Disease relevance of SKP1

• Here we describe the fortuitous cloning of cDNAs for two Skp1 homologues from the plant Arabidopsis thaliana on account of their ability to activate reporter gene expression in yeast directed by the cyt-1 element from the promoter of the Agrobacterium tumefaciens T-cyt gene, which is essential for expression of the gene in plants [1].

High impact information on SKP1

• Phosphorylated Sic1p substrate is specifically targeted for ubiquitination by binding to a Cdc4p/Skp1p subcomplex [2].
• Regulating the yeast kinetochore by ubiquitin-dependent degradation and Skp1p-mediated phosphorylation [3].
• The budding yeast SKP1 gene, identified as a dosage suppressor of a known kinetochore protein mutant, encodes an intrinsic 22.3 kDa subunit of CBF3, a multiprotein complex that binds centromere DNA in vitro [4].
• Budding yeast SKP1 encodes an evolutionarily conserved kinetochore protein required for cell cycle progression [4].
• Cdc53 contains independent binding sites for Cdc34 and Skp1 suggesting it functions as a scaffold protein within an E2/E3 core complex [5].

Biological context of SKP1

• We have previously shown that SKP1 and SGT1 balance the assembly and turnover of CBF3 complexes, a cycle that we suggest is independent of its role in chromosome segregation (Rodrigo-Brenni, M.C., S. Thomas, D.C. Bouck, and K.B. Kaplan. 2004. Mol. Biol. Cell. 15:3366-3378) [6].
• Thus, in contrast to the current view, phosphorylation of Ctf13p and Skp1p is not essential for the formation of CBF3-centromere DNA complexes [7].
• A stable truncated Cdc4pF-beta-gal hybrid protein capable of binding Skp1p and entering into an SCF complex interfered with proteolysis of SCF targets and inhibited cell proliferation [8].
• Here, we show that the silencing suppressor protein P0 of two Arabidopsis-infecting poleroviruses interacts by means of a conserved minimal F-box motif with Arabidopsis thaliana orthologs of S-phase kinase-related protein 1 (SKP1), a component of the SCF family of ubiquitin E3 ligases [9].
• Point mutations in the F-box-like motif abolished the P0-SKP1 ortholog interaction, diminished virus pathogenicity, and inhibited the silencing suppressor activity of P0 [9].

Anatomical context of SKP1

• Rav1, Rav2 and Skp1 form a complex that we have named 'regulator of the (H+)-ATPase of the vacuolar and endosomal membranes' (RAVE), which associates with the V1 domain of the vacuolar membrane (H+)-ATPase (V-ATPase) [10].
• Suppression of Skp1 in mitotic HeLa cells by siRNA resulted in accumulation of telophase cells with elongated inter-cell bridges and with midbodies stretched 2-3 times longer than that of normal cells [11].

Associations of SKP1 with chemical compounds

• The SKP1 gene of Kluyveromyces lactis was isolated as a suppressor of a lethal temperature-sensitive mutation in the Saccharomyces cerevisiae CTF13 gene (Chromosome Transmission Factor 13) [12].
• The Grr1-Skp1 interaction is enhanced by high levels of glucose [13].
• The fragmin60 C2 domain does not bind phospholipids but interacts with the endogenous homologue of Saccharomyces cerevisiae S-phase kinase-associated protein (Skp1), as shown by pull-down assays and co-expression in mammalian cells [14].
• The association of Met30 with Skp1 but not with its substrate Met4 was inhibited in cells treated with cadmium [15].
• Furthermore, nuclear concentration occurred in a mutant that attached only the core disaccharide to Skp1 [16].

Physical interactions of SKP1

• Here, we investigate how the Ctf13p/Skp1p complex becomes competent to form the CBF3-centromere DNA complex [7].
• Formation of the active Ctf13-Skp1 complex also requires Hsp90, a molecular chaperone [17].
• Skp1 binds a motif called the F-box and in turn F-box proteins appear to recruit specific substrates for ubiquitination [5].
• Coimmunoprecipitation assays reveal that Mfb1p interacts with Skp1p in an F-box-dependent manner [18].
• Importantly, Skp1p was the only major partner that copurified with Rcy1p [19].

Enzymatic interactions of SKP1

• Cdc4 assembled with Skp1 functions as the receptor that selectively binds phosphorylated Sic1 [20].
• These data suggest that Grr1 is required for degradation of Cln2 through linking phosphorylated Cln2 to Skp1 in a SCFGrr1 complex [21].

Other interactions of SKP1

• Sgt1p physically associates with Skp1p in vivo and in vitro [22].
• As revealed by mass spectrometry, Ctf13p and Skp1p carry two and four phosphate groups, respectively [7].
• A skp1 mutation together with Hsp90 mutations exhibits synthetic lethality [7].
• These results strongly suggest that Grr1 functions in the ubiquitin pathway through association with Skp1 [23].
• In Saccharomyces cerevisiae, an SCF complex contains a common set of components, namely, Cdc53p, Skp1p, and Hrt1p [24].

Analytical, diagnostic and therapeutic context of SKP1

• Skp1 and the F-box protein Pof6 are essential for cell separation in fission yeast [25].
• In addition, Dictyostelium Skp1 consists of 2 genetic isoforms, Skp1A and Skp1B, which differ by a single amino acid and appear to be expressed throughout the life cycle based on reverse-transcription polymerase chain reactions [16].
• Our yeast two-hybrid assays mapped the binding interfaces to the central stalk region of CENP-E (955-1571 aa) and the C-terminal 33 amino acids of Skp1, respectively [11].

References