Krueppel-like factor 9 is a
protein
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residue (biochemistry), residues. Proteins perform a vast array of functions within organisms, including Enzyme catalysis, catalysing metab ...
that in humans is encoded by the ''KLF9''
gene
In biology, the word gene has two meanings. The Mendelian gene is a basic unit of heredity. The molecular gene is a sequence of nucleotides in DNA that is transcribed to produce a functional RNA. There are two types of molecular genes: protei ...
.
Previously known as Basic Transcription Element Binding Protein 1 (BTEB Protein 1), Klf9 is part of the Sp1 C2H2-type
zinc finger
A zinc finger is a small protein structural motif that is characterized by the coordination of one or more zinc ions (Zn2+) which stabilizes the fold. The term ''zinc finger'' was originally coined to describe the finger-like appearance of a ...
family of
transcription factor
In molecular biology, a transcription factor (TF) (or sequence-specific DNA-binding factor) is a protein that controls the rate of transcription (genetics), transcription of genetics, genetic information from DNA to messenger RNA, by binding t ...
s. Several previous studies showed Klf9-related regulation of animal development, including cell differentiation of
B cell
B cells, also known as B lymphocytes, are a type of the lymphocyte subtype. They function in the humoral immunity component of the adaptive immune system. B cells produce antibody molecules which may be either secreted or inserted into the plasm ...
s,
keratinocyte
Keratinocytes are the primary type of cell found in the epidermis, the outermost layer of the skin. In humans, they constitute 90% of epidermal skin cells. Basal cells in the basal layer (''stratum basale'') of the skin are sometimes referre ...
s, and
neuron
A neuron (American English), neurone (British English), or nerve cell, is an membrane potential#Cell excitability, excitable cell (biology), cell that fires electric signals called action potentials across a neural network (biology), neural net ...
s.
Klf9 is also a key transcriptional regulator for uterine
endometrial
The endometrium is the inner epithelium, epithelial layer, along with its mucous membrane, of the mammalian uterus. It has a basal layer and a functional layer: the basal layer contains stem cells which regenerate the functional layer. The funct ...
cell proliferation, adhesion, and differentiation, all factors that are essential during the process of pregnancy and are turned off during
tumorigenesis
Carcinogenesis, also called oncogenesis or tumorigenesis, is the formation of a cancer, whereby normal cells are transformed into cancer cells. The process is characterized by changes at the cellular, genetic, and epigenetic levels and abn ...
.
Function
The protein encoded by this gene is a transcription factor that binds to GC box elements located in the promoter. Binding of the encoded protein to a single GC box inhibits mRNA expression while binding to tandemly repeated GC box elements activates transcription.
Oxidative stress increases expression of Klf9 and overexpression of Klf9 gene sensitizes the cell to oxidative stress and
reactive oxygen species
In chemistry and biology, reactive oxygen species (ROS) are highly Reactivity (chemistry), reactive chemicals formed from diatomic oxygen (), water, and hydrogen peroxide. Some prominent ROS are hydroperoxide (H2O2), superoxide (O2−), hydroxyl ...
(ROS).
Using a
short hairpin RNA (shRNA) to silence expression of Klf9 provides resistance for the cell to oxidative stress and ROS-related cell death. Klf9 is upregulated by ROS and promotes ROS-related cell death.
Klf9 exhibits similarities to other known oxidative stress genes like
NQO1 and
HMOX1. When exposed to the same amount of hydrogen peroxide, both mouse embryo cells and human cells produced similar amounts of Klf9 and NQO1/HMOX.
The opposite of this effect also occurs; Klf9 overexpression within the cell leads to an increase in intracellular ROS. The result of the increase in intracellular ROS and Klf9 is increase in cell death; with the overexpressed Klf9 gene, more cells die. Similar cell death was found in vivo when wild-type mice were exposed to oxidative stress agent paraquat intranasally, which validated the oxidative stress-dependent Klf9 expression found in just the cell lines.
Regions around 10 kb upstream and 1 kb downstream of Klf9 transcription start site contain conserved antioxidant response elements (AREs), which are binding sites for Nrf2.
Nrf2
Nuclear factor erythroid 2-related factor 2 (NRF2), also known as nuclear factor erythroid-derived 2-like 2, is a transcription factor that in humans is encoded by the ''NFE2L2'' gene. NRF2 is a basic leucine zipper (bZIP) protein that may regu ...
is a major regulator of the antioxidant response to ROS within the cell. Klf9 is upregulated by Nrf2; when oxidative stress is high and concentration of intracellular ROS is high, Nrf2 binds to Klf9 promoter, which increases the amount of intracellular ROS, leading to cell death. When oxidative stress is low, Nrf2 goes through its normal pathway by increasing the amount of antioxidant species within the cell and decreasing the amount of intracellular ROS.
Animal studies
A Klf9 deficiency suppresses
bleomycin
-13- (1''H''-imidazol-5-yl)methyl9-hydroxy-5- 1''R'')-1-hydroxyethyl8,10-dimethyl-4,7,12,15-tetraoxo-3,6,11,14-tetraazapentadec-1-yl}-2,4'-bi-1,3-thiazol-4-yl)carbonyl]amino}propyl)(dimethyl)sulfonium
, C=55 , H=84 , N=17 , O=21 , S=3
, SMI ...
-induced
fibrosis
Fibrosis, also known as fibrotic scarring, is the development of fibrous connective tissue in response to an injury. Fibrosis can be a normal connective tissue deposition or excessive tissue deposition caused by a disease.
Repeated injuries, ch ...
in the lungs of mice. By introducing bleomycin to lung tissue, the tissue will produce ROS and develop fibrotic lung tissue to combat the damage done by the bleomycin. When Klf9 was knocked out in these mice, not as much fibrotic lung tissue was formed.
Because of this finding, the researchers proposed that manipulations of Klf9 levels within the body may be a valid treatment for other diseases as well, including certain types of cancer.
Interactions
KLF9 has been shown to
interact with
progesterone receptor
The progesterone receptor (PR), also known as NR3C3 or nuclear receptor subfamily 3, group C, member 3, is a protein found inside cells. It is activated by the steroid hormone progesterone.
In humans, PR is encoded by a single ''PGR'' gene resi ...
.
References
Further reading
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External links
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{{Transcription factors, g2
Transcription factors