SPIN1 is a proto-oncogene and SPIN3 is a tumor suppressor in human seminoma SPIN1 is a proto-oncogene and SPIN3 is a tumor suppressor in human seminoma

The p53 protein is one of the transcription factors responsible for cell cycle regulation and prevention of cancer development. Its expression is regulated at the transcriptional, translational and post-translational levels. Recent years of research have shown that the 5ʹ terminus of p53 mRNA plays an important role in this regulation. This region seems to be a docking platform for proteins involved in p53 expression, particularly under stress conditions. Here, we applied RNA-centric affinity chromatography to search for proteins that bind to the 5ʹ terminus of p53 mRNA and thus may be able to regulate the p53 expression profile. We found heterogeneous nuclear ribonucleoprotein K, hnRNP K, to be one of the top candidates. Binding of hnRNP K to the 5ʹ-terminal region of p53 mRNA was confirmed in vitro. We demonstrated that changes in the hnRNP K level in the cell strongly affected the p53 expression profile under various stress conditions. Downregulation or overexpression of hnRNP K caused a decrease or an increase in the p53 mRNA amount, respectively, pointing to the transcriptional mode of expression regulation. However, when hnRNP K was overexpressed under endoplasmic reticulum stress and the p53 amount was elevated no changes in the p53 mRNA level were detected suggesting translational regulation of p53 expression. Our findings have shown that hnRNP K is not only a mutual partner of p53 in the transcriptional activation of target genes under stress conditions but it also acts as a regulator of p53 expression at the transcriptional and potentially translational levels.

Nanos RNA-binding proteins are critical factors of germline development throughout the animal kingdom and their dysfunction causes infertility. During evolution, mammalian Nanos paralogues adopted divergent roles in germ cell biology. However, the molecular basis behind this divergence, such as their target mRNAs, remains poorly understood. Our RNA-sequencing analysis in a human primordial germ cell model-TCam-2 cell line revealed distinct pools of genes involved in the cell cycle process downregulated upon NANOS1 and NANOS3 overexpression. We show that NANOS1 and NANOS3 proteins influence different stages of the cell cycle. Namely, NANOS1 is involved in the G1/S and NANOS3 in the G2/M phase transition. Many of their cell cycle targets are known infertility and cancer-germ cell genes. Moreover, NANOS3 in complex with RNA-binding protein PUM1 causes 3′UTR-mediated repression of FOXM1 mRNA encoding a transcription factor crucial for G2/M phase transition. Interestingly, while NANOS3 and PUM1 act as post-transcriptional repressors of FOXM1, FOXM1 potentially acts as a transcriptional activator of NANOS3, PUM1, and itself. Finally, by utilizing publicly available RNA-sequencing datasets, we show that the balance between FOXM1-NANOS3 and FOXM1-PUM1 expression levels is disrupted in testis cancer, suggesting a potential role in this disease.

In this review, the latest research concerning the structure and function of the 5′-terminal region of p53 mRNA was discussed. Special attention was focused on defined structural motifs which are present in this region, as well as their conservation and plausible functional role in translation. It is known that the length of the 5′-terminal region and the structural environment of initiation codons can strongly modulate translation initiation. The ability of this region of p53 mRNA to bind protein factors was also described with special emphasis on general principles that govern, such RNA-protein interactions. The structural alterations within the 5′-terminal region of p53 mRNA and proteins that bind to this region have a strong impact on the rate of mRNA scanning and on translation efficiency in in vitro assays, in selected cell lines, and under stress conditions. Thus, the structural features of the 5′-terminal region of p53 mRNA seem to be very important for translation and for translation regulation mechanisms. Finally, we suggested topics that, in our opinion, should be further explored for better understanding of the mechanisms of the p53 gene expression regulation at the translational level.

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.