Imbalanced Expression of IGF2 and PCSK4 Is Associated with Overproduction of Big IGF2 in SFT with NICTH: A Pilot Study

Abstract

Context Nonislet cell tumor hypoglycemia (NICTH) is a rare but serious paraneoplastic syndrome associated with large tumors. The high molecular weight IGF2, known as "big" IGF2, is produced by culprit tumors and leads to severe hypoglycemia. The detailed mechanism of its production in NICTH, however, remains unclear. Objective To clarify the mechanism of production of big IGF2 in light of the processing of pro-IGF2 in patients with solitary fibrous tumor (SFT) and NICTH. Design We enrolled 14 patients with SFT and divided them based on the presence or absence of hypoglycemia. In light of the processing of pro-IGF2 in SFT with hypoglycemia, we, retrospectively, compared the production levels of big IGF2 and the expression levels of IGF2 and proprotein convertase subtilisin/kexin type 4 (PCSK4), a proteolytic enzyme of pro-IGF2. Results In all patients with NICTH, big IGF2 was detected in serum by western immunoblotting analysis. Moreover, we showed that two patients without hypoglycemia also had a small amount of big IGF2 in their serum. By immunohistochemical analysis, the protein expression level of IGF2 was significantly higher in the NICTH group than in the non-NICTH group (P = 0.043). The IGF2/PCSK4 protein expression-level ratio in the NICTH group was significantly higher than that in the non-NICTH group (P = 0.021). Conclusion In patients with SFT and hypoglycemia, an imbalance of IGF2 and PCSK4 expression could lead to increased serum levels of big IGF2.