EXPRESSION OF ID2 AND ID3 MESSENGER-RNA IN HUMAN-LYMPHOCYTES

Helix-loop-helix (HLH) transcription factors are involved in cellular growth and differentiation. The Id (inhibitor of DNA binding and diffe rentiation) HLH proteins, in a dominantly negative fashion, regulate t ranscriptional activities of basic HLH proteins. We examined by northe rn hybridization the expression of Id2 and Id3 mRNA in human leukemia/ lymphoma lines and patient samples, as well as resting and activated n ormal human lymphocytes from peripheral blood (PBL). The Id2 mRNA was abundantly expressed in 5/12 T-cell and 3/4 B-cell lines, and Id3 mRNA was detected in 4/12 T-cell and 3/4 B-cell lines. Interestingly, Id2, but not Id3, mRNA was strongly expressed in 4/5 T-cell lines infected with human T-cell leukemia virus type I (HTLV-I) (ATL-1k, MT-2, S-LB1 ) and type II (Mo). Another unexpected finding was that T-cell leukemi as and T-cell lines often expressed either Id2 or Id3 mRNA. In additio n, resting PBL constitutively expressed prominent levels of Id2 mRNA, but not Id3 mRNA. Upon PHA-stimulation, Id2 expression decreased and I d3 levels increased with biphasic kinetics. Taken together, our studie s revealed three unexpected findings which require further analysis: ( 1) expression of Id2 mRNA is often associated with lymphocytic transfo rmation by HTLV-I or -II; (2) T-cells usually express either Id2 or Id 3 mRNA, but B-cells often express both simultaneously; (3) non-dividin g, normal PBL express high levels of Id2 and no Id3 mRNA; and with the onset of cellular proliferation, levels of Id2 mRNA decrease while le vels of Id3 mRNA increase, suggesting that regulation of expression of these closely related genes is disparate.