HIF1A and neoplasm: To better verify endogenous tumor microenvironment-mediated HIF-1 activation and Nox4 expression in the solid tumor, we identified subpopulations of tumor cells from GBM8401/hif-1-r xenografts based on differential Hoechst 33342 and GFP fluorescence and investigated Nox4 expression in these subpopulations using flow cytometry.