Revealing the Anti-cancer Region within KL1 Subunit of the Hormone Klotho

Background:
Klotho is a 1012 amino acids transmembrane protein, composed of two internal repeats, KL1 and KL2, that can be cleaved, shed and act as a circulating hormone. Klotho regulates several pathways, including fibroblast growth factor 23 (FGF23) and the Wnt-β/catenin. Our group and other labs identified klotho as a potent tumor suppressor in various cancer types, and identified KL1 as the domain responsible for this activity. Yet, the mechanism mediating anti-cancer activity remains unresolved.

Aim:
Reveal the region within KL1 that mediate the anti-cancer activity and reveal the mechanism of action.

Methods:
We used MCF-7, MDA-MB-231, PANC1, MIAPaca-2, HCT116 and HT29 cancer cell lines. Cells were transfected with a series of C and N -terminal KL1 truncated expression vectors. Wnt-β/catenin pathway was studied by monitoring it transcriptional activity and expression of Wnt3A. Tumorigenic activity was studied by colony formation assay.

Results:
Over expression of C-terminal truncated vectors showed that KL340 is the shortest plasmid that retained ability to inhibit colony formation. None of the N-terminal truncated vectors was able to inhibit colony formation. In accordance with these results, only KL1 and KL340 decreased the levels of wnt3a and inhibited Wnt-β/catenin transcriptional activity.

Conclusion:
This study reveals that klotho’s anti-cancer resides within the 340 amino acids N-terminal region. The correlation between the anti-cancer activity and Wnt-β/catenin pathway suggest this pathway plays a role in mediating anti-cancer activity. It is still yet to be determined the precise mechanism KL340 affects this pathway.