Downregulation of specific FBXW7 isoforms with differential effects in T-cell lymphoblastic lymphoma.

FBXW7 is a driver gene in T-cell lymphoblastic neoplasia acting through proteasome degradation of key proto-oncogenes. FBXW7 encodes three isoforms, α, ß and γ, which differ only in the N-terminus. In this work, massive sequencing revealed significant downregulation of FBXW7 in a panel of primary T-cell lymphoblastic lymphomas characterised by the absence of mutations in its sequence. We observed that decreased expression mainly affected the FBXW7ß isoform and to a lesser extent FBXW7α and may be attributed to the combined effect of epigenetic changes, alteration of upstream factors and upregulation of miRNAs. Transient transfections with miRNA mimics in selected cell lines resulted in a significant decrease of total FBXW7 expression and its different isoforms separately, with the consequent increment of critical substrates and the stimulation of cell proliferation. Transient inhibition of endogenous miRNAs in a T-cell lymphoblastic-derived cell line (SUP-T1) was capable of reversing these proliferative effects. Finally, we show how FBXW7 isoforms display different roles within the cell. Simultaneous downregulation of the α and γ isoforms modulates the amount of CCNE1, whilst the ß-isoform alone was found to have a prominent role in modulating the amount of c-MYC. Our data also revealed that downregulation of all isoforms is a sine qua non condition to induce a proliferative pattern in our cell model system. Taking these data into account, potential new treatments to reverse downregulation of all or a specific FBXW7 isoform may be an effective strategy to counteract the proliferative capacity of these tumour cells.

TERRA recruitment of polycomb to telomeres is essential for histone trymethylation marks at telomeric heterochromatin.

TERRAs are long non-coding RNAs generated from the telomeres. Lack of TERRA knockout models has hampered understanding TERRAs' functions. We recently identified chromosome 20q as one of the main origins of human TERRAs, allowing us to generate the first 20q-TERRA knockout models and to demonstrate that TERRAs are essential for telomere length maintenance and protection. Here, we use ALT 20q-TERRA knockout cells to address a direct role of TERRAs in telomeric heterochromatin formation. We find that 20q-TERRAs are essential for the establishment of H3K9me3, H4K20me3, and H3K27me3 heterochromatin marks at telomeres. At the mechanistic level, we find that TERRAs bind to PRC2, responsible for catalyzing H3K27 tri-methylation, and that its localization to telomeres is TERRA-dependent. We further demonstrate that PRC2-dependent H3K27me3 at telomeres is required for the establishment of H3K9me3, H4K20me3, and HP1 binding at telomeres. Together, these findings demonstrate an important role for TERRAs in telomeric heterochromatin assembly.

Beckwith-Wiedemann syndrome and uniparental disomy 11p: fine mapping of the recombination breakpoints and evaluation of several techniques.

Beckwith-Wiedemann syndrome (BWS) is a phenotypically and genotypically heterogeneous overgrowth syndrome characterized by somatic overgrowth, macroglossia and abdominal wall defects. Other usual findings are hemihyperplasia, embryonal tumours, adrenocortical cytomegaly, ear anomalies, visceromegaly, renal abnormalities, neonatal hypoglycaemia, cleft palate, polydactyly and a positive family history. BWS is a complex, multigenic disorder associated, in up to 90% of patients, with alteration in the expression or function of one or more genes in the 11p15.5 imprinted gene cluster. There are several molecular anomalies associated with BWS and the large proportion of cases, about 85%, is sporadic and karyotypically normal. One of the major categories of BWS molecular alteration (10-20% of cases) is represented by mosaic paternal uniparental disomy (pUPD), namely patients with two paternally derived copies of chromosome 11p15 and no maternal contribution for that. In these patients, in addition to the effects of IGF2 overexpression, a decreased level of the maternally expressed gene CDKN1C may contribute to the BWS phenotype. In this paper, we reviewed a series of nine patients with BWS because of pUPD using several methods with the aim to evaluate the percentage of mosaicism, the methylation status at both loci, the extension of the pUPD at the short arm and the breakpoints of recombination. Fine mapping of mitotic recombination breakpoints by single-nucleotide polymorphism-array in individuals with UPD and fine estimation of epigenetic defects will provide a basis for understanding the aetiology of BWS, allowing more accurate prognostic predictions and facilitating management and surveillance of individuals with this disorder.