Cell surface CD55 traffics to the nucleus leading to cisplatin resistance and stemness by inducing PRC2 and H3K27 trimethylation on chromatin in ovarian cancer.

BACKGROUND: Platinum resistance is the primary cause of poor survival in ovarian cancer (OC) patients. Targeted therapies and biomarkers of chemoresistance are critical for the treatment of OC patients. Our previous studies identified cell surface CD55, a member of the complement regulatory proteins, drives chemoresistance and maintenance of cancer stem cells (CSCs). CSCs are implicated in tumor recurrence and metastasis in multiple cancers. METHODS: Protein localization assays including immunofluorescence and subcellular fractionation were used to identify CD55 at the cell surface and nucleus of cancer cells. Protein half-life determinations were used to compare cell surface and nuclear CD55 stability. CD55 deletion mutants were generated and introduced into cancer cells to identify the nuclear trafficking code, cisplatin sensitivity, and stem cell frequency that were assayed using in vitro and in vivo models. Detection of CD55 binding proteins was analyzed by immunoprecipitation followed by mass spectrometry. Target pathways activated by CD55 were identified by RNA sequencing. RESULTS: CD55 localizes to the nucleus of a subset of OC specimens, ascites from chemoresistant patients, and enriched in chemoresistant OC cells. We determined that nuclear CD55 is glycosylated and derived from the cell surface pool of CD55. Nuclear localization is driven by a trafficking code containing the serine/threonine (S/T) domain of CD55. Nuclear CD55 is necessary for cisplatin resistance, stemness, and cell proliferation in OC cells. CD55 S/T domain is necessary for nuclear entry and inducing chemoresistance to cisplatin in both in vitro and in vivo models. Deletion of the CD55 S/T domain is sufficient to sensitize chemoresistant OC cells to cisplatin. In the nucleus, CD55 binds and attenuates the epigenetic regulator and tumor suppressor ZMYND8 with a parallel increase in H3K27 trimethylation and members of the Polycomb Repressive Complex 2. CONCLUSIONS: For the first time, we show CD55 localizes to the nucleus in OC and promotes CSC and chemoresistance. Our studies identify a therapeutic mechanism for treating platinum resistant ovarian cancer by blocking CD55 nuclear entry.

Mechanistic Insights on Hyperthermic Intraperitoneal Chemotherapy in Ovarian Cancer.

Epithelial ovarian cancer is an aggressive disease of the female reproductive system and a leading cause of cancer death in women. Standard of care includes surgery and platinum-based chemotherapy, yet patients continue to experience a high rate of recurrence and metastasis. Hyperthermic intraperitoneal chemotherapy (HIPEC) treatment in highly selective patients extends overall survival by nearly 12 months. The clinical studies are highly supportive of the use of HIPEC in the treatment of ovarian cancer, though the therapeutic approach is limited to academic medical centers. The mechanism underlying HIPEC benefit remains unknown. The efficacy of HIPEC therapy is impacted by several procedural and patient/tumor factors including the timing of surgery, platinum sensitivity, and molecular profiling such as homologous recombination deficiency. The present review aims to provide insight into the mechanistic benefit of HIPEC treatment with a focus on how hyperthermia activates the immune response, induces DNA damage, impairs DNA damage repair pathways, and has a synergistic effect with chemotherapy, with the ultimate outcome of increasing chemosensitivity. Identifying the points of fragility unmasked by HIPEC may provide the key pathways that could be the basis of new therapeutic strategies for ovarian cancer patients.