Dock4

Short description: Protein-coding gene in the species Homo sapiens

Generic protein structure example

Dock4, (Dedicator of cytokinesis 4) also known as DOCK4, is a large (~190 kDa) protein involved in intracellular signalling networks.[1] It is a member of the DOCK-B subfamily of the DOCK family of guanine nucleotide exchange factors (GEFs) which function as activators of small G proteins. Dock4 activates the small G proteins Rac and Rap1.

## Contents

* 1 Discovery
* 2 Structure and function
* 3 Regulation of Dock4 activity
* 4 Signalling downstream of Dock4
* 5 Dock4 in cancer
* 6 References
* 7 Further reading

## Discovery

Dock4 was discovered as a gene product which was disrupted during tumour progression in a murine cancer model-derived osteosarcoma cell line.[2] Subsequent Northern blot analysis revealed high levels of Dock4 expression in skeletal muscle, prostate and ovary as well as lower levels in the heart, placenta and colon. A separate study has reported expression of a Dock4 splice variant (Dock4-Ex49) in the brain, inner ear and eye.[3]

## Structure and function

Dock4 is part of a large class of proteins (GEFs) which contribute to cellular signalling events by activating small G proteins. In their resting state G proteins are bound to Guanosine diphosphate (GDP) and their activation requires the dissociation of GDP and binding of guanosine triphosphate (GTP). GEFs activate G proteins by promoting this nucleotide exchange.

The domain arrangement of Dock4 is largely equivalent to that of Dock180 (the archetypal member of the DOCK family) and other DOCK-A/B family members (35% sequence identity with Dock180, 39% with Dock2 and 54% with Dock3[2]). Dock4, however, contains a unique set of motifs at its proline-rich C-terminus which include a Src-binding site that is shared with CED-5, the C. elegans ortholog of mammalian DOCK proteins.[2] Dock4 also contains a DHR2 domain (also known as Docker2 or CZH2) which is conserved among DOCK family proteins and mediates GEF-dependent functions, and a DHR1 domain (CZH1/Docker1) which has been shown to bind PtdIns(3,4,5)P3,[4] an important step in recruitment to the plasma membrane.

## Regulation of Dock4 activity

DOCK family proteins are inefficient at promoting nucleotide exchange on their own since they appear to adopt an autoinhibitory conformation in their resting state. The adaptor protein ELMO has been shown to bind DOCK proteins and induce a conformational change which relieves the inhibition and allows G proteins access to the DHR2 domain.[5] Binding to ELMO requires the atypical PH domain of ELMO and also involves an interaction between the N-terminal SH3 domain of DOCK and a proline-rich motif at the ELMO C-terminus.[6] ELMO also binds the activated form of the small G protein RhoG and this has been shown to promote DOCK-dependent signalling by helping recruit the ELMO-DOCK complex to areas of high substrate availability (usually the plasma membrane).[7] The C-terminus of DOCK proteins interacts with another adaptor protein, Crk.[8][9] Dock4 undergoes RhoG/ELMO-dependent recruitment to the plasma membrane and promotes migration in fibroblasts.[10] In rat hippocampal neurones Dock4 forms a trimeric complex with ELMO2 and CrkII which is required for the normal development of dendrites.[11] More recently, a role has been described for Dock4 as part of the Wnt signalling pathway which regulates cell proliferation and migration. In this system Dock4 was reported to undergo phosphorylation by Glycogen synthase kinase 3 (GSK-3) which stimulated an increase in Dock4 GEF activity.[12]

## Signalling downstream of Dock4

DOCK family proteins contribute to cell signalling by activating G proteins of the Rho family, such as Rac and Cdc42.[13] Dock4 has also been shown to activate Rap1,[2] a feature not reported in any of the other DOCK family proteins to date. Dock4 dependent Rac activation regulates reorganisation of the cytoskeleton and leads to the formation of membrane protrusions (e.g. lamellipodia) which are a crucial step in neuronal development and cell migration.[10][11] The effect of Dock4 on the Wnt pathway appears to be mediated through Rac activation as well as through GEF-independent associations with components of the "β-catenin degradation complex".[12]

## Dock4 in cancer

Mutations in Dock4 have been described in a number of cancers.[2][14][15] The exact mechanism and extent to which it regulates cancer-associated signalling pathways is poorly understood thus far although a mutation in Dock4 which affects its GEF specificity has been reported to promote detachment and invasion of cancer cells.[2]

## References

1. ↑ "Entrez Gene: DOCK4 dedicator of cytokinesis 4". https://www.ncbi.nlm.nih.gov/sites/entrez?Db=gene&Cmd=ShowDetailView&TermToSearch=9732.
2. ↑ 2.0 2.1 2.2 2.3 2.4 2.5 "DOCK4, a GTPase activator, is disrupted during tumorigenesis". Cell 112 (5): 673–684. March 2003. doi:10.1016/S0092-8674(03)00155-7. PMID 12628187.
3. ↑ "An isoform of GTPase regulator DOCK4 localizes to the stereocilia in the inner ear and binds to harmonin (USH1C)". Journal of Molecular Biology 357 (3): 755–764. March 2006. doi:10.1016/j.jmb.2006.01.017. PMID 16464467.
4. ↑ "Identification of DOCK4 and its splicing variant as PIP3 binding proteins". IUBMB Life 60 (7): 467–472. July 2008. doi:10.1002/iub.67. PMID 18459162.
5. ↑ "A Steric-inhibition model for regulation of nucleotide exchange via the Dock180 family of GEFs". Current Biology 15 (4): 371–377. February 2005. doi:10.1016/j.cub.2005.01.050. PMID 15723800.
6. ↑ "An Alpha-Helical Extension of the ELMO1 Pleckstrin Homology Domain Mediates Direct Interaction to DOCK180 and Is Critical in Rac Signaling". Molecular Biology of the Cell 19 (11): 4837–4851. September 2008. doi:10.1091/mbc.E08-04-0345. PMID 18768751.
7. ↑ "RhoG activates Rac1 by direct interaction with the Dock180-binding protein Elmo". Nature 424 (6947): 461–464. July 2003. doi:10.1038/nature01817. PMID 12879077.
8. ↑ "DOCK180, a major CRK-binding protein, alters cell morphology upon translocation to the cell membrane". Molecular and Cellular Biology 16 (4): 1770–1776. April 1996. doi:10.1128/mcb.16.4.1770. PMID 8657152.
9. ↑ "C-terminal SH3 domain of CrkII regulates the assembly and function of the DOCK180/ELMO Rac-GEF". Journal of Cellular Physiology 204 (1): 344–351. July 2005. doi:10.1002/jcp.20288. PMID 15700267.
10. ↑ 10.0 10.1 "Dock4 is regulated by RhoG and promotes Rac-dependent cell migration". Experimental Cell Research 312 (20): 4205–4216. December 2006. doi:10.1016/j.yexcr.2006.09.006. PMID 17027967.
11. ↑ 11.0 11.1 "Dock4 regulates dendritic development in hippocampal neurons". Journal of Neuroscience Research 86 (14): 3052–3061. July 2008. doi:10.1002/jnr.21763. PMID 18615735.
12. ↑ 12.0 12.1 "Molecular association between beta-catenin degradation complex and Rac guanine exchange factor DOCK4 is essential for Wnt/beta-catenin signaling". Oncogene 27 (44): 5845–5855. July 2008. doi:10.1038/onc.2008.202. PMID 18641688.
13. ↑ "Identification of an evolutionarily conserved superfamily of DOCK180-related proteins with guanine nucleotide exchange activity". Journal of Cell Science 115 (Pt 24): 4901–4913. December 2002. doi:10.1242/jcs.00219. PMID 12432077.
14. ↑ "Common molecular pathways involved in human CD133+/CD34+ progenitor cell expansion and cancer". Cancer Cell International 7: 11. June 2007. doi:10.1186/1475-2867-7-11. PMID 17559657.
15. ↑ "Finer delineation and transcript map of the 7q31 locus deleted in myeloid neoplasms". Cancer Genetics and Cytogenetics 162 (2): 151–159. October 2005. doi:10.1016/j.cancergencyto.2005.03.019. PMID 16213364.

## Further reading

* "GEF what? Dock180 and related proteins help Rac to polarize cells in new ways". Trends in Cell Biology 17 (8): 383–393. 2007. doi:10.1016/j.tcb.2007.05.001. PMID 17765544.
* "In vitro guanine nucleotide exchange activity of DHR-2/DOCKER/CZH2 domains". Methods in Enzymology 406: 41–57. 2006. doi:10.1016/S0076-6879(06)06004-6. ISBN 9780121828110. PMID 16472648.
* "CZH proteins: a new family of Rho-GEFs". Journal of Cell Science 118 (Pt 21): 4937–4946. 2005. doi:10.1242/jcs.02671. PMID 16254241.
* "The DNA sequence of human chromosome 7.". Nature 424 (6945): 157–164. 2003. doi:10.1038/nature01782. PMID 12853948. Bibcode: 2003Natur.424..157H.
* "Diversification of transcriptional modulation: large-scale identification and characterization of putative alternative promoters of human genes.". Genome Research 16 (1): 55–65. 2006. doi:10.1101/gr.4039406. PMID 16344560.

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