Opposite association of two PPARG variants with cancer: overrepresentation of H449H in endometrial carcinoma cases and underrepresentation of P12A in renal cell carcinoma cases

Abstract.

Peroxisome proliferator activated receptor γ (PPARγ) is a nuclear hormone receptor that has been shown to regulate differentiation and cell growth. Studies of the differentiative effects of PPARγ agonists on several cancer cell lines led to the hypothesis that dysfunction of PPARγ contributes to tumorigenesis. These functional observations were strengthened by genetic evidence: somatic loss-of-function mutations in PPARG, encoding PPARγ, in sporadic colorectal carcinomas and somatic translocation of PAX8 and PPARG in follicular thyroid carcinoma. Recently overrepresentation of the H449H variant was found in a cohort of American patients with glioblastoma multiforme. The glioblastoma multiforme data suggest that PPARG contributes common, low-penetrance alleles for cancer susceptibility. To test this hypothesis in a broader range of cancers we examined a series of carcinomas of the cervix, endometrium, ovary, prostate, and kidney for germline sequence variation in PPARG. In addition to the two common sequence variants, P12A and H449H, there were five other sequence variants. P12A alleles were underrepresented in renal cell carcinoma patients compared to country-of-origin race-matched controls (3.75% vs. 12.1%, P<0.04). In contrast, the H449H variant was overrepresented in individuals with endometrial carcinoma compared to controls (14.4% vs. 6.25%, P<0.02). These observations lend genetic evidence consistent with our hypothesis that PPARG serves as a common, low-penetrance susceptibility gene for cancers of several types, especially those epidemiologically associated with obesity and fat intake.