Phenotypic Screening Identifies Protein Synthesis Inhibitors as H-Ras-Nanocluster-Increasing Tumor Growth Inducers

A1 Journal article (refereed)


Internal Authors/Editors


Publication Details

List of Authors: Najumudeen AK, Posada IMD, Lectez B, Zhou Y, Landor SK, Fallarero A, Vuorela P, Hancock J, Abankwa D
Publisher: American Chemical Society
Publication year: 2015
Journal: Biochemistry
Volume number: 54
Issue number: 49
Start page: 7212
End page: 7221
eISSN: 1520-4995


Abstract





Ras isoforms H-, N-, and K-ras are each
mutated in speci
fic cancer types at varying frequencies and
have di
fferent activities in cell fate control. On the plasma
membrane, Ras proteins are laterally segregated into isoform-
speci
fic nanoscale signaling hubs, termed nanoclusters. As Ras
nanoclusters are required for Ras signaling, chemical
modulators of nanoclusters represent ideal candidates for the
speci
fic modulation of Ras activity in cancer drug development.
We therefore conducted a chemical screen with commercial
and in-house natural product libraries using a cell-based
H-ras-nanoclustering FRET assay. Next to established Ras
inhibitors, such as a statin and farnesyl-transferase inhibitor, we surprisingly identi
fied five protein synthesis inhibitors as positive regulators. Using commonly employed cycloheximide as a representative compound, we show that protein synthesis inhibition increased nanoclustering and effector recruitment specifically of active H-ras but not of K-ras. Consistent with these data, cycloheximide treatment activated both Erk and Akt kinases and specifically promoted H-rasG12V-induced, but not K-rasG12V- induced, PC12 cell differentiation. Intriguingly, cycloheximide increased the number of mammospheres, which are enriched for cancer stem cells. Depletion of H-ras in combination with cycloheximide significantly reduced mammosphere formation, suggesting an exquisite synthetic lethality. The potential of cycloheximide to promote tumor cell growth was also reflected in its ability to increase breast cancer cell tumors grown in ovo. These results illustrate the possibility of identifying Ras-isoform-specific modulators using nanocluster-directed screening. They also suggest an unexpected feedback from protein synthesis inhibition to Ras signaling, which might present a vulnerability in certain tumor cell types.






Last updated on 2019-17-07 at 05:07