Activation of a GPCR leads to eIF4G phosphorylation at the 5' cap and to IRES-dependent translation

Testicular piRNA Analysis Identified Dysregulated piRNAs in Non-obstructive Azoospermia

Male infertility has remained idiopathic in a remarkable proportion of all cases. Gonadal expression of PIWI-interacting RNAs (piRNAs) has been shown to be vital to normal spermatogenesis, as they are expressed in almost all types of testicular germ cells. These molecules and their related Piwi proteins strictly regulate transposable elements' activity and gene expression. We aimed to identify dysregulated piRNAs in idiopathic non-obstructive azoospermic (NOA) testis by global expression analysis. Testis tissue samples from 18 azoospermic patients (ten NOA and eight OA) were studied by small RNA sequencing. To validate high-throughput sequencing data, quantitative real-time polymerase chain reactions for two differentially altered piRNAs were performed. Bioinformatics analyses were undertaken to identify pathways affected by piRNA dysregulation. In the NOA group, 1328 piRNAs were identified to be differentially expressed, of which 1322 were downregulated and 6 were upregulated. Bioinformatics analysis corroborated the involvement of dysregulated piRNA in spermatogenesis. We also identified 64 clusters of differentially expressed piRNAs, of which 42 clusters had a minimum of ten absolute piRNA hits. Our study suggests that piRNAs show significant dysregulation in infertility. Their target genes play a role in their self-biogenesis, probably by regulating their own production through a feedback mechanism. The downregulated piRNAs may find value as biomarkers for the presence of spermatozoa in the testis of azoospermic individuals, while the upregulated piRNAs are great candidates for further investigation of their precise functions in spermatogenesis.

FSH for the Treatment of Male Infertility

Follicle-stimulating hormone (FSH) supports spermatogenesis acting via its receptor (FSHR), which activates trophic effects in gonadal Sertoli cells. These pathways are targeted by hormonal drugs used for clinical treatment of infertile men, mainly belonging to sub-groups defined as hypogonadotropic hypogonadism or idiopathic infertility. While, in the first case, fertility may be efficiently restored by specific treatments, such as pulsatile gonadotropin releasing hormone (GnRH) or choriogonadotropin (hCG) alone or in combination with FSH, less is known about the efficacy of FSH in supporting the treatment of male idiopathic infertility. This review focuses on the role of FSH in the clinical approach to male reproduction, addressing the state-of-the-art from the little data available and discussing the pharmacological evidence. New compounds, such as allosteric ligands, dually active, chimeric gonadotropins and immunoglobulins, may represent interesting avenues for future personalized, pharmacological approaches to male infertility.

FSH Receptor Signaling: Complexity of Interactions and Signal Diversity

FSH is synthesized in the pituitary by gonadotrope cells. By binding to and interacting with its cognate receptor [FSH receptor (FSHR)] in the gonads, this gonadotropin plays a key role in the control of gonadal function and reproduction. Upon activation, the FSHR undergoes conformational changes leading to transduction of intracellular signals, including dissociation of G protein complexes into components and activation of several associated interacting partners, which concertedly regulate downstream effectors. The canonical Gs/cAMP/protein kinase A pathway, considered for a long time as the sole effector of FSHR-mediated signaling, is now viewed as one of several mechanisms employed by this receptor to transduce intracellular signals in response to the FSH stimulus. This complex network of signaling pathways allows for a fine-tuning regulation of the gonadotropic stimulus, where activation/inhibition of its multiple components vary depending on the cell context, cell developmental stage, and concentration of associated receptors and corresponding ligands. Activation of these multiple signaling modules eventually converge to the hormone-integrated biological response, including survival, proliferation and differentiation of target cells, synthesis and secretion of paracrine/autocrine regulators, and, at the molecular level, functional selectivity and differential gene expression. In this mini-review, we discuss the complexity of FSHR-mediated intracellular signals activated in response to ligand stimulation. A better understanding of the signaling pathways involved in FSH action might potentially influence the development of new therapeutic strategies for reproductive disorders.

G protein-dependent signaling triggers a β-arrestin-scaffolded p70S6K/ rpS6 module that controls 5'TOP mRNA translation

Many interaction partners of β-arrestins intervene in the control of mRNA translation. However, how β-arrestins regulate this cellular process has been poorly explored. In this study, we show that β-arrestins constitutively assemble a p70S6K/ribosomal protein S6 (rpS6) complex in HEK293 cells and in primary Sertoli cells of the testis. We demonstrate that this interaction is direct, and experimentally validate the interaction interface between β-arrestin 1 and p70S6K predicted by our docking algorithm. Like most GPCRs, the biological function of follicle-stimulating hormone receptor (FSHR) is transduced by G proteins and β-arrestins. Upon follicle-stimulating hormone (FSH) stimulation, activation of G protein-dependent signaling enhances p70S6K activity within the β-arrestin/p70S6K/rpS6 preassembled complex, which is not recruited to the FSHR. In agreement, FSH-induced rpS6 phosphorylation within the β-arrestin scaffold was decreased in cells depleted of Gα_s. Integration of the cooperative action of β-arrestin and G proteins led to the translation of 5' oligopyrimidine track mRNA with high efficacy within minutes of FSH input. Hence, this work highlights new relationships between G proteins and β-arrestins when acting cooperatively on a common signaling pathway, contrasting with their previously shown parallel action on the ERK MAP kinase pathway. In addition, this study provides insights into how GPCR can exert trophic effects in the cell.-Tréfier, A., Musnier, A., Landomiel, F., Bourquard, T., Boulo, T., Ayoub, M. A., León, K., Bruneau, G., Chevalier, M., Durand, G., Blache, M.-C., Inoue, A., Fontaine, J., Gauthier, C., Tesseraud, S., Reiter, E., Poupon, A., Crépieux, P. G protein-dependent signaling triggers a β-arrestin-scaffolded p70S6K/ rpS6 module that controls 5'TOP mRNA translation.

Regulation of mRNA Translation in Neurons-A Matter of Life and Death

Dynamic regulation of mRNA translation initiation and elongation is essential for the survival and function of neural cells. Global reductions in translation initiation resulting from mutations in the translational machinery or inappropriate activation of the integrated stress response may contribute to pathogenesis in a subset of neurodegenerative disorders. Aberrant proteins generated by non-canonical translation initiation may be a factor in the neuron death observed in the nucleotide repeat expansion diseases. Dysfunction of central components of the elongation machinery, such as the tRNAs and their associated enzymes, can cause translational infidelity and ribosome stalling, resulting in neurodegeneration. Taken together, dysregulation of mRNA translation is emerging as a unifying mechanism underlying the pathogenesis of many neurodegenerative disorders.

Nucleolin enhances internal ribosomal entry site (IRES)-mediated translation of Sp1 in tumorigenesis

Our previous study indicated that specificity protein-1 (Sp1) is accumulated during hypoxia in an internal ribosomal entry site (IRES)-dependent manner. Herein, we found that the Sp1 was induced strongly at the protein level, but not in the mRNA level, in lung tumor tissue, indicating that translational regulation might contribute to the Sp1 accumulation during tumorigenesis. A further study showed that the translation of Sp1 was dramatically induced through an IRES-dependent pathway. RNA immunoprecipitation analysis of proteins bound to the 5'-untranslated region (5'-UTR) of Sp1 identified interacting protein - nucleolin. Knockdown of nucleolin significantly inhibited IRES-mediated translation of Sp1, suggesting that nucleolin positively facilitates Sp1 IRES activation. Further analysis of the interaction between nucleolin and the 5'-UTR of Sp1 mRNA revealed that the GAR domain was important for IRES-mediated translation of Sp1. Moreover, gefitinib, and LY294002 and MK2206 compounds inhibited IRES-mediated Sp1 translation, implying that activation of the epithelial growth factor receptor (EGFR) pathway via Akt activation triggers the IRES pathway. In conclusion, EGFR activation-mediated nucleolin phosphorylated at Thr641 and Thr707 was recruited to the 5'-UTR of Sp1 as an IRES trans-acting factor to modulate Sp1 translation during lung cancer formation.