De novo and acquired resistance, largely attributed to genetic alterations, are barriers to effective anti-EGFR therapy. We generated cetuximab-resistant cells following prolonged cetuximab exposure to cetuximab-sensitive colorectal cancer cells in three-dimensional culture. Through whole exome sequencing and transcriptional profiling, we found overexpression of lncRNA MIR100HG and two embedded miRNAs, miR-100 and miR-125b, in the absence of known genetic events linked to cetuximab resistance. MIR100HG and miR-100/125b overexpression was also observed in cetuximab-resistant colorectal cancer and head and neck squamous cell cancer cell lines and in tumors from colorectal cancer patients that progressed on cetuximab. miR-100/125b coordinately represses five Wnt/β-catenin negative regulators, resulting in increased Wnt signaling, and Wnt inhibition in cetuximab-resistant cells restored cetuximab responsiveness. We describe a double-negative feedback loop between MIR100HG and GATA6, whereby GATA6 represses MIR100HG, but this repression is relieved by miR-125b targeting of GATA6. These studies identify a clinically actionable, epigenetic cause of cetuximab resistance.

Wnt and EGFR signaling play key roles in embryonic development and cell proliferation. It is well documented that dysregulation of these two pathways often leads to tumorigenesis with poor prognosis. However, the possible crosstalk between the two pathways in cancer development is largely unknown. Although some reports show that EGFR might antagonize Wnt signaling during development in Drosophila, an increasing body of evidence indicates that Wnt and EGFR signaling crosstalk and transactivate one another in development and cancer. This review summarizes recent studies on the crosstalk between Wnt and EGFR signaling in cancers and points out several possible convergence points. Wnt ligands can activate EGFR signaling through their 7-transmembrane domain receptor Frizzled while EGFR can activate β-catenin via receptor tyrosine kinase-PI3K/Akt pathway; EGFR has been shown to form a complex with β-catenin and increase the invasion and metastasis of cancer cells. NKD2, a Wnt antagonist by interacting with Dishevelled, also escorts TGFα-containing exocytic vesicles to the basolateral membrane of polarized epithelial cells. Down-regulation of NKD2 causes Wnt activation and TGFα misdelivery, suggesting its functions in cell homeostasis and prevention of tumorigenesis.

Mutations of the polycystic kidney and hepatic disease 1 (PKHD1) gene have been shown to cause autosomal recessive polycystic kidney disease (ARPKD), but the cellular functions of the gene product (PKHD1) remain uncharacterized. To illuminate its properties, the spatial and temporal expression patterns of PKHD1 were determined in mouse, rat, and human tissues by using polyclonal Abs and mAbs recognizing various specific regions of the gene product. During embryogenesis, PKHD1 is widely expressed in epithelial derivatives, including neural tubules, gut, pulmonary bronchi, and hepatic cells. In the kidneys of the pck rats, the rat model of which is genetically homologous to human ARPKD, the level of PKHD1 was significantly reduced but not completely absent. In cultured renal cells, the PKHD1 gene product colocalized with polycystin-2, the gene product of autosomal dominant polycystic disease type 2, at the basal bodies of primary cilia. Immunoreactive PKHD1 localized predominantly at the apical domain of polarized epithelial cells, suggesting it may be involved in the tubulogenesis and͞or maintenance of duct-lumen architecture. Reduced PKHD1 levels in pck rat kidneys and its colocalization with polycystins may underlie the pathogenic basis for cystogenesis in polycystic kidney diseases.