Expression of FKHR, FKHRL1, and AFX genes in the rodent ovary: evidence for regulation by IGF-I, estrogen, and the gonadotropins

Mol Endocrinol. 2002 Mar;16(3):580-99. doi: 10.1210/mend.16.3.0806.

Abstract

Follicular development is dependent on both intraovarian growth regulatory factors, such as IGF-I and estrogen, as well as the pituitary gonadotropins, FSH and LH. Recently, we have shown that FSH impacts the IGF-I pathway via stimulation of the PI3K cascade leading to phosphorylation of protein kinase B (PKB)/Akt and the PKB-related kinase, Sgk. This study was undertaken to determine if during ovarian follicular development FSH regulates putative targets of PKB and Sgk, namely specific Forkhead transcription factor family members. Using in vivo and in vitro mouse and rat models, we show 1) that FKHR [Forkhead homolog of rhabdomysarcoma = Forkhead box binding protein (Foxo1), FKHRL1 (Forkhead-like protein-1 = Foxo3), and AFX (a Forkhead transcription factor = Foxo4); all defined according to the Human and Mouse Gene Nomenclature Committee) are expressed in the rodent ovary and 2) that FSH regulates transcription of the FKHR gene as well as phosphorylation of FKHR protein. Specifically, FSH/PMSG (primarily via E2) enhance expression of the FKHR gene in granulosa cells of developing follicles. Furthermore, E2 enhances expression of other IGF-I pathway components (IGF-1Rbeta and Glut-1), and IGF-I enhances expression of ERbeta, indicating that these two hormones comprise an autocrine regulatory network within growing follicles. In contrast, FSH and LH/human CG (via cAMP, PKA, and PI3K pathways) terminate FKHR expression as granulosa cells differentiate to luteal cells. In naïve granulosa cells, both FSH and IGF-I stimulate rapid phosphorylation of FKHR at multiple sites causing its redistribution from the nucleus to the cytoplasm in a PI3K-dependent manner. However, the effects of FSH and IGF-I differ markedly in differentiated granulosa cells in which FSH (but not IGF-I) induces Sgk and enhances phosphorylation of FKHR, PKB, and Sgk. The elevated expression of FKHR in granulosa cells of growing follicles indicates that FKHR may be linked to the proliferation of granulosa cells and that its phosphorylation by FSH, IGF-I, and other factors may impact its functional activity in this process. Thus, as a target of FSH (cAMP), E2 and IGF-I signaling in granulosa cells, FKHR likely coordinates numerous cell survival mechanisms.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Blotting, Western
  • Cell Culture Techniques
  • Cell Cycle Proteins
  • Cell Nucleus / metabolism
  • Chorionic Gonadotropin / pharmacology
  • Corpus Luteum / chemistry
  • Cytoplasm / metabolism
  • DNA-Binding Proteins / genetics*
  • Estradiol / pharmacology
  • Estrogen Receptor beta
  • Female
  • Follicle Stimulating Hormone / pharmacology
  • Forkhead Box Protein O1
  • Forkhead Box Protein O3
  • Forkhead Transcription Factors
  • Gene Expression Regulation / drug effects*
  • Glucose Transporter Type 1
  • Gonadotropins, Equine / pharmacology
  • Granulosa Cells / chemistry
  • In Situ Hybridization
  • Insulin-Like Growth Factor I / genetics
  • Insulin-Like Growth Factor I / pharmacology
  • Luteinizing Hormone / pharmacology
  • Male
  • Mice
  • Mice, Inbred C57BL
  • Monosaccharide Transport Proteins / genetics
  • Nerve Tissue Proteins*
  • Ovarian Follicle / chemistry
  • Ovary / metabolism*
  • Phosphorylation
  • Protein-Serine-Threonine Kinases*
  • Proto-Oncogene Proteins / metabolism
  • Proto-Oncogene Proteins c-akt
  • RNA, Messenger / analysis
  • RNA, Messenger / metabolism
  • Rats
  • Rats, Sprague-Dawley
  • Receptors, Estrogen / genetics
  • Reverse Transcriptase Polymerase Chain Reaction
  • Time Factors
  • Transcription Factors / genetics*

Substances

  • Cell Cycle Proteins
  • Chorionic Gonadotropin
  • DNA-Binding Proteins
  • Estrogen Receptor beta
  • FOXO3 protein, rat
  • FOXO4 protein, human
  • Forkhead Box Protein O1
  • Forkhead Box Protein O3
  • Forkhead Transcription Factors
  • FoxO3 protein, mouse
  • Foxo1 protein, mouse
  • Glucose Transporter Type 1
  • Gonadotropins, Equine
  • Monosaccharide Transport Proteins
  • Nerve Tissue Proteins
  • Proto-Oncogene Proteins
  • RNA, Messenger
  • Receptors, Estrogen
  • Slc2a1 protein, mouse
  • Slc2a1 protein, rat
  • Transcription Factors
  • Foxo1 protein, rat
  • Estradiol
  • Insulin-Like Growth Factor I
  • Luteinizing Hormone
  • Follicle Stimulating Hormone
  • Akt1 protein, rat
  • Protein-Serine-Threonine Kinases
  • Proto-Oncogene Proteins c-akt