Cancer cell-associated cytoplasmic B7-H4 is induced by hypoxia through hypoxia-inducible factor-1α and promotes cancer cell proliferation

Biochem Biophys Res Commun. 2015 Apr 3;459(2):277-283. doi: 10.1016/j.bbrc.2015.02.098. Epub 2015 Feb 26.

Abstract

Aberrant B7-H4 expression in cancer tissues serves as a novel prognostic biomarker for poor survival in patients with cancer. However, the factor(s) that induce cancer cell-associated B7-H4 remain to be fully elucidated. We herein demonstrate that hypoxia upregulates B7-H4 transcription in primary CD138(+) multiple myeloma cells and cancer cell lines. In support of this finding, analysis of the Multiple Myeloma Genomics Portal (MMGP) data set revealed a positive correlation between the mRNA expression levels of B7-H4 and the endogenous hypoxia marker carbonic anhydrogenase 9. Hypoxia-induced B7-H4 expression was detected in the cytoplasm, but not in cancer cell membranes. Chromatin immunoprecipitation analysis demonstrated binding of hypoxia-inducible factor-1α (HIF-1α) to proximal hypoxia-response element (HRE) sites within the B7-H4 promoter. Knockdown of HIF-1α and pharmacological inhibition of HIF-1α diminished B7-H4 expression. Furthermore, knockdown of cytoplasmic B7-H4 in MCF-7 decreased the S-phase cell population under hypoxia. Finally, MMGP analysis revealed a positive correlation between the transcript levels of B7-H4 and proliferation-related genes including MKI67, CCNA1, and Myc in several patients with multiple myeloma. Our results provide insight into the mechanisms underlying B7-H4 upregulation and its role in cancer cell proliferation in a hypoxic tumor microenvironment.

Keywords: B7–H4; Hypoxia; Hypoxia-inducible factor-1α; Proliferation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Cell Hypoxia / physiology
  • Cell Line, Tumor
  • Cell Proliferation / physiology
  • Chromatin Immunoprecipitation
  • Cytoplasm / metabolism
  • Gene Expression Regulation, Neoplastic
  • Gene Knockdown Techniques
  • Humans
  • Hypoxia-Inducible Factor 1, alpha Subunit / antagonists & inhibitors
  • Hypoxia-Inducible Factor 1, alpha Subunit / genetics
  • Hypoxia-Inducible Factor 1, alpha Subunit / metabolism*
  • MCF-7 Cells
  • Multiple Myeloma / genetics
  • Multiple Myeloma / metabolism*
  • Multiple Myeloma / pathology
  • Promoter Regions, Genetic
  • Recombinant Proteins / genetics
  • Recombinant Proteins / metabolism
  • Tumor Microenvironment / genetics
  • Tumor Microenvironment / physiology
  • V-Set Domain-Containing T-Cell Activation Inhibitor 1 / antagonists & inhibitors
  • V-Set Domain-Containing T-Cell Activation Inhibitor 1 / biosynthesis*
  • V-Set Domain-Containing T-Cell Activation Inhibitor 1 / genetics

Substances

  • HIF1A protein, human
  • Hypoxia-Inducible Factor 1, alpha Subunit
  • Recombinant Proteins
  • V-Set Domain-Containing T-Cell Activation Inhibitor 1
  • VTCN1 protein, human