ZAP-70 constitutively regulates gene expression and protein synthesis in chronic lymphocytic leukemia

Abstract

The expression of ZAP-70 in a subset of CLL patients strongly correlates with a more aggressive clinical course, though the exact underlying mechanisms remain elusive. The ability of ZAP-70 to enhance B cell receptor (BCR) signaling, independently of its kinase function, is considered to contribute. Here we employed RNA-sequencing and proteomic analyses of primary cells differing only in their expression of ZAP-70 to further define how ZAP-70 increases aggressiveness of CLL. We identified that ZAP-70 is directly required for cell survival in the absence of an overt BCR signal, which can compensate for ZAP-70 deficiency as an anti-apoptotic signal. In addition, the expression of ZAP-70 regulates the transcription of factors regulating recruitment and activation of T cells, such as CCL3, CCL4 and IL4I1. Quantitative mass spectrometry of double-cross linked ZAP-70 complexes further demonstrated constitutive and direct protein-protein interactions between ZAP-70 and BCR-signaling components. Unexpectedly, ZAP-70 also binds to ribosomal proteins, which is not dependent on, but further increased by BCR-stimulation. Importantly, decreased expression of ZAP-70 significantly reduced MYC-expression and global protein synthesis, providing evidence that ZAP-70 contributes to translational dysregulation in CLL. In conclusion, ZAP-70 constitutively promotes cell survival, microenvironment-interactions and protein synthesis in CLL cells, likely to improve cellular fitness and to further drive disease progression.

B cell receptor signaling and associated pathways in the pathogenesis of chronic lymphocytic leukemia

“…These chemokines stimulate the recruitment of T cells into proliferation centers, where they provide a supportive microenvironment. Thereby, ZAP-70 improves CLL cell fitness to survive and proliferate and further drives disease progression ( 101 ). This tonic BCR signaling is solely present in U-CLL patients and relies on the ability of ZAP-70 to stimulate the activation of AKT ( 102 ).…”

Amino acid metabolism: challenges and opportunities for the therapeutic treatment of leukemia and lymphoma

“…Although IDO1 inhibitors can improve immunotherapy efficacy, potential therapeutic challenges should be considered 146 . IL‐4I1, recognized as an immunosuppressive enzyme for chronic lymphoblastic leukemia (CLL) and B‐cell lymphoma, 168,169 is part of a resistance mechanism against IDO1 inhibitors 146 . In the context of IDO1 inhibition, IL‐4I1 is regulated to produce indole‐3‐pyruvic acid that activates the AHR pathway, suppresses the inhibitory effects of IDO inhibitors on the AHR pathway and sustains an immunosuppressive TME 146 .…”

CD160 receptor in CLL: Current state and future avenues

“…Malignant B cells also express CD5, which, upon activation by Lyn kinase recruits SHP-1 or SHIP to dephosphorylate signaling molecules and maintain B-cell anergy. Adapted from ( 36 , 43 ).…”

“…Third, B-cell receptor (BCR) signaling plays a key pathological role by activating the signaling pathways implicated in CLL cell survival, metabolism, proliferation, and resistance to apoptosis ( 40 – 42 ). Furthermore, CLL is characterized by the expression of several markers specific to certain immune cells, such as ζ-associated protein kinase 70 (ZAP-70) ( 43 ) and lymphocyte-specific tyrosine kinase (Lck) ( 44 ), which favor CLL cell survival, and CD5, which maintains CLL cell anergy ( 45 ). CD160 is also a crucial marker of CLL and a key activator of CLL cell survival and resistance to apoptosis ( 46 ).…”