4.6 Article

EAPP modulates the activity of p21 and Chk2

Journal

CELL CYCLE
Volume 10, Issue 13, Pages 2077-2082

Publisher

TAYLOR & FRANCIS INC
DOI: 10.4161/cc.10.13.16247

Keywords

DNA damage; checkpoint; EAPP; Chk2; p21; phosphorylation

Categories

Funding

  1. Austrian FWF [P18417]
  2. Herzfelder'sche Familienstiftung
  3. University of Vienna
  4. Austrian Science Fund (FWF) [P18417] Funding Source: Austrian Science Fund (FWF)

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Genomic instability is thought to be critical for the development of cancer. Among its causes microsatellite instability (MIN) and chromosomal instability (CIN) have attracted the most attention. Cell cycle checkpoints and DNA repair mechanisms are the first line of defense against DNA damage. Among the most dangerous DNA lesions are double-strand breaks. The response to DNA double strand breaks is regulated mainly by the serine/threonine kinases ATM and Chk2 and their downstream target the tumor suppressor p53, which in turn stimulates the expression of growth-inhibitory genes like CDKN1A (encoding p21) or proapoptotic genes like Bax. The balance between these gene products determines the fate of a cell. EAPP is a nuclear phosphoprotein that is frequently upregulated in human tumors. We have recently shown that EAPP levels are critical for cellular homeostasis. DNA damage elevates EAPP levels and its overexpression results in G 1 arrest and impairs apoptosis in a p21-dependent manner. EAPP binds to the p21 promoter, stimulates its activity and seems to be essential for transcription initiation. In the present work we show that EAPP also regulates the phosphorylation status and thus the activity of Chk2. EAPP binding seems to trigger the dephosphorylation of P-Chk2 resulting in its inactivation. A newly described function of Chk2 in mitosis that secures genomic integrity might also be affected by EAPP overexpression. This might explain the abundance of EAPP in aneuploid tumor cells.

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