MGr1-Ag promotes invasion and bone metastasis of small-cell lung cancer in vitro and in vivo

Bone metastasis of small-cell lung cancer (SCLC) usually occurs early in the progression of the disease. However, the molecular mechanism underlying bone metastasis is largely unknown. MGr1-Ag, a multifunction protein, has been suggested to play important roles in cell growth, differentiation and migration. In our present study, MGr1-Ag was found to be highly expressed in bone-metastatic SCLC cells (SBC-5 cell line) as compared with the expression in cells without bone-metastatic ability (SBC-3 cell line). Therefore, we hypothesized that MGr1-Ag is involved in bone metastasis of SCLC. Using a sense vector to upregulate MGr1-Ag expression in SBC-3 cells, we found that forced overexpression of MGr1-Ag enhanced cell invasion and migration in vitro and promoted bone metastases in vivo. Furthermore, specific siRNA-induced knockdown of MGr1-Ag expression in SBC-5 cells suppressed the potential of cell invasion and migration in vitro and dramatically decreased the number and sites of bone metastasis in vivo. We also found that MGr1-Ag induced SCLC cells to undergo epithelial-mesenchymal transition (EMT), as demonstrated by cell morphological changes, decreased expression of epithelial markers and increased expression of mesenchymal markers. Taken together, we conclude that MGr1-Ag promotes SCLC cell invasion and bone metastasis in vitro and in vivo, and that this is partially mediated via the EMT pathway.