Tropomyosin-related kinase B and brain-derived neurotrophic factor in ovarian cancer

Abstract

Introduction: Ovarian epithelial tumors are common tumours in women and contribute to the highest mortality among all gynecological cancers. Studies have been carried out on drugs targeting at different signaling pathways during the progression of cancers especially those activated by the growth factors. Brain-derived neurotrophic factor (BDNF) belongs to the neurotrophin family which comprises a group of related polypeptide growth factor. It preferentially binds and activates Tropomyosin-related kinase B(TrkB). There are three forms of TrkB in human: a full-length form (TrkB-fl)and two truncated isoforms (TrkB-Shc and TrkB-T1). The TrkB-fl contains a cytoplasmic kinase domain that can trigger downstream signals while the other two isoforms lack the kinase activity. It has been shown that activation of TrkB by BDNF promotes cell survival and invasion in some cancers. However, their role in ovarian cancer has not been fully understood.

Aim: We planned to explore the role of trkB in ovarian cancer by studying its differential expression at different stages of tumor progression in ovarian epithelial tumors and correlate it with clinicopathological parameters as well as to investigate the in vitro effect of the TrkB-BDNF pathway on the ovarian cancer cell growth.

Method: Immunohistochemistry was carried out on the archival paraffin sections of ovarian tumors including 57 carcinomas, 17 borderline tumors and 4 cystadenomas.

The mRNA and protein expression levels of TrkB in three "immortalized"human ovarian surface epithelium (OSE) cell lines and five ovarian carcinoma cell lines were analyzed by quantitative real time PCR and Western Blotting using an antibody specific to the cytoplasmic terminus of TrkB-fl respectively. To study the effect of BDNF stimulation on cell growth, different doses of BDNF was administered to a TrkB-expressing ovarian cancer cell line, OVCAR420, followed by cell proliferation assessment by MTT assay.

Result: By immunohistochemistry, there was no TrkB expression in benign cystadenomas. Significantly higher TrkB expression was found in ovarian carcinomas when compared with borderline tumor (p=0.02). It was discovered that TrkB was predominantly expressed in the cytoplasm. Higher TrkB mRNA and protein expression was further confirmed in ovarian carcinoma cell lines when compared with normal ovarian epithelium cell lines. The in vitro study showed that exogenous BDNF could stimulate the growth of OVCAR420 after a 48-hour culture with BDNFat the doses of 50 or 100 ng/mL.

Conclusion: The higher TrkB expression in borderline tumors and carcinoma compared to the cystadenoma implicated that TrkB may play a crucial role in ovarian carcinogenesis. The proliferation-stimulating effect of BDNF on the cancer cell line showed that the TrkB-BDNF pathway may be important regulators for the progression of ovarian cancer, with potential impacts on the development of targeted anticancer therapies.