New mechanisms underlying oncogenesis in Dbl family Rho guanine nucleotide exchange factors .

Transmembrane signaling is a critical process by which changes in the extracellular environment are relayed to intracellular systems that induce changes in homeostasis. One common intracellular system involves guanine nucleotide exchange factors (GEFs), which catalyzes the exchange of GTP for GDP bound to inactive guanine nucleotide binding proteins (G proteins). The resulting active G proteins then interact with downstream targets that control cell proliferation, growth, shape, migration, adhesion, and transcription. Dysregulation of any of these processes is a hallmark of cancer. The Dbl family of GEFs activate Rho family G proteins, which in turn alter the actin cytoskeleton and promote gene transcription. Although they have a common catalytic mechanism exercised by their conserved Dbl homology (DH) domains, Dbl GEFs are regulated in very diverse ways. Often, this regulation involves the release of autoinhibition imposed by accessory domains. Amongst these domains, the pleckstrin homology (PH) domain is the most conserved and is almost always found immediately C-terminal to the DH domain. The domain been associated with both positive and negative regulation. Recently, some atomic structures of Dbl GEFs have been determined which reemphasize the complex and central role that the PH domain can play in orchestrating regulation of the DH domain. Here we discuss these newer structures, put them into context by cataloging the various ways that PH domains are known to contribute to signaling across the Dbl family, and discuss how the PH might be exploited to achieve selective inhibition of this protein family by small molecule therapeutics. Significance Statement Dysregulation via overexpression or mutation of Dbl family RhoGEFs contributes disease. Targeting the Dbl homology (DH) catalytic domain by small molecule therapeutics has been challenging due to its high conservation and the lack of a discrete binding pocket. By evaluating some new autoinhibitory mechanisms in the Dbl family, we demonstrate the great diversity of roles played by the regulatory domains, in particular the PH domain, and how this holds tremendous potential for development of selective therapeutics that modulate GEF activity.