Programmed Cell Death-4 Tumor Suppressor Protein Contributes to Retinoic Acid-Induced Terminal Granulocytic Differentiation of Human Myeloid Leukemia Cells

Department of Experimental Therapeutics, The University of Texas M. D. Anderson Cancer Center, Houston, TX 77030, USA.
Molecular Cancer Research (Impact Factor: 4.38). 02/2007; 5(1):95-108. DOI: 10.1158/1541-7786.MCR-06-0125
Source: PubMed


Programmed cell death-4 (PDCD4) is a recently discovered tumor suppressor protein that inhibits protein synthesis by suppression of translation initiation. We investigated the role and the regulation of PDCD4 in the terminal differentiation of acute myeloid leukemia (AML) cells. Expression of PDCD4 was markedly up-regulated during all-trans retinoic acid (ATRA)-induced granulocytic differentiation in NB4 and HL60 AML cell lines and in primary human promyelocytic leukemia (AML-M3) and CD34(+) hematopoietic progenitor cells but not in differentiation-resistant NB4.R1 and HL60R cells. Induction of PDCD4 expression was associated with nuclear translocation of PDCD4 in NB4 cells undergoing granulocytic differentiation but not in NB4.R1 cells. Other granulocytic differentiation inducers such as DMSO and arsenic trioxide also induced PDCD4 expression in NB4 cells. In contrast, PDCD4 was not up-regulated during monocytic/macrophagic differentiation induced by 1,25-dihydroxyvitamin D3 or 12-O-tetradecanoyl-phorbol-13-acetate in NB4 cells or by ATRA in THP1 myelomonoblastic cells. Knockdown of PDCD4 by RNA interference (siRNA) inhibited ATRA-induced granulocytic differentiation and reduced expression of key proteins known to be regulated by ATRA, including p27(Kip1) and DAP5/p97, and induced c-myc and Wilms' tumor 1, but did not alter expression of c-jun, p21(Waf1/Cip1), and tissue transglutaminase (TG2). Phosphatidylinositol 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) signaling pathway was found to regulate PDCD4 expression because inhibition of PI3K by LY294002 and wortmannin or of mTOR by rapamycin induced PDCD4 protein and mRNA expression. In conclusion, our data suggest that PDCD4 expression contributes to ATRA-induced granulocytic but not monocytic/macrophagic differentiation. The PI3K/Akt/mTOR pathway constitutively represses PDCD4 expression in AML, and ATRA induces PDCD4 through inhibition of this pathway.

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    • "The regulatory role of PDCD4 differed by cell type. In Bon-1 pancreatic neuroendocrine cells [23], ovarian cancer cells [36] and intraductal papillary mucinous neoplasm samples [37], PDCD4 acted opposite to our finding in regulating p21Waf1/Cip1, and in NB4 human acute promyelocytic cells, PDCD4 had no significant effect on p21Waf1/Cip1 expression [38]. "
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    • "Western blot analysis. After treatment, the cells were trypsinized and collected by centrifugation, and whole-cell lysates were obtained using a lysis buffer as described previously.48 Total protein concentration was determined using a protein assay kit (Bio-Rad, Hercules, CA, USA). "
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    • "We have also shown that ATRA and ATO inhibit the activity PI3K/Akt/mTOR and p70S6 kinase in APL cells [33] [34]. The current study is in agreement with our previous findings that ATRA inhibits translation initiation by multiple mechanisms, including inhibition of initiation factors and induction of PDCD4 and DAP5 (inhibitors of translation initiation), inhibition of p- 4E-BP1 and EF4E (Figure 11) [32] [33] [34]. DAP5 and PDCD4, a novel tumor suppressor protein, were recently identified as inhibitors of translation initiation. "
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