Article Aberrant Expression of ZIP and ZnT Zinc Transporters in UROtsa Cells Transformed to Malignant Cells by Cadmium Soisungwan Satarug 1,2, *, Scott H. Garrett 2 , Seema Somji 2 , Mary Ann Sens 2 and Donald A. Sens 2   Citation: Satarug, S.; Garrett, S.H.; Somji, S.; Sens, M.A.; Sens, D.A. Aberrant Expression of ZIP and ZnT Zinc Transporters in UROtsa Cells Transformed to Malignant Cells by Cadmium. Stresses 2021, 1, 78–89. https://doi.org/10.3390/ stresses1020007 Academic Editor: Luigi Sanita’ di Toppi Received: 18 March 2021 Accepted: 21 April 2021 Published: 22 April 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 Kidney Disease Research Collaborative, Centre for Health Service Research, The University of Queensland Translational Research Institute, Woolloongabba, Brisbane 4102, Australia 2 Department of Pathology, University of North Dakota School of Medicine and Health Sciences, Grand Forks, ND 58202, USA; scott.garrett@med.und.edu (S.H.G.); seema.somji@med.und.edu (S.S.); mary.sens@med.und.edu (M.A.S.); donald.sens@med.und.edu (D.A.S.) * Correspondence: sj.satarug@yahoo.com.au Abstract: Maintenance of zinc homeostasis is pivotal to the regulation of cell growth, differentiation, apoptosis, and defense mechanisms. In mammalian cells, control of cellular zinc homeostasis is through zinc uptake, zinc secretion, and zinc compartmentalization, mediated by metal transporters of the Zrt-/Irt-like protein (ZIP) family and the Cation Diffusion Facilitators (CDF) or ZnT family. We quantified transcript levels of ZIP and ZnT zinc transporters expressed by non-tumorigenic UROtsa cells and compared with those expressed by UROtsa clones that were experimentally transformed to cancer cells by prolonged exposure to cadmium (Cd). Although expression of the ZIP8 gene in parent UROtsa cells was lower than ZIP14 (0.1 vs. 83 transcripts per 1000 β-actin transcripts), an increased expression of ZIP8 concurrent with a reduction in expression of one or two zinc influx transporters, namely ZIP1, ZIP2, and ZIP3, were seen in six out of seven transformed UROtsa clones. Aberrant expression of the Golgi zinc transporters ZIP7, ZnT5, ZnT6, and ZnT7 were also observed. One transformed clone showed distinctively increased expression of ZIP6, ZIP10, ZIP14, and ZnT1, with a diminished ZIP8 expression. These data suggest intracellular zinc dysregulation and aberrant zinc homeostasis both in the cytosol and in the Golgi in the transformed UROtsa clones. These results provide evidence for zinc dysregulation in transformed UROtsa cells that may contribute in part to their malignancy and/or muscle invasiveness. Keywords: bladder cancer; cadmium; gene expression; qRT/PCR; zinc homeostasis; zinc trans- porters; ZIP; ZnT 1. Introduction Cadmium (Cd) is one of the environmental toxicants of continuing public health concern worldwide due to its persistence, widespread exposure, and wide-ranging adverse health effects, cancer risk included [1–3]. Although Cd can be inhaled in polluted air as Cd oxide, it is acquired primarily from food or tobacco grown in contaminated soil [1–3]. Blood Cd levels in cigarette smokers were higher than non-smokers by 2 to 6 fold [2]. The International Agency for Research on Cancer has classified Cd as a cancer causing agent in humans [4]. However, the mechanism underlying the carcinogenicity of Cd remains elusive, as does the mechanism of its entry into a relevant target such as urinary bladder epithelium, where the metal Cd may initiate cancer cell transformation. Bladder cancer ranks the sixth most common cancer in the U.S., with annual incidence rates of 30 to 33 cases per 100,000. In most cases, cancer originated from the transitional cells of bladder mucosal epithelium, and it is named transitional cell carcinoma (TCC) [5–7]. One third of bladder cancer cases manifested as non-papillary tumors with high invasive and metastasis potential, while two thirds manifested as non-invasive, resettable papillary tumors, with recurrence rates between 30% and 70% [5]. Such high recurrence rates Stresses 2021, 1, 78–89. https://doi.org/10.3390/stresses1020007 https://www.mdpi.com/journal/stresses