Anaerobic nucleolar proteome dynamics

Abstract

Anaerobic metabolism as a consequence of low oxygen tension (hypoxia) is observed in various physiological and pathological conditions. Through the study of adaptive mechanisms to anaerobic metabolism, it was recently shown that an increase in the extracellular [H+] causes the relocalization and sequestration of the von Hippel-Lindau (VHL) tumor suppressor to the nucleolus. This results in an indirect increase in energy production through HIF transcription factor stabilization and a decrease in energy demand through silencing of ribosomal biogenesis. Mutagenesis of VHL revealed a pH-dependent nucleolar targeting sequence, NoDSH+. A bioinformatic search of this sequence identified proteins involved in major metabolic activities including: POLD1, the catalytic subunit of DNA polymerase delta; TAF1, subunit 1 of the general transcription factor TFIID; APC2, subunit of cell cycle protein APC/C; and UAP56, an mRNA splicing and export factor. Here we demonstrate that in response to acidic conditions, these proteins accumulate and become detained within the nucleolus. We also show that disruption of pH-dependent nucleolar sequestration of NoDSH+-containing proteins reduces cell viability through increasing cellular energy consumption. This data suggests that during anaerobic metabolism, cells utilize the nucleolus to sequester key proteins of basal metabolic processes, preventing their function, in order to maintain energy equilibrium by reducing metabolic demand.