Background Therapies targeting epidermal growth factor receptors (EGFR/ErbB/Her) fail to achieve clinical benefit in patients with colorectal cancer (CRC) who have alterations in components of the downstream RAS-ERK1/2 and PI3K signaling pathways. Herein, KRAS and BRAF gene mutations lead to constitutive signal activation, thereby preventing the transport of anti-mitotic transcription factors from the cytosol to the nucleus. Thus, novel strategies are of clinical need that bypass this resistance mechanism and sensitize cancer cells to growth inhibition. Overexpression of the transmembrane nuclear pore protein POM121 is a negative prognostic marker for CRC and is associated with metabolic diseases (e.g. diabetes). We thus hypothesized that inhibition of POM121 allows nuclear transport of peroxisome proliferator-activated receptor-gamma (PPARg), a drugable transcription factor with anti-diabetic and anti-tumoral efficacies, to restore its transactivating ability on target genes.

Methods CRISPR/Cas9-sgRNA and siRNA knock-down of POM121A/C was performed in human KRAS/BRAF-mutant CRC cell lines (HT29, SW480, HCT116). Rosiglitazone was used as PPARg-agonist. Genes and proteins were studied using immunoprecipitation, mass spectrometry, microscopy, and reporter gene assays complemented by bioinformatic analyses. Tissue samples from patients with CRC (n=208 cases) were analyzed by immunohistochemistry.

Results POM121 was enriched and co-expressed with PPARg in patients (*p < 0.0001, r2 = 0.3658). Its predicted interactome comprised proteins of the tumor metabolism and immunity (e.g. CTLA4). In silico modeling provided 3D structures of holo-POM121 and its subdomains, where the nuclear location sequence (NLS) interacted with PPARg. POM121 co-localized with PPARg at the nuclear membrane and inhibited its translocation. Conversely, POM121 silencing allowed nuclear import of PPARg and activated target genes involved in lipid metabolism and differentiation (e.g. P21 CIP1/WAF1), resulting in reduced proliferation of CRC cells (by ~50%, *p < 0.05, ANOVA, n=3 per line).

Conclusions Our data suggest the POM121-PPARg complex as a potential drugable target in CRC. Thus, anti-diabetics might be suitable as metabolic sensitizers for current clinical therapies of KRAS/BRAF-mutant tumors.