{"type":"root","children":[{"type":"paragraph","children":[{"type":"text","value":"CD117, also known as c-kit or stem cell factor receptor, is a protein in the receptor tyrosine kinase family. It acts as a receptor for stem cell factor (SCF), a cytokine that regulates hematopoiesis, melanogenesis, and gametogenesis. Binding of SCF to CD117 leads to receptor dimerization and activation of downstream signaling pathways, including the Ras/MAPK and PI3K/Akt pathways, which regulate cell survival, proliferation, and differentiation.\nCD117 is expressed on the surface of hematopoietic stem cells (HSCs) and progenitor cells, where it plays a crucial role in maintaining HSC self-renewal and differentiation into mature blood cell lineages. Mutations or dysregulation of CD117 signaling can lead to hematological disorders, such as myeloproliferative neoplasms (e.g., systemic mastocytosis) or acute myeloid leukemia (AML). CD117 is also expressed on the surface of melanocytes, where it regulates melanocyte development, proliferation, and survival. Aberrant activation of CD117 signaling can contribute to the pathogenesis of melanoma. CD117 is used by pathologists for identifying gastrointestinal stromal tumors (GISTs), which are mesenchymal neoplasms arising from the interstitial cells of Cajal in the gastrointestinal tract. The majority of GISTs harbor activating mutations in the c-kit gene (KIT mutations), resulting in constitutive activation of CD117 signaling. CD117 expression has also been observed in various other cancers and conditions, including germ cell tumors (e.g., testicular seminomas), small cell lung cancer, and certain types of sarcomas."}]}]}