Expression of CD 73 (ecto-5 '-nucleotidase) in 165 glioblastomas by immunohistochemistry and electronmicroscopic histochemistry

Background: CD 73 (5'-nucleotidase) is an ectoenzyme. which is expressed on normal and neoplastic glial plasma membranes. The enzyme binds to intracel lular filamentous actin and the extracellular matrix proteins laminin and f ibronectin. CD 73 is a signalling pathway metabolite in the immune response of lymphocytes. The ectoenzyme catalyzes the conversion of purine and pyri midine ribo- and deoxyribo-nucleoside monophosphates (AMP, GMP, IMP) and le ads to elevation of the coresponding nucleosides (adenosine) in the extracl lular space and might therefore modulate neuronal signalling and vascular p erfusion CD 73 has also been called a cellular motility factor. There is an increasing amount of evidence for the modulatory role of PKC-mediated CD 7 3 activity in ischemia, regeneration and repair, glioma cell proliferation and a possible invasion promoting feature of the ectoenzyme. The aim of the present study was to investigate the expression patterns of CD 73 together with the labelling of PKC and EGFR. The latter is known as a marker fbr pr imary glioblastomas. Patients and methods: We investigated the expression o f CD 73 in 165 glioblastoma specimens together with the expression patterns of PKC and EGFR by immunocytochemistry on cryosections with a 4-step gradi ng evaluation by two independent observers. CD 73 was further investigated morphologically by electron-microscopic histochemistry in cell cultures of glioblastoma specimens. Results: With these methods it was possible to demo nstrate a dense labelling pattern of glioblastoma specimens with anti-CD 73 . 95.7 % of the glioblastomas were identified with staining products, 63% w ith labelling grades 2 and 3. The dense staining of the endo-plasmatic reti culum, vesicles, caveolar structures and glial membranes was demonstrated b y electron-microscopic histochemistry. Some free enzymatic activity was loc ated bound to the ECM components. We observed a significant coexpressions o f CD 73 with PKC (p=0.001) and CD 73 with EGFR (p=0.022), which is a prospe ctive marker for a high rate of early recurrency. Conclusions: The CD 73 ac tivity was densely distributed on the membranes of glioblastoma cells in vi vo and in cell cultures. The electron-microscopic histochemical studies cou ld demonstrate enzymatic activity at the cell membranes and in vesicular st ructures and caveolae. Free staining deposits located on ECM components may result in a migration- and infiltration promoting activity. The CD 73 expr ession could be correlated with the expression grades of PKC and EGFR. The latter has been identified as a prognostic factor which is expressed mainly on primary glioblastomas. PKC is a known tumour metabolite in several prol iferation promoting pathways of EGF receptor signalling.