The characteristic features of
cancer cells are aberrant (acidic) intracellular pH and elevated levels of
phosphatidylserine. The primary focus of
cancer research is concentrated on the discovery of
biomarkers directed towards early diagnosis and
therapy. It has been observed that
azoxymethane-treated mice demonstrate an increased expression of
calnuc (a multi-domain, Ca2+- and
DNA-binding protein) in their colon, suggesting it to be a good
biomarker of
carcinogenesis. We show that culture supernatants from
tumor cells have significantly higher amounts of secreted
calnuc compared to non-
tumor cells, selectively packaged into exosomes. Exosomal
calnuc is causal for epithelial-mesenchymal transition and atypical migration in non-
tumor cells, which are key events in
tumorigenesis and
metastasis. In vitro studies reveal a significant affinity for
calnuc towards
phosphatidylserine, specifically to its C-terminal region, leading to the formation of 'molten globule' conformation. Similar structural changes are observed at acidic pH (pH 4), which demonstrates the role of the acidic microenvironment in causing the molten globule conformation and membrane interaction. On a precise note, we propose that the molten globule structure of
calnuc caused by aberrant conditions in
cancer cells to be the causative mechanism underlying its exosome-mediated secretion, thereby driving
metastasis.