CDKN1B and myeloid sarcoma: Notably, in contrast to the elevated Hrd1 protein expression levels, p27kip1 protein, but not its mRNA expression levels are decreased in CD4 T cells from MS patients comparing with healthy controls (Fig. 7b–d), suggesting that Hrd1 regulates p27kip1 protein stability in human CD4 T cells and that Hrd1 promotes CD4 T-cell autoimmunity through p27kip1 protein destruction.