FOXK1 interaction with FHL2 promotes proliferation, invasion and metastasis in colorectal cancer

The transcriptional factor Forkhead box k1 (FOXK1) is a member of the FOX family. The abnormal expression of FOXK1 may have an important role in tumour development. Our previous studies showed that four-and-a-half LIM protein 2 (FHL2) is a critical inducer of the epithelial-to-mesenchymal transition (EMT) and invasion. However, the molecular mechanism by which FOXK1 synergizes with FHL2 tumour proliferation, EMT and metastasis is not well defined. We evaluated that messenger RNA (mRNA) and protein expression levels by quantitative RT–PCR, western blot, immunofluorescence and immunohistochemistry (IHC) assays. The migration and invasive abilities of colorectal cancer (CRC) cells were evaluated using short hairpin RNA (shRNA)-mediated inhibition in vitro and in vivo. We showed that FOXK1 expression was upregulated in CRC compared with matched normal tissues. FOXK1 physically interacts with FHL2 in CRC. Moreover, higher expression levels of the two proteins were significantly associated with differentiation, lymph node metastasis, AJCC stage and poorer prognosis. Furthermore, the overexpression of FOXK1 in CRC cells is associated with EMT, invasion and metastasis. However, the siRNA-mediated repression of FHL2 in FOXK1-overexpressing cells reversed EMT and both the proliferative and metastatic phenotypes in vitro and in vivo. These data identified that the co-expression of FOXK1 and FHL2 enhances cell proliferation and metastasis through the induction of EMT. Thus, FOXK1 and FHL2 may serve as putative targets in the combined therapy of CRC.