Thrombopoietin upregulates the promoter conformation of p53 in a proliferation-independent manner coincident with a decreased expression of Bax: Potential mechanisms for survival enhancing effects

Alec Ritchie, Akihiko Gotoh, Jay Gaddy, Stephen E. Braun, Hal Broxmeyer

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21 Citations (Scopus)

Abstract

Thrombopoietin (Tpo) has proliferative and maturational effects on immature and more committed cells, respectively. We previously reported a role for Tpo as a survival factor in the factor-dependent human cell line M07e by demonstrating that Tpo suppresses apoptosis in the absence of induced proliferation. Wild-type p53 is a tumor suppressor gene that can play a vital role in mediating growth factor withdrawal-induced apoptosis in factor- dependent hematopoietic cells. Wild-type p53 can switch from a suppressor conformation, with an antiproliferative, pro-apoptotic phenotype, to a promoter conformation that has a diminished ability to mediate cell cycle arrest and apoptosis. In an effort to elucidate the mechanisms through which Tpo suppresses apoptosis, we investigated the effects of Tpo treatment on p53-mediated apoptosis in M07e cells. Tpo upregulated the expression of the promoter conformation of p53 in M07e cells coincident with a downregulation of Bax and Mdm2 protein levels. Protein levels of Bcl-2 and Bcl-x(L) did not significantly vary as a function of growth-factor stimulation. Conversely, the levels of suppressor conformation p53 were maximal when M07e was in a growth arrested state and decreased during factor stimulation. Furthermore, Tpo treatment induced an extranuclear buildup and greatly weakened the DNA binding capacity of p53. p53-specific antisense oligonucleotide treatment recapitulated the effects of Tpo treatment on the levels of Bax, Mdm-2, and Bcl-2. These results suggest that Tpo is suppressing growth factor withdrawal induced-apoptosis, at least in part, by downregulating the expression of pro- apoptotic Bax protein levels, through modulating the conformation of p53, which results in a functional inactivation of its pro-apoptotic abilities.

Original languageEnglish
Pages (from-to)4394-4402
Number of pages9
JournalBlood
Volume90
Issue number11
StatePublished - Dec 1 1997

Fingerprint

Thrombopoietin
Conformations
Up-Regulation
Survival
Apoptosis
bcl-2-Associated X Protein
Intercellular Signaling Peptides and Proteins
Proto-Oncogene Proteins c-mdm2
Down-Regulation
Cells
Apoptosis Regulatory Proteins
Antisense Oligonucleotides
Cell Cycle Checkpoints
Tumor Suppressor Genes
Tumors
Genes
Switches
Phenotype
Cell Line

ASJC Scopus subject areas

  • Hematology

Cite this

Thrombopoietin upregulates the promoter conformation of p53 in a proliferation-independent manner coincident with a decreased expression of Bax : Potential mechanisms for survival enhancing effects. / Ritchie, Alec; Gotoh, Akihiko; Gaddy, Jay; Braun, Stephen E.; Broxmeyer, Hal.

In: Blood, Vol. 90, No. 11, 01.12.1997, p. 4394-4402.

Research output: Contribution to journalArticle

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abstract = "Thrombopoietin (Tpo) has proliferative and maturational effects on immature and more committed cells, respectively. We previously reported a role for Tpo as a survival factor in the factor-dependent human cell line M07e by demonstrating that Tpo suppresses apoptosis in the absence of induced proliferation. Wild-type p53 is a tumor suppressor gene that can play a vital role in mediating growth factor withdrawal-induced apoptosis in factor- dependent hematopoietic cells. Wild-type p53 can switch from a suppressor conformation, with an antiproliferative, pro-apoptotic phenotype, to a promoter conformation that has a diminished ability to mediate cell cycle arrest and apoptosis. In an effort to elucidate the mechanisms through which Tpo suppresses apoptosis, we investigated the effects of Tpo treatment on p53-mediated apoptosis in M07e cells. Tpo upregulated the expression of the promoter conformation of p53 in M07e cells coincident with a downregulation of Bax and Mdm2 protein levels. Protein levels of Bcl-2 and Bcl-x(L) did not significantly vary as a function of growth-factor stimulation. Conversely, the levels of suppressor conformation p53 were maximal when M07e was in a growth arrested state and decreased during factor stimulation. Furthermore, Tpo treatment induced an extranuclear buildup and greatly weakened the DNA binding capacity of p53. p53-specific antisense oligonucleotide treatment recapitulated the effects of Tpo treatment on the levels of Bax, Mdm-2, and Bcl-2. These results suggest that Tpo is suppressing growth factor withdrawal induced-apoptosis, at least in part, by downregulating the expression of pro- apoptotic Bax protein levels, through modulating the conformation of p53, which results in a functional inactivation of its pro-apoptotic abilities.",
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