5-Aza-2'-deoxycytidine advances the epithelial-mesenchymal transition of breast cancer cells by demethylating Sipa1 promoter-proximal elements

Human breast cancer cells exhibit considerable diversity in the methylation status of genomic DNA CpGs that regulate metastatic transcriptome networks. In this study, we identified human Sipa1 promoter-proximal elements that contained a CpG island and demonstrated that the methylation status of the CpG island was inversely correlated with SIPA1 protein expression in cancer cells. 5-Aza-2′-deoxycytidine (5-Aza-CdR), a DNA methyltransferase inhibitor, promoted the expression of Sipa1 in the MCF7 breast cancer cells with a low level of SIPA1 expression. On the contrary, in MDA-MB-231 breast cancer cells with high SIPA1 expression levels, hypermethylation of the CpG island negatively regulated the transcription of Sipa1. In addition, the epithelial–mesenchymal transition (EMT) was reversed after knocking down Sipa1 in MDA-MB-231 cells. However, the EMT was promoted in MCF7 cells with over-expression of SIPA1 or treated with 5-Aza-CdR. Taken together, hypomethylation of the CpG island in Sipa1 promoter-proximal elements could enhance SIPA1 expression in breast cancer cells, which could facilitate EMT of cancer cells, possibly increasing a risk of cancer cell metastasis in individuals treated with 5-Aza-CdR.

Summary: Hypomethylation by 5-Aza-CdR upregulates the SIPA1 expression and promotes epithelial–mesenchymal transition in breast cancer cells, possibly increasing the risk of cancer cell metastasis.

Rap G protein signal in normal and disordered lymphohematopoiesis

Rap proteins (Rap1, Rap2a, b, c) are small molecular weight GTPases of the Ras family. Rap G proteins mediate diverse cellular events such as cell adhesion, proliferation, and gene activation through various signaling pathways. Activation of Rap signal is regulated tightly by several specific regulatory proteins including guanine nucleotide exchange factors and GTPase-activating proteins. Beyond cell biological studies, increasing attempts have been made in the past decade to define the roles of Rap signal in specific functions of normal tissue systems as well as in cancer. In the immune and hematopoietic systems, Rap signal plays crucial roles in the development and function of essentially all lineages of lymphocytes and hematopoietic cells, and importantly, deregulated Rap signal may lead to unique pathological conditions depending on the affected cell types, including various types of leukemia and autoimmunity. The phenotypical studies have unveiled novel, even unexpected functional aspects of Rap signal in cells from a variety of tissues, providing potentially important clues for controlling human diseases, including malignancy.