Mesothelin promotes acute myeloid leukemia progression through LYN-dependent signaling.

Mesothelin (MSLN) is a glycosylphosphatidylinositol-anchored cell surface protein that is overexpressed in several solid tumors and in one-third of pediatric acute myeloid leukemia (AML) cases. It represents a validated immunotherapeutic target owing to its lack of expression in normal bone marrow. The function of MSLN in AML is unknown, but it is implicated to regulate adhesion in solid tumors through interaction with its only known binding partner, MUC16/CA125. This study uses CRISPR/Cas9 mutagenesis to generate knockout (KO) of MSLN in NOMO-1 and a MSLN-expressing patient-derived xenograft model to investigate its biological role in AML. We show that MSLN-KO cells proliferate slower, have reduced mitochondrial metabolism, are arrested in G1 cell cycle phase, adhere less to extracellular matrix in vitro and engraft slower in vivo. MSLN-KO cells also exhibit increased sensitivity to Ara-C and reduced extracellular matrix-mediated chemoprotection. Using an unbiased approach, we identify Src-family kinase member LYN, and guanine nucleotide-binding protein G(i) alpha subunit proteins, GNAI1, GNAI2, and GNAI3 as novel binding partners of MSLN in AML and show that pharmacological or genetic inhibition of LYN signaling restores NOMO-1 cell sensitivity to Ara-C. Together, these findings demonstrate that MSLN functions as an oncogenic driver in AML and reveal a previously unrecognized MSLN-LYN signaling axis, the therapeutic targeting of which may enhance responses to chemotherapy.