UniProt functional annotation for O00522



	UniProt functional annotation for O00522

UniProt code: O00522.

Organism: Homo sapiens (Human).

Taxonomy: Eukaryota; Metazoa; Chordata; Craniata; Vertebrata; Euteleostomi; Mammalia; Eutheria; Euarchontoglires; Primates; Haplorrhini; Catarrhini; Hominidae; Homo.

Function: Component of the CCM signaling pathway which is a crucial regulator of heart and vessel formation and integrity (By similarity). Negative regulator of angiogenesis. Inhibits endothelial proliferation, apoptosis, migration, lumen formation and sprouting angiogenesis in primary endothelial cells. Promotes AKT phosphorylation in a NOTCH- dependent and independent manner, and inhibits ERK1/2 phosphorylation indirectly through activation of the DELTA-NOTCH cascade. Acts in concert with CDH5 to establish and maintain correct endothelial cell polarity and vascular lumen and these effects are mediated by recruitment and activation of the Par polarity complex and RAP1B. Required for the localization of phosphorylated PRKCZ, PARD3, TIAM1 and RAP1B to the cell junction, and cell junction stabilization. Plays a role in integrin signaling via its interaction with ITGB1BP1; this prevents the interaction between ITGB1 and ITGB1BP1. Microtubule- associated protein that binds to phosphatidylinositol 4,5-bisphosphate (PIP2)-containing membranes in a GTP-bound RAP1-dependent manner. Plays an important role in the maintenance of the intracellular reactive oxygen species (ROS) homeostasis to prevent oxidative cellular damage. Regulates the homeostasis of intracellular ROS through an antioxidant pathway involving FOXO1 and SOD2. Facilitates the down-regulation of cyclin-D1 (CCND1) levels required for cell transition from proliferative growth to quiescence by preventing the accumulation of intracellular ROS through the modulation of FOXO1 and SOD2 levels. {ECO:0000250|UniProtKB:Q6S5J6, ECO:0000269|PubMed:11741838, ECO:0000269|PubMed:17916086, ECO:0000269|PubMed:20332120, ECO:0000269|PubMed:20616044, ECO:0000269|PubMed:20668652, ECO:0000269|PubMed:21633110, ECO:0000269|PubMed:23317506}.

Subunit: Interacts with CDH5 (PubMed:20332120). Found in a complex, at least composed of ITGB1BP1, KRIT1 and RAP1A. Interacts (via C-terminus FERM domain) with RAP1A (active GTP-bound form preferentially); the interaction does not induce the opening conformation of KRIT1. Interacts (via FERM domain) with RAP1B. Interacts (via N-terminus NPXY motif) with ITGB1BP1; the interaction induces the opening conformation of KRIT1 and competes with ITGB1 for ITGB1BP1 interaction. Interacts with HEG1 and CCM2; greatly facilitates CCM2-binding to HEG1. Associates (via N-terminus and C-terminus regions) with microtubules; the interaction is inhibited in presence of ITGB1BP1 and active GTP- bound RAP1A. {ECO:0000269|PubMed:11741838, ECO:0000269|PubMed:11854171, ECO:0000269|PubMed:17916086, ECO:0000269|PubMed:20332120, ECO:0000269|PubMed:21633110, ECO:0000269|PubMed:22577140, ECO:0000269|PubMed:23007647, ECO:0000269|PubMed:23317506, ECO:0000269|PubMed:9285558}.

Subcellular location: Cytoplasm, cytoskeleton. Cell membrane; Peripheral membrane protein. Cell junction. Note=KRIT1 and CDH5 reciprocally regulate their localization to endothelial cell-cell junctions. Association with RAP1 relocalizes KRIT1 from microtubules to cell junction membranes. Translocates from the cytoplasm along microtubules to the cell membrane in a ITGB1BP1-dependent manner.

Tissue specificity: Low levels in brain. Very weak expression found in heart and muscle. {ECO:0000269|PubMed:9285558}.

Domain: The FERM domain mediates binding to RAP1A and RAP1B and is necessary for binding to phosphatidylinositol 4,5-bisphosphate (PIP2). {ECO:0000269|PubMed:23317506}.

Domain: The N-terminal domain has structural similarity to the nudix hydrolase domain, despite the absence of a nudix box and low sequence similarity with nudix hydrolase domains. The N-terminus and the C- terminus part associate together via the NPAY binding motif and adopt a lose conformation that is disrupted by ITGB1BP1, but not by RAP1A. {ECO:0000269|PubMed:23317506}.

Domain: Contains 4 ANK repeats that precede the FERM domain. {ECO:0000269|PubMed:26458359}.

Disease: Cerebral cavernous malformations 1 (CCM1) [MIM:116860]: A congenital vascular anomaly of the central nervous system that can result in hemorrhagic stroke, seizures, recurrent headaches, and focal neurologic deficits. The lesions are characterized by grossly enlarged blood vessels consisting of a single layer of endothelium and without any intervening neural tissue, ranging in diameter from a few millimeters to several centimeters. {ECO:0000269|PubMed:12172908}. Note=The disease is caused by variants affecting the gene represented in this entry.

Annotations taken from UniProtKB at the EBI.


Organism:		Homo sapiens (Human).
Taxonomy:		Eukaryota; Metazoa; Chordata; Craniata; Vertebrata; Euteleostomi; Mammalia; Eutheria; Euarchontoglires; Primates; Haplorrhini; Catarrhini; Hominidae; Homo.



Function:		Component of the CCM signaling pathway which is a crucial regulator of heart and vessel formation and integrity (By similarity). Negative regulator of angiogenesis. Inhibits endothelial proliferation, apoptosis, migration, lumen formation and sprouting angiogenesis in primary endothelial cells. Promotes AKT phosphorylation in a NOTCH- dependent and independent manner, and inhibits ERK1/2 phosphorylation indirectly through activation of the DELTA-NOTCH cascade. Acts in concert with CDH5 to establish and maintain correct endothelial cell polarity and vascular lumen and these effects are mediated by recruitment and activation of the Par polarity complex and RAP1B. Required for the localization of phosphorylated PRKCZ, PARD3, TIAM1 and RAP1B to the cell junction, and cell junction stabilization. Plays a role in integrin signaling via its interaction with ITGB1BP1; this prevents the interaction between ITGB1 and ITGB1BP1. Microtubule- associated protein that binds to phosphatidylinositol 4,5-bisphosphate (PIP2)-containing membranes in a GTP-bound RAP1-dependent manner. Plays an important role in the maintenance of the intracellular reactive oxygen species (ROS) homeostasis to prevent oxidative cellular damage. Regulates the homeostasis of intracellular ROS through an antioxidant pathway involving FOXO1 and SOD2. Facilitates the down-regulation of cyclin-D1 (CCND1) levels required for cell transition from proliferative growth to quiescence by preventing the accumulation of intracellular ROS through the modulation of FOXO1 and SOD2 levels. {ECO:0000250\|UniProtKB:Q6S5J6, ECO:0000269\|PubMed:11741838, ECO:0000269\|PubMed:17916086, ECO:0000269\|PubMed:20332120, ECO:0000269\|PubMed:20616044, ECO:0000269\|PubMed:20668652, ECO:0000269\|PubMed:21633110, ECO:0000269\|PubMed:23317506}.


Subunit:		Interacts with CDH5 (PubMed:20332120). Found in a complex, at least composed of ITGB1BP1, KRIT1 and RAP1A. Interacts (via C-terminus FERM domain) with RAP1A (active GTP-bound form preferentially); the interaction does not induce the opening conformation of KRIT1. Interacts (via FERM domain) with RAP1B. Interacts (via N-terminus NPXY motif) with ITGB1BP1; the interaction induces the opening conformation of KRIT1 and competes with ITGB1 for ITGB1BP1 interaction. Interacts with HEG1 and CCM2; greatly facilitates CCM2-binding to HEG1. Associates (via N-terminus and C-terminus regions) with microtubules; the interaction is inhibited in presence of ITGB1BP1 and active GTP- bound RAP1A. {ECO:0000269\|PubMed:11741838, ECO:0000269\|PubMed:11854171, ECO:0000269\|PubMed:17916086, ECO:0000269\|PubMed:20332120, ECO:0000269\|PubMed:21633110, ECO:0000269\|PubMed:22577140, ECO:0000269\|PubMed:23007647, ECO:0000269\|PubMed:23317506, ECO:0000269\|PubMed:9285558}.
Subcellular location:		Cytoplasm, cytoskeleton. Cell membrane; Peripheral membrane protein. Cell junction. Note=KRIT1 and CDH5 reciprocally regulate their localization to endothelial cell-cell junctions. Association with RAP1 relocalizes KRIT1 from microtubules to cell junction membranes. Translocates from the cytoplasm along microtubules to the cell membrane in a ITGB1BP1-dependent manner.
Tissue specificity:		Low levels in brain. Very weak expression found in heart and muscle. {ECO:0000269\|PubMed:9285558}.
Domain:		The FERM domain mediates binding to RAP1A and RAP1B and is necessary for binding to phosphatidylinositol 4,5-bisphosphate (PIP2). {ECO:0000269\|PubMed:23317506}.
Domain:		The N-terminal domain has structural similarity to the nudix hydrolase domain, despite the absence of a nudix box and low sequence similarity with nudix hydrolase domains. The N-terminus and the C- terminus part associate together via the NPAY binding motif and adopt a lose conformation that is disrupted by ITGB1BP1, but not by RAP1A. {ECO:0000269\|PubMed:23317506}.
Domain:		Contains 4 ANK repeats that precede the FERM domain. {ECO:0000269\|PubMed:26458359}.
Disease:		Cerebral cavernous malformations 1 (CCM1) [MIM:116860]: A congenital vascular anomaly of the central nervous system that can result in hemorrhagic stroke, seizures, recurrent headaches, and focal neurologic deficits. The lesions are characterized by grossly enlarged blood vessels consisting of a single layer of endothelium and without any intervening neural tissue, ranging in diameter from a few millimeters to several centimeters. {ECO:0000269\|PubMed:12172908}. Note=The disease is caused by variants affecting the gene represented in this entry.