Selective expression of RT6 superfamily in human bronchial epithelial cells

RT6 proteins are glycosylphosphatidylinositol (GPI)-linked alloantigens tha t are localized to cytotoxic T lymphocytes and that have nicotinamide adeni ne dinucleotide glycohydrolase and adenosine diphosphate (ADP)-ribosyltrans ferase activities. In view of the importance, of GPI-linked surface protein s in mediating interactions of cells with their milieu, and the varied func tions of airway cells in inflammation, we undertook the present study to de termine whether human homologues of the RT6 superfamily of ADP-ribosyltrans ferases (ART) are expressed in pulmonary epithelial cells. We hypothesized that these surface proteins or related family members may be present in cel ls that interact with inflammatory cells, and that they may thereby be invo lved in intercellular signaling. Using in situ analysis and Northern blot a nalysis, we identified ART1 messenger RNA (mRNA) in airway epithelial cells . As expected for GPI-anchored proteins, the localization of ART1 at the ap ical surface of ciliated epithelial cells was demonstrated by staining with polyclonal anti-ART1 antibody, and was confirmed by loss of this immunorea ctivity after treatment with phosphatidylinositol-specific phospholipase C (PI-PLC), which selectively cleaves GPI anchors and releases proteins from the plasma membrane. Using in situ hybridization with specific ART3 and ART 4 oligonucleotides, we also identified two additional members of the RT6 su perfamily in epithelial cells. In accord with these findings, we identified ART3 and ART4 mRNAs through reverse transcription-polymerase chain reactio n of polyadenine-positive RNA from human trachea. Interestingly, these prot eins appeared to be preferentially localized to the airway epithelium. The localized expression of these members of the RT6 superfamily in human pulmo nary epithelial cells may reflect a role for them in cell-cell signaling du ring immune responses within the airway.