SIAH1 and cancer: Siah1 exhibits the function of decreasing P‐glycoprotein level, and low expression level of Siah1 was shown to induce multidrug resistance in cancer cells.51, 52 Therefore, the treatment of drug‐resistant cells with β‐elemene was shown to increase the expression of E3 ubiquitin ligases to enhance the efficacy of DOX treatment.53 This evidence, as well as our study, indicated the important role of ubiquitination in tumor progression.