Novel hypoxia-induced HIF1α-circTDRD3-positive feedback loop promotes the growth and metastasis of colorectal cancer.

Tumor hypoxia and circular RNAs (circRNAs) are considered to play key roles in tumor progression and malignancy, respectively. Nevertheless, the biological functions and underlying mechanisms of specific circRNAs exposed to hypoxic microenvironments in colorectal cancer (CRC) remain largely elusive. Herein, a novel circRNA, circTDRD3, which is upregulated under hypoxic conditions, was identified. The expression of circTDRD3 was highly expressed in CRC tissues and positively correlated with overall survival, tumor size, lymph node invasion and clinical stage. CircTDRD3 facilitated CRC cell proliferation, migration and metastasis in vitro and in vivo. Mechanistically, circTDRD3 promoted HIF1α expression by sponging miR-1231, which facilitated CRC progression. Meanwhile, HIF1α directly combined with TDRD3 promoter to increase the expression of TDRD3 pre-mRNA. Then HIF1a-induced PTBP1 accelerated the formation of circTDRD3. Our findings reveal that circTDRD3 facilitates the proliferation and metastasis of CRC through a positive feedback loop mediated by the HIF1α/PTBP1/circTDRD3/miR-1231/HIF1α axis. Therefore, circTDRD3 may serve as a prognostic biomarker and therapeutic target for patients with CRC.