Z. Liu1, H. Shao1, M. G. Moller1, O. C. Velazquez1 1University Of Miami,Surgery/Sylvester Comprehensive Cancer Center,Miami, FL, USA
Introduction: Cancer-associated fibroblasts (CAF) play critical roles in promoting primary tumor development, growth and progression by stimulating tumor cell proliferation, survival, migration, angiogenesis as well as providing a niche supporting the metastatic colonization of disseminated tumor cells in distant organs. Moreover, CAF appear to be relevant to the development of drug resistance and tumor recurrence. Hence, CAF are a promising therapeutic target. We have previously demonstrated that activation of the Notch1 signaling pathway confers normal human dermal fibroblasts a suppressive phenotype to melanoma growth. Here, we further investigated whether manipulation of Notch signaling in melanoma-associated fibroblasts (MAF) isolated from human melanoma patients alter their regulatory phenotype by which affects melanoma growth.
Methods: MAF were isolated from human primary and metastatic melanoma lesions and characterized. Notch pathway activity in MAF versus normal human dermal fibroblasts was examined using Notch pathway RT2-PCRArray and immunoblotting. Enforced activation of Notch pathway was achieved by transducing MAF with lentiviral vector encoding active form of Notch1 (NIC). The effect of MAF engineered to carry high Notch activity on melanoma growth was tested by in vitro co-culture and in vivo co-engrafting animal model.
Results: Isolated MAF are a-smooth muscle actin (a-SMA) and fibroblast activation protein (FAP) positive. MAF exhibited a relatively lower Notch activity compared to normal human dermal fibroblasts. Enforced activation of Notch1 pathway downgraded cellular activities of MAF. MAF engineered to carry high Notch activity significantly inhibited melanoma cell growth in vitro and retarded xenografted human melanoma cell growth on mouse skin.
Conclusion:
Notch signaling pathway appears to be a ‘molecular switch’ in determining the function of tumor stromal fibroblasts. Notch signaling activity is lower in MAF. Increasing Notch signaling activity in MAF confers them a tumor-suppressing phenotype towards melanoma growth. Our study demonstrated that Notch signaling functions as a critical molecular determinant in governing the tumor-regulating role of tumor stromal fibroblasts and provided a novel approach to target tumor microenvironment by manipulation of Notch signaling in stromal fibroblasts.