Abstract 4941: Epigenetic silencing of the imprinted gene ZAC (PLAGL1) by DNA methylation in sarcomas
Authors: PEILLE Anne-Lise , CHIBON Frédéric , MORVAN Valerie Le , BRESSON-BEPOLDIN Laurence 
Published: February 2011

ZAC (Zinc-finger gene involved in Apoptosis and Cell-cycle control 1 gene) is a zinc-finger nuclear transcription factor, which induces apoptotic cell death and G1 cell cycle arrest. ZAC is an imprinted gene, which is expressed only from the paternal allele.

Interestingly, ZAC is localized at human chromosome 6q24-25, a region known to harbor a tumor suppressor gene. Due to the functional properties of ZAC protein and its chromosomal localization, it has been postulated that ZAC could be the tumor suppressor gene of 6q24-25. ZAC mRNA is ubiquitously expressed in normal tissues but frequently silenced in cancers by mechanisms involving hypermethylation of its promoter or lost of heterozygosity.

Soft tissue sarcomas are uncommon but aggressive cancers, for which no efficient treatment is available. Given the tumor suppressor properties of ZAC, we have studied ZAC expression and its regulation in sarcomas to determine its role in the oncogenesis of these tumours.

DNA microarray analysis shows that the expression profile of ZAC mRNA is highly correlated with sarcoma subtypes: ZAC is not expressed in LMS (leiomyosarcoma), highly expressed in GIST (Gastro Intestinal Stromal Tumor) and weakly expressed in LPS (liposarcoma) and MFH (Malignant Fibrous Hystiocytoma). These observations suggest that ZAC may be a good candidate as diagnostic or prognostic factor in sarcomas.

To determine the mechanism by which ZAC expression is regulated in sarcomas, four sarcoma cell lines derived from various sarcoma sub-types, expressing ZAC mRNA at variable levels were studied as models. ZAC expression has previously been shown to be regulated by CpG methylation.

For the first time, we performed an extensive study of the methylation status of 105 CpG sites of ZAC promoter by pyrosequencing.

We have found that the ZAC promoter is hypomethylated in the cell line expressing high levels of ZAC mRNA, whereas it's hypermethylated in the cell line that exhibits no ZAC mRNA expression. The two cell lines with moderate ZAC mRNA expression show hemimethylation of the promoter. These observations suggest a correlation between the abundance of ZAC expression and the methylation status of ZAC promoter.

We then enlarged our study to 130 patient tumors (LMS, MFH, LPS . . .). Unlike cell lines which have a homogeneous methylation profile for all CpG island, tumors exhibit variability of the methylation rate only on particular CpG sites, which seems directed the level of ZAC mRNA expression.

In conclusion, we show here for the first time that 1) ZAC is differentially expressed in sarcoma subtypes. 2) Its expression profile appears to be regulated by methylation of “hot spots” CpG, which may be particularly crucial for the binding of transcription factors targeting ZAC promoter.

Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4941.