Numb and NumbL inhibit melanoma tumor growth by influencing the immune microenvironment.

Objective: Many investigation have sought to identify therapeutic targets and treatment strategies for skin cutaneous melanoma (SKCM). Numb, an endocytic adaptor protein, is known to act as a tumor suppressor in various human cancers. However, the roles of Numb and its homolog NumbL in immune microenvironment, and their effect on melanoma remain largely unexplored.

Methods: We analyzed the expression levels of Numb and NumbL, as well as immune signatures of SKCM patients by UCSCXenaShiny v1 database. We also constructed animal model using Numb and NumbL conditional knockout (cKO) mice. Distribution analysis of immune cells in tumors was performed by flow cytometry and pathology staining.

Results: Numb and NumbL were found to be consistently expressed at low levels in SKCM patients. In addition, alterations in tumor immune microenvironment were identified. The CD8⁺ T, CD19⁺ B, and NK1.1⁺ CD49⁺ cells were decreased in tumors of Numb and NumbL cKO mice, confirming previous bioinformatics analysis of immune signatures. Additionally, we observed CD68⁺ macrophages to be increased as judged by tumor pathology staining.

Conclusion: Numb and NumbL were found to inhibit melanoma cell growth by modulating immune cell activity. These results suggested that Numb and NumbL may be potential therapeutic targets for SKCM patient immunotherapy.