A Novel Truncated Form of Nephronectin Is Present in Small Extracellular Vesicles Isolated from 66cl4 Cells

Extracellular vesicles are emerging
as biomarkers in breast cancer.
Our recent report suggested that an intracellular granular staining
pattern of the extracellular matrix protein nephronectin (NPNT) in
breast tumor sections correlated with a poor prognosis. Furthermore,
the results showed that NPNT is localized in extracellular vesicles
derived from mouse breast cancer cells. In this study, we performed
proteomic analysis that revealed that several proteins, including
tumor-promoting molecules, are differentially expressed in the cargo
of small extracellular vesicles (sEVs) derived from NPNT-expressing
mouse breast cancer cells. We also identified three different forms
of NPNT at 80, 60, and 20 kDa. We report that the native form of NPNT
at 60 kDa becomes further glycosylated and is detected as the 80 kDa
NPNT, which may be processed by matrix metalloproteinases to a shorter
form of around 20 kDa, which has not previously been described. Although
both 80 and 20 kDa NPNT are detected in sEVs derived from breast cancer
cells, the 20 kDa form of NPNT is concentrated in sEVs. In summary,
we show that a novel truncated form of NPNT is found in sEVs derived
from breast cancer cells.