Rictor regulates the vasculogenic mimicry of melanoma via the AKT-MMP-2/9 pathway

Vasculogenic mimicry (VM)-positive melanomas are usually associated with poor prognosis. Rictor, the key component of the rapamycin-insensitive complex of mTOR (mTORC2), is up-regulated in several cancers, especially in melanomas with poor prognosis. The aim of this study was to investigate the role of Rictor in the regulation of VM and the mechanism underlying this possible regulation. VM channels were found in 35 of 81 tested melanoma samples and high Rictor expression correlated with VM structures. Moreover, Kaplan-Meier survival curves indicated that VM structures and high Rictor expression correlated with shorter survival in patients with melanoma. In vitro, Rictor knockdown by short hairpin RNA (shRNA) significantly inhibited the ability of A375 and MUM-2B melanoma cells to form VM structures, as evidenced by most tubes remaining open. Cell cycle analysis revealed that Rictor knockdown blocked cell growth and resulted in the accumulation of cells in G2/M phase, and cell migration and invasion were greatly affected after Rictor down-regulation. Western blotting assays indicated that down-regulating Rictor significantly inhibited the phosphorylation of AKT at Ser⁴⁷³ and Thr³⁰⁸ , which subsequently inhibited the expression and activity of downstream MMP-2/9, as confirmed by real-time PCR and gelatin Zymography. MK-2206, a small-molecule inhibitor of AKT, similarly inhibited the activity of AKT and secretion of MMP-2/9, further supporting that Rictor down-regulation inhibits the phosphorylation of AKT and activity of downstream MMP-2/9 to affect VM formation. In conclusion, Rictor plays an important role in melanoma VM via the Rictor-AKT-MMP-2/9 signalling pathway.