Fibroblast activation protein-alpha in tumor cells promotes colorectal cancer angiogenesis via the Akt and ERK signaling pathways

摘要

Fibroblast activation protein-alpha (FAP-alpha) is a cell surface serine protease of the post-prolyl peptidase family, and stromal FAP-alpha expression may serve important functions in tumor occurrence and progression. In recent years, FAP-alpha expression in tumor cells has been detected in a number of types of tumor, and its roles in tumor growth and metastasis have been reported. However, the presence of FAP-alpha in colorectal cancer (CRC) cells lacks sufficient evidence and its role in angiogenesis remains unknown. The present study confirmed FAP-alpha expression in CRC cells at the tissue and cellular level, using immunohistochemistry and western blot analysis, respectively; it additionally identified that FAP-alpha in CRC cells was positively associated with vascular endothelial growth factor (VEGF)-A expression and microvessel density in stained tissue samples for the first time. In addition, western blotting identified that FAP-alpha overexpression in SW1116 cells significantly upregulated VEGF-A expression, and silencing of FAP-alpha in HT29 cells markedly inhibited VEGF-A expression. Survival analysis demonstrated that patients with high expression of FAP-alpha and VEGF-A had the shortest survival time. To detect the effects of FAP-alpha on human umbilical vein endothelial cells (HUVECs), conditioned medium (CM) from CRC cell lines was used and it was identified that CM from SW1116 cells with overexpressed FAP-alpha exhibited significantly increased VEGF-R2, phosphorylated extracellular signal-regulated kinase (p-ERK) and p-RAC-alpha serine/threonine-protein kinase (Akt) in HUVECs, in addition to the proliferation rate. Conversely, CM from HT29 cells with FAP-alpha silenced exhibited a significantly inhibited proliferation rate. Molecular mechanism analysis demonstrated that p-ERK and p-Akt in SW1116 and HT29 cells were affected by alterations in FAP-alpha expression, and treatment with a p-ERK inhibitor (U0126) and p-Akt inhibitor (LY294002) ameliorated VEGF-A upregulation induced by FAP-alpha overexpression. All the results confirmed the presence of FAP-alpha in CRC cells and suggested that FAP-alpha may effectively promote angiogenesis in CRC via the Akt and ERK signaling pathways.