Histone H1°is synthesized by human lymphocytic leukemia cells but not by normal lymphocytes

Using a two-dimensional gel electrophoresis system (sodium dodecyl sulphate/acetic acid-urea-hexadecyltrimethylammonium bromide) coupled with fluorography, we investigated the synthesis of H1 isoproteins in leukemic cells obtained from peripheral blood of eight children suffering from acute lymphoblastic leukemia (ALL) (four T-ALL, three common ALL, and one B-ALL) and in normal peripheral lymphocytes. H1°was synthesized in leukemic cells but not in normal lymphocytes. Inhibition of DNA synthesis with hydroxyurea and 1-β-D-arabinofuranosylcytosine induced an increase of relative synthesis of H1°in leukemic cells but did not induce any detectable synthesis of H1°in normal lymphocytes. H1°synthesis was also undetectable in peripheral lymphocytes of leukemic children in complete remission after chemotherapy and in lymphocytes of a homozygotic twin of a leukemic patient. H1°may be a marker of malignant transformation of lymphocytes and as such could be of use for early detection of relapse in patients with acute lymphocytic leukemia in apparent complete remission.