Objective. Molecular identification and characterization of the bone marrow
nuclear protein detected by the B92 monoclonal antibody.
Materials and Methods. The protein was purified to homogeneity from acute m
yeloid leukemia cells and was subjected to peptide digestion and amino acid
sequencing. Identified sequences were used to screen a bone marrow cDNA li
brary in search of matching transcripts. The protein was further studied in
different cells and tissues by examination of protease inhibitors and hars
h lytic conditions and during apoptosis in HL-60 cells,
Results. We found that the apparent bone marrow specific protein is a 47 kD
proteolytic cleavage product of PSF, an essential pre-mRNA splicing factor
, PSF is completely cleaved to p47 during lysis of immature myeloid cells d
ue to potent proteolytic activity found in these cells but is rare in other
cells and tissues. Furthermore, p47 is abundant in intact normal and tumor
myeloid cells while in other cell types it is undetectable, The cleavage o
f PSF is accompanied by digestion of the PTB splicing regulator but not oth
er proteins tested, In contrast, during apoptosis PTB is degraded while PSF
remains intact,
Conclusions, The bone marrow 47 kD protein is a fragment constituting the N
-terminal, protease-resistant half of the splicing factor PSF, Proteolytic
degradation of PSF specifically occurs in intact myeloid cells and this pro
cess is enhanced upon myeloid cell lysis, (C) 2000 International Society fo
r Experimental Hematology. Published by Elsevier Science Inc.