Regulation Of miRNA Biogenesis Research Articles

MDA-7/IL-24 regulates the miRNA processing enzyme DICER through downregulation of MITF

Melanoma differentiation-associated gene-7/interleukin-24 (mda-7/IL-24) is a multifunctional cytokine displaying broad-spectrum anticancer activity in vitro or in vivo in preclinical animal cancer models and in a phase 1/2 clinical trial in patients with advanced cancers. mda-7/IL-24 targets specific miRNAs, including miR-221 and miR-320, for down-regulation in a cancer-selective manner. We demonstrate that mda-7/IL-24, administered through a replication incompetent type 5 adenovirus (Ad.mda-7) or with His-MDA-7/IL-24 protein, down-regulates DICER, a critical regulator in miRNA processing. This effect is specific for mature miR-221, as it does not affect Pri-miR-221 expression, and the DICER protein, as no changes occur in other miRNA processing cofactors, including DROSHA, PASHA, or Argonaute. DICER is unchanged by Ad.mda-7/IL-24 in normal immortal prostate cells, whereas Ad.mda-7 down-regulates DICER in multiple cancer cells including glioblastoma multiforme and prostate, breast, lung, and liver carcinoma cells. MDA-7/IL-24 protein down-regulates DICER expression through canonical IL-20/IL-22 receptors. Gain- and loss-of-function studies confirm that overexpression of DICER rescues deregulation of miRNAs by mda-7/IL-24, partially rescuing cancer cells from mda-7/IL-24-mediated cell death. Stable overexpression of DICER in cancer cells impedes Ad.mda-7 or His-MDA-7/IL-24 inhibition of cell growth, colony formation, PARP cleavage, and apoptosis. In addition, stable overexpression of DICER renders cancer cells more resistant to Ad.mda-7 inhibition of primary and secondary tumor growth. MDA-7/IL-24-mediated regulation of DICER is reactive oxygen species-dependent and mediated by melanogenesis-associated transcription factor. Our research uncovers a distinct role of mda-7/IL-24 in the regulation of miRNA biogenesis through alteration of the MITF-DICER pathway.

MicroRNA Biogenesis is Enhanced by Liposome-Encapsulated Pin1 Inhibitor in Hepatocellular Carcinoma.

Hepatocellular carcinoma (HCC) is in an urgent need of new, effective therapies to reduce morbidity and mortality. We have previously demonstrated that peptidyl-prolyl cis/trans isomerase Pin1 is a potential target for HCC therapy, due to its pivotal role in HCC development through regulating miRNA biogenesis, and discovered the small molecule API-1 as a novel and specific Pin1 inhibitor. Despite its significant anti-HCC activity, the low water solubility and in vivo bioavailability of API-1 limit its clinical application. To address these issues, we herein developed a liposomal formulation of API-1 to improve API-1 delivery and enhance its anti-HCC efficacy.Methods: We designed and developed a nanoscale liposomal formulation of API-1, named as API-LP. Subsequently, the mean diameter, polydispersity, zeta potential, encapsulation efficiency and thermal properties of the optimization API-LP were characterized. The enhanced anti-HCC activity and the molecular mechanism of API-LP were investigated both in vitro and in vivo. Finally, the safety and pharmacokinetic property of API-LP were evaluated systematically.Results: API-LP had good formulation characteristics and exhibited an enhanced in vitro activity of suppressing proliferation and migration of HCC cells when compared with free API-1. The mechanism study showed that API-LP upregulated miRNA biogenesis via inhibiting Pin1 activity followed by restoring the nucleus-to-cytoplasm export of XPO5. Because of the increased delivery efficiency, API-LP displayed a stronger ability to promote miRNA biogenesis than free API-1. Importantly, API-LP displayed higher systemic exposure than free API-1 in mice without apparent toxicity, resulting in an enhanced tumor inhibition in xenograft mice.Conclusion: The development and assessment of API-LP provide an attractive and safe anti-HCC agent, highlighting the miRNA-based treatment for human cancers.

Alternative processing of its precursor is related to miR319 decreasing in melon plants exposed to cold

miRNAs are fundamental endogenous regulators of gene expression in higher organisms. miRNAs modulate multiple biological processes in plants. Consequently, miRNA accumulation is strictly controlled through miRNA precursor accumulation and processing. Members of the miRNA319 family are ancient ribo-regulators that are essential for plant development and stress responses and exhibit an unusual biogenesis that is characterized by multiple processing of their precursors. The significance of the high conservation of these non-canonical biogenesis pathways remains unknown. Here, we analyze data obtained by massive sRNA sequencing and 5′ - RACE to explore the accumulation and infer the processing of members of the miR319 family in melon plants exposed to adverse environmental conditions. Sequence data showed that miR319c was down regulated in response to low temperature. However, the level of its precursor was increased by cold, indicating that miR319c accumulation is not related to the stem loop levels. Furthermore, we found that a decrease in miR319c was inversely correlated with the stable accumulation of an alternative miRNA (#miR319c) derived from multiple processing of the miR319c precursor. Interestingly, the alternative accumulation of miR319c and #miR319c was associated with an additional and non-canonical partial cleavage of the miR319c precursor during its loop-to-base-processing. Analysis of the transcriptional activity showed that miR319c negatively regulated the accumulation of HY5 via TCP2 in melon plants exposed to cold, supporting its involvement in the low temperature signaling pathway associated with anthocyanin biosynthesis. Our results provide new insights regarding the versatility of plant miRNA processing and the mechanisms regulating them as well as the hypothetical mechanism for the response to cold-induced stress in melon, which is based on the alternative regulation of miRNA biogenesis.

Quantitative identification of proteins that influence miRNA biogenesis by RNA pull-down-SILAC mass spectrometry (RP-SMS).

RNA-binding proteins mediate and control gene expression. As some examples, they regulate pre-mRNA synthesis and processing; mRNA localisation, translation and decay; and microRNA (miRNA) biogenesis and function. Here, we present a detailed protocol for RNA pull-down coupled to stable isotope labelling by amino acids in cell culture (SILAC) mass spectrometry (RP-SMS) that enables quantitative, fast and specific detection of RNA-binding proteins that regulate miRNA biogenesis. In general, this method allows for the identification of RNA-protein complexes formed using in vitro or chemically synthesized RNAs and protein extracts derived from cultured cells.

Membrane‐anchored E‐cadherin/AGO2 complex promote non‐canonical miRNA biogenesis of miR‐451a

Micro‐RNAs are small non‐coding RNAs which regulate target mRNAs expression. Canonical miRNA biogenesis requires two‐step processing conducted by Drosha/DGCR8 and Dicer/AGO2 complexes in the nucleus and cytoplasm, respectively. Aberrant miRNA biogenesis have been reported in malignant human cancers. E‐cadherin is a junctional protein which localizes on plasma membrane to maintain cell‐cell adhesion. Downregulation of E‐cadherin is widely observed in cancers and correlates with epithelial–mesenchymal transition (EMT), it maintains cell‐cell contact and epithelial‐like phenotype to suppress migratory and invasive abilities of cancer cells. Although abnormal regulation of miRNA biogenesis has been reported in cancer, the integrated spatial and temporal regulatory pathways remains unclear. Here, we study the physical interaction between E‐cadherin and AGO2, and the effects on miRNA biogenesis. We found that E‐cadherin enhance the accumulation of AGO2 protein on cell membrane. Membrane‐anchored E‐cadherin/AGO2 complex promotes AGO2‐mediated specific miRNA, miR‐451a, biogenesis in a Dicer‐independent manner. Furthermore, the induced miR‐451 targeted EPH receptor A6 (EphA6) 3′UTR and downregulated EphA6, a metastasis‐promoting gene family member in breast cancer. Our findings demonstrate the spatial and temporal regulation of an AGO2‐dependent miRNA biogenesis pathway modulated by E‐cadherin, which provides new insight into the reciprocal interaction between EMT and miRNA biogenesis.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Pin1 impairs microRNA biogenesis by mediating conformation change of XPO5 in hepatocellular carcinoma.

MicroRNA (miRNA) dysregulation is associated with the tumorigenesis and development of numerous human cancers. The defect in miRNA biogenesis is the main cause of miRNA dysregulation. We previously demonstrated that ERK-induced phosphorylation of XPO5 followed by peptidyl-prolyl cis/trans isomerase Pin1-mediated isomerization downregulates miRNA expression and contributes to hepatocellular carcinoma (HCC) development. However, how Pin1 precisely regulates miRNA biogenesis in HCC remains elusive. Here we reveal that Pin1 has a pivotal role in the miRNA maturation process by modulating phosphorylated Serine-Proline (pS-P) motif of XPO5 in a phosphorylation-dependent manner. By recognizing and binding to XPO5 via its WW domain, Pin1 catalyzes the conformation change of XPO5 and diminishes XPO5 ability to export pre-miRNAs from the nucleus to the cytoplasm, resulting in the reduced mature miRNA levels and promoted HCC development. Furthermore, downregulation of Pin1 by shRNA restores XPO5-dependent pre-miRNA export and effective biogenesis of mature miRNAs, leading to both in vitro and in vivo HCC inhibition. Therefore, our research discloses a new posttranscriptional regulatory mechanism of miRNA biosynthesis and provides the experimental basis for a novel HCC therapy by targeting Pin1.

Identification of microRNA Precursor-Associated Proteins.

MicroRNA (miRNA) biogenesis is regulated intricately at multiple levels. In addition to transcriptional control of pri-miRNA loci, sequence as well as structural features of the pri-miRNA-stem loop determine its processing efficiency by the endonucleases Drosha and Dicer. On the one hand, general features are necessary to allow a hairpin to be recognized by the processing machinery; on the other hand, specific sequence motifs of individual miRNA precursors can be read by RNA binding proteins (RBPs) that regulate processing, leading to increased or decreased levels of functional miRNAs. In a pulldown experiment using the pri-miRNA hairpin as immobilized bait, cognate RBPs can be isolated and analyzed by immunoblotting or mass spectrometry, allowing for the discovery or analysis of protein regulators of miRNA biogenesis.

The landscape of miRNA editing in animals and its impact on miRNA biogenesis and targeting.

Adenosine-to-inosine (A-to-I) RNA editing regulates miRNA biogenesis and function. To date, fewer than 160 miRNA editing sites have been identified. Here, we present a quantitative atlas of miRNA A-to-I editing through the profiling of 201 pri-miRNA samples and 4694 mature miRNA samples in human, mouse, and Drosophila. We identified 4162 sites present in ∼80% of the pri-miRNAs and 574 sites in mature miRNAs. miRNA editing is prevalent in many tissue types in human. However, high-level editing is mostly found in neuronal tissues in mouse and Drosophila. Interestingly, the edited miRNAs in neuronal and non-neuronal tissues in human gain two distinct sets of new targets, which are significantly associated with cognitive and organ developmental functions, respectively. Furthermore, we reveal that miRNA editing profoundly affects asymmetric strand selection. Altogether, these data provide insight into the impact of RNA editing on miRNA biology and suggest that miRNA editing has recently gained non-neuronal functions in human.

An expression atlas of miRNAs in Arabidopsis thaliana.

MicroRNAs (miRNAs) are small non-coding RNAs that regulate a variety of biological processes. MiRNA expression often exhibits spatial and temporal specificity. However, genome-wide miRNA expression patterns in different organs during development of Arabidopsis thaliana have not yet been systemically investigated. In this study, we sequenced small RNA libraries generated from 27 different organ/tissue types, which cover the entire life cycle of Arabidopsis. Analysis of the sequencing data revealed that most miRNAs are ubiquitously expressed, whereas a small set of miRNAs display highly specific expression patterns. In addition, different miRNA members within the same family have distinct spatial and temporal expression patterns. Moreover, we found that some miRNAs are produced from different arms of their hairpin precursors at different developmental stages. This work provides new insights into the regulation of miRNA biogenesis and a rich resource for future investigation of miRNA functions in Arabidopsis.

The RNA binding protein EWS is broadly involved in the regulation of pri-miRNA processing in mammalian cells.

The Ewing Sarcoma protein (EWS) is a multifaceted RNA binding protein (RBP) with established roles in transcription, pre-mRNA processing and DNA damage response. By generating high quality EWS–RNA interactome, we uncovered its specific and prevalent interaction with a large subset of primary microRNAs (pri-miRNAs) in mammalian cells. Knockdown of EWS reduced, whereas overexpression enhanced, the expression of its target miRNAs. Biochemical analysis revealed that multiple elements in target pri-miRNAs, including the sequences flanking the stem–loop region, contributed to high affinity EWS binding and sequence swap experiments between target and non-target demonstrated that the flanking sequences provided the specificity for enhanced pri-miRNA processing by the Microprocessor Drosha/DGCR8. Interestingly, while repressing Drosha expression, as reported earlier, we found that EWS was able to enhance the recruitment of Drosha to chromatin. Together, these findings suggest that EWS may positively and negatively regulate miRNA biogenesis via distinct mechanisms, thus providing a new foundation to understand the function of EWS in development and disease.

MicroRNA Biogenesis in Hypoxia.

MicroRNAs (miRNAs) are 17-22 nucleotide, non-coding, single stranded RNA molecules that play a key role in post-transcriptional gene regulation. Hypoxia is a reduction in the normal level of tissue oxygen (O2) tension, and is a feature of chronic vascular disease, pulmonary disease and many cancers. Tissue hypoxia can have widespread effects on cellular functions, as O2 availability is critical for many cellular processes. Cells respond to changes in O2 tension through multiple molecular and cellular mechanisms, including changes in gene expression through transcriptional and translational mechanisms. The transcription factor, hypoxia inducible factor-1, plays a dominant role in transcriptional gene regulation in hypoxia. Several hypoxically induced miRNAs have been shown to play important roles in the hypoxic adaptation of cancer cells. Global repression of enzymes critical for miRNA biogenesis seems to be a widespread phenomenon with several different mechanisms operating. This review describes the effects of hypoxia on specific miRNAs and more global effects on miRNA biogenesis, demonstrating that hypoxia is an important regulator of miRNA biogenesis and function.

Abstract 299: RNA editing enzyme ADAR1 accelerates normal hematopoiesis cell cycle by regulation microRNA biogenesis

Abstract Compelling murine studies demonstrate that adenosine-to-inosine (A-to-I) RNA editing mediated by adenosine deaminase associated with RNA1 (ADAR1) is vital for both fetal and adult hematopoiesis. While genetic ablation of ADAR1 leads to murine embryonic lethality due to severe defects in erythropoiesis, conditional deletion in the hematopoietic system impairs maintenance indicative of cell type and context specific roles for ADAR1 in cell fate specification and self-renewal. By regulating mRNA and microRNA (miRNA) stability, ADAR1 exhibit wide-ranging effects on embryonic development and stem cell regulation. We have previously shown that inflammation-responsive ADAR1 plays important roles in both stem cell differentiation and self-renewal in CML (chronic myeloid leukemia) disease progression. Here, we describe a novel function of ADAR1 in cell cycle regulation of normal hematopoietic stem cell and progenitors (HSPC) by regulation of miRNA biogenesis. Our results demonstrated that ADAR1 induces G0 to G1 phase transition in normal cord blood HSPCs, as demonstrated by elevated expression of Ki67, reduced DiR signal, and enhanced in vivo cord blood engraftment. Cell cycle qRT-qPCR microarray of 84 cell cycle transcripts and whole transcriptome RNA-sequencing analysis of KEGG cell cycle pathway indicate that several cell cycle genes are differentially expression upon overexpression of ADAR1 WT or an A-to-I editing deficient ADAR1 mutant (ADAR1E912A). We previously demonstrated that impaired biogenesis of let-7 miRNAs by ADAR1 WT induces enhanced self-renewal in cord blood CD34+ HSPCs. To determine the miRNA targets of ADAR1-mediated RNA editing, we performed miRNome miScript PCR array of 1008 miRNA candidates in cord blood CD34+ HSPCs overexpressing ADAR1 WT or ADAR1E912A. Total of 263 miRNAs were differentially expressed (142 upregulated and 121 downregulated) by comparing ADAR1 WT to the backbone control. Interestingly, ADAR1E912A mutant also exhibit A-to-I editing independent regulation of miRNAs (307 upregulated and 59 downregulated). We found that the expression of miR-26a-5p, a miRNA frequently downregulated in leukemia, is inhibited by ADAR1-mediated RNA editing. ADAR1 directly binds and edits the DROSHA cleavage site of primary miR-26a transcript, thereby prevent miR26a-5p maturation. Moreover, lentiviral expression of mature miR26-5p reverses the effect of ADAR1 WT, including enhanced CDKN1A expression, inhibition of cord blood proliferation in vivo, as well as reduced HSC self-renewal as measured by colony-formation assay. Our finding suggests carefully regulated A-to-I editing by ADAR1 is essential for the maintenance of proper cell proliferation in HSC. For future study, it will be interesting to investigate if the elevated expression of ADAR1 in CML BC LSC contributes to false regulation of cell cycle that leads to the expansion of malignant leukemia stem cells. Citation Format: Qingfei Jiang, Maria Anna Zipeto, Nathan Delos Santos, Sheldon Morris, Catriona Jamieson. RNA editing enzyme ADAR1 accelerates normal hematopoiesis cell cycle by regulation microRNA biogenesis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 299. doi:10.1158/1538-7445.AM2017-299

Poly(C)-binding protein 1 (Pcbp1) regulates skeletal muscle differentiation by modulating microRNA processing in myoblasts

Regulation of gene expression during muscle development and disease remains incompletely understood. microRNAs are a class of small non-coding RNAs that regulate gene expression and function post-transcriptionally. The poly(C)-binding protein1 (Pcbp1, hnRNP-E1, or αCP-1) is an RNA-binding protein that has been reported to bind the 3'-UTRs of target genes to regulate mRNA stability and protein translation. However, Pcbp1's biological function and the general mechanism of action remain largely undetermined. Here, we report that Pcbp1 is a component of the miRNA-processing pathway that regulates miRNA biogenesis. siRNA-based inhibition of Pcbp1 in mouse skeletal muscle myoblasts led to dysregulated cellular proliferation and differentiation. We also found that Pcbp1 null mutant mice exhibit early embryonic lethality, indicating that Pcbp1 is indispensable for embryonic development. Interestingly, hypomorphic Pcbp1 mutant mice displayed defects in muscle growth due to defects in the proliferation and differentiation of myoblasts and muscle satellite cells, in addition to a slow to fast myofibril switch. Moreover, Pcbp1 modulated the processing of muscle-enriched miR-1, miR-133, and miR-206 by physically interacting with argonaute 2 (AGO2) and other miRNA pathway components. Our study, therefore, uncovers the important function of Pcbp1 in skeletal muscle and the microRNA pathway, signifying its potential as a therapeutic target for muscle disease.

Genetic variation and RNA structure regulate microRNA biogenesis

MiRNA biogenesis is highly regulated at the post-transcriptional level; however, the role of sequence and secondary RNA structure in this process has not been extensively studied. A single G to A substitution present in the terminal loop of pri-mir-30c-1 in breast and gastric cancer patients had been previously described to result in increased levels of mature miRNA. Here, we report that this genetic variant directly affects Drosha-mediated processing of pri-mir-30c-1 in vitro and in cultured cells. Structural analysis of this variant revealed an altered RNA structure that facilitates the interaction with SRSF3, an SR protein family member that promotes pri-miRNA processing. Our results are compatible with a model whereby a genetic variant in pri-mir-30c-1 leads to a secondary RNA structure rearrangement that facilitates binding of SRSF3 resulting in increased levels of miR-30c. These data highlight that primary sequence determinants and RNA structure are key regulators of miRNA biogenesis.

A Compendium of RNA-Binding Proteins that Regulate MicroRNA Biogenesis

During microRNA (miRNA) biogenesis, two endonucleolytic reactions convert stem-loop-structured precursors into mature miRNAs. These processing steps can be posttranscriptionally regulated by RNA-binding proteins (RBPs). Here, we have used aproteomics-based pull-down approach to map andcharacterize the interactome of a multitude of pre-miRNAs. We identify ∼180 RBPs that interact specifically with distinct pre-miRNAs. For functional validation, we combined RNAi and CRISPR/Cas-mediated knockout experiments to analyze RBP-dependent changes in miRNA levels. Indeed, a large number of the investigated candidates, including splicing factors and other mRNA processing proteins, have effects on miRNA processing. As an example, we show that TRIM71/LIN41 is a potent regulator of miR-29a processing and its inactivation directly affects miR-29a targets. We provide an extended database of RBPs that interact with pre-miRNAs in extracts of different cell types, highlighting a widespread layer of co- and posttranscriptional regulation of miRNA biogenesis.

Exportin-5 Functions as an Oncogene and a Potential Therapeutic Target in Colorectal Cancer.

Purpose: Dysregulated expression of miRNAs has emerged as a hallmark feature in human cancers. Exportin-5 (XPO5), a karyopherin family member, is a key protein responsible for transporting precursor miRNAs from the nucleus to the cytoplasm. Although XPO5 is one of the key regulators of miRNA biogenesis, its functional role and potential clinical significance in colorectal cancer remains unclear.Experimental Design: The expression levels of XPO5 were initially assessed in three genomic datasets, followed by determination and validation of the relationship between XPO5 expression and clinicopathologic features in two independent colorectal cancer patient cohorts. A functional characterization of XPO5 in colorectal cancer was examined by targeted gene silencing in colorectal cancer cell lines and a xenograft animal model.Results: XPO5 is upregulated, both at mRNA and protein levels, in colorectal cancers compared with normal tissues. High XPO5 expression is associated with worse clinicopathologic features and poor survival in colorectal cancer patient cohorts. The siRNA knockdown of XPO5 resulted in reduced cellular proliferation, attenuated invasion, induction of G1-S cell-cycle arrest, and downregulation of key oncogenic miRNAs in colorectal cancer cells. These findings were confirmed in a xenograft animal model, wherein silencing of XPO5 resulted in the attenuation of tumor growth.Conclusions: XPO5 acts like an oncogene in colorectal cancer by regulating the expression of miRNAs and may be a potential therapeutic target in colorectal cancer. Clin Cancer Res; 23(5); 1312-22. ©2016 AACR.

Regulation of microRNA Activity in Stress

Stressors substantially affect the physiology of cells. Depending on the severity and duration of stress exposure, cells either strive to maintain homeostasis or adapt by adjusting their gene expression patterns. One of the mechanisms to change gene expression is regulating the microRNA (miRNA) levels and activities of microRNA-protein complexes. A fine tuning of the interaction of miRNAs with their mRNA targets determines the specificity of protein synthesis and the quantitative composition of the protein pool in stress. The review considers the mechanisms that regulate miRNA biogenesis, miRNA-mediated mRNA repression, and activity of miRNA-protein complexes in animal cells exposed to various stress factors.

Virus-Mediated Alterations in miRNA Factors and Degradation of Viral miRNAs by MCPIP1.

Kaposi’s sarcoma-associated herpesvirus (KSHV), the causative agent of Kaposi’s sarcoma, encodes 25 mature viral miRNAs. MCP-1-induced protein-1 (MCPIP1), a critical regulator of immune homeostasis, has been shown to suppress miRNA biosynthesis via cleavage of precursor miRNAs through its RNase domain. We demonstrate that MCPIP1 can directly cleave KSHV and EBV precursor miRNAs and that MCPIP1 expression is repressed following de novo KSHV infection. In addition, repression with siRNAs to MCPIP1 in KSHV-infected cells increased IL-6 and KSHV miRNA expression, supporting a role for MCPIP1 in IL-6 and KSHV miRNA regulation. We also provide evidence that KSHV miRNAs repress MCPIP1 expression by targeting the 3’UTR of MCPIP1. Conversely, expression of essential miRNA biogenesis components Dicer and TRBP is increased following latent KSHV infection. We propose that KSHV infection inhibits a negative regulator of miRNA biogenesis (MCPIP1) and up-regulates critical miRNA processing components to evade host mechanisms that inhibit expression of viral miRNAs. KSHV-mediated alterations in miRNA biogenesis represent a novel mechanism by which KSHV interacts with its host and a new mechanism for the regulation of viral miRNA expression.

MiRNA Biogenesis: A Dynamic Pathway.

MicroRNAs (miRNAs) modulate plant homeostasis through the inactivation of specific mRNAs, especially those encoding transcription factors. A delicate spatial/temporal balance between a miRNA and its targets is central to achieving the appropriate biological outcomes. In this review we discuss our growing understanding of the dynamic regulation of miRNA biogenesis. We put special emphasis on crosstalk between miRNA biogenesis and other cellular processes such as transcription and splicing. We also discuss how the pathway is regulated in specific tissues to achieve harmonious plant development through a subtle balance between gene expression and silencing.

Abstract 1926: Hippo pathway effectors YAP/TAZ integrate tissue mechanics and Wnt signaling to regulate microRNA biogenesis

Abstract Although mechanical cues including extracellular matrix (ECM) stiffness are known to regulate cell and tissue behavior, it remains unclear how these mechanical cues integrate with biochemical signals to control these processes. The Hippo pathway and its transcriptional coactivators YAP and TAZ, which have emerged as major regulators of organ size, proliferation and cancer development, are thought to be involved in this integration. In addition to being regulated by the canonical Hippo pathway, YAP/TAZ have been found to mediate responses to both biochemical and mechanical signals including ECM stiffness and Wnt signaling. Moreover, recent studies have shown that microRNAs (miRNAs) are sensitive to mechanical cues and YAP/TAZ may regulate miRNA biogenesis through mechanotransduction. Although misregulation of YAP/TAZ and miRNA expression are frequently observed in multiple cancers, which appears to be associated with the altered mechanics of the tumor microenvironment, the signaling mechanisms controlling these processes remain poorly understood and controversial. Here we examine how YAP/TAZ integrate biochemical and mechanical signals to regulate miRNA biogenesis. We found that Wnt3A and stiff ECM synergistically lead to nuclear accumulation and activation of YAP/TAZ. Surprisingly, ECM stiffness induces miRNA-18a expression while Wnt3A signaling has an opposite effect on miRNA-18a expression depending on the stiffness of the cellular microenvironment. Thus, YAP/TAZ activity may define a mechanism by which cells respond to ECM stiffness and Wnt signaling to control miRNA biogenesis. Citation Format: Siyang Han, Celeste M. Nelson. Hippo pathway effectors YAP/TAZ integrate tissue mechanics and Wnt signaling to regulate microRNA biogenesis. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1926.