Background: Extracellular signal-regulated kinase (ERK) cascades are key signaling pathways involved in regulation of normal cell proliferation, survival and differentiation. Abberrant regulation of the ERK pathway contributes to tumourigenesis. The ERK signalling cascade partially controls transcription of the cell cycle regulator cyclin D1 and also expression and protein stability of the c-Myc proto-oncogene.
Methods: Western Blotting was used to investigate relative expression of total-ERK1/2, phospho-ERK1/2 (Thr185), total-c-Myc, phospho-c-Myc (Ser 62) and total-cyclin D1 in 16 normal pituitary samples and adenoma groups: PRL-oma (n=6), ACTH-oma (n=6), GH-oma (n=6) and non-functioning pituitary adenomas (NFPAs, n=16). Expression of ERK1, ERK2, cyclin D1 and c-Myc mRNA was assessed by Taqman real-time PCR in 10 normal pituitary samples in comparison to adenoma groups: ACTH-omas (n=5), GH-omas (n=9) and NFPAs (n=10). Data were normalised to β-actin.
Results: The expression of pERK at the protein level was significantly higher in PRL-oma (45±15%; P=0.006), ACTH-oma (141±10%; P<0.0001), GH-oma (45±9%; P<0.0001) and NFPAs (70±6%; P<0.0001) than in normal pituitaries (21±1%). The ratio between normalised pERK and tERK was significantly higher in all analysed groups of pituitary tumours compared to normal pituitary: PRL-oma (108±32%; P=0.006), ACTH-oma (151±43%; P<0.0001), GH-oma (128±54%; P<0.0001) and NFPAs (131±26%; P<0.0001) compared to normals (40±5%). No significant difference in cyclin D1 expression was observed between the groups. Total c-myc protein and phosphorylated c-myc (Ser62) were not significantly different in any of the adenoma groups. No significant difference in mRNA expression of ERK1, ERK2, Cyclin D1 or c-Myc was observed.
Conclusions: Our results suggest that the ERK1/2 pathway is over-activated in pituitary adenomas due to increased phosphorylation rather than increased expression of total ERK1/2. The overactive ERK1/2 signal does not lead to an increase in cyclin D1 or c-Myc, suggesting some form of compensatory down-regulation. These data suggest new targets for the medical therapy of these tumours.