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X inactivation in human testicular tumors. XIST expression and androgen receptor methylation status
L H Looijenga1, A J Gillis, R J van Gurp
1Laboratory for Experimental Patho-Oncology, Dr. Daniel den Hoed Cancer Center, Academic Hospital Rotterdam, The Netherlands.
Abstract:
In female mammalian cells, inactivation of one of the X chromosomes compensates the increased dosage of X-linked genes as compared with their male counterparts. This process is initiated by the X-inactive specific transcripts of the xist/XIST gene in cis, resulting in methylation of specific sites of genes to be silenced. However, in male germ cells, X inactivation is established by xist/XIST expression only. We investigated the X inactivation pattern in human testicular tumors of different histogenesis by analysis of XIST expression and methylation of the androgen receptor gene. XIST was expressed only in tumors derived from the germ cell lineage with supernumerical X chromosomes: seminomas, nonseminomas, and spermatocytic seminomas. Although low expression was present in testicular parenchyma with spermatogenesis, XIST was expressed at a higher level in parenchyma with carcinoma in situ, the precursor lesion of seminomas and nonseminomas. Despite the consistent expression of XIST in germ-cell-derived tumors with gain of X chromosomes, methylation of the androgen receptor gene was present in all differentiated but only in a proportion of the undifferentiated nonseminomas. This differential pattern of methylation was also found in a number of representative cell lines. Our data indicate that the counting mechanism resulting in X inactivation is functional in testicular cancers of different histogenesis. Moreover, the differentiation-dependent pattern of X inactivation as reported during normal development in the case of multiple X chromosomes by methylation is retained in these tumors. We conclude therefore that X inactivation allows the excessive gain of X chromosomes found in germ-cell-derived tumors of the adult testis. In addition, this offers an interesting model to study the fundamental mechanisms of these processes.
Insights
X chromosome inactivation is functional in human testicular tumors, retaining normal differentiation patterns. This process allows cells to manage extra X chromosomes in germ cell-derived cancers.
Area of Science:
- Genetics
- Epigenetics
- Cancer Biology
Background:
- Mammalian X chromosome inactivation equalizes gene dosage between sexes.
- XIST gene expression initiates X inactivation, leading to gene silencing via methylation.
- X inactivation mechanisms in male germ cells and testicular tumors are not fully understood.
Purpose of the Study:
- Investigate X inactivation patterns in human testicular tumors.
- Analyze XIST expression and androgen receptor gene methylation in various tumor types.
- Determine if X inactivation is functional and retains normal developmental patterns in testicular cancers.
Main Methods:
- Analysis of XIST gene expression in tumor samples and cell lines.
- Methylation analysis of the androgen receptor gene.
- Comparison of XIST expression and methylation patterns across different testicular tumor histologies and normal testicular parenchyma.
Main Results:
- XIST expression was detected in germ cell-derived tumors (seminomas, nonseminomas, spermatocytic seminomas) with extra X chromosomes.
- Elevated XIST expression was observed in carcinoma in situ compared to normal testicular parenchyma with spermatogenesis.
- Androgen receptor gene methylation was consistent in differentiated tumors but variable in undifferentiated nonseminomas, mirroring normal development.
Conclusions:
- The X chromosome counting mechanism for inactivation is functional in testicular cancers.
- Testicular tumors retain differentiation-dependent X inactivation patterns observed during normal development.
- X inactivation facilitates the management of supernumerary X chromosomes in germ cell-derived testicular tumors.