DIFFERENTIAL EXPRESSION OF NUCLEAR HMG1, HMG2 PROTEINS AND H1(0) HISTONE IN VARIOUS BLOOD-CELLS

Changes in the levels of chromosomal high-mobility group proteins HMG1, HMG2 and histone H1(0) were investigated in blood cells of various types, proliferation activity and stage of differentiation. The relative amounts of proteins HMG1, HMG2 and histone H1(0) were evaluated densitometrically by SDS-PAGE of 5 per cent w/v perchloric acid extracts of blood cells. Concerning the HMG1 and HMG2, the main conclusions were: the expression of these HMG proteins was higher in malignant cells, namely leukemia cell lines, then in lymphocytes or granulocytes and the distribution of HMG1 and HMG2 was highly cell-specific. In comparison with lymphoid cells, the levels of HMG1/2 were higher in myeloid cells. The results revealed that in myeloid cells HMG2 prevails over HMG1. There was no direct correlation between HMG1/2 expression and proliferation activity. The levels of HMG1/2 did not depend on the transcription of chromatin either. However, there was some connection between irreversibly differentiated nonproliferating cells and a loss of HMG1/2 proteins. Reversibly differentiated leukemic cells retain their HMG1/2 levels. Similarly to HMG1/2, H1(0) showed a strong cell specificity. The level of H1(0) was different in the various blood cell types. As compared with lymphoid cells, the level of H1(0) was several-fold higher in myeloid cells, regardless of whether they were normal or malignant. Moreover, there was an accumulation of H1(0) in differentiating HL-60 cells accompanied by only a slight decline in cell proliferation; this agrees with the idea that H1 degrees expression is not directly associated with the inhibition of cell growth. Rather higher expression of H1(0) is related to changes during cell differentiation.