MicroRNAs (miRNAs) are short non-coding RNAs that post-transcriptionally regulate the expression of different target genes and, thus, enable engineered gene networks to achieve complex phenotypic changes in mammalian cells. We hypothesized that exploiting this feature of miRNAs could improve therapeutic protein production processes by increasing viable cell densities and/or productivity of the mammalian cells used for manufacturing. To identify miRNAs that increase the productivity of producer cells, we performed a genome wide functional miRNA screen by transient transfection of Chinese hamster ovary (CHO) cells stably expressing an IgG1 antibody (CHO-IgG1). Using this approach, we identified nine human miRNAs that improved the productivities not only of the CHO-IgG1 cells but also of CHO cells expressing recombinant human serum albumin (HSA), demonstrating that the miRNAs act in a product-independent manner. We selected two miRNAs (miR-557 and miR-1287) positively impacting the viable cell density and the specific productivity, respectively, and then stably co-expressed them in IgG1 expressing CHO cells. In these cells, higher IgG1 titers were observed in fed-batch cultures whilst product quality was conserved, demonstrating that miRNA-based cell line engineering provides an attractive approach toward the genetic optimization of CHO producer cells for industrial applications.

Deregulated molecular signaling pathways are responsible for the altered adhesive, migratory, and invasive properties of cancer cells. The different breast cancer subtypes are characterized by the expression of distinct miRNAs, short non-coding RNAs that posttranscriptionally modulate the expression of entire gene networks. Profiling studies have revealed downregulation of miR149 in basal breast cancer. Here, we show that miR149 expression severely impairs cell spreading, migration, and invasion of basal-like breast cancer cells. We identify signaling molecules, including the small GTPases Rap1a and Rap1b, downstream of integrin receptors as miR149 targets, providing an explanation for the defective Src and Rac activation during cell adhesion and spreading upon miR149 expression. Suppression of cell spreading by miR149 could be rescued, at least in part, by expression of constitutively active Rac. Finally, we demonstrate that increased miR149 levels block lung colonization in vivo. On the basis of our findings, we propose that miR149 downregulation in basal breast cancer facilitates the metastatic dissemination of tumor cells by supporting aberrant Rac activation. Cancer Res; 74(18); 5256-65. Ó2014 AACR.

Paracrine activation of cells contained in the tumor microenvironment promotes tumor progression and metastasis. In breast cancer, malignant cells recruit and educate macrophages into a M2 tumor-promoting phenotype that supports the metastatic spread of cancer cells. Here, we show that miR-149 functions as a metastasissuppressing microRNA in breast cancer cells by limiting colonystimulating factor-1 (CSF1)-dependent recruitment and M2 polarization of macrophages. In lymph node-positive, triple-negative breast cancer (TNBC) tissues, low miR-149 expression correlated with macrophage infiltration and reduced patient survival. By directly targeting CSF1, miR-149 expression in TNBC cell lines (MDA-MB-231 and BT-549) inhibited the recruitment of human monocytic THP-1 cells and primary human macrophages. Furthermore, in macrophages cocultured with MDA-MB-231 cells expressing miR-149, epidermal growth factor (EGF) and amphiregulin expression levels were strongly reduced, resulting in reduced EGF receptor activation in the cancer cells. In vivo, lung metastases developing from orthotopic MDA-MB-231 tumors were reduced by 75% by miR-149 expression, and this was associated with impaired M2 macrophage infiltration of the primary tumors. These data suggest that miR-149 downregulation functionally contributes to breast tumor progression by recruiting macrophages to the tumor and facilitating CSF1 and EGF receptor cross-talk between cancer cells and macrophages.

The PI3K-Akt pathway is one of the most commonly dysregulated cancer-associated signaling pathways. Here we report an oncogenic function for the miR-181 family in luminal breast cancer cells that involves Akt hyperactivation. We show that miR-181a and miR-181d posttranscriptionally suppress the expression of PHLPP2 and INPP4B phosphatases, resulting in elevated growth factor-induced Akt phosphorylation. Ectopic expression of miR-181a and miR-181d promoted S-phase entry and cell proliferation, which was reversed by pharmacological Akt inhibition. Importantly, the expression of miR-181 family members and PHLPP2/INPP2B are inversely correlated in primary human estrogen receptor-positive breast cancers, supporting the clinical relevance of our findings.

BackgroundThe growth factor heregulin (HRG) potently stimulates epithelial cell survival and proliferation through the binding of its cognate receptor ErbB3 (also known as HER3). ErbB3-dependent signal transmission relies on the dimerization partner ErbB2, a receptor tyrosine kinase that is frequently overexpressed and/or amplified in breast cancer cells. Substantial evidence suggests that deregulated ErbB3 expression also contributes to the transformed phenotype of breast cancer cells.ResultsBy genome-wide screening, we identify 43 microRNAs (miRNAs) that specifically impact HRG-induced activation of the PI3K-Akt pathway. Bioinformatic analysis combined with experimental validation reveals a highly connected molecular miRNA-gene interaction network particularly for the negative screen hits. For selected miRNAs, namely miR-149, miR-148b, miR-326, and miR-520a-3p, we demonstrate the simultaneous downregulation of the ErbB3 receptor and multiple downstream signaling molecules, explaining their efficient dampening of HRG responses and ascribing to these miRNAs potential context-dependent tumor suppressive functions.ConclusionsGiven the contribution of HRG signaling and the PI3K-Akt pathway in particular to tumorigenesis, this study not only provides mechanistic insight into the function of miRNAs but also has implications for future clinical applications.Electronic supplementary materialThe online version of this article (doi:10.1186/s12964-015-0084-z) contains supplementary material, which is available to authorized users.