Analysis of PTEN Methylation Patterns in Soft Tissue Sarcomas by MassARRAY Spectrometry

Abstract

Soft tissue sarcomas (STSs) are a rare and fascinating group of diseases that can be subdivided into specific reciprocal translocations in STSs (SRTSs) and nonspecific reciprocal translocations in STSs (NRTSs). PTEN mutations are rare in STSs, suggesting that PTEN expression may be lost by alternative mechanisms such as methylation. In order to reveal whether aberrant PTEN methylation occurs in STSs, MassARRAY Spectrometry was carried to detect methylation patterns of PTEN in STSs. We evaluated methylation levels in 41 CpG sites from −2,515 to −2,186 bp (amplicon A) and −1,786 to −1,416 bp (amplicon B) relative to the translation initiation site in 110 different cases (46 cases of SRTSs, 40 cases of NRTSs, and 24 cases of normal controls). In addition, immunohistochemistry (IHC) was used to detect the loss of PTEN to determine whether PTEN alterations were responsible for decreased PTEN expression. Our data showed that expression of PTEN was diminished in 49 (57%) STSs, whereas the remaining cases (43%) were classified as high expression. Our previous results found that only 2 of 86 cases (2.3%) had a PTEN mutation suggesting that PTEN may be mainly downregulated in STSs by methylation, but not by mutation of PTEN itself. We observed that amplicon A was hypermethylated in STSs with low PTEN expression, whereas normal controls had low methylation levels (P<0.0001), which was not present in amplicon B (P>0.05), nor were there significant differences in the methylation levels in PTEN between SRTS and NRTS cases. The majority of individual CpG units within two amplicons was demonstrated to be hypermethylated. These findings indicate that PTEN hypermethylation is a common event in STSs suggesting that the inactivation of PTEN may be due to hypermethylation in the promoter of PTEN. The aberrant methylation of the CpG sites within PTEN promoter may serve as a potential candidate biomarker for STSs.

Epigenetic regulation of RTK signaling

“…PTEN promoter hypermethylation was also observed in approximately 39% (26 of 66 cases) of human gastric carcinomas, of which 73% (19 of 26) of the cases correlated with a loss of PTEN expression by immunohistochemistry [28]. Later studies demonstrated PTEN promoter hypermethylation in other cancers including soft tissue sarcomas, which is especially important due to the low frequency with which PTEN genomic alterations occur in this cancer subtype[30]. …”

Hypermethylation of potential tumor suppressor miR-34b/c is correlated with late clinical stage in patients with soft tissue sarcomas

“…Previous studies have identified that genomic alterations, including the amplification or point mutation of oncogenes and the methylation or deletion of tumor suppressor genes (e.g., MDM2 amplification, P53 mutation, and PTEN methylation), are involved in the carcinogenesis of subtype-specific STSs (Barretina et al, 2010;Hettmer et al, 2014;Ware et al, 2014;Yin et al, 2013). Moreover, p53 mutations were detected in 25.6% of STSs, the date has suggested that p53 mutations may be involved in the oncogenesis of STS (Yin et al, 2012).…”

Dermatofibrosarcoma Protuberans in a Patient With Cowden Syndrome

“…In a study examining PTEN immunohistochemical expression in 10 cases of DFSP, 4 retained the expression of PTEN and 6 showed decreased expression. 12 Therefore, it is possible that the loss of PTEN function may play a role in at least some sporadic cases of DFSP, and that our patient could potentially be more susceptible to DFSP tumorigenesis given his germline PTEN mutation.…”