The 1.8 Å Crystal Structure of ACTIBIND Suggests a Mode of Action for T2 Ribonucleases As Antitumorigenic Agents

Expression, Location, Clinical Implication, and Bioinformatics Analysis of RNASET2 in Gastric Adenocarcinoma

Background: In addition to exploiting its ribonuclease capacity, Ribonuclease T2 (RNASET2) has been reported to exert anti-angiogenic and anti-tumorigenic effects in several tumors. However, the role of RNASET2 in gastric adenocarcinoma (GAC) remains unclear. The purpose of this study was to explore the expression, location, and clinical implications of RNASET2 in GAC.

Methods: Data of RNASET2 mRNA expression in GAC and normal gastric mucosa tissues were extracted from three GSE series and 388 TCGA samples and reanalyzed. Genome-wide CRISPR/Cas9 proliferation screening datasets were used to investigate cell growth changes after RNASET2 knockout in 19 GAC cell lines. The biological processes involved in RNASET2 were studied by the bioinformatics analysis. Furthermore, the corresponding experiments including immunohistochemical staining, clinicopathological features analysis, survival curve, microvessel density detection, cell viability assay, and colony formation assay were performed to validate the expression and function of RNASET2 in GAC.

Results: An abundance of RNASET2 was present in the fundus glands and pylorus glands of the normal gastric mucosa. RNASET2 mRNA and protein were down-regulated in GAC compared with adjacent non-cancerous or normal gastric mucosa tissues. The expression of RNASET2 mRNA and protein in early GAC was higher than that in advanced GAC. 79/134 gene sets involved in the early GAC pathway were enriched in the RNASET2 mRNA high expression group. Genome-wide shRNA and CRISPR/Cas9 proliferation screening showed that knockdown or knockout of RNASET2 could not significantly promote GAC cell growth. AlamarBlue cell viability assay and colony formation assay in AGS cells further validated these results. Clinicopathologic features and survival analysis demonstrated that RNASET2 protein was significantly correlated with tumor cell differentiation, Lauren's classification, and TM4SF1 protein expression, but not correlated with lymph nodal metastasis and patient's prognosis. Microvessel density detection indicated that no significant correlation was found between the expression of RNASET2 protein and the angiogenesis of GAC.

Conclusions: Down-regulation of RNASET2 in GAC was only the consequence of the GAC, instead of the driver. The expression of RNASET2 could be regarded as a good biomarker for identifying the early stage of GAC.

RNASET2 impairs the sperm motility via PKA/PI3K/calcium signal pathways

Asthenozoospermia is one of the leading causes of male infertility owing to a decline in sperm motility. Herein, we determined if there is a correlation between RNASET2 content on human spermatozoa and sperm motility in 205 semen samples from both asthenozoospermia patients and normozoospermia individuals. RNASET2 content was higher in sperm from asthenozoospermia patients than in normozoospermia individuals. On the other hand, its content was inversely correlated with sperm motility as well as progressive motility. Moreover, the inhibitory effect of RNASET2 on sperm motility was induced by incubating normozoospermic sperm with RNase T2 protein. Such treatment caused significant declines in intracellular spermatozoa PKA activity, PI3K activity and calcium level, which resulted in severely impaired sperm motility, and the sperm motility was largely rescued by cAMP supplementation. Finally, protein immunoprecipitation and mass spectrometry identified proteins whose interactions with RNASET2 were associated with declines in human spermatozoa motility. AKAP4, a protein regulating PKA activity, coimmunoprecipated with RNASET2 and they colocalized with one another in the sperm tail, which might contribute to reduced sperm motility. Thus, RNASET2 may be a novel biomarker of asthenozoospermia. Increases in RNASET2 can interact with AKAP4 in human sperm tail and subsequently reduce sperm motility by suppressing PKA/PI3K/calcium signaling pathways.

Human RNASET2 derivatives as potential anti-angiogenic agents: actin binding sequence identification and characterization

Human RNASET2 (hRNASET2) has been demonstrated to exert antiangiogenic and antitumorigenic effects independent of its ribonuclease capacity. We suggested that RNASET2 exerts its antiangiogenic and antitumorigenic activities via binding to actin and consequently inhibits cell motility. We focused herein on the identification of the actin binding site of hRNASET2 using defined sequences encountered within the whole hRNASET2 protein. For that purpose we designed 29 different hRNASET2-derived peptides. The 29 peptides were examined for their ability to bind immobilized actin. Two selected peptides-A103-Q159 consisting of 57 amino acids and peptide K108-K133 consisting of 26 amino acids were demonstrated to have the highest actin binding ability and concomitantly the most potent anti-angiogenic activity.

Further analyses on the putative mechanisms associated with angiogenesis inhibition exerted by peptide K108-K133 involved its location during treatment within the HUVE cells. Peptide K108-K133 readily penetrates the cell membrane within 10 min of incubation. In addition, supplementation with angiogenin delays the entrance of peptide K108-K133 to the cell suggesting competition on the same cell internalization route. The peptide was demonstrated to co-localize with angiogenin, suggesting that both molecules bind analogous cellular epitopes, similar to our previously reported data for ACTIBIND and trT2-50.

Structure and activity of the only human RNase T2

Mutations in the gene of human RNase T2 are associated with white matter disease of the human brain. Although brain abnormalities (bilateral temporal lobe cysts and multifocal white matter lesions) and clinical symptoms (psychomotor impairments, spasticity and epilepsy) are well characterized, the pathomechanism of RNase T2 deficiency remains unclear. RNase T2 is the only member of the Rh/T2/S family of acidic hydrolases in humans. In recent years, new functions such as tumor suppressing properties of RNase T2 have been reported that are independent of its catalytic activity. We determined the X-ray structure of human RNase T2 at 1.6 Å resolution. The α+β core fold shows high similarity to those of known T2 RNase structures from plants, while, in contrast, the external loop regions show distinct structural differences. The catalytic features of RNase T2 in presence of bivalent cations were analyzed and the structural consequences of known clinical mutations were investigated. Our data provide further insight into the function of human RNase T2 and may prove useful in understanding its mode of action independent of its enzymatic activity.