Evidence for the association of the human regulatory protein Ki-1/57 with the translational machinery

Ki-1/57 is a cytoplasmic and nuclear protein of 57 kDa first identified in malignant cells from Hodgkin’s lymphoma. Based on yeast-two hybrid protein interaction we found out that Ki-1/57 interacts with adaptor protein RACK1 (receptor of activated kinase 1), CIRP (cold-inducible RNA-binding protein), RPL38 (ribosomal protein L38) and FXR1 (fragile X mental retardation-related protein 1). Since these proteins are involved in the regulation of translation we suspected that Ki-1/57 may have a role in it. We show by immunoprecipitation the association of Ki-1/57 with FMRP. Confocal microscopy revealed that Ki-1/57 colocalizes with FMRP/FXR1/2 to stress granules. Furthermore Ki-1/57 cosediments with free ribosomal particles and enhances translation, when tethered to a reporter mRNA, suggesting that Ki-1/57 may be involved in translational regulation.Structured summary of protein interactions:Ki-1/57 and TIA-1 colocalize by fluorescence microscopy (View interaction)Ki-1/57 physically interacts with CIRP by two hybrid (View interaction)FMRP physically interacts with Ki-1/57 by anti bait coimmunoprecipitation (View interaction)Ki-1/57 physically interacts with FXR1 by two hybrid (View interaction)Ki-1/57 physically interacts with RPL38 by two hybrid (View interaction)

► Ki-1/57 interacts with several translation regulatory proteins.
► Ki-1/57 co-localizes with members of fragile X protein family to stress granules.
► Ki-1/57 co-sediments with free ribosome particles.
► Ki-1/57 enhances translation when tethered to a reporter mRNA construct.
► Our findings suggest that Ki-1/57 may be associated to translation control.