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.
"The regulatory role of PDCD4 differed by cell type. In Bon-1 pancreatic neuroendocrine cells , ovarian cancer cells  and intraductal papillary mucinous neoplasm samples , 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 . "
[Show abstract][Hide abstract] ABSTRACT: We recently found low level of tumor suppressor programmed cell death 4 (PDCD4) associated with reduced atherosclerotic plaque area (unpublished). We investigated whether atheroprotective unidirectional pulsatile shear stress affects the expression of PDCD4 in endothelial cells.
En face co-immunostaining of the mouse aortic arch revealed a low level of PDCD4 in endothelial cells undergoing pulsatile shear stress. Application of unidirectional pulsatile shear stress to human umbilical vein endothelial cells (HUVECs) decreased PDCD4 protein but not mRNA level. Immunoprecipitation revealed that pulsatile shear stress induced the coupling of ubiquitin with PDCD4 expression. The phosphatidyl inositol 3-kinase (PI3K)/Akt pathway was involved in this ubiquitin-proteasome-mediated degradation of PDCD4. Gain of function and loss of function experiments showed that PDCD4 induced turnover (proliferation and apoptosis) of HUVECs. Low PDCD4 level was associated with reduced proliferation but not apoptosis or phosphorylation of endothelial nitric oxide synthase caused by pulsatile shear stress to help maintain the homeostasis of endothelial cells.
Pulsatile shear stress induces ubiquitin-proteasome-mediated degradation of PDCD4 via a PI3K/Akt pathway in HUVECs. PDCD4 induces turnover (proliferation and apoptosis) of HUVECs. Low PDCD4 level is associated with reduced proliferation for maintenance of HUVEC homeostasis under pulsatile shear stress.
PLoS ONE 03/2014; 9(3):e91564. DOI:10.1371/journal.pone.0091564 · 3.23 Impact Factor
"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). "
[Show abstract][Hide abstract] ABSTRACT: Bcl-2 is overexpressed in about a half of human cancers and 50-70% of breast cancer patients, thereby conferring resistance to conventional therapies and making it an excellent therapeutic target. Small interfering RNA (siRNA) offers novel and powerful tools for specific gene silencing and molecularly targeted therapy. Here, we show that therapeutic silencing of Bcl-2 by systemically administered nanoliposomal (NL)-Bcl-2 siRNA (0.15 mg siRNA/kg, intravenous) twice a week leads to significant antitumor activity and suppression of growth in both estrogen receptor-negative (ER(-)) MDA-MB-231 and ER-positive (+) MCF7 breast tumors in orthotopic xenograft models (P < 0.05). A single intravenous injection of NL-Bcl-2-siRNA provided robust and persistent silencing of the target gene expression in xenograft tumors. NL-Bcl-2-siRNA treatment significantly increased the efficacy of chemotherapy when combined with doxorubicin in both MDA-MB-231 and MCF-7 animal models (P < 0.05). NL-Bcl-2-siRNA treatment-induced apoptosis and autophagic cell death, and inhibited cyclin D1, HIF1α and Src/Fak signaling in tumors. In conclusion, our data provide the first evidence that in vivo therapeutic targeting Bcl-2 by systemically administered nanoliposomal-siRNA significantly inhibits growth of both ER(-) and ER(+) breast tumors and enhances the efficacy of chemotherapy, suggesting that therapeutic silencing of Bcl-2 by siRNA is a viable approach in breast cancers.Molecular Therapy-Nucleic Acids (2013) 2, e121; doi:10.1038/mtna.2013.45; published online 10 September 2013.
"We have also shown that ATRA and ATO inhibit the activity PI3K/Akt/mTOR and p70S6 kinase in APL cells  . 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)   . DAP5 and PDCD4, a novel tumor suppressor protein, were recently identified as inhibitors of translation initiation. "
[Show abstract][Hide abstract] ABSTRACT: Translation initiation and activity of eukaryotic initiation factor-alpha (eIF2α), the rate-limiting step of translation initiation, is often overactivated in malignant cells. Here, we investigated the regulation and role of eIF2α in acute promyelocytic (APL) and acute myeloid leukemia (AML) cells in response to all-trans retinoic acid (ATRA) and arsenic trioxide (ATO), the front-line therapies in APL. ATRA and ATO induce Ser-51 phosphorylation (inactivation) of eIF2α, through the induction of protein kinase C delta (PKCδ) and PKR, but not other eIF2α kinases, such as GCN2 and PERK in APL (NB4) and AML cells (HL60, U937, and THP-1). Inhibition of eIF2α reduced the expression of cellular proteins that are involved in apoptosis (DAP5/p97), cell cycle (p21Waf1/Cip1), differentiation (TG2) and induced those regulating proliferation (c-myc) and survival (p70S6K). PI3K/Akt/mTOR pathway is involved in regulation of eIF2α through PKCδ/PKR axis. PKCδ and p-eIF2α protein expression levels revealed a significant association between the reduced levels of PKCδ (P = 0.0378) and peIF2 (P = 0.0041) and relapses in AML patients (n = 47). In conclusion, our study provides the first evidence that PKCδ regulates/inhibits eIF2α through induction of PKR in AML cells and reveals a novel signaling mechanism regulating translation initiation.
Data provided are for informational purposes only. Although carefully collected, accuracy cannot be guaranteed. The impact factor represents a rough estimation of the journal's impact factor and does not reflect the actual current impact factor. Publisher conditions are provided by RoMEO. Differing provisions from the publisher's actual policy or licence agreement may be applicable.