Cluster of differentiation (CD) molecules are markers on the cell surface, as recognized by specific sets of antibodies, used to identify the cell type, stage of differentiation and activity of a cell. CD135 is an important cell surface marker used to identify certain types of hematopoietic (blood) progenitors in the bone marrow. Specifically, multipotent progenitors (MPP) and common lymphoid progenitors (CLP) expresse high surface levels of CD135. This marker is therefore used to differentiate hematopoietic stem cells (HSC), which are CD135 negative, from MPPs, which are CD135 positive.
CD135 is the receptor for the cytokine Flt3 ligand (Flt3L).
CD135 is a receptor tyrosine kinase type III. When this receptor binds to Flt3L it forms a dimer with itself (homodimer) which activates signaling through second messengers. Signaling through CD135 plays a role in cell survival, proliferation, and differentiation. CD135 is important for lymphocyte (B cell and T cell) development, but not for the development of other blood cells (myeloid development).
Role in cancer
CD135 is a proto-oncogene, meaning that mutations of this protein can lead to cancer. Mutations of the Flt3 receptor can lead to the development of leukemia, a cancer of bone marrow hematopoietic progenitors. Internal tandem duplications of Flt3 (Flt3-ITD) are the most common mutations associated with acute myelogenous leukemia (AML) and are a poor prognostic indicator.
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