Differentiation-Dependent Regulation of Human Endogenous Retrovirus K Sequences and Neighboring Genes in Germ Cell Tumor Cells

Abstract

Under physiological conditions, most human endogenous retroviruses (HERVs) are transcriptionally silent. However, re-activation of HERVs is observed under pathological conditions like inflammation or cancer. In addition to expression of HERV sequences, an impact of HERV-loci on expression of adjacent genes has been suggested as probably important patho-physiological mechanism. A candidate for such a gene is PRODH (proline dehydrogenase 1), which is located on chromosome 22 adjacent to HERVK-24. Germ cell tumors (GCTs) are known to express high level of HERVK sequences. In addition, non-seminomatous GCT are useful models to study HERV expression in the context of differentiation since they reflect aspects of cellular development during embryogenesis and usually contain different cell types. This is due to the embryonal carcinoma (EC) cells, which are the stem cell component of GCT. They are pluripotent, show high expression of pluripotency markers like OCT4 and LIN28A and can differentiate into either somatic derivatives (teratoma cells) or choriocarcinoma or yolk-sac tumor cells reflecting extra-embryonal differentiation. OCT4 is lost upon differentiation. We used GCT derived cell lines of varying differentiation stages to analyze expression of HERVK and PRODH. Differentiation status and cellular relationship of GCT cells was determined using microarray analysis and western blotting of the embryonic pluripotency markers OCT4 and LIN28A. The highest expression of HERVK was found in undifferentiated EC cells, which retain a stem cell phenotype and express both OCT4 and LIN28. In contrast, the lowest expression of HERVK was observed in somatic differentiated GCT cells which also lack OCT4 and LIN28A whereas GCT cells with differentiation characteristics of yolk-sac tumor expressed LIN28A but not OCT4 and showed intermediate level of HERVK. A similar pattern was found for PRODH. Differentiation of EC cells by siRNA mediated knock-down of OCT4 or treatment with differentiation inducing medium decreased expression of HERVK and PRODH. Treatment of differentiated GCT cells with 5′-azacytidine and trichostatin A increased expression of HERVK and PRODH, indicating that epigenetic mechanisms are responsible for altered expression of these genes. Our data suggest that HERVK expression is dependent on cellular differentiation stages regulated by epigenetic mechanisms, which can also affect expression of neighboring genes.

Differential gene expression in cisplatin-resistant and -sensitive testicular germ cell tumor cell lines

“…Accordingly, analysis of POU5F1 on the protein level clearly separates sensitive TGCT cell lines showing high POU5F1 expression in resistant TGCT cell lines lacking POU5F1 expression [ 34 , 57 ]. A recent study investigating the differentiation-dependent regulation of expression of human endogenous retrovirus K sequences (HERVK) using these TGCT cell lines confirmed POU5F1 expression pattern and showed high HERVK expression in POU5F1 -expressing sensitive EC cells (e.g., H12.1), whereas the POU5F1 -negative, resistant cells could be further distinguished into cells with extra-embryonic differentiation characteristics towards YST (e.g., 1411HP) showing intermediate level of HERVK, and cells with somatic differentiation characteristics (1777NRpmet and H12.1D) showing low HERVK expression [ 58 ]. Therefore, in accordance with pluripotency markers, additional factors found in the present study to be down-regulated in all resistant TGCT cell lines may reflect the loss of the pluripotent state in general ( DNMT3L , WNT6 and ZFP42 ), whereas factors which also differ among resistant cell lines ( GAL , IGDCC3 , IGFBP2 , IGFBP7 , L1TD1 and NTF3 ) may further reflect a differentiation towards different lineages.…”

Expression of A New Endogenous Retrovirus-Associated Transcript in Hodgkin Lymphoma Cells

“…The phenotype of the few established HL cell lines is not uniform. Among the investigated HL cell lines, L-1236 cells showed also highest expression of ERV-K transcripts [37]. ERV-K transcripts are detectable in high amounts in embryonic carcinoma cells and the embryonic transcription profile seems to correlate with the increased ERV-K expression in these cells [37].…”

Endogenous Retroviruses in Nervous System Disorders

“…Moreover, polymorphisms in HERV loci or adjacent genes have been associated with schizophrenia [ 188 , 189 , 190 , 191 , 192 , 193 ]. One of these loci, proline dehydrogenase 1 (PRODH) from human chromosome 22, is an interesting example for the co-regulation of HERV and neighboring genes [ 193 , 194 ]. Here, the LTR form of an HERV (ERVK-24) drives the expression of HERV sequences as well as the expression of PRODH.…”

“…Here, the LTR form of an HERV (ERVK-24) drives the expression of HERV sequences as well as the expression of PRODH. Germ cell tumors with high expression of this HERV also show high expression of PRODH and forced differentiation of these tumor cells results in concomitant down-regulation of PRODH and ERVK-24 [ 194 ].…”