The embryonic stem cell (ESC) transcriptional and epigenetic networks are controlled by a multilayer regulatory circuitry, including core transcription factors (TFs), posttranscriptional modifier microRNAs (miRNAs), and some other regulators. However, the role of large intergenic noncoding RNAs (lincRNAs) in this regulatory circuitry and their underlying mechanism remains undefined. Here, we demonstrate that a lincRNA, linc-RoR, may function as a key competing endogenous RNA to link the network of miRNAs and core TFs, e.g., Oct4, Sox2, and Nanog. We show that linc-RoR shares miRNA-response elements with these core TFs and that linc-RoR prevents these core TFs from miRNA-mediated suppression in self-renewing human ESC. We suggest that linc-RoR forms a feedback loop with core TFs and miRNAs to regulate ESC maintenance and differentiation. These results may provide insights into the functional interactions of the components of genetic networks during development and may lead to new therapies for many diseases.

Tumor infiltrated type II (M2) macrophages promote tumorigenesis by suppressing immune clearance, promoting proliferation, and stimulating angiogenesis. Interestingly, macrophages were also found to enrich in small foci of altered hepatocytes containing liver tumor-initiating cells (TICs). However, whether and how TICs specifically recruit macrophages and the function of these macrophages in tumor initiation remain unknown due to technical difficulties. In this study, by generating genetically defined liver TICs, we demonstrate that TICs actively recruit M2 macrophages from as early as the single-cell stage. Elimination of TIC-associated macrophages (TICAMs) abolishes tumorigenesis in a manner dependent on the immune system. Mechanistically, activation of the Hippo pathway effector Yes-associated protein (YAP) underlies macrophage recruitment by TICs. These results demonstrate for the first time that macrophages play a decisive role in the survival of single TICs in vivo and provide a proof of principle for TIC elimination by targeting YAP or M2 macrophages.

Background: Substrates of the Hippo pathway kinases Lats1/2 are largely unknown besides YAP/TAZ. Results: Phosphorylation of angiomotin by Lats1/2 inhibits interaction with F-actin thus impairs cell migration and angiogenesis. Conclusion: AMOTp130 is a physiological and functional substrate of Lats1/2 and the Hippo pathway. Significance: Demonstrating how identification of novel substrates would facilitate understanding the physiology of the Hippo pathway.

The Hippo pathway regulates cell proliferation, apoptosis, and stem cell self-renewal, and its inactivation in animal models causes organ enlargement followed by tumorigenesis. Hippo pathway deregulation occurs in many human cancers, but the underlying mechanisms are not fully understood. Here, we report tyrosine phosphorylation of the Hippo pathway tumor suppressor LATS1 as a mechanism underlying its regulation by cell adhesion. A tyrosine kinase library screen identified Src as the kinase to directly phosphorylate LATS1 on multiple residues, causing attenuated Mob kinase activator binding and structural alteration of the substrate-binding pocket in the kinase domain. Cell matrix adhesion activated the Hippo pathway effector transcription coactivator YAP partially through Src-mediated phosphorylation and inhibition of LATS1. Aberrant Src activation abolished the tumor suppressor activity of LATS1 and induced tumorigenesis in a YAP-dependent manner. Protein levels of Src in human breast cancer tissues correlated with accumulation of active YAP dephosphorylated on the LATS1 target site. These findings reveal tyrosine phosphorylation of LATS1 by Src as a novel mechanism of Hippo pathway regulation by cell adhesion and suggest Src activation as an underlying reason for YAP deregulation in tumorigenesis. .

Organ size determination is one of the most intriguing unsolved mysteries in biology. Aberrant activation of the major effector and transcription co-activator YAP in the Hippo pathway causes drastic organ enlargement in development and underlies tumorigenesis in many human cancers. However, how robust YAP activation is achieved during organ size control remains elusive. Here we report that the YAP signaling is sustained through a novel microRNA-dependent positive feedback loop. miR-130a, which is directly induced by YAP, could effectively repress VGLL4, an inhibitor of YAP activity, thereby amplifying the YAP signals. Inhibition of miR-130a reversed liver size enlargement induced by Hippo pathway inactivation and blocked YAP-induced tumorigenesis. Furthermore, the Drosophila Hippo pathway target bantam functionally mimics miR-130a by repressing the VGLL4 homolog SdBP/Tgi. These findings reveal an evolutionarily conserved positive feedback mechanism underlying robustness of the Hippo pathway in size control and tumorigenesis.

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Par-1 regulates the Hippo signaling pathway in Drosophila melanogaster by modifying the phosphorylation status of Hippo and also by inhibiting the interaction of Hippo and Salvador.

M2-polarized macrophages, also known as alternatively activated macrophages, have long been associated with pulmonary fibrosis; however, the mechanism has not been fully defined. Gab1 and Gab2 proteins belong to the Gab family of adaptors and are integral components of the signal specificity in response to various extracellular stimuli. In this report, we found that levels of both Gab1 and Gab2 were elevated in M2-polarized macrophages isolated from bleomycin-induced fibrotic lungs. Gab1/2 deficiency in bone marrow-derived macrophages abrogated IL-4-mediated M2 polarization. Furthermore, conditional removal of (Gab1) and germ line knock-out of (Gab2) in macrophages prevented a bias toward the M2 phenotype and attenuated bleomycin-induced fibrotic lung remodeling. In support of these observations, Gab1/2 were involved in responses predominated by IL-4 signaling, an essential determinant for macrophage M2 polarization. Further investigation revealed that both Gab1 and -2 are recruited to the IL-4 receptor, synergistically enhancing downstream signal amplification but conferring IL-4 signal preference. Mechanistically, the loss of Gab1 attenuated AKT activation, whereas the absence of Gab2 suppressed STAT6 activation in response to IL-4 stimulation, both of which are commonly attributed to M2-driven pulmonary fibrosis in mice. Taken together, these observations define a non-redundant role of Gab docking proteins in M2 polarization, adding critical insights into the pathogenesis of idiopathic pulmonary fibrosis.