Mendelian susceptibility to mycobacterial disease (MSMD) is a rare congenital disorder characterized by susceptibility to infection by poorly virulent intracellular pathogens such as BCG, non-tuberculosis mycobacterium and Salmonellae. MSMD is associated with genetic defects in the IL-12/IFN-γ pathway, and six responsible genes, IFNGR1, IFNGR2, IL12B, IL12RB1, STAT1, and NEMO have been identified so far. Singnal transducer and activation of transcription 1 (STAT1) is a DNA-binding factor which regulates specific gene transcription. IFN-γ stimulation results in phosphorylation of STAT1 at Tyr701 (Y701) to induce the homodimerization, so called a gamma-activated factor (GAF), through the conformational change and the nuclear import. The GAF binds to the gamma-activated sequence (GAS) to induce the transcriptional activities. Patients with STAT1 deficiency were known in both recessive and dominant forms and three mutations in STAT1, L706S, E320Q and Q463H, have previously been reported from three family with an autosomal-dominant form of STAT1 partial deficiency. L706S mutation in the tail segment domain of STAT1 is shown to impair the phosphorylation at Tyr701. Although the phosphorylation is normal in other two mutations, the E320Q or Q463H mutant, in which the DNA-binding ability was abolished. Here we identified a novel heterozygous STAT1 mutation, 2018A>G (K673R), in a Japanese patient with MSMD. This was thought to be first report whose mutation was identified in the SH2 domain of autosomal-dominant form of STAT1. He had a past history of BCGitis after vacctination and multifocal osteomyelitis at the age of 5. Bone biopsy revealed granulomatous change without detecting Mycobacterium. The same mutation was also identified in his father and older sister. Although his sister had a history of BCGitis, his father had no clinical manifestations. A peripheral blood mononuclear cells from the patient could not sufficiently produce TNF-α in response to IFN-γ. EB-transformed B cells from the patient showed that induction of STAT1 phosphorylation by IFN-γ was partially impaired. We generated Flag-tagged STAT1 expression constructs of wild-type (WT) and three mutants including our mutant and analyzed molecular functions along with STAT1 signaling. K673R STAT1 showed partial impairment in the phosphorylation in response to both IFN-α and IFN-γ. Further, the electrophoretic mobility shift assay revealed that the K673R mutant abolished the DNA-binding ability. The nuclear translocation was normally detected. Curiously, dose-dependent negative effect on WT STAT1 was observed in K673R mutant by the reporter assay. K673R mutant interacted with WT to abrogate the DNA-binding activity, thus, exerted a dominant-negative effect on the transcription activity of WT STAT1. Based on these results, a novel heterozygous mutation, K673R, in SH2 domain of the STAT1 gene impaired the STAT1 signal transduction in a dominant-negative manner. K673R mutation in STAT1 may play an important role in molecular pathogenesis of MSMD.
No relevant conflicts of interest to declare.
Asterisk with author names denotes non-ASH members.