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Ski/Dach domain-containing protein 1 is a human protein encoded by the SKIDA1 gene. It is also known as c10orf140 and DLN-1. It is found in vertebrates. It has two domains: the Ski/Sno/Dac domain and a domain of unknown function, DUF4854. It is associated with multiple types of cancer, like leukemia, ovarian cancer, and colon cancer. It's predicted to be a nuclear protein. It may interact with PRC2.

Orthologs
SKIDA1 has orthologs in vertebrate species. The species least related to humans with an SKIDA1 ortholog is the lancelet Branchiostoma belcheri. The clades amphibia and chondrichthyes have a couple species with SKIDA1, but SKIDA1 is not found throughout the clades. No orthologs have been found in lungfish or invertebrate species.

Paralogous Domains
SKIDA1 shares the Ski/Sno/Dac domain with Ski oncogene (Ski), Ski-like protein (Sno), and dachshund (Dac). It shares DUF4584 with Elongin BC Polycomb Repressive Complex 2 associated Protein (EPOP).

Structure
In humans, SKIDA1 is located on the reverse strand of chromosome 10 at locus 10p12.31. It contains five exons. Three introns are located in the 5' UTR region in humans. The fourth intron is located in the coding sequence.

Isoforms
There is not consensus on whether humans have one or two SKIDA1 isoforms. NCBI Gene claims there is one, while UniProt claims there is two. It's possible isoform 2 is recorded in NCBI Gene as DLN-1 (accession BAE93016.1). Isoform 1 is 908 amino acids long, while isoform 2 is 827 amino acids long; isoform 2 is missing amino acids 240-318 in isoform 1. Isoform 1 is predicted to weigh 98 kDa and have an isoelectric point of 8.7, while isoform 2 is predicted to weigh 90 kDa and have an isoelectric point of 7.6.

Other mammalian species also have multiple isoforms of SKIDA1, including carnivorans, rodents, and primates. The number of isoforms each species has varies; cheetahs have five recorded isoforms, chimpanzees have three recorded, and brown rats have two recorded.



Amino Acid Repeats
Human SKIDA1 contains two poly-alanine regions, one poly-histidine region, and one poly-glutamic acid region. It's unknown if they have any function. The poly-alanine and poly-histidine regions are not highly conserved among orthologs; for example, while they are found in the house mouse ortholog, they are not found in the Western lowland gorilla ortholog. The poly-glutamic acid region shows more conservation, and is found abbreviated in species as distantly related from humans as the tire track eel.

Domains
SKIDA1 contains two domains: Ski/Sno/Dac and DUF4854. The Ski/Sno/Dac domain is at the N-terminus end of the protein. The Ski/Sno/Dac domain is also found in the Ski oncogene (Ski), Ski-like protein (Sno), and dachshund (Dac). It is potentially a DNA-binding domain.

The other domain, DUF4854, is also found in EPOP, near its C-terminus. However, the DUF4584 found in EPOP is roughly a fifth the size of that in SKIDA1. The C-termini of SKIDA1 (amino acids 844-908) and EPOP (amino acids 313-379) have 52% identity. The C-terminus of EPOP binds to the SUZ12 subunit of Polycomb Repressive Complex 2 (PRC2), suggesting that of SKIDA1 may as well.

Promoter & Transcription Factors
There are five predicted potential promoters. Two align with the second half of the mRNA transcript, suggesting they are not used or only produce an incomplete polypeptide.

The promoter that aligns best with the start of the mRNA transcript is potentially bound to by many transcription factors, including Transcription factor II B, Nuclear factor Y, Early growth response 1, and Krueppel-like factor 6.

Transcript Regulation
SKIDA1 is likely regulated by microRNAs. miR-93 binds to the SKIDA1 3'-UTR. Multiple microRNAs are predicted to bind to the SKIDA1 3'UTR, including miR-130, miR-301, miR-454, and miR-494.

Polypeptide Modification
SKIDA1 is SUMOylated at five sites. Other sites are predicted to be SUMOylated. It is also predicted to be phosphorylated and O-GlcNAcylated.

Subcellular Localization
SKIDA1 is predicted to be localized primarily in the nucleus and less so in the cytosol.

Tissue Expression
SKIDA1 is expressed at high levels in the brain, thyroid, and testes. It's expressed at medium to low levels in adipose tissue, lymph nodes, and skeletal muscle. In mice, it's noted to have medium-to-high expression in the olfactory bulb, retina, and salivary gland.

Developmental Expression
SKIDA1 expression changes during organism development. Expression is low in the zygote, peaks during embryonic development, and is low post-birth. In the house mouse, it's expressed most during organogenesis. In the fetus, its expression is low in the liver but not other organs. Expression in the adult liver is much higher. In contrast, SKIDA1 expression in the fetal brain is higher than in the adult brain.

SKIDA1 in the African clawed frog is expressed faintly in the marginal zone of gastrulae. During neurulation, it's expressed in the brain and cranial neural crest. During tailbud, SKIDA1 expression increases in sensory placodes. By the end of tailbud, neural expression has faded except in the olfactory organ.

Function
SKIDA1 is predicted to function primarily in the nucleus also in the cytosol. The predicted functions of its domains suggest interactions with histones and DNA: it's possible the Ski/Sno/Dac domain binds to DNA while the DUF4584 binds to SUZ12. SUZ12 is a subunit of PRC2, which methylates histone protein H3 to reduce transcription. Altered expression during organism development suggest it's related to cell differentiation or organogenesis.

Clinical Significance
SKIDA1 expression is associated with multiple types of cancer. It is over-expressed in epithelial ovarian cancer cells. Its expression is altered by various cancer-treatment compounds: human alpha-lactalbumin made lethal to tumor cells; oleate salts; metformin; aspirin. In cell lines of cancerous cells, altered expression is associated with resistance to dasatinib and docetaxel, which are used to treat cancer.

Altered methylation of SKIDA1 is associated with human pancreatic cancer, rheumatoid arthritis, and lupus erythematosus. Additionally, it is expressed less in women with Down syndrome compared to their identical twins without Down syndrome. Its expression is dramatically reduced in brains affected by untreated HIV1-associated neurocognitive disorders (HAND) in comparison to healthy brains and brains affected by HAND but treated with antiretrovirals.