The interactome of Insulin-like growth factor 2 mRNA binding protein 2 (IGF2BP2)

Insulin-like growth factor 2 mRNA binding protein 2 (IGF2BP2) binds various RNA transcripts and functions as a tumor promoter, although little is known regarding the mechanisms that regulate its roles in RNA metabolism (1-3). Here we find that IGF2BP2 binds to the 3’ untranslated region of the transcript encoding ATP6V1A, a major catalytic subunit of the vacuolar ATPase (v-ATPase), and regulates its degradation in a lysine acetylation and SIRT1-dependent manner. We show that the regulation of IGF2BP2 is significantly compromised in breast cancer cells where SIRT1 expression is low or knocked-down. Reduced SIRT1 expression leads to an increase in acetylated IGF2BP2, which enables IGF2BP2 to recruit the XRN2 nuclease to the ATP6V1A transcript, resulting in its degradation and a reduction in the expression of functional v-ATPase complexes. This impairs lysosomal activity and produces a cellular secretome consisting of increased numbers of exosomes enriched in ubiquitinated protein cargo and soluble hydrolases including cathepsins, which combine to promote tumor progression and invasiveness. Collectively, these findings describe a previously unrecognized role for IGF2BP2 in mediating the degradation of an mRNA transcript essential for lysosomal function and highlight how its sirtuin-regulated acetylation state can have significant biological and disease consequences.