Lipid starvation and hypoxia synergistically activate ICAM1 and multiple genes in an Sp1-dependent manner to promote the growth of ovarian cancer

Abstract

BackgroundElucidation of the molecular mechanisms by which cancer cells overcome hypoxia is potentially important for targeted therapy. Complexation of hypoxia-inducible factors (HIFs) with aryl hydrocarbon receptor nuclear translocators can enhance gene expression and initiate cellular responses to hypoxia. However, multiple molecular mechanisms may be required for cancer cells to adapt to diverse microenvironments. We previously demonstrated that a physical interaction between the ubiquitously expressed transcription factor Sp1 and HIF2 is a major cause of FVII gene activation in poor prognostic ovarian clear cell carcinoma (CCC) cells under hypoxia. Furthermore, it was found that FVII activation is synergistically enhanced when serum-starved cells are cultured under hypoxic conditions. In this study, we investigated whether HIFs and transcription factor Sp1 cooperate to activate multiple genes in CCC cells under conditions of serum starvation and hypoxia (SSH) and then contribute to malignant phenotypes.MethodsTo identify genes activated under hypoxic conditions in an Sp1-dependent manner, we first performed cDNA microarray analyses. We further investigated the molecular mechanisms of synergistic gene activations including the associated serum factors by various experiments such as real-time RT-PCR, western blotting and chromatin immunoprecipitation. The study was further extended to animal experiments to investigate how it contributes to CCC progression in vivo.ResultsICAM1 is one such gene dramatically induced by SSH and is highly induced by SSH and its synergistic activation involves both the mTOR and autonomously activated TNFα-NFκB axes. We identified long chain fatty acids (LCFA) as a major class of lipids that is associated with albumin, a serum factor responsible for synergistic gene activation under SSH. Furthermore, we found that ICAM1 can be induced in vivo to promote tumor growth.ConclusionSp1 and HIFs collaborate to activate genes required for the adaptation of CCC cells to severe microenvironments, such as LCFA starvation and hypoxia. This study highlights the importance of transcriptional regulation under lipid starvation and hypoxia in the promotion of CCC tumor growth.Electronic supplementary materialThe online version of this article (doi:10.1186/s12943-015-0351-z) contains supplementary material, which is available to authorized users.

Time- and oxygen-dependent expression and regulation of NDRG1 in human brain cancer cells

“…It has been shown that hypoxic conditions raise the expression of these transcription factors in nuclear extracts (59), suggesting that the hypoxia-stimulated upregulation of NDRG1 may be mainly mediated by a combined effect of these factors and to a lesser extend by Smad7 and YB-1. A cooperative mechanism, as suggested in the present study, has been shown to promote the regulation of genes necessary for cell adaptation to varying microenvironments such as during starvation and hypoxia (60). Indeed, NDRG1 promoter studies revealed that a SP1 site partially is responsible for the VHL-induced suppression of NDRG1 (61,62).…”

Tissue Factor–Factor VII Complex as a Key Regulator of Ovarian Cancer Phenotypes

“…Pimonidazole is a chemical agent that reacts with amino acid residues of proteins in cells exposed to severe reducing (hypoxic) conditions. IHC analysis of A2780 tumors orthotopically (intraperitoneally) implanted into nude mice 74 and OVISE tumors subcutaneously implanted into non-obese diabetic/severe combined immunodeficiency mice 75 using antibodies raised against pimonidazole amino acid adducts demonstrated that ovarian tumor tissues are severely hypoxic. Furthermore, a SKOV-3 tumor model revealed that ovarian cancer cells form spheroids and grow in the peritoneal cavity, and their core was severely hypoxic.…”

“… 76 These results are consistent with the general concept that solid tumors contain areas of severe hypoxia. 75 …”

Neem Leaf Glycoprotein Restrains VEGF Production by Direct Modulation of HIF1α-Linked Upstream and Downstream Cascades

“…Next, we look further into the binding capacity of HIF1α with other cofactors, like Sp1, CBP, p300, and we found that NLGP prevents colocalization of HIF1α with CBP, p300 and Sp1 but not with Sp3, which can competitively target HIF1α and Sp1 binding. Sp1 and Sp3 compete for binding to the HRE region as they share more than 90% sequence homology (39)(40)(41). Consequently, we observed significant less binding of active HIF1α complex with HRE region.…”