Heterologous expression of the transcriptional regulator escargot inhibits megakaryocytic endomitosis.
Certain cell types escape the strict mechanisms imposed on the majority of somatic cells to ensure the faithful inheritance of parental DNA content. This is the case in many embryonic tissues and certain adult cells such as mammalian hepatocytes and megakaryocytes. Megakaryocytic endomitosis is characterized by repeated S phases followed by abortive mitoses, resulting in mononucleated polyploid cells. Several cell cycle regulators have been proposed to play an active role in megakaryocytic polyploidization; however, little is known about upstream factors that could control endomitosis. Here we show that ectopic expression of the transcriptional repressor escargot interferes with the establishment of megakaryocytic endomitosis. Phorbol ester-induced polyploidization was inhibited in stably transfected megakaryoblastic HEL cells constitutively expressing escargot. Analysis of the expression and activity of different cell cycle factors revealed that Escargot affects the G(1)/S transition by influencing Cdk2 activity and cyclin A transcription. Nuclear proteins that specifically bind the Escargot-binding element were detected in endomitotic and non-endomitotic megakaryoblastic cells, but down-regulation occurred only during differentiation of cells that become polyploid. As Escargot was originally implicated in ploidy maintenance of Drosophila embryonic and larval cells, our results suggest that polyploidization in megakaryocytes might respond to mechanisms conserved from early development to adult cells that need to escape normal control of the diploid state.
Ballester
A
A
Department of Biochemistry, Instituto de Investigaciones Biomédicas "Alberto Sols," Universidad Autónoma-Consejo Superior de Investigaciones Cientificas, Arturo Duperier 4, 28029 Madrid, Spain.
Frampton
J
J
Vilaboa
N
N
Calés
C
C
D042846:CDC2-CDC28 Kinases; D002453:Cell Cycle; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D002478:Cells, Cultured; D003001:Cloning, Molecular; D051357:Cyclin-Dependent Kinase 2; D018844:Cyclin-Dependent Kinases / Q000378:metabolism; D004247:DNA / Q000378:metabolism; D018076:DNA, Complementary / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism* / Q000502:physiology*; D004171:Diploidy; D015536:Down-Regulation; D006801:Humans; D015151:Immunoblotting; D007150:Immunohistochemistry; D008533:Megakaryocytes / Q000378:metabolism*; D008938:Mitosis; D009841:Oligonucleotides / Q000378:metabolism; D010641:Phenotype; D010703:Phorbol Esters / Q000494:pharmacology; D011003:Ploidies; D011233:Precipitin Tests; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D000071250:Snail Family Transcription Factors; D013997:Time Factors; D014157:Transcription Factors / Q000378:metabolism* / Q000502:physiology*; D014158:Transcription, Genetic; D014162:Transfection
D018076:DNA, Complementary; D004268:DNA-Binding Proteins; D009841:Oligonucleotides; D010703:Phorbol Esters; D000071250:Snail Family Transcription Factors; D014157:Transcription Factors; C000604451:sna protein, Drosophila; D004247:DNA; D017346:Protein Serine-Threonine Kinases; D042846:CDC2-CDC28 Kinases; C495894:CDK2 protein, human; D051357:Cyclin-Dependent Kinase 2; D018844:Cyclin-Dependent Kinases