Reduced association of anti-apoptotic protein Mcl-1 with E3 ligase Mule increases the stability of Mcl-1 in breast cancer cells

• Published in: British journal of cancer Vol. 105; no. 3; pp. 428 - 437
• Main Authors: Pervin, S, Tran, A, Tran, L, Urman, R, Braga, M, Chaudhuri, G, Singh, R
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 26.07.2011; Nature Publishing Group
• Subjects: 631/80/304; 631/80/82/23; 692/699/67/1347; Apoptosis; Apoptosis Regulatory Proteins - chemistry; Apoptosis Regulatory Proteins - metabolism; Biological and medical sciences; Biomedical and Life Sciences; Biomedicine; Breast cancer; Breast Neoplasms - metabolism; Cancer Research; Cell Line, Tumor; Down-Regulation; Drug Resistance; Epidemiology; Epithelial Cells - metabolism; Gynecology. Andrology. Obstetrics; Humans; Kinases; Macromolecular Substances - metabolism; Mammary gland diseases; Medical research; Medical sciences; Medicine; Mitochondria; Mitogen-Activated Protein Kinase 1 - metabolism; Mitogen-Activated Protein Kinase 3 - metabolism; Molecular Diagnostics; Molecular Medicine; Myeloid Cell Leukemia Sequence 1 Protein; Oncology; Protein Stability; Protein synthesis; Proteins; Proto-Oncogene Proteins c-bcl-2 - chemistry; Proto-Oncogene Proteins c-bcl-2 - metabolism; Tumors; Ubiquitin-Protein Ligases - chemistry; Ubiquitin-Protein Ligases - metabolism; Ubiquitination; Los Angeles California; United States > US; apoptosis; E3 ligase; ubiquitin; proteosome; Ubiquitin; Breast disease; Stability; Enzyme; Breast cancer; Malignant tumor; Mammary gland diseases; Antiapoptotic agent; Cancerology; Apoptosis inhibitory protein; MCL1 gene; Ligases; Cell death; Tumor cell; Cancer; Apoptosis
• ISSN: 0007-0920; 1532-1827
• DOI: 10.1038/bjc.2011.242

Background: Mechanisms that increase resistance to apoptosis help promote cellular transformation. Cancer cells have deregulated apoptotic pathways, where increased expression and stability of anti-apoptotic proteins Mcl-1 and Bcl-2 increases resistance to apoptosis. Pathways that increase the stability of proteins in cancer cells remain poorly understood. Methods: Using human mammary epithelial and established breast cancer cell lines, we assessed the mechanisms that increase the stability of anti-apoptotic proteins in breast cancer cells by caspase assay, western blot, small-inhibitory RNA treatment and immunoprecipitation. Results: While breast cancer cells were resistant to de novo inhibition of protein synthesis, a rapid proteosome-mediated degradation of Mcl-1 and Bcl-2 induced apoptosis in mammary epithelial cells. Although Mule, an E3 ligase that targets Mcl-1 for degradation was expressed in mammary epithelial and breast cancer cell lines, rapid increase of polyubiquitinated Mcl-1 and Bcl-2 was detected only in mammary epithelial cells. Only transient formation of the Mule–Mcl-1 complex was detected in breast cancer cells. Downregulation of pERK1/2 in breast cancer cells reduced Mcl-1 levels and increased Mcl-1/Mule complex. Conclusion: Our findings suggest that reduced Mule/Mcl-1 complex has a significant role in increasing the stability of Mcl-1 in breast cancer cells and increased resistance to apoptosis.