Adrenocortical carcinomas (ACCs) are rare endocrine tumors with poor prognosis. They overexpress the insulin-like growth factor 2 (IGF2), that drives a proliferative autocrine loop by binding to IGF1R and IR. The majority of studies focused on IGF1R as mediator of IGF2 biological effects, but recently a high expression of IR, in particular of the isoform A, was observed in most ACCs, suggesting a potential role of this receptor in modulating IGF2 effects in adrenocortical tumorigenesis. However, the relative contribution of IGF1R and IR to the biological effects of IGF2 in ACC is still unknown. Aim of this study was to investigate the specific roles of IGF1R and IR in mediating IGF2 tumorigenic effects in ACC. To this purpose we performed genetic silencing of both IGF1R and IR by transfecting H295R, MUC1 and primary ACC cells with specific siRNAs directed against IGF1R and IR. We found that the IGF2 anti-apoptotic effects were enhanced in H295R and ACC primary cultured cells silenced for both IGF1R (−15.16±3.27%, P<0.01 and −45%, P<0.05, of caspase 3/7 activity, respectively) and IR (−23.62±16.03%, P<0.05 and −32.4%, P<0.001, respectively). In addition, we demonstrated that IGF2 was still able to promote ERK and AKT phosphorylation after IGF1R and IR silencing in H295R and ACC primary cultured cells. Moreover, both IGF1R and IR silencing did not affect the IGF2-mediated proliferation in H295R. In MUC1 cells, IGF1R silencing did not alter IGF2-induced cell apoptosis and proliferation. Heterogeneous results were obtained in primary cultured cells obtained from 2 different ACC. In one of them IGF1R silencing decreased IGF2-induced cell proliferation, underlining the importance of this receptor in mediating IGF2-mitogenic effects. In the other one IGF2-mediated cell proliferation was reduced after IR, but not IGF1R, silencing. IGF1R, but not IR, knockdown reduced the antiproliferative effects of IGF1R/IR inhibitor Linsitinib in H295R and ACC primary cultured cells (−32.76±20.81% in control cells, P<0.05 and −18.36±11% in IGF1R silenced H295R cells, P<0.05), suggesting a main role of IGF1R in the response to Linsitinib. In conclusion, our data demonstrated a differential involvement of IGF1R and IR in mediating IGF2 tumorigenic effects in adrenocortical cancer cells.
21 May 2022 - 24 May 2022