Person:

Pearson, Daniel

MicroRNAs (miRNAs) are important regulators and potential therapeutic targets of metabolic disease. In this study we show by in vivo administration of locked nucleic acid (LNA) inhibitors that suppression of endogenous miR-29 lowers plasma cholesterol levels by ~40%, commensurate with the effect of statins, and reduces fatty acid content in the liver by ~20%. Whole transcriptome sequencing of the liver reveals 883 genes dysregulated (612 down, 271 up) by inhibition of miR-29. The set of 612 down-regulated genes are most significantly over-represented in lipid synthesis pathways. Among the up-regulated genes are the anti-lipogenic deacetylase sirtuin 1 (Sirt1) and the anti-lipogenic transcription factor aryl hydrocarbon receptor (Ahr), the latter of which we demonstrate is a direct target of miR-29. In vitro radiolabeled acetate incorporation assays confirm that pharmacologic inhibition of miR-29 significantly reduces de novo cholesterol and fatty acid synthesis. Our findings indicate that miR-29 controls hepatic lipogenic programs, likely in part through regulation of Ahr and Sirt1, and therefore may represent a candidate therapeutic target for metabolic disorders such as dyslipidemia.

Poor prognosis in neuroblastoma is associated with genetic amplification of MYCN. MYCN is itself a target of let-7, a tumor suppressor family of microRNAs implicated in numerous cancers. LIN28B, an inhibitor of let-7 biogenesis, is overexpressed in neuroblastoma and has been reported to regulate MYCN. However, here we show that LIN28B is dispensable in MYCN-amplified neuroblastoma cell lines, despite de-repression of let-7. We further demonstrate that MYCN mRNA levels in amplified disease are exceptionally high and sufficient to sponge let-7, which reconciles the dispensability of LIN28B. We found that genetic loss of let-7 is common in neuroblastoma, inversely associated with MYCN-amplification, and independently associated with poor outcomes, providing a rationale for chromosomal loss patterns in neuroblastoma. We propose that let-7 disruption by LIN28B, MYCN sponging, or genetic loss is a unifying mechanism of neuroblastoma pathogenesis with broad implications for cancer pathogenesis.

Mast cells are critical components of the innate immune system and important for host 48 defense, allergy, autoimmunity, tissue regeneration, and tumor progression.Dysregulated 49 mastcell development leads to systemic mastocytosis, a clinically variable but often 50 devastating family of hematologic disorders. Here we report that induced expression of 51 Lin28, a heterochronic gene and pluripotency factor implicated in driving a fetal 52 hematopoietic program, caused mast cell accumulation in adult mice in target organs such 53 as the skin and peritoneal cavity. In vitro assays revealed a skewing of myeloid 54 commitment in LIN28B-­‐expressing hematopoietic progenitors, with increased levels of 55 LIN28B in common myeloid and basophil-­‐mast cell progenitors altering gene expression 56 patterns to favor cell fate choices that enhanced mast cell specification. In addition, 57 LIN28B-­‐induced mast cells appeared phenotypically and functionally immature, and in 58 vitro assays suggested a slowing of mast cell terminal differentiation in the context of 59 LIN28B upregulation. Finally, interrogation of human mast cell leukemia samples revealed 60 upregulation of LIN28B in abnormal mast cells from patients with systemic mastocytosis 61 (SM). This work identifies Lin28 as a novel regulator of innate immune function and a new 62 protein of interest in mast cell disease.

Signaling and post-transcriptional gene control are both critical for the regulation of pluripotency1,2, yet how they are integrated to influence cell identity remains poorly understood. LIN28 (also known as LIN28A), a highly conserved RNA-binding protein (RBP), has emerged as a central post-transcriptional regulator of cell fate through blockade of let-7 microRNA (miRNA) biogenesis and direct modulation of mRNA translation3. Here we show that LIN28 is phosphorylated by MAPK/ERK in pluripotent stem cells (PSCs), which increases its levels via post-translational stabilization. LIN28 phosphorylation had little impact on let-7 but enhanced LIN28’s effect on its direct mRNA targets, revealing a mechanism that uncouples LIN28’s let-7-dependent and independent activities. We have linked this mechanism to the induction of pluripotency by somatic cell reprogramming and the transition from naïve to primed pluripotency. Collectively, our findings indicate that MAPK/ERK directly impacts LIN28, defining an axis that connects signaling, post-transcriptional gene control, and cell fate regulation.