Abstract
PIWI family proteins have recently emerged as essential contributors in numerous biological processes including germ cell development, stem cell maintenance and epigenetic reprogramming. Expression of some of the family members has been shown to be elevated in tumors. In particular, PIWIL2 has been probed as a potential neoplasia biomarker in many cancers in humans. Previously, PIWIL2 was shown to be expressed in most tumours as a set of its shorter isoforms. In this work, we demonstrated the presence of its 60 kDa (PL2L60A) and 80 kDa (PL2L80A) isoforms in testicular cancer cell lines. We also ascertained the transcriptional boundaries of mRNAs and alternative promoter regions for these PIWIL2 isoforms. Further, we probed a range of testicular germ cell tumor (TGCT) samples and found PIWIL2 to be predominantly expressed as PL2L60A in most of them. Importantly, the levels of both PL2L60A mRNA and protein products were found to vary depending on the differentiation subtype of TGCTs, i.e., PL2L60A expression is significantly higher in undifferentiated seminomas and appears to be substantially decreased in mixed and nonseminomatous TGCTs. The higher level of PL2L60A expression in undifferentiated TGCTs was further validated in the model system of retinoic acid induced differentiation in NT2/D1 cell line. Therefore, both PL2L60A mRNA and protein abundance could serve as an additional marker distinguishing between seminomas and nonseminomatous tumors with different prognosis and therapy approaches.
Highlights
PIWI family proteins [1,2] have come to light as a new set of players in transcriptional and post-transcriptional regulation of gene expression [3,4,5,6,7,8,9,10]
RTPCR with cDNA from normal testis, teratoma, TERA1 and NT2/ D1 cell lines confirmed the absence of mRNA for the full-length PIWIL2 in all samples except testis (Fig. 1C)
There has been a significant body of statistics collected on the presence of PIWIL2 protein and its mRNA transcript in various types of cancers including breast tumors [21,22], acute myeloid leukemia [87], papillary thyroid carcinoma [26], as well as colorectal [31], colon [24,27], gastric [25], ovarian [32] and cervical cancers [23,28]
Summary
PIWI family proteins [1,2] have come to light as a new set of players in transcriptional and post-transcriptional regulation of gene expression [3,4,5,6,7,8,9,10] Their contribution has been shown to be significant for processes ranging from protection of genome against transposon activity during spermatogenesis [11,12] and stem cell maintenance [13,14] to somatic regulation and establishment of epigenetic states [15,16,17,18]. PIWIL2 knockdown in murine bone marrow mesenchymal stem cells has been shown to enhance cell proliferation and decrease expression of tumor suppressors [40]
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