Defining The Mechanism Of Enhanced Cellular Invasion Induced By Mechanical Stimulation

Metastasis is a multistep process driven by various biochemical and mechanical factors, which eventually leads to formation of secondary tumors. The tumor mass is surrounded by basement membrane (BM) and stroma made of various extracellular matrix (ECM) proteins. During metastasis tumor cells disseminate from the primary tumor, breach the BM, invade the stroma, travel through blood and lymph and colonize tissues distant from the primary tumor. Formation of secondary tumors by metastasis is a leading cause of death in cancer patients. Even though plenty of research has been focused on biochemical factors affecting metastasis, information on role of mechanical factors in this process is very limited. Using our previously developed in vitro mechano-invasion assay, we had observed enhanced cellular invasion in response to tugging forces in the stroma during cancer cell invasion. In vivo, such tugging forces would be produced by contractile cells within the stroma as they migrate and remodel the matrix fibers. In addition, we found this mechanically enhanced invasion by cancer cells to be dependent on the presence of fibronectin in the extracellular matrix. The objective of our study is to understand the mechanotransduction pathway leading to enhanced invasion. We hypothesized that in response to mechanical forces in the stroma, tumor cells will show an altered expression of genes involved in mechanosensing. We performed expression profiling of several genes related to cell migration, adhesion and tumor metastasis by real-time PCR analysis. Six genes were confirmed to be differentially expressed between mechanically stimulated and non-stimulated conditions. Surprisingly, one of the genes found to be significantly down-regulated in the mechanically stimulated invasion culture is a fibronectin specific integrin subunit, integrin β3. Over-expression of this gene resulted in a significant decrease in enhanced invasion, supporting its role in sensing the mechanical stimulus. Furthermore, down-regulation of integrin β3 resulted in decrease in amounts of inactive form of cofilin (Ser3 phospho-cofilin)

Endomembrane targeting of human OAS1 p46 augments antiviral activity

Many host RNA sensors are positioned in the cytosol to detect viral RNA during infection. However, most positive-strand RNA viruses replicate within a modified organelle co-opted from intracellular membranes of the endomembrane system, which shields viral products from cellular innate immune sensors. Targeting innate RNA sensors to the endomembrane system may enhance their ability to sense RNA generated by viruses that use these compartments for replication. Here, we reveal that an isoform of oligoadenylate synthetase 1, OAS1 p46, is prenylated and targeted to the endomembrane system. Membrane localization of OAS1 p46 confers enhanced access to viral replication sites and results in increased antiviral activity against a subset of RNA viruses including flaviviruses, picornaviruses, and SARS-CoV-2. Finally, our human genetic analysis shows that the OAS1 splice-site SNP responsible for production of the OAS1 p46 isoform correlates with protection from severe COVID-19. This study highlights the importance of endomembrane targeting for the antiviral specificity of OAS1 and suggests that early control of SARS-CoV-2 replication through OAS1 p46 is an important determinant of COVID-19 severity

RNA-binding protein isoforms ZAP-S and ZAP-L have distinct antiviral and immune resolution functions

The initial response to viral infection is anticipatory, with host antiviral restriction factors and pathogen sensors constantly surveying the cell to rapidly mount an antiviral response through the synthesis and downstream activity of interferons. After pathogen clearance, the host's ability to resolve this antiviral response and return to homeostasis is critical. Here, we found that isoforms of the RNA-binding protein ZAP functioned as both a direct antiviral restriction factor and an interferon-resolution factor. The short isoform of ZAP bound to and mediated the degradation of several host interferon messenger RNAs, and thus acted as a negative feedback regulator of the interferon response. In contrast, the long isoform of ZAP had antiviral functions and did not regulate interferon. The two isoforms contained identical RNA-targeting domains, but differences in their intracellular localization modulated specificity for host versus viral RNA, which resulted in disparate effects on viral replication during the innate immune response