Cullin 7 is a predictor of poor prognosis in breast cancer patients and is involved in the proliferation and invasion of breast cancer cells by regulating the cell cycle and microtubule stability.

Cullin 7 is the 'scaffold' of the cullin-RING-based E3 ligases which catalyze the final step of the ubiquitination cascade in eukaryotic organisms. Although one study has reported the involvement of cullin 7 in the invasion and migration of breast cancer cells without further exploration of its mechanisms, the expression of cullin 7 in breast cancer tissues and its clinical significance have not been reported. The present study evaluated cullin 7 protein expression in malignant and benign breast tissues using immunochemistry, and further analyzed the association of positive cullin 7 expression in breast cancer tissues with clinicopathological characteristics of breast cancer patients. Cullin 7 expression was further silenced in breast cancer cells by siRNA and its functions and mechanisms in cell proliferation and invasion were investigated. The results showed that high cullin 7 expression was significantly correlated with pathological stage (P=0.013) and lymph node metastasis (P=0.022) of breast cancer. Patients with high cullin 7 expression had a shorter overall survival rate than those with low cullin 7 expression (P=0.037). Silencing of cullin 7 expression significantly inhibited the proliferation (P<0.05) and invasion (P<0.05), increased S1 phase (P<0.05), but decreased G2 phase (P<0.05) in MDA-MB-231 and BT549 cells. In addition, silencing of cullin 7 expression decreased cyclin A, but increased p21 protein expression. Moreover, silencing of cullin 7 expression altered the cell shape, caused disorder in microtubules, and increased the microtubule regeneration in MDA-MB-231 and BT549 cells. In conclusion, cullin 7 is overexpressed in breast cancer tissues which is associated with the development and prognosis of breast cancer. Cullin 7 is involved in the proliferation and invasion of breast cancer cells by regulating the cell cycle and microtubule stability.