The inhibition of KDM2B promotes the differentiation of basal-like breast cancer cells via the posttranslational destabilization of SLUG

KDM2B is a JmjC domain H3K36me2/H3K36me1 demethylase, which immortalizes cells in culture and contributes to the biology of both embryonic and adult stem and progenitor cells. It also functions as an oncogene that contributes to the self-renewal of breast cancer stem cells by regulating polycomb complexes. Here we show that the silencing of KDM2B results in the downregulation of SNAI2 (SLUG), SNAI1 (SNAIL) and SOX9, which also contribute to the biology of mammary stem and progenitor cells. The downregulation of these molecules is posttranscriptional and in the case of the SNAI2-encoded SLUG, it is due to calpain-dependent proteolytic degradation. Mechanistically, the latter depends on the activation of calpastatin-sensitive classical calpain(s) and on the phosphorylation-dependent inhibition of GSK3 via paracrine mechanisms. GSK3 inhibition sensitizes its target SLUG to classical calpains, which are activated by Ca2+ influx and calpastatin down regulation. The degradation of SLUG, induced by the KDM2B knockdown, promotes the differentiation of breast cancer stem cells in culture and reveals an unexpected mechanism of stem cell regulation by a histone demethylase.

KDM2B 为一种 JmjC 结构域的 H3K36me2/H3K36me1 去甲基化酶，能够在培养条件下使细胞获得永生化，并对胚胎及成体干细胞和祖细胞的生物学特性产生影响。此外，KDM2B 作为一种原癌基因，通过调控多梳复合体，促进乳腺癌干细胞的自我更新。本研究揭示，KDM2B 的沉默导致 SNAI2（SLUG）、SNAI1（SNAIL）和 SOX9 的下调，这些分子同样对乳腺干细胞和祖细胞的生物学特性具有贡献。这些分子的下调作用发生在转录后水平，其中 SNAI2 编码的 SLUG 的下调是由于钙蛋白酶依赖性的蛋白水解降解。从机制上讲，这一过程依赖于经典钙蛋白酶（classical calpain）的钙蛋白酶抑制蛋白（calpastatin）敏感性激活以及通过旁分泌机制依赖磷酸化的 GSK3 抑制。GSK3 的抑制使得其靶标 SLUG 对经典钙蛋白酶的敏感性增加，而经典钙蛋白酶则被 Ca2+ 内流和钙蛋白酶抑制蛋白的下调所激活。KDM2B 敲低引起的 SLUG 降解促进了培养条件下乳腺癌干细胞的分化，并揭示了组蛋白去甲基化酶调节干细胞的意外机制。