Disease relevance of RHO1

• In Saccharomyces cerevisiae the ras-related protein Rho1p is essentially the only target for ADP-ribosylation by exoenzyme C3 of Clostridium botulinum [1].
• Yeast rho GDI expressed in Escherichia coli was active not only on yeast rho1 but also on mammalian rho family members which were post-translationally modified [2].

High impact information on RHO1

• Finally, another small G protein, Rho1, is required for activity of beta (1-->3)glucan synthase, the enzyme that catalyzes the synthesis of the major structural component of the yeast cell wall [3].
• SAC7 is a novel GTPase-activating protein for RHO1 [4].
• Co-expression of MAP-1B and the rho1 subunit in COS cells results in a dramatic redistribution of the rho1 subunit [5].
• Cdc24 acts as a guanylyl-nucleotide-exchange factor for the Rho-type GTPase Cdc42, which has been shown to be a fundamental component of the molecular machinery controlling morphogenesis in eukaryotic cells [6].
• Experiments with a dominant positive PKC1 gene showed that the two effects of Rho1p are independent of each other [7].

Biological context of RHO1

• A yeast strain in which RHO1 is replaced with RhoA shows a recessive temperature-sensitive growth phenotype [8].
• The RHO1 gene encodes a homolog of the mammalian RhoA small GTP binding protein in the yeast Saccharomyces cerevisiae [9].
• The effects of the deletion of ROM2 on sensitivity to hydrogen peroxide, paraquat, and cobalt ions, but not to caffeine, were reduced when a constitutive allele of RHO1 was introduced on a single copy plasmid [10].
• Here we demonstrate a hitherto unknown function of Rho1p required for cell cycle progression and cell polarization [11].
• Here, we show that Rom2p, the Rho1 GTP/GDP exchange factor, can mediate stress responses and cell growth via the Ras-cAMP pathways [10].

Anatomical context of RHO1

• We present evidence that cell wall defects activate RHO1 [12].
• In Saccharomyces cerevisiae, the small GTPase RHO1 plays an essential role in the control of cell wall synthesis and organization of the actin cytoskeleton [13].
• These findings reveal a novel function for the Tor2-Rho1 pathway in controlling endocytosis in yeast, a function that is mediated in part through the plasma membrane protein Fks1 [14].
• Based on these results, we propose that Rho1p is kept inactive in intracellular secretory organelles, resulting in repression of the activity of the cell wall-synthesizing enzyme within cells [15].
• Lack of GTP-bound Rho1p in secretory vesicles of Saccharomyces cerevisiae [15].

Associations of RHO1 with chemical compounds

• Activation of RHO1, a subunit of the cell wall synthesis enzyme glucan synthase, by a cell wall alteration would ensure that cell wall synthesis occurs only when and where needed [12].
• The mechanism of RHO1 activation by a cell wall alteration is via the exchange factor ROM2 and could be analogous to signalling by integrin receptors in mammalian cells [12].
• CDC24, which is required for bud emergence and encodes a GEF (guanine-nucleotide exchange factor) for the essential Rho-type GTPase Cdc42p, was identified during both screens [16].
• This cell lysis defect can be rescued by adding osmotic stabilizers, such as 1 M sorbitol, to the medium, and by overexpressing PKC1 or RHO1 [17].
• Glucan synthase from mutants expressing constitutively active Rho1p did not require exogenous guanosine triphosphate for activity [18].

Physical interactions of RHO1

• A downstream target of RHO1 small GTP-binding protein is PKC1, a homolog of protein kinase C, which leads to activation of the MAP kinase cascade in Saccharomyces cerevisiae [8].
• ROM7/BEM4 encodes a novel protein that interacts with the Rho1p small GTP-binding protein in Saccharomyces cerevisiae [19].
• However, Pxl1p directly binds to Rho1p-GDP in vitro, and inhibits the growth of rho1-2 and rho1-3 mutants in a dosage-dependent manner [20].
• Rho1p comigrated with post-Golgi transport vesicles during fractionation of P3 organelles from wild-type or sec6 cells [1].
• Gel overlay analysis indicated that an unmodified form of GST-Rho1p fails to interact with Fks1p [21].

Regulatory relationships of RHO1

• The dominant activating mutation of PKC1 suppressed the temperature sensitivity of two effector mutants of RHO1, rho1(F44Y) and rho1(E451), but not that of rho1(V43T) [8].
• Yeast Tor2 has an additional role in regulating the integrity of the cell wall by activating the Rho1 guanine nucleotide exchange factor Rom2 [14].
• The lethality of an S. cerevisiae cdc43 mutant can be suppressed by simultaneous overexpression of RHO1 and CDC42 on high-copy-number plasmids (Y. Ohya et al., Mol. Biol. Cell 4:1017, 1991; C. A. Trueblood, Y. Ohya, and J. Rine, Mol. Cell. Biol. 13:4260, 1993) [22].
• Bem2p is a Rho-GTPase activating protein (GAP) previously shown to act on Rho1p, and we now show that it also acts on Cdc42p, the GTPase primarily responsible for establishment of cell polarity in yeast [23].
• Lrg1p-GAP domain strongly and specifically stimulated the GTPase activity of Rho1p, a regulator of beta(1-3)-glucan synthase in vitro. beta(1-3)-glucan deposition was increased in lrg1Delta strains and mislocalized to the tip of the mating projection in fus2Delta strains [24].

Other interactions of RHO1

• These results indicate that there are at least two signaling pathways regulated by Rho1p and that one of the downstream targets is Pkc1p, leading to the activation of the MAP kinase cascade [8].
• Moreover, the temperature-sensitive growth phenotype of deltarom2 was suppressed by overexpression of RHO1 or RHO2, but not of CDC42 [9].
• Rom1p and Rom2p are GDP/GTP exchange proteins (GEPs) for the Rho1p small GTP binding protein in Saccharomyces cerevisiae [9].
• We have recently shown that Bni1p is a potential target of Rho1p [25].
• Previous studies have shown that BEM2, which encodes a GTPase-activating protein (GAP) that is specific for the Rho-type GTPase Rho1p in vitro, is required for proper bud site selection and bud emergence [26].

Analytical, diagnostic and therapeutic context of RHO1

• Dissection of upstream regulatory components of the Rho1p effector, 1,3-beta-glucan synthase, in Saccharomyces cerevisiae [27].
• (2) Using two-hybrid assays an interaction between the GAP domain of Lrg1p and Rho1p was demonstrated [28].
• Indirect immunofluorescence study with cells overexpressing RHO1 suggested that the Rho1p-binding site was saturable [29].
• From the opportunistic pathogenic fungus Candida albicans, we cloned the RHO1 gene by the PCR and cross-hybridization methods [30].
• Sequence analysis revealed that the Candida RHO1 gene has a 597-nucleotide region which encodes a putative 22.0-kDa peptide [30].

References