FOXK2 is a transcription factor that plays a dual role in cancer, acting either as a tumor suppressor or an oncogene, depending on the tissue type. In breast cancer, FOXK2 acts as a tumor suppressor, preventing carcinogenesis and favoring drug responses. Therefore, we aimed to evaluate FOXK2 gene expression as a potential biomarker in different tumor types and the role of FOXK2 at the interface between chemosensitivity and tumor progression in breast cancer.

An in silico analysis compared FOXK2 gene expression between normal and tumor patient’s samples in different tumor types by analyzing transcriptome-level data from TNMplotter platform. The impact of FOXK2 on patient’s overall survival was evaluated by Kaplan-Meier curves from KMplotter. FOXK2 promoter methylation status was assessed by OncoDB; copy number variation and FOXK2 mutational status by XENA platform. The role of FOXK2 modulation in breast cancer was assessed by shRNA viral transductions in MCF-7 (chemosensitive) and MDA-MB-231 (chemoresistant) cell lines. The validation of these shFOXK2 cells was assessed by western blotting and real time RT-qPCR assays. Docetaxel and doxorubicin-induced cytotoxicity was evaluated by MTT and colony formation by clonogenic assays. To link FOXK2 gene expression and response to therapy on breast cancer patient’s samples, we evaluated patient’s pathological complete response to therapy and relapse-free survival at 5 years by ROCplotter.

We have found FOXK2 overexpression in most tumor types, which was associated with high copy number variation, but not with FOXK2 gene mutations or promoter methylation status. This points to additional transcriptional or post-translational mechanisms governing FOXK2 regulation. From all tumors analyzed, low FOXK2 levels in patients with kidney renal clear cell carcinoma and liver hepatocellular carcinoma showed up a remarkable improvement on overall survival. Also, our in vitro results show that knocking-down FOXK2 renders breast cancer cells more resistant to chemotherapeutics. Additionally, grade II patients who received chemotherapy and relapsed before 5 years showed low FOXK2 expression. Similarly, reduced FOXK2 expression has also been found in non-responders patients, particularly luminal B, treated with the FEC chemotherapeutic combination. Therefore, FOXK2 low expression has been related to poor responses to treatment in breast cancer. Finally, ongoing in vitro experiments with shFOXK2 drug resistant cells are currently exploring the interface between breast cancer drug resistance and tumor progression.

Altogether, our findings suggest that analyzing FOXK2 gene expression might be a good predictor of response to therapy, diagnosis and prognosis in some tumor types.