Reproductive Hormones and Their Receptors May Affect Lung Cancer

Abstract

Background/aims: In contrast to men, women have experienced a rapid increase in lung cancer mortality. Numerous studies have found that the sex differences in lung cancer are due to reproductive hormones. Experiments in female mice with and without ovariectomy were performed to explore the possible mechanism by which sex hormones (and their receptors) influence lung cancer.

Methods: Twenty-four female C57BL/6 mice aged 56-62 days were randomly divided into the ovariectomized group and the control group. In the ovariectomized group, the bilateral ovaries were removed via the dorsal approach, while the control group underwent a sham operation with bilateral ovarian fat resection at the same sites. After 3 weeks of recovery, Lewis lung cancer cells were transplanted into these mice by subcutaneous inoculation of a tumour cell suspension to establish the ovariectomized lung cancer model. Beginning on the 6th day after subcutaneous inoculation, mouse weight and transplanted tumour volume were measured every 3 days. After 3 weeks, all the mice were killed by cervical dislocation, and we measured the tumour weight. Mouse serum and tumour tissues were removed. Then, the serum levels of E2 (oestradiol) and T (testosterone) were detected by ELISA; the protein expression levels of AR (androgen receptor), ERα (oestrogen receptor α) and ERβ (oestrogen receptor β) were detected by Western Blot and IHC (immunohistochemistry); and the mRNA expression levels of AR, ERα and ERβ were detected by qRT-PCR (quantitative real-time polymerase chain reaction) in the ovariectomized and control groups.

Results: Compared with the control group, both mouse weight and transplanted tumour volume increased rapidly in the ovariectomized group, and the transplanted tumour weight was significantly heavier in the ovariectomized group (1.83±0.40 and 3.13±0.43, P<0.05). E2 and T serum levels decreased exponentially in the ovariectomized group, while the E2/T ratio increased compared with the control group (E2: 55.88±11.45 and 78.21±9.37; T: 0.82±0.14 and 1.46±0.16; ratio: 69.62±14.43±29.81 and 52.22±5.42; all P<0.05). The Western blot and IHC results indicated that AR, ERα and ERβ protein expression levels were obviously higher in transplanted tumour and lung tissues from the ovariectomized group, with particular increases in ERβ in transplanted tumour tissue and in ERα in lung tissue. The PCR results also showed markedly higher mRNA expression levels of AR, ERα and ERβ in the ovariectomized group, and in particular, ERβ in transplanted tumour tissue and ERα in lung tissue were significantly increased in the ovariectomized group.

Conclusion: Ovariectomy decreased E2 and T serum levels and increased the E2/T ratio in mice, and this imbalance in the internal environment promoted the growth of transplanted tumours. Sex hormone disorder not only promoted transplanted tumour growth but also significantly reduced the protein and mRNA expression levels of sex hormone receptors. The metabolism of E2 and T may affect the growth, proliferation and metabolism of lung cancer cells, and the mechanism by which sex hormones and their receptors influence lung cancer is worthy of further research.

Keywords: Lung cancer; Oestradiol; Ovariectomized mice; Testosterone.