PIG-A, DAF AND PROTOONCOGENE EXPRESSION IN PAROXYSMAL-NOCTURNAL HEMOGLOBINURIA-ASSOCIATED ACUTE MYELOGENOUS LEUKEMIA BLASTS

Failed surface expression of the complement decay-accelerating factor (DAF) due to mutation of the PIG-A gene is a hallmark of affected paro xysmal nocturnal haemoglobinuria (PNH) blood elements. Previous findin gs that acute myelogenous leukaemia (AML) blasts evolving in a PNH pat ient differed from idiopathic AML blasts in that they exhibited DAF ne gativity suggested that the leukaemic blasts derived from an affected PNH cell. To investigate whether these cells differ from untransformed PNH cells in PIG-A genetic alterations or in DAF mRNA processing, or are distinguishable from conventional AML blasts in protooncogene acti vation or chromosomal structure, their DNA and RNA were examined using PIG-A, DAF and protooncogene probes and their karyotype was analysed. Analyses of the PIG-A genome revealed dual exchanges of A(1110) --> G and T-1130 --> A resulting in conversions of T-370 to R and I-377 to N in the coding region but no deletions or rearrangements. Investigati ons of DAF mRNA processing showed mRNA species differing in 3' UT regi ons from those in untransformed cells but similar to those in DAF-posi tive leukaemia cell lines. Studies of c-myb, c-myc, c-fos and c-fms sh owed no gross genetic alterations, amplifications or variations in mRN A transcripts deriving from these genes. Karyotypic analysis showed no alterations. The results indicate that in AML blasts evolving in PNH: (1) the PIG-A genome exhibits multiple point mutations but no gross g enetic changes; (2) DAF mRNA transcripts exhibit differentiation-depen dent variations that do not affect GPI-anchoring; (3) c-myb, c-myc, c- fos and c-fms activation show no differences from idiopathic AML; and (4) no karyotypic abnormalities are associated with AML transformation .