Point mutations within a dimer interface homology domain of c-Mpl induce constitutive receptor activity and tumorigenicity.
c-Mpl, a receptor for thrombopoietin (TPO), belongs to the haemopoietin/cytokine receptor superfamily, a group of cell surface molecules characterized by conserved sequence motifs within their ligand binding domains. A recurring mechanism for the activation of haemopoietin receptors is the formation of functional complexes by receptor subunit oligomerization. Within the growth hormone receptor, a cluster of extracellular amino acids forms a dimer interface domain that stabilizes ligand-induced homodimers. This domain appears to be functionally conserved in the erythropoietin (EPO) receptor because substitution of cysteines for residues in the analogous region causes EPO-independent receptor activation via disulfide-linked homodimerization. This report identifies an homologous domain within the c-Mpl receptor. The substitution of cysteine residues for specific amino acids in the dimer interface homology regions of c-Mpl induced constitutive receptor activity. Factor-dependent FDC-P1 and Ba/F3 cells expressing the active receptor mutants no longer required exogenous factors and proliferated autonomously. The results imply that the normal process of TPO-stimulated Mpl activation occurs through receptor homodimerization and is mediated by a conserved haemopoietin receptor dimer interface domain. Moreover, cells expressing activated mutant Mpl receptors were tumorigenic in transplanted mice. Thus, like v-mpl, its viral counterpart, mutated forms of the cellular mpl gene also have oncogenic potential.
Walter and Eliza Hall Institute of Medical Research, Royal Melbourne Hospital Victoria, Australia.
W S
WS
Alexander
D
D
Metcalf
A R
AR
Dunn
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002452:Cell Count; D002460:Cell Line; D002999:Clone Cells; D003545:Cysteine / Q000378:metabolism; D006801:Humans; D051379:Mice; D008807:Mice, Inbred BALB C; D008811:Mice, Inbred DBA; D008969:Molecular Sequence Data; D009363:Neoplasm Proteins; D009374:Neoplasms, Experimental / Q000209:etiology*; D009838:Oligodeoxyribonucleotides; D017354:Point Mutation; D011518:Proto-Oncogene Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D018121:Receptors, Cytokine / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D053628:Receptors, Thrombopoietin; D013926:Thrombopoietin / Q000378:metabolism
D009363:Neoplasm Proteins; D009838:Oligodeoxyribonucleotides; D011518:Proto-Oncogene Proteins; D018121:Receptors, Cytokine; D053628:Receptors, Thrombopoietin; C082218:MPL protein, human; D013926:Thrombopoietin; D003545:Cysteine