PRODUCT OF THE ONCOGENE-ACTIVATING GENE TPR IS A PHOSPHORYLATED PROTEIN OF THE NUCLEAR-PORE COMPLEX

We have identified a component of the human nuclear pore complex and h ave shown that it is the product of a gene involved in oncogenic activ ation. A monoclonal antibody raised against purified nuclear matrix pr oteins recognizes a single protein with an electrophoretic mobility of approximately 300 kDa and stains the nuclear envelope in a punctate p attern typical of nuclear pores. The antibody was used to screen lambd a gt11 human cDNA libraries, and the resulting clones were sequenced a nd compared to sequences in the Genbank database. An exact match was f ound with the human tpr (for translocated promoter region) gene, a gen e shown previously to be involved in the oncogenic activation of sever al protein kinases. Double-label immunofluorescent microscopy with the anti-Tpr antibody and an antibody to the previously characterized nuc lear pore complex protein nup153 confirms that Tpr is localized to the nuclear pore complex. Tpr is located on the cytoplasmic face of the n ucleus, as demonstrated by immunofluorescent staining of cells permeab ilized with digitonin. Tpr is a 2,349-amino acid protein with extensiv e coiled-coil domains and an acidic globular C-terminus. The protein c ontains 10 leucine zipper motifs and numerous sites for phosphorylatio n by a variety of protein kinases. Immunoprecipitation of Tpr from P-3 2-orthophosphate-labeled cells shows that it is a phosphoprotein. Pote ntial functions for Tpr and possible mechanisms for the transforming a ctivity of Tpr fusion proteins are discussed. (C) 1996 Wiley-Liss, Inc .