Regulation of the Dbl Proto-oncogene by Heat Shock Cognate Protein 70 (Hsc70)

• Published in: The Journal of biological chemistry Vol. 280; no. 22; pp. 21638 - 21644
• Main Authors: Kauppinen, Krista P., Duan, Faping, Wels, Jared I., Manor, Danny
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 03.06.2005; American Society for Biochemistry and Molecular Biology
• Subjects: Animals; Brain - metabolism; Catalytic Domain; COS Cells; Genes, Dominant; Glutathione Transferase - metabolism; GTP Phosphohydrolases - metabolism; Guanine Nucleotide Exchange Factors - metabolism; Hot Temperature; HSC70 Heat-Shock Proteins; HSP70 Heat-Shock Proteins - metabolism; Immunoprecipitation; Mice; Models, Biological; Molecular Chaperones - metabolism; NIH 3T3 Cells; Nucleosides - metabolism; Protein Binding; Protein Structure, Tertiary; Retroviridae Proteins, Oncogenic - biosynthesis; Retroviridae Proteins, Oncogenic - metabolism; Spectrin - chemistry; Transfection
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M413984200

The dbl oncogene product is the defining member of a family of onco-proteins known as Dbl guanine nucleotide exchange factors (GEFs) that facilitate the activation of the small GTP-binding proteins Cdc42, Rac, and Rho. Oncogenic activation of proto-Dbl occurs through loss of the amino-terminal 497 residues, rendering the protein constitutively active. Because both onco- and proto-Dbl contain the structural elements required for GEF activity (i.e. the Dbl homology (DH) and pleckstrin homology (PH) domains), it is thought that the amino terminus of proto-Dbl somehow inhibits the biochemical activity of the protein. To better understand the molecular basis of this regulation, we set forth to identify cellular proteins that preferentially bind the proto-oncogenic form of Dbl. We identified the molecular chaperone heat shock cognate protein (Hsc70) as a binding partner that preferentially interacts with the proto-oncogenic form of Dbl. Dbl is complexed with Hsc70 in transfected cells, as well as in native mouse brain extracts. The interaction between Hsc70 and proto-Dbl is mediated by at least two regions in Dbl, the aminoterminal spectrin homology domain (residues 224–417) and the pleckstrin homology domain (residues 711–808). Overexpression of a dominant negative Hsc70 mutant leads to activation of proto-Dbl GEF activity, indicating that the chaperone negatively regulates proto-Dbl function in vivo. We propose that Hsc70 attenuates Dbl activity by maintaining an inactive conformation in which the amino terminus is “folded over” the catalytic DH-PH domain.