Cells have a mailing system of sorts. They can release tiny molecular balls, called extracellular vesicles (EVs), that contain biological matter or messages and attach to other cells to share whatever they contain.
In cancer, EVs often depart from tumor cells to seed the cancer elsewhere in the body, leading to metastasis. However, how the EVs connected to recipient cells to deliver their payload has remained a mystery—until now. A team of researchers based in Japan has revealed the molecular mechanisms underpinning the process for small EVs (sEVs), which they said could have implications for developing better cancer treatments.
The team published their findings in the Journal of Cell Biology.
“In recent years, EVs have garnered significant attention as mediators of intercellular communication,” said corresponding author Kenichi G.N. Suzuki, a professor at the Institute for Glyco-core Research at Gifu University in Gifu and a chief at the Division of Advanced Bioimaging, National Cancer Center Research Institute in Tokyo, Japan.
He explained that EVs can serve as biomarkers, since they carry specific proteins and genetic material that can indicate disease progression. Researchers have also started to explore their potential to treat cancers, either by inhibiting their binding to host cells or by encouraging the binding of EVs with therapeutic payloads.
“However, the mechanisms underlying their selective binding to recipient cell membranes have remained elusive,” Suzuki said. “In this study, we sought to elucidate these mechanisms.”
The researchers focused on understanding the role of integrin heterodimers, which are molecules that help sEVs adhere to the host cell. The team previously found that sEVs could be sorted into subtypes with different properties, depending on which tetraspanin protein it has. This type of protein is small but critical to EV formation and regulation, Suzuki said.
Using this understanding, the researchers sorted and tracked the sEVs with single-molecule resolution.
They examined the sorted subtypes with super-resolution microscopy to find that all subtypes primarily used integrin heterodimers associated with a specific tetraspanin protein known as CD151 and a molecule containing carbohydrates and fats called GM1 to bind to laminin, a protein critical to cellular membranes and heavily involved in cell membrane structure and cell adhesion, among other responsibilities.
Laminin is specifically a glycoprotein, meaning it is a protein with a carbohydrate, or sugar, molecule attached to it. It exists in the extracellular matrix, or the molecular network surrounding cells and supports their signaling and structure.
“Quantitative analysis using single-molecule imaging and super-resolution microscopy demonstrated that all EV subtypes derived from four distinct tumor cell lines, irrespective of size, predominantly bind to laminin via CD151-associated integrin heterodimers and GM1, thereby eliciting responses in recipient cells,” Suzuki said, noting that EVs bound to laminin significantly more than they bound to fibronectin, which is another protein responsible for cell adhesion in the extracellular matrix.
He also pointed out that two other proteins associated with adhesion in the EVs, talin and kindlin, did not activate the integrin heterodimers. Taken all together, the researchers concluded that GM1 and integrin heterodimers associated with CD151 are key for EV binding. This understanding, Suzuki said, could help researchers better inhibit or encourage binding as needed in the name of disease treatment.
“While EVs have been widely explored as biomarkers, attempts to use EVs as therapeutic agents have begun,” Suzuki said. “Given our elucidation of the molecular mechanisms underlying EV binding to recipient cells, our findings are expected to advance the development of EV-based therapeutics.”
Provided by
Tokai National Higher Education and Research System
