Cellular prion protein mediates early apoptotic proteome alternation and phospho-modification in human neuroblastoma cells

Anti-apoptotic properties of physiological and elevated levels of the cellular prion protein (PrP(c)) under stress conditions are well documented. Yet, detrimental effects of elevated PrP(c) levels under stress conditions, such as exposure to staurosporine (STS) have also been described. In the present study, we focused on discerning early apoptotic STS-induced proteome and phospho-proteome changes in SH-SY5Y human neuroblastoma cells stably transfected either with an empty or PRNP-containing vector, expressing physiological or supraphysiological levels of PrP(c), respectively. PrP(c)-overexpression per se appears to stress the cells under STS-free conditions as indicated by diminished cell viability of PrP(c)-overexpressing versus control cells. However, PrP(c)-overexpression becomes advantageous following exposure to STS. Thus, only a short exposure (2 h) to 1 μM STS results in lower survival rates and significantly higher caspase-3 activity in control versus PrP(c)-overexpressing cells. Hence, by exposing both experimental groups to the same apoptotic conditions we were able to induce apoptosis in control, but not in PrP(c)-overexpressing cells (as assessed by caspase-3 activity), which allowed for filtering out proteins possibly contributing to protection against STS-induced apoptosis in PrP(c)-overexpressing cells. Among other proteins regulated by different PrP(c) levels following exposure to STS, those involved in maintenance of cytoskeleton integrity caught our attention. In particular, the finding that elevated PrP(c) levels significantly reduce profilin-1 (PFN-1) expression. PFN-1 is known to facilitate STS-induced apoptosis. Silencing of PFN-1 expression by siRNA significantly increased viability of PrP(c)-overexpressing versus control cells, under STS treatment. In addition, PrP(c)-overexpressing cells depleted of PFN-1 exhibited increased viability versus PrP(c)-overexpressing cells with preserved PFN-1 expression, both subjected to STS. Concomitant increase in caspase-3 activity was observed in control versus PrP(c)-overexpressing cells after treatment with siRNA- PFN-1 and STS. We suggest that reduction of PFN-1 expression by elevated levels of PrP(c) may contribute to protective effects PrP(c)-overexpressing SH-SY5Y cells confer against STS-induced apoptosis.