THE MTCP-1 C6.1B GENE ENCODES FOR A CYTOPLASMIC 8-KD PROTEIN OVEREXPRESSED IN T-CELL LEUKEMIA BEARING A T(X,14)-TRANSLOCATION

The t(X;14)(q28;q11.2) translocation is associated with mature T-cell proliferations. Recently this translocation has been shown to implicat e the MTCP-1/c6.1B gene on chromosome Xq28, leading to aberrant or ove rexpressed MTCP-1 transcripts. The potential coding role of this gene was made uncertain by the lack of a long open reading frame in its maj or transcripts. However, a short 204 bases open reading frame is poten tially coding for a 68 amino-acid protein. Here, we show that this ope n reading frame sequence and the deduced product are well conserved in mouse. A 8 kD protein (p8), which corresponds to the predicted molecu lar weight was revealed in transient transfectants and in cell lines b y Western blotting, using a rabbit antiserum. This product was absent in lymphoblastoid cell lines with deletions of the MTCP-1/c6.1B locus. A dramatic overexpression of p8 was found in leukemic cells from a pa tient with a t(X;14). This small protein was localized in the cytoplas m by immunofluorescence. In conclusion, MTCP-1 encodes for a cytoplasm ic 8 kD product. Its potential role in leukemogenesis is supported by its overexpression in leukemia with t(X;14), but its function remains unknown.