Interferon-gamma improves splicing efficiency of CYBB gene transcripts in an interferon-responsive variant of chronic granulomatous disease due to a splice site consensus region mutation

Improved superoxide-generating ability by interferon gamma due to splicing pattern change of transcripts in neutrophils from patients with a splice site mutation in CYBB gene

Chronic granulomatous disease (CGD) is an inherited disorder of host defense against microbial infections caused by defective activity of the phagocyte NADPH oxidase. Based on an increase of neutrophil superoxide-generating ability in response to interferon gamma (IFN-gamma) in a single patient with CGD, multicentered group studies demonstrated a beneficial effect of prophylactic IFN-gamma. However, no apparent increase of the phagocyte superoxide generation was found in patients enrolled in these studies. The present report offers an additional kindred in whom an IFN-gamma-dependent increase in neutrophil superoxide production was observed in 3 affected patients. The defect in the CYBB gene for gp91-phox was identified as an otherwise silent mutation adjacent to the third intron of the CYBB gene that alters messenger RNA splicing. By molecular analysis, significant differences were found in the splicing pattern of CYBB gene transcripts in patient neutrophils between 1 and 25 days after administration of IFN-gamma. Furthermore, a complete transcript containing the missing exons could be detected in all specimens after the treatment. The changes in the splicing pattern of the transcripts and the prolonged effect on superoxide-generating ability of patient neutrophils indicate that IFN-gamma induced a partial correction of the abnormal splicing of CYBB gene transcripts in myeloid progenitor cells.

Molecular basis of the Kell-null phenotype: a mutation at the splice site of human KEL gene abolishes the expression of Kell blood group antigens

The Kell blood group system is polymorphic, and 23 antigens have been defined to date. The Kell antigens are located on a single red cell transmembrane glycoprotein, encoded by the 19 exons of the KEL gene. The different Kell phenotypes result from point mutations leading to amino acid changes in the Kell glycoprotein. An unusual phenotype, which is defined as the complete lack of all of the Kell antigens, has been identified and designated as the Kell-null or Ko phenotype. The coding region of the KEL gene of the Ko individual showed a normal KEL2/KEL4/KEL7 gene sequence; nevertheless, a G to C mutation at the splice donor site (5' splice site) of intron 3 was found to be present as a homozygote in the individual. The mutation destroys the conserved GT sequence of the splice donor site. Reverse transcription-polymerase chain reaction analysis showed the absence of the complete KEL mRNA. Instead, a major transcript with the exon 3 region skipped was found. The exon 3 of the KEL gene encodes the transmembrane domain of the Kell glycoprotein, and a transcript without exon 3 is predicted to have a premature stop codon that abolishes the translation of C-terminal segment. The segment contains all of the known positions responsible for characterizing different Kell antigens, and this explains the lack of all Kell antigens in Ko red cells.

A 3'-transcribed region of the HLA-A2 gene mediates posttranscriptional stimulation by IFN-gamma

The expression of several MHC class I genes is up-regulated at the transcriptional level by IFN-gamma. Posttranscriptional mechanisms also have been implicated, but not well characterized. To investigate the mechanism of IFN-gamma stimulation of the human MHC class I gene HLA-A2, several human tumor cell lines were transfected with reporter gene constructs driven by the HLA-A2 promoter. We have previously shown that the extended 525-bp HLA-A2 promoter alone, which includes a 5' IFN-stimulated response element consensus sequence, is not sufficient for IFN-gamma response in either K562 or Jurkat cells. In the current study, stable transfection of a genomic HLA-A2 gene construct, containing both 5'- and 3'-flanking sequences, resulted in stimulation of the gene by IFN-gamma. Nuclear run-on assays revealed that, unlike other class I genes, IFN-gamma stimulation of HLA-A mRNA accumulation occurs almost entirely through posttranscriptional mechanisms. RNA stability assays showed that the effect is not mediated by alteration of the half-life of the HLA-A2 mRNA. Formation of the 3' end was unaffected by IFN-gamma treatment. Sequences that mediate the majority of IFN-gamma induction of HLA-A2 mRNA reside in a 127-bp 3'-transcribed region of the gene. This region contains the terminal splice site, the usage of which is not affected by IFN-gamma treatment. These results demonstrate a novel posttranscriptional mechanism of regulation of MHC class I genes by IFN-gamma.

Clinical aspects of chronic granulomatous disease

Data from a registry of 368 patients with chronic granulomatous disease (CGD) documenta shift in the most common infecting organisms away from staphylococci and enteric bacteria to Aspergillus species, although staphylococci remain a threat. A. nidulans appears to have a particular virulence in CGD. Burkholderia cepacia sepsis/pneumonia was the second most lethal infection in patients in the registry. Seventy-six percent of registry patients had the X-linked recessive (XLR) form of CGD. Chorioretinitis may be more common than previously appreciated, and boys with the XLR disease should probably have routine full eye exams. A new variant of CGD has been described that is caused by an inhibitory mutation in Rac2, which regulates activity of the neutrophil respiratory burst and actin assembly. Interferon-gamma, antibacterial prophylaxis, and, probably, antifungal prophylaxis with itraconazole reduce the rate of infection, and bone marrow transplantation can cure the disease if a histocompatible donor is available. Gene therapy can cure CGD in knockout mouse models. Having even a small percentage of phagocytes that are nicotinamide adenine dinucleotide phospate oxidase-positive can reduce the risk of serious infection, and procedures now under study appear close to achieving that goal, if not a cure.

Regulation of human neutrophil granule protein expression

The function of the mature polymorphonuclear neutrophil is dependent on its granules, each with its characteristic content of proteins. The granule proteins are formed at different stages during maturation of neutrophils from myeloblasts to segmented cells. The regulation of granule protein expression is controlled by a number of transcription factors, many of which are also essential for commitment of multipotent hematopoietic stem cells to lineage-committed myeloid progenitor cells and for differentiation of these progenitor cells; among these, PU.1 and C/EBPalpha stand out as critical for all granule proteins whereas AML-1 is critical for primary granule protein expression and C/EBPepsilon for secondary and tertiary granule protein expression.