Expression and Function of the c-myb Oncogene During Hematopoietic Differentiation

Abstract

The c-myb proto-oncogene encodes a 72,000 Dalton phosphoprotein which binds DNA (Klempnauer et al, 1986). Unlike the c-myc protein, which is associated with the nuclear matrix, the c-myb protein is localized in chromatin. Although c-myb mRNA is expressed predominantly in normal and tumor cells of hematopoietic origin (Gonda et al, 1982), there is increasing evidence that it is expressed at some level in many — perhaps most — nonhematopoie-tic tissues (e.g. Torelli et al, 1987). However, for all hematopoietic lineages examined, c-myb mRNA is at higher levels in immature than in mature cells. The function of c-myb is unknown, although it may be involved in cell proliferation since: 1) truncated forms of c-myb mRNA expressed by a retrovirus or after insertional mutagenesis are associated with enhanced cell proliferation and tumorigenesis (Ness et al, 1987; Sheng-Ong et al, 1986), and 2) c-myb mRNA expression is up-regulated in late G1 or early S phase when normal, resting T lymphocytes are stimulated by mitogens (in contrast up-regulation of c-myc mRNA occurs as an early event when T cells progress from G0 to G1) (Reed et al, 1986).