Compared with normal, the expression of miR-375 in patients with multiple myeloma (MM) was significantly reduced, and the introduction of miR-375 down-regulated PDPK1 in human myeloma cell lines (HMCLs), which probably affected the development of MM through phosphoinositide-dependent protein kinase 1 (PDPK1)/ribosomal protein S6 kinase A3 (RPS6KA3). Here, RPS6KA3 is linked to AL amyloidosis.