In addition to its demethylating function, 5-aza-2'-deoxycytidine (5-aza-CdR) also plays an important role in inducing cell cycle arrest, differentiation and cell death. However, the mechanism by which 5-aza-CdR induces antineoplastic activity is not clear. In this study, we found that 5-aza-CdR at limited concentrations (0.01-5

Deregulated expression of E2F1 not only promotes S-phase entry but also induces apoptosis. Although it has been well documented that E2F1 is able to induce p53-dependent apoptosis via raising ARF activity, the mechanism by which E2F induces p53-independent apoptosis remains unclear. Here we report that E2F1 can directly bind to and activate the promoter of Smac/DIABLO, a mitochondrial proapoptotic gene, through the E2F1-binding sites BS2 (-542～-535 bp) and BS3 (-200～-193 bp). BS2 and BS3 appear to be utilized in combination rather than singly by E2F1 in activation of Smac/DIABLO. Activation of BS2 and BS3 are E2F1-specific, since neither E2F2 nor E2F3 is able to activate BS2 or BS3. Using the H1299 ER-E2F1 cell line where E2F1 activity can be conditionally induced, E2F1 has been shown to upregulate the Smac/DIABLO expression at both mRNA and protein levels upon 4-hydroxytamoxifen treatment, resulting in an enhanced mitochondria-mediated apoptosis. Reversely, reducing the Smac/DIABLO expression by RNA interference significantly diminishes apoptosis induced by E2F1. These results may suggest a novel mechanism by which E2F1 promotes p53-independent apoptosis through directly regulating its downstream mitochondrial apoptosis-inducing factors, such as Smac/DIABLO.

DNA methylation in the promoter of certain genes is associated with transcriptional silencing. Methylation affects gene expression directly by interfering with transcription factor binding and/or indirectly by recruiting histone deacetylases through methyl-DNA-binding proteins. In this study, we demonstrate that the human lung cancer cell line H719 lacks p53-dependent and -independent p21Cip1 expression. p53 response to treatment with gamma irradiation or etoposide is lost due to a mutation at codon 242 of p53 (C3W). Treatment with depsipeptide, an inhibitor of histone deacetylase, was unable to induce p53-independent p21Cip1 expression because the promoter of p21Cip1 in these cells is hypermethylated. By analyzing luciferase activity of transfected p21Cip1 promoter vectors, we demonstrate that depsipeptide functions on Sp1-binding sites to induce p21Cip1 expression. We hypothesize that hypermethylation may interfere with Sp1/Sp3 binding. By using an electrophoretic mobility shift assay, we show that, although methylation within the consensus Sp1-binding site did not reduce Sp1/Sp3 binding, methylation outside of the consensus Sp1 element induced a significant decrease in Sp1/Sp3 binding. Depsipeptide induced p21Cip1 expression was reconstituted when cells were pretreated with 5-aza-2α-deoxycytidine. Our data suggest, for the first time, that hypermethylation around the consensus Sp1-binding sites may directly reduce Sp1/Sp3 binding, therefore leading to a reduced p21Cip1 expression in response to depsipeptide treatment.

Generally, histone deacetylase (HDAC) inhibitor-induced p21Waf1/Cip1 expression is thought to be p53 independent. Here we found that an inhibitor of HDAC, depsipeptide (FR901228), but not trichostatin A (TSA), induces p21Waf1/Cip1 expression through both p53 and Sp1/Sp3 pathways in A549 cells (which retain wild-type p53). This is demonstrated by measuring relative luciferase activities of p21 promoter constructs with p53 or Sp1 binding site mutagenesis and was further confirmed by transfection of wild-type p53 into H1299 cells (p53 null). That p53 was acetylated after depsipeptide treatment was tested by sequential immunoprecipitation/Western immunoblot analysis with anti-acetylated lysines and anti-p53 antibodies. The acetylated p53 has a longer half-life due to a significant decrease in p53 ubiquitination. Further study using site-specific antiacetyllysine antibodies and transfection of mutated p53 vectors (K319/K320/K321R mutated and K373R/K382R mutations) into H1299 cells revealed that depsipeptide specifically induces p53 acetylation at K373/K382, but not at K320. As assayed by coimmunoprecipitation, the K373/K382 acetylation is accompanied by a recruitment of p300, but neither CREB-binding protein (CBP) nor p300/CBP-associated factor (PCAF), to the p53 C terminus. Furthermore, activity associated with the binding of the acetylated p53 at K373/K382 to the p21 promoter as well as p21Waf1/Cip1 expression is significantly increased after depsipeptide treatment, as tested by chromatin immunoprecipitations and Western blotting, respectively. In addition, p53 acetylation at K373/K382 is confirmed to be required for recruitment of p300 to the p21 promoter, and the depsipeptide-induced p53 acetylation at K373/K382 is unlikely to be dependent on p53 phosphorylation at Ser15, Ser20, and Ser392 sites. Our data suggest that p53 acetylation at K373/K382 plays an important role in depsipeptide-induced p21Waf1/Cip1 expression.

Amplification of oncogenes is an important mechanism that can cause gene overexpression and contributes to tumor development. The identification of amplified regions might have both prognostic and therapeutic significance. We used primary lung carcinomas and lung cancer cell lines for restriction landmark genomic scanning (RLGS) to identify novel amplified sequences. Enhanced RLGS fragments that indicate gene amplification were observed in primary tumors and lung cancer cell lines of both non-small cell lung cancer and small cell lung cancer. We identified one novel amplicon on chromosome 11q22, in addition to previously reported amplicons that include oncogenes MYCC, MYCL1 and previously identified amplification of chromosomal regions 6q21 and 3q26-27. Amplification of 11q22 has been reported in other types of cancer and was refined to an 1.19 Mbp region for which the complete sequence is available. Based on a patient sample with a small region of low-level amplification we were able to further narrow this region to 0.92 Mbp. Genes localized in this region include two inhibitors of apoptosis (cIAP1 and cIAP2). Immunohistochemistry and western blot analysis identified cIAP1 and cIAP2 as potential oncogenes in this region as both are overexpressed in multiple lung cancers with or without higher copy numbers.