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Concept
P14arf
Summary
p14ARF (also called ARF tumor suppressor, ARF, p14ARF) is an alternate reading frame protein product of the CDKN2A locus (i.e. INK4a/ARF locus). p14ARF is induced in response to elevated mitogenic stimulation, such as aberrant growth signaling from MYC and Ras (protein). It accumulates mainly in the nucleolus where it forms stable complexes with NPM or Mdm2. These interactions allow p14ARF to act as a tumor suppressor by inhibiting ribosome biogenesis or initiating p53-dependent cell cycle arrest and apoptosis, respectively. p14ARF is an atypical protein, in terms of its transcription, its amino acid composition, and its degradation: it is transcribed in an alternate reading frame of a different protein, it is highly basic, and it is polyubiquinated at the N-terminus.
Both p16INK4a and p14ARF are involved in cell cycle regulation. p14ARF inhibits mdm2, thus promoting p53, which promotes p21 activation, which then binds and inactivates certain cyclin-CDK complexes, which would otherwise promote transcription of genes that would carry the cell through the G1/S checkpoint of the cell cycle. Loss of p14ARF by a homozygous mutation in the CDKN2A (INK4A) gene will lead to elevated levels in mdm2 and, therefore, loss of p53 function and cell cycle control.
The equivalent in mice is p19ARF.
The p14ARF transcript was first identified in humans in 1995, and its protein product confirmed in mice that same year. Its gene locus is on the short arm of chromosome 9 in humans, and on a corresponding location on chromosome 4 in mice. It is located near the genes for the tandem repeats INK4a and INK4b, which are 16 kDa (p16INK4a) and 15 kDa (p15INK4b) proteins, respectively. These INK4 proteins directly inhibit the cyclin D-dependent kinases CDK4 and CDK6. There are other INK4 genes on other chromosomes, however these are not linked to cancer, and so their functions are not likely to be overlapping. An important cyclin-dependent substrate is the retinoblastoma protein Rb, which is phosphorylated in late gap 1 phase (G1 phase), allowing G1 exit.
Official source
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