LY294002, INHIBITOR OF PI3K, REGULATES SUPERFICIAL EXPRESSION OF NGF RECEPTORS IN HUMAN CANCER CELL LINES

Several experimental data have shown a relevant involvement of Nerve Growth Factor (NGF) in neoplastic proliferation and survival. NGF acts through two receptors: high affinity TrKA receptor (connected to proliferation) and low-affinity p75 receptor (connected to cell survival and apoptosis). The reciprocal interactions between their transduction pathways determine the final biological role of NGF. To better analyze these interactions, we have used LY294002, a specific inhibitor of PI3K, an intermediate step for TrKA transduction. Furthermore, studies reported that inhibition of PI3K induces activation of BAD, an intermediate step for p75. The aim of our study was to investigate the biological effects of this inhibitor by a cytofluorimetric quantification of the superficial levels of TrKA and p75 in some human cancer cell lines: HTB114, HTB82 (muscle sarcomas) and PC3 (prostatic adenocarcinoma), in basal conditions and following treatment with LY294002. Cytofluorimetric analysis shows that our cellular populations can be divided in three subsets: a) double negative for TrKA and p75; b) positive only for TrKA; c) double positive for TrKA and p75. At basal conditions in the latter subset we found a prevalence of TrKA on p75, with a TrKA/p75 ratio of about 3:1. In this group the treatment with LY294002 (50M) did not influence TrKA levels, but it induced an important increase in p75 levels, changing the TrKA/p75 ratio from 3:1 to 1:2. This treatment did not effect the double negative TrKA/p75 and the single TrKA positive subsets. This relevant modification in TrKA/p75 ratio following LY294002 treatment was associated to a decrease in the proliferation and an increase in the apoptosis. In conclusion, our study for the first time shows that an interaction on TrKA pathway is able to influence the superficial expression of p75 that, in turn, induces an increase in apoptosis. This effect has a preclinical importance, suggesting the relevance of TrKA/p75 targeting in oncology.