FBXW7 is a cell cycle regulatory gene that ubiquitinates positive cell cycle regulators such as c-Myc and
cyclin E, allowing for cell cycle exit. Defects in the FBXW7 gene that lead to cell cycle re-entry and expedite the G1-S transition is thought to be one of the causes of
cancer development. However, its clinical importance for
breast cancer patients remains undetermined. This prompted us to investigate its expression level in
breast cancer patients to establish its clinical significance. The expression level of FBXW7
mRNA was assessed in 186 cases of primary invasive
breast cancer. Correlations between FBXW7
mRNA expression and clinicopathological factors, prognoses and immunohistochemical expression levels of Ki-67, FBXW7, c-Myc and
cyclin E were analyzed. In vitro investigation of FBXW7 gene silencing in a
breast cancer cell line was conducted. FBXW7
mRNA was expressed at significantly lower levels in patients with high histological grade and
hormone receptor-negative
tumors. Patients with lower FBXW7
mRNA expression had a poorer prognosis for
breast cancer-specific survival than those with higher expression. A high Ki-67 labeling index and positive
cyclin E protein expression were significantly correlated with lower FBXW7
mRNA expression. In vitro, silencing FBXW7 enhanced expression of c-Myc and
cyclin E proteins and upregulated both cell proliferation and G1-S transition. In
breast cancer, reduced FBXW7
mRNA expression may have independent prognostic potential through the enhanced function of
cell cycle regulatory proteins.