Nucleoplasmic LAP2alpha-lamin A complexes are required to maintain a proliferative state in human fibroblasts.
In human diploid fibroblasts (HDFs), expression of lamina-associated polypeptide 2 alpha (LAP2alpha) upon entry and exit from G(0) is tightly correlated with phosphorylation and subnuclear localization of retinoblastoma protein (Rb). Phosphoisoforms of Rb and LAP2alpha are down-regulated in G(0). Although RbS780 phosphoform and LAP2alpha are up-regulated upon reentry into G(1) and colocalize in the nucleoplasm, RbS795 migrates between nucleoplasmic and speckle compartments. In HDFs, which are null for lamins A/C, LAP2alpha is mislocalized within nuclear aggregates, and this is correlated with cell cycle arrest and accumulation of Rb within speckles. Nuclear retention of nucleoplasmic Rb during G(1) phase but not of speckle-associated Rb depends on lamin A/C. siRNA knock down of LAP2alpha or lamin A/C in HDFs leads to accumulation of Rb in speckles and G(1) arrest, probably because of activation of a cell cycle checkpoint. Our results suggest that LAP2alpha and lamin A/C are involved in controlling Rb localization and phosphorylation, and a lack or mislocalization of either protein leads to cell cycle arrest in HDFs.
Pekovic
Vanja
V
School of Biological and Biomedical Sciences, University of Durham, Durham DH1 3LE, England, UK.
Harborth
Jens
J
Broers
Jos L V
JL
Ramaekers
Frans C S
FC
van Engelen
Baziel
B
Lammens
Martin
M
von Zglinicki
Thomas
T
Foisner
Roland
R
Hutchison
Chris
C
Markiewicz
Ewa
E
D002453:Cell Cycle / Q000502:physiology; D049109:Cell Proliferation; D002478:Cells, Cultured; D004268:DNA-Binding Proteins / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D005347:Fibroblasts / Q000737:chemistry / Q000166:cytology / Q000378:metabolism*; D006801:Humans; D042581:Intranuclear Space / Q000737:chemistry / Q000378:metabolism; D019394:Ki-67 Antigen / Q000378:metabolism; D034904:Lamin Type A / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D034921:Lamin Type B / Q000378:metabolism; D008565:Membrane Proteins / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D009687:Nuclear Proteins / Q000032:analysis / Q000378:metabolism; D017830:Octoxynol / Q000737:chemistry; D010766:Phosphorylation; D034741:RNA, Small Interfering / Q000235:genetics; D016160:Retinoblastoma Protein / Q000032:analysis / Q000378:metabolism; D012261:Ribonucleoproteins / Q000032:analysis / Q000378:metabolism; D000068103:Serine-Arginine Splicing Factors; D012995:Solubility; D017381:Spliceosomes / Q000737:chemistry / Q000378:metabolism
D004268:DNA-Binding Proteins; D019394:Ki-67 Antigen; C494847:LMNA protein, human; D034904:Lamin Type A; D034921:Lamin Type B; D008565:Membrane Proteins; D009687:Nuclear Proteins; D034741:RNA, Small Interfering; D016160:Retinoblastoma Protein; D012261:Ribonucleoproteins; C093413:lamina-associated polypeptide 2; C073288:SRSF2 protein, human; D000068103:Serine-Arginine Splicing Factors; D017830:Octoxynol