Alternative splicing of Rac1 generates Rac1b, a self-activating GTPase

Expression of Rac1b stimulates NF-κB-mediated cell survival and G1/S progression

“…These differences are in agreement with the structure of recombinant Rac1b protein [16] that is predominantly found in the active GTP-bound state. In addition, activated Rac1b exhibited selective downstream signaling: while Rac1 pathways such as the activation of PAK, or JNK, or lamellipodia formation were poorly supported by active Rac1b, the phosphorylation of InBa and the nuclear translocation of p65 (RelA), a DNA-binding subunit of NF-nB, were clearly stimulated by this variant [15].…”

“…1A). This could reflect the more efficient activation of Rac1b observed in vivo [15,16] and in vitro [13,16]. When Rac1b was coexpressed with the super-repressor InBa(A32A36) (InBAA, a non-phosphorylatable InBa that is not marked for proteolytic degradation; [17]), however, no increase in cyclin D1 levels was observed (Fig.…”

“…We reasoned that wild-type Rac1b is not activated in complete absence of serum and that therefore its expression in this experiment did not result in increased cell survival. This assumption is based on previous observations that although Rac1b is a highly activated variant, it differs from constitutively active mutants because its activation is inhibited in the absence of stimulating GEFs and it can be downregulated by GAPs [15,16]. In order to provide experimental support for this explanation, we incubated cells in 0%, 0.25%, and 1% serum and isolated the active fractions of Rac1 and Rac1b using CRIB peptide pull-down assays [15,18].…”

The Role of the Conserved Switch II Glutamate in Guanine Nucleotide Exchange Factor-Mediated Nucleotide Exchange of GTP-Binding Proteins

“…Glu is also conserved in members of the Rho subfamily except for Rnd1, Rnd2, Rnd3 and RhoBTB1/2; Rnd1, Rnd2 and Rnd3 do not require a GEF because they are believed to be constitutively GTP bound. 25 Wrch-1 and RhoD contain an Asp at this position. The glutamate is more or less fully conserved in 57 Rab proteins.…”

GTPase activating proteins: structural and functional insights 18 years after discovery

“…Small GNBPs are ineffi cient enzymes and exhibit a large variation in the GTP hydrolysis reaction rates, e.g. Rac1 (0.11 min -1 ) [46], Ras (0.028 min -1 ) [47,48], Rap (0.0031 min -1 ) [49]. Arf, on the other hand, lacks intrinsic GTPase activity [50,51].…”