Abstract 2692: Elucidation of the pre-B-cell receptor signaling network in acute lymphocytic leukemia cells

Abstract

Abstract Antigen receptors transduce complex signals and thereby control important cell fate decisions of the B-lineage including differentiation, proliferation and B-cell survival. The initial steps of B-cell development take place in the bone marrow, and the first dependency of a developing B-cell on antigen receptor signaling occurs at the pre-B-cell stage where expression of the pre-BCR is essential for cell survival. In contrast to B-cell-receptor (BCR) signaling, the nature of pre-BCR signals is far less characterized. It is believed that pre-BCRs transduce a constitutive baseline signal that is essential for survival and differentiation of pre-B-cells into immature B-cells. Since pre-BCRs are crucial regulators of pre-B-cell survival and differentiation, it is not surprising that dysregulation of pre-BCR signaling is observed in acute lymphocytic leukemia (ALL) cells where it contributes to survival of the malignant cell clones. To identify drug targets in the pre-BCR signaling network, we have systematically characterized pre-BCR signaling in two pre-BCR-dependent ALL cell lines by quantitative phosphoproteomics. Because pre-BCRs transduce a constitutive baseline signal, we interfered with pre-BCR signaling by either Syk inhibitor treatment or by an inducible shRNA-mediated knock-down of the pre-BCR component Ig-α to monitor pre-BCR-dependent signals. We identified and quantified more than 15,000 phospho-sites. Among these sites, more than 500 were regulated upon interference with pre-BCR signaling. Although the upstream components are shared between pre-BCRs and BCRs, the wiring of their downstream signals occurred to be different which is reflected by our finding that the majority of the identified pre-BCR signaling effectors have not been described in the context of BCR signaling in mature B-cells or lymphomas. Finally, we have identified vulnerabilities in the pre-BCR signaling network by intersecting our phosphoproteomic data with data from loss-of-function CRISPR-Cas9 screens for essential genes in ALL cell lines. Taken together, this study provides a comprehensive dataset for pre-BCR signaling and identifies effector proteins that are relevant for the regulation of ALL cell survival and proliferation. Citation Format: Roland Walter, Khouloud Kouidri, Jessica Peter, Martine Pape, Laura Merschen, Bjoern Haeupl, Carmen Doebele, Hubert Serve, Yanlong Yi, Henning Urlaub, Thomas Oellerich. Elucidation of the pre-B-cell receptor signaling network in acute lymphocytic leukemia cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2692.