Sumoylation of forkhead L2 by Ubc9 is required for its activity as a transcriptional repressor of the Steroidogenic Acute Regulatory gene.
Forkhead L2 (FOXL2) is a member of the forkhead/hepatocyte nuclear factor 3 (FKH/HNF3) gene family of transcription factors and acts as a transcriptional repressor of the Steroidogenic Acute Regulatory (StAR) gene, a marker of granulosa cell differentiation. FOXL2 may play a role in ovarian follicle maturation and prevent premature follicle depletion leading to premature ovarian failure. In this study, we found that FOXL2 interacts with Ubc9, an E2-conjugating enzyme that mediates sumoylation, a key mechanism in transcriptional regulation. FOXL2 and Ubc9 are co-expressed in granulosa cells of small and medium ovarian follicles. FOXL2 is sumoylated by Ubc9, and this Ubc9-mediated sumoylation is essential to the transcriptional activity of FOXL2 on the StAR promoter. As FOXL2 is endogenous to granulosa cells, we generated a stable cell line expressing FOXL2 and found that activity of the StAR promoter in this cell line is greatly decreased in the presence of Ubc9. The sumoylation site was identified at lysine 25 of FOXL2. Mutation of lysine 25 to arginine leads to loss of transcriptional repressor activity of FOXL2. Taken together, we propose that Ubc9-mediated sumoylation at lysine 25 of FOXL2 is required for transcriptional repression of the StAR gene and may be responsible for controlling the development of ovarian follicles.
Kuo
Fang-Ting
FT
Center for Fertility and Reproductive Medicine, Division of REI, Department of Ob/Gyn, Cedars-Sinai Medical Center, Los Angeles, CA 90048, United States.
Bentsi-Barnes
Ikuko K
IK
Barlow
Gillian M
GM
Bae
Jeehyeon
J
Pisarska
Margareta D
MD
D000595:Amino Acid Sequence; D000818:Animals; D016466:CHO Cells; D002467:Cell Nucleus / Q000378:metabolism / Q000648:ultrastructure; D006224:Cricetinae; D003412:Cricetulus; D005260:Female; D000074842:Forkhead Box Protein L2; D051858:Forkhead Transcription Factors / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D006107:Granulosa Cells / Q000378:metabolism* / Q000648:ultrastructure; D006801:Humans; D008969:Molecular Sequence Data; D010053:Ovary / Q000166:cytology; D010750:Phosphoproteins / Q000235:genetics* / Q000378:metabolism; D011401:Promoter Regions, Genetic; D016415:Sequence Alignment; D025841:Small Ubiquitin-Related Modifier Proteins / Q000378:metabolism*; D014158:Transcription, Genetic; D044763:Ubiquitin-Conjugating Enzymes / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D000098682:Steroidogenic Acute Regulatory Protein; D000098843:Ubiquitin-Conjugating Enzyme UBC9
C421604:FOXL2 protein, human; D000074842:Forkhead Box Protein L2; D051858:Forkhead Transcription Factors; D010750:Phosphoproteins; D025841:Small Ubiquitin-Related Modifier Proteins; D000098682:Steroidogenic Acute Regulatory Protein; D044763:Ubiquitin-Conjugating Enzymes; D000098843:Ubiquitin-Conjugating Enzyme UBC9