Low tumoral mRNA IGF2 might balance the mechanism of tumorigenesis in GH-secreting adenomas
A. Diaz1, A. Barlier2, M. Kral1, F. Garcia1, A. Paes de Lima1, M. Manavela1, A. Enjalbert2 & O. Bruno1
Pituitary adenomas may show alterations of PI3K/Akt pathway. IGF2, binding the IGF1-R, is able to active it. LOI of IGF2 has been implicated in the pathogenesis of many tumours. Activation of PI3K produces phosphorylation of p27 and its cytoplasmic mislocalization. Loss of nuclear p27 was associated with worse prognosis. In this study we correlated IGF2 imprinting with activation of PI3K/Akt pathway in a series of 29 somatotropinomas. After surgery, tumors were embedded in RNAlater and stored at −20 °C. Macroadenomas (n=25) were defined as tumors >10 mm and 18 of them as aggressive, because of cavernous and/or sphenoidal sinus invasion and/or Ki-67 ≥3%. Tumoral total RNA was isolated and RT-PCR was performed. ApaI polymorphic site in exon 9 of IGF2 was used to evaluate allelic expression. qPCR showed the tumoral expression of IGF2 normalized with β-glucuronidase (high expression: IGF2 copies/β-glu copies >2). Immunohistochemistry analysis with p-Akt (Ser 473) and p27 (C-19) antibodies was perfomed in 21 tumours. Cytoplasmic or nuclear staining was assessed as negative (negative or weak, <10% of the cells) or positive (moderate or strong). Fourteen out of 29 patients (48.2%) exhibited LOI of IGF2 in the tumour. Thirteen of 14 tumours with LOI had IGF2 <2 vs 7/15 without LOI (P=0.009). Seventy-six % (19/25) of macroadenomas presented IGF2 <2 vs 25% (1/4) of microadenomas (P=0.076). Most aggressive tumours (15/18, 83%) showed IGF2 <2, whereas 6/11 (54.5%) non-aggressive tumours had IGF2 >2 (P=0.043). The pattern of nuclear p27 immunostaining seemed opposed to that of cytoplasmic p-Akt (P=0.063). Tumors with LOI of IGF2 tended to show loss of nuclear p27 staining (P=0.063), without reaching statistical significance. In conclusion, LOI seems not to alter IGF2 gene expression in GH-secreting tumours. Low levels of IGF2 mRNA would be related to aggressive clinical traits, suggesting that IGF2 might counteract somatotropic tumorigenesis.
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 research did not receive any specific grant from any funding agency in the public, commercial or not-for-profit sector