Protein Kinase CK1α Sustains B-Cell Receptor Signaling in Mantle Cell Lymphoma

FPFT-2216, a Novel Anti-lymphoma Compound, Induces Simultaneous Degradation of IKZF1/3 and CK1α to Activate p53 and Inhibit NFκB Signaling

Reducing casein kinase 1α (CK1α) expression inhibits the growth of multiple cancer cell lines, making it a potential therapeutic target for cancer. Herein, we evaluated the antitumor activity of FPFT-2216-a novel low molecular weight compound-in lymphoid tumors and elucidated its molecular mechanism of action. In addition, we determined whether targeting CK1α with FPFT-2216 is useful for treating hematopoietic malignancies. FPFT-2216 strongly degraded CK1α and IKAROS family zinc finger 1/3 (IKZF1/3) via proteasomal degradation. FPFT-2216 exhibited stronger inhibitory effects on human lymphoma cell proliferation than known thalidomide derivatives and induced upregulation of p53 and its transcriptional targets, namely, p21 and MDM2. Combining FPFT-2216 with an MDM2 inhibitor exhibited synergistic antiproliferative activity and induced rapid tumor regression in immunodeficient mice subcutaneously transplanted with a human lymphoma cell line. Nearly all tumors in mice disappeared after 10 days; this was continuously observed in 5 of 7 mice up to 24 days after the final FPFT-2216 administration. FPFT-2216 also enhanced the antitumor activity of rituximab and showed antitumor activity in a patient-derived diffuse large B-cell lymphoma xenograft model. Furthermore, FPFT-2216 decreased the activity of the CARD11/BCL10/MALT1 (CBM) complex and inhibited IκBα and NFκB phosphorylation. These effects were mediated through CK1α degradation and were stronger than those of known IKZF1/3 degraders. In conclusion, FPFT-2216 inhibits tumor growth by activating the p53 signaling pathway and inhibiting the CBM complex/NFκB pathway via CK1α degradation. Therefore, FPFT-2216 may represent an effective therapeutic agent for hematopoietic malignancies, such as lymphoma.

SIGNIFICANCE

We found potential vulnerability to CK1α degradation in certain lymphoma cells refractory to IKZF1/3 degraders. Targeting CK1α with FPFT-2216 could inhibit the growth of these cells by activating p53 signaling. Our study demonstrates the potential therapeutic application of CK1α degraders, such as FPFT-2216, for treating lymphoma.

DOK3 promotes atopic dermatitis by enabling the phosphatase PP4C to inhibit the T cell signaling mediator CARD11

The scaffolding protein CARD11 is a critical mediator of antigen receptor signaling in lymphocytes. Hypomorphic (partial loss-of-function) mutations in CARD11 are associated with the development of severe atopic dermatitis, in which T cell receptor signaling is reduced and helper T cell differentiation is skewed to an allergy-associated type 2 phenotype. Here, we found that the docking protein DOK3 plays a key role in the pathogenesis of atopic dermatitis by suppressing CARD11 activity. DOK3 interacted with CARD11 and decreased its phosphorylation in T cells by recruiting the catalytic subunit of protein phosphatase 4, thereby dampening downstream signaling. Knocking out Dok3 enhanced the production of the cytokine IFN-γ by T cells, which conferred protection against experimental atopic dermatitis-like skin inflammation in mice. The expression of DOK3 was increased in T cells isolated from patients with atopic dermatitis and inversely correlated with IFNG expression. A subset of hypomorphic CARD11 variants found in patients with atopic dermatitis bound more strongly than wild-type CARD11 to DOK3. Our findings suggest that the strength of the interaction of DOK3 with CARD11 may predispose individuals to developing atopic dermatitis.

CK1α/RUNX2 Axis in the Bone Marrow Microenvironment: A Novel Therapeutic Target in Multiple Myeloma

Simple Summary

Multiple myeloma (MM) is an incurable disease for which novel therapeutic approaches targeting the malignant cells and the associated bone disease are urgently needed. CK1α is a protein kinase that plays a crucial role in the signaling network that sustains plasma cell (PC) survival and bone disease. This protein regulates Wnt/β-catenin signaling, which is fundamental for both MM cell survival and mesenchymal stromal cell (MSC) osteogenic differentiation. In this study, we investigated its involvement in MM–MSC cross-talk. We found that, by lowering CK1α expression levels in co-cultures of MM and MSC cells, expression of RUNX2—the master regulator of osteogenic differentiation—was regulated differently in the two cell types. Our data suggest the possibility of using a specific CK1α inhibitor as part of a novel therapeutic approach to selectively kill malignant PCs and overcome the blocking of osteogenic differentiation induced by MM cells in MSCs.

Abstract

Multiple myeloma (MM) is a malignant plasma cell (PC) neoplasm, which also displays pathological bone involvement. Clonal expansion of MM cells in the bone marrow causes a perturbation of bone homeostasis that culminates in MM-associated bone disease (MMABD). We previously demonstrated that the S/T kinase CK1α sustains MM cell survival through the activation of AKT and β-catenin signaling. CK1α is a negative regulator of the Wnt/β-catenin cascade, the activation of which promotes osteogenesis by directly stimulating the expression of RUNX2, the master gene regulator of osteoblastogenesis. In this study, we investigated the role of CK1α in the osteoblastogenic potential of mesenchymal stromal cells (MSCs) and its involvement in MM–MSC cross-talk. We found that CK1α silencing in in vitro co-cultures of MMs and MSCs modulated RUNX2 expression differently in PCs and in MSCs, mainly through the regulation of Wnt/β-catenin signaling. Our findings suggest that the CK1α/RUNX2 axis could be a potential therapeutic target for constraining malignant PC expansion and supporting the osteoblastic transcriptional program of MSCs, with potential for ameliorating MMABD. Moreover, considering that Lenalidomide treatment leads to MM cell death through Ikaros, Aiolos and CK1α proteasomal degradation, we examined its effects on the osteoblastogenic potential of MSC compartments.

Protein Kinase CK2 represents a new target to boost Ibrutinib and Venetoclax induced cytotoxicity in mantle cell lymphoma

Mantle cell lymphoma (MCL) is an incurable B cell non-Hodgkin lymphoma, characterized by frequent relapses. In the last decade, the pro-survival pathways related to BCR signaling and Bcl-2 have been considered rational therapeutic targets in B cell derived lymphomas. The BTK inhibitor Ibrutinib and the Bcl-2 inhibitor Venetoclax are emerging as effective drugs for MCL. However, primary and acquired resistance also to these agents may occur. Protein Kinase CK2 is a S/T kinase overexpressed in many solid and blood-derived tumours. CK2 promotes cancer cell growth and clonal expansion, sustaining pivotal survival signaling cascades, such as the ones dependent on AKT, NF-κB, STAT3 and others, counteracting apoptosis through a “non-oncogene” addiction mechanism. We previously showed that CK2 is overexpressed in MCL and regulates the levels of activating phosphorylation on S529 of the NF-κB family member p65/RelA. In the present study, we investigated the effects of CK2 inactivation on MCL cell proliferation, survival and apoptosis and this kinase’s involvement in the BCR and Bcl-2 related signaling. By employing CK2 loss of function MCL cell models, we demonstrated that CK2 sustains BCR signaling (such as BTK, NF-κB and AKT) and the Bcl-2-related Mcl-1 expression. CK2 inactivation enhanced Ibrutinib and Venetoclax-induced cytotoxicity. The demonstration of a CK2-dependent upregulation of pathways that may antagonize the effect of these drugs may offer a novel strategy to overcome primary and secondary resistance.