YY1 and breast cancer: Importantly, the CP2c protein level in YY1 high breast cancers was further downregulated to the CP2c protein level of adjacent normal tissues, which is different from the CP2c-dependent YY1 degradation mechanism through the 20S proteasome pathway (28), suggesting an additional unknown mechanism of YY1-dependent CP2c protein degradation is operational in YY1 high breast cancer tissues.