WNT4 executes estrogen regulation of cellular metabolism via intracellular activity at the mitochondria

Abstract

ABSTRACTInvasive lobular carcinoma of the breast (ILC) has a distinct metabolic phenotype among breast cancer, characterized by relative metabolic quiescence and limited glucose uptake. However, recent work suggests ILC preferentially use fuels such as lipids and amino acids, and that ILC metabolism is linked to estrogen receptor α (ER) signaling. We previously reported that in ILC, estrogen-induced expression of Wnt ligand WNT4 activates an atypical intracellular WNT4 pathway that regulates cellular metabolism and mitochondrial dynamics. However, mechanisms by which intracellular WNT4 regulates mitochondria are unknown. To address this, we performed proximity-dependent biotinylation with mass spectrometry (BioID) to profile WNT4 trafficking, localization, and intracellular functions. BioID showed that whereas canonical Wnt ligand WNT3A trafficked through the endoplasmic reticulum for secretion, WNT4 is predominantly in the cytosol and at the mitochondria. We also identified DHRS2, mTOR, and STAT1 as putative WNT4 cytosolic/mitochondrial signaling partners. These findings support a role for intracellular WNT4 regulating mitochondrial function and metabolism. We further investigated regulation of metabolism by ER-WNT4 using global metabolomics, following WNT4 knockdown versus over-expression compared to siRNA or small molecule inhibition of ER-WNT4 signaling. We found WNT4 signaling regulates oxidative phosphorylation (OXPHOS), with WNT4 knockdown suppressing OXPHOS as well as fatty acid and glutamate metabolism pathways, but not glycolytic activity. Taken together, WNT4 has atypical intracellular localization and signaling activity directly at the mitochondria that mediates ER regulation of cellular metabolism. ER-WNT4 signaling may play a key role in regulating the distinct metabolic phenotype of ILC by regulating mitochondrial activity and fuel usage.