Biology subjects

Mendez, E.

Publications and source records attributed to Mendez, E..

3 recordsLinked to original sources

bioRxiv2025

Tetraspanin positivity as a function of extracellular vesicle size measured by a modified immuno-TEM protocol

The identification of surface markers that correlate with specific subpopulations of extracellular vesicles (EVs) is important for EV identification, classification, purification, sorting, and functional analysis. Tetraspanins such as CD9, CD63 and CD81 were once considered to be universal markers of exosomes: small EVs released into the extracellular space when late endosomes / multivesicular bodies fuse with the plasma membrane. In contrast, plasma membrane-derived ectosomes (also called microvesicles) have a different biogenesis, were often regarded as being larger than exosomes, and display a different surface proteome. However, recent studies have shown that tetraspanins such as CD9 and CD81 are highly enriched on ectosomes derived from various sources. Thus, it is currently unclear how tetraspanin content correlates with specific EV subpopulations. Here, we present a modified immuno-TEM protocol that can be easily applied to heterogeneous EV populations comprising both small and large EVs (and presumably also a collection of exosomes and ectosomes). In EVs purified from U-2 OS cells by size-exclusion chromatography, we show that the percentage of particles positive for CD9 and CD81 is significantly higher in the subpopulation of EVs [≤] 100 nm (i.e., small EVs). These results also explain discrepancies in the size distribution profiles that we obtained using the same EV preparations by alternative single-vesicle characterization platforms such as nano flow cytometry and SP-IRIS / ExoView. The latter, when used to capture tetraspanin-positive particles, returns a population that is relatively small in size.

molecular biology↗

bioRxiv2020

Recurrent human papillomavirus-related head and neck cancer undergoes metabolic re-programming and is driven by oxidative phosphorylation

Human papillomavirus (HPV) infection drives the development of some head and neck cancer squamous cell carcinomas (HNSC). This disease is rapidly increasing in incidence worldwide. Although these tumors are sensitive to treatment, ~10% of patients fail therapy. However, the mechanisms that underlie treatment failure remain unclear. Here, we show that the oxidative phosphorylation (OXPHOS) pathway is enriched in recurrent HPV-associated HNSC and may contribute to treatment failure. Nrf2-enriched HNSC samples from the Cancer Genome Atlas with enrichment in OXPHOS, fatty acid metabolism, Myc, Mtor, ROS, and glycolytic signaling networks exhibited worse survival. HPV-positive HNSC cells demonstrated sensitivity to the OXPHOS inhibitor, IACS-010759, in a Nrf2-dependent manner. Further, using murine xenograft models, we identified Nrf2 as a driver of tumor growth. Mechanistically, Nrf2 drives ROS and mitochondrial respiration, and Nrf2 is a critical regulator of redox homeostasis that can be crippled by disruption of OXPHOS. Nrf2 also mediated cisplatin sensitivity in endogenously overexpressing primary HPV-related HNSC cells. Cisplatin treatment demonstrated Nrf2-dependent synergy with OXPHOS inhibition. These results unveil a paradigm shifting translational target harnessing Nrf2-mediated metabolic reprogramming in HPV-related HNSC.

cancer biology↗

bioRxiv2017

spe-43 is required for sperm activation in C. elegans

Successful fertilization requires that sperm are activated prior to contacting an oocyte. In C. elegans, this activation process, called spermiogenesis, transforms round immobile spermatids into motile, fertilization-competent spermatozoa. We describe the phenotypic and genetic characterization of spe-43, a new component of the spe-8 pathway, which is required for spermiogenesis in hermaphrodites; spe-43 hermaphrodites are self-sterile, while spe-43 males show wild-type fertility. When exposed to Pronase to activate sperm in vitro, spe-43 spermatids form long rigid spikes radiating outward from the cell periphery instead of forming a motile pseudopod, indicating that spermiogenesis initiates but is not completed. Using a combination of recombinant and deletion mapping and whole genome sequencing, we identified F09E8.1 as spe-43. SPE-43 is predicted to exist in two isoforms; one isoform appears to be a single-pass transmembrane protein while the other is predicted to be a secreted protein. SPE-43 can bind to other known sperm proteins, including SPE-4 and SPE-29, which are known to impact spermiogenesis. In summary, we have identified a membrane protein that is present in C. elegans sperm and is required for sperm activation via the hermaphrodite activation signal.

developmental biology↗