HGH1 (HGH1 homolog; also known as BRP16/brain protein 16, FAM203A or C8orf30A) is a 390-residue, armadillo-repeat protein of the HGH1 family that acts as a co-chaperone of eukaryotic elongation factor 2 (eEF2) (PMID: 30876804). In yeast, it binds the dynamic central domain III of nascent eEF2 through a bipartite interface and recruits the chaperonin TRiC/CCT to the C-terminal module, and without HGH1 a substantial fraction of newly synthesized eEF2 is degraded or aggregates. HGH1 also cooperates with the Hsp90 co-chaperone Cns1 in a quaternary complex with eEF2 and Hsp90 (PMID: 30876805), and hgh1-deleted yeast contain eEF2 that lacks the diphthamide modification (PMID: 39825589). In human breast cancer cells, HGH1 depletion reduces global translation efficiency and proliferation (PMID: 38844963). HGH1 is upregulated in breast tumors, predicts poor prognosis and promotes proliferation, migration and invasion through PI3K/AKT/NF-kappa B signaling (PMID: 40256249).