Does myb lie downstream of pim-1?
If one combined our recent data showing that myb and myc can cooperate, with the results linking pim-1 signaling to c-Myb activation (Leverson et al., 1998), it seems possible that c-myb might lie downstream of pim-1 in tumorigenesis. At this point, it is impossible to predict the precise nature of the relationship between the two genes. Pim-1 is a good candidate as an important activator of c-Myb in both normal and tumorigenic hematopoietic cells. Like c-myb, pim-1 is widely expressed during hematopoiesis (Amson et al., 1989) and is an immediate early gene, induced by JAK activation in response to a wide range of cytokines (Damen et al., 1995; Dautry et al., 1988; Lilly et al., 1992; Miura et al., 1994; Mui et al., 1996; Quelle et al., 1996; Sakai and Kraft, 1997; Sato et al., 1993). Mutations of any components in the multiple pathways leading to JAK activation would all cause increases in pim-1 expression, which in turn would super-activate c-Myb protein. However, it would be unreali
