Sperm-Associated Antigen 4, a Novel Hypoxia-Inducible Factor 1 Target, Regulates Cytokinesis, and Its Expression Correlates with the Prognosis of Renal Cell Carcinoma

Abstract

Hypoxia plays a crucial role in many pathophysiological conditions, including cancer biology, and hypoxia-inducible factor (HIF) regulates transcriptional responses under hypoxia. To elucidate the cellular responses to hypoxia, we performed chromatin immunoprecipitation with deep sequencing in combination with microarray analysis and identified HIF-1 targets. We focused on one of the novel targets, sperm-associated antigen 4 (SPAG4), whose function was unknown. SPAG4, an HIF-1-specific target, is up-regulated in various cultured cells under hypoxia. Examination of SPAG4 expression using a tissue microarray consisting of 190 human renal cell carcinoma (RCC) samples revealed that SPAG4 is an independent prognostic factor of cancer-specific mortality. Live-cell imaging revealed localization of SPAG4 at the intercellular bridge in telophase. We also studied cells in which SPAG4 was knocked down. Hypoxia enhances tetraploidy, which disturbs cell proliferation, and knockdown of SPAG4 increased tetraploid formation and decreased cell proliferation under both normoxic and hypoxic conditions. Studies using deletion mutants of SPAG4 also suggested the involvement of SPAG4 in cytokinesis. Microarray analysis confirmed dysregulation of cytokinesis-related genes by knockdown of SPAG4. In conclusion, SPAG4 is an independent prognostic factor in RCC and plays a crucial role in cytokinesis to defend against hypoxia-induced tetraploid formation. This defensive mechanism may promote survival of cancer cells under hypoxic conditions, thus leading to poor prognosis.

Comparative and Experimental Studies on the Genes Altered by Chronic Hypoxia in Human Brain Microendothelial Cells

“…Notably, the recent studies have also implicated SPAG4 in cell cycle regulation (Shoji et al, 2013). The upregulation of SPAG4 with chronic hypoxia may be crucial in both cell-cycle arrest and cell migration which are critical steps in hypoxia-induced angiogenesis and other acclimatization responses.…”

Up-Regulation of pVHL along with Down-Regulation of HIF-1α by NDRG2 Expression Attenuates Proliferation and Invasion in Renal Cancer Cells

“…And VEGF is the mainstay amid all angiogenic factors and promotes both tumorigenesis and invasion of RCC [32]. HIF-1α are also frequently overexpressed in renal cancer, which correlate with poor clinical prognosis [33]. Since elevated HIF-1α expression up-regulates the expression of PDK1 and VEGF, which promotes tumor progression.…”

Role of hypoxia in progressive chronic kidney disease and implications for therapy

“…Recent studies, including ours, have utilized the ChIP-seq approach with a next-generation sequencer and identified HIF target genes in a genome-wide manner [50][51][52][53]. We performed chromatin immunoprecipitation with deep sequencing, in combination with microarray analysis, and identified a novel HIF target; spermassociated antigen 4 (SPAG4).…”