HIGH-MOBILITY-GROUP (HMG) PROTEINS AND HISTONE H1 SUBTYPES EXPRESSION IN NORMAL AND TUMOR-TISSUES OF MOUSE

Exhaustive extraction of mouse tissues with perchloric acid has been used together with reverse-phase HPLC and electrophoresis to quantify the amounts of chromosomal proteins HMG17, HMG14 and HMGI, relative to histone H1. Normal lung and thymus contain almost-equal-to 3% HMG17/HMG14 but only almost-equal-to 2% HMGI. In tumor tissues (Lewis lung carcinoma and lymphoma NQ35), the amount of HMG17/HMG14 is not greatly alterated but HMGI levels rise considerably, reaching 10% in Lewis lung carcinoma. HMGI synthesis does not replace HMG1 7/HMG 1 4 proteins, suggesting that HMGI proteins contribute to the structure of chromatin regions in a manner distinct from those of HMG17/HMG14. Ion-spray mass spectrometry has been used to determine the molecular masses of H1 subtypes from the same four mouse tissues. In addition to the six known species H1-degrees, H1a, H1b, H1c, H1d and H1e, a newly defined subtype of mass 21756 Da from Lewis lung carcinoma, named HlL was identified. Several phosphorylated Hl subtypes have also been defined by mass spectrometry. The combined use of reverse-phase HPLC and electrophoresis permitted quantification of these seven histone Hl subtypes in the four mouse tissues. Increased phosphorylation of H1 subtypes in tumors parallels the phosphorylation of HMGI proteins which are present in great amounts, showing that both are involved as post-translational-modified forms in the structure of the chromatin of neoplastic systems.