Proteomics analysis of expi293 conditioned media purified with immobilized metal affinity chromatography

Isthmin-1 (ISM1) is a recently described adipokine with insulin-like properties, reported to regulate hyperglycemia and liver steatosis. However, contrary to earlier studies, we demonstrate that highly purified ISM1 does not stimulate AKT phosphorylation in 3T3-F442A pre-adipocytes. Instead, this activity is attributed to co-purifying factors. Using proteomic mass spectrometry, we analyzed the ISM1-free sample that exhibits activity on AKT phosphorylation in 3T3-F442A cells and identified the growth factors PDGF-AA and/or GDF15 as the likely contributors to this effect.