ACK Family Tyrosine Kinase Activity Is a Component of Dcdc42 Signaling during Dorsal Closure inDrosophila melanogaster

Abstract

We have characterized Drosophila melanogaster ACK (DACK), one of two members of the ACK family of nonreceptor tyrosine kinases in Drosophila. The ACKs are likely effectors for the small GTPase Cdc42, but signaling by these proteins remains poorly defined. ACK family tyrosine kinase activity functions downstream of Drosophila Cdc42 during dorsal closure of the embryo, as overexpression of DACK can rescue the dorsal closure defects caused by dominant-negative Dcdc42. Similar to known participants in dorsal closure, DACK is enriched in the leading edge cells of the advancing epidermis, but it does not signal through activation of the Jun amino-terminal kinase cascade operating in these cells. Transcription of DACK is responsive to changes in Dcdc42 signaling specifically at the leading edge and in the amnioserosa, two tissues involved in dorsal closure. Unlike other members of the ACK family, DACK does not contain a conserved Cdc42-binding motif, and transcriptional regulation may be one route by which Dcdc42 can affect DACK function. Expression of wild-type and kinase-dead DACK transgenes in embryos, and in the developing wing and eye, reveals that ACK family tyrosine kinase activity is involved in a range of developmental events similar to that of Dcdc42.Cdc42 is a member of the Rho family of Ras-related small GTPases originally identified through a mutation in Saccharomyces cerevisiae that affects formation of the bud site. The Cdc42 protein is required for the assembly of a ring of F-actin filaments in the neck of the bud (1). Subsequent work in mammalian fibroblasts demonstrated that Cdc42 drives the formation of F-actin-rich filopodia (40, 50), and numerous later studies have confirmed that Cdc42 regulates the actin cytoskeleton and, as a consequence, cell shape (65). Cdc42 participates in a diverse range of cellular processes including membrane trafficking, transcription, cell growth, and Ras-mediated transformation (65). The various effects of Cdc42 are presumed to be mediated through the interaction of the activated, GTP-bound form of the protein with downstream effectors.Given the important events controlled by Cdc42, intensive efforts have been made to elucidate the signaling pathways activated by this GTPase. This work has largely focused on identifying proteins that interact with GTP-bound Cdc42. Two such proteins are ACK-1 and ACK-2, closely related mammalian nonreceptor tyrosine kinases that bind GTP-bound Cdc42 and not its inactive GDP-bound form (44, 67). ACK-1 and ACK-2 cannot bind either version of the closely related Rho family GTPases Rac1 and RhoA, and these kinases represent likely effectors in Cdc42-specific signaling.To date, much of what is known about Rho family signaling has come from biochemical and cell biological work, but it is now being studied with genetic approaches in a number of model organisms, including Drosophila melanogaster. The Drosophila homolog of Cdc42, Dcdc42, has been studied by using dominantly acting mutant transgenes and loss-of-function mutations. This work has in...

Leading edge‐secreted Dpp cooperates with ACK‐dependent signaling from the amnioserosa to regulate myosin levels during dorsal closure

“…The activation of Cdc42 throughout the embryo leads to increased expression of DACK specifically in the amnioserosa, and we have shown here that overexpressing DACK in this tissue can suppress tkv dorsal closure defects (Sem et al, 2002). Our results indicate a tissuespecific regulation of DACK levels by Cdc42 that may be part of a sophisticated signaling network enabling the coordinated morphogenesis of tissues in the embryo.…”

Activated Tyrosine Kinase Ack1 Promotes Prostate Tumorigenesis: Role of Ack1 in Polyubiquitination of Tumor Suppressor Wwox

“…Ack1 specifically interacts with GTP-bound Cdc42 (activated Cdc42) and inhibits both intrinsic and GTPase-activating protein-stimulated GTPase activities of Cdc42 (19). Ack1 activity has been implicated in cell spreading (20), vesicle trafficking (21), axonal guidance (22), and dorsal closure in Drosophila melanogaster (23). However, the physiologic role of Ack1 and its molecular mechanism of action are not fully understood, nor has Ack1 been linked to any specific pathologic condition (24).…”

Kos1, a nonreceptor tyrosine kinase that suppresses Ras signaling

“…For example, the presence of an immunoreceptor tyrosine-based activation motif (ITAM) in Kos1 suggests that 'crosstalk' with other NRPTKs or adaptor molecules, such as Src, Syk and STAMs, may occur (Isakov et al, 1995;Pandey et al, 2000;Sada et al, 2001). However, unlike Kos1, both Tnk1 and the Acks contain an SH3 domain while only the Acks, with the exception of Drosophila melanogaster Ack (D-Ack; Sem et al, 2002), possess a CRIB motif that binds the GTP-bound form of Cdc42 (Hoehn et al, 1996;Manser et al, 1993). Since both Ack1 (Teo et al, 2001) and Ack 2 (Lin et al, 2002;) possess endocytic activity, the presence of a putative endocytic motif in Kos1 (Figure 1a) and Tnk1 (Hoehn et al, 1996) suggests that they may also play a role in endocytosis.…”