We investigated the direct effects of the somatostatin analog octreotide on hallmarks of autophagy and of cell viability and metabolic activity in rat pituitary tumor cells (GH1 and GH3 cells). The Western blot analysis of cell lysates suggested that octreotide (100 nM) treatment could induce changes in hallmarks related to autophagy activation (increased LC3-I protein lipidation) and to enhanced autophagic flux (SQSTM1/p62 protein downregulation) in pituitary tumor cells in different experimental conditions which included incubation in Hanks balanced salt solution (HBSS), in Hams F10 medium without serum and in the same medium supplemented with serum. Actually, these effects of octreotide were observed after short treatments (up to 4-h long) whereas they were not seen after 20-h long treatment. The primary antibodies were from Cell Signalling. In the same experimental conditions, we analyzed the MTT reduction activity as an index of cell metabolic activity and cell viability. Our results did not suggest any decrease in redox activity of the cells following to their treatment with octreotide in all the experimental conditions tested. On the other hand, in GH3 cells incubated in HBSS for short time (2-h), the addition of octreotide to HBSS tended to enhance the MTT reduction activity (112%±6% vs vehicle, N=4) and to increase the ATP levels in cell lysates (112%±8% vs vehicle, N=4), as measured by ATPlite kit (PerkinElmer). Finally, an increase of the pyruvate dehydrogenase (PDH) complex activity (PDH Enzyme Activity Microplate Assay Kit, Abcam) in lysates from GH3 cells treated with octreotide for 2-h, was observed compared to control cells (111%±4% vs vehicle, N=3). Actually, this effect was not related to any change in the phosphorylation of the regulatory subunit E1alpha (ser-293 in PDHE1-alpha), as assessed by Western blot (primary antibody from Abcam). In conclusion, we provided evidence that octreotide can affect autophagy in pituitary tumor cells. The observed effects of octreotide were not related to decreased cell viability and metabolic activity. Finally, the induction of autophagy was either short-lived or overshadowed by other factors in the long term and this limit does not help clarifying their real impact on the pharmacological activity of somatostatin analogs.
18 - 21 May 2019
European Society of Endocrinology