Background: Bone marrow-derived mesenchymal stromal cells (MSCs) are multipotent cells with a high\nconstitutive level of autophagy and low expression of CD99. Under certain conditions, MSCs may develop\ntumorigenic properties. However, these transformation-induced conditions are largely unknown. Recently, we\nhave identified an association between Hsp70, a main participant in cellular stress response and tumorigenesis,\nand CD99. Preliminary observations had revealed upregulation of both proteins in stressed long-term cultured\nMSCs. And so we hypothesized that CD99 is implicated in stress-induced mechanisms of cellular transformation\nin MSCs. Hence, we investigated the effects of prolonged stress on MSCs and the role of CD99 and autophagy in\ntheir survival.\nMethods: Human telomerase reverse transcriptase (hTERT) overexpressing immortalized MSCs and primary bone\nmarrow stromal cells were used to investigate the influence of long-term serum deprivation and hypoxia on\ngrowth and differentiation of MSCs. Cell proliferation and apoptosis were evaluated using flow cytometry,\ndifferentiation capabilities of MSCs were assessed by immunohistochemical staining followed by microscopic\nexamination. CD99, Hsp70 expression were analyzed using flow cytometry, western blotting, and reverse\ntranscriptase polymerase chain reaction. Autophagy was explored with specific inhibitors using cell morphology\nexamination and western blotting.\nResults: Chronic stress factors are able to change the morphology of MSCs and to inhibit spontaneous\ndifferentiation into adipocyte lineage. Furthermore, CD99 elevation and downregulation of p53 and p21\naccompanied defective autophagy, which is usually associated with tumor formation. We found that inhibition\nof autophagy by chloroquine promoted cell detachment and modulated CD99 expression level whereas\nincorporation of CD99 recombinant protein into the cells suppressed autophagy.\nConclusions: Obtained results provide a model for chronic stress-induced transformation of MSCs via CD99 and\nmay therefore be highly relevant to mesenchymal tumorigenesis.
Loading....