Overexpression of Pin1 regulated by TOP2A, which subsequently stabilizes Pyk2 to promote bortezomib resistance in multiple myeloma.

Multiple myeloma (MM), a hematological malignancy of plasma cells, has remained largely incurable owing to drug resistance and disease relapse, which requires novel therapeutic targets and treatment approaches. Peptidyl-prolyl cis/trans isomerase NIMA-interacting 1 (Pin1) acts as an oncoprotein linked to the development of various tumors. However, the functional consequence of Pin1 overexpression in modulating MM biology has not been established. In the present study, we show that Pin1 expression is highly variable in myeloma cell lines and primary MMs and that high Pin1 expression is associated with poor survival of MM patients. Next, TOP2A is identified to be a Pin1 promoter-binding protein and CK2 activates TOP2A to promote the expression level of Pin1. Additionally, we demonstrate that Pin1 positively modulates the stability and function of Pyk2 to enhance bortezomib resistance in MM. Pin1 recognizes three phosphorylated Ser/Thr-Pro motifs in Pyk2 via its WW domain and increases the cellular levels of Pyk2 in an isomerase activity-dependent manner by inhibiting the ubiquitination and proteasomal degradation of Pyk2. Moreover, Pin1 inhibition combined with Pyk2 inhibition decreases myeloma burden both in vitro and in vivo. Altogether, our findings reveal the tumor-promoting role of Pin1 in MM and provide evidence that targeting Pin1 could be a therapeutic strategy for MM.