Inorganic Arsenic–Related Changes in the Stromal Tumor Microenvironment in a Prostate Cancer Cell–Conditioned Media Model

Abstract

Background:The tumor microenvironment plays an important role in the progression of cancer by mediating stromal–epithelial paracrine signaling, which can aberrantly modulate cellular proliferation and tumorigenesis. Exposure to environmental toxicants, such as inorganic arsenic (iAs), has also been implicated in the progression of prostate cancer.Objective:The role of iAs exposure in stromal signaling in the tumor microenvironment has been largely unexplored. Our objective was to elucidate molecular mechanisms of iAs-induced changes to stromal signaling by an enriched prostate tumor microenvironment cell population, adipose-derived mesenchymal stem/stromal cells (ASCs).Results:ASC-conditioned media (CM) collected after 1 week of iAs exposure increased prostate cancer cell viability, whereas CM from ASCs that received no iAs exposure decreased cell viability. Cytokine array analysis suggested changes to cytokine signaling associated with iAs exposure. Subsequent proteomic analysis suggested a concentration-dependent alteration to the HMOX1/THBS1/TGFβ signaling pathway by iAs. These results were validated by quantitative reverse transcriptase–polymerase chain reaction (RT-PCR) and Western blotting, confirming a concentration-dependent increase in HMOX1 and a decrease in THBS1 expression in ASC following iAs exposure. Subsequently, we used a TGFβ pathway reporter construct to confirm a decrease in stromal TGFβ signaling in ASC following iAs exposure.Conclusions:Our results suggest a concentration-dependent alteration of stromal signaling: specifically, attenuation of stromal-mediated TGFβ signaling following exposure to iAs. Our results indicate iAs may enhance prostate cancer cell viability through a previously unreported stromal-based mechanism. These findings indicate that the stroma may mediate the effects of iAs in tumor progression, which may have future therapeutic implications.Citation:Shearer JJ, Wold EA, Umbaugh CS, Lichti CF, Nilsson CL, Figueiredo ML. 2016. Inorganic arsenic–related changes in the stromal tumor microenvironment in a prostate cancer cell–conditioned media model. Environ Health Perspect 124:1009–1015; http://dx.doi.org/10.1289/ehp.1510090

In Vivo Exposure to Inorganic Arsenic Alters Differentiation-Specific Gene Expression of Adipose-Derived Mesenchymal Stem/Stromal Cells in C57BL/6J Mouse Model

“…Interestingly, the changes we identified in our differentiationspecific gene panels mirrored the changes detected in TGFb expression as assessed by RT-qPCR. We have shown in previous studies that iAs is able to alter TGFb signaling in human ASCs in vitro (Shearer et al, 2016), which might explain the concentration-dependent decrease in osteogenic/chondrogenicrelated genes seen in the present study.…”

“…The remaining mice (N ¼ 3, per exposure) continuously received iAs H 2 O for 3 more weeks in order to monitor the stability of urinary arsenic levels over time. We chose these concentrations by mimicking the exposure required to induce a similar induction in heme-oxygenase 1 gene expression in mouse ASCs (300 ppb) relative to human ASCs (75 ppb) in vitro (data not shown), which we previously have suggested plays a role in altering ASC signaling (Shearer et al, 2016). Exposure to 75 ppb iAs in humans represents a high level of arsenic that exceeds the safety limit set by the EPA but is not uncommon in certain portions of the world including Bangladesh who are at times exposed to levels of iAs exceeding 300 ppb (Smith et al, 2000).…”

“…Western blot analysis was performed as previously described (Shearer et al, 2016), with minor modifications. Thirty micrograms total protein per isolated ASC group pre-and post-differentiation following iAs exposure in vivo (N ¼ 1) was assessed as follows, Smad 2/3 (catalog no.…”

“…One environmental contaminant of particular concern is inorganic arsenic (iAs), which we have demonstrated previously can adversely affect the secretome associated with ASCs in vitro following as little as 1 week of exposure (Shearer et al, 2016). iAs is a ubiquitously distributed environmental contaminant found in food, the air, and many sources of drinking water.…”

Low-level arsenic exposure from drinking water is associated with prostate cancer in Iowa

“…Based on these studies several mechanisms of arsenic-induction of prostate cancer have been proposed including overexpression of matrix metalloproteinase-9, heme oxygenase-1, and ras, the decreased expression of thrombospondin, and the induction of acquired androgen independence (Benbrahim-Tallaa and Waalkes, 2008; Benbrahim-Tallaa et al, 2005; Benbrahim-Tallaa et al, 2007; Witz, 2008). In a recent study, the alteration of stromal TGFβ signaling by arsenic exposure was shown to be related to progression of prostate cancer (Shearer et al, 2016). …”