The cellular protein p107, like the retinoblastoma gene product, has been shown to form a specific complex
with adenovirus E1A and SV40 large T antigen (T). The binding characteristics implied that RB1 and p107 share a
common biochemical function.
NCBI Summary:
The protein encoded by this gene is similar in sequence and possibly function to the product of the retinoblastoma 1 (RB1) gene. The RB1 gene product is a tumor suppressor protein that appears to be involved in cell cycle regulation, as it is phosphorylated in the S to M phase transition and is dephosphorylated in the G1 phase of the cell cycle. Both the RB1 protein and the product of this gene can form a complex with adenovirus E1A protein and SV40 large T-antigen, with the SV40 large T-antigen binding only to the unphosphorylated form of each protein. In addition, both proteins can inhibit the transcription of cell cycle genes containing E2F binding sites in their promoters. Due to the sequence and biochemical similarities with the RB1 protein, it is thought that the protein encoded by this gene may also be a tumor suppressor. Two transcript variants encoding different isoforms have been found for this gene.
General function
Cell death/survival, Cell cycle regulation, DNA Replication, Nucleic acid binding, DNA binding, Transcription factor
Comment
Cellular localization
Nuclear
Comment
Ovarian function
Luteinization
Comment
Green C, et al 2001 reported that
p107 is active in the nucleolus in non-dividing human granulosa
lutein cells.
Cells are maintained in a quiescent state by members of the retinoblastoma
protein family, pRb and p130. Both are phosphoproteins and hypophosphorylated
forms of pRb and p130 bind and repress the activity of E2F transcription
factors, thereby preventing entry into the cell cycle. Mitogenic stimulation causes activation of cyclin dependent kinases (cdk) that phosphorylate both
pRb and p130, thereby releasing E2F factors which stimulate the transcription
of a number of genes that are required for DNA synthesis and for regulating
the cell cycle. In non-dividing cells, cdks are maintained in an inactive
state by cdk inhibitor proteins such as p27(Kip1).
The CL is
formed in the ovary after ovulation at the terminal stage of folliculogenesis
after completion of maturation and differentiation of Graafian follicles. As
shown by flow cytometry granulosa luteal cells (GLC) are not dividing, being predominantly in the
G(0)/G(1) phase of the cell cycle and, consistent with this, they contain the
cdk inhibitor protein, p27(Kip1) but not E2F-1 which is normally expressed
only in proliferating cells. The GLC do express E2F-4, hypophosphorylated pRb,
p130 forms 1 and 2 and, surprisingly, hypophosphorylated p107. p107 is
normally present only in dividing cells where it regulates E2F activity during
the cell cycle. These forms of pRb, p130 as well as p107, together with E2F-4
are all active in that they can bind an E2F DNA-binding site in a pull-down
assay. Immunocytochemistry shows that these proteins are expressed in almost
all GLC but have different sub-cellular distribution: p107 is concentrated in
nucleoli, while p130 and E2F-4 show relatively even nuclear and cytoplasmic
distributions. Thus, p107 is active in human primary GLC but its
nucleolar localisation would suggest that it represses ribosomal RNA synthesis
rather than E2F activity.