Background: Inhibitor of DNA binding 1 (Id1) is upregulated in multiple cancers, and Id1overexpression correlates with cancer aggressiveness and poor clinical outcomes in cancer patients. However, its roles in cancer stem-like cells (CSCs) and epithelial-mesenchymal transition (EMT) are still elusive.
Purpose: This study aimed to examine the role of Id1  on the mediation of CRC stemness and explore the underlying mechanisms.
Methods: Id1 and CD133 expression was detected by qPCR assay and immunohistochemistry (IHC) in normal mucosal and primary colorectal cancer (CRC) specimens. Id1  was stably knocked down (KD) in human CRC cell lines. Spheres forming assay and tumorigenic assay were performed to evaluate self-renewal capacity and tumor initiation. Expression of CSC- and EMT-related markers and TCF/LEF activity were assessed in HCT116 cells after Id1  KD.
Results: qPCR assay showed higher Id1  and CD133  expression in CRC specimens than in normal mucosal specimens (P <0.05). IHC detected high cytoplasmic Id1 expression in 35 CRC specimens (46.7%), and high CD133 expression in 22 CRC specimens (29.3%) and negative expression in 18 normal mucosal specimens. High Id1 expression positively correlated with poor differentiation (P =0.034), and CD133 expression correlated with T category in CRC patients (P =0.002). Spearman correlation analysis revealed a positive correlation between Id1 and CD133 expression in CRC patients (P <0.05). Id1  KD resulted in suppression of proliferation, cell-colony formation, self-renewal capability and CSC-like features in HCT116 cells, and impaired the tumor-initiating capability in CRC cells. In addition, Id1 maintained the stemness of CRC cells via the Id1-c-Myc-PLAC8 axis through activating the Wnt/β-catenin and Shh signaling pathways.
Conclusions: Id1 expression significantly correlates with CD133 expression in CRC patients, and Id1  KD impairs CSC-like capacity and reverses EMT traits, partially via the Wnt/β-catenin signaling. Id1 may be a promising therapeutic target against colon CSCs.
Keywords: inhibitor of DNA binding 1, Id1, self-renewal, stemness, epithelial-mesenchymal transition, colon cancer, Wnt/β-catenin signaling pathway