Disease tropism of c-erbB: effects of carboxyl-terminal tyrosine and internal mutations on tissue-specific transformation.

Abstract

Avian leukosis virus induces erythroleukemia in chickens by proviral insertional mutation of the protooncogene c-erbB. The product of the insertionally activated c-erbB locus lacks the extracellular ligand-binding domain and is strictly leukemogenic. It has previously been demonstrated that the disease spectrum associated with aberrant c-erbB expression can be expanded by structural perturbation of the cytoplasmic domain of this protein. In this report, we use mutagenesis and retroviral vectors to identify specific mutations in the carboxyl-terminal domain of the insertionally activated c-erbB product that are sufficient to activate the sarcomagenic potential of this protein. Interestingly, a point mutation in the kinase domain appears to be sufficient for sarcomagenic activation. However, removal of the terminal tyrosine residue of the c-erbB product, implicated in modulating kinase activity, does not lead to a fully transforming phenotype. These studies suggest that there are multiple ways to activate the fibroblast-transforming potential of the insertionally activated c-erbB product. The conformation of this protein may play a more significant role in oncogenic activation than the phosphorylation status of the putative carboxylterminal autophosphorylation site.Avian leukosis virus can induce erythroleukemia by proviral insertional mutagenesis of the protooncogene c-erbB (1,2). The avian c-erbB gene encodes a growth factor receptor that is structurally homologous to the human epidermal growth factor (EGF) receptor (3-5). Proviral integration results in separation of the ligand-binding domain of this receptor from its transmembrane and cytoplasmic domains (6). Transcripts expressed from the proviral insertionally activated c-erbB locus (IA c-erbB) code for an amino-terminal-truncated cerbB gene product that has been postulated to have constitutive tyrosine kinase activity.One fascinating feature ofthe IA c-erbB product is its strict tissue specificity of transformation. When placed in a retroviral vector or carried by naturally occurring transducing viruses, the IA c-erbB gene induces only erythroleukemia (7-10). On the other hand, a number of v-erbB genes isolated from acute leukemia viruses have the ability to generate leukemias, sarcomas, and hemangiomas (2,(11)(12)(13)(14). A comparison of the coding sequences of these v-erbB genes [found in the R (ES-4) and H strains ofavian erythroblastosis (AEV)]with the IA c-erbB coding sequence reveals that the former contain multiple point mutations as well as truncations in their carboxyl-terminal sequences. It is not clear which of these mutations is responsible for the sarcomagenic activities of these v-erbB gene products (4, 12, 15).The carboxyl-terminal domain (arbitrarily defined as the region 3' of the tyrosine kinase domain) of the human EGF receptor contains three tyrosine residues identified as sites of autophosphorylation: the tyrosine residue most proximal to the carboxyl terminus, Tyr-1173, is the major autophosphorylation site (16). Evidence that...

Protein tyrosine kinase activities of the epidermal growth factor receptor and ErbB proteins: correlation of oncogenic activation with altered kinetics.

“…ErbB has an activating point mutation in the region of its kinase domain as well as a C-termir (21,24). Our results indicate that each of the E differed from the chEGFR in the kinetics of kinase activities.…”

“…Many also contain point mutations, truncations, or internal deletions in the cytoplasmic domain of the receptor. These mutations determine differences in the potential to induce erythroblastosis, angiosarcoma, hemangioma, or fibrosarcoma (7,21,22,24,27).The tyrosine kinase activity of the EGFR is required for its mitogenic activity (28). Analysis of the transformation potential of a series of linker insertion mutations in ErbB suggests that kinase activity is required for transformation (20).…”

“…Many also contain point mutations, truncations, or internal deletions in the cytoplasmic domain of the receptor. These mutations determine differences in the potential to induce erythroblastosis, angiosarcoma, hemangioma, or fibrosarcoma (7,21,22,24,27).…”

Analysis of the role of the Shc and Grb2 proteins in signal transduction by the v-ErbB protein.

“…9, the addition of TGF-ox to the TGF-aR (c-ErbB)-expressing CEF results in the appearance of the slower-migrating, activated form of MAP kinase, designated MAPK*, and a loss of most of the form of MAP 14). These changes can be attributed to additional mutations in the intracellular domain of the protein, including point mutations in the kinase domain and deletions in the region carboxy terminal to the kinase domain (18,39,46). From these analyses, a picture has emerged in which the loss of the extracellular domain leads to a constitutive tyrosine kinase activity that is essential for transformation and in which the carboxy-terminal domain plays regulatory roles in determining which cell types the virus can transform.…”

Tandem duplication of the epidermal growth factor receptor tyrosine kinase and calcium internalization domains in A-172 glioma cells

“…In contrast, certain mutations of erbB-1 occurring in the C-terminal region produce sarcomas (Yamamoto et al, 1983). Such mutations include C-terminal truncation, point mutations and internal deletions within the tyrosine kinase domain (Pelley et al, 1988). Therefore, the erbB-1 gene can become oncogenic by way of a number of di erent structural alterations.…”