MALAT1 has previously been described as a metastasis-promoting long non-coding RNA (lncRNA). Unexpectedly, we found that targeted inactivation of the Malat1 gene without altering the expression of its adjacent genes in a transgenic mouse model of breast cancer promoted lung metastasis, and importantly, this phenotype was reversed by genetic add-back of Malat1 . Similarly, knockout of MALAT1 in human breast cancer cells induced their metastatic ability, which was reversed by Malat1 re-expression. Conversely, overexpression of Malat1 suppressed breast cancer metastasis in transgenic, xenograft, and syngeneic models. Mechanistically, MALAT1 binds and inactivates the pro-metastatic transcription factor TEAD, blocking TEAD from associating with its co-activator YAP and target gene promoters. Moreover, MALAT1 levels inversely correlate with breast cancer progression and metastatic ability. These findings demonstrate that MALAT1 is a metastasis-suppressing lncRNA rather than a metastasis promoter in breast cancer, calling for rectification of the model for a highly abundant and conserved lncRNA.

Although circumcision reduces male acquisition of human immunodeficiency virus type-1 (HIV-1) by 60%, the initial mechanisms of HIV-1 transmission at the foreskin remain elusive. We have established two novel and complementary models of the human adult foreskin epithelium, namely, ex vivo foreskin explants and in vitro reconstructed immunocompetent foreskins. In these models, efficient HIV-1 transmission occurs after 1 h of polarized exposure of the inner, but not outer, foreskin to mononuclear cells highly infected with HIV-1, but not to cell-free virus. HIV-1-infected cells form viral synapses with apical foreskin keratinocytes, leading to polarized budding of HIV-1, which is rapidly internalized by Langerhans cells (LCs) in the inner foreskin. In turn, LCs migrate toward the epidermis-dermis interface to form conjugates with T cells, thereby transferring HIV-1. Seminal plasma mixed with cervicovaginal secretions inhibits HIV-1 translocation. This set of results rationalizes at the cellular level the apparent protective outcome of circumcision against HIV-1 acquisition by men.

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The role of enhancers, a key class of non-coding regulatory DNA elements, in cancer development has increasingly been appreciated. Here, we present the detection and characterization of a large number of expressed enhancers in a genome-wide analysis of 8928 tumor samples across 33 cancer types using TCGA RNA-seq data. Compared with matched normal tissues, global enhancer activation was observed in most cancers. Across cancer types, global enhancer activity was positively associated with aneuploidy, but not mutation load, suggesting a hypothesis centered on "chromatin-state" to explain their interplay. Integrating eQTL, mRNA co-expression, and Hi-C data analysis, we developed a computational method to infer causal enhancer-gene interactions, revealing enhancers of clinically actionable genes. Having identified an enhancer ∼140 kb downstream of PD-L1, a major immunotherapy target, we validated it experimentally. This study provides a systematic view of enhancer activity in diverse tumor contexts and suggests the clinical implications of enhancers.

Adenosine (A) to inosine (I) RNA editing introduces many nucleotide changes in cancer transcriptomes. However, due to the complexity of post-transcriptional regulation, the contribution of RNA editing to proteomic diversity in human cancers remains unclear. Here, we performed an integrated analysis of TCGA genomic data and CPTAC proteomic data. Despite limited site diversity, we demonstrate that A-to-I RNA editing contributes to proteomic diversity in breast cancer through changes in amino acid sequences. We validate the presence of editing events at both RNA and protein levels. The edited COPA protein increases proliferation, migration, and invasion of cancer cells in vitro. Our study suggests an important contribution of A-to-I RNA editing to protein diversity in cancer and highlights its translational potential.

RNA editing, a widespread post-transcriptional mechanism, has emerged as a new player in cancer biology. Recent studies have reported key roles for individual miRNA editing events, but a comprehensive picture of miRNA editing in human cancers remains largely unexplored. Here, we systematically characterized the miRNA editing profiles of 8595 samples across 20 cancer types from miRNA sequencing data of The Cancer Genome Atlas and identified 19 adenosine-to-inosine (A-to-I) RNA editing hotspots. We independently validated 15 of them by perturbation experiments in several cancer cell lines. These miRNA editing events show extensive correlations with key clinical variables (e.g., tumor subtype, disease stage, and patient survival time) and other molecular drivers. Focusing on the RNA editing hotspot in miR-200b, a key tumor metastasis suppressor, we found that the miR-200b editing level correlates with patient prognosis opposite to the pattern observed for the wild-type miR-200b expression. We further experimentally showed that, in contrast to wild-type miRNA, the edited miR-200b can promote cell invasion and migration through its impaired ability to inhibit ZEB1/ZEB2 and acquired concomitant ability to repress new targets, including LIFR, a well-characterized metastasis suppressor. Our study highlights the importance of miRNA editing in gene regulation and suggests its potential as a biomarker for cancer prognosis and therapy.

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Male circumcision reduces acquisition of HIV-1 by 60%. Hence, the foreskin is an HIV-1 entry portal during sexual transmission. We recently reported that efficient HIV-1 transmission occurs following 1 h of polarized exposure of the inner, but not outer, foreskin to HIV-1-infected cells, but not to cell-free virus. At this early time point, Langerhans cells (LCs) and T-cells within the inner foreskin epidermis are the first cells targeted by the virus. To gain in-depth insight into the molecular mechanisms governing inner foreskin HIV-1 entry, foreskin explants were inoculated with HIV-1-infeceted cells for 4 h. The chemokine/cytokine milieu secreted by the foreskin tissue, and resulting modifications in density and spatial distribution of T-cells and LCs, were then investigated. Our studies show that in the inner foreskin, inoculation with HIV-1-infected cells induces increased CCL5/RANTES (1.63-fold) and decreased CCL20/MIP-3-alpha (0.62-fold) secretion. Elevated CCL5/RANTES mediates recruitment of T-cells from the dermis into the epidermis, which is blocked by a neutralizing CCL5/RANTES Ab. In parallel, HIV-1-infected cells mediate a bi-phasic modification in the spatial distribution of epidermal LCs: attraction to the apical surface at 1 h, followed by migration back towards the basement membrane later on at 4 h, in correlation with reduced CCL20/MIP-3-alpha at this time point. T-cell recruitment fuels the continuous formation of LC-T-cell conjugates, permitting the transfer of HIV-1 captured by LCs. Together, these results reveal that HIV-1 induces a dynamic process of immune cells relocation in the inner foreskin that is associated with specific chemokines secretion, which favors efficient HIV-1 entry at this site.