To address the potential of CHIP to serve as an E3 ubiquitin ligase towards ErbB2 in ErbB2-overexpressing breast cancer cells, we performed immunoprecipitation analyses in both CHIP-overexpressing vs. empty vector control and CHIP shRNA knockdown vs. control shRNA-expressing ErbB2-overexpressing breast cancer cell lines. The gene discussed is ERBB2; the disease is breast cancer.