Abstract A061: Grb7 is dispensible for normal development and ERBB2-driven mammary tumorigenesis, but maternal Grb7 deletion causes lactational insufficiency

Abstract Growth factor receptor-bound 7 (Grb7) is an adaptor protein implicated in signal transduction downstream of multiple receptor tyrosine kinases, including ERBB, FGFR and PDGFR pathways. Experimental studies have implicated Grb7 in regulating cell proliferation, survival, migration, and invasion through its large repertoire of protein-protein interactions. Here, we describe the generation and characterization of a Grb7 knockout (KO) mouse. These mice are viable and fertile. A lacZ knock-in reporter was used to visualize Grb7 promoter activity patterns in adult tissues, indicating widespread Grb7 expression in glandular epithelium, the central nervous system and other tissues. The sole defect observed in these animals was a failure of Grb7 KO females to successfully raise pups to weaning age, a phenotype that was independent of both paternal and pup genotypes. These data suggest a regulatory role for Grb7 in mammary lactational physiology. Grb7 is genomically adjacent to ERBB2 and commonly co-amplified with ERBB2 in human breast cancer. This adaptor protein physically interacts with ERBB2 and has been implicated in oncogenic signal propagation to intracellular pathways. We intercrossed Grb7 KO and MMTV-Neu mice to determine whether Grb7 is required for ERBB2-driven tumorigenesis. Surprisingly, there was no difference in time to tumor detection between cohorts, indicating that Grb7 is not obligately required for ERBB2-driven tumorigenesis. In conclusion, despite a considerable body of literature suggesting key roles for Grb7 in signal transduction pathways involved in both normal and malignant processes, our analysis of Grb7 KO mice demonstrates that Grb7 is largely dispensable for both development and ERBB2-driven tumorigenesis. These data raise the possibility that other Grb family members, Grb10 and Grb14, might compensate for Grb7 loss. Accordingly, a comprehensive assessment of all Grb family members may be needed to fully clarify their physiological roles. Citation Format: Kristopher A. Lofgren, Peter Feiszt, Paraic A. Kenny. Grb7 is dispensible for normal development and ERBB2-driven mammary tumorigenesis, but maternal Grb7 deletion causes lactational insufficiency [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Breast Cancer Research; 2023 Oct 19-22; San Diego, California. Philadelphia (PA): AACR; Cancer Res 2024;84(3 Suppl_1):Abstract nr A061.