Notch signaling in acute lymphoblastic leukemia: any role for stromal microenvironment?

Notch signaling pathway regulates many different events of embryonic and adult development; among them, Notch plays an essential role in the onset of hematopoietic stem cells and influences multiple maturation steps of developing lymphoid and myeloid cells. Deregulation of Notch signaling determines several human disorders, including cancer. In the last decade it became evident that Notch signaling plays pivotal roles in the onset and development of T- and B-cell acute lymphoblastic leukemia by regulating the intracellular molecular pathways involved in leukemia cell survival and proliferation. On the other hand, bone marrow stromal cells are equally necessary for leukemia cell survival by preventing blast cell apoptosis and favoring their reciprocal interactions and cross-talk with bone marrow microenvironment. Quite surprisingly, the link between Notch signaling pathway and bone marrow stromal cells in acute lymphoblastic leukemia has been pointed out only recently. In fact, bone marrow stromal cells express Notch receptors and ligands, through which they can interact with and influence normal and leukemia T- and B-cell survival. Here, the data concerning the development of T- and B-cell acute lymphoblastic leukemia has been critically reviewed in light of the most recent findings on Notch signaling in stromal microenvironment.