title: Ets-1 mediates upregulation of Mcl-1 downstream of XBP-1 in human melanoma cells upon ER stress.
abstract: Past studies have shown that upregulation of the anti-apoptotic Bcl-2 family protein Mcl-1 is a major adaptive mechanism of melanoma cells to endoplasmic reticulum (ER) stress, and has an important role in resistance of the cells to apoptosis. In this study, we show that the increase in transcription of Mcl-1 in melanoma cells triggered by pharmacological ER stress inducers is mediated by the transcription factor Ets-1. By incremental deletion analysis of the Mcl-1 promoter, we identified a DNA fragment containing an Ets-1 binding site that is transcriptionally responsive to ER stress. Mutations in the Ets-1 binding site or knockdown of Ets-1 inhibited the increase in Mcl-1, indicating that Ets-1 has a critical role in transcriptional upregulation of Mcl-1. Similar to Mcl-1, Ets-1 was transcriptionally upregulated by ER stress. This was mediated by the IRE1α/XBP-1 branch of the unfolded protein response, as upregulation of Ets-1 was inhibited in melanoma cell lines deficient in IRE1α or XBP-1 established by short hairpin RNA knockdown. Activation of the PI3k/Akt pathway downstream of XBP-1 was also involved, in that inhibition of the pathway blocked upregulation of Ets-1. Inhibition of Ets-1 enhanced ER stress-induced apoptosis in melanoma cell lines and in fresh melanoma isolates, recapitulating the effect of inhibition of Mcl-1. These results reveal a key mechanism by which Mcl-1 is transcriptionally upregulated in melanoma cells by ER stress, and identify Ets-1 as a potential target for inhibition to sensitize melanoma cells to apoptosis.
authors.affiliation: Immunology and Oncology Unit, Calvary Mater Newcastle Hospital, Newcastle, New South Wales, Australia.
authors.forename: L
authors.initials: L
authors.lastname: Dong
authors.forename: C C
authors.initials: CC
authors.lastname: Jiang
authors.forename: R F
authors.initials: RF
authors.lastname: Thorne
authors.forename: A
authors.initials: A
authors.lastname: Croft
authors.forename: F
authors.initials: F
authors.lastname: Yang
authors.forename: H
authors.initials: H
authors.lastname: Liu
authors.forename: C E
authors.initials: CE
authors.lastname: de Bock
authors.forename: P
authors.initials: P
authors.lastname: Hersey
authors.forename: X D
authors.initials: XD
authors.lastname: Zhang
mesh_terms: D017209:Apoptosis; D001483:Base Sequence; D015153:Blotting, Western; D045744:Cell Line, Tumor; D047369:Chromatin Immunoprecipitation; D017931:DNA Primers; D004268:DNA-Binding Proteins / Q000502:physiology*; D024202:Electrophoretic Mobility Shift Assay; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D006801:Humans; D008545:Melanoma / Q000378:metabolism* / Q000473:pathology; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D016133:Polymerase Chain Reaction; D011401:Promoter Regions, Genetic; D050784:Proto-Oncogene Protein c-ets-1 / Q000502:physiology*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics / Q000502:physiology*; D000071701:Regulatory Factor X Transcription Factors; D014157:Transcription Factors / Q000502:physiology*; D014158:Transcription, Genetic; D015854:Up-Regulation / Q000502:physiology*; D000071717:X-Box Binding Protein 1
chemical_list: D017931:DNA Primers; D004268:DNA-Binding Proteins; C494041:ETS1 protein, human; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D050784:Proto-Oncogene Protein c-ets-1; D019253:Proto-Oncogene Proteins c-bcl-2; D000071701:Regulatory Factor X Transcription Factors; D014157:Transcription Factors; D000071717:X-Box Binding Protein 1; C000605543:XBP1 protein, human