A nongenomic mechanism for "metalloestrogenic" effects of cadmium in human uterine leiomyoma cells through G protein-coupled estrogen receptor.

Cadmium (Cd) is a ubiquitous environmental metal that is reported to be a "metalloestrogen." Uterine leiomyomas (fibroids) are estrogen-responsive gynecologic neoplasms that can be the target of xenoestrogens. Previous epidemiology studies have suggested Cd may be associated with fibroids. We have shown that Cd can stimulate proliferation of human uterine leiomyoma (ht-UtLM) cells, but not through classical estrogen receptor (ER) binding. Whether nongenomic ER pathways are involved in Cd-induced proliferation is unknown. In the present study, by evaluating G protein-coupled estrogen receptor (GPER), ERα36, and phospho-epidermal growth factor receptor (EGFR) expression in human tissues, we found that GPER, ERα36 and phospho-EGFR were all highly expressed in fibroids compared to patient-matched myometrial tissues. In ht-UtLM cells, cell proliferation was increased by low doses of Cd (0.1 µM and 10 µM), and this effect could be inhibited by GPER-specific antagonist (G15) pretreatment, or silencing (si) GPER, but not by siERα36. Cd-activated MAPK was dependent on GPER/EGFR transactivation, through significantly increased phospho-Src, matrix metalloproteinase-2 (MMP2) and MMP9, and heparin-binding EGF-like growth factor (HB-EGF) expression/activation. Also, phospho-Src could interact directly to phosphorylate EGFR. Overall, Cd-induced proliferation of human fibroid cells was through a nongenomic GPER/p-src/EGFR/MAPK signaling pathway that did not directly involve ERα36. This suggests that Cd may be a risk factor for uterine fibroids through cross talk between hormone and growth factor receptor pathways.

Osmotic stress resistance imparts acquired anti-apoptotic mechanisms in lymphocytes.

Apoptosis is a stochastic, physiological form of cell death that is characterized by unique morphological and biochemical properties. A defining feature of apoptosis in all cells is the apoptotic volume decrease or AVD, which has been considered a passive component of the cell death process. Most cells have inherent volume regulatory increase (RVI) mechanisms to contest an imposed loss in cell size, however T-cells are unique in that they do not have a RVI response. We utilized this property to explore potential regulatory roles of a RVI response in apoptosis. Exposure of immature T-cells to hyperosmotic stress resulted in a rapid, synchronous, and caspase-dependent apoptosis. Multiple rounds of osmotic stress followed by recovery of cells in normal media resulted in the development of a population of cells that were resistant to osmotic stress induced apoptosis. These cells were also resistant to other apoptotic stimuli that activate via the intrinsic cell death pathway, while remaining sensitive to extrinsic apoptotic stimuli. Interestingly, these osmotic stress resistant cells showed no increase in anti-apoptotic proteins, and released cytochrome c from their mitochondria following exposure to intrinsic apoptotic stimuli. The osmotic stress resistant cells developed a RVI response, and inhibition of the RVI restored sensitivity to apoptotic agents. Analysis of apoptotic signaling pathways showed a sustained increase in phospho-AKT, whose inhibition also prevented an RVI response resulting in apoptosis. These results define a critical role of volume regulation mechanisms in apoptotic resistance.

Functional Pdgfra fibroblast heterogeneity in normal and fibrotic mouse lung.

Aberrant fibroblast function plays a key role in the pathogenesis of idiopathic pulmonary fibrosis, a devastating disease of unrelenting extracellular matrix deposition in response to lung injury. Platelet-derived growth factor α-positive (Pdgfra+) lipofibroblasts (LipoFBs) are essential for lung injury response and maintenance of a functional alveolar stem cell niche. Little is known about the effects of lung injury on LipoFB function. Here, we used single-cell RNA-Seq (scRNA-Seq) technology and PdgfraGFP lineage tracing to generate a transcriptomic profile of Pdgfra+ fibroblasts in normal and injured mouse lungs 14 days after bleomycin exposure, generating 11 unique transcriptomic clusters that segregated according to treatment. While normal and injured LipoFBs shared a common gene signature, injured LipoFBs acquired fibrogenic pathway activity with an attenuation of lipogenic pathways. In a 3D organoid model, injured Pdgfra+ fibroblast-supported organoids were morphologically distinct from those cultured with normal fibroblasts, and scRNA-Seq analysis suggested distinct transcriptomic changes in alveolar epithelia supported by injured Pdgfra+ fibroblasts. In summary, while LipoFBs in injured lung have not migrated from their niche and retain their lipogenic identity, they acquire a potentially reversible fibrogenic profile, which may alter the kinetics of epithelial regeneration and potentially contribute to dysregulated repair, leading to fibrosis.

A novel role for the T-box transcription factor Tbx1 as a negative regulator of tumor cell growth in mice.

The T-box transcription factor, Tbx1, an important regulatory gene in development, is highly expressed in hair follicle (HF) stem cells in adult mice. Because mouse models of skin carcinogenesis have demonstrated that HF stem cells are a carcinogen target population and contribute significantly to tumor development, we investigated whether Tbx1 plays a role in skin carcinogenesis. We first assessed Tbx1 expression levels in mouse skin tumors, and found down-regulation in all tumors examined. To study the effect of Tbx1 expression on growth and tumorigenic potential of carcinoma cells, we transfected mouse Tbx1 cDNA into a mouse spindle cell carcinoma cell line that did not express endogenous Tbx1. Following transfection, two cell lines expressing different levels of the Tbx1/V5 fusion protein were selected for further study. Intradermal injection of the cell lines into mice revealed that Tbx1 expression significantly suppressed tumor growth, albeit with no change in tumor morphology. In culture, ectopic Tbx1 expression resulted in decreased cell growth and reduced development into multilayered colonies, compared to control cells. Tbx1-transfectants exhibited a reduced proliferative rate compared to control cells, with fewer cells in S and G2/M phases. The Tbx1 transfectants developed significantly fewer colonies in soft agar, demonstrating loss of anchorage-independent growth. Taken together, our data show that ectopic expression of Tbx1 restored contact inhibition to the skin tumor cells, suggesting that this developmentally important transcription factor may have a novel dual role as a negative regulator of tumor growth. © 2011 Wiley Periodicals, Inc.

Bisphenol A induces human uterine leiomyoma cell proliferation through membrane-associated ERα36 via nongenomic signaling pathways.

The role of ERα36 in regulating BPA's effects and its potential as a risk factor for human uterine fibroids were evaluated. BPA at low concentrations (10-6 µM - 10 µM) increased proliferation by facilitating progression of hormonally regulated, immortalized human uterine leiomyoma (ht-UtLM; fibroid) cells from G0-G1 into S phase of the cell cycle; whereas, higher concentrations (100 µM-200 µM) decreased growth. BPA upregulated ERα36 gene and protein expression, and induced increased SOS1 and Grb2 protein expression, both of which are mediators of the MAPKp44/42/ERK1/2 pathway. EGFR (pEGFR), Ras, and MAPKp44/42 were phosphorylated with concurrent Src activation in ht-UtLM cells within 10 min of BPA exposure. BPA enhanced colocalization of phosphorylated Src (pSrc) to ERα36 and coimmunoprecipitation of pSrc with pEGFR. Silencing ERα36 with siERα36 abolished the above effects. BPA induced proliferation in ht-UtLM cells through membrane-associated ERα36 with activation of Src, EGFR, Ras, and MAPK nongenomic signaling pathways.

New approaches for determining apoptotic volume decrease in cells.

The loss of cell volume or cell shrinkage, termed apoptotic volume decrease (AVD), is a classical characteristic of apoptosis. Microscopy, Coulter electronic sizing, and/or flow cytometry has traditionally been the means to measure this characteristic of apoptosis. Although electronic cell sizing allows for precise determination of changes in cell size, these measurements provide data on the entire population of apoptotic cells. In contrast, flow cytometry examines and separates unique populations of apoptotic cells based on the light-scattering properties of the cells to determine alterations in cellular dimensions. However, this technique does not provide exact measurements of cell size and volume. The Cell Lab Quanta SC flow cytometer combines the power of electronic sizing with the ability to isolate and examine unique populations of apoptotic cells to determine exact changes in cell size as they undergo cell death. This chapter describes several methods for using the Cell Lab Quanta SC to study AVD during apoptosis.

Cationic gradient reversal and cytoskeleton-independent volume regulatory pathways define an early stage of apoptosis.

Cell shrinkage, or apoptotic volume decrease (AVD), is a ubiquitous characteristic of programmed cell death that is independent of the death stimulus and occurs in all examples of apoptosis. Here we distinguished two specific stages of AVD based on cell size and a unique early reversal of intracellular ions that occurs in response to activation of both intrinsic and extrinsic cell death signal pathways. The primary stage of AVD is characterized by an early exchange of the normal intracellular ion distribution for sodium from 12 to 113.6 mm and potassium from 139.5 to 30 mm. This early ionic reversal is associated with a 20-40% decrease in cell volume, externalization of phosphatidylserine, loss of mitochondrial membrane potential, and caspase activation and activity along with nuclear condensation that occurs independent of actin cytoskeleton disruption. Disruption of the actin cytoskeleton, however, prevents a secondary stage of AVD in apoptotic cells, characterized by a loss of both potassium and sodium that results in an 80-85% loss in cell volume, DNA degradation, and apoptotic body formation. Together these studies demonstrate that AVD occurs in two distinct stages with the earliest stage reflecting a cellular cationic gradient reversal.

Arsenic-induced aberrant gene expression in fetal mouse primary liver-cell cultures.

Exposure of maternal mice to inorganic arsenic through the drinking water induces liver tumors and aberrant gene expression in offspring when they reach adulthood. To help define if these are direct fetal effects of arsenic, fetal liver cells were isolated from untreated mice at gestation day 13.5 by mechanical dissection and centrifugation. Two hours after seeding the cells on collagen1-coated plates in William E media containing 10% fetal bovine serum, 1x ITS (insulin, transferrin, and selenium) and antibiotics, inorganic arsenite (0, 0.1, 0.3, and 1.0 microM) was added to the fresh media for 72 h. Cell morphology and viability were not significantly altered by these arsenic concentrations. At the end of arsenic exposure, cells were harvested into Trizol, and total RNA was extracted, purified, and subjected to real-time reverse transcriptase polymerase chain reaction (RT-PCR) analysis. Arsenite exposure produced a concentration-dependent induction of heme oxygenase-1 (up to eight-fold) and metallothionein-1 (up to five-fold), indicative of stress response to adapt to arsenic insult. Expression of genes related to steroid metabolism, such as 17beta-hydroxysteroid dehydrogenase-7 (HSD17beta7) and Cyp2a4, were increased approximately two-fold, together with increases in estrogen receptor-alpha (ER-alpha) and ER-alpha-linked genes, such as anterior gradient-2, keratin 1-19, and trefoil factor-3. Arsenic in vitro induced a three-fold increase in the expression of alpha-fetoprotein (AFP), a biomarker associated with transplacental arsenic-induced mouse liver tumors. Thus, exposure of mouse fetal liver cells to arsenic induces adaptive responses and aberrant gene expression, which could alter genetic programming at a very early life stage, potentially contributing to tumor formation much later in life.

Glutathione depletion and disruption of intracellular ionic homeostasis regulate lymphoid cell apoptosis.

Intracellular glutathione (GSH) depletion is an important hallmark of apoptosis. We have recently shown that GSH depletion by its extrusion regulates apoptosis independently of excessive reactive oxygen species accumulation. However, the mechanisms by which GSH depletion regulates apoptosis are still unclear. Because disruption of intracellular ionic homeostasis, associated with apoptotic volume decrease (AVD), is necessary for the progression of apoptotic cell death, we sought to evaluate the relationship between GSH transport and ionic homeostasis during Fas ligand (FasL)-induced apoptosis in Jurkat cells. GSH depletion in response to FasL was paralleled by distinct degrees of AVD identified by differences in cellular forward scatter and electronic impedance analysis. Inhibition of GSH efflux prevented AVD, K+ loss, and the activation of two distinct ionic conductances, mediated by Kv1.3 and outward rectifying Cl- channels. Reciprocally, stimulation of GSH loss accelerated the loss of K+, AVD, and consequently the progression of the execution phase of apoptosis. Although high extracellular K+ inhibited FasL-induced apoptosis, GSH depletion was largely independent of K+ loss. These results suggest that deregulation of GSH and ionic homeostasis converge in the regulation of apoptosis in lymphoid cells.