CANCER PROCOAGULANT IN THE HUMAN PROMYELOCYTIC CELL-LINE NB4 AND ITS MODULATION BY ALL-TRANS-RETINOIC ACID

Acute promyelocytic leukemia (APL) cells express different types of pr ocoagulant activity (PCA), including tissue factor (TF), and cancer pr ocoagulant (CP). The aim of this study was to investigate whether the NB4 cell line, the first ever isolated human APL line, with the typica l t(15;17) chromosomal balance translocation, possess CP as well as th e cells freshly isolated from APL patients. Secondly, since the NB4 li ne is maturation inducible by all-trans-retinoic acid (ATRA), we wante d to verify whether CP, if present, was affected by ATRA treatment. Th e NB4 cells were able to shorten the recalcification assay of normal h uman plasma (total PCA). To distinguish CP in the assay for clotting a ctivity, two criteria were used, the independence from factor VII to t rigger blood coagulation and the sensitivity to cysteine proteinase in hibitors. Forty-seven per cent of total PCA of cell extracts was found to be FVII-independent PCA. A similar proportion of FVII-independent activity (42%) was detected in the cell serum-free supernatants. The a ctivity was significantly decreased by cysteine proteinase inhibitors, including HgCl2 lodoacetic acid and Z-Ala-AlaCHN(2). Additionally CP was directly identified and quantified by an immunocapture enzyme assa y. The mean +/- SD concentration of CP detected by this assay in the N B4 cells, before any treatment, was 1.89 +/- 0.5 mu g/mg protein. Trea tment of NB4 cells with 10(-6) M ATRA for 5 days significantly decreas ed the expression of CP, which became virtually undetectable by the cl otting assay, and was 64% less than the untreated control by the immun ocapture enzyme assay. This study provides the first evidence that the human promyelocytic cell line NB4 possess CP. The expression of this procoagulant is modulated by ATRA.