Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.1.4.3 (phospholipase C)
 18,461 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The expression of a membrane-associated folate receptor (FR) was elevated in spleen samples from patients with chronic (CML) and acute (AML) myelogenous leukemias compared with normal spleen. Contrary to earlier reports, antibodies to a purified FR from placenta cross-reacted quantitatively with this protein in solution radioimmunoassays. Similar to FR-alpha (KB cells) and FR-beta (placenta), the protein was released from the membrane by phosphatidylinositol-specific phospholipase C, indicating a glycosylphosphatidylinositol (GPI) membrane anchor. Screening of a cDNA library from CML spleen with a heterologous murine FR cDNA and also amplification of FR cDNAs from spleen and bone marrow in CML, AML, chronic lymphocytic leukemia (CLL), and acute lymphocytic leukemia (ALL) by polymerase chain reaction (PCR) using degenerate oligonucleotides yielded cDNA clones representing FR-beta, a novel FR (type gamma), and an aberrant transcript of FR-gamma with a 2 base pair deletion resulting in a truncated 104-residue polypeptide; FR-alpha was not detected in these tissues. The cDNA for FR-gamma predicts a 243-residue polypeptide with an amino acid sequence homology of 71% and 79% with FR-alpha and FR-beta, respectively, a 23-residue amino-terminal signal peptide, and 3 potential sites for N-linked glycosylation. Transfection of COS-1 cells with the cDNA for FR-gamma resulted in low expression of a [3H]folic acid binding protein on the cell surface that was GPI-anchored. PCR analysis of total RNA from a number of normal and malignant tissues and cell lines indicated a limited tissue specificity of FR-gamma.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Identification of a novel folate receptor, a truncated receptor, and receptor type beta in hematopoietic cells: cDNA cloning, expression, immunoreactivity, and tissue specificity. 811 Jul 52

Proteins having a glycosyl-phosphatidylinositol (GPI) membrane anchor are synthesized with a carboxyl-terminal signal that is cleaved in the endoplasmic reticulum prior to GPI modification. The signal is characterized by a moderately hydrophobic domain downstream from the cleavage/modification site. The essential features of this domain were characterized using a truncated version of folate receptor (FR) type beta (FR-beta delta 5) in which its five carboxyl-terminal amino acid residues were deleted without affecting the efficiency of GPI modification. The amino acids at various positions in the hydrophobic domain were systematically altered and the extent of GPI modification of the recombinant proteins was determined by measuring [3H]folic acid binding at the cell surface, by Western blot analysis and from the sensitivity of the proteins to phosphatidylinositol-specific phospholipase C (PI-PLC). The results indicate that a threshold level of hydrophobicity exists at a single position below which the efficiency of GPI modification decreases with increasing hydrophilicity. Further, the hydrophobic domain is characterized by a hydrophobicity profile and not merely a minimum overall hydrophobicity. Thus, a leucine-rich core hydrophobic segment of six to eight amino acid residues is more sensitive to relatively small hydrophilic substitutions compared to its flanking regions and such mutations could be compensated by a hydrophobic substitution elsewhere within this core segment. Such a hydrophobicity profile is characteristic of the amino-terminal leader peptide. When the entire hydrophobic domain of the leader peptide of FR-beta (12 amino acid residues) was substituted with the hydrophobic domain of the GPI signal (13 amino acids), it was possible to obtain expression of FR-beta on the cell surface. In this construct, point mutations in the core hydrophobic segment and in the flanking regions within the substituting peptide produced a similar pattern of effects on the cell surface receptor expression compared to the corresponding mutations in the GPI signal of FR-beta. The results suggest that common principles may govern interactions of the hydrophobic domains of the GPI signal and the leader peptide with the endoplasmic reticulum.
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PMID:The hydrophobic domains in the carboxyl-terminal signal for GPI modification and in the amino-terminal leader peptide have similar structural requirements. 945 36

Up-regulation of folate receptor (FR) type-beta in acute myelogenous leukemia (AML) by all-trans retinoic acid (ATRA) and its restricted normal tissue distribution makes it a potential target for therapeutic intervention. The FR-beta in peripheral blood granulocytes was unable to bind folate and appeared to have a variant GPI membrane anchor, evident from its insensitivity to phosphatidylinositol-specific phospholipase C but not nitrous acid. Granulocyte FR-beta lacked mutations, and neither deglycosylation nor detergent solubilization restored folate binding. The posttranslational modification causing its nonfunctionality was evidently absent in FR-beta from AML cells from patient marrow, which bound folate. From flow cytometric analysis of 78 AML bone marrow specimens of different subtypes, 68% expressed FR-beta, most of which were also CD34+. In model cell lines that are FR - (KG-1a, L1210, and Chinese hamster ovary [CHO]) or FR + (KG-1, L1210 JF, and recombinant CHO-FR-beta), selective FR-mediated binding and cytotoxicity was obtained using folate-coated liposomes encapsulating fluorescent calcein (f-L-calcein) and doxorubicin (f-L-DOX), respectively, which could be blocked by 1 mM free folic acid. In the FR-beta-expressing KG-1 human AML cells, treatment with ATRA further increased this specificity. In mouse ascites leukemia models generated using L1210JF or KG-1 cells, increased median survival times were obtained with f-L-DOX treatment compared to nontargeted L-DOX. In the KG-1 model, ATRA treatment increased the cure rate with f-L-DOX from 10% to 60%. The above combined data from our 2 laboratories further support the feasibility and potential usefulness of selective ATRA-facilitated liposomal drug delivery in FR-beta + AMLs.
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PMID:Strategy for the treatment of acute myelogenous leukemia based on folate receptor beta-targeted liposomal doxorubicin combined with receptor induction using all-trans retinoic acid. 1209 53