GENOMIC ORGANIZATION AND EXPRESSION OF TPL-2 IN NORMAL-CELLS AND MOLONEY MURINE LEUKEMIA VIRUS-INDUCED RAT T-CELL LYMPHOMAS - ACTIVATION BYPROVIRUS INSERTION

Tpl-2 is a gene encoding a protein kinase which is primarily expressed in normal spleen, thymus, and lung tissue and is activated by proviru s insertion in Moloney murine leukemia virus-induced T-cell lymphomas during the late stages of oncogenesis. Tpl-2 is composed of eight exon s and spans a 35-kb genomic DNA region. The provirus integrates reprod ucibly in the last intron and in the same transcriptional orientation as the Tpl-2 gene. This genetic change leads to the expression of enha nced steady-state levels of a truncated Tpl-2 RNA transcript which is predicted to encode a protein with an altered C-terminal domain. Tpl-2 is transcribed from two alternating promoters, P1 and P2. The RNA tra nscripts originating in the two promoters harbor different 5' untransl ated regions derived from the alternate noncoding exons IA and IB. Uti lization of the P2 promoter, which gives rise to exon IB containing Tp l-2 RNA transcripts, was detected primarily in tumor cells. The Tpl-2 protein was expressed in COS-1 cells as an N-terminal fusion with a 12 -amino-acid hemagglutinin tag. Immunoprecipitation of transfected COS- 1 cell lysates with antihemagglutinin or anti-Tpl-2 antibodies, follow ed by incubation With [gamma-P-32 P]ATP, confirmed that Tpl-2 possesse s protein kinase activity.