Molecular cloning of a gene on chromosome 19q12 coding for a novel intracellular protein: Analysis of expression in human and mouse tissues and in human tumor cells, particularly Reed-Sternberg cells in Hodgkin disease

A novel protein, named NNX3, was molecularly characterized by cloning its c DNA, and its gene was mapped to chromosome 19q12. The equivalent mouse cDNA and gene were also cloned to allow us to analyze expression in murine in a ddition to human cells and tissues. Human and mouse NNX3 genes are composed of nine exons coding for proteins that are unrelated to any known protein. Signal peptides and hydrophobic domains are absent, corroborating their lo calization in the cytoplasm in transfected Cos cells. In Western blotting a nd immunoprecipitation, human NNX3 appeared as a doublet of M-r 64K-66K, wh ile mouse NNX3 was a 70-kDa protein, both apparently much larger than the p redicted 50 kDa, due in part to a stretch of 16-18 acidic residues hinging two nearly equally sized domains. In addition, phosphorylation of serine re sidues was demonstrated. Putative nuclear targeting signals were predicted, but NNX3 protein and two truncated versions remained localized in the cyto plasm of transfected Cos cells. NNX3 was expressed in embryonic and adult m ouse tissues, particularly in brain, muscle, and lung. The expression of hu man NNX3 was most notable in human skeletal muscle and in ganglion cells an d was also evident in human tumors and derived cell lines. This was confirm ed by entries appearing in the GenBank EST database during the later phase of this study, representing partial NNX3 cDNA isolated from diverse neoplas tic and developing tissues. Surprisingly, NNX3 was immunochemically detecte d in Reed-Sternberg cells of Hodgkin disease, in parallel with restin, a cy toplasmic protein we previously characterized (J. Delabie ct al., 1993, Leu k. Lymphoma 12, 21-26). The cloning and comprehensive molecular analysis of NNX3 as presented will form the basis for elucidating its function and, co nversely, will constitute a marker for Reed-Sternberg cells in Hodgkin dise ase. (C) 1998 Academic Press.