Involvement of Sox-4 in the cytochrome c-dependent AIF-independent apoptotic pathway in HeLa cells induced by Δ¹²-prostaglandin J₂

Abstract

Δ¹²-Prostaglandin (PG) J₂ is known to elicit an anti-neoplastic effects via apoptosis induction. Previous study showed Δ¹²-PGJ₂-induced apoptosis utilized caspase cascade through cytochrome c-dependent pathways in HeLa cells. In this study, the cellular mechanism of Δ¹²-PGJ₂- induced apoptosis in HeLa cells, specifically, the role of two mitochondrial factors; bcl-2 and apoptosis-inducing factor (AIF) was investigated. Bcl-2 attenuated Δ¹²-PGJ₂-induced caspase activation, loss of mitochondrial transmembrane potential (Δ ψ m), nuclear fragmentation, DNA laddering, and growth curve inhibition for approximately 24 h, but not for longer time. AIF was not released from mitochondria, even if the Δ ψ m was dissipated. One of the earliest events observed in Δ¹²-PGJ₂-induced apoptotic events was dissipation of Δ ψ m, the process known to be inhibited by bcl-2. Pre-treatment of z-VAD- fmk, the pan-caspase inhibitor, resulted in the attenuation of Δ ψ m depolarization in Δ¹²-PGJ₂- induced apoptosis. Up-regulation of Sox-4 protein by Δ¹²-PGJ₂ was observed in HeLa and bcl-2 overexpressing HeLa B4 cell lines. Bcl-2 overexpression did not attenuate the expression of Sox-4 and its expression coincided with other apoptotic events. These results suggest that Δ¹²-PGJ₂ induced Sox-4 expression may activate another upstream caspases excluding the caspase 9-caspase 3 cascade of mitochondrial pathway. These and previous findings together suggest that Δ¹²-PGJ₂-induced apoptosis in HeLa cells is caspase-dependent, AIF-independent events which may be affected by Sox-4 protein expression up-regulated by Δ¹²-PGJ₂.