Regulatory Role of the MicroRNA-29b-IL-6 Signaling in the Formation of Vascular Mimicry

Vascular mimicry (VM) is a critical complement for microcirculation and is implicated in tumor progression. We showed that IL-6 derived from tumor cells and stroma cells promoted tumor cells to form a VM structure, whereas blocking the IL-6 signaling by RNA interference, IL-6-neutralizing antibody, or STAT3 inhibitor suppressed the VM formation of tumor cells. Mechanism investigations revealed that IL-6 stimulated VM formation by activating STAT3, in turn upregulating VE-cadherin expression and MMP2 activity. Further analyses identified a positive association between the activation of IL-6-STAT3 signaling and the formation of the VM structure in human HCC tissues. However, miR-29b repressed the expression of STAT3 and MMP2 by directly binding to the 3′ UTRs of their mRNAs. Consistently, both gain- and loss-of-function analyses showed that miR-29b suppressed tumor cells to form tube structures in vitro. The in vivo studies further disclosed that intratumoral injection of the miR-29b-expressing viruses significantly inhibited the IL-6-promoted VM formation in mouse xenografts, and downregulation of miR-29b was correlated with the presence of VM in human HCC tissues. This study elucidates a miR-29b-IL-6 signaling cascade and its role in VM formation, which provide potential targets for cancer therapy.