SIRT4 and neoplasm: SIRT4 also inhibits glutamine metabolism to regulate thyroid cancer cell proliferation and migration (223), and acts as a tumor suppressor in prostate cancer by the same mechanism (224); however, in A172 glioma cells, SIRT4 up-regulates glutamate metabolism to prevent excitotoxicity by increasing glutamate transporter 1 (GLT-1) and GDH expression and decreasing glutamine synthetase levels (225).