Potential tumour suppressive role of testis-specific Y-encoded-like protein 2 (TSPYL2)

Abstract

Testis-specific Y-encoded-like protein 2 (TSPYL2) is a nucleosome assembly protein encoded by an X-linked gene. Previous studies have reported the tumour suppressive function of TSPYL2 by inhibiting cell proliferation and colony formation in cancer cell lines. TSPYL2 has also been revealed to form a repressor complex with the transcription factor REST to enhance TGFβ signalling. Furthermore, TSPYL2 enhances the function of p53 in response to DNA damage through its regulatory activity on SIRT1 deacetylase and p300 acetyltransferase. Nonetheless, the transcriptional regulatory mechanism of TSPYL2 and evidence on the in vivo tumour suppressive role of TSPYL2 are still lacking. Here, bioinformatic analyses were performed to examine the transcriptional regulation of TSPYL2. Using the ConTra v3 web server, MAZ, Zfp281, CKROX and E2F1 were predicted to bind the 2kb region upstream of the TSPYL2 transcription start site. ChIP-seq clusters from the ENCODE database supported the presence of MAZ and E2F1 binding in the promoter region of TSPYL2 in K562 cells, coinciding with the high intensity of DNase I hypersensitive clusters, H3K4me3 and H3K27ac marks. This supported a role of MAZ and E2F1 in the transcriptional regulation of TSPYL2. Since enhanced TSPYL2 protein expression has been reported in cancer cell lines treated with genotoxic agents or under serum starvation, we hypothesised that TSPYL2 would be induced in non-transformed cells to inhibit cell proliferation. Mouse embryonic fibroblasts (MEFs) were employed to address this hypothesis. Semi-quantitative RT-PCR showed that etoposide treatment promoted Tspyl2 expression in 24 hours. An increase in cell density also enhanced the expression of Tspyl2 (about 1.5-fold change). For treatment with ionising radiation, a mild induction (about 1.4-fold change) of Tspyl2 was indicated only in Trp53 null MEFs. Lastly, we generated double mutant mice by crossing Trp53 mutant mice with Tspyl2 mutant mice to study whether tumour development was enhanced, since Tspyl2 mutant mice did not develop tumours spontaneously. The double null mice had a longer median survival compared with the Trp53 null mice (5.75 months vs 4.5 months, n=20 in each group) and a higher occurrence of sarcoma (5 out of 13 vs 2 out of 11 tumour-bearing mice) in this pilot study. The data suggested the participation of TSPYL2 in tumorigenesis, especially in sarcoma. In summary, the current study provided novel insight into the transcriptional regulation of TSPYL2 and its functional interaction with p53 in vivo.