Tina Solvik

Bio: Tina Solvik is an academic researcher from University of California, San Francisco. The author has contributed to research in topics: Secretion & Autophagy. The author has an hindex of 3, co-authored 5 publications receiving 141 citations. Previous affiliations of Tina Solvik include University of California, Berkeley.

The LC3-conjugation machinery specifies the loading of RNA-binding proteins into extracellular vesicles.

Abstract: Traditionally viewed as an autodigestive pathway, autophagy also facilitates cellular secretion; however, the mechanisms underlying these processes remain unclear. Here, we demonstrate that components of the autophagy machinery specify secretion within extracellular vesicles (EVs). Using a proximity-dependent biotinylation proteomics strategy, we identify 200 putative targets of LC3-dependent secretion. This secretome consists of a highly interconnected network enriched in RNA-binding proteins (RBPs) and EV cargoes. Proteomic and RNA profiling of EVs identifies diverse RBPs and small non-coding RNAs requiring the LC3-conjugation machinery for packaging and secretion. Focusing on two RBPs, heterogeneous nuclear ribonucleoprotein K (HNRNPK) and scaffold-attachment factor B (SAFB), we demonstrate that these proteins interact with LC3 and are secreted within EVs enriched with lipidated LC3. Furthermore, their secretion requires the LC3-conjugation machinery, neutral sphingomyelinase 2 (nSMase2) and LC3-dependent recruitment of factor associated with nSMase2 activity (FAN). Hence, the LC3-conjugation pathway controls EV cargo loading and secretion.

Secretory autophagy maintains proteostasis upon lysosome inhibition

Abstract: Solvik et al. reveal that the autophagy machinery facilitates the secretion of autophagy cargo receptors and other cellular components via extracellular vesicles and particles in response to lysosome inhibition or impaired autophagosome maturation.

Bacterial alginate regulators and phage homologs repress CRISPR-Cas immunity.

Abstract: CRISPR-Cas systems are adaptive immune systems that protect bacteria from bacteriophage (phage) infection1. To provide immunity, RNA-guided protein surveillance complexes recognize foreign nucleic acids, triggering their destruction by Cas nucleases2. While the essential requirements for immune activity are well understood, the physiological cues that regulate CRISPR-Cas expression are not. Here, a forward genetic screen identifies a two-component system (KinB-AlgB), previously characterized in the regulation of Pseudomonas aeruginosa alginate biosynthesis3,4, as a regulator of the expression and activity of the P. aeruginosa Type I-F CRISPR-Cas system. Downstream of KinB-AlgB, activators of alginate production AlgU (a σE orthologue) and AlgR repress CRISPR-Cas activity during planktonic and surface-associated growth5. AmrZ, another alginate regulator6, is triggered to repress CRISPR-Cas immunity upon surface association. Pseudomonas phages and plasmids have taken advantage of this regulatory scheme and carry hijacked homologs of AmrZ that repress CRISPR-Cas expression and activity. This suggests that while CRISPR-Cas regulation may be important to limit self-toxicity, endogenous repressive pathways represent a vulnerability for parasite manipulation.

Autophagy cargo receptors are secreted via extracellular vesicles and particles in response to endolysosomal inhibition or impaired autophagosome maturation

Abstract: The endosome-lysosome (endolysosome) system plays central roles in both autophagic degradation and secretory pathways, including the exocytic release of extracellular vesicles and particles (EVPs). Although previous work has revealed important interconnections between autophagy and EVP-mediated secretion, our molecular understanding of these secretory events during endolysosome inhibition remains incomplete. Here, we delineate a secretory autophagy pathway upregulated in response to endolysosomal inhibition that mediates the EVP-associated extracellular release of autophagic cargo receptors, including p62/SQSTM1. This extracellular secretion is highly regulated and critically dependent on multiple ATGs required for the progressive steps of early autophagosome formation as well as Rab27a-dependent exocytosis. Furthermore, the disruption of autophagosome maturation, either due to genetic inhibition of the autophagosome-to-autolyosome fusion machinery or blockade via the SARS-CoV2 viral protein ORF3a, is sufficient to induce robust EVP-associated secretion of autophagy cargo receptors. Finally, we demonstrate that this ATG-dependent, EVP-mediated secretion pathway buffers against the intracellular accumulation of autophagy cargo receptors when classical autophagic degradation is impaired. Based on these results, we propose that secretory autophagy via EVPs functions as an alternate route to clear sequestered material and maintain proteostasis in response to endolysosomal dysfunction or impaired autophagosome maturation.

At the crossroads of autophagy and infection: Noncanonical roles for ATG proteins in viral replication

Abstract: Autophagy-related (ATG) proteins have increasingly demonstrated functions other than cellular self-eating. In this issue, Mauthe et al. (2016. J. Cell Biol. http://dx.doi.org/10.1083/jcb.201602046) conduct an unbiased RNA interference screen of the ATG proteome to reveal numerous noncanonical roles for ATG proteins during viral infection.

RNA delivery by extracellular vesicles in mammalian cells and its applications.

Abstract: The term 'extracellular vesicles' refers to a heterogeneous population of vesicular bodies of cellular origin that derive either from the endosomal compartment (exosomes) or as a result of shedding from the plasma membrane (microvesicles, oncosomes and apoptotic bodies). Extracellular vesicles carry a variety of cargo, including RNAs, proteins, lipids and DNA, which can be taken up by other cells, both in the direct vicinity of the source cell and at distant sites in the body via biofluids, and elicit a variety of phenotypic responses. Owing to their unique biology and roles in cell-cell communication, extracellular vesicles have attracted strong interest, which is further enhanced by their potential clinical utility. Because extracellular vesicles derive their cargo from the contents of the cells that produce them, they are attractive sources of biomarkers for a variety of diseases. Furthermore, studies demonstrating phenotypic effects of specific extracellular vesicle-associated cargo on target cells have stoked interest in extracellular vesicles as therapeutic vehicles. There is particularly strong evidence that the RNA cargo of extracellular vesicles can alter recipient cell gene expression and function. During the past decade, extracellular vesicles and their RNA cargo have become better defined, but many aspects of extracellular vesicle biology remain to be elucidated. These include selective cargo loading resulting in substantial differences between the composition of extracellular vesicles and source cells; heterogeneity in extracellular vesicle size and composition; and undefined mechanisms for the uptake of extracellular vesicles into recipient cells and the fates of their cargo. Further progress in unravelling the basic mechanisms of extracellular vesicle biogenesis, transport, and cargo delivery and function is needed for successful clinical implementation. This Review focuses on the current state of knowledge pertaining to packaging, transport and function of RNAs in extracellular vesicles and outlines the progress made thus far towards their clinical applications.

Challenges and directions in studying cell–cell communication by extracellular vesicles

Abstract: Extracellular vesicles (EVs) are increasingly recognized as important mediators of intercellular communication. They have important roles in numerous physiological and pathological processes, and show considerable promise as novel biomarkers of disease, as therapeutic agents and as drug delivery vehicles. Intriguingly, however, understanding of the cellular and molecular mechanisms that govern the many observed functions of EVs remains far from comprehensive, at least partly due to technical challenges in working with these small messengers. Here, we highlight areas of consensus as well as contentious issues in our understanding of the intracellular and intercellular journey of EVs: from biogenesis, release and dynamics in the extracellular space, to interaction with and uptake by recipient cells. We define knowledge gaps, identify key questions and challenges, and make recommendations on how to address these. Extracellular vesicles (EVs) mediate cell–cell communication in physiology and pathology but many questions remain about the mechanisms governing their delivery to recipient cells. This Expert Recommendation article highlights areas of progress and challenges in establishing the importance of EV-mediated communication in vivo.

Challenges and directions in studying cell–cell communication by extracellular vesicles

Abstract: Extracellular vesicles (EVs) are increasingly recognized as important mediators of intercellular communication. They have important roles in numerous physiological and pathological processes, and show considerable promise as novel biomarkers of disease, as therapeutic agents and as drug delivery vehicles. Intriguingly, however, understanding of the cellular and molecular mechanisms that govern the many observed functions of EVs remains far from comprehensive, at least partly due to technical challenges in working with these small messengers. Here, we highlight areas of consensus as well as contentious issues in our understanding of the intracellular and intercellular journey of EVs: from biogenesis, release and dynamics in the extracellular space, to interaction with and uptake by recipient cells. We define knowledge gaps, identify key questions and challenges, and make recommendations on how to address these. Extracellular vesicles (EVs) mediate cell–cell communication in physiology and pathology but many questions remain about the mechanisms governing their delivery to recipient cells. This Expert Recommendation article highlights areas of progress and challenges in establishing the importance of EV-mediated communication in vivo.

Methods for Separation and Characterization of Extracellular Vesicles: Results of a Worldwide Survey Performed by the ISEV Rigor and Standardization Subcommittee

Abstract: Research on extracellular vesicles (EVs) is growing exponentially due to an increasing appreciation of EVs as disease biomarkers and therapeutics, an expanding number of EV-containing materials under study, and application of new preparation, detection, and cargo analysis methods. Diversity of both sources and methodologies imposes challenges on the comparison of measurement results between studies and laboratories. While reference guidelines and minimal requirements for EV research have achieved the important objective of assembling community consensus, it is also essential to understand which methodologies and quality controls are currently being applied, and how usage trends are evolving. As an initial response to this need, the International Society for Extracellular Vesicles (ISEV) performed a worldwide survey in 2015 on “Techniques used for the isolation and characterization of extracellular vesicles” and published the results from this survey in 2016. In 2019, a new survey was performed to assess the changing state of the field. The questionnaire received more than 600 full or partial responses, and the present manuscript summarizes the results of this second worldwide survey. The results emphasize that separation methods such as ultracentrifugation and density gradients are still the most commonly used methods, the use of size exclusion chromatography has increased, and techniques based on tangential flow and microfluidics are now being used by more than 10% of respondents. The survey also reveals that most EV researchers still do not perform sample quality controls before or after isolation of EVs. Finally, the majority of EV researchers emphasize that separation and characterization of EVs should receive more attention.