Role of Apaf-1 and cathepsin B in pituitary tumor progression

Aims: Apaf-1 (apoptotic protease-activating factor 1), is commonly known as an indicator of apoptosis regulation. It is the core protein of the apoptosome and its dosage is also critical in various cancer types. The aim of our study was to investigate the expression of Apaf-1 and cathepsin B (as caspase-dependent and non-caspase-dependent) effectors of cell death, in order to correlate them with the invasivity of pituitary adenoma. Design:

Immunohistochemical analysis was performed on 30 paraffin-embeded pituitary adenomas: 21 functioning and 9 non-functioning; 22 with local invasiveness, 16 invasive in cavernous sinus; 4 were recidives. The following antibodies were used: Apaf-1– rabbit polyclonal (1:100), cathepsin B – mouse monoclonal NCL-Cath-B (CB131) (1:40), and Ki67– MIB1 (1:50). Apoptosis was measured as apoptotic index by TUNEL method. Results: A positive relation between high proliferation and high apoptotic index in invasive adenomas was revealed. The loss of Apaf-1 expression was observed in most of the invasive adenoma with increased Ki67 proliferative index. In low-grade invasive tumors Apaf-1 was expressed in variable degree with a zonal distribution. Most of the non-invasive adenoma presented positive Apaf-1 reaction, with zonal or diffuse aspect. On the contrary, cathepsin B was commonly expressed with a granular pattern, routinely lying on the plasma membrane, in invasive pituitary tumors. In cells undergoing apoptosis, cathepsin B appeared diffusely re-distributed in the cytosol. A negative correlation between Apaf-1 and invasiveness was noted. On the other hand, a positive correlation between cathepsin-B and invasiveness was recorded. Conclusion: These data demonstrated an inverse correlation between Apaf-1 and cathepsin B expressions. Shifting the balance between cell death mediators might result in changes in tumor behavior.