Sumoylation of Forkhead L2 by Ubc9 is required for its activity as a transcriptional repressor of the Steroidogenic Acute Regulatory gene

• Published in: Cellular signalling 2009-12, Vol.21 (12), p.1935-1944
• Main Authors: Kuo, Fang-Ting, Bentsi-Barnes, Ikuko K., Barlow, Gillian M., Bae, Jeehyeon, Pisarska, Margareta D.
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Animals; Arginine; Cell Nucleus - metabolism; Cell Nucleus - ultrastructure; CHO Cells; Cricetinae; Cricetulus; Differentiation; Enzymes; Female; Follicles; Forkhead; Forkhead Box Protein L2; Forkhead protein; Forkhead Transcription Factors - analysis; Forkhead Transcription Factors - genetics; Forkhead Transcription Factors - metabolism; FOXL2; Gene families; Gene regulation; Gene silencing; Granulosa cell; Granulosa cells; Granulosa Cells - metabolism; Granulosa Cells - ultrastructure; Hepatocyte nuclear factor 3; Humans; Lysine; Molecular Sequence Data; Mutation; Ovary - cytology; Phosphoproteins - genetics; Phosphoproteins - metabolism; Premature ovarian failure; Promoter Regions, Genetic; Promoters; Repressors; Sequence Alignment; Signal transduction; Small Ubiquitin-Related Modifier Proteins - metabolism; Star protein; SUMO protein; Sumoylation; Transcription factors; Transcription, Genetic; Transcriptional regulation; UBC9; Ubiquitin-Conjugating Enzymes - analysis; Ubiquitin-Conjugating Enzymes - genetics; Ubiquitin-Conjugating Enzymes - metabolism
• ISSN: 0898-6568; 1873-3913
• DOI: 10.1016/j.cellsig.2009.09.001

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.