Currently, arsenic has been clinically investigated as a therapeutic agent for a variety of solid malignancies, including breast cancer. However, the exact underlying molecular mechanisms through which arsenic trioxide (As(2)O(3)) induces cell growth arrest and apoptosis in solid tumors have not been clearly understood. The aim of our study was to gain an insight into the effect of As(2)O(3) on the human breast cancer MCF-7 cell line and investigate cell growth inhibition, apoptosis, and the molecular mechanism after As(2)O(3) treatment in MCF-7 cells. Expression of FOXO3a, nuclear-FOXO3a, caspase-3, and IκB kinase β (IKKβ) mRNA levels in MCF-7 cells was determined by reverse transcription-polymerase chain reaction (RT-PCR). The protein expression was examined by the Western blot analysis and immunocytochemical staining. The distribution of apoptotic cells was assessed by flow cytometry, and the morphology of the apoptotic cells was investigated by Hoechest33258 staining. Our results showed that As(2)O(3) significantly induced the apoptosis of MCF-7 cells tested in this study in a dose-dependent manner. As(2)O(3) induced the decrease of IKKβ expression and the increase of total as well as nuclear FOXO3a expression, which triggered the phosphorylation of cytoplasmic FOXO3a at the Thr32 residue decrease. RT-PCR, Western blot analysis, and immunocytochemistry revealed that the expression of IKKβ in MCF-7 cells was upregulated when As(2)O(3) was combined with tumor necrosis factor-α (TNF-α), whereas the expression of FOXO3a was downregulated in comparison with the As(2)O(3)-alone group. These findings indicated a specific molecular mechanism by which MCF-7 cell lines were susceptible to the As(2)O(3) therapy through FOXO3a expression and localization. This FOXO3a accumulation may be well correlated with the As(2)O(3)-induced reduction of active IKKβ, which may provide new insights into As(2)O(3)-related signaling activities.

CSN6 is one subunit of the highly conserved constitutive photomorphogenesis 9 (COP9) signalosome (CSN), which is overexpressed in many types of cancers, and has received great attention as a regulator of the degradation of cancer-related proteins, suggesting its importance in oncogenic activity. CSN6 has been shown to be overexpressed in cervical cancer (CC) and associated with CC development. CC remains to be one of the most aggressive cancers affecting women. Cathepsin L (CTSL), significantly associated with the autophagy, plays a critical role in degradation of extracellular matrix for metastasis. However, the detailed biological functions of CSN6 on CTSL in CC metastasis have not been well clarified. Our data has shown that CSN6 and CTSL are positively correlated. The overexpression of CSN6 and CTSL might be a strong indicator for CC enhanced aggressiveness. CSN6 could suppress the degradation of CTSL, then facilitated the migration and invasion of CC cells. Interestingly, our results indicated that autophagy is essential for decreasing CTSL, while CSN6 could inhibit the autophagy ability of CC cells. In addition, blocking of the mammalian target of rapamycin (mTOR) pathway reversed CSN6-mediated autophagy inhibition. We further demonstrated that CSN6 positively regulated CTSL expression through an autophagy-lysosomal system. Taken together, we concluded that CSN6 might promote the migration and invasion of cervical cancer cells by inhibiting autophagic degradation of CTSL and serve as a potential gene therapy target for the treatment of CC metastasis.

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