IRF1 and neoplasm: It has been shown that the absence of PSMB9 is associated with the development of spontaneous uLMS, where ~36% of the homozygous PSMB9-deficient mice developed the tumor by 12 months of age [7], and the malignancy of uLMS driven by the deficiency of PSMB9 is directly correlated to the Interferon Regulatory Factor 1 (IRF1) expression.