Peroxisome proliferator-activated receptor gamma (PPARG) inactivation has been identified as an important step in colorectal cancer (CRC) progression, although the events involved have been partially ...clarified. UHRF1 is emerging as a cofactor that coordinates the epigenetic silencing of tumor suppressor genes, but its role in CRC remains elusive. Here, we report that UHRF1 negatively regulates PPARG and is associated with a higher proliferative, clonogenic and migration potential. Consistently, UHRF1 ectopic expression induces PPARG repression through its recruitment on the PPARG promoter fostering DNA methylation and histone repressive modifications. In agreement, UHRF1 knockdown elicits PPARG re-activation, accompanied by positive histone marks and DNA demethylation, corroborating its role in PPARG silencing. UHRF1 overexpression, as well as PPARG-silencing, imparts higher growth rate and phenotypic features resembling those occurring in the epithelial-mesenchymal transition. In our series of 110 sporadic CRCs, high UHRF1-expressing tumors are characterized by an undifferentiated phenotype, higher proliferation rate and poor clinical outcome only in advanced stages III-IV. In addition, the inverse relationship with PPARG found in vitro is detected in vivo and UHRF1 prognostic significance appears closely related to PPARG low expression, as remarkably validated in an independent dataset. The results demonstrate that UHRF1 regulates PPARG silencing and both genes appear to be part of a complex regulatory network. These findings suggest that the relationship between UHRF1 and PPARG may have a relevant role in CRC progression.
Impairment of the immune response and aberrant expression of microRNAs are emerging hallmarks of tumour initiation/progression, in addition to driver gene mutations and epigenetic modifications. We ...performed a preliminary survey of independent adenoma and colorectal cancer (CRC) miRnoma data sets and, among the most dysregulated miRNAs, we selected miR-27a and disclosed that it is already upregulated in adenoma and further increases during the evolution to adenocarcinoma. To identify novel genes and pathways regulated by this miRNA, we employed a differential 2DE-DIGE proteome analysis. We showed that miR-27a modulates a group of proteins involved in MHC class I cell surface exposure and, mechanistically, demonstrated that calreticulin is a miR-27a direct target responsible for most downstream effects in epistasis experiments. In vitro miR-27a affected cell proliferation and angiogenesis; mouse xenografts of human CRC cell lines expressing different miR-27a levels confirmed the protein variations and recapitulated the cell growth and apoptosis effects. In vivo miR-27a inversely correlated with MHC class I molecules and calreticulin expression, CD8(+) T cells infiltration and cytotoxic activity (LAMP-1 exposure and perforin release). Tumours with high miR-27a, low calreticulin and CD8(+) T cells' infiltration were associated with distant metastasis and poor prognosis. Our data demonstrate that miR-27a acts as an oncomiRNA, represses MHC class I expression through calreticulin downregulation and affects tumour progression. These results may pave the way for better diagnosis, patient stratification and novel therapeutic approaches.
We report a novel
PPARG germline mutation in a patient affected by colorectal cancer that replaces serine 289 with cysteine in the mature protein (S289C). The mutant has impaired transactivation ...potential and acts as dominant negative to the wild type receptor. In addition, it no longer restrains cell proliferation both in vitro and in vivo. Interestingly, the S289C mutant poorly activates target genes and interferes with the inflammatory pathway in tumor tissues and proximal normal mucosa. Consistently, only mutation carriers exhibit colonic lesions that can evolve to dysplastic polyps. The proband presented also dyslipidemia, hypertension and overweight, not associated to type 2 diabetes; of note, family members tested positive for the mutation and display only a dyslipidemic profile at variable penetrance with other biochemical parameters in the normal range. Finally, superimposing the mutation to the crystal structure of the ligand binding domain, the new Cys289 becomes so closely positioned to Cys285 to form an S–S bridge. This would reduce the depth of the ligand binding pocket and impede agonist positioning, explaining the biological effects and subcellular distribution of the mutant protein. This is the first
PPARG germline mutation associated with dyslipidemia and colonic polyp formation that can progress to full-blown adenocarcinoma.
Novel chromosomal rearrangements involving tyrosine-kinase receptors FGFR3 and EGFR and resulting in actionable fusion proteins with strong oncogenic activity have been recently described in ...glioblastoma (GBM). 602 gliomas 380 grade IV (GBM), 116 grade III, 106 grade II from the Pitie-Salpetriere brain tumor bank "Onconeurotheque" were analyzed for the presence of FGFR3-TACC3 and EGFR-SEPT14 by RT-PCR and sequencing . We identified 30 patients with fusion transcripts: 11 (8 GBM, one grade III, two grade II) with FGFR3-TACC3 and 19 (18 GBM and one grade III) with EGFR-SEPT14 fusion, including a GBM patient recurring after standard treatment. None of the 144 IDH1 mutated and 12 IDH2 mutated gliomas (including 28 GBM) had FGFR3-TACC3 or EGFR-SEPT14 fusions (P < 0.0002). EGFR-SEPT14 was associated with EGFR amplification 13/16 cases (81%) (12/14 in GBM EGFR-SEPT14+ vs 79/207 in GBM EGFR-SEPT14-, P = 0.001) and with EGFR vIII variant in 8/15 (53%), whereas none of the FGFR3-TACC3 fusions had EGFR abnormalities (0/8 in GBM FGFR3-TACC3+ vs 79/207 in GBM FGFR3-TACC3-, P = 0.027). Of particular interest, FGFR3-TACC3 positive tumors showed a very strong, diffuse and homogeneous FGFR3 expression by immunostaining, in contrast to fusion negative tumors, suggesting that FGFR3-TACC3 protein is expressed in nearly all tumor cells. In GBM patients, median overall survival was 32.80 months for FGFR3-TACC3+ patients, 25.50 months for EGFR-SEPT14+ patients compared to 17.20 for the other GBM patients (P = 0.60; NS). In conclusion we found that these gene fusions are not restricted to GBM but involve also grade II and III IDH wild-type tumors. Due to their oncogenic activity these genes fusions define a subset of patients that could benefit from specific molecular targeting at recurrence. We are now planning anti-FGFR and anti-EGFR treatment in this preselected population.
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