Atp2c2 Is Transcribed From a Unique Transcriptional Start Site in Mouse Pancreatic Acinar Cells

Integrative single-cell characterization of a frugivorous and an insectivorous bat kidney and pancreas

Frugivory evolved multiple times in mammals, including bats. However, the cellular and molecular components driving it remain largely unknown. Here, we use integrative single-cell sequencing (scRNA-seq and scATAC-seq) on insectivorous (Eptesicus fuscus; big brown bat) and frugivorous (Artibeus jamaicensis; Jamaican fruit bat) bat kidneys and pancreases and identify key cell population, gene expression and regulatory differences associated with the Jamaican fruit bat that also relate to human disease, particularly diabetes. We find a decrease in loop of Henle and an increase in collecting duct cells, and differentially active genes and regulatory elements involved in fluid and electrolyte balance in the Jamaican fruit bat kidney. The Jamaican fruit bat pancreas shows an increase in endocrine and a decrease in exocrine cells, and differences in genes and regulatory elements involved in insulin regulation. We also find that these frugivorous bats share several molecular characteristics with human diabetes. Combined, our work provides insights from a frugivorous mammal that could be leveraged for therapeutic purposes.

Integrative single-cell characterization of frugivory adaptations in the bat kidney and pancreas

Frugivory evolved multiple times in mammals, including bats. However, the cellular and molecular components driving it remain largely unknown. Here, we used integrative single-cell sequencing on insectivorous and frugivorous bat kidneys and pancreases and identified key cell population, gene expression and regulatory element differences associated with frugivorous adaptation that also relate to human disease, particularly diabetes. We found an increase in collecting duct cells and differentially active genes and regulatory elements involved in fluid and electrolyte balance in the frugivore kidney. In the frugivorous pancreas, we observed an increase in endocrine and a decrease in exocrine cells and differences in genes and regulatory elements involved in insulin regulation. Combined, our work provides novel insights into frugivorous adaptation that also could be leveraged for therapeutic purposes.

Subtype specific targeting of calcium signaling in breast cancer

An important component of breast milk, calcium also appears as radiographically prominent microcalcifications in breast tissue that are often the earliest sign of malignancy. Ionic Ca²⁺ is a universal second messenger that controls a wide swathe of effector pathways integral to gene transcription, cell cycle control, differentiation, proliferation, cell migration, and apoptosis. Whereas prolonged elevation in resting Ca²⁺ levels drives proliferation to initiate and sustain tumor growth, depletion of calcium stores and attenuation of calcium influx pathways underlies tumor chemoresistance and evasion of apoptosis. This paradox of Ca²⁺ homeostasis highlights the challenge of targeting Ca²⁺ signaling pathways for breast cancer therapy. Furthermore, breast cancer is a heterogeneous disease classified into distinct subtypes based on tumor origin, stage of invasiveness and hormone receptor status. Classification is important for tailoring treatment, and in predicting clinical outcome or response to chemotherapy. There have been numerous reports of dysregulated expression, localization or activity of Ca²⁺ channels, regulators and pumps in breast cancer. An important aspect of these alterations is that they are specific to breast cancer subtype, as exemplified by a reciprocal switch in secretory pathway Ca²⁺-ATPase isoforms SPCA1 and SPCA2 depending on receptor status. In this review, we discuss the current knowledge of subtype specific changes in calcium channels and pumps, with a focus on functional insights that may inform new opportunities for breast cancer therapy.

The pancreas-specific form of secretory pathway calcium ATPase 2 regulates multiple pathways involved in calcium homeostasis

Acinar cell exocytosis requires spatiotemporal Ca²⁺ signals regulated through endoplasmic reticulum (ER) stores, Ca²⁺ATPases, and store-operated Ca²⁺ entry (SOCE). The secretory pathway Ca²⁺ATPase 2 (SPCA2) interacts with Orai1, which is involved in SOCE and store independent Ca²⁺ entry (SICE). However, in the pancreas, only a C-terminally truncated form of SPCA2 (termed SPAC2C) exists. The goal of this study was to determine if SPCA2C effects Ca²⁺ homeostasis in a similar fashion to the full-length SPCA2. Using epitope-tagged SPCA2C (SPCA2C^FLAG) expressed in HEK293A cells and Fura2 imaging, cytosolic [Ca²⁺] was examined during SICE, SOCE and secretagogue-stimulated signaling. Exogenous SPCA2C expression increased resting cytosolic [Ca²⁺], Ca²⁺ release in response to carbachol, ER Ca²⁺ stores, and store-mediated and independent Ca²⁺ influx. Co-IP detected Orai1-SPCA2C interaction, which was altered by co-expression of STIM1. Importantly, SPCA2C's effects on store-mediated Ca²⁺ entry were independent of Orai1. These findings indicate SPCA2C influences Ca²⁺ homeostasis through multiple mechanisms, some of which are independent of Orai1, suggesting novel and possibly cell-specific Ca²⁺ regulation.

Genome-wide DNA methylation analysis reveals loci that distinguish different types of adipose tissue in obese individuals

BACKGROUND

Epigenetic mechanisms provide an interface between environmental factors and the genome and are known to play a role in complex diseases such as obesity. These mechanisms, including DNA methylation, influence the regulation of development, differentiation and the establishment of cellular identity. Here we employ two approaches to identify differential methylation between two white adipose tissue depots in obese individuals before and after gastric bypass and significant weight loss. We analyse genome-wide DNA methylation data using (a) traditional paired t tests to identify significantly differentially methylated loci (Bonferroni-adjusted P ≤ 1 × 10^-7) and (b) novel combinatorial algorithms to identify loci that differentiate between tissue types.

RESULTS

Significant differential methylation was observed for 3239 and 7722 CpG sites, including 784 and 1129 extended regions, between adipose tissue types before and after significant weight loss, respectively. The vast majority of these extended differentially methylated regions (702) were consistent across both time points and enriched for genes with a role in transcriptional regulation and/or development (e.g. homeobox genes). Other differentially methylated loci were only observed at one time point and thus potentially highlight genes important to adipose tissue dysfunction observed in obesity. Strong correlations (r > 0.75, P ≤ 0.001) were observed between changes in DNA methylation (subcutaneous adipose vs omentum) and changes in clinical trait, in particular for CpG sites within PITX2 and fasting glucose and four CpG sites within ISL2 and HDL. A single CpG site (cg00838040, ATP2C2) gave strong tissue separation, with validation in independent subcutaneous (n = 681) and omental (n = 33) adipose samples.

CONCLUSIONS

This is the first study to report a genome-wide DNA methylome comparison of subcutaneous abdominal and omental adipose before and after weight loss. The combinatorial approach we utilised is a powerful tool for the identification of methylation loci that strongly differentiate between these tissues. This study provides a solid basis for future research focused on the development of adipose tissue and its potential dysfunction in obesity, as well as the role DNA methylation plays in these processes.

The Ca2+/Mn2+-transporting SPCA2 pump is regulated by oxygen and cell density in colon cancer cells

The mammalian SPCA1 and SPCA2 ATPases localize in membranes of the secretory pathway and transport ions of Ca(2+) and Mn(2+) The role of tissue-specific SPCA2 isoform, highly expressed in lungs, mammary gland and gastrointestinal tract, is poorly understood. To elucidate the function of SPCA2, we studied human colon cancer HCT116 cells, grown under ambient and decreased O2 levels. We found that in contrast with other Ca(2+)-ATPase isoforms the expression of SPCA2 was up-regulated under hypoxia (3% O2), in both adherent (2D) and spheroid (3D) cultures. In spheroids, experiencing lowest O2 levels (30-50 μM, measured by phosphorescence lifetime imaging microscopy), we observed lower staining with reactive oxygen species (ROS)-specific fluorescent probe, which correlated with increased SPCA2. However, SPCA2 expression was up-regulated in cells exposed to reactive oxygen and nitrogen species donors, and when grown at higher density. We noticed that the culture exposed to hypoxia showed overall increase in S phase-positive cells and hypothesized that SPCA2 up-regulation under hypoxia can be linked to Mn(2+)-dependent cell cycle arrest. Consequently, we found that SPCA2-transfected cells display a higher number of cells entering S phase. Altogether, our results point at the important role of SPCA2 in regulation of cell cycle in cancer cells.