Sp1 Is Involved in Akt-mediated Induction of VEGF Expression through an HIF-1–independent Mechanism

Pore, Nabendu; Liu, Shuang; Shu, Hui; Li, Bin; Haas‐Kogan, Daphne A.; Stokoe, David; Milanini, Julie; Pagès, Gilles; O’Rourke, Donald M.; Bernhard, Eric J.; Maity, Amit

doi:10.1091/mbc.e04-05-0374

Cited by 214 publications

(189 citation statements)

References 49 publications

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“…In fact, data from other groups evidenced that Sp1 is required for PI3K-mediated induction of VEGF (Pore et al, 2004) and that phosphorylation of Sp1 by ERK1/2 MAPK is a crucial event for the regulation of VEGF (Berra et al, 2000, Milanini-Mongiat et al, 2002. We are currently investigating the involvement of Sp1 and the RAS/RAF pathway on bcl-2-induced HIF-1/ VEGF expression.…”

Section: Discussionmentioning

confidence: 94%

Involvement of PI3K and MAPK Signaling in bcl-2-induced Vascular Endothelial Growth Factor Expression in Melanoma Cells

Trisciuoglio¹,

Iervolino²,

Zupi³

et al. 2005

MBoC

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We have previously demonstrated that bcl-2 overexpression in tumor cells exposed to hypoxia increases the expression of vascular endothelial growth factor (VEGF) gene through the hypoxia-inducible factor-1 (HIF-1). In this article, we demonstrate that exposure of bcl-2 overexpressing melanoma cells to hypoxia induced phosphorylation of AKT and extracellular signal-regulated kinase (ERK)1/2 proteins. On the contrary, no modulation of these pathways by bcl-2 was observed under normoxic conditions. When HIF-1␣ expression was reduced by RNA interference, AKT and ERK1/2 phosphorylation were still induced by bcl-2. Pharmacological inhibition of mitogen-activated protein kinase (MAPK) and phosphatidylinositol 3-kinase (PI3K) signaling pathways reduced the induction of VEGF and HIF-1 in response to bcl-2 overexpression in hypoxia. No differences were observed between control and bcl-2-overexpressing cells in normoxia, in terms of VEGF protein secretion and in response to PI3K and MAPK inhibitors. We also demonstrated that RNA interference-mediated down-regulation of bcl-2 expression resulted in a decrease in the ERK1/2 phosphorylation and VEGF secretion only in bcl-2-overexpressing cell exposed to hypoxia but not in control cells. In conclusion, our results indicate, for the first time, that bcl-2 synergizes with hypoxia to promote expression of angiogenesis factors in melanoma cells through both PI3K-and MAPK-dependent pathways. INTRODUCTIONAngiogenesis is a complex and multilevel process of new capillary formation on the basis of already existing blood vessels. Physiologically, it is a very strictly regulated process, which results in a balance between stimulatory (angiogenic) and inhibitory (angiostatic) factors to control the correct development of blood vessels. Angiogenesis is a rate-limiting step in tumor growth and progression, and many tumors develop a severely hypoxic microenvironment and secrete angiogenesis-stimulating factors (Folkman et al., 1971;Talks et al., 2000). Vascular endothelial growth factor (VEGF), a potent and specific mitogen for vascular endothelial cells, is a critical mediator of angiogenesis. Its expression is induced in cancer cells as a result of hypoxia and multiple genetic alterations, including p53 and PTEN loss-of-function, RAS and SRC gain-of-function, and autocrine tyrosine kinase signaling pathways (Mukhopadhyay et al., 1995;Arbiser et al., 1997;Petit et al., 1997;Akagi et al., 1998;Ellis et al., 1998;Yen et al., 2000). Based on the analysis of melanoma and breast cancer cells recently reported by our group Iervolino et al., 2002;Del Bufalo et al., 2003;Trisciuoglio et al., 2004), this list can now be extended to include the increased VEGF expression resulting from bcl-2 overexpression. Hypoxia-and growth factor-induced VEGF expression in tumor cells is regulated by the hypoxia inducible factor 1 (HIF-1) (Jiang et al., 1997;Mazure et al., 1997;Ravi et al., 2000;Zhong et al., 2000;Zundel et al., 2000;Laughner et al., 2001;Fukuda et al., 2002), a transcription factor that is compose...

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Section: Discussionmentioning

confidence: 94%

Involvement of PI3K and MAPK Signaling in bcl-2-induced Vascular Endothelial Growth Factor Expression in Melanoma Cells

Trisciuoglio¹,

Iervolino²,

Zupi³

et al. 2005

MBoC

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“…We next asked whether there was an effect on nontransformed cells. These experiments were done using an immortalized normal human astrocyte line (NHA) that has been described previously (36,37). Pretreatment of these cells with LY294002 blunted the hypoxic induction of HIF-1a (Fig.…”

Section: Resultsmentioning

confidence: 99%

Akt1 Activation Can Augment Hypoxia-Inducible Factor-1α Expression by Increasing Protein Translation through a Mammalian Target of Rapamycin–Independent Pathway

Pore

Jiang

Shu

et al. 2006

Molecular Cancer Research

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169

134

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The phosphoinositide 3-kinase (PI3K)/Akt pathway is commonly activated in cancer; therefore, we investigated its role in hypoxia-inducible factor-1A (HIF-1A) regulation. Inhibition of PI3K in U87MG glioblastoma cells, which have activated PI3K/Akt activity secondary to phosphatase and tensin homologue deleted on chromosome 10 (PTEN) mutation, with LY294002 blunted the induction of HIF-1A protein and its targets vascular endothelial growth factor and glut1 mRNA in response to hypoxia. Introduction of wild-type PTEN into these cells also blunted HIF-1A induction in response to hypoxia and decreased HIF-1A accumulation in the presence of the proteasomal inhibitor MG132. Akt small interfering RNA (siRNA) also decreased HIF-1A induction under hypoxia and its accumulation in normoxia in the presence of dimethyloxallyl glycine, a prolyl hydroxylase inhibitor that prevents HIF-1A degradation. Metabolic labeling studies showed that Akt siRNA decreased HIF-1A translation in normoxia in the presence of dimethyloxallyl glycine and in hypoxia. Inhibition of mammalian target of rapamycin (mTOR) with rapamycin (10-100 nmol/L) had no significant effect on HIF-1A induction in a variety of cell lines, a finding that was confirmed using mTOR siRNA. Furthermore, neither mTOR siRNA nor rapamycin decreased HIF-1A translation as determined by metabolic labeling studies. Therefore, our results indicate that Akt can augment HIF-1A expression by increasing its translation under both normoxic and hypoxic conditions; however, the pathway we are investigating seems to be rapamycin insensitive and mTOR independent. These observations, which were made on cells grown in standard tissue culture medium (10% serum), were confirmed in PC3 prostate carcinoma cells. We did find that rapamycin could decrease HIF-1A expression when cells were cultured in low serum, but this seems to represent a different pathway. (Mol Cancer Res 2006;4(7):471 -9)

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“…Firstly, Sp1 activity is increased following phosphorylation by oncogenic signalling pathways such as the RAS/RAF/MAPK and the PI3K/Akt pathways (Kivinen et al, 1999;Milanini-Mongiat et al, 2002;Pore et al, 2004). Secondly, Sp1 is overexpressed and/or hyperactivated in a number of human tumours (Lietard et al, 1997;Zannetti et al, 2000;Shi et al, 2001;Chiefari et al, 2002;Wang et al, 2003).…”

Section: Discussionmentioning

confidence: 99%

Overexpression of Sp1 transcription factor induces apoptosis

et al. 2006

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Transcription factor Sp1 has recently been shown to be overexpressed in a number of human cancers and its overexpression contributes to malignant transformation. Sp1 regulates the expression of a number of genes participating in multiple aspects of tumorigenesis such as angiogenesis, cell growth and apoptosis resistance. To better understand the role of increased Sp1 levels on apoptosis regulation we have used retroviruses to overexpress this protein in haematopoietic Baf-3 cells and in 3T3 fibroblasts. We have also used inducible expression systems to control ectopic Sp1 levels in different cell types. Surprisingly, Sp1 overexpression on its own induces apoptosis in all the cellular models tested. The apoptotic pathways induced by Sp1 overexpression are cell type specific. Finally, using a truncated form of Sp1, we show that Sp1-induced apoptosis requires its DNA-binding domain. Our results highlight that Sp1 levels in untransformed cells must be tightly regulated as Sp1 overexpression leads to the induction of apoptosis. Our results also suggest that cancer cells overexpressing Sp1 can avoid Sp1-induced apoptosis.

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Sp1 Is Involved in Akt-mediated Induction of VEGF Expression through an HIF-1–independent Mechanism

Cited by 214 publications

References 49 publications

Involvement of PI3K and MAPK Signaling in bcl-2-induced Vascular Endothelial Growth Factor Expression in Melanoma Cells

Involvement of PI3K and MAPK Signaling in bcl-2-induced Vascular Endothelial Growth Factor Expression in Melanoma Cells

Akt1 Activation Can Augment Hypoxia-Inducible Factor-1α Expression by Increasing Protein Translation through a Mammalian Target of Rapamycin–Independent Pathway

Overexpression of Sp1 transcription factor induces apoptosis

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