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Seema Somji, Chandra S. Bathula, Xu Dong Zhou, Mary Ann Sens, Donald A. Sens, and Scott H. Garrett

Department of Pathology, School of Medicine and Health Sciences, University of North Dakota, Grand Forks, North Dakota, USA

Abstract
Background: Cadmium and arsenite can directly and malignantly transform the UROtsa cell line. The tumor heterotransplants produced from these transformed cells have histologic features consistent with human bladder cancer. Previous microarray analysis of total RNA from the parental and transformed cells suggested that keratin 6a was overexpressed as a result of cell transformation.

Objectives: Our goals were to verify overexpression of keratin 6a in Cd²⁺- and As³⁺-transformed UROtsa cells, the corresponding tumor heterotransplants, and human bladder cancer biopsy specimens and to assess what factors may be involved in keratin 6a overexpression.

Methods: Expression was assessed with real-time polymerase chain reaction, Western blot analysis, and immunohistochemistry. We used the effect of addition and deletion of potential growth factors in the cell culture growth medium to assess possible pathways used in keratin 6a overexpression.

Results: Cd²⁺- and As³⁺-transformed cells grown in serum-containing growth medium, as well as the derived tumor heterotransplants, overexpressed keratin 6a mRNA and protein compared with UROtsa cells grown in serum-containing growth medium. Immunostaining of keratin 6a in tumor heterotransplants showed focal staining of the tumor cells that was localized to the cytoplasm. Focal immunostaining of keratin 6a was also found in some but not all archival patient specimens of high-grade bladder cancer, confirming translation of the results to human bladder cancer. Studies on growth factor deletion and addition indicated that the level of keratin 6a expression was regulated by the presence of both insulin and epidermal growth factor (EGF) . In contrast, growth factors had no effect on the elevated levels of keratin 6a expression found in transformed UROtsa cells.

Conclusions: Our present studies suggest that keratin 6a expression may be a biomarker for malignant urothelial cells that possess an activated EGF and or insulin growth factor pathway.

Key words: arsenic, bladder cancer, cadmium, keratin, urothelium, UROtsa. Environ Health Perspect 116:434–440 (2008) . doi:10.1289/ehp.10279 available via http://dx.doi.org/ [Online 17 December 2007]

Address correspondence to S.H. Garrett, Department of Pathology, School of Medicine and Health Sciences, University of North Dakota, 501 N. Columbia Rd., Grand Forks, ND 58202 USA. Telephone: (701) 777-2657. Fax: (701) 777-3108. E-mail: sgarrett@medicine.nodak.edu

This project was supported by grants R01 CA094997 from the National Cancer Institute and R01 ES015100 from the National Institute of Environmental Health Sciences, National Institutes of Health (NIH) .

The contents of this article are solely the responsibility of the authors and do not necessarily represent the official views of the NIH.

The authors declare they have no competing financial interests.

Received 19 March 2007 ; accepted 17 December 2007.