The Impact of High Adiposity on Endometrial Progesterone Response and Metallothionein Regulation

CONTEXT

Obesity is a disease with deleterious effects on the female reproductive tract, including the endometrium.

OBJECTIVE

We sought to understand the effects of excess adipose on the benign endometrium.

DESIGN

A physiologic in vitro coculture system was developed, consisting of multicellular human endometrial organoids, adipose spheroids, and menstrual cycle hormones. Native human endometrial tissue samples women with and without obesity were also analyzed.

SETTING

Academic institution.

PATIENTS

Benign endometrial tissues from premenopausal women were obtained following written consent.

MAIN OUTCOME MEASURES

Gene expression, protein expression, chromatin binding, and expression of DNA damage and oxidative damage markers were measured.

RESULTS

Under high-adiposity conditions, endometrial organoids downregulated endometrial secretory phase genes, suggestive of an altered progesterone response. Progesterone specifically upregulated the metallothionein (MT) gene family in the epithelial cells of endometrial organoids, while high adiposity significantly downregulated the MT genes. Silencing MT genes in endometrial epithelial cells resulted in increased DNA damage, illustrating the protective role of MTs. Native endometrium from women with obesity displayed increased MT expression and oxidative damage in the stroma and not in the epithelium, indicating the cell-specific impact of obesity on MT genes.

CONCLUSIONS

Taken together, the in vitro and in vivo systems used here revealed that high adiposity or obesity can alter MT expression by decreasing progesterone response in the epithelial cells and increasing oxidative stress in the stroma.

The HAPSTR2 retrogene buffers stress signaling and resilience in mammals

We recently identified HAPSTR1 (C16orf72) as a key component in a novel pathway which regulates the cellular response to molecular stressors, such as DNA damage, nutrient scarcity, and protein misfolding. Here, we identify a functional paralog to HAPSTR1: HAPSTR2. HAPSTR2 formed early in mammalian evolution, via genomic integration of a reverse transcribed HAPSTR1 transcript, and has since been preserved under purifying selection. HAPSTR2, expressed primarily in neural and germline tissues and a subset of cancers, retains established biochemical features of HAPSTR1 to achieve two functions. In normal physiology, HAPSTR2 directly interacts with HAPSTR1, markedly augmenting HAPSTR1 protein stability in a manner independent from HAPSTR1's canonical E3 ligase, HUWE1. Alternatively, in the context of HAPSTR1 loss, HAPSTR2 expression is sufficient to buffer stress signaling and resilience. Thus, we discover a mammalian retrogene which safeguards fitness.

ISL2 is a putative tumor suppressor whose epigenetic silencing reprograms the metabolism of pancreatic cancer

Pancreatic ductal adenocarcinoma (PDA) cells reprogram their transcriptional and metabolic programs to survive the nutrient-poor tumor microenvironment. Through in vivo CRISPR screening, we discovered islet-2 (ISL2) as a candidate tumor suppressor that modulates aggressive PDA growth. Notably, ISL2, a nuclear and chromatin-associated transcription factor, is epigenetically silenced in PDA tumors and high promoter DNA methylation or its reduced expression correlates with poor patient survival. The exogenous ISL2 expression or CRISPR-mediated upregulation of the endogenous loci reduces cell proliferation. Mechanistically, ISL2 regulates the expression of metabolic genes, and its depletion increases oxidative phosphorylation (OXPHOS). As such, ISL2-depleted human PDA cells are sensitive to the inhibitors of mitochondrial complex I in vitro and in vivo. Spatial transcriptomic analysis shows heterogeneous intratumoral ISL2 expression, which correlates with the expression of critical metabolic genes. These findings nominate ISL2 as a putative tumor suppressor whose inactivation leads to increased mitochondrial metabolism that may be exploitable therapeutically.

Abstract 2360: Deregulated APA and cancer specific APA isoforms

Certain aspects of diagnosis, prognosis, and treatment of cancer patients are still important challenges to be addressed. We developed a pipeline to uncover patterns of alternative polyadenylation (APA), a hidden complexity in cancer transcriptomes, to further accelerate efforts to discover novel cancer genes and pathways. Here, we found a significant shift in usage of poly(A) signals in six common tumor types compared to normal tissues. We further defined specific subsets of APA events to efficiently classify cancer types/subtypes. Triple negative breast cancers, for example, have specific 3'UTR length alterations where the significant majority are shortening events (70%, 113 of 165) of mostly proliferation-related transcripts compared with normal breast tissue. Such shortening events correlate with increased protein levels and relapse free survival of patients, suggesting functional significance of isoform variability. In line with this isoform diversity, we also detected deregulated expression of mRNA polyadenylation complex proteins in breast cancer cells. Of note, APA proteins are responsive to proliferative signals including estrogen and epidermal growth factor, suggesting a potential explanation to 3'-end isoform diversity in cancer cells. Overall, our study offers a computational and experimental approach for use of APA in novel gene discovery and classification in common tumor types, with important implications in basic research, biomarker discovery, and precision medicine approaches.

Citation Format: Oguzhan Begik, Melda Ercan, Harun Cingoz, Tolga Can, Merve Oyken, Ayse Elif Erson-Bensan. Deregulated APA and cancer specific APA isoforms [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2360.