Hrr25/CK1δ-directed release of Ltv1 from pre-40S ribosomes is necessary for ribosome assembly and cell growth.
Bottom Line: Conversely, phosphomimetic Ltv1 variants rescued viability after Hrr25 depletion.Finally, Ltv1 knockdown in human breast cancer cells impaired apoptosis induced by CK1δ/ε inhibitors, establishing that the antiproliferative activity of these inhibitors is due, at least in part, to disruption of ribosome assembly.These findings validate the ribosome assembly pathway as a novel target for the development of anticancer therapeutics.
Affiliation: Department of Cancer Biology and Department of Chemistry, The Scripps Research Institute, Jupiter, FL 33458.Show MeSH
Related in: MedlinePlus
License 1 - License 2
Mentions: To confirm the role of Hrr25 in releasing Ltv1 in vivo, we used suppression analysis. While Hrr25 is an essential protein, Ltv1 is not (Fig. 4 A; Hoekstra et al., 1991; Winzeler et al., 1999; Seiser et al., 2006). Thus, we reasoned that if displacement of Ltv1 from pre-40S ribosomes was the essential function of Hrr25, then deletion of Ltv1 would be predicted to rescue the lethal phenotype of Hrr25 depletion. Depletion of Hrr25 in yeast cells engineered to express a galactose-inducible/glucose-repressible Hrr25 transgene (Gal::Hrr25) essentially abolished growth in glucose, as expected because Hrr25 is an essential gene (Fig. 4, A and B). Strikingly, however, loss of Ltv1 rescued growth of this mutant strain when grown in glucose (Fig. 4, A and B), and the ΔLtv1ΔHrr25 strain is viable (Fig. 4 A). Thus, the essential function of Hrr25 is linked to Ltv1. The more profound growth defect in the ΔLtv1ΔHrr25 cells relative to ΔLtv1 cells likely reflects roles of Hrr25 in other cellular processes as discussed above (Knippschild et al., 2005a). ΔLtv1ΔHrr25 cells also do not grow well on galactose, which indicates a role for Hrr25 in the regulation of galactose metabolism, consistent with previously observed interactions between Hrr25 and Gal10, as well as Sgm1 (Ho et al., 2002; Fasolo et al., 2011).
Affiliation: Department of Cancer Biology and Department of Chemistry, The Scripps Research Institute, Jupiter, FL 33458.