Functional Proteomics of Breast Cancer Metabolism Identifies GLUL as Responder during Hypoxic Adaptation

Hypoxia as well as metabolism are
central hallmarks of cancer,
and hypoxia-inducible factors (HIFs) and metabolic effectors are crucial
elements in oxygen-compromised tumor environments. Knowledge of changes
in the expression of metabolic proteins in response to HIF function
could provide mechanistic insights into adaptation to hypoxic stress,
tumorigenesis, and disease progression. We analyzed time-resolved
alterations in metabolism-associated protein levels in response to
different oxygen potentials across breast cancer cell lines. Effects
on the cellular metabolism of both HIF-dependent and -independent
processes were analyzed by reverse-phase protein array profiling and
a custom statistical model. We revealed a strong induction of glucose
transporter 1 (GLUT1) and lactate dehydrogenase A (LDHA) as well as
reduced glutamate-ammonia ligase (GLUL) protein levels across all
cell lines tested as consistent changes upon hypoxia induction. Low
GLUL protein levels were correlated with aggressive molecular subtypes
in breast cancer patient data sets and also with hypoxic tumor regions
in a xenograft mouse tumor model. Moreover, low GLUL expression was
associated with poor survival in breast cancer patients and with high
HIF-1α-expressing patient subgroups. Our data reveal time-resolved
changes in the regulation of metabolic proteins under oxygen-deprived
conditions and elucidate GLUL as a strong responder to HIFs and the
hypoxic environment.