The ensemble database shows five Tiam1 transcripts, only one of which is encoding for the full length protein. Two transcripts are not translated and two others encode only for parts of the Tiam1 protein.

The Tiam1 gene constist of 29 exons encoding for a 7200 bp transcript.

Tiam1 is expressed in almost all adult tissues with highest expression levels in brain and testis. Tiam1 is also expressed during embryogenesis as Tiam1 mRNA is detectable from day 10 onwards in mice.

The human Tiam1 gene encodes a protein of 1,591 amino acids with a predicted molecular mass of 177 kD and several distinct domains.

The Tiam1 protein is myristoylated at its N-terminus and contains 2 N-terminal PEST domains, an N-terminal pleckstrin homology domain (PHn), a coiled-coil region with adjacent sequence (CC-Ex), a Ras-binding domain (RBD), a PSD-95/DlgA/ZO-1 domain (PDZ) and a catalytic Dbl homology (DH)-PH (PHc) combination. While the PHn-CC-Ex domain of Tiam1 is crucial for membrane localisation of the protein, the DH-PHc combination is characteristic for all members of the Dbl-like family of guanine nucleotide exchange factors (GNEFs) (Engers, 2009).

Tiam1 is ubiquitously expressed with highest expression levels in brain and testis. Accordingly, many different cell lines have been shown to express Tiam1 on the RNA and/or protein level.

Tiam1 is primarily located in the cytoplasm of cells, but upon activation it is translocated to the plasma membrane. The activity of Tiam1 is regulated by different mechanisms: relief of intramolecular inhibition, post-translational modifications (e.g. threonine phosphorylation) and interaction with other proteins, including Nm23-H1, c-Myc, CD44, Ankyrin, Spinophilin, JIP2/IB2, Par3, Arp2/3, Ras, Trk-B, Rac, phospho-inositides (Mertens et al., 2003; Minard et al., 2004; Engers, 2009).

Tiam1 is a specific activator of the Rho-like GTPase Rac and is implicated in the regulation of different cell biological functions, including cell polarity, adhesion, migration, invasion, metastasis and carcinogenesis. Originally, Tiam1 has been identified as a gene that confers an invasive and metastatic phenotype to otherwise noninvasive murine T-lymphoma cells. In contrast, Tiam1 inhibits migration and invasion of epithelial cells by promoting E-cadherin-mediated cell-cell adhesion and by shifting the balance between distinct invasion-promoting matrix metalloproteinases (MMP-2 and -9) and invasion-inhibiting tissue inhibitors of metalloproteinases (TIMP-1 and -2) towards the TIMPs. However, in other studies Tiam1 was shown to promote migration and invasion of epithelial cells. These seemingly opposing effects of Tiam1 on migration and invasion in epithelial cells depend at least partly on the cell type studied, the fact as to whether or not the cell substrate used affects the formation of E-cadherin-mediated cell-cell adhesion, and the relative levels of Rac and Rho. Aside from these functions Tiam1 has also been implicated in the development of malignant tumors either as a mediator of oncogenic Ras-signaling (in skin tumors) or as a Wnt-responsive gene (in intestinal tumors) (Engers, 2009).
Morphologically, overexpression of Tiam1 in different cell types induces a distinct phenotype, characterised by large flat cells with epithelioid or sickle-shaped morphology and extensive membrane ruffling. In addition, many of these Tiam1-transfected cells are either polynucleated or contain large numbers of pinocytic vesicles (Minard et al., 2004). Mutational analysis revealed that the PHn-CC-Ex domain is required for membrane localisation of the protein and Tiam1-induced membrane ruffling.

95 % identical to the mouse homolog, Tiam1 is conserved among vertrebrates. Still life (SIF) is the Drosophila homologue of Tiam1.

Investigations on mutations in the Tiam1 gene have only been reported in human renal-cell carcinomas.

None reported.

A study on human renal cell carcinomas (RCCs) reported up to five different point mutations in RCC cell lines (Engers et al., 2000). One of these mutations (A441G) was located in the N-terminal PH domain, which is essential for membrane localisation and functional activity of Tiam1. This mutation was found in 11.5 % of primary human RCCs, but not in the corresponding normal kidney tissues. Stable overexpression of A441G-Tiam1 proved to be sufficient for oncogenic transformation of NIH 3T3 cells in vitro.