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.
Jingyu Chen, Vijitha Sathiaseelan, Andrew Douglas Moore, Shengjiang Tan, Chandra Sr Chilamakuri, Valar Nila Roamio Franklin, Arash Shahsavari, Constanze A Jakwerth, Sandra B Hake, Alan J Warren, Irina Mohorianu, Clive S D'Santos, Ingo Ringshausen