EXPRESSION AND REGULATION OF G(1) CELL-CYCLE INHIBITORS (P16(INK4A), P15(INK4B), P18(INK4C), P19(INK4D)) IN HUMAN ACUTE MYELOID-LEUKEMIA AND NORMAL MYELOID CELLS

In hematological malignancies, structural alterations of genes for G(1 )-specific cyclin dependent kinases inhibitors (CKls) have been extens ively investigated. G(1)-CKls might play an important role not only as tumor suppressor genes but also in cellular differentiation. We exami ned constitutive and differentiation-induced expression and regulation of the four members of the G(1)-CKl family p16(INK4A), p15(INK4B), p1 8(INK4C) and p19(INK4D) in acute myeloid leukemia as well as their exp ression in normal granulocytes and monocytes. p18(INK4C) and p19(INK4D ) mRNA were expressed constitutively at high levels in seven myeloid c ell lines and 16 AML patient samples, whereas expression of p15(INK4B) mRNA was very low and only detectable by nested RT-PCR analysis. Duri ng phorbol ester-induced monocytic differentiation of leukemic HL-60 c ells expression of particular G(1)-CKls was disparately regulated. Thi s process was associated with growth arrest of the majority of the cel ls (greater than or equal to 80%) in G(1)/G(0), and in parallel p15(IN K4B) were upregulated whereas p18(INK4C) and p19(INK4D) expression was downregulated. In contrast, granulocytic differentiation induced by D MSO was accompanied by an increase of p18(INK4C) and p19(INK4D) expres sion only. PMA treatment of blast cells from two AML patients confirme d these cell line results. Disparate regulation of p15(INK4B) and p18( INK4C) mRNA was dependent on intermediary protein synthesis and occurr ed at the post-transcriptional level as shown by nuclear run-on analys is and mRNA half-life studies. In normal granulocytes and monocytes lo w constitutive p15(INK4B) and p18(INK4C) mRNA expression was detectabl e by RT-PCR only, but p19(INK4D) transcripts were noted by Northern bl otting in both cell types. Disparate expression of G(1)-specific cell cycle inhibitors indicates complex and divergent roles of particular C Kls during normal and leukemic myeloid hematopoiesis.