In this study, we have examined the role of post-translational modification of the myeloid master regulator C/EBPα by small
ubiquitin-related modifier (SUMO). We have used transient transfection analysis,
oligonucleotide pulldown assays and
chromatin immuno-precititation in
all-trans retinoic acid (ATRA)-inducible promyelocytic cell lines MPRO and NB4. We demonstrate that sumoylated wild-type p42-C/EBPα is associated with negative regulation of the myeloid specific
lactoferrin (LF) gene in early myeloid cells and that a reduction in p42-C/EBPα sumoylation coincides with expression of the LF gene in maturing myeloid cells. In the
acute promyelocytic leukemia cell line NB4 however, sumoylated p42 remains persistently bound to the LF promoter following ATRA-induction. This correlates with lack of
lactoferrin expression in these cells. Changes in sumoylation status of C/EBPα thus appear to contribute to a switch that regulates transcriptional activity of this master regulator during normal neutrophil development. We also demonstrate that sumoylation of the AML associated dominant negative p30-C/EBPα
isoform does not alter transactivation activity of the LF promoter. This may be because the p30 C/EBPα
isoform binds to the LF promoter much less efficiently than its full length counterpart. Our data suggest that the activity of p42-C/EBPα in the developing neutrophil is more sensitive to changes in sumoylation than the p30
isoform. This difference may contribute to the leukemogenic potential of p30-C/EBPα.