Macrophages facilitate interclonal cooperation-induced tumor heterogeneity and malignancy by activating the innate immune signaling

Abstract

Tumor heterogeneity is a common hallmark of cancer and is considered a major cause of treatment failure and relapse, yet it remains poorly understood how various types of cells communicate within the tumor microenvironment (TME) to regulate tumor progression in vivo. Here we establish a tumor heterogeneity model in Drosophila eye epithelium by mutating the tricellular junction protein M6 in cells surrounding RasV12benign tumors and dissect the in vivo mechanisms underlying interclonal cooperation-induced malignancy by utilizing sophisticated genetic techniques in conjunction with single-cell RNA sequencing (scRNA-seq). Our findings reveal that loss of M6 facilitates the malignant transformation of neighboring RasV12 tumors by activating the Toll signaling, the innate immune response pathway. Notably, inhibiting Toll signaling impedes tumor progression, whereas its activation synergistically promotes RasV12 tumor malignancy by inactivating the Hippo pathway. Mechanistically, RasV12 tumors surrounded by M6 mutant clones lead to increased recruitment of hemocytes, which are the equivalent of macrophages in Drosophila, in a JNK pathway-dependent manner. Consequently, these tumor-associated macrophages secrete the Spatzle (Spz) ligand, which subsequently activates the Toll receptor within the RasV12 tumors, thereby triggering tumorigenesis. In summary, our study elucidates the complex in vivo interactions between genetically distinct oncogenic cells and between tumors and macrophages, shedding light on how macrophages exploit the innate immune signaling within tumors to regulate tumor heterogeneity and promote tumor progression. Significance statementIntratumoral heterogeneity profoundly affects cancer development and treatment in human tumors. The intricate nature of tumor cells and the presence of diverse cell types pose challenges to uncovering in vivo mechanisms responsible for heterogeneity. Our Drosophila tumor heterogeneity model reveals that fruit fly macrophages promotes both tumor heterogeneity and malignancy. Following recruitment by tumor cells, these macrophages secrete the ligand Spz to activate the Toll signaling pathway within tumor cells, which subsequently inactivates the Hippo pathway to drive tumorigenesis. Our study highlights the crucial role of hemocytes as intermediaries in coordinating tumor heterogeneity and facilitating intercellular communication between different cells within the TME.