HOXC8 regulates self-renewal, differentiation and transformation of breast cancer stem cells

Abstract

BackgroundHomeobox genes are master regulators of cell fate during embryonic development and their expression is altered in cancer. By regulating the balance between cell proliferation and differentiation, they maintain homeostasis of normal tissues. Here, we screened the expression of homeobox genes in mammary stem cells to establish their role in stem cells transformation in breast cancer.MethodsUsing a Homeobox Genes PCR array, we screened 83 homeobox genes in normal cancer breast stem/progenitor cells isolated by flow cytometry. The candidate gene HOXC8 epigenetic regulation was studied by DNA methylation and miRNA expression analyses. Self-renewal and differentiation of HOXC8-overexpressing or knockdown cells were assessed by flow cytometry and mammosphere, 3D matrigel and soft agar assays. Clinical relevance of in vitro findings were validated by bioinformatics analysis of patient datasets from TCGA and METABRIC studies.ResultsIn this study we demonstrate altered expression of homeobox genes in breast cancer stem/progenitor cells. HOXC8 was consistently downregulated in stem/progenitor cells of all breast molecular subtypes, thus representing an interesting tumour suppressor candidate. We show that downregulated expression of HOXC8 is associated with DNA methylation at the gene promoter and expression of miR196 family members. Functional studies demonstrated that HOXC8 gain of function induces a decrease in the CD44+/CD24-/low cancer stem cell population and proportion of chemoresistant cells, with a concomitant increase in CD24+ differentiated cells. Increased HOXC8 levels also decrease the ability of cancer cells to form mammospheres and to grow in anchorage-independent conditions. Furthermore, loss of HOXC8 in non-tumorigenic mammary epithelial cells expands the cancer stem/progenitor cells pool, increases stem cell self-renewal, prevents differentiation induced by retinoic acid and induces a transformed phenotype.ConclusionsTaken together, our study points to an important role of homeobox genes in breast cancer stem/progenitor cell function and establishes HOXC8 as a suppressor of stemness and transformation in the mammary gland lineage.Electronic supplementary materialThe online version of this article (doi:10.1186/s12943-017-0605-z) contains supplementary material, which is available to authorized users.

Retinoic Acids in the Treatment of Most Lethal Solid Cancers

“…Finally, they showed that the induction of HOXA5 expression was correlated with ATRA-mediated apoptosis and cellular growth inhibition [255,256]. More recently, similar down-regulated expression was found for HOXC8 gene in breast CSCs, and associated with DNA methylation in its gene promoter and expression of miR196 family members (Figure 3) [257].…”

The miR-582/CD1B Axis Is Involved in Regulation of Dendritic Cells and Is Associated with Clinical Outcomes in Advanced Lung Adenocarcinoma

“…Among these miR-NAs, miR-582 has been reported to promote tumorigenesis by targeting phosphatase and tensin homolog in colorectal cancer [36]. Moreover, miR-196b promotes cell migration and invasion by targeting FOXP2 in hepatocellular carcinoma and regulates self-renewal, differentiation, and transformation by targeting HOXC8 in breast cancer stem cells [37,38]. miR-9 has an inhibitory role in papillary thyroid cancer by targeting BRAF and reduces metastatic behavior in triple-negative breast cancer by targeting NOTCH1 [39,40].…”

Cancer Stem Cell Plasticity – A Deadly Deal

“…For example, in basal like breast cancer cells, Chaffer and colleagues observed that ZEB1 promoter of non-CSCs is maintained in a bivalent configuration and in response to TGFβ, the chromatin switches to an active state leading to the transcription of ZEB1, consequently converting non-CSCs to CSCs (Chaffer et al, 2013). On the other hand, loss of function of HOXC8, a homeobox gene, in non-tumorigenic mammary epithelial cells due to its promoter DNA hypermethylation has been shown to be associated with CSC pool expansion, increased self-renewal and a transformed phenotype (Shah et al, 2017). A histone modifier, enhancer of zeste homolog 2 (EZH2) is a core member of polycomb repressor complex 2 (PRC2) and mediates transcriptional repression of target genes via the trimethylation of lysine 27 of histone 3 (H3K27me3) (Gan et al, 2018).…”