抄録
The FXYD family proteins are small proteins which contain a single transmembrane domain, and the conserved FXYD (Phe-Xaa-Tyr-Asp) motif in the ectodomain. They associate with the Na+,K+-ATPase to modulate its function. They also modulate epithelial membrane transport of small solutes and ions. Among seven members of human FXYD proteins, the FXYD3 (Mat-8) associates with the Na+,K+-ATPase , and slightly decreases its affinity for Na+ and K+. The FXYD3 was also involved in cell proliferation and tumorigenesis. Its mRNA was highly expressed in human and murine breast tumors. However, there has been no report about the relationship between cell proliferation and modulation of Na+,K+-ATPase function by the FXYD3. Here, we studied the mRNA and protein expression of FXYD3 in human cultured cell lines and normal tissues. The mRNA expression was high in a breast cancer cell line, MCF-7 and a pancreatic cancer cell line, T3M-4. Among normal tissues, the mRNA expression of FXYD3 was highest in colons. By using a monoclonal antibody raised against human FXYD3, the protein was observed as a single band with a molecular mass of 13 kDa in the membrane fraction of human colon mucosae as well as MCF-7 and T3M4 cells. It should be noted that the FXYD3 protein was down-regulated in human colorectal cancers compared with the surrounding normal mucosae. [J Physiol Sci. 2007;57 Suppl:S45]
