Multiplexed screening reveals how cancer-specific alternative polyadenylation shapes tumor growth in vivo.

Alternative polyadenylation (APA) is strikingly dysregulated in many cancers. Although global APA dysregulation is frequently associated with poor prognosis, the importance of most individual APA events is controversial simply because few have been functionally studied. Here, we address this gap by developing a CRISPR-Cas9-based screen to manipulate endogenous polyadenylation and systematically quantify how APA events contribute to tumor growth in vivo. Our screen reveals individual APA events that control mouse melanoma growth in an immunocompetent host, with concordant associations in clinical human cancer. For example, forced Atg7 3' UTR lengthening in mouse melanoma suppresses ATG7 protein levels, slows tumor growth, and improves host survival; similarly, in clinical human melanoma, a long ATG7 3' UTR is associated with significantly prolonged patient survival. Overall, our study provides an easily adaptable means to functionally dissect APA in physiological systems and directly quantifies the contributions of recurrent APA events to tumorigenic phenotypes.

Discovery of EP300/CBP histone acetyltransferase inhibitors through scaffold hopping of 1,4-oxazepane ring.

EP300 and its paralog CBP play an important role in post-translational modification as histone acetyltransferases (HATs). EP300/CBP inhibition has been gaining attention as an anticancer treatment target in recent years. Herein, we describe the identification of a novel, highly selective EP300/CBP inhibitor, compound 11 (DS17701585), by scaffold hopping and structure-based optimization of a high-throughput screening hit 1. Compound 11 (DS17701585) shows dose-dependent inhibition of SRY-box transcription factor 2 (SOX2) mRNA expression in a human lung squamous cell carcinoma cell line LK2-xenografted mouse model.

Haemodynamically dependent valvulogenesis of zebrafish heart is mediated by flow-dependent expression of miR-21.

Heartbeat is required for normal development of the heart, and perturbation of intracardiac flow leads to morphological defects resembling congenital heart diseases. These observations implicate intracardiac haemodynamics in cardiogenesis, but the signalling cascades connecting physical forces, gene expression and morphogenesis are largely unknown. Here we use a zebrafish model to show that the microRNA, miR-21, is crucial for regulation of heart valve formation. Expression of miR-21 is rapidly switched on and off by blood flow. Vasoconstriction and increasing shear stress induce ectopic expression of miR-21 in the head vasculature and heart. Flow-dependent expression of mir-21 governs valvulogenesis by regulating the expression of the same targets as mouse/human miR-21 (sprouty, pdcd4, ptenb) and induces cell proliferation in the valve-forming endocardium at constrictions in the heart tube where shear stress is highest. We conclude that miR-21 is a central component of a flow-controlled mechanotransduction system in a physicogenetic regulatory loop.

Gain-of-function mutations in RIT1 cause Noonan syndrome, a RAS/MAPK pathway syndrome.

RAS GTPases mediate a wide variety of cellular functions, including cell proliferation, survival, and differentiation. Recent studies have revealed that germline mutations and mosaicism for classical RAS mutations, including those in HRAS, KRAS, and NRAS, cause a wide spectrum of genetic disorders. These include Noonan syndrome and related disorders (RAS/mitogen-activated protein kinase [RAS/MAPK] pathway syndromes, or RASopathies), nevus sebaceous, and Schimmelpenning syndrome. In the present study, we identified a total of nine missense, nonsynonymous mutations in RIT1, encoding a member of the RAS subfamily, in 17 of 180 individuals (9%) with Noonan syndrome or a related condition but with no detectable mutations in known Noonan-related genes. Clinical manifestations in the RIT1-mutation-positive individuals are consistent with those of Noonan syndrome, which is characterized by distinctive facial features, short stature, and congenital heart defects. Seventy percent of mutation-positive individuals presented with hypertrophic cardiomyopathy; this frequency is high relative to the overall 20% incidence in individuals with Noonan syndrome. Luciferase assays in NIH 3T3 cells showed that five RIT1 alterations identified in children with Noonan syndrome enhanced ELK1 transactivation. The introduction of mRNAs of mutant RIT1 into 1-cell-stage zebrafish embryos was found to result in a significant increase of embryos with craniofacial abnormalities, incomplete looping, a hypoplastic chamber in the heart, and an elongated yolk sac. These results demonstrate that gain-of-function mutations in RIT1 cause Noonan syndrome and show a similar biological effect to mutations in other RASopathy-related genes.

Heartbeat regulates cardiogenesis by suppressing retinoic acid signaling via expression of miR-143.

Cardiogenesis proceeds with concomitant changes in hemodynamics to accommodate the circulatory demands of developing organs and tissues. In adults, circulatory adaptation is critical for the homeostatic regulation of blood circulation. In these hemodynamics-dependent processes of morphogenesis and adaptation, a mechanotransduction pathway, which converts mechanical stimuli into biological outputs, plays an essential role, although its molecular nature is largely unknown. Here, we report that expression of zebrafish miR-143 is dependent on heartbeat. Knocking-down miR-143 results in de-repression of retinoic acid signaling, and produces abnormalities in the outflow tracts and ventricles. Our data uncover a novel epigenetic link between heartbeat and cardiac development, with miR-143 as an essential component of the mechanotransduction cascade.