Immunohistochemical analysis of the Akt/mTOR/4E-BP1 signalling pathway in canine haemangiomas and haemangiosarcomas

The specific signalling pathways that are deregulated in canine endothelial tumours have not yet fully elucidated. Therefore, the aim of the present study was to examine activation of the Akt/mammalian target of rapamycin (mTOR)/eukaryotic initiation factor 4E-binding protein 1 (4E-BP1) signalling pathway in spontaneously arising canine haemangiomas (HAs) and haemangiosarcomas (HSAs) in order to identify novel molecular targets for treatment. Surgically-resected samples of HA (n = 27), HSA (n = 37), granulation tissue (n = 4) and normal skin (n = 4) were investigated by immunohistochemistry. Approximately 80% of the HSA samples had moderate to intense expression of phosphorylated Akt at Ser473 (p-Akt Ser473), p-Akt Thr308, p-4E-BP1 Thr37/46 and eukaryotic initiation factor 4E, which was significantly higher than in the HAs and was similar to the expression in activated endothelial cells (ECs). Although p-mTOR complex1 (p-mTORC1) Ser2448 was expressed by most of the activated ECs, only 35% of the HSA samples had weak to moderate expression. Because mTORC2 and phosphorylates Akt Ser473 was activated in HSA samples, the present findings suggest that the mTORC2/Akt/4E-BP1 pathway, regulated independently of mTORC1, may be important for targeting therapy in canine HSAs.