Osteocyte CIITA Aggravates Osteolytic Bone Lesions in Myeloma

Osteolytic destruction is a hallmark of multiple myeloma, resulting from activation of osteoclast mediated bone resorption and reduction of osteoblast-mediated bone formation. However, the molecular mechanism underlying the differentiation and activity of osteoclasts and osteoblasts within a myelomatous microenvironment remains unclear. Here, we demonstrate that the osteocyte-expressed major histocompatibility complex class II transactivator (CIITA) contributes to myeloma-induced bone lesions. CIITA upregulates the secretion of osteolytic cytokines from osteocytes through acetylation at histone 3 lysine 14 in the promoter of TNFSF11 (encoding RANKL) and SOST (encoding sclerostin), leading to enhanced osteoclastogenesis and decreased osteoblastogenesis. In turn, myeloma cell–secreted 2-deoxy-D-ribose, the product of thymidine catalyzed by the function of thymidine phosphorylase, upregulates CIITA expression in osteocytes through the STAT1/IRF1 signaling pathway. Our work thus broadens the understanding of myeloma-induced osteolysis and indicates a potential strategy for disrupting tumor-osteocyte interaction to prevent, or treat patients with, myeloma bone disease. Define a heretofore unrecognized role for osteocytes in genesis of myeloma-associated bone disease