Gi protein-mediated translocation of serine/threonine phosphatase to the plasma membrane and apoptosis of ovarian cancer cell in response to gonadotropin-releasing hormone antagonist cetrorelix

Abstract

Serine/threonine protein phosphatase 2A (PP2A), a crucial enzyme in apoptosis control, has been demonstrated within the plasma membrane as well as in the soluble fraction. This study aimed to examine hormonal translocation of PP2A to the plasma membrane in gonadotropin-releasing hormone (GnRH)-responsive ovarian cancer cells. Apoptosis of ovarian cancer cell lines Caov-3 and SK-Ov-3 was quantified by nuclear morphology after staining with Hoechst 33342 dye. PP2A protein and activity in plasma membrane were assessed by immunohistochemical staining with PP2A-specific antibodies and by the measurement of the dephosphorylation of phosphopeptide highly selective for the PP2A, respectively. Incubation for 48 h with a GnRH antagonist cetrorelix caused parallel increases in the percentage of cells undergoing apoptosis and the membrane-associated PP2A activity; half-maximal effects occurred with 5 nmol/l cetrorelix. PP2A protein was also localised to the plasma membrane when the cell lines were exposed to cetrorelix. Pretreatment of the cells with pertussis toxin, but not cholera toxin, completely inhibited cetrorelix-stimulated apoptotic cell death and PP2A redistribution. These findings demonstrate that translocation of PP2A to plasma membrane is closely coupled to the onset of apoptosis in ovarian cancer cells exposed to GnRH antagonist. These GnRH-induced cellular events may be mediated through pertussis toxin-sensitive Gi protein-linked GnRH receptor.

Gonadotropin-Releasing Hormone Type II Antagonists Induce Apoptotic Cell Death in Human Endometrial and Ovarian Cancer Cells In vitro and In vivo

“…The GnRH-II antagonist-induced increase of caspase-3 activity was reduced by pertussis toxin, indicating that it is mediated at least in part by G protein ai. Comparable data were obtained by Imai et al (26). They have shown that GnRH-I antagonist cetrorelix-induced apoptotic cell death of human ovarian cancer cells was mediated through pertussis toxin-sensitive Gi protein-linked GnRH receptor.…”

The regulatory roles of phosphatases in cancer

“…Expression of CIP2A, studied in 562 serous ovarian cancer patients by IHC, showed strong cytoplasmic staining in 40% of the samples and was associated with high grade, advanced stage and poor outcome (195).On the other hand, inhibition of PP2A was essential for the apoptosis induced by doxorubicin (196) and translocation of PP2A to plasma membrane was essential for gonadotropin-releasing hormone (GnRH) antagonist, cetrorelix induced apoptosis in GnRH responsive ovarian cancer cells (197).…”

Gonadotropin‐releasing hormone and ovarian cancer: a functional and mechanistic overview

“…An equimolar concentration of the GnRH‐I antagonist cetrorelix induced apoptosis by upregulating p53 and p21 protein levels, whereas concentrations as low as 10 −9 m resulted in antiproliferative effects [46]. Recently, apoptosis was shown to be induced by a low concentration of cetrorelix in ovarian cancers [50]. We also observed DNA fragmentation after prolonged (6 days) low‐dose GnRH‐I agonist treatment [36].…”