CCR1 and plasma cell myeloma: Moreover, UBE2O also downregulates the transcriptional activity of c-Maf and the expression of c-Maf downstream genes, including cyclin D2, integrin β7, CCR1 (C-C Motif Chemokine Receptor 1), and ARK5 (AMPK-related protein kinase 5), which are responsible for cell cycle progress, MM cell proliferation, and myeloma cell invasion [62,63].