Commentary: The carboxyl‐terminal Crk SH3 domain: Regulatory strategies and new perspectives

Abstract

a b s t r a c tSince their discovery as cellular counterparts of viral oncogenes more than two decades ago, enormous progress has been made in unraveling the complex regulatory pathways of signal transduction initiated by the Crk family of proteins. New structural and biochemical studies have uncovered novel insights into both negative and positive regulation of Crk mediated by its atypical carboxylterminal SH3 domain (SH3C). Moreover, SH3C is tyrosine phosphorylated by receptor tyrosine kinases and non-receptor tyrosine kinases, thereby permitting assemblages of other SH2/PTB domain containing proteins. Such non-canonical signaling by the Crk SH3C reveals new regulatory strategies for adaptor proteins.Ó 2012 Federation of European Biochemical Societies. Published by Elsevier B.V.Named for their ability to elevate cellular tyrosine phosphorylation and transform primary chicken embryo fibroblasts (CEFs) [1], CT10 regulator of kinase (Crk) is the prototypical member of a class of Src Homology-2 (SH2) and Src Homology-3 (SH3) domain-containing proteins that lack intrinsic enzymatic activity but instead function to promote protein-protein interactions [2,3]. Over the past two decades, enormous progress in our understanding of signal transduction has emerged from studies on Crk. The canonical signaling pathway, defined by recognition of specific phosphotyrosine motifs by the SH2 domain (in the context of p-Tyr.X.X.Pro) [4] and Polyproline Type II motifs by the N-terminal SH3 domain {in the context of Pro. X. X. Pro. X. (Lys/Arg)} [5], identified Crk as a connector between Receptor Tyrosine Kinases (RTKs) and/or their substrates and GTPase effector pathways (Fig. 1). Along with efforts on Grb2 [6], these insights were instrumental in defining missing links between integrins and/or tyrosine phosphorylated growth factor receptors and downstream effector pathways that regulate growth and differentiation, and also more generally for defining elements of modular domains in signaling. In recent years, new layers of regulation for Crk have emerged, pointing to not only unusual levels of auto-inhibition mediated by its atypical carboxylterminal SH3 domain, but also unexpected features of SH3 domain signaling that activate non-canonical pathways.CrkII and CrkL each contain an atypical C-terminal SH3 domain (SH3C), defined by its inability to bind to Polyproline Type II (PPII) motifs [7,22]. In both proteins, the atypical SH3 domain retains core structural characteristics of SH3 domains, consisting of a five-stranded b-barrel which forms the standard SH3 fold. However, the aromatic amino acids -F141, W169, Y186 which line the canonical PPII binding pocket on the Crk SH3N and are conserved in conventional SH3 domains, are replaced by polar residues -Q244, Q274 and H290 on the SH3C surface (Fig. 2), thereby rationalizing the drastically reduced affinity of this domain for proline rich sequences.The carboxyl-terminal region of Crk is considered inhibitory, since it contains elements that constrain binding to the N-terminal SH2 and...

Crk and Abi1: Binary Molecular Switches That Regulate Abl Tyrosine Kinase and Signaling to the Cytoskeleton

“…Phosphotyrosine residues implicated in Abl kinase regulation: pY221 and pY251. 61,93 Phosphotyrosine pY207 that binds to the Crk SH2 domain to form an autoinhibited structure in CrkL 59 (not shown). Abl kinase regulatory domain binding regions are indicated in brackets.…”

The F-Actin Binding Protein Cortactin Regulates the Dynamics of the Exocytotic Fusion Pore through its SH3 Domain

“…For instance, cortactin phosphorylation by pERK1/2 enhances its association to N-WASP (Martinez-Quiles et al, 2004), whereas its phosphorylation by Src kinase appears to favor its interaction with dynamin-2 (Cao et al, 2010). Another explanation is that the cortactin SH3 domain could display non-conventional interactions, as observed with other SH3 domains (Jia et al, 2005; Sriram and Birge, 2012). For instance, cortactin interacts with the myosin light chain kinase (MLCK), in a cortactin SH3 domain dependent manner (Dudek et al, 2002, 2004); however, the substitution of proline residues by alanines in the full length MLCK does not alter its association to cortactin (Belvitch et al, 2014).…”

“…Then, MLCK could be a cortactin partner that regulates the amount of exocytosis. Nevertheless, it is important to keep in mind that SH3 domains can exhibit high versatility and promiscuity (Agrawal and Kishan, 2002; Li, 2005), and that the association to PRD-containing partners is regulated by post-transcriptional modifications (Lua and Low, 2005; Sriram and Birge, 2012). These properties allow them to be involved in different types of cellular processes.…”

Rap-Interacting Proteins are Key Players in the Rap Symphony Orchestra

“…Multiple PKC isoforms phosphorylate CalDAG-GEF3 adjacent to its CDC25-HD, which promotes catalytic activity without affecting membrane recruitment [25,[157][158][159]. The tyrosine kinases Src can phosphorylate C3G with the help of the adapter protein Crk, which is phosphorylated by receptor tyrosine kinases (RTKs) and located to cell membrance [69,[160][161][162] and another tyrosine kinase c-Abl can also phosphorylate C3G with the help of F-actin, and furtherly induce cell death [163]. In addition to targeting C3G to its substrate Rap, membrane recruitment by Crk might indirectly control the nucleotide exchange activity of C3G by allowing its phosphorylation [164].…”