Sinulariolide, an active compound isolated from the cultured soft coral Sinularia
flexibilis, has potent anti-microbial and anti-tumorigenesis effects towards melanoma
and bladder cancer cells. In this study, we investigated the effects of sinulariolide on
hepatocellular carcinoma (HCC) cell growth and protein expression. Sinulariolide
suppressed the proliferation and colony formation of HCC HA22T cells in a
dose-dependent manner and induced both early and late apoptosis according to flow
cytometry, Annexin V/PI stain and TUNEL/DAPI stain analyses. A mechanistic analysis
demonstrated that sinulariolide-induced apoptosis was activated through a
mitochondria-related pathway, showing up-regulation of Bax, Bad and AIF, and downregulation
of Bcl-2, Bcl-xL, MCl-1 and p-Bad. Sinulariolide treatment led to loss of the
mitochondrial membrane potential, release of mitochondrial cytochrome c to the cytosol,
and activation of both caspase-9 and caspase-3. Sinulariolide-induced apoptosis was
significantly blocked by the caspase inhibitors Z-VAD-FMK and Z-DEVD-FMK. The
increased expression of cleaved PARP also suggested that caspase-independent apoptotic
pathway was involved. In the western blotting; the elevation of ER chaperones GRP78;
GRP94; and CALR; as well as up-regulations of PERK/eIF2α/ATF4/CHOP; and diminished
cell death with pre-treatment of eIF2α phosphatase inhibitor; salubrinal; implicated the
involvement of ER stress-mediated PERK/eIF2α/ATF4/CHOP apoptotic pathway following
sinulariolide treatment in hepatoma cells. The current study suggested sinulariolide-induced
hepatoma cell cytotoxicity involved multiple apoptotic signal pathways. This may implicate
that sinulariolide is a potential compound for the treatment of hepatocellular carcinoma.
