Aquaporin 3 (AQP-3) is the protein product of the human AQP3 gene. [5] It is found in the basolateral cell membrane of principal collecting duct cells and provides a pathway for water to exit these cells. [6] Aquaporin-3 is also permeable to glycerol, ammonia, urea, and hydrogen peroxide. It is expressed in various tissues including the skin, respiratory tract, and kidneys as well as various types of cancers. [7] In the kidney, aquaproin-3 is unresponsive to the antidiuretic hormone vasopressin, unlike aquaporin-2. [8] This protein is also a determinant for the GIL blood group system. [9]
Suberoylanilide hydroxamic acid (SAHA) (a HDAC inhibitor) increases expression of aquaporin-3 in normal skin cells (keratinocytes). [10]
Aquaporin 3 levels are often lower in psoriasis than in healthy skin. [10]
Aquaporin 3 is expressed more in atopic eczema. [11]
Recent studies indicate that aquaporin 3 is overexpressed in many types of malignancies such as melanoma [7] and primary effusion lymphomas [12] as well as cancers of the lung, colon, stomach, esophagus, mouth, liver, and pancreatic duct. [5] [12] Based on these as well as cell culture studies, it is suggested that this overexpression contributes to the growth and spread of at least some of these cancers and therefore may be a therapeutic target for the treatment of these cancers. [5] [7] [12]
Aquaporins, also called water channels, are channel proteins from a larger family of major intrinsic proteins that form pores in the membrane of biological cells, mainly facilitating transport of water between cells. The cell membranes of a variety of different bacteria, fungi, animal and plant cells contain aquaporins through which water can flow more rapidly into and out of the cell than by diffusing through the phospholipid bilayer. Aquaporins have six membrane-spanning alpha helical domains with both carboxylic and amino terminals on the cytoplasmic side. Two hydrophobic loops contain conserved asparagine–proline–alanine which form a barrel surrounding a central pore-like region that contains additional protein density. Because aquaporins are usually always open and are prevalent in just about every cell type, this leads to a misconception that water readily passes through the cell membrane down its concentration gradient. Water can pass through the cell membrane through simple diffusion because it is a small molecule, and through osmosis, in cases where the concentration of water outside of the cell is greater than that of the inside. However, because water is a polar molecule this process of simple diffusion is relatively slow, and in tissues with high water permeability the majority of water passes through aquaporin.
CD59 glycoprotein, also known as MAC-inhibitory protein (MAC-IP), membrane inhibitor of reactive lysis (MIRL), or protectin, is a protein that in humans is encoded by the CD59 gene. It is an LU domain and belongs to the LY6/uPAR/alpha-neurotoxin protein family.
Peptide transporter 1 also known as solute carrier family 15 member 1 (SLC15A1) is a protein that in humans is encoded by SLC15A1 gene. PepT 1 is a solute carrier for oligopeptides. It functions in renal oligopeptide reabsorption and in the intestines in a proton dependent way, hence acting like a cotransporter.
Sphingosine-1-phosphate receptor 3 also known as S1PR3 is a human gene which encodes a G protein-coupled receptor which binds the lipid signaling molecule sphingosine 1-phosphate (S1P). Hence this receptor is also known as S1P3.
Disintegrin and metalloproteinase domain-containing protein 9 is an enzyme that in humans is encoded by the ADAM9 gene.
Meprin A subunit alpha also known as endopeptidase-2 or PABA peptide hydrolase is the alpha subunit of the meprin A enzyme that in humans is encoded by the MEP1A gene. The MEP1A locus is on chromosome 6p in humans and on chromosome 17 in mice.
Hyaluronan synthase 2 is an enzyme that in humans is encoded by the HAS2 gene.
Sarcoplasmic/endoplasmic reticulum calcium ATPase 3 is an enzyme that in humans is encoded by the ATP2A3 gene.
Flotillin-2 is a protein that in humans is encoded by the FLOT2 gene. Flotillin 2 (flot-2) is a highly conserved protein isolated from caveolae/lipid raft domains that tether growth factor receptors linked to signal transduction pathways. Flot-2 binds to PAR-1, a known upstream mediator of major signal transduction pathways implicated in cell growth and metastasis, and may influence tumour progression.
Equilibrative nucleoside transporter 2 (ENT2) is a protein that in humans is encoded by the SLC29A2 gene.
Concentrative nucleoside transporter 2 (CNT2) is a protein that in humans is encoded by the SLC28A2 gene.
Hyaluronan synthase 1 is an enzyme that in humans is encoded by the HAS1 gene.
Concentrative nucleoside transporter 1 (CNT1) is a protein that in humans is encoded by the SLC28A1 gene.
Aquaporin-5 (AQP-5) is a protein that in humans is encoded by the AQP5 gene.
Aquaporin-9 (AQP-9) is a protein that in humans is encoded by the AQP9 gene.
Rh family, C glycoprotein, also known as RHCG, is a protein that in humans is encoded by the RHCG gene.
Aquaporin-8 is a protein that in humans is encoded by the AQP8 gene.
Aquaporin-7 (AQP-7) is a protein that in humans is encoded by the AQP7 gene.
Ankyrin-3 (ANK-3), also known as ankyrin-G, is a protein from ankyrin family that in humans is encoded by the ANK3 gene.
Mitochondrial ferritin is a ferroxidase enzyme that in humans is encoded by the FTMT gene.