Induction of Lumen Formation in a Three-dimensional Model of Mammary Morphogenesis by Transcriptional Regulator ID4: ROLE OF CaMK2D IN THE EPIGENETIC REGULATION OF ID4 GENE EXPRESSION.

ABSTRACT

Concomitant loss of lumen formation and cell adhesion protein CEACAM1 is a hallmark feature of breast cancer. In a three-dimensional culture model, transfection of CEACAM1 into MCF7 breast cells can restore lumen formation by an unknown mechanism. ID4, a transcriptional regulator lacking a DNA binding domain, is highly up-regulated in CEACAM1-transfected MCF7 cells, and when down-regulated with RNAi, abrogates lumen formation. Conversely, when MCF7 cells, which fail to form lumena in a three-dimensional culture, are transfected with ID4, lumen formation is restored, demonstrating that ID4 may substitute for CEACAM1. After showing the ID4 promoter is hypermethylated in MCF7 cells but hypomethylated in MCF/CEACAM1 cells, ID4 expression was induced in MCF7 cells by agents affecting chromatin remodeling and methylation. Mechanistically, CaMK2D was up-regulated in CEACAM1-transfected cells, effecting phosphorylation of HDAC4 and its sequestration in the cytoplasm by the adaptor protein 14-3-3. CaMK2D also phosphorylates CEACAM1 on its cytoplasmic domain and mutation of these phosphorylation sites abrogates lumen formation. Thus, CEACAM1 is able to maintain the active transcription of ID4 by an epigenetic mechanism involving HDAC4 and CaMK2D, and the same kinase enables lumen formation by CEACAM1. Because ID4 can replace CEACAM1 in parental MCF7 cells, it must act downstream from CEACAM1 by inhibiting the activity of other transcription factors that would otherwise prevent lumen formation. This overall mechanism may be operative in other cancers, such as colon and prostate, where the down-regulation of CEACAM1 is observed.