MicroRNA-200, associated with metastatic breast cancer, promotes traits of mammary luminal progenitor cells.

MicroRNAs are critical regulators of gene networks in normal and abnormal biological processes. Focusing on invasive ductal breast cancer (IDC), we have found dysregulated expression in tumor samples of several microRNAs, including the miR-200 family, along progression from primary tumors to distant metastases, further reflected in higher blood levels of miR-200b and miR-7 in IDC patients with regional or distant metastases relative to patients with primary node-negative tumors. Forced expression of miR-200s in MCF10CA1h mammary cells induced an enhanced epithelial program, aldehyde dehydrogenase (ALDH) activity, mammosphere growth and ability to form branched tubuloalveolar structures while promoting orthotopic tumor growth and lung colonization in vivo. MiR-200s also induced the constitutive activation of the PI3K-Akt signaling through downregulation of PTEN, and the enhanced mammosphere growth and ALDH activity induced in MCF10CA1h cells by miR-200s required the activation of this signaling pathway. Interestingly, the morphology of tumors formed in vivo by cells expressing miR-200s was reminiscent of metaplastic breast cancer (MBC). Indeed, the epithelial components of MBC samples expressed significantly higher levels of miR-200s than their mesenchymal components and displayed a marker profile compatible with luminal progenitor cells. We propose that microRNAs of the miR-200 family promote traits of highly proliferative breast luminal progenitor cells, thereby exacerbating the growth and metastatic properties of transformed mammary epithelial cells.

Characterization of splice variants of human caspase-activated DNase with CIDE-N structure and function.

Internucleosomal DNA fragmentation is an apoptotic event that depends on the activity of different nucleases. Among them, the DNA fragmentation factor B, better known as caspase-activated DNase (CAD), is mainly responsible for this DNA fragmentation in dying cells. CAD is an endonuclease that is chaperoned and inhibited by inhibitor of CAD (ICAD). Activation of CAD needs the cleavage of ICAD by activated caspase-3. During the characterization of the staurosporine-induced apoptotic process in human neuroblastoma cell lines, we have found three novel splice variants of CAD. In all three messengers, the open reading frame is truncated after the second exon of the CAD gene. This truncated open reading frame codifies the CAD protein amino terminal part corresponding to the cell death-inducing DFF45-like effector-N (CIDE-N) domain. We have detected these splicing variants in human tissues and in peripheral white blood cells from 10 unrelated individuals, and their products have been showed to be expressed in certain mouse tissues. We demonstrate that these truncated forms of CAD are soluble proteins that interact with ICAD. We also provided evidences that these CIDE-N forms of CAD promote apoptosis in a caspase-dependent manner.