HGF/c-met system targeting PI3K/AKT and STAT3/phosphorylated-STAT3 pathways in pituitary adenomas: an immunohistochemical characterization in view of targeted therapies

The ligand/receptor hepatocyte growth factor (HGF)/c-met signaling system promotes cellular growth and angiogenesis through PI3K/phosphor-Akt and STAT3/phosphor-STAT3 downstream effectors. In this study, we have evaluated the expression of molecules of the HGF/c-met pathway in pituitary adenomas (PA). The expression of HGF, c-met, PI3K (p85αsubunit) pAkt, STAT3, and pSTAT3 was analyzed by immunohistochemistry in an archival series of 30 PA (12 non-functioning and 18 functioning; 25 macroadenomas and 5 microadenomas). PAs expressed all six proteins in tumor epithelial cells. The proportion of c-met^+ve cells was greater than HGF^+ve cells (49 ± 19 vs 34 ± 17 %, P < 0.01), the pAkt^+ve cells greater than PI3K^+ve cells (39 ± 16.0 vs 1.3 ± 0.5 %, P < 0.001), and the STAT3^+ve cells greater than active pSTAT3^+ve cells (14 ± 8 vs 7 ± 6 %, P < 0.01). Furthermore, endothelial Akt immunostaining was detected on the vascular surface area of 17 PAs, in macroadenomas more frequently than in microadenomas (82 vs 18 %). The percentage of immunostained endothelial cells was greater in macro than in microadenomas (19 ± 7 and 7 ± 3 %; P < 0.05). In conclusion, HGF and c-met are widely expressed in PA, and correlate with pAkt expression. These data, together with the finding of pAkt immunostaining on microvascular areas related to tumor size, suggest a major role of the pAKT signaling in tumor growth and angiogenesis. There might be practical implications for the targeted therapy of PA.