The Fos gene family consists of 4 members: FOS , FOSB , FRA1 , and FRA2. These genes
encode leucine zipper proteins that can dimerize with proteins of the JUN family, thereby forming the transcription factor
complex AP-1.
NCBI Summary:
The Fos gene family consists of 4 members: FOS, FOSB, FOSL1, and FOSL2. These genes encode leucine zipper proteins that can dimerize with proteins of the JUN family, thereby forming the transcription factor complex AP-1. As such, the FOS proteins have been implicated as regulators of cell proliferation, differentiation, and transformation.
General function
Nucleic acid binding, DNA binding, Transcription factor
Comment
Cellular localization
Nuclear
Comment
Ovarian function
Follicle development, Luteinization
Comment
Expression regulated by
FSH, LH
Comment
Sharma SC, et al 2000 reported the regulation of AP1 (Jun/Fos) Factor expression and activation in ovarian
granulosacells and the relation of JunD and Fra2 to terminal differentiation.
The expression patterns of Jun and Fos family
members in response to hormones(FSH and LH) were distinct. c-Jun, JunB, c-Fos and Fra2 were
rapidly but transiently induced by FSH in immature granulosa cells. JunD and Fra2 were induced by
LH and maintained as granulosa cells terminally differentiated into luteal cells. FSH and forskolin
induced expression of AP1 factors by A-kinase-dependent (Fra2) and A-kinase-independent
mechanisms (c-Fos, JunB), one of which involves p38MAPK. Forskolin and PMA acted
synergistically to enhance transcription of an AP1(-73COL)-luciferase construct. JunD appears to be
one mediator of this effect.
Ovarian localization
Granulosa, Luteal cells
Comment
Rusovici R, et al 2003 reported the expression and Distribution of AP-1 Transcription Factors in the Porcine Ovary.
The activator protein-1 (AP-1) transcription factors are important regulators of cell proliferation and differentiation. The developmental distribution of AP-1 family members in porcine ovary has not been previously investigated. The authors examined the expression of AP-1 factors in porcine ovarian follicles, granulosa cells, and corpora lutea at different stages of development. Immunoblot analyses confirmed that c-Jun, JunD, JunB, c-Fos, Fra-1, Fra-2, and FosB immunoreactive proteins were present in whole-cell extracts (WCE) of all antral follicles and midluteal phase corpora lutea (CL) as well as granulosa cells (GC) isolated from different-sized antral follicles. The intensities of c-Jun and c-Fos protein bands were decreased in CL WCE compared to antral follicles. In granulosa cells from preovulatory follicles (8-10 mm), Fra-2 exhibited a shift from 43 kDa to 46 kDa when compared to granulosa cells from smaller antral follicles. Separation of cytoplasmic and nuclear extracts was performed to determine if developmental differences between these fractions existed. Most AP-1 factors predominated in the nuclear fraction with notable exceptions. c-Fos predominated in the nucleus in GC and follicles but predominated in the cytoplasmic fraction of CL. With the exception of GC from 1-2-mm follicles, in which expression was similar between fractions, Fos-B was found predominantly in the cytoplasmic fraction. Fra-1 exhibited similar expression between cytoplasmic and nuclear fractions for all tissues. Immunohistochemical (IHC) analyses of porcine ovary sections were performed to determine the cellular distribution of these factors at different follicular stages, and immunopositive nuclei were evaluated. In primordial and primary unilaminar follicles, all AP-1 factors studied except for FosB were detected in granulosa nuclei. Granulosa cell nuclei of multilaminar preantral follicles were immunopositive for all factors, with lower expression of FosB. Antral follicles exhibited GC and thecal cell nuclear staining for all factors with the exception of FosB in theca. Luteal cells exhibited the most intense nuclear staining for JunD and Fra-2, whereas all other factors were present in luteal cell nuclei although to a lesser extent. IHC with FosB antibodies yielded mostly cytoplasmic staining but only weak luteal nuclear staining. In corpora albicantia, low levels of staining were seen for all AP-1 factors. The DNA-binding abilities of these factors in granulosa cells and CL were evaluated by EMSA. Nuclear extracts from granulosa cells from 1-2-mm or 8-10-mm antral follicles bound an AP-1 DNA consensus sequence and complexes consisted predominantly of c-Jun, JunD, JunB, c-Fos, and Fra-2. In CL, c-Jun, JunD, JunB, and Fra-2 were present in DNA-binding complexes, and c-Fos binding was not detected. In conclusion, the results suggest that expression and DNA-binding activity of AP-1 factors in follicular structures changes with luteinization. Differentiation to the luteal phenotype involves a reduction in nuclear c-Jun and c-Fos and a predominance of JunD and Fra-2.