Hypermethylation of the APC promoter but lack of APC mutations in myxoid/round‐cell liposarcoma

Abstract

The adenomatous polyposis coli (APC) protein is a key component of the WNT signalling pathway wherein it acts as a scaffolding protein in controlling the level of the proto-oncoprotein b-catenin. Although APC has been shown to be genetically or epigenetically inactivated in a variety of carcinomas, little is known about its role in sarcoma. Liposarcomas (LPSs) are the second most common soft tissue sarcoma in adults. Despite different histology and malignancy, the myxoid and round-cell LPSs belong to one tumour entity characterized by a specific chromosomal translocation. We assessed the extent of genetic and epigenetic inactivation of the APC gene in myxoid/round-cell LPS. Sequencing of the mutation cluster region, the protein truncation test and a loss of heterozygosity (LOH) analysis did not reveal any genetic alterations of the APC gene in all of the liposarcoma samples. Methylation of the APC promoter was detected by methylation-specific PCR in 9 of 20 (45%) tumours. Analysis of APC expression by semiquantitative RT-PCR in a subset of the samples demonstrated that tumours with a methylated APC promoter showed a downregulation of the APC transcript. However, APC downregulation was not correlated with a stabilisation of the b-catenin protein.Thus, the epigenetic regulation of the APC gene might play an important role in the pathogenesis of myxoid/round-cell LPS. However, the impact of APC methylation on liposarcoma development is quite likely not mediated through WNT signalling. ' 2006 Wiley-Liss, Inc.Key words: adenomatous polyposis coli; methylation; liposarcoma Even though genetic hits leading to carcinogenesis have been well characterized, the role of epigenetic factors in tumour formation is just emerging. Epigenetics makes an impact on such different fields as chromosomal stability, silencing of retroelements and the setup and maintenance of a cell's expression status, thereby functioning as cellular memory. In the latter context, the promoter hypermethylation of tumour suppressor genes leading to their aberrant transcriptional silencing has been intensively studied. 1 It has also been shown that epigenetic phenomena such as DNA methylation and histone modification can be considered diagnostic or even prognostic markers. 2,3 The APC tumour suppressor protein exhibits diverse functions in the cell, whereby its role in the WNT signalling pathway is especially well described. It therein acts as a scaffolding protein in a multimeric protein complex, together with Axin and glycogen synthase kinase-3b (GSK-3b), which binds and phosphorylates the proto-oncoprotein b-catenin. Upon binding of a WNT protein to one of its receptors, the intracellular protein dishevelled inactivates GSK-3b. As a consequence, b-catenin can no longer be phosphorylated and hence marked for degradation. b-catenin then translocates into the nucleus, where it interacts with transcription factors of the TCF/LEF (T-cell factor/lymphoid enhancing factor) family. This interaction stimulates the transcription of WNT target genes like myc and...

A Case of Myxoid Liposarcoma of the Retroperitoneum: A Challenging Tumour for Diagnosis and Treatment

“…However, they have demonstrated the presence of methylation of the APC promoter that induces a downregulation of the APC transcript [6]. …”

Frzb, a Secreted Wnt Antagonist, Decreases Growth and Invasiveness of Fibrosarcoma Cells Associated with Inhibition of Met Signaling

“…Haydon et al (36) have shown that cytoplasmic and nuclear accumulation of h-catenin occurred in osteosarcoma without any activating mutation. Sievers et al (37) reported that APC gene promoter was hypermethylated without mutations in myxoid liposarcoma. Protocols are in progress in our laboratory to obtain clinical specimens to determine whether down-regulation of secreted Wnt antagonists or APC by hypermethylation or deletion are responsible for enhanced Wnt activity in STSs.…”

Wnt pathway and breast cancer

“…This results in the transcriptional activation of Wnt-1 gene that leads to the development of lobuloalveolar hyperplasia and eventually cancer (2). Furthermore, epigenetic changes or mutation at any nodal point of the Wnt pathway also leads to the development of cancer (79)(80)(81). It is well established that dysregulation in components of the Wnt pathway are responsible for tumorigenesis, and among them, betacatenin/TCF component has been widely used in transgenic mouse model to elucidate and characterize canonical Wnt pathway.…”