Abstract 3557: The aging suppressor hormone Klotho inhibits ovarian cancer cell proliferation by down-regulation of the estrogen receptor.
Authors: Lojkin Irina , Schwartzman Omer , Rubinek Tami , Wolf Ido 
Published: August 2014

Klotho is a 1012 amino acid (aa) long transmembranal protein, which can be cleaved, shed and act as a circulating hormone. Klotho contains two regions named KL1 and KL2, each about 500aa long. Klotho deficient mice present a syndrome of early aging, while overexpression of klotho extends lifespan. Klotho is an essential co-factor for the activity of FGF23 and thus serves as a major regulator of phosphate homeostasis. Klotho is also a potent inhibitor of the insulin growth factor (IGF)-1 pathway. We have identified klotho as a tumor suppressor in breast and pancreatic cancer. Recently, klotho activity as a tumor suppressor was observed also in melanoma and in cervix, lung, colon and gastric cancers. As klotho is expressed in the normal ovary, we undertook to study the expression and activity of klotho in ovarian cancer.

We first analyzed klotho expression, using quantitative RT-PCR and Western blotting, in 18 ovarian cancer cell lines and noted high levels of klotho mRNA and protein in only three lines. We next used immunohistochemistry analysis to study klotho expression in a tissue array containing 277 primary and recurrent ovarian, fallopian and primary peritoneal cancers, along with 22 normal and benign tumor samples. While high klotho expression was noted in all normal samples, reduced expression was noted in 30% of the tumors. Reduced expression was not associated with histology, tumor location or stage. Overexpression of either full length klotho or KL1 reduced clonal growth of OvCa432, SKOV3 and ES2 ovarian cancer cell lines by 80%, 60%, and 0%, respectively.

Klotho inhibits the IGF-1 pathway in pancreatic and breast cancer cells. As the IGF-1 pathway plays an important role in ovarian cancer development, we studied the effect of klotho on this pathway in ovarian cancer cell lines. Klotho inhibited IGF-1-mediated AKT activation, and to a lesser degree ERK1/2 phosphorylation, in SKOV3 and OvCa432 cells. Interestingly, ES2 cells did not respond to IGF-1.

Estrogen receptor (ER)α and progesterone receptor (PR) have a significant role in ovarian cancer development. ERα is expressed in a majority of ovarian cancers, while PR is less abundant, and its expression is a marker for better prognosis. We found that klotho reduces ERα expression and activity in SKOV3 and OvCa432. Interestingly, klotho elevated PR-A isoform expression in these cell lines.

In conclusion, unlike in breast and pancreas cancer, where klotho was identified as a potent tumor suppressor in most cancer subtypes, and the IGF-1 pathway was inhibited in a wide array of cell lines, in the ovary, klotho plays a role in a smaller subset of tumors. The characteristics of this group have not been identified yet. However, it appears that ERα inhibition and PR-A up-regulation may play a role in mediating klotho activities in this subset.

Citation Format: Irina Lojkin, Omer Schwartzman, Tami Rubinek, Ido Wolf. The aging suppressor hormone Klotho inhibits ovarian cancer cell proliferation by down-regulation of the estrogen receptor. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3557. doi:10.1158/1538-7445.AM2013-3557