Drug-activated multiple pathways of defensin mRNA regulation in HL-60 cells are defined by reversed roles of participating protein kinases

Assessment of the cellular response to the induced expression of defensin sense and antisense cDNA in acute promyelocytic leukemia cell lines

Defensins are 20-30 amino acid-long, cystine- and arginine-rich peptides that constitute more than 5% of the total cellular proteins in mature granulocytes and at least 30% of proteins in primary granules. Human defensins were reported to have antimicrobial, antifungal, antiviral and tumor lysis activities. Defensin mRNA was isolated using the differential display technique from the well-characterized all-trans retinoic acid (ATRA)-responsive acute promyelocytic leukemia cell line, NB4. The differential display analysis showed an up-regulation of defensin mRNA in NB4 cells after treatment with 10(-7) M ATRA for 24 h. This expression was not seen in an NB4:R2 cell line, an ATRA-resistant subclone of NB4 cells. In order to investigate further the effects of this gene on our cellular model, we virally infected our cells with full-length defensin cDNA in the sense and antisense directions. Sense defensin induced cell growth arrest and cell death in both cell lines. While NB4 cells died within 48-73 h, NB4:R2 cells survived for 96 h before dying in culture. Phenotypic analysis showed high expression of Annexin V in sense-infected cells compared with antisense and uninfected cells in both cell lines. There was not a significant increase in CD11b expression in any of the 2 cell lines used. No cellular response was encountered in antisense-infected cells. Our data suggest that defensin is not only a reliable marker for granulocytic differentiation, but can also be considered a candidate target for molecular therapy in acute promyelocytic leukemia.

PU.1 and a TTTAAA Element in the MyeloidDefensin-1Promoter Create an Operational TATA Box That Can Impose Cell Specificity onto TFIID Function

Defensins are major components of a peptide-based, antimicrobial system in human neutrophils. While packed with peptide, circulating cells contain no defensin-1 (def1) transcripts, except in some leukemia patients and in derivative promyelocytic leukemia cell lines. Expression is modulated by serum factors, mediators of inflammation, and kinase activators and inhibitors, but the underlying mechanisms are not fully understood. A minimal def1 promoter drives transcription in HL-60 cells under control of PU.1 and a def1-binding protein ("D1BP"), acting through, respectively, proximal (-22/-19) and distal (-62/-59) GGAA elements. In this study, we identify D1BP, biochemically and functionally, as GA-binding protein (GABP)alpha/GABPbeta. Whereas GABP operates as an essential upstream activator, PU.1 assists the flanking "TTTAAA" element (-32/-27), a "weak" but essential TATA box, to bring TBP/TFIID to the transcription start site. PU.1 thus imparts a degree of cell specificity to the minimal promoter and provides a potential link between a number of signaling pathways and TFIID. However, a "strong" TATA box ("TATAAA") eliminates the need for the PU.1 binding site and for PU.1, but not for GABP. As GABP is widely expressed, a strong TATA box thus alleviates promyelocytic cell specificity of the def1 promoter. These findings suggest how the myeloid def1 promoter may have evolutionarily acquired its current properties.

Delayed-late activation of a myeloid defensin minimal promoter by retinoids and inflammatory mediators

Alpha-defensin-1 gene expression in promyelocytic HL-60 cells is ('delayed-late' > or =1-2 days) activated by retinoic acid (RA), lipopolysaccharide, tumor necrosis factor-alpha and elevated levels of cAMP. Using stably integrated reporter constructs, we show that this activation is directed through a proximal and distal element within a minimal (-83/+82) def1 promoter, and is mediated by phosphorylation of the associated factors, PU.1 and D1BP, in an inducer-dependent manner. Whereas binding of PU.1 to the proximal element confers cell specificity and relays the effects of most inducers, the selectively enhancing capacity of the distal element for RA- and cAMP-dependent activation is uniquely correlated with D1BP-binding. We propose that D1BP and PU.1 are the end-points of separate pathways.

Differential gene expression in retinoic acid-induced differentiation of acute promyelocytic leukemia cells, NB4 and HL-60 cells

Acute promyelocytic leukemia (APL) is characterized by a specific chromosome translocation t(15;17), which results in the fusion of the promyelocytic leukemia gene (PML) and retinoic acid receptor alpha gene (RARalpha). APL can be effectively treated with the cell differentiation inducer all-trans retinoic acid (ATRA). NB4 cells, an acute promyelocytic leukemia cell line, have the t(15;17) translocation and differentiate in response to ATRA, whereas HL-60 cells lack this chromosomal translocation, even after differentiation by ATRA. To identify changes in the gene expression patterns of promyelocytic leukemia cells during differentiation, we compared the gene expression profiles in NB4 and HL-60 cells with and without ATRA treatment using a cDNA microarray containing 10,000 human genes. NB4 and HL-60 cells were treated with ATRA (10(-6)M) and total RNA was extracted at various time points (3, 8, 12, 24, and 48h). Cell differentiation was evaluated for cell morphology changes and CD11b expression. PML/RARalpha degradation was studied by indirect immunofluoresence with polyclonal PML antibodies. Typical morphologic and immunophenotypic changes after ATRA treatment were observed both in NB4 and HL-60 cells. The cDNA microarray identified 119 genes that were up-regulated and 17 genes that were down-regulated in NB4 cells, while 35 genes were up-regulated and 36 genes were down-regulated in HL60 cells. Interestingly, we did not find any common gene expression profiles regulated by ATRA in NB4 and HL-60 cells, even though the granulocytic differentiation induced by ATRA was observed in both cell lines. These findings suggest that the molecular mechanisms and genes involved in ATRA-induced differentiation of APL cells may be different and cell type specific. Further studies will be needed to define the important molecular pathways involved in granulocytic differentiation by ATRA in APL cells.