Disease relevance of EPB41

• EPB41 gene expression was unchanged in all analyzed meningiomas [1].
• The mutations responsible for hereditary elliptocytosis (HE) and its aggravated form, poikilocytosis (HP), lie in the SPTA1 and SPTB gene, already mentioned, and in the EPB41 gene encoding protein 4 [2].
• Alterations of protein 4.1 family members in ependymomas: a study of 84 cases [3].
• In adult amphibian retinas, protein 4.1 is detected in photoreceptors, bipolar cells, and ganglion cell axons [4].
• Recently, we identified another protein 4.1 gene, DAL-1 (differentially expressed in adenocarcinoma of the lung) located on chromosome 18p11.3, which is lost in approximately 60% of non-small cell lung carcinomas, and exhibits growth-suppressing properties in lung cancer cell lines [5].

Psychiatry related information on EPB41

• Evidence for the association of protein 4.1 immunoreactive forms with neurofibrillary tangles in Alzheimer's disease brains [6].

High impact information on EPB41

• Indirect evidence suggests that the genetic defect in hereditary spherocytosis lies in the erythrocyte membrane skeleton, a submembranous meshwork of proteins (principally spectrin, actin, and protein 4.1) responsible for membrane shape and structural stability [7].
• A genetic defect in the binding of protein 4.1 to spectrin in a kindred with hereditary spherocytosis [7].
• We show that Crb controls localization of the adherens junction through its intracellular domain containing a putative binding site for a protein 4.1 superfamily protein (FERM) [8].
• Spectrin, the most abundant component of this assembly, is an elongated and flexible molecule that, with potentiation by protein 4.1, is cross-linked at its ends by short actin filaments to form a lattice beneath the membrane [9].
• Fractionally mobile integral proteins, such as band 3, and highly mobile receptors, such as CD59 as well as glycophorin C in protein 4.1-deficient cells, appeared to be squeezed out of areas dense in the underlying network and enriched in areas of network dilation [10].

Chemical compound and disease context of EPB41

• Additionally, frozen tissue from nine ependymomas (four intracranial and five spinal) was obtained for Western blot analysis for merlin, 4.1B and 4.1R expression [3].
• We here analyze the molecular basis of heterozygous 4.1(-) hereditary elliptocytosis, associated with protein 4.1 partial deficiency, in nine related French families. cDNA sequencing revealed a single codon deletion (AAA) resulting in a lysine residue deletion within the 10-kD binding domain, 3' of Motif I [11].
• Erythrocyte membranes (ghosts) and membrane skeletons (submembranous reticula of spectrin, actin, and protein 4.1 prepared by extracting ghosts with Triton X-100) from 15 patients with hereditary elliptocytosis (HE) were elliptical, which indicates that the primary defect responsible for the abnormal shape of these cells resides in the skeleton [12].

Biological context of EPB41

• The EPB41 and EPB41L3 genes from fish, bird, amphibian, and mammal genomes exhibit shared features including alternative first exons and differential splice acceptors in exon 2 [13].
• The EPB41 (protein 4.1) genes epitomize the resourcefulness of the mammalian genome to encode a complex proteome from a small number of genes [14].
• GADD45A and EPB41 as tumor suppressor genes in meningioma pathogenesis [1].
• Nineteen samples with 1p LOH (12 grade I; 7 grade II, WHO classification) and 20 samples without 1p LOH (18 grade I; 2 grade II) were also analyzed by means of real-time polymerase chain reaction to find abnormalities in EPB41 mRNA levels in meningioma [1].
• Some patients with recessive HS have a mutation in the spectrin alpha-2 domain (S.L.M. et al., unpublished observations), and a few dominant HS patients have an unstable beta-spectrin that is easily oxidized, which damages the protein 4.1 binding site and weakens spectrin-actin interactions [15].

Anatomical context of EPB41

• Identification of the binding interface involved in linkage of cytoskeletal protein 4.1 to the erythrocyte anion exchanger [16].
• Human CASK/LIN-2 binds syndecan-2 and protein 4.1 and localizes to the basolateral membrane of epithelial cells [17].
• These data suggest that the stability of 4.1R association with centrosomes requires an intact C-terminal end, either for a proper conformation of the protein, for a direct binding to an unknown centrosome-cytoskeletal network, or for both [18].
• Furthermore, phosphorylation of these residues appears to be essential for the targeting of 4.1R to the spindle poles and for mitotic microtubule aster assembly in vitro [19].
• Finally, we used siRNA inhibition to deplete 4.1R from HeLa cells and provide the first direct genetic evidence that 4.1R is required to efficiently focus mitotic spindle poles [19].

Associations of EPB41 with chemical compounds

• In the present study, we characterized the interaction of 4.1R with phosphatidylinositol-4,5-bisphosphate (PIP(2)) and assessed the effect of PIP(2) on the interaction of 4.1R with membrane proteins [20].
• The others and we have been focusing on the structure and function of the 30 kDa NH2-terminal domain of 4.1R, which is responsible for 4.1R interaction with the transmembrane proteins described above [21].
• This suggests that tyrosine phosphorylation of protein 4.1 occurs in vivo and may be functionally significant [22].
• 1. Glycophorin C is retained by Triton shells prepared from normal membranes, whereas Triton shells prepared from protein 4.1-deficient membranes are totally devoid of this sialoglycoprotein [23].
• We show that falcipain-2-mediated cleavage of protein 4.1 occurs immediately after lysine 437, which lies within a region of the spectrin-actin-binding domain critical for erythrocyte membrane stability [24].

Physical interactions of EPB41

• A nonerythroid isoform of protein 4.1R interacts with the nuclear mitotic apparatus (NuMA) protein [25].
• PIP(2) had no effect on 4.1R binding to p55 [20].
• To evaluate the functional significance of protein 4.1R binding for subcellular localization of hDlg in vivo, we expressed full-length recombinant constructs of two naturally occurring isoforms of hDlg termed hDlg-I2 and hDlg-I3 [26].
• Protein 4.1 interacts with TRPC4 and the membrane skeleton [27].
• Protein 4.1R binding to eIF3-p44 suggests an interaction between the cytoskeletal network and the translation apparatus [28].

Enzymatic interactions of EPB41

• Here, we show that protein 4.1 is phosphorylated on tyrosine by the epidermal growth factor receptor (EGFR) tyrosine kinase [22].
• Protein 4.1 phosphorylated by casein kinase A and protein kinase C, but not cAMP-dependent protein kinase, exhibits a reduced binding to KI-extracted inside-out vesicles [29].

Regulatory relationships of EPB41

• Phosphorylation of 4.1R also enhances its association with NuMA and tubulin [19].
• Glycophorin C content of human erythrocyte membrane is regulated by protein 4.1 [23].

Other interactions of EPB41

• The minimal sequence sufficient for this interaction has been mapped to the amino acids encoded by exons 20 and 21 of 4.1R and residues 1788-1810 of NuMA [25].
• These findings led to the postulate that the coexpression at the spindle poles of 2 related proteins, 4.1R and 4.1G, might reflect a functional redundancy in mitotic cells [18].
• Using a yeast two-hybrid system, we isolated a novel human centrosomal protein, CPAP (centrosomal P4.1-associated protein), which specifically interacts with the head domain of the 135-kDa protein 4.1R isoform (4.1R-135) [30].
• Furthermore, GPC was more readily extracted by Titon X-100 from adenosine triphosphate (ATP)-depleted erythrocytes, implying that the GPC-4.1R interaction may be regulated by PIP(2) in situ [20].
• The protein 4.1 tumor suppressor, DAL-1, impairs cell motility, but regulates proliferation in a cell-type-specific fashion [31].

Analytical, diagnostic and therapeutic context of EPB41

• In this study, we define important 4.1R isoforms expressed in interphase and mitotic cells by RT-PCR and mini-cDNA library construction [19].
• We observed loss of Protein 4.1R expression in two meningioma cell lines (IOMM-Lee, CH157-MN) by Western blotting as well as in 6 of 15 sporadic meningiomas by immunohistochemistry and fluorescence in situ hybridization [32].
• Immunoblotting with anti-phosphotyrosine antibodies showed that purified protein 4.1 contained phosphorylated tyrosine, and this increased upon phosphorylation by EGFR [22].
• To identify the precise peptide sequence at the hydrolysis site of protein 4.1, we used a recombinant construct of protein 4.1 as substrate followed by MALDI-MS analysis of the cleaved product [24].
• Quantitation by flow cytometry showed that the glycophorin C content of cells totally deficient in protein 4.1 was 9% of normal and that of cells partially deficient in protein 4.1 was 44% of normal [23].

References