Carolina Votino

UHRF1 coordinates peroxisome proliferator activated receptor gamma (PPARG) epigenetic silencing and mediates colorectal cancer progression

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.

Emerging role of the β-catenin-PPARγ axis in the pathogenesis of colorectal cancer.

Multiple lines of evidence indicate that Wnt/β-catenin signaling plays a fundamental role in colorectal cancer (CRC) initiation and progression. Recent genome-wide data have confirmed that in CRC this pathway is one of the most frequently modified by genetic or epigenetic alterations affecting almost 90% of Wnt/β-catenin gene members. A major challenge is thus learning how the corrupted coordination of this pathway is tied to other signalings to enhance cell growth. Peroxisome proliferator activated receptor γ (PPARγ) is emerging as a growth-limiting and differentiation-promoting factor. In tumorigenesis it exerts a tumor suppressor role and is potentially linked with the Wnt/β-catenin pathway. Based on these results, the identification of new selective PPARγ modulators with inhibitory effects on the Wnt/β-catenin pathway is becoming an interesting perspective. Should, in fact, these molecules display such properties, new research avenues would be opened aimed at developing new molecular targeted drugs. Herein, we review the basic principles and present new hypotheses underlying the crosstalk between Wnt/β-catenin and PPARγ signaling. Furthermore, we discuss the advances in our understanding as to how their altered regulation can culminate in colon cancer and the efforts aimed at designing novel PPARγ agonists endowed with Wnt/β-catenin inhibitory effects to be used as therapeutic and/or preventive agents.

Ensemble of Gene Signatures Identifies Novel Biomarkers in Colorectal Cancer Activated through PPARγ and TNFα Signaling

We describe a novel bioinformatic and translational pathology approach, gene Signature Finder Algorithm (gSFA) to identify biomarkers associated with Colorectal Cancer (CRC) survival. Here a robust set of CRC markers is selected by an ensemble method. By using a dataset of 232 gene expression profiles, gSFA discovers 16 highly significant small gene signatures. Analysis of dichotomies generated by the signatures results in a set of 133 samples stably classified in good prognosis group and 56 samples in poor prognosis group, whereas 43 remain unreliably classified. AKAP12, DCBLD2, NT5E and SPON1 are particularly represented in the signatures and selected for validation in vivo on two independent patients cohorts comprising 140 tumor tissues and 60 matched normal tissues. Their expression and regulatory programs are investigated in vitro. We show that the coupled expression of NT5E and DCBLD2 robustly stratifies our patients in two groups (one of which with 100% survival at five years). We show that NT5E is a target of the TNF-α signaling in vitro; the tumor suppressor PPARγ acts as a novel NT5E antagonist that positively and concomitantly regulates DCBLD2 in a cancer cell context-dependent manner.

Right-sided rhabdoid colorectal tumors might be related to the Serrated Pathway

BackgroundRhabdoid colorectal tumor (RCT) is a rare, highly aggressive neoplasm recurrent in elderly patients, commonly at the caecum. The molecular mechanisms underlying RCT pathogenesis remain poorly elucidated. The differential diagnosis is with the malignant rhabdoid tumors of infancy characterized by genetic inactivation of SMARCB1 (INI1) or deletions of chromosome 22q12 locus.Materials and methodsTo shed light on RCT pathogenesis, we investigated genetic and epigenetic alterations in two cases of pure and composite RCT and compared them with the profiles of matched adenomas and normal mucosa. Immunohistochemical analysis, FISH, methylation specific PCR and DNA sequencing analysis were performed on paraffin-embedded tissues.ResultsLoss of epithelial markers, (CK20, CDX2 and E-cadherin) and intense vimentin expression was observed in RCTs but neither in the normal mucosa or adenomas. INI1 expression was detected in normal mucosa, adenomas and retained in pure RCT, while it was undetected in composite RCT. Rearrangement of the 22q12 locus was found only in pure RCT. The APC/β-catenin pathway was not altered, while MLH1 immunostaining was negative in RCTs and positive in adenomas and normal mucosa. These expression profiles were associated with V600E BRAF mutation, a progressive accumulation of promoter methylation at specific CIMP loci and additional genes from the normal mucosa to tubular adenoma and RCT.ConclusionsRight-sided RCT could be characterized by epigenetic events and molecular features likely similar to those occurring in the serrated pathway and associated with epithelial-mesenchymal transition. These extremely rare tumors may benefit from the use of new biological molecules specific for colorectal carcinoma.Virtual slidesThe virtual slide(s) for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/1641385210804556

Peroxisome proliferator-activated receptor γ-mediated induction of microRNA-145 opposes tumor phenotype in colorectal cancer

UNLABELLED MicroRNAs (miRNAs) regulate diverse biological processes by inhibiting translation or inducing degradation of target mRNAs. miR-145 is a candidate tumor suppressor in colorectal carcinoma (CRC). Colorectal carcinogenesis involves deregulation of cellular processes controlled by a number of intertwined chief transcription factors, such as PPARγ and SOX9. Since PPAR family members are able to modulate complex miRNAs networks, we hypothesized a role of miRNA-145 in the interaction between PPARγ and SOX9 in colorectal carcinogenesis. To address this issue, we evaluated gene expression in tissue specimens of CRC patients and we took advantage of invitro models represented by CRC derived cell lines (CaCo2, SW480, HCT116, and HT-29), employing PPARγ activation and/or miRNA-145 ectopic overexpression to analyze how their interplay impact the expression of SOX9 and the development of a malignant phenotype. RESULTS PPARγ regulates the expression of miR-145 by directly binding to a PPAR response element (PPRE) in its promoter at -1207/-1194bp from the transcription start site. The binding is essential for miR-145 upregulation by PPARγ upon rosiglitazone treatment. Ectopic expression of miR-145, in turn, regulates SOX9 expression through the binding to specific seed motifs. The PPARγ-miR-145-SOX9 axis overarches cell cycle progression, invasiveness and differentiation of CRC derived cell lines. Together, these results suggest that miR-145 is a novel target of PPARγ, acts as a tumor suppressor in CRC cell lines and is a key regulator of intestinal cell differentiation by directly targeting SOX9, a marker of undifferentiated progenitors in the colonic crypts.

The antiproliferative and proapoptotic effects of cladosporols A and B are related to their different binding mode as PPARγ ligands

Cladosporols are secondary metabolites from Cladosporium tenuissimum characterized for their ability to control cell proliferation. We previously showed that cladosporol A inhibits proliferation of human colon cancer cells through a PPARγ-mediated modulation of gene expression. In this work, we investigated cladosporol B, an oxidate form of cladosporol A, and demonstrate that it is more efficient in inhibiting HT-29 cell proliferation due to a robust G0/G1-phase arrest and p21(waf1/cip1) overexpression. Cladosporol B acts as a PPARγ partial agonist with lower affinity and reduced transactivation potential in transient transfections as compared to the full agonists cladosporol A and rosiglitazone. Site-specific PPARγ mutants and surface plasmon resonance (SPR) experiments confirm these conclusions. Cladosporol B in addition displays a sustained proapoptotic activity also validated by p21(waf1/cip1) expression analysis in the presence of the selective PPARγ inhibitor GW9662. In the DMSO/H2O system, cladosporols A and B are unstable and convert to the ring-opened compounds 2A and 2B. Finally, docking experiments provide the structural basis for full and partial PPARγ agonism of 2A and 2B, respectively. In summary, we report here, for the first time, the structural characteristics of the binding of cladosporols, two natural molecules, to PPARγ. The binding of compound 2B is endowed with a lower transactivation potential, higher antiproliferative and proapoptotic activity than the two full agonists as compound 2A and rosiglitazone (RGZ).

Aberrant BLM cytoplasmic expression associates with DNA damage stress and hypersensitivity to DNA-damaging agents in colorectal cancer

BackgroundBloom syndrome is a rare and recessive disorder characterized by loss-of-function mutations of the BLM gene, which encodes a RecQ 3′–5′ DNA helicase. Despite its putative tumor suppressor function, the contribution of BLM to human sporadic colorectal cancer (CRC) remains poorly understood.MethodsThe transcriptional regulation mechanism underlying BLM and related DNA damage response regulation in independent CRC subsets and a panel of derived cell lines was investigated by bioinformatics analysis, the transcriptomic profile, a CpG island promoter methylation assay, Western blot, and an immunolocalization assay.ResultsIn silico analysis of gene expression data sets revealed that BLM is overexpressed in poorly differentiated CRC and exhibits a close connection with shorter relapse-free survival even after adjustment for prognostic factors and pathways that respond to DNA damage response through ataxia telangiectasia mutated (ATM) signaling. Functional characterization demonstrated that CpG island promoter hypomethylation increases BLM expression and associates with cytoplasmic BLM mislocalization and increased DNA damage response both in clinical CRC samples and in derived cancer cell lines. The DNA-damaging agent S-adenosylmethionine suppresses BLM expression, leading to the inhibition of cell growth following accumulation of DNA damage. In tumor specimens, cytoplasmic accumulation of BLM correlates with DNA damage and γH2AX and phosphorylated ATM foci and predicts long-term progression-free survival in metastatic patients treated with irinotecan.ConclusionsTaken together, the findings of this study provide the first evidence that cancer-linked DNA hypomethylation and cytosolic BLM mislocalization might reflect compromised levels of DNA-repair activity and enhanced hypersensitivity to DNA-damaging agents in CRC patients.