Stable expression of HB24, a diverged human homeobox gene, in T lymphocytes induces genes involved in T cell activation and growth.

A diverged homeobox gene, HB24, which is known to be induced following lymphocyte activation, was introduced into Jurkat T cells under the control of a constitutive promoter. Stable transfectants of HB24 were established that expressed high levels of HB24 mRNA and possessed an altered phenotype suggestive of activated T cells. A number of genes known to be induced following T cell activation and associated with cell growth were increased in the transfectants, including c-fos, c-myc, c-myb, HLA-DR, lck, NF-kappa B, interleukin-2 and interleukin-2 receptor alpha (IL-2R alpha). Analysis of IL-2R alpha expression by transient transfection of IL-2R alpha promoter constructs into the HB24 transfectants revealed constitutive expression (about 60% of phytohemagglutinin- and phorbol ester-activated Jurkat cells) that was dependent on the kappa B site in the IL-2R alpha promoter. Furthermore, as a consequence of the increased HB24 mRNA levels, the Jurkat HB24 transfectants proliferated more rapidly than control cell lines. Thus, stable expression of HB24 confers an activation phenotype on a human T cell line, implicating this gene as an important transcriptional factor during T cell activation and growth.