Loss of the MAF Transcription Factor in Laryngeal Squamous Cell Carcinoma.

MAF is a transcription factor that may act either as a tumor suppressor or as an oncogene, depending on cell type. We have shown previously that the overexpressed miR-1290 influences MAF protein levels in LSCC (laryngeal squamous cell carcinoma) cell lines. In this study, we shed further light on the interaction between miR-1290 and MAF, as well as on cellular MAF protein localization in LSCC. We confirmed the direct interaction between miR-1290 and MAF 3'UTR by a dual-luciferase reporter assay. In addition, we used immunohistochemistry staining to analyze MAF protein distribution and observed loss of MAF nuclear expression in 58% LSCC samples, of which 10% showed complete absence of MAF, compared to nuclear and cytoplasmatic expression in 100% normal mucosa. Using TCGA data, bisulfite pyrosequencing and CNV analysis, we excluded the possibility that loss-of-function mutations, promoter region DNA methylation or CNV are responsible for MAF loss in LSCC. Finally, we identified genes involved in the regulation of apoptosis harboring the MAF binding motif in their promoter region by applied FIMO and DAVID GO analysis. Our results highlight the role of miR-1290 in suppressing MAF expression in LSCC. Furthermore, MAF loss or mislocalization in FFPE LSCC tumor samples might suggest that MAF acts as a LSCC tumor suppressor by regulating apoptosis.

Role of PUM RNA-Binding Proteins in Cancer.

Until recently, post-transcriptional gene regulation (PTGR), in contrast to transcriptional regulation, was not extensively explored in cancer, even though it seems to be highly important. PUM proteins are well described in the PTGR of several organisms and contain the PUF RNA-binding domain that recognizes the UGUANAUA motif, located mostly in the 3' untranslated region (3'UTR) of target mRNAs. Depending on the protein cofactors recruited by PUM proteins, target mRNAs are directed towards translation, repression, activation, degradation, or specific localization. Abnormal profiles of PUM expression have been shown in several types of cancer, in some of them being different for PUM1 and PUM2. This review summarizes the dysregulation of PUM1 and PUM2 expression in several cancer tissues. It also describes the regulatory mechanisms behind the activity of PUMs, including cooperation with microRNA and non-coding RNA machineries, as well as the alternative polyadenylation pathway. It also emphasizes the importance of future studies to gain a more complete picture of the role of PUM proteins in different types of cancer. Such studies may result in identification of novel targets for future cancer therapies.

Characterization of RNP Networks of PUM1 and PUM2 Post-Transcriptional Regulators in TCam-2 Cells, a Human Male Germ Cell Model.

Mammalian Pumilio (PUM) proteins are sequence-specific, RNA-binding proteins (RBPs) with wide-ranging roles. They are involved in germ cell development, which has functional implications in development and fertility. Although human PUM1 and PUM2 are closely related to each other and recognize the same RNA binding motif, there is some evidence for functional diversity. To address that problem, first we used RIP-Seq and RNA-Seq approaches, and identified mRNA pools regulated by PUM1 and PUM2 proteins in the TCam-2 cell line, a human male germ cell model. Second, applying global mass spectrometry-based profiling, we identified distinct PUM1- and PUM2-interacting putative protein cofactors, most of them involved in RNA processing. Third, combinatorial analysis of RIP and RNA-Seq, mass spectrometry, and RNA motif enrichment analysis revealed that PUM1 and PUM2 form partially varied RNP-regulatory networks (RNA regulons), which indicate different roles in human reproduction and testicular tumorigenesis. Altogether, this work proposes that protein paralogues with very similar and evolutionary highly conserved functional domains may play divergent roles in the cell by combining with different sets of protein cofactors. Our findings highlight the versatility of PUM paralogue-based post-transcriptional regulation, offering insight into the mechanisms underlying their diverse biological roles and diseases resulting from their dysfunction.

Human NANOS1 Represses Apoptosis by Downregulating Pro-Apoptotic Genes in the Male Germ Cell Line.

While two mouse NANOS paralogues, NANOS2 and NANOS3, are crucial for maintenance of germ cells by suppression of apoptosis, the mouse NANOS1 paralogue does not seem to regulate these processes. Previously, we described a human NANOS1 p.[(Pro34Thr);(Ser83del)] mutation associated with the absence of germ cells in seminiferous tubules of infertile patients, which might suggest an anti-apoptotic role of human NANOS1. In this study, we aimed to determine a potential influence of human NANOS1 on the maintenance of TCam-2 model germ cells by investigating proliferation, cell cycle, and apoptosis. Constructs encoding wild-type or mutated human NANOS1 were used for transfection of TCam-2 cells, in order to investigate the effect of NANOS1 on cell proliferation, which was studied using a colorimetric assay, as well as apoptosis and the cell cycle, which were measured by flow cytometry. RNA-Seq (RNA sequencing) analysis followed by RT-qPCR (reverse transcription and quantitative polymerase chain reaction) was conducted for identifying pro-apoptotic genes repressed by NANOS1. Here, we show that overexpression of NANOS1 downregulates apoptosis in TCam-2 cells. Moreover, we found that NANOS1 represses a set of pro-apoptotic genes at the mRNA level. We also found that the infertility-associated p.[(Pro34Thr);(Ser83del)] mutation causes NANOS1 to functionally switch from being anti-apoptotic to pro-apoptotic in the human male germ cell line. Thus, this report is the first to show an anti-apoptotic role of NANOS1 exerted by negative regulation of mRNAs of pro-apoptotic genes.