title: Stabilization of the retinoblastoma protein by A-type nuclear lamins is required for INK4A-mediated cell cycle arrest.
abstract: Mutations in the LMNA gene, which encodes all A-type lamins, including lamin A and lamin C, cause a variety of tissue-specific degenerative diseases termed laminopathies. Little is known about the pathogenesis of these disorders. Previous studies have indicated that A-type lamins interact with the retinoblastoma protein (pRB). Here we probe the functional consequences of this association and further examine links between nuclear structure and cell cycle control. Since pRB is required for cell cycle arrest by p16(ink4a), we tested the responsiveness of multiple lamin A/C-depleted cell lines to overexpression of this CDK inhibitor and tumor suppressor. We find that the loss of A-type lamin expression results in marked destabilization of pRB. This reduction in pRB renders cells resistant to p16(ink4a)-mediated G(1) arrest. Reintroduction of lamin A, lamin C, or pRB restores p16(ink4a)-responsiveness to Lmna(-/-) cells. An array of lamin A mutants, representing a variety of pathologies as well as lamin A processing mutants, was introduced into Lmna(-/-) cells. Of these, a mutant associated with mandibuloacral dysplasia (MAD R527H), as well as two lamin A processing mutants, but not other disease-associated mutants, failed to restore p16(ink4a) responsiveness. Although our findings do not rule out links between altered pRB function and laminopathies, they fail to support such an assertion. These findings do link lamin A/C to the functional activation of a critical tumor suppressor pathway and further the possibility that somatic mutations in LMNA contribute to tumor progression.
authors.affiliation: Department of Biochemistry, University of Washington, Seattle, WA 98195, USA. bkenn@u.washington.edu
authors.forename: Ryan T
authors.initials: RT
authors.lastname: Nitta
authors.forename: Samantha A
authors.initials: SA
authors.lastname: Jameson
authors.forename: Brian A
authors.initials: BA
authors.lastname: Kudlow
authors.forename: Lindus A
authors.initials: LA
authors.lastname: Conlan
authors.forename: Brian K
authors.initials: BK
authors.lastname: Kennedy
mesh_terms: D000818:Animals; D001483:Base Sequence; D002453:Cell Cycle / Q000502:physiology*; D002460:Cell Line; D019941:Cyclin-Dependent Kinase Inhibitor p16 / Q000378:metabolism*; D018076:DNA, Complementary / Q000235:genetics; D004355:Drug Stability; D016193:G1 Phase; D006801:Humans; D034904:Lamin Type A / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D009154:Mutation; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D016160:Retinoblastoma Protein / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*
chemical_list: D019941:Cyclin-Dependent Kinase Inhibitor p16; D018076:DNA, Complementary; D034904:Lamin Type A; D016160:Retinoblastoma Protein; D046988:Proteasome Endopeptidase Complex