Apatinib, a novel tyrosine kinase inhibitor (TKI), has been confirmed for its efficacy and safety in the treatment of advanced gastric carcinoma and some other solid tumors. However, the direct functional mechanisms of tumor lethality mediated by apatinib have not yet been fully characterized, and the precise mechanisms of drug resistance are largely unknown. Here, in this study, we demonstrated that apatinib could induce both apoptosis and autophagy in human colorectal cancer (CRC) via a mechanism that involved endoplasmic reticulum (ER) stress. Moreover, activation of the IRE1α pathway from apatinib-induced ER stress is responsible for the induction of autophagy; however, blocking autophagy could enhance the apoptosis in apatinib-treated human CRC cell lines. Furthermore, the combination of apatinib with autophagy inhibitor chloroquine (CQ) tends to have the most significant anti-tumor effect of CRC both in vitro and in vivo. Overall, our data show that because apatinib treatment could induce ER stress-related apoptosis and protective autophagy in human CRC cell lines, targeting autophagy is a promising therapeutic strategy to relieve apatinib drug resistance in CRC.

ETS transcription factors play important roles in tumor cell invasion, differentiation and angiogenesis. In this study, we initially demonstrated that ETS translocation variant 5 (ETV5) is abnormally upregulated in colorectal cancer (CRC), is positively correlated with CRC tumor size, lymphatic metastasis and tumor node metastasis (TNM) stage and indicates shorter survival and disease‐free survival in CRC patients. In vitro and in vivo experiments revealed that the downregulation of ETV5 could significantly suppress CRC cell proliferation. Moreover, overexpression of ETV5 could stimulate CRC angiogenesis in vitro and in vivo, which is consistent with RNA‐seq results. Then, we identified platelet‐derived growth factor BB (PDGF‐BB) as a direct target of ETV5 that plays an important role in ETV5‐mediated CRC angiogenesis through an angiogenesis antibody microarray. Additionally, PDGF‐BB could activate VEGFA expression via the PDGFR‐β/Src/STAT3 pathway in CRC cells and appeared to be positively correlated with ETV5 in CRC tissues. Finally, we revealed that ETV5 could bind directly to the promoter region of PDGF‐BB and regulate its expression through ChIP and luciferase assays. Overall, our study suggested that the transcription factor ETV5 could stimulate CRC malignancy and promote CRC angiogenesis by directly targeting PDGF‐BB. These findings suggest that EVT5 may be a potential new diagnostic and prognostic marker in CRC and that targeting ETV5 might be a potential therapeutic option for inhibiting CRC angiogenesis.

MicroRNAs (miRNAs) are a group of small non-coding RNA molecules that potentially play a critical role in tumorigenesis. Increasing evidences indicate that miR-378-5p is dysregulated in numerous human cancers including colorectal cancer (CRC) which hypothesizes that miR-378-5p may play an important role in tumorigenesis. However, its role in CRC carcinogenesis remains poorly defined because of lacking target genes information. In the present study, it was demonstrated that the expression of miR-378-5p was down-regulated in CRC tissues and cell lines as determined by quantitative reverse transcription-polymerase chain reaction (qRT-PCR). Furthermore, overexpression of miR-378-5p suppressed cell proliferation, as indicated by CCK-8 assay. Flow cytometric analysis demonstrated that overexpression of miR-378-5p induced cell cycle arrest and promoted apoptosis in CRC cells. A luciferase reporter assay indicated that BRAF was a direct target of miR-378-5p. Western blot and qRT-PCR analysis indicated that BRAF was significantly down-regulated by miR-378-5p in CRC cells. Moreover, miR-378-5p was negatively associated with BRAF in CRC tissues compared to adjacent non-tumor tissues. These results demonstrate that down-regulation of miR-378-5p promotes CRC cells growth by targeting BRAF and restoration of their levels is a potentially promising therapeutic in CRC.