Definition of pRB- and p53-dependent and -independent steps in HIRA/ASF1a-mediated formation of senescence-associated heterochromatin foci.
Cellular senescence is an irreversible proliferation arrest triggered by short chromosome telomeres, activated oncogenes, and cell stress and mediated by the pRB and p53 tumor suppressor pathways. One of the earliest steps in the senescence program is translocation of a histone chaperone, HIRA, into promyelocytic leukemia (PML) nuclear bodies. This relocalization precedes other markers of senescence, including the appearance of specialized domains of facultative heterochromatin called senescence-associated heterochromatin foci (SAHF) and cell cycle exit. SAHF represses expression of proliferation-promoting genes, thereby driving exit from the cell cycle. HIRA bound to another histone chaperone, ASF1a, drives formation of SAHF. Here, we show that HIRA's translocation to PML bodies occurs in response to all senescence triggers tested. Dominant negative HIRA mutants that block HIRA's localization to PML bodies prevent formation of SAHF, as does a PML-RARalpha fusion protein which disrupts PML bodies, directly supporting the idea that localization of HIRA to PML bodies is required for formation of SAHF. Significantly, translocation of HIRA to PML bodies occurs in the absence of functional pRB and p53 tumor suppressor pathways. However, our evidence indicates that downstream of HIRA's localization to PML bodies, the HIRA/ASF1a pathway cooperates with pRB and p53 to make SAHF, with the HIRA/ASF1a and pRB pathways acting in parallel. We present evidence that convergence of the HIRA/ASF1a and pRB pathways occurs through a DNAJ-domain protein, DNAJA2.
Ye
Xiaofen
X
Department of Basic Science, Fox Chase Cancer Center, 333 Cottman Avenue, Philadelphia, PA 19111, USA.
Zerlanko
Brad
B
Zhang
Rugang
R
Somaiah
Neeta
N
Lipinski
Marc
M
Salomoni
Paolo
P
Adams
Peter D
PD
D002453:Cell Cycle; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism*; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000378:metabolism; D016922:Cellular Senescence / Q000502:physiology*; D050956:HSP40 Heat-Shock Proteins / Q000378:metabolism; D006570:Heterochromatin / Q000502:physiology*; D056488:Histone Chaperones; D006801:Humans; D018832:Molecular Chaperones; D009154:Mutation; D015514:Oncogene Proteins, Fusion / Q000378:metabolism; D021381:Protein Transport; D016160:Retinoblastoma Protein / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism*
C491641:ASF1A protein, human; D018797:Cell Cycle Proteins; C494645:DNAJA2 protein, human; C086057:HIRA protein, human; D050956:HSP40 Heat-Shock Proteins; D006570:Heterochromatin; D056488:Histone Chaperones; D018832:Molecular Chaperones; D015514:Oncogene Proteins, Fusion; D016160:Retinoblastoma Protein; D014157:Transcription Factors; D016159:Tumor Suppressor Protein p53; C093476:promyelocytic leukemia-retinoic acid receptor alpha fusion oncoprotein