Xue Zhong

LIN28B promotes growth and tumorigenesis of the intestinal epithelium via Let-7.

The RNA-binding proteins LIN28A and LIN28B have diverse functions in embryonic stem cells, cellular reprogramming, growth, and oncogenesis. Many of these effects occur via direct inhibition of Let-7 microRNAs (miRNAs), although Let-7-independent effects have been surmised. We report that intestine targeted expression of LIN28B causes intestinal hypertrophy, crypt expansion, and Paneth cell loss. Furthermore, LIN28B fosters intestinal polyp and adenocarcinoma formation. To examine potential Let-7-independent functions of LIN28B, we pursued ribonucleoprotein cross-linking, immunoprecipitation, and high-throughput sequencing (CLIP-seq) to identify direct RNA targets. This revealed that LIN28B bound a substantial number of mRNAs and modestly augmented protein levels of these target mRNAs in vivo. Conversely, Let-7 had a profound effect; modulation of Let-7 levels via deletion of the mirLet7c2/mirLet7b genes recapitulated effects of Lin28b overexpression. Furthermore, intestine-specific Let-7 expression could reverse hypertrophy and Paneth cell depletion caused by Lin28b. This was independent of effects on insulin-PI3K-mTOR signaling. Our study reveals that Let-7 miRNAs are critical for repressing intestinal tissue growth and promoting Paneth cell differentiation. Let-7-dependent effects of LIN28B may supersede Let-7-independent effects on intestinal tissue growth. In summary, LIN28B can definitively act as an oncogene in the absence of canonical genetic alterations.

Illumina human exome genotyping array clustering and quality control

With the rise of high-throughput sequencing technology, traditional genotyping arrays are gradually being replaced by sequencing technology. Against this trend, Illumina has introduced an exome genotyping array that provides an alternative approach to sequencing, especially suited to large-scale genome-wide association studies (GWASs). The exome genotyping array targets the exome plus rare single-nucleotide polymorphisms (SNPs), a feature that makes it substantially more challenging to process than previous genotyping arrays that targeted common SNPs. Researchers have struggled to generate a reliable protocol for processing exome genotyping array data. The Vanderbilt Epidemiology Center, in cooperation with Vanderbilt Technologies for Advanced Genomics Analysis and Research Design (VANGARD), has developed a thorough exome chip–processing protocol. The protocol was developed during the processing of several large exome genotyping array-based studies, which included over 60,000 participants combined. The protocol described herein contains detailed clustering techniques and robust quality control procedures, and it can benefit future exome genotyping array–based GWASs.

Network-based stratification analysis of 13 major cancer types using mutations in panels of cancer genes

BackgroundCancers are complex diseases with heterogeneous genetic causes and clinical outcomes. It is critical to classify patients into subtypes and associate the subtypes with clinical outcomes for better prognosis and treatment. Large-scale studies have comprehensively identified somatic mutations across multiple tumor types, providing rich datasets for classifying patients based on genomic mutations. One challenge associated with this task is that mutations are rarely shared across patients. Network-based stratification (NBS) approaches have been proposed to overcome this challenge and used to classify tumors based on exome-level mutations. In routine research and clinical applications, however, usually only a small panel of pre-selected genes is screened for mutations. It is unknown whether such small panels are effective in classifying patients into clinically meaningful subtypes.ResultsIn this study, we applied NBS to 13 major cancer types with exome-level mutation data and compared the classification based on the full exome data with those focusing only on small sets of genes. Specifically, we investigated three panels, FoundationOne (240 genes), PanCan (127 genes) and TruSeq (48 genes). We showed that small panels not only are effective in clustering tumors but also often outperform full exome data for most cancer types. We further associated subtypes with clinical data and identified 5 tumor types (CRC-Colorectal carcinoma, HNSC-Head and neck squamous cell carcinoma, KIRC-Kidney renal clear cell carcinoma, LUAD-Lung adenocarcinoma and UCEC-Uterine corpus endometrial carcinoma) whose subtypes are significantly associated with overall survival, all based on small panels.ConclusionOur analyses indicate that effective patient subtyping can be carried out using mutations detected in smaller gene panels, probably due to the enrichment of clinically important genes in such panels.

A comparison of microRNA sequencing reproducibility and noise reduction using mirVana and TRIzol isolation methods

MicroRNAseq (miRNAseq) is a form of RNAseq technology that has become an increasingly popular alternative to miRNA expression profiling. Unlike messenger RNA (mRNA), miRNA extraction can be difficult, and sequencing such small RNA can also be problematic. We designed a study to test the reproducibility of miRNAseq technology and the performance of the two popular miRNA isolation methods, mirVana and TRIzol, by sequencing replicated samples using microRNA isolated with each kit. Through careful analysis of our data, we found excellent repeatability of miRNAseq technology. The mirVana method performed better than TRIzol in terms of useful reads sequenced, number of miRNA identified, and reproducibility. Finally, we identified a baseline noise level for miRNAseq technology; this baseline noise level can be used as a filter in future miRNAseq studies.

Assessing Computational Steps for CLIP-Seq Data Analysis

RNA-binding protein (RBP) is a key player in regulating gene expression at the posttranscriptional level. CLIP-Seq, with the ability to provide a genome-wide map of protein-RNA interactions, has been increasingly used to decipher RBP-mediated posttranscriptional regulation. Generating highly reliable binding sites from CLIP-Seq requires not only stringent library preparation but also considerable computational efforts. Here we presented a first systematic evaluation of major computational steps for identifying RBP binding sites from CLIP-Seq data, including preprocessing, the choice of control samples, peak normalization, and motif discovery. We found that avoiding PCR amplification artifacts, normalizing to input RNA or mRNAseq, and defining the background model from control samples can reduce the bias introduced by RNA abundance and improve the quality of detected binding sites. Our findings can serve as a general guideline for CLIP experiments design and the comprehensive analysis of CLIP-Seq data.

LNK deficiency promotes acute aortic dissection and rupture

Aortic dissection (AD) is a life-threatening vascular disease with limited treatment strategies. Here, we show that loss of the GWAS-identified SH2B3 gene, encoding lymphocyte adaptor protein LNK, markedly increases susceptibility to acute AD and rupture in response to angiotensin (Ang) II infusion. As early as day 3 following Ang II infusion, prior to the development of AD, Lnk-/- aortas display altered mechanical properties, increased elastin breaks, collagen thinning, enhanced neutrophil accumulation, and increased MMP-9 activity compared with WT mice. Adoptive transfer of Lnk-/- leukocytes into Rag1-/- mice induces AD and rupture in response to Ang II, demonstrating that LNK deficiency in hematopoietic cells plays a key role in this disease. Interestingly, treatment with doxycycline prevents the early accumulation of aortic neutrophils and significantly reduces the incidence of AD and rupture. PrediXcan analysis in a biobank of more than 23,000 individuals reveals that decreased expression of SH2B3 is significantly associated with increased frequency of AD-related phenotypes (odds ratio 0.81). Thus, we identified a role for LNK in the pathology of AD in experimental animals and humans and describe a new model that can be used to inform both inherited and acquired forms of this disease.

Abstract 2788: Comprehensive high-depth target sequencing in circulating tumor DNAs of patients with inflammatory and non-inflammation breast cancers

Inflammatory breast cancer (IBC) is an extremely aggressive form of locally advanced breast cancer that affects about 5% of breast cancer patients. The prognosis of IBC patients is remarkably poor, with a three-year survival rate of approximately 30% compared to 60% for patients with non-IBC breast cancers. These facts highlight the importance of accurate characterization, early detection, and timely treatment of IBC patients. Thus, it is important to develop novel and clinically applicable non-invasive biomarkers to characterize the unique presentation of IBC. In this study, we searched for somatic mutations in the circulating tumor DNAs (ctDNAs) that could be used to non-invasively characterize IBC patients and inform their clinical management. Using ctDNAs extracted from plasma of 10 pairs of IBC and non-IBC patients that were matched on major demographic and clinical variables, we conducted a high-depth target next-generation sequencing study that interrogated a comprehensive panel of 127 TCGA (The Cancer Genome Atlas)-reported cancer-related genes with >7000 uniquely designed and validated probes. Overall, we obtained >500x coverage in >80% of the interrogated regions, and >100x coverage in >97% of the regions. We found that C>T mutations predominated in well-reported mutated genes such as TP53, PIK3CA, EGFR, and CDH1. Compared to non-IBC patients, IBC patients appeared to have a higher percentage of mutations in PIK3CA but a lower percentage in TP53. Interestingly, about 78% of mutated genes that were only detected in IBC patients encode zinc finger-related proteins, a family of transcriptional factors that have been implicated in IBC development. In comparison, about 43% of genes that were detected only in non-IBC patients encode proteins important to cell division regulation. Furthermore, network-based stratification (NBS) analysis of the mutation profile revealed clusters of IBC relative to non-IBC samples, indicating the potential of mutation profiling in identifying molecularly distinct subtypes of IBC patients. Preliminary longitudinal analysis of ctDNAs from three patients with multiple plasma samples indicated that de novo mutations in important genes including PIK3CA, RB1, and KRAS appeared in patient blood after chemotherapy and/or targeted therapy treatments. Moreover, the emergence of some of these mutations was temporally correlated with the responses of patients to the treatments they received. Overall, this study provides novel evidence that ctDNA mutation status may help to non-invasively characterize IBC tumors, and might also serve as a novel non-invasive marker to monitor treatment efficacy and prognosis of breast cancer patients. Future studies with larger sample sizes are warranted to confirm our findings and identify additional clinically useful markers for the characterization and management of IBC and non-IBC patients. Citation Format: Hushan Yang, Xue Zhong, Qiang Wei, Zhaomei Mu, Zhong Ye, Yinzhi Lai, Huei-Wen Lin, Rebecca Jaslow, Tiffany Avery, Laura Austin, Zhaohui Sun, Shengrong Lin, Grace Zhao, Ling Fang Tang, Ronald E. Myers, Juan P. Palazzo, Laura Biederman, Bingshan Li, Massimo Cristofanilli. Comprehensive high-depth target sequencing in circulating tumor DNAs of patients with inflammatory and non-inflammation breast cancers. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2788. doi:10.1158/1538-7445.AM2015-2788

CLIP-EZ: a computational tool for HITS-CLIP data analysis

Background Mapping the binding regions of mRNA-binding proteins is critical to the understanding of their regulatory roles in cellular processes. Recent development in experimental technologies combines high throughput sequencing with crosslink immunoprecipitation (HITS-CLIP), which has the merit of detecting RNA-protein interaction sites at a high resolution to single nucleotide level. Analysis of such data typically involves many steps, and teasing out true signals from noise requires crosslink induced mutations (CIMS) analysis, peak identification, integration of the two signal types, and some downstream analysis such as motif finding and conservation evaluation. To our knowledge, there is a lack of a single computational tool that can perform all the tasks as mentioned in an easily accessible manner. Despite the fact that there are several tools available, each performs an individual task.

Abstract PR04: LIN28B promotes growth and tumorigenesis of the intestinal epithelium primarily via Let-7 repression

The RNA-binding proteins LIN28A and LIN28B have diverse functions in embryonic stem cells, cellular reprogramming, growth, and oncogenesis. Many of these effects occur via direct inhibition of Let-7 miRNAs, although Let-7 independent effects have been surmised. Our past studies have shown that LIN28B expression in colorectal cancers is associated with poor prognosis and cancer recurrence, and that LIN28B promotes migration, invasion, and metastasis of CRC cell lines in mouse xenograft models. Considering these studies, and the observation that LIN28B is more frequently up-regulated in a variety of other cancers, we sought to elucidate the molecular mechanisms of LIN28B function in intestinal homeostasis and colorectal cancer. We report that intestine-targeted expression of Lin28b in mice causes intestinal hypertrophy, crypt expansion, and Paneth cell loss. Lgr5-positive crypt base columnar cells were not expanded, nor compromised by the depletion of Paneth cells. However, Lin28b fostered intestinal polyp and adenocarcinoma formation. We observed that higher Lin28b levels also correlated with increased incidence of adenocarcinoma. This is consistent with human epidemiological data illustrating that increased LIN28B levels are observed at early stages of CRC, with high expression at both stages I and II disease correlating inversely with patient survival and higher probability of recurrence. To examine potential Let-7-independent functions of LIN28B, we pursued ribonucleoprotein cross-linking, immunoprecipitation, and high-throughput sequencing (CLIP-Seq) to identify direct RNA targets. This revealed that LIN28B protein binds a substantial number of mRNAs, many of which are specific to epithelial cells. LIN28B modestly augmented protein levels of these target mRNAs, in vivo. Conversely, Let-7 had a profound effect; modulation of Let-7 levels via deletion of the mirLet7c2/mirLet7b genes recapitulated effects of Lin28b overexpression. Furthermore, intestine-specific Let-7 expression could reverse hypertrophy and Paneth cell depletion caused by Lin28b. Previous reports have linked Let-7 to the regulation of the PI3K-Akt-mTOR signaling pathway via regulation of Insr, Igf1r, and Irs2 mRNAs, yet we found that Lin28b did not have a significant impact on these mRNAs or insulin-PI3K-mTOR signaling. Kras and Myc mRNAs, which are also reported to be Let-7 targets, were likewise unaffected. Instead, we found profound up-regulation of Hmga2, Igf2bp1, Igf2bp2, and E2f5 in the context of Let-7 depletion or Lin28b over-expression. Our study reveals that Let-7 miRNAs are critical for repressing tissue growth and promoting Paneth cell differentiation. These results highlight the critical nature of LIN28B and Let-7 dosage, where a stepwise reduction of Let-7 levels has a direct effect on target mRNAs and adenocarcinoma risk. These Let-7 dependent effects of LIN28B appear to supersede any Let-7 independent effects. In sum, LIN28B can definitively act as an oncogene in the absence of canonical genetic alteration in intestinal carcinogenesis. This abstract is also presented as poster A42. Citation Format: Blair Madison, Qi Liu, Xue Zhong, Christopher M. Hahn, Nan Lin, Matthew Emmet, Ben Z. Stanger, Anil K. Rustgi. LIN28B promotes growth and tumorigenesis of the intestinal epithelium primarily via Let-7 repression. [abstract]. In: Proceedings of the Third AACR International Conference on Frontiers in Basic Cancer Research; Sep 18-22, 2013; National Harbor, MD. Philadelphia (PA): AACR; Cancer Res 2013;73(19 Suppl):Abstract nr PR04.