CHEK1 and circCHEK1_246aa Promote Multiple Myeloma Malignancy By Evoking Chromosomal Instability and Bone Lesion

Key findings

CHEK1 and circCHEK1_246aa induce multiple myeloma cell proliferation, drug resistance, and bone lesion formation

CHEK1 and circCHEK1_246aa evoke myeloma chromosomal instability, partially through CEP170 activation

Abstract

Multiple myeloma (MM) is characterized by clonal expansion of plasma cells in the bone marrow (BM). Therefore, effective therapeutic interventions must target both myeloma cells and the BM niche. In the present study, we first demonstrated that CHEK1 expression was significantly increased in human MM samples relative to normal plasma cells, and that in MM patients, high CHEK1 expression was associated with poor outcomes. CHEK1 overexpression increased cellular proliferation in MM cells and evoked drug resistance in vitro, while CHEK1 knockdown abrogated this effect. Moreover, CHEK1 was a high-risk gene for poor outcome in MM patients, and, in paired samples from MM patients taken from newly diagnosed and relapsed MM, CHEK1 expression was upregulated. CHEK1-mediated increases in cell proliferation and drug resistance were due in part to CHEK1-induced chromosomal instability (CIN), as demonstrated by Giemsa staining, exon sequencing, and immunofluorescence. CHEK1 activated CIN, partly by phosphorylating CEP170. Interestingly, CHEK1 promoted osteoclast differentiation by direct phosphorylation and activation of NFATc1, indicating that CHEK1 inhibition could target both MM cell proliferation and macrophage osteoclast differentiation in the BM niche. Intriguingly, we also discovered that MM cells expressed circCHEK1_246aa, a circular CHEK1 RNA, which encoded and was translated to the CHEK1 kinase catalytic center. Transfection of circCHEK1_246aa increased MM CIN and osteoclast differentiation similarly to CHEK1 overexpression, suggesting that MM cells could secrete circCHEK1_246aa in the BM niche to increase the invasive potential of MM cells and promote osteoclast differentiation. Finally, we demonstrated in vivo in xenograft models that CHEK1 overexpression prompted MM proliferation and drug resistance, while CHEK1 knockdown conversely inhibited MM growth. Together, these findings suggest that targeting the enzymatic catalytic center encoded by CHEK1 mRNA and circCHEK1_246aa is a promising therapeutic modality to target both MM cells and the BM niche.