Cyclin D1 is frequently overexpressed in esophageal squamous cell carcinoma (ESCC) and is considered a key driver of this disease. Mutations in FBXO4, F-box specificity factor that directs SCF-mediated ubiquitylation of cyclin D1, occur in ESCC with concurrent overexpression of cyclin D1 suggesting a potential tumor suppressor role for FBXO4. To evaluate the contribution of FBXO4-dependent regulation cyclin D1 in esophageal squamous cell homeostasis, we exposed FBXO4 knockout mice to N-nitrosomethylbenzylamine (NMBA), an esophageal carcinogen. Our results revealed that loss of FBXO4 function facilitates NMBA induced papillomas in FBXO4 het (+/-) and null (-/-) mice both by numbers and sizes 11 months after single dose NMBA treatment at 2mg/kg by gavage when compared to that in wt (+/+) mice (P < 0.01). No significant difference was noted between heterozygous or nullizygous mice consistent with previous work. To assess cyclin D1/CDK4 dependence, mice were treated with the CDK4/6 specific inhibitor, PD0332991, for 4 weeks. PD0332991 treatment (150mg/kg daily), reduced tumor size and tumor number. Collectively, our data support a role for FBXO4 as a suppressor of esophageal tumorigenesis.
Keywords: BrdU, Bromodeoxyuridine; CDK, Cyclin Dependent Kinase; CDK4; DMSO, Dimethyl Sulfoxide; EGFR, Epidermal Growth Factor Receptor; ESCC; ESCC, Esophageal Squamous Cell Carcinoma; FBXO4; FBXO4, F box only protein 4; GI, Gastrointestinal tract; H&E, Hematoxylin and Eosin; Het, Heterozygous; NMBA, N-nitrosomethylbenzylamine; PBS, Phosphate Buffered Saline; PD0332991; PE, Preneoplastic Esophagus; PI, Propidium Iodide; Rb, Retinoblastoma Protein; SCC, Squamous Cell Carcinoma; SCF, Skp1-Cul1-F box protein; TNFa, Tumor Necrosis Factor alpha; Wt, Wild Type; cyclin D1.