EGFL7 silencing inactivates the Notch signaling pathway; enhancing cell apoptosis and suppressing cell proliferation in human cutaneous melanoma

Hua Tang, Wei-Rong Xiao, Yang-Ying Liao, Lan Li, Xiao Xiao, Xiao-Peng Xu,  Hao Feng

Abstract:

Melanoma is the main cause of death in patients with skin cancer. While the pathogenesis of cutaneous melanoma is poorly understood, increasing evidence shows that epidermal growth factor (EGF) may be involved. Herein, we tested the hypothesis that down-regulation of EGFL7 inhibits development and progression of human cutaneous melanoma (CM). Initially, we performed immunohistochemical analysis of EGFL7 in 130 specimens and the findings indicated that EGFL7 was highly expressed in CM. The expressions of EGFL7 and Notch signaling pathway-related genes in CM were then measured by reverse transcription quantitative polymerase chain reaction (RT-qPCR) and Western blot assay. In order to assess biological functions of EGFL7 in CM we up-regulated or down-regulated endogenous EGFL7 using EGFL7-OE or shRNA against EGFL7 in the A375 CM cell line. To better understand the pivotal role of Notch signaling pathway in CM, we blocked this pathway in A375 cells by inhibitor treatment. Finally, tumor xenograft in nude mice was performed to test the in vivo tumorigenesis of the transfected A375 cells. While EGFL7 activated the Notch signaling pathway in CM, gain- and loss-of-function studies established that decreased EGFL7 inhibited cell proliferation and promoted apoptosis in A375 cells. Moreover, down-regulated EGFL7 suppressed in vivo tumorigenesis. Most importantly, we determined that down-regulating EGFL7 inhibited CM development by suppressing the Notch signaling pathway. The combined findings define potential roles of decreased EGFL7 as inhibitors of CM development by suppressing the Notch signaling pathway, and EGFL7 may therefore be a novel therapeutic target in cutaneous melanoma patients.