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.

Nucleotide supply is essential for DNA replication in proliferating cells, including cancer cells. Ribose-phosphate diphosphokinase 1 (PRPS1) is a key enzyme to produce the consensus precursor of nucleotide synthesis. PRPS1 participates in the pentose phosphate pathway (PPP) by catalyzing the phosphoribosylation of D-ribose 5-phosphate (R-5P) to 5-phosphoribosyl-1-pyrophosphate. Therefore, PRPS1 not only controls purine biosynthesis and supplies precursors for DNA and RNA biosynthesis but also regulates PPP through a feedback loop of the PRPS1 substrate R-5P. However, it is still elusive whether PRPS1 enhances nucleotide synthesis during cell-cycle progression. In this study, we explore the role and activation mechanism of PRPS1 in cell-cycle progression of colorectal cancer, and observed a peak in its enzymatic activity during S phase. CDK1 contributes to upregulation of PRPS1 activity by phosphorylating PRPS1 at S103; loss of phosphorylation at S103 delayed the cell cycle and decreased cell proliferation. PRPS1 activity in colorectal cancer samples is higher than in adjacent tissue, and the use of an antibody that specifically detects PRPS1 phosphorylation at S103 showed consistent results in 184 colorectal cancer tissues. In conclusion, compared with upregulation of PRPS1 expression levels, increased PRPS1 activity, which is marked by S103 phosphorylation, is more important in promoting tumorigenesis and is a promising diagnostic indicator for colorectal cancer. Significance: These findings show that the enzymatic activity of PRPS1 is crucial for cell-cycle regulation and suggest PRPS1 phosphorylation at S103 as a direct therapeutic target and diagnostic biomarker for colorectal cancer.

Leukemia inhibitory factor receptor (LIFR) has been documented as a cancer promoter and to be present at high levels in various types of tumor tissues. In our search for molecules prognostic of colorectal cancer (CRC), we found high levels of LIFR in CRC tissue samples. Further analyses revealed that LIFR was indeed prognostic of CRC patient survival, and was associated with tumor size, lymphatic metastasis and stages. LIFR was found to promote tumor growth, metastasis and angiogenesis both in vitro and in vivo. High levels of LIFR in CRC facilitated proliferation and migration of endothelial cells, resulting in an increase in angiogenic activity. Moreover, interleukin 8 (IL-8) was found to play a role in the LIFR induced angiogenesis. IL-8 levels were correlated with LIFR levels in CRC tissues, whereas depletion of IL-8 led to a reduced angiogenic activity of LIFR in CRC cells. In addition, LIFR increased phosphorylation level of Erk, which regulates il-8 transcription. We conclude that LIFR is possibly a valuable prognostic marker for CRC. Our results also implicate a mechanism by which LIFR regulates tumor angiogenesis through Erk/IL-8 pathway, and that LIFR could be a potential therapeutic target for CRC.

Asporin has been implicated as an oncogene in various types of human cancers; however, the roles of asporin in the development and progression of colorectal cancer (CRC) have not yet been determined. With clinical samples, we found that asporin was highly expressed in CRC tissues compared to adjacent normal tissues and the asporin expression levels were significantly associated with lymph node metastasis status and TNM stage of the patients. Through knockdown of asporin in CRC cell lines RKO and SW620 or overexpression of asporin in cell lines HT-29 and LoVo, we found that asporin could enhance wound healing, migration and invasion abilities of the CRC cells. Further more, with the human umbilical vein endothelial cells (HUVECs) tube formation assays and the xenograft model, we found that asporin promoted the tumor growth through stimulating the VEGF signaling pathway. The portal vein injection models suggested that asporin overexpression stimulated the liver metastasis of HT29 cell line, while asporin knockdown inhibited the liver metastasis of RKO cell line. In addition, asporin was found to augment the phosphorylation of EGFR/Src/cortactin signaling pathway, which might be contributed to the biological functions of asporin in CRC metastasis. These results suggested that asporin promoted the tumor growth and metastasis of CRC, and it could be a potential therapeutic target for CRC patients in future.

Cortactin (CTTN) is overexpressed in various tumors, including head and neck squamous cell carcinoma and colorectal cancer (CRC), and can serve as a biomarker of cancer metastasis. We observed that CTTN promotes cancer cell proliferation in vitro and increases CRC tumor xenograft growth in vivo. CTTN expression increases EGFR protein levels and enhances the activation of the MAPK signaling pathway. CTTN expression also inhibits the ubiquitin-mediated degradation of EGFR by suppressing the coupling of c-Cbl with EGFR. CoIP experiments indicate CTTN can interact with c-Cbl in CRC cells. These results demonstrate that CTTN promotes the proliferation of CRC cells and suppresses the degradation of EGFR.

Cortactin (CTTN), a major substrate of the Src tyrosine kinase, has been implicated in cell proliferation, motility and invasion in various types of cancer. However, the molecular mechanisms of CTTN-driven malignant behavior remain unclear. In the current study, we determined the expression of CTTN in colorectal cancer and investigated its underlying mechanism in the metastasis of colorectal cancer. We confirmed increased CTTN expression in lymph node-positive CRC specimens and highly invasive CRC cell lines. Further study has shown that overexpression of CTTN promoted CRC cell migration and invasion, whereas CTTN silencing inhibited CRC cell migratory and invasive capacities in vitro. Mechanistically, CTTN increases expression of dedicator of cytokinesis 1 (DOCK1) and gene silencing of DOCK1 partially abolishes the migration and invasion capacity by CTTN. Our findings indicate that CTTN promotes metastasis of CRC cells by increasing DOCK1 expression and this could offer a promising therapeutic target for colorectal cancer treatment.