Molecular Cloning of Murine STAP-1, the Stem-Cell-Specific Adaptor Protein Containing PH and SH2 Domains

• DOI: 10.1006/bbrc.2000.2223
• Publication Date: 2002-09-16T14:49:19Z
• Authors: Masaaki Masuhara; Kenji Nagao; Mitsuo Nishikawa; Mika Sasaki; Akihiko Yoshimura; Masatake Osawa
• Keywords: 0303 health sciences; Base Sequence; Sequence Homology, Amino Acid; Molecular Sequence Data; Gene Expression; Membrane Proteins; Antigens, CD34; Hematopoietic Stem Cells; Protein Structure, Tertiary; src Homology Domains; Mice; Proto-Oncogene Proteins c-kit; 03 medical and health sciences; Animals; Antigens, Ly; Amino Acid Sequence; RNA, Messenger; Cloning, Molecular; Phosphorylation; DNA Primers

To identify the novel substrate of c-kit which is important for hematopoietic stem cell self-renewal or differentiation, CD34-low/negative, Sca-1-positive, c-kit-positive, and lineage marker-negative (CD34(low/-)Sca-1(+)c-kit(+)Lin(-)) cells were sorted by a fluorescence-activated cell sorter from mouse bone marrow cells and a yeast two-hybrid cDNA library was constructed. By screening with c-kit as bait, we cloned a novel cDNA, designed STAP-1, encoding an adaptor protein with a Pleckstrin homology domain, the Src homology 2 (SH2) domain, and a number of tyrosine phosphorylation sites. RT-PCR analysis revealed that STAP-1 expression is restricted in the bone marrow cell fraction expressing c-kit. The highest expression was observed in the CD34(low/-)Sca-1(+)c-kit(+)Lin(-) stem cell-enriched fraction. The murine myeloid cell line, M1, expressed a high level of STAP-1. However, the expression was strongly repressed in response to leukemia inhibitory factor (LIF) which induced monocytic differentiation of M1 cells, suggesting that STAP-1 is associated with the undifferentiated cell type. A two-hybrid assay indicated that STAP-1 bound not only to c-kit but also to c-fms but not to JAK2 or Pyk2. In 293 cells, STAP-1 was tyrosine-phosphorylated by activated c-kit. An in vitro binding assay suggested that the STAP-1 SH2 domain interacted with several tyrosine-phosphorylated proteins including c-kit and STAT5. These suggest that STAP-1 functions as an adaptor molecule downstream of c-kit in hematopoietic stem cells.