Characterization of the human Ly‐6 antigens, the newly annotated member Ly‐6K included, as molecular markers for head‐and‐neck squamous cell carcinoma

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Abstract
The E48 antigen is a successfully explored molecular marker for the diagnosis and therapy of HNSCC. The applicability of E48 as an HNSCC‐associated antigen, however, is restricted due to its heterogeneous expression in 30% of tumors; and identification of additional target antigens is therefore desired. E48 belongs to the Ly‐6 antigen family, comprising a group of highly homologous, low m.w., GPI‐anchored surface proteins, of which some show tissue‐restricted expression patterns. To identify novel human HNSCC‐associated Ly‐6 members with squamous cell‐associated expression patterns, we performed comprehensive gene‐screening consisting of BLAST searches within GenBank databases, followed by expression analysis. Using this approach, the Ly‐6K gene could be annotated as a novel member of the human Ly‐6 family. Expression of the human Ly‐6 genes E48, Ly‐6K, PSCA, GML,RIG‐E, G6C and Ly‐6H was prescreened by qualitative RT‐PCR and subsequently analyzed by quantitative RT‐PCR in normal keratinocytes, HNSCC cell lines, normal mucosa, HNSCC tumors as well as normal peripheral blood and bone marrow cells. PSCA was highly expressed in normal mucosa, but 100‐fold decreased expression was seen in HNSCC. For Ly‐6H, GML and G6C, no or very low expression was observed in keratinocytes and HNSCC. Expression of RIG‐E was high in normal and malignant squamous cells and in peripheral blood and bone marrow cells, thus limiting its applicability as an HNSCC‐associated marker. In contrast, besides the E48 gene, the Ly‐6K gene also appeared to be selectively expressed in HNSCC and normal squamous cells. Moreover, expression of Ly‐6K was shown in HNSCC cell lines, in which no E48 expression could be detected. These data justify further evaluation of Ly‐6K as potential target antigen for the diagnosis and therapy of HNSCC.

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