Mutations in XLF/NHEJ1/Cernunnos gene results in downregulation of telomerase genes expression and telomere shortening

Abstract

NHEJ1-patients develop severe progressive lymphocytopenia and premature aging of hematopoietic stem cells (HSCs) at a young age. Here we show a patient with a homozygous-NHEJ1 mutation identified by whole exome-sequencing that developed severe pancytopenia and bone marrow aplasia correlating with the presence of short telomeres. The mutation resulted in a truncated protein. In an attempt to identify the mechanism behind the short telomere phenotype found in the NHEJ1-patient we downregulated NHEJ1 expression in 293T and CD34+cells. This downregulation resulted in reduced telomerase activity and decreased expression of several telomerase/shelterin genes. Interestingly, cell lines derived from two other NHEJ1-deficient patients with different mutations also showed increased p21 expression, inhibition in expression of several telomerase complex genes and shortened telomeres. Decrease in expression of telomerase/shelterin genes did not occur when we inhibited expression of other NHEJ genes mutated in SCID patients: DNA-PK, Artemis or LigaseIV. Because premature aging of HSCs is observed only in NHEJ1 patients, we propose that is the result of senescence induced by decreased expression of telomerase/shelterin genes that lead to an inhibition of telomerase activity. Previous reports failed to find this connection because of the use of patient´s cells immortalized by TERT expression or recombined telomeres by ALT pathway. In summary, defective regulation of telomere biology together with defective V(D)J recombination can negatively impact on the evolution of the disease in these patients. Identification of telomere shortening is important since it may open new therapeutic interventions for these patients by treatments aimed to recover the expression of telomerase genes.

Genetic screening of children with marrow failure. The role of primary Immunodeficiencies

“…19 This diagnostic scenario may be even more complicated since other rare congenital disorders are characterized by the concomitant impairment of both marrow precursor growth and the immune system, 20 as in the case of deficiencies of GATA2 or ADA2 (DADA2) 21,22 or in chromosomal breakage syndromes (CBS). 23,24 The correct identification of the disorders potentially underlying MFs is an important diagnostic challenge because of the relevant treatment and follow-up implications. 25 However, there are no data available on the prevalence of such conditions, especially in pediatric patients.…”

Extreme Phenotypes With Identical Mutations: Two Patients With Same Non-sense NHEJ1 Homozygous Mutation

“…However, clinical presentation and immunological profile were extremely different. The first patient showed a senescent phenotype with decreased TRECs, RTE and naive T-cells counts suggesting that the sustained self-renewal of T-cell pool was impaired, while P2 presented only a slight reduction in T-cell counts as it has been reported in Cernunnos/XLF deficient patients reported up to date with normal TRECs/KRECs and IgG levels (22).…”

The master energy homeostasis regulator PGC-1α couples transcriptional co-activation and mRNA nuclear export

“…To functionally validate these findings, we tested whether these transcripts are novel gene expression targets regulated by PGC-1α. We also included telomeric repeat binding factor 2 (TERF2), a protein directly associated with age-related maintenance of telomeres 69, 70 . RNA immunoprecipitation assays in induced Sham, WT-res and ΔRS-res cells further showed that PGC-1α specifically binds XRCC5 , XRCC6 , NHEJ1 and TERF2 mRNAs via the RS domain ( Fig.…”

“…7c, Supplementary Table 1 tab 5). Interestingly, they are linked to age-related telomere maintenance [67][68][69] , premature ageing and alteration of telomerase gene expression 70 . To functionally validate these findings, we tested whether these transcripts are novel gene expression targets regulated by PGC-1α.…”