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IKBKAP (inhibitor of kappa light polypeptide gene enhancer in B-cells, kinase complex-associated protein) is a human gene encoding the IKAP protein, which is ubiquitously expressed at varying levels in all tissue types, including brain cells. The IKAP protein is thought to participate as a sub-unit in the assembly of the six-protein putative human holo-Elongator complex, which allows for transcriptional elongation by RNA polymerase II. Further evidence has implicated the IKAP protein as being critical in neuronal development, and directs that decreased expression of IKAP is the molecular basis for the severe, neurodevelopmental disorder familial dysautonomy. Other pathways that have been connected to IKAP protein function in a variety of organisms include tRNA modification, cell motility, and cytosolic stress signalling.

Homologs of the IKBKAP gene have been identified in multiple other Eukaryotic model organisms. Notable homologs include Elp1p in yeast, Ikbkap in mice, and D-elp1 in fruit flies. The fruit fly homolog (D-elp1) has RNA-dependent RNA polymerase activity and is involved in RNA interference.

The IKBKAP gene is located on the long (q) arm of chromosome 9 at position 31, from base pair 108,709,355 to base pair 108,775,950.

- upload image of protein structure

Function and mechanism

Originally, it was proposed that the IKBKAP gene in humans was encoding a scaffolding protein (IKAP) for the IκB enzyme kinase (IKK) complex, which is involved in pro-inflammatory cytokine signal transduction in the NF-κB signalling pathway. However, this was subsequently disproven when researchers applied a gel filtration method and could not identify IKK complexes contained in fractions with IKAP, thus dissociating IKAP from having a role in the NF-κB signalling pathway.

Later, it was discovered that IKAP functions as a cytoplasmic scaffold protein in the mammalian JNK-signalling pathway which is activated in response to stress stimuli. In an in vivo experiment, researchers showed direct interaction between IKAP and JNK induced by the application of stressors such as ultraviolet light and TNF-α (a pro-inflammatory cytokine).

IKAP is now also widely aknowledged to have a role in transcriptional elongation in humans. The RNA polymerase II holoenzyme constitutes partly of a multi-subunit histone acetyltransferase element known as the RNA polymerase II elongator complex, of which IKAP is one subunit.  The association of the elongator complex with RNA polymerase II holoenzyme is necessary for subsequent binding to nascent pre-mRNA of certain target genes, and thus their successful transcription. Specifically, the depletion of functional elongator complexes within the cell has been found to have a profound effect on transcription of genes involved in cell migration.

In yeast, experimental data shows functions of the elongator complex varying from exocytosis to tRNA modification.

Related conditions

Familial Dysautonomia

Familial dysautonomia (also known as “Riley-Day syndrome”) is a complex congenital neurodevelopmental disease, characterized by unusually low numbers of neurons in the sensory and autonomic nervous systems. The resulting symptoms of patients include gastrointestinal dysfunction, scoliosis, and pain insensitivity. This disease is especially prevalent in the Ashkenazi Jewish population, where 1/3600 live births present familial dysautonomia.

By 2001, the genetic cause of familial dysautonomia was localized to a dysfunctional region spanning 177kb on chromosome 9q31. With the use of blood samples from diagnosed patients, the implicated region was successfully sequenced. The IKBKAP gene, one of the five genes identified in that region, was found to have a single-base mutation in over 99.5% of cases of familial dysautonomia seen.

The single-base mutation, overwhelmingly noted as a transition from cytosine to thymine, is present in the 5’ splice donor site of intron 20 in the IKBKAP pre-mRNA. This prevents recruitment of splicing machinery, and thus exon 19 is spliced directly to exon 21 in the final mRNA product – exon 20 is removed from the pre-mRNA with the introns. The unintentional removal of an exon from the final mRNA product is termed exon skipping. Therefore, there is a decreased level of functional IKAP protein expression within affected tissue. However, this disorder is tissue-specific. Lymphoblasts, even with the mutation present, may continue to express the wild-type IKAP protein. In contrast, brain tissue with the single-base mutation in the IKBKAP gene predominantly results in a truncated, mutant IKAP protein. The exact mechanism for how the familial dysautonomia phenotype is induced due to reduced IKAP expression is unclear; still, as a protein involved in transcriptional regulation, there have been a variety of proposed mechanisms. One such theory suggests that critical genes in the development of wild-type sensory and autonomic neurons are improperly transcribed. Extended research suggests that genes involved in cell migration are impaired in the nervous system, creating a foundation for this disorder.

In a small number of reported familial dysautonomia cases, researchers have identified other mutations that cause a change in amino acids (the building blocks of proteins). In these cases, arginine is replaced by proline at position 696 in the IKAP protein's chain of amino acids (also written as Arg696Pro), or proline is replaced by leucine at position 914 (also written as Pro914Leu). People with one of these improper amino acid substitutions also experience exon skipping. Together, these mutations cause the resulting IKAP protein to malfunction.

As an autosomal recessive disorder, two mutated alleles of the IKBKAP gene are required for the disorder to manifest. However, despite the predominance of the same single-base mutation being the reputed cause of familial dysautonomia, the severity of the affected phenotype varies within and between families.

Kinetin (6-furfurylaminopurine) has been found to have the capacity to repair the splicing defect and increase wild-type IKBKAP mRNA expression in vivo. Further research is still required to assess the fitness of kinetin as a possible future oral treatment.

Model systems

Model organisms have been used in the study of IKBKAP gene function.

Mouse

A conditional knockout mouse line, called Ikbkap^{tm1a(KOMP)Wtsi}was generated as part of the International Knockout Mouse Consortium program — a high-throughput mutagenesis project to generate and distribute animal models of disease to interested scientists — at the Wellcome Trust Sanger Institute.

Male and female animals underwent a standardized phenotypic screen to determine the effects of deletion. Twenty five tests were carried out and two phenotypes were reported. No homozygous mutant embryos were identified during gestation, and in a separate study none survived until weaning. The remaining tests were carried out on heterozygous mutant adult mice; no significant abnormalities were observed in these animals.

Saccharomyces cerevisiae

The homologous protein for IKAP in yeast is Elp1, with 29% identity and 46% similarity having been detected between the proteins. The yeast Elp1 protein is a subunit of the three-protein RNA polymerase II-associated elongator complex.

Drosophila melanogaster

The IKBKAP gene homologue in fruit flies is the CG10535 gene, encoding the D-elp1 protein.

Improvement Project Topic Choices

1. Pribnow Box
2. Kozack consensus sequence
3. TATA box
4. Lectin
5. Hayflick limit

Article Evaluation

I chose to evaluate the article on the Hayflick limit. This article is rated as Start Class quality and Low Importance. Regarding the content, I found that some parts were presented more as narrative than fact. This is especially noticeable in the "Experiment and discovery" sub-topic; I feel that talking about the suspicions and thoughts of researchers without proper citation detracts from the scientific purpose of that section and makes it feel like a story. The lack of proper citation is evident in other areas as well, such as in the sub-topic of "Cell phases". This takes away from the credibility of the article.

The article had a sub-topic titled "The belief in cell immortality" but provides a singular example of one individual who promoted this school of thought; there was no indication of this being an accepted belief in the general scientific community. More detail describing the pervasiveness of this belief would help support this point. Once again, citations are missing as well.

The sub-topic "Telomere length" covered both the connection of telomeres to the Hayflick limit and the medical applications/cancer research being done around the Hayflick limit. This amalgamation of ideas seemed at times distracting and hard to follow; perhaps separating the ideas into two distinct categories such as "telomere length" and "medical applications" would make it less so.

I checked some of the citations that were there, and found that the links worked properly and were supportive of claims made in the article. The references I checked came from reputable sources, mainly high impact science journals.

On the talk page, it has been noticed that adequate citation and referencing has not been employed. Other comments from earlier on discuss the structure of the article (too much repetition in description of immortality, for example) and general conflicting ideas about the underlying mechanisms of this phenomena.

The way that the information is presented in the Wikipedia article is different from how it is presented in class in that it focuses more on the discovery and social factors of the concept rather than the scientific basis for it; as well, I am unsure of whether some of the information is true considering the lack of sourcing.

Good job. Keep it up! AdamCF87 (talk) 17:37, 5 October 2017 (UTC)