Abstract
Rho family small guanosine triphosphatases (GTPases) are important regulators of the cytoskeleton, and are critical in many aspects of cellular and developmental biology, as well as in pathological processes such as intellectual disability and cancer. Of the three members of the family, Rac3 has a more restricted expression in normal tissues compared to the ubiquitous member of the family, Rac1. The Rac3 polypeptide is highly similar to Rac1, and orthologues of the gene for Rac3 have been found only in vertebrates, indicating the late appearance of this gene during evolution. Increasing evidence over the past few years indicates that Rac3 plays an important role in neuronal development and in tumor progression, with specificities that distinguish the functions of Rac3 from the established functions of Rac1 in these processes. Here, results highlighting the importance of Rac3 in distinct aspects of neuronal development and tumor cell biology are presented, in support of the non-redundant role of different members of the two Rac GTPases in physiological and pathological processes.
Highlights
In vertebrates the Rac family of guanosine triphosphatases (GTPases) includes three different genes that encode three highly similar proteins: the ubiquitously expressed Rac1 with its alternative spliced variant Rac1b [1,2]; Rac2 that is expressed only in hematopoietic cells [3]; and the Rac3 protein that is co-expressed with Rac1 in developing neurons and in other cell types, with a pattern of expression more restricted compared to Rac1 [4,5]
Rac1 and Rac3 GTPases, the function of these proteins cannot be explained by functional redundancy, since an increasing number of examples are demonstrating specific effects of Rac3 that cannot be accomplished by Rac1
The very limited but significant differences in amino acid sequence concentrated at hot spots along the Rac1 and Rac3 polypeptides suggest that these differences may drive the interaction with specific effectors/regulators for each GTPase, and/or guide their subcellular localization at specific locations within the cell
Summary
In vertebrates the Rac family of guanosine triphosphatases (GTPases) includes three different genes that encode three highly similar proteins: the ubiquitously expressed Rac with its alternative spliced variant Rac1b [1,2]; Rac that is expressed only in hematopoietic cells [3]; and the Rac protein that is co-expressed with Rac in developing neurons and in other cell types, with a pattern of expression more restricted compared to Rac1 [4,5]. The very carboxy-terminal end of the Rac proteins (residues 183–192) is the most divergent region between the Rac and Rac proteins (Figure 1A). This part includes a polybasic region and an adjacent CAAX box, where CAAX stands for the last 4 amino acid residues: a cysteine (C), followed by two aliphatic residues (AA), followed by any residue (X). The human gene for Rac maps to chromosome band 17q25.3 [7,12], near a region that is frequently. The human gene for Rac maps to chromosome band 17q25.3 [7,12], near a region that is deleted in breast cancer [13,14]. Pointing to importantfunctions and unique of the Rac indevelopment neuronal development and cancer
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