Autophagy in ovarian cancer development and response to SHetA2 therapy.

摘要

SHetA2 is a small molecule flexible heteroarotinoid (Flex-Het) that induces apoptosis in cancer cells, but not healthy cells. This study focused on understanding how autophagy modulates sensitivity after SHetA2 treatment, identifying the molecular target of SHetA2, and determining if there is any association between autophagy-related proteins or HSPA family proteins with ovarian cancer progression in clinical specimens. In vitro tissue culture studies demonstrated that induction of autophagy correlated with decreased SHetA2 sensitivity in cancer cells. Electron microscopy demonstrated SHetA2 induction of double-membraned autophagic vesicles in the human ovarian cancer cell lines but not in healthy cells. Western blot and fluorescence microscopy demonstrated that SHetA2 resistance correlated with relative increasing amounts of autophagy. Inhibition of autophagy only affected three out of four cancer cell lines, indicating variable contributions to cell survival by autophagy in cancer. Similarly, induction of autophagy prior to SHetA2 treatment showed significant protection in one of the cancer cell lines. Mitochondrial damage was detected immediately after SHetA2 treatment and selective removal of mitochondria, called mitophagy, occurred within a few hours of SHetA2 treatment. Mortalin/HSPA9 function was inhibited in both cancer cell lines suggesting mortalin/HSPA9 is a functional target of SHetA2 and may contribute to the mechanism of SHetA2-mediated cell death. Immunohistochemical staining of a human ovarian cancer progression tissue microarray (TMA) was used to demonstrate a correlation between autophagy-related and HSPA family proteins with cancer severity. Although reduced basal levels of autophagy and increased basal levels of apoptosis correlated with ovarian cancer progression, inducible autophagy interferes with SHetA2-apoptosis in a cancer cell line-dependent manner, and not in healthy cells, suggesting that addition of an autophagy inhibitor could enhance SHetA2 therapy in a subset of ovarian cancer patients. These results provide a cell line dependent, rather than a universal, role for autophagy and other stress-related cellular responses to SHetA2 and provide further insight into how specific stress response proteins may be used to identify and treat different types and stages of cancer.