Published online before print November 5, 2009

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(American Journal of Pathology. 2009;175:2646-2656.)
© 2009 American Society for Investigative Pathology
DOI: 10.2353/ajpath.2009.080571

Down-Regulation of FXYD3 Expression in Human Lung Cancers

Its Mechanism and Potential Role in Carcinogenesis

Koji Okudela^*, Takuya Yazawa^*, Jun Ishii^*, Tetsukan Woo, Hideaki Mitsui^*, Tomoyasu Bunai, Masashi Sakaeda^*, Hiroaki Shimoyamada^*, Hanako Sato^*¶, Michihiko Tajiri, Nobuo Ogawa, Munetaka Masuda, Haruhiko Sugimura^¶ and Hitoshi Kitamura^*

From the Departments of Pathology^* and Surgery, Yokohama City University Graduate School of Medicine, Yokohama; the Division of General Thoracic Surgery, Kanagawa Prefectural Cardiovascular and Respiratory Disease Center Hospital, Yokohama; the Department of Pathology, Hamamatsu Medical University, School of Medicine, Hamamatsu; and the Department of Anatomy,^¶ St. Marianna University School of Medicine, Kawasaki, Japan

FXYD3 is a FXYD-containing Na,K-ATPase ion channel regulator first identified as a protein overexpressed in murine breast tumors initiated by oncogenic ras or neu. However, our preliminary study revealed that FXYD3 expression was down-regulated in oncogenic KRAS-transduced airway epithelial cells. This contradiction led us to investigate the role of FXYD3 in carcinogenesis of the lung. FXYD3 mRNA and protein levels were lower in most of the lung cancer cell lines than in either the noncancerous lung tissue or airway epithelial cells. Protein levels were also lower in a considerable proportion of primary lung cancers than in nontumoral airway epithelia; FXYD3 expression levels decreased in parallel with the dedifferentiation process. Also, a somatic point mutation, g55c (D19H), was found in one cell line. Forced expression of the wild-type FXYD3, but not the mutant, restored the well-demarcated distribution of cortical actin in cancer cells that had lost FXYD3 expression, suggesting FXYD3 plays a role in the maintenance of cytoskeletal integrity. However, no association between FXYD3 expression and its promoter’s methylation status was observed. Therefore, inactivation of FXYD3 through a gene mutation or unknown mechanism could be one cause of the atypical shapes of cancer cells and play a potential role in the progression of lung cancer.