Expression of a G-protein β subunit-related gene during lymphocyte activation

Using a subtractive strategy, we have cloned an activation-related gene from a human B cell cDNA library. Sequence analysis revealed that this gene was identical to H12.3, a gene belonging to an expanding family of guanine nucleotide-binding protein beta subunits. The expression of H12.3 was inducible in the late phase of mitogen-stimulated T and B cells. In T cells, IL-2 and IL-4 by themselves had no direct effect on the expression of H12.3, but they could augment the level of steady-state H12.3 mRNA stimulated by phytohemagglutinin. On the other hand, IFN-gamma and IL-6 had no obvious effect on the expression in B cells with or without Staphylococcus aureus Cowan I-stimulation. Cyclosporin A, a strong immunosuppressant, inhibited the mitogen-stimulated expression of H12.3, but rapamycin, another such agent, did not. In synchronized Jurkat cells, the expression of H12.3 had no cell cycle-dependent decrease in S and G2/M phase, while cyclin E, which controls the progression of the cell cycle in late G1 phase, did show a periodic expression pattern. The results suggest that H12.3 might be involved in regulation of lymphocyte activation.