Overexpression of Sp1 leads to p53‐dependent apoptosis in cancer cells

Abstract

Numerous studies have documented that Sp1 expression level were elevated in various human cancers. However, the promoters of many pro-apoptotic genes have been found to contain the Sp1 binding elements and are activated by Sp1 overexpression. To better understand the role and the mechanism of increased Sp1 levels on apoptosis, we used adenovirus to ectopically express GFP-Sp1 protein in various cancer cell lines. First, in HeLa and A549 cells, we found that Sp1 overexpression suppressed the cell growth and increased the detection of sub-G1 fraction, caspase-3 cleavage, and annexin-V signal revealed that apoptosis occurred. Furthermore, when cells entered the mitotic stage, the cell apoptosis was induced by Sp1 overexpression through affecting mitotic chromatin packaging. We also verified that p53 protein was accumulated and activated the p53-dependent apoptotic pathways in the wildtype p53 cells but not in the p53-mutated or p53-deleted cell lines when these cells were infected with adeno-GFP-Sp1 virus. In addition, A549 (p53) cells could be protected from apoptosis under Sp1 overexpression when p53 was knockdown by p53 shRNA. Finally, H1299 (p53 2/2 ) cell viability was significantly inhibited by adeno-GFP-Sp1 virus infection in the expression of p53. In conclusion, p53 was an essential factor for Sp1 overexpression-induced apoptotic cell death in transforming cells. ' UICCKey words: Sp1; p53; apoptosis The specificity protein/Kr€ uppel-like factor (Sp/XKLF) family is composed of transcription factors in which a particular combination of 3 conserved Cys 2 His 2 zinc fingers form the DNA-binding domain.1 The transcription factor Sp1 is ubiquitously expressed in mammalian cells and is important in a variety of physiological processes, including cell-cycle regulation, apoptosis, and differentiation. Recent studies and our previous studies have revealed that the posttranslational modifications of Sp1 could alter its transcriptional activity, DNA-binding affinity, or protein stability. Sp1 commonly undergoes posttranslational modifications such as phosphorylation, glycosylation, acetylation, ubiquitination, and sumoylation. [2][3][4][5][6] Numerous studies have documented that Sp1 activity and/or expression levels are elevated in human pancreatic cancer, breast cancer, colorectal cancer, gastric carcinoma, hepatocellular carcinoma, and thyroid carcinoma.7-12 Although Sp1 regulates a number of oncogenes such as those coding for the vascular endothelial growth factor, urokinase plasminogen activator (uPA), uPA receptor, and epithelial growth factor receptor, [13][14][15] it also induces the expression of many tumor suppressor genes such as p27 kip1 , p21 WAF1/CIP1 , p16 INK4a , and pp2a-c. [16][17][18] In addition, the promoters of many proapoptotic genes have been found to contain Sp1-binding elements; for instance, fas, fas ligand, bax, and caspase 3.19,20 Interestingly, it has been found that Sp1 can also induce the expression of many antiapoptotic genes (such as survivin, bcl-x, and bcl-w).20,21 Moreover, severa...

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“…High levels of Sp1 in highly invasive lung adenocarcinoma cells were associated with increased E-cadherin expression and metastasis inhibition [55] . In addition, Chuang et al found that Sp1 cooperates with p53 to induce apoptosis in a variety of cancer cells, including lung adenocarcinoma, cervical adenocarcinoma, breast carcinoma, colon carcinoma and glioma cells [56] . Recently, Zhang et al reported that aberrant overexpression of Sp1 was observed in advanced tumor stages in NPC, and knockdown of Sp1 by siRNA inhibited proliferation and led to cell cycle arrest in NPC cells [21] , suggesting the potential of Sp1 as a therapeutic target in NPC treatment.…”

Mitochondrial uncoupling protein (UCP2) gene expression is regulated by miR-2909

“…Recent findings have established that AATF genome encoded miR-2909 not only requires nuclear RelA translocation for its expression but also this microRNA regulates gene expression through repression of KLF4 gene expression resulting in the up-regulation of SP1 gene expression [7,8]. At this stage, it is pertinent to note that: a) SP1 has been shown to induce genes coding for AATF, CCL5 and p53 [13][14][15]; b) p53 gene expression is also induced by CCL5 and AATF-dependent translocation of RelA to p53 gene promoter [6,16]; c) KLF4 has been shown to induce IL-17 gene expression [12] and p53 binds RelA to block its translocation either to nucleus or mitochondria [4]; d) KLF4 is known to repress Bmi-1 gene which is known to degrade the p53 protein [17,18]. The results reported here together with above-mentioned findings in the literature, led us to the mechanism which reveals as to how AATF RNome can regulate UCP2 gene in a cyclic fashion (Fig.…”

“…2A) and KLF4 has been shown to induce IL-17 expression [12] whereas SP1 has been shown to induce genes coding for CCL5, AATF and p53 [13][14][15]. Both ectopic miR-2909 expression and its down-regulation with antagomiR-2909 resulted in the corresponding modulation of genes coding for IL-17 and UCP2 (Fig.…”

The oncoprotein hepatitis B X-interacting protein promotes the migration of ovarian cancer cells through the upregulation of S-phase kinase-associated protein 2 by Sp1

“…Sp1 is a transcription factor that either enhance or repress the activity of promoters of genes involved in differentiation, cell cycle progression and oncogenesis (34). In comparison to normal tissues or cells, Sp1 level is greater in breast carcinomas, thyroid cancer, hepatocellular carcinomas, pancreatic cancer, colorectal cancer, gastric cancer and lung cancer (34)(35)(36)(37). Sp1 is also overexpressed in ovarian cancer (38) and plays an important role in the process of cancer.…”