Casein kinase 2 prevents mesenchymal transformation by maintaining Foxc2 in the cytoplasm

Abstract

Nuclear Foxc2 is a transcriptional regulator of mesenchymal transformation during developmental EMT and has been associated with EMT in malignant epithelia. Our laboratory has shown that in normal epithelial cells Foxc2 is maintained in the cytoplasm where it promotes an epithelial phenotype. The Foxc2 amino terminus has a consensus casein kinase 2 phosphorylation site at serine 124, and we now show that CK2 associates with Foxc2 and phosphorylates this site in vitro. Knock-down or inhibition of the CK2α/α′ kinase subunit in epithelial cells causes de novo accumulation of Foxc2 in the nucleus. Mutation of serine 124 to leucine promotes constitutive nuclear localization of Foxc2 and expression of mesenchymal genes, whereas an S124D phosphomimetic leads to constitutive cytoplasmic localization and epithelial maintenance. In malignant breast cancer cells the CK2β regulatory subunit is downregulated and FOXC2 is found in the nucleus, correlating with an increase in α-SMA expression. Restoration of CK2β expression in these cells results in cytoplasmic localization of Foxc2, decreased α-SMA expression and reduced cell migration and invasion. In contrast, knockdown of CK2β in normal breast epithelial cells leads to FOXC2 nuclear localization, decreased E-cadherin expression, increased α-SMA and vimentin expression, and enhanced cell migration and invasion. Based on these findings we propose that Foxc2 is functionally maintained in the cytoplasm of normal epithelial cells by CK2α/α′-mediated phosphorylation at serine 124 that is dependent on proper targeting of the holoenzyme via the CK2β regulatory subunit.

Overexpression of transcription factor FOXC2 in cultured human podocytes upregulates injury markers and increases motility

“…Recently, Ivanov et al identified eight evolutionary conserved phosphorylation sites in FOXC2 which are on proline-directed serine/threonine residues, and that FOXC2 is phosphorylated in primary lymphatic endothelial cells [40]. Hence, based on earlier literature of FOXC2 in other cell types [33,40,54] and our own observation in this study, we came to the conclusion that in human podocytes FOXC2 is a phosphoprotein. It can thus be speculated that multiple signals can modify the expression levels of nuclear FOXC2 or its post-translational modification or sometimes both, that further determine whether FOXC2 promotes differentiation or dedifferentiation.…”

“…Earlier studies also indicate that the subcellular localization of Foxc2 is cell-type specific, and that the localization determines the regulatory function of Foxc2 [51][52][53][54]. From several in vitro studies using non-malignant epithelial cells in different experimental settings, it has been established that epithelial cell differentiation corresponded with increased cytoplasmic Foxc2 whereas dedifferentiation corresponded with increased nuclear Foxc2 [52,54].…”

“…From several in vitro studies using non-malignant epithelial cells in different experimental settings, it has been established that epithelial cell differentiation corresponded with increased cytoplasmic Foxc2 whereas dedifferentiation corresponded with increased nuclear Foxc2 [52,54].…”

53BP1 suppresses epithelial–mesenchymal transition by downregulating ZEB1 through microRNA‐200b/429 in breast cancer

“…The function of EMT in enhancing migration and invasion of cancers has drawn great attention from scientists. During the regulation of EMT, many oncogene and tumor suppressor genes play crucial roles …”

“…During the regulation of EMT, many oncogene and tumor suppressor genes play crucial roles. (9)(10)(11)(12) The new tumor suppressor gene p53 binding protein 1 (53BP1) has been the research focus of our team over recent years. It is mainly reported as an important regulator of the cellular response to DNA double-strand breaks.…”