Antitumor Macrophage Response to Bacillus pumilus Ribonuclease (Binase)

Antitumour Activity of the Ribonuclease Binase from Bacillus pumilus in the RLS40 Tumour Model Is Associated with the Reorganisation of the miRNA Network and Reversion of Cancer-Related Cascades to Normal Functioning

The important role of miRNA in cell proliferation and differentiation has raised interest in exogenous ribonucleases (RNases) as tools to control tumour-associated intracellular and extracellular miRNAs. In this work, we evaluated the effects of the RNase binase from Bacillus pumilus on small non-coding regulatory RNAs in the context of mouse RLS₄₀ lymphosarcoma inhibition. In vitro binase exhibited cytotoxicity towards RLS₄₀ cells via apoptosis induction through caspase-3/caspase-7 activation and decreased the levels of miR-21a, let-7g, miR-31 and miR-155. Intraperitoneal injections of binase in RLS₄₀-bearing mice resulted in the retardation of primary tumour growth by up to 60% and inhibition of metastasis in the liver by up to 86%, with a decrease in reactive inflammatory infiltration and mitosis in tumour tissue. In the blood serum of binase-treated mice, decreases in the levels of most studied miRNAs were observed, excluding let-7g, while in tumour tissue, the levels of oncomirs miR-21, miR-10b, miR-31 and miR-155, and the oncosuppressor let-7g, were upregulated. Analysis of binase-susceptible miRNAs and their regulatory networks showed that the main modulated events were transcription and translation control, the cell cycle, cell proliferation, adhesion and invasion, apoptosis and autophagy, as well as some other tumour-related cascades, with an impact on the observed antitumour effects.

Surveillance of Tumour Development: The Relationship Between Tumour-Associated RNAs and Ribonucleases

Tumour progression is accompanied by rapid cell proliferation, loss of differentiation, the reprogramming of energy metabolism, loss of adhesion, escape of immune surveillance, induction of angiogenesis, and metastasis. Both coding and regulatory RNAs expressed by tumour cells and circulating in the blood are involved in all stages of tumour progression. Among the important tumour-associated RNAs are intracellular coding RNAs that determine the routes of metabolic pathways, cell cycle control, angiogenesis, adhesion, apoptosis and pathways responsible for transformation, and intracellular and extracellular non-coding RNAs involved in regulation of the expression of their proto-oncogenic and oncosuppressing mRNAs. Considering the diversity/variability of biological functions of RNAs, it becomes evident that extracellular RNAs represent important regulators of cell-to-cell communication and intracellular cascades that maintain cell proliferation and differentiation. In connection with the elucidation of such an important role for RNA, a surge in interest in RNA-degrading enzymes has increased. Natural ribonucleases (RNases) participate in various cellular processes including miRNA biogenesis, RNA decay and degradation that has determined their principal role in the sustention of RNA homeostasis in cells. Findings were obtained on the contribution of some endogenous ribonucleases in the maintenance of normal cell RNA homeostasis, which thus prevents cell transformation. These findings directed attention to exogenous ribonucleases as tools to compensate for the malfunction of endogenous ones. Recently a number of proteins with ribonuclease activity were discovered whose intracellular function remains unknown. Thus, the comprehensive investigation of physiological roles of RNases is still required. In this review we focused on the control mechanisms of cell transformation by endogenous ribonucleases, and the possibility of replacing malfunctioning enzymes with exogenous ones.

RNases Disrupt the Adaptive Potential of Malignant Cells: Perspectives for Therapy

Exogenous RNases are selectively toxic to tumor cells. The reasons for this selectivity are not quite clear and should be searched for in the properties that distinguish malignant from normal cells. During onco-transformation, cells acquire properties allowing them to adapt to the altered microenvironment, such as resistance to hypoxia, changes in intracellular pH, disruption of ion transport, reduced adhesion and increased mobility, and production of specific exosomes. These adaptation mechanisms distinguish malignant cells from normal ones and give them a competitive advantage, ensuring survival and spread in the organism. Here, we analyze if the directed cytotoxic effect of exogenous RNases is linked to the disruption of the adaptive potential of tumor cells and how it can be used in anticancer therapy.

Zeolites as Carriers of Antitumor Ribonuclease Binase

Natural and synthetic zeolites have many applications in biomedicine and nutrition. Due to its properties, zeolites can absorb therapeutically active proteins and release them under physiological conditions. In this study we tested the clinoptilolite, chabazite, and natrolite ability to be loaded by antitumor ribonuclease binase and the cytotoxicity of the obtained complexes. We found the optimal conditions for binase loading into zeolites and established the dynamic of its release. Cytotoxic effects of zeolite-binase complexes toward colorectal cancer Caco2 cells were characterized after 24 and 48 h of incubation with cells using MTT-test. Zeolites were toxic by itselfs and reduced cells viability by 30% (clinoptilolite), 40% (chabazite), and 70% (natrolite) after 48 h of incubation. Binase complexes with clinoptilolite as well as chabazite always demonstrated enhanced toxicity (up to 57 and 60% for clinoptilolite and chabazite, respectively) in comparison with binase and zeolites separately. Our results contribute to the perspective development of binase-based complexes for therapy of colorectal cancer for or the treatment of malignant skin neoplasms where the complexes can be used in pasty form.

Immune Modulation by Human Secreted RNases at the Extracellular Space

The ribonuclease A superfamily is a vertebrate-specific family of proteins that encompasses eight functional members in humans. The proteins are secreted by diverse innate immune cells, from blood cells to epithelial cells and their levels in our body fluids correlate with infection and inflammation processes. Recent studies ascribe a prominent role to secretory RNases in the extracellular space. Extracellular RNases endowed with immuno-modulatory and antimicrobial properties can participate in a wide variety of host defense tasks, from performing cellular housekeeping to maintaining body fluid sterility. Their expression and secretion are induced in response to a variety of injury stimuli. The secreted proteins can target damaged cells and facilitate their removal from the focus of infection or inflammation. Following tissue damage, RNases can participate in clearing RNA from cellular debris or work as signaling molecules to regulate the host response and contribute to tissue remodeling and repair. We provide here an overall perspective on the current knowledge of human RNases’ biological properties and their role in health and disease. The review also includes a brief description of other vertebrate family members and unrelated extracellular RNases that share common mechanisms of action. A better knowledge of RNase mechanism of actions and an understanding of their physiological roles should facilitate the development of novel therapeutics.