Phosphoinositide-specific phospholipase C isoforms are conveyed by osteosarcoma-derived extracellular vesicles

Abstract

Cancer cells are able to release high amounts of extracellular vesicles, thereby conditioning the normal cells in the surrounding tissue and/or in distant target organs. In the context of bone cancers, previous studies suggested that osteosarcoma cancer cells produce transforming extracellular vesicles able to induce a tumour‐like phenotype in normal recipient cells. Indeed, phosphoinositide‐specific phospholipase C (PI‐PLC) enzymes are differentially expressed in osteosarcoma cell lines with increasing aggressiveness, thus providing helpful insights to better define their role and functions in this bone tumour. By confocal microscopy analysis, we demonstrated that osteosarcoma‐derived extracellular vesicles convey all the assessed PI‐PLC isoforms, and that they localize into cell membrane bubble‐like structures, resembling extracellular vesicles about to be released, as conveyed and/or membrane protein. Cytofluorimetric analysis confirmed the presence of PI‐PLC isoforms in the extracellular vesicles collected from conditioned media of osteosarcoma cells. These findings suggest the feasibility to use circulating extracellular vesicles as biomarkers of osteosarcoma progression and/or the monitoring of this distressing disease.

Phosphoinositide Signal Transduction Pathway and Osteosarcoma Metastases

“…In addition to the aforementioned roles, PLC γ isoforms induce actin polymerization leading to the formation of cell protrusions, involved in sticking to the extracellular matrix, controlling migration direction, and initiating cell crawling (181). PLC γ2 was identified in the EV's membrane, more markedly in the 143B cell line (179), corroborating the previous hypothesis indicating that PLC γ2 plays a role in aggressiveness (115,142).…”

“…Furthermore, malignant cells can share membrane molecules, intracellular proteins, and genetic information, which might underlie events leading to metastasis formation (178). More recently, research has addressed the proteins/phospholipids in the EVs' membrane, and PLC enzymes are described in the EVs produced by human osteoblasts and OS cell lines (179).…”

“…Osteoblasts and OS cell lines release PLCs-containing EVs at different levels, suggesting that EVs in the bone are used by the cell to vehicle PLC enzymes and transduce signals (179). The expression panel of PLCs and their localization inside the EVs slightly differ depending on the specific cell lines.…”

“…As PLC enzymes work at the cell membrane and EVs are vesicle coated with cell membrane, we expected to find them in the EVs. Some PLCs are described both in the EV's membrane and as cargo, others in the membrane or within the vesicle (179).…”

Expression and Localization of Phosphoinositide-Specific Phospholipases C in Cultured, Differentiating and Stimulated Human Osteoblasts

“…The subcellular distribution of PLC enzymes influences the activity, suggesting specific roles for each PLC enzyme beside the cleavage of PIP2 [52][53][54]. PLC enzymes were also recently described in extracellular vesicles (EVs), suggesting a possible role in extracellular signaling [55].…”