SAMSN (HACS1) is a member of a novel gene family of putative adaptors and scaffold proteins containing SH3 and SAM (sterile alpha motif) domains. It encodes a 441 amino acid protein that is differentially expressed in hematopoietic cells and malignancies including myeloid leukemia, lymphoma, and myeloma. SAMSN has restricted expression in human tissues. It has been shown to be up-regulated by B cell activation signals and is a participant in B cell activation and differentiation. SAMSN is an immunoinhibitory adaptor that might be a useful target for immune suppression therapy.Synonyms: HACS1, Hematopoietic adaptor containing SH3 and SAM domains 1, SAM domain SH3 domain and nuclear localization signals protein 1, SAM domain-containing protein SAMSN-1, SAMSN-1, SH3-SAM adaptor protein