motifs; D051381:Rats; D016196:S Phase / Q000187:drug effects* / Q000235:genetics; D013936:Thymidine / Q000494:pharmacology*; D020703:ras GTPase-Activating Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: C101203:IQ motif containing GTPase activating protein 1; D020703:ras GTPase-Activating Proteins; C000605506:GSK3B protein, human; D000071679:Glycogen Synthase Kinase 3 beta; C000605507:Gsk3b protein, mouse; C000605508:Gsk3b protein, rat; D038362:Glycogen Synthase Kinase 3; D013936:Thymidine; D006918:Hydroxyurea