Global analysis of chromosome X gene expression in primary cultures of normal ovarian surface epithelial cells and epithelial ovarian cancer cell lines

Abstract

The interpretation of loss of heterozygosity (LOH) in cancers is complicated as genes that map to LOH regions may be transcriptionally active (Xa) or inactive (Xi) due to X chromosome inactivation (XCI). We have analyzed the chromosome X transcriptome in four epithelial ovarian cancer (EOC) cell lines (TOV21G, TOV81D, TOV112D, and OV90) and 12 primary cultures of normal ovarian surface epithelial (NOSE) cells in relation to chromosome X integrity. Two-way comparative analysis using HuGeneFL Affymetrix GeneChips ® of TOV21G, TOV81D and OV90 relative to the NOSE samples was highly correlated (>89%) in contrast to that of TOV112D (56-69%). TOV112D, followed by TOV21G, exhibited the largest number of up-regulated genes. XIST expression by RT-PCR was not detectable in TOV112D or TOV21G. Allele-specific transcription by cDNA sequence analysis of genes known to be subjected to XCI revealed maintenance of XCI in TOV81D and OV90, but not TOV21G. Biallelic expression could not be assessed in TOV112D due to reduction to hemizygosity of chromosome X. Chromosome X rearrangements were observed in FISH analysis of TOV112D and TOV21G, and both of these EOC cell lines were negative for Barr body analysis. The differentially expressed genes did not appear to map to any particular region of the X chromosome in any EOC cell line. The absence of XIST expression is consistent with Barr body loss in TOV112D and TOV21G. The combined evidence is consistent with two proposed mechanisms to account for absence of Xi in female cancers: Xi loss followed by Xa duplication (exemplified by TOV112D) and transcriptional reactivation of Xi (exemplified by TOV21G). Despite an alteration in XIST expression and differences in allelic content in the EOC cell lines, the chromosome X transcriptome was modified modestly when compared with that of NOSE samples.

Sexual dimorphism in cancer

“…Although inactivation of one X chromosome over the other is generally random, preferential inactivation of one chromosome (skewed Xi) can protect women against the consequences of X-linked gene mutations 104 . On the contrary the absence of Xi can have detrimental effects: for instance loss of Xist has been reported in breast, ovarian and cervical cancer cell lines 105,106 and, only in female mutant mice, it caused deregulation of hematopoietic lineages and emergence of myeloid neoplasms associated with genome wide changes in gene expression 107 .…”

Downregulation of BC200 in ovarian cancer contributes to cancer cell proliferation and chemoresistance to carboplatin

“…These lncRNAs are involved in various biological processes of ovarian cancer, including chemotherapy, proliferation, apoptosis and metastasis (21)(22)(23)(24). Previous studies have suggested the potential role of lncRNAs in ovarian cancer to a certain extent (15)(16)(17)(18)(19)(20)(21)(22)(23)(24), however, further investigation is required to explain their respective functions and mechanisms of action.…”

“…X-inactive specific transcript, long stress-induced non-coding transcript 5, Pvt1 oncogene, serum resistance-associated gene and host genes 2 (15)(16)(17)(18)(19)(20). These lncRNAs are involved in various biological processes of ovarian cancer, including chemotherapy, proliferation, apoptosis and metastasis (21)(22)(23)(24).…”

Calcified tissue of fetal origin in utero

“…To determine whether the origin of the specimen was fetal or maternal, we extracted DNA from peripheral lymphocytes from the patient and performed a polymerase chain reactionbased genotyping assay using 17 polymorphic microsatellite repeat markers as described elsewhere (1).…”

“…genome.ucsc.edu/cgi-bin/hgGateway). b Genetic markers described in Genome Database (www.gdb.org) and Benoit et al(1). c Results were not obtained in the analysis of tissue DNA for the following genetic markers: D3S1263, D13S1701, MHBPNT2, AR.PCR1, and DX8074.…”