CDNA CLONING OF A HUMAN MESSENGER-RNA PREFERENTIALLY EXPRESSED IN HEMATOPOIETIC-CELLS AND WITH HOMOLOGY TO A GDP-DISSOCIATION INHIBITOR FOR THE RHO-GTP-BINDING PROTEINS

We have identified the mRNA for a human gene, denoted D4, which is expressed at very high levels in hematopoietic cell lines and in normal cells of lymphoid and myeloid origin. The 1.5-kb transcript is absent or detectable only at low levels in nonhematopoietic tissues. D4 encodes a 201-amino acid protein with homology to rhoGDI, an inhibitor of GDP dissociation for the ras-homologous protein rho. D4 might function also as a regulator of guanine nucleotide exchange for small GTP-binding proteins. A homologous transcript of similar size is also preferentially expressed in murine hematopoietic tissues. When totipotent murine embryonic stem cells develop in vitro into hematopoietic cells, the gene is activated with the onset of hematopoiesis. When hematopoietic cell lines are induced to differentiate, the expression of D4 is modulated. Thus, D4 appears to be a developmentally regulated gene. Its preferential expression in hematopoietic cells indicates that D4 likely plays some significant role in the growth and differentiation processes of hematopoietic cells. This significance is underscored by increasing evidence for the involvement of regulators of G proteins in clinical diseases.