title: Mutant Forkhead L2 (FOXL2) proteins associated with premature ovarian failure (POF) dimerize with wild-type FOXL2, leading to altered regulation of genes associated with granulosa cell differentiation.
abstract: Premature ovarian failure in the autosomal dominant disorder blepharophimosis-ptosis-epicanthus inversus is due to mutations in the gene encoding Forkhead L2 (FOXL2), producing putative truncated proteins. We previously demonstrated that FOXL2 is a transcriptional repressor of the steroidogenic acute regulatory (StAR), P450SCC (CYP11A), P450aromatase (CYP19), and cyclin D2 (CCND2) genes, markers of ovarian follicle proliferation and differentiation. Furthermore, we found that mutations of FOXL2 may regulate wild-type FOXL2, leading to loss of transcriptional repression of CYP19, similar to StAR. However, the regulatory mechanisms underlying these premature ovarian failure-associated mutations remain largely unknown. Therefore, we examined the effects of a FOXL2 mutant protein on the transcriptional repression of the CYP19 promoter by the full-length protein. We found that mutant FOXL2 exerts a dominant-negative effect on the repression of CYP19 by wild-type FOXL2. Both wild-type and mutant FOXL2 and can form homo- and heterodimers. We identified a minimal -57-bp human CYP19 promoter containing two potential FOXL2-binding regions and found that both wild-type and mutant FOXL2 can bind to either of these regions. Mutational analysis revealed that either site is sufficient for transcriptional repression by wild-type FOXL2, and the dominant-negative effect of mutant FOXL2, but these are eliminated when both sites are mutated. These findings confirm that mutant FOXL2 exerts a dominant-negative effect on wild-type FOXL2's activity as a transcriptional repressor of key genes in ovarian follicle differentiation and suggest that this is likely due to heterodimer formation and possibly also competition for DNA binding.
authors.affiliation: Division of Reproductive Endocrinology and Infertility, Department of Obstetrics/Gynecology, Cedars-Sinai Medical Center, 8635 West Third Street, Los Angeles, California 90048, USA.
authors.forename: Fang-Ting
authors.initials: FT
authors.lastname: Kuo
authors.forename: Ikuko K
authors.initials: IK
authors.lastname: Bentsi-Barnes
authors.forename: Gillian M
authors.initials: GM
authors.lastname: Barlow
authors.forename: Margareta D
authors.initials: MD
authors.lastname: Pisarska
mesh_terms: D001141:Aromatase / Q000235:genetics; D001665:Binding Sites; D002454:Cell Differentiation; D005260:Female; D000074842:Forkhead Box Protein L2; D051858:Forkhead Transcription Factors / Q000737:chemistry* / Q000502:physiology*; D005786:Gene Expression Regulation; D006107:Granulosa Cells / Q000166:cytology*; D006801:Humans; D050505:Mutant Proteins / Q000502:physiology; D016649:Primary Ovarian Insufficiency / Q000209:etiology* / Q000235:genetics; D011401:Promoter Regions, Genetic; D055503:Protein Multimerization; D012097:Repressor Proteins / Q000502:physiology*
chemical_list: C421604:FOXL2 protein, human; D000074842:Forkhead Box Protein L2; D051858:Forkhead Transcription Factors; D050505:Mutant Proteins; D012097:Repressor Proteins; D001141:Aromatase