Sp100 as a potent tumor suppressor: accelerated senescence and rapid malignant transformation of human fibroblasts through modulation of an embryonic stem cell program.
Identifying the functions of proteins, which associate with specific subnuclear structures, is critical to understanding eukaryotic nuclear dynamics. Sp100 is a prototypical protein of ND10/PML nuclear bodies, which colocalizes with Daxx and the proto-oncogenic PML. Sp100 isoforms contain SAND, PHD, Bromo, and HMG domains and are highly sumoylated, all characteristics suggestive of a role in chromatin-mediated gene regulation. A role for Sp100 in oncogenesis has not been defined previously. Using selective Sp100 isoform-knockdown approaches, we show that normal human diploid fibroblasts with reduced Sp100 levels rapidly senesce. Subsequently, small rapidly dividing Sp100 minus cells emerge from the senescing fibroblasts and are found to be highly tumorigenic in nude mice. The derivation of these tumorigenic cells from the parental fibroblasts is confirmed by microsatellite analysis. The small rapidly dividing Sp100 minus cells now also lack ND10/PML bodies, and exhibit genomic instability and p53 cytoplasmic sequestration. They have also activated MYC, RAS, and TERT pathways and express mesenchymal to epithelial transdifferentiation (MET) markers. Reintroduction of expression of only the Sp100A isoform is sufficient to maintain senescence and to inhibit emergence of the highly tumorigenic cells. Global transcriptome studies, quantitative PCR, and protein studies, as well as immunolocalization studies during the course of the transformation, reveal that a transient expression of stem cell markers precedes the malignant transformation. These results identify a role for Sp100 as a tumor suppressor in addition to its role in maintaining ND10/PML bodies and in the epigenetic regulation of gene expression.
The Wistar Institute, Philadelphia, Pennsylvania 19104, USA.
Dmitri G
DG
Negorev
Olga V
OV
Vladimirova
Andrew V
AV
Kossenkov
Elena V
EV
Nikonova
Renee M
RM
Demarest
Anthony J
AJ
Capobianco
Michael K
MK
Showe
Frank J
FJ
Rauscher
Louise C
LC
Showe
Gerd G
GG
Maul
D000818:Animals; D034961:Antigens, Nuclear / Q000235:genetics* / Q000378:metabolism; D001324:Autoantigens / Q000235:genetics* / Q000378:metabolism; D015153:Blotting, Western; D002471:Cell Transformation, Neoplastic / Q000235:genetics; D002478:Cells, Cultured; D016922:Cellular Senescence / Q000235:genetics; D053595:Embryonic Stem Cells / Q000378:metabolism*; D058750:Epithelial-Mesenchymal Transition / Q000235:genetics; D005347:Fibroblasts / Q000166:cytology / Q000378:metabolism*; D020869:Gene Expression Profiling; D057809:HEK293 Cells; D006801:Humans; D008297:Male; D051379:Mice; D008819:Mice, Nude; D009374:Neoplasms, Experimental / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D009687:Nuclear Proteins / Q000378:metabolism; D020411:Oligonucleotide Array Sequence Analysis; D000071156:Promyelocytic Leukemia Protein; D016271:Proto-Oncogene Proteins c-myc / Q000378:metabolism; D034622:RNA Interference; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014157:Transcription Factors / Q000378:metabolism; D014183:Transplantation, Heterologous; D025521:Tumor Suppressor Proteins / Q000235:genetics* / Q000378:metabolism; D018631:ras Proteins / Q000378:metabolism
D034961:Antigens, Nuclear; D001324:Autoantigens; C094297:CALCOCO2 protein, human; C489427:MYC protein, human; D009687:Nuclear Proteins; D000071156:Promyelocytic Leukemia Protein; D016271:Proto-Oncogene Proteins c-myc; D014157:Transcription Factors; D025521:Tumor Suppressor Proteins; C066642:SP100 protein, human; C070576:PML protein, human; D018631:ras Proteins