Project description:Next generation sequencing of 28 thymic epithelial tumors (TETs) revealed a high frequency of GTF2I missense mutation (chr7:74146970T/A) in A thymomas, a relatively indolent subtype. The GTF2I mutation was confirmed in 82% of A and 74% of AB thymomas in a series of 274 TETs but was rare in aggressive subtypes, where recurrent mutations of known cancer genes were identified. Therefore, GTF2I mutation correlated with a better survival. GTF2I Beta and Delta isoforms were expressed in TETs and both mutant isoforms were able to stimulate cell proliferation in vitro. Thymic carcinomas presented a higher number of mutations than thymomas (average 43.5 and 18.4, respectively). Recurrent mutations of known cancer genes, including TP53, CYLD, CDKN2A, BAP1 and PBRM1 were identified in thymic carcinomas. These findings will complement the diagnostic work up of these rare tumors, and also help the development of a molecular classification, and assessment of prognosis and treatment strategies. Tumor samples of 286 patients were collected from 4 different institutions: National Cancer Institute (Bethesda MD), Pisa University Hospital (Pisa, Italy), Padua University Hospital (Padua, Italy) and IRCCS Istituto Clinico Humanitas (Rozzano, Italy).
Project description:The pathogenesis of thymic epithelial tumors (TETs) is poorly understood. Recently we reported the frequent occurrence of a missense mutation in the GTF2I gene in TETs and hypothesized that GTF2I mutation might contribute to thymic tumorigenesis. Expression of mutant TFII-I altered the transcriptome of normal thymic epithelial cells and upregulated several oncogenic genes. Gtf2i L424H knockin cells exhibited cell transformation, aneuploidy, and increase tumor growth and survival under glucose deprivation or DNA damage. Gtf2i mutation also increased the expression of several glycolytic enzymes, cyclooxygenase-2, and caused modifications of lipid metabolism. Elevated cyclooxygenase-2 expression by Gtf2i mutation was required for survival under metabolic stress and cellular transformation of thymic epithelial cells. Our findings identify GTF2I mutation as a new oncogenic driver that is responsible for transformation of thymic epithelial cells.
Project description:Next generation sequencing of 28 thymic epithelial tumors (TETs) revealed a high frequency of GTF2I missense mutation (chr7:74146970T/A) in A thymomas, a relatively indolent subtype. The GTF2I mutation was confirmed in 82% of A and 74% of AB thymomas in a series of 274 TETs but was rare in aggressive subtypes, where recurrent mutations of known cancer genes were identified. Therefore, GTF2I mutation correlated with a better survival. GTF2I Beta and Delta isoforms were expressed in TETs and both mutant isoforms were able to stimulate cell proliferation in vitro. Thymic carcinomas presented a higher number of mutations than thymomas (average 43.5 and 18.4, respectively). Recurrent mutations of known cancer genes, including TP53, CYLD, CDKN2A, BAP1 and PBRM1 were identified in thymic carcinomas. These findings will complement the diagnostic work up of these rare tumors, and also help the development of a molecular classification, and assessment of prognosis and treatment strategies.
Project description:The molecular mechanisms underlying the pathogenesis of TETs are poorly understood. Recently we reported a common missense mutation on GTF2I gene in thymic tumors and hypothesized that GTF2I mutation might contribute to thymic tumorigenesis. Expression of mutant TFII-I altered the transcriptome of thymic epithelial cells and up-regulated several oncogenic genes. Using CRISPR/Cas9n, Gtf2i T1211A knock-in cells exhibited distinct features of cancerous cells including cell transformation, aneuploidy, tumor growth in xenograft, and survival after DNA damage or glucose deprivation. We also observed that Gtf2i mutation increased the expression of several glycolytic enzymes, cyclooxygenase-2, and altered lipid metabolism. Elevated COX-2 expression by Gtf2i mutation was required for survival under metabolic stress and cellular transformation of thymic epithelial cells. Our findings identify GTF2I mutation as a new oncogenic driver mutation that is responsible for transformation of thymic epithelial cells.
Project description:The molecular mechanisms underlying the pathogenesis of TETs are poorly understood. Recently we reported a common missense mutation on GTF2I gene in thymic tumors and hypothesized that GTF2I mutation might contribute to thymic tumorigenesis. Expression of mutant TFII-I altered the transcriptome of thymic epithelial cells and up-regulated several oncogenic genes. Using CRISPR/Cas9n, Gtf2i T1211A knock-in cells exhibited distinct features of cancerous cells including cell transformation, aneuploidy, tumor growth in xenograft, and survival after DNA damage or glucose deprivation. We also observed that Gtf2i mutation increased the expression of several glycolytic enzymes, cyclooxygenase-2, and altered lipid metabolism. Elevated COX-2 expression by Gtf2i mutation was required for survival under metabolic stress and cellular transformation of thymic epithelial cells. Our findings identify GTF2I mutation as a new oncogenic driver mutation that is responsible for transformation of thymic epithelial cells.
Project description:We previously identified a recurrent mutation L424H in the transcription factor GTF2I in thymic epithelial tumors. The precise role of the GTF2I mutation in these tumors is unclear. Here we describe the generation and characterization of a mouse model in which the Gtf2i L424H mutation was conditionally knocked-in in the Foxn1+ thymic epithelial cells. The Gtf2i mutation impairs development of thymic medulla and maturation of medullary thymic epithelial cells in the young mice and causes tumor formation in the thymus of the aged KI mice. To characterize the molecular features of murine thymomas, we performed digital spatial profiling with GeoMx moue whole transcriptome atlas assay with FFPE thymic tissues of 4 KI and 4 control mice.
Project description:Inactivation of Pten occurs by multiple mechanisms including epigenetic silencing, point mutations, insertion, and deletion, which are tissue dependent. Although frequent loss of heterozygosity around Pten locus and plausible involvement of epigenetic silencing have been reported in radiation-induced thymic lymphomas, the frequency of Pten inactivation and the spectrum of causal aberrations have not yet been extensively characterized. Here, we assessed the principal mode of inactivation by comprehensively analyzing expression and alterations of Pten gene in 23 radiation-induced thymic lymphomas developed in B6C3F1 mice. We found no evidence for methylation-associated silencing of Pten gene. Instead, we found complex structural abnormalities in 8 lymphomas (35%) that included missense and nonsense mutations, 1- and 3-bp insertions, and focal deletions. Sequencing of deletion breakpoints suggested that illegitimate V(D)J recombination and microhomology-mediated rearrangement were responsible for the focal deletions. Seven out of these 8 lymphomas had biallelic alterations, and 4 of them did not express any Pten protein. These aberrations of Pten were well coincided with downstream Akt phosphorylation on Ser473. In conclusion, Pten inactivation, which is frequently biallelic and is caused by a variety of structural abnormalities but not by epigenetic silencing, is involved in radiation-induced lymphomagenesis. Three thymic lymphomas were analyzed by array-CGH method.