ESR1 mutations are frequent in newly diagnosed metastatic and loco-regional recurrence of endocrine-treated breast cancer and carry worse prognosis

BACKGROUND

Emerging mutations in the ESR1 gene that encodes for the estrogen receptor (ER) are associated with resistance to endocrine therapy. ESR1 mutations rarely exist in primary tumors (~ 1%) but are relatively common (10-50%) in metastatic, endocrine therapy-resistant cancers and are associated with a shorter progression-free survival. Little is known about the incidence and clinical implication of these mutations in early recurrence events, such as local recurrences or newly diagnosed metastatic disease.

METHODS

We collected 130 archival tumor samples from 103 breast cancer patients treated with endocrine therapy prior to their local/metastatic recurrence. The cohort consisted of 41 patients having at least 1 sample from local/loco-regional recurrence and 62 patients with metastatic disease (of whom 41 newly diagnosed and 28 with advanced disease). The 5 most common ESR1 hotspot mutations (D538G, L536R, Y537S/N/C) were analyzed either by targeted sequencing or by droplet digital PCR. Progression-free survival (PFS), disease-free survival (DFS), and distant recurrence-free survival (DRFS) were statistically tested by Kaplan-Meier analysis.

RESULTS

The prevalence of ESR1 mutations was 5/41 (12%) in newly diagnosed metastatic patients and 5/28 (18%) for advanced metastases, detected at allele frequency > 1%. All mutations in advanced metastases were detected in patients previously treated with both tamoxifen (TAM) and aromatase inhibitors (AI). However, in newly diagnosed metastatic patients, 4/5 mutations occurred in patients treated with TAM alone. PFS on AI treatment in metastatic patients was significantly shorter for ESR1 mutation carriers (p = 0.017). In the local recurrence cohort, ESR1 mutations were identified in 15/41 (36%) patients but only 4/41 (10%) were detected at allele frequency > 1%. Again, most mutations (3/4) were detected under TAM monotherapy. Notably, 1 patient developed ESR1 mutation while on neoadjuvant endocrine therapy. DFS and DRFS were significantly shorter (p = 0.04 and p = 0.017, respectively) in patients that had ESR1 mutations (> 1%) in their loco-regional recurrence tumor.

CONCLUSIONS

Clinically relevant ESR1 mutations are prevalent in newly diagnosed metastatic and local recurrence of endocrine-treated breast cancer. Since local recurrences are amenable to curative therapy, these mutations may inform the selection of subsequent endocrine therapies.

Guided Protocol for Fecal Microbial Characterization by 16S rRNA-Amplicon Sequencing

The human intestinal microbiome plays a central role in protecting cells from injury, in processing energy and nutrients, and in promoting immunity. Deviations from what is considered a healthy microbiota composition (dysbiosis) may impair vital functions leading to pathologic conditions. Recent and ongoing research efforts have been directed toward the characterization of associations between microbial composition and human health and disease. Advances in high-throughput sequencing technologies enable characterization of the gut microbial composition. These methods include 16S rRNA-amplicon sequencing and shotgun sequencing. 16S rRNA-amplicon sequencing is used to profile taxonomical composition, while shotgun sequencing provides additional information about gene predictions and functional annotation. An advantage in using a targeted sequencing method of the 16S rRNA gene variable region is its substantially lower cost compared to shotgun sequencing. Sequence differences in the 16S rRNA gene are used as a microbial fingerprint to identify and quantify different taxa within an individual sample. Major international efforts have enlisted standards for 16S rRNA-amplicon sequencing. However, several studies report a common source of variation caused by batch effect. To minimize this effect, uniformed protocols for sample collection, processing, and sequencing must be implemented. This protocol proposes the integration of broadly used protocols starting from fecal sample collection to data analyses. This protocol includes a column-free, direct-PCR approach that enables simultaneous handling and DNA extraction of large numbers of fecal samples, along with PCR amplification of the V4 region. In addition, the protocol describes the analysis pipeline and provides a script using the latest version of QIIME (QIIME 2 version 2017.7.0 and DADA2). This step-by-step protocol is aimed to guide those interested in initiating the use of 16S rRNA-amplicon sequencing in a robust, reproductive, easy to use, detailed way.

Whole-genome sequencing reveals principles of brain retrotransposition in neurodevelopmental disorders

Neural progenitor cells undergo somatic retrotransposition events, mainly involving L1 elements, which can be potentially deleterious. Here, we analyze the whole genomes of 20 brain samples and 80 non-brain samples, and characterized the retrotransposition landscape of patients affected by a variety of neurodevelopmental disorders including Rett syndrome, tuberous sclerosis, ataxia-telangiectasia and autism. We report that the number of retrotranspositions in brain tissues is higher than that observed in non-brain samples and even higher in pathologic vs normal brains. The majority of somatic brain retrotransposons integrate into pre-existing repetitive elements, preferentially A/T rich L1 sequences, resulting in nested insertions. Our findings document the fingerprints of encoded endonuclease independent mechanisms in the majority of L1 brain insertion events. The insertions are "non-classical" in that they are truncated at both ends, integrate in the same orientation as the host element, and their target sequences are enriched with a CCATT motif in contrast to the classical endonuclease motif of most other retrotranspositions. We show that L1Hs elements integrate preferentially into genes associated with neural functions and diseases. We propose that pre-existing retrotransposons act as "lightning rods" for novel insertions, which may give fine modulation of gene expression while safeguarding from deleterious events. Overwhelmingly uncontrolled retrotransposition may breach this safeguard mechanism and increase the risk of harmful mutagenesis in neurodevelopmental disorders.

Global regulation of alternative splicing by adenosine deaminase acting on RNA (ADAR)

Alternative mRNA splicing is a major mechanism for gene regulation and transcriptome diversity. Despite the extent of the phenomenon, the regulation and specificity of the splicing machinery are only partially understood. Adenosine-to-inosine (A-to-I) RNA editing of pre-mRNA by ADAR enzymes has been linked to splicing regulation in several cases. Here we used bioinformatics approaches, RNA-seq and exon-specific microarray of ADAR knockdown cells to globally examine how ADAR and its A-to-I RNA editing activity influence alternative mRNA splicing. Although A-to-I RNA editing only rarely targets canonical splicing acceptor, donor, and branch sites, it was found to affect splicing regulatory elements (SREs) within exons. Cassette exons were found to be significantly enriched with A-to-I RNA editing sites compared with constitutive exons. RNA-seq and exon-specific microarray revealed that ADAR knockdown in hepatocarcinoma and myelogenous leukemia cell lines leads to global changes in gene expression, with hundreds of genes changing their splicing patterns in both cell lines. This global change in splicing pattern cannot be explained by putative editing sites alone. Genes showing significant changes in their splicing pattern are frequently involved in RNA processing and splicing activity. Analysis of recently published RNA-seq data from glioblastoma cell lines showed similar results. Our global analysis reveals that ADAR plays a major role in splicing regulation. Although direct editing of the splicing motifs does occur, we suggest it is not likely to be the primary mechanism for ADAR-mediated regulation of alternative splicing. Rather, this regulation is achieved by modulating trans-acting factors involved in the splicing machinery.

Topology of the human and mouse m6A RNA methylomes revealed by m6A-seq

An extensive repertoire of modifications is known to underlie the versatile coding, structural and catalytic functions of RNA, but it remains largely uncharted territory. Although biochemical studies indicate that N(6)-methyladenosine (m(6)A) is the most prevalent internal modification in messenger RNA, an in-depth study of its distribution and functions has been impeded by a lack of robust analytical methods. Here we present the human and mouse m(6)A modification landscape in a transcriptome-wide manner, using a novel approach, m(6)A-seq, based on antibody-mediated capture and massively parallel sequencing. We identify over 12,000 m(6)A sites characterized by a typical consensus in the transcripts of more than 7,000 human genes. Sites preferentially appear in two distinct landmarks--around stop codons and within long internal exons--and are highly conserved between human and mouse. Although most sites are well preserved across normal and cancerous tissues and in response to various stimuli, a subset of stimulus-dependent, dynamically modulated sites is identified. Silencing the m(6)A methyltransferase significantly affects gene expression and alternative splicing patterns, resulting in modulation of the p53 (also known as TP53) signalling pathway and apoptosis. Our findings therefore suggest that RNA decoration by m(6)A has a fundamental role in regulation of gene expression.

MDR1 expression identifies human melanoma stem cells

ABC transporters are often found to be inherently expressed in a wide variety of stem cells, where they provide improved protection from toxins. We found a subpopulation of human melanoma cells expressing multidrug-resistance gene product 1 (MDR1). This fraction co-expresses the ABC transporters, ABCB5 and ABCC2 in addition to the stem cell markers, nanog and human telomerase reverse transcriptase (hTERT). The clonogenicity and self-renewal capacity of MDR1(+) melanoma cells were investigated in single cell settings using the limiting dilution assay. We found that the MDR1(+) cells, isolated by FACS sorting, demonstrated a higher self-renewal capacity than the MDR1(-) fraction, a key stem cell feature. Moreover, MDR1(+) cells had higher ability to form spheres in low attachment conditions, a hallmark of cancer. In conclusion, these novel findings imply that the MDR1(+) cells represent melanoma stem cells and thus should be considered as a unique cellular target for future anti-melanoma therapies.

Aym1, a mouse meiotic gene identified by virtue of its ability to activate early meiotic genes in the yeast Saccharomyces cerevisiae

Our understanding of the molecular mechanisms that operate during differentiation of mitotically dividing spermatogonia cells into spermatocytes lags way behind what is known about other differentiating systems. Given the evolutionary conservation of the meiotic process, we screened for mouse proteins that could specifically activate early meiotic promoters in Saccharomyces cerevisiae yeast cells, when fused to the Gal4 activation domain (Gal4AD). Our screen yielded the Aym1 gene that encodes a short peptide of 45 amino acids. We show that a Gal4AD-AYM1 fusion protein activates expression of reporter genes through the promoters of the early meiosis-specific genes IME2 and HOP1, and that this activation is dependent on the DNA-binding protein Ume6. Aym1 is transcribed predominantly in mouse primary spermatocytes and in gonads of female embryos undergoing the corresponding meiotic divisions. Aym1 immunolocalized to nuclei of primary spermatocytes and oocytes and to specific type A spermatogonia cells, suggesting it might play a role in the processes leading to meiotic competence. The potential functional relationship between AYM1 and yeast proteins that regulate expression of early meiotic genes is discussed.