SOCS1 and acute promyelocytic leukemia: The SOCS1 expression reduction was most pronounced in U937 and THP-1 monocytic cell lines among all analysed AML cell lines, followed by K562 and HL-60 APL cell line, the human erythroleukemia cell (HEL) and KG-1 erythroleukaemia cell lines, and ML-1 and ML-2 myelomonocytic cell lines (Fig. 1).