Characterization of mutant AIPV49M in somatotroph cells
García-Rendueles1, E. Díaz-Rodríguez1, G. Trivellin2, M. García-Lavandeira1, T. Vila Vila1, C. Dieguez1, M. Korbonitz2 & C. Alvarez1
Introduction: About 30% of all familial isolated pituitary adenoma (FIPA) and 50% of acromegaly families have a mutation in the aryl hydrocarbon receptor-interacting protein gene (AIP; Chahal, TEM, 2010). The functional role of AIP in somatotroph cells is unknown. Recently, it has been proposed that wild type AIP (wtAIP) is a tumor suppressor gene, role that is lost in the different mutant AIPs (mAIP; Leontiou, JCEM, 2008). In the adenomas, mAIPs are usually found as loss of heterozygosity with both alleles mutated. However, the point mutant V49M-AIP was found in a single giant male patient but there was no LOH, coexisting with a normal allele. Previous and different functional studies found that V49M-AIP was behaving as the wtAIP.
Aims: To study the effects of V49M-AIP in comparison to wtAIP in the proliferation and apoptosis of somatotroph cells.
Matherials and methods: We use the somatotroph rat pituitary cell line GH4C1 cell line that express basal levels of AIP. Thus they are a good model for heterozygosis. The cells were transiently transfected by nucleofection. As a standard of transfection efficiency a vector expressing GFP under a CMV promoter was co-transfected. Cells were counted with a cytometer. Apoptosis was detected by Hoechst staining.
Results: The nucleofection provided a transfection efficiency over 90% in all cases. In the presence of complete medium with growth factors we observed no difference in the proliferation between the empty vector, wtAIP or V49M-AIP. In deprived medium (0.1% serum) the cells transfected with the mutant V49M-AIP presented a 40% apoptosis. There was no relevant apoptosis in cells transfected with empty vector or with wtAIP.
Conclusions: In somatotroph cells V49M-AIP mutation does not affect proliferation but induces apoptosis. In cells expressing endogenous AIP this mutant seems to act as a toxic mutation. This would explain why this mutant is always in heterozygosis. The results also suggest that pro-tumoral effects of mutant AIP require other factors still unknown.
Declaration of interest: The authors declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project.
Funding: This work was supported, however funding details unavailable.