Identification of TFG- and Autophagy-Regulated Proteins and Glycerophospholipids in B Cells

Autophagy supervises
the proteostasis and survival of B lymphocytic
cells. Trk-fused gene (TFG) promotes autophagosome–lysosome
flux in murine CH12 B cells, as well as their survival. Hence, quantitative
proteomics of CH12tfgKO and WT B cells in combination
with lysosomal inhibition should identify proteins that are prone
to lysosomal degradation and contribute to autophagy and B cell survival.
Lysosome inhibition via NH4Cl unexpectedly reduced a number
of proteins but increased a large cluster of translational, ribosomal,
and mitochondrial proteins, independent of TFG. Hence, we propose
a role for lysosomes in ribophagy in B cells. TFG-regulated proteins
include CD74, BCL10, or the immunoglobulin JCHAIN. Gene ontology (GO)
analysis reveals that proteins regulated by TFG alone, or in concert
with lysosomes, localize to mitochondria and membrane-bound organelles.
Likewise, TFG regulates the abundance of metabolic enzymes, such as
ALDOC and the fatty acid-activating enzyme ACOT9. To test consequently
for a function of TFG in lipid metabolism, we performed shotgun lipidomics
of glycerophospholipids. Total phosphatidylglycerol is more abundant
in CH12tfgKO B cells. Several glycerophospholipid
species with similar acyl side chains, such as 36:2 phosphatidylethanolamine
and 36:2 phosphatidylinositol, show a dysequilibrium. We suggest a
role for TFG in lipid homeostasis, mitochondrial functions, translation,
and metabolism in B cells.