PDZ-GEF1, a Guanine Nucleotide Exchange Factor Specific for Rap1 and Rap2

Johan De Rooij,Nienke M Boenink,Miranda Van Triest,Robbert H Cool,Alfred Wittinghofer,Johannes L Bos

doi:10.1074/jbc.274.53.38125

Johan De Rooij, Nienke M Boenink + Show 4 more

Open Access

https://doi.org/10.1074/jbc.274.53.38125

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Abstract

The small GTPase Rap1 has been implicated in a variety of cellular processes including the control of cell morphology, proliferation, and differentiation. Stimulation of a large variety of cell surface receptors results in the rapid activation of Rap1, i.e. an increase in the GTP-bound form. This activation is mediated by second messengers like calcium, cAMP, and diacylglycerol, but additional pathways may exist as well. Here we describe a ubiquitously expressed guanine nucleotide exchange factor of 200 kDa that activates Rap1 both in vivo and in vitro. This exchange factor has two putative regulatory domains: a domain with an amino acid sequence related to cAMP-binding domains and a PDZ domain. Therefore, we named it PDZ-GEF1. PDZ-GEFs are closely related to Epacs, Rap-specific exchange factors with a genuine cAMP binding site, that are directly regulated by cAMP. The domain related to cAMP-binding domains, like the cAMP binding site in Epac, serves as a negative regulatory domain. However, PDZ-GEF1 does not interact with cAMP or cGMP. Interestingly, PDZ-GEF1 also activates Rap2, a close relative of Rap1. This is the first example of an exchange factor acting on Rap2. We conclude that PDZ-GEF1 is a guanine nucleotide exchange factor, specific for Rap1 and Rap2, that is controlled by a negative regulatory domain.

Highlights

Rap1 is a Ras-like small GTPase that has been implicated in a variety of cellular processes like T-cell anergy [1], platelet activation [2], and the reversion of oncogenic transformation [3] as well as the induction of oncogenic transformation [4]
The PDZ-GEFs form a new family of exchange factors that is most closely related to Epacs, which are Rap1-specific GEFs directly regulated by cAMP (Fig. 1a)
A conserved structure is present in PDZ-GEFs that is related to the cAMP-binding domains in Epac and PKA

Summary

Introduction

Rap1 is a Ras-like small GTPase that has been implicated in a variety of cellular processes like T-cell anergy [1], platelet activation [2], and the reversion of oncogenic transformation [3] as well as the induction of oncogenic transformation [4]. To further identify GEFs that may be specific for Rap1 we searched data bases and found a conserved family of genes, which we named PDZ-GEFs. The encoded proteins contain the characteristic Ras exchange motif and GEF sequences present in all GEFs for the Ras-like GTPases, as well as a proline-rich motif, a PDZ-domain [26], and a structure that is related to the cAMP-binding domains in Epac and PKA (RCBD).

Results

Conclusion