ATF4

Activating transcription factor 4 (tax-responsive enhancer element B67), also known as ATF4, is a is_associated_with::protein that in humans is encoded by the ATF4 is_associated_with::gene.

Function
This gene encodes a is_associated_with::transcription factor that was originally identified as a widely expressed mammalian DNA binding protein that could bind a tax-responsive enhancer element in the LTR of HTLV-1. The encoded protein was also isolated and characterized as the cAMP-response element binding protein 2 (CREB-2). The protein encoded by this gene belongs to a family of DNA-binding proteins that includes the AP-1 family of transcription factors, cAMP-response element binding proteins (is_associated_with::CREBs) and CREB-like proteins. These transcription factors share a is_associated_with::leucine zipper region that is involved in protein–protein interactions, located C-terminal to a stretch of basic amino acids that functions as a is_associated_with::DNA-binding domain. Two alternative transcripts encoding the same protein have been described. Two is_associated_with::pseudogenes are located on the X chromosome at q28 in a region containing a large inverted duplication.

ATF4 transcription factor is also known to play role in is_associated_with::osteoblast differentiation along with is_associated_with::RUNX2 and osterix. Terminal osteoblast differentiation, represented by matrix mineralization, is significantly inhibited by the inactivation of JNK. JNK inactivation downregulates expression of ATF-4 and, subsequently, matrix mineralization.

Translation
The translation of ATF4 is dependent on upstream open reading frames located in the is_associated_with::5'UTR. The location of the second uORF, aptly named uORF2, overlaps with the ATF4 open-reading frame. During normal conditions, the uORF1 is translated, and then translation of uORF2 occurs only after eIF2-TC has been reacquired. Translation of the uORF2 requires that the ribosomes pass by the ATF4 ORF, whose start codon is located within uORF2. This leads to its repression. However, during stress conditions, the is_associated_with::40S ribosome will bypass uORF2 because of a decrease in concentration of eIF2-TC, which means the ribosome does not acquire one in time to translate uORF2. Instead ATF4 is translated.

Interactions
Kir2.1 has been shown to interact with:
 * is_associated_with::DLG4,
 * IL16, and
 * is_associated_with::TRAK2.