Choline functions
Precursor of
Choline transport
Choline catabolism
Choline synthesis
Choline Transport for Phospholipid Synthesis 2006
Choline Transporters: Affinity, Localization, and Expression
Choline is activated first by phosphorylation and then by coupling to CDP prior to attachment to phosphatidic acid. PC is also synthesized by the addition of choline to CDP-activated 1,2-diacylglycerol. A third pathway to PC synthesis, involves the conversion of either PS or PE to PC. The conversion of PS to PC first requires decarboxylation of PS to yield PE; this then undergoes a series of three methylation reactions utilizing S-adenosylmethionine (SAM) as methyl group donor.
Choline is activated first by phosphorylation and then by coupling to CDP prior to attachment to phosphatidic acid.
Choline kinase
is a kinase with a broad specificity able to phosphorylate both choline and a set of proteins involved in the regulation of cell cycle, promoting entry into S phase, including:
Fulltext
Phospholipase D in Cell Proliferation and Cancer 2003
Phospholipase D (PLD) has emerged as a regulator of
several critical aspects of cell physiology. PLD, which
catalyzes the hydrolysis of phosphatidylcholine (PC) to
phosphatidic acid (PA) and choline, is activated in
response to stimulators of vesicle transport, endocytosis,
exocytosis, cell migration, and mitosis. Dysregulation
of these cell biological processes occurs in the
development of a variety of human tumors. It has now
been observed that there are abnormalities in PLD
expression and activity in many human cancers. In this
review, evidence is summarized implicating PLD as a
critical regulator of cell proliferation, survival signaling,
cell transformation, and tumor progression.
Kegg Pathway: Glycerophospholipid metabolism - Homo sapiens
Phospholipids synthesis and cell cycle
Relationship between phospholipid metabolism and the cell cycle. G1 phase is characterized by a high rate of PtdCho degradation and resynthesis that is dependent on growth factor and terminates at the G1/S boundary. Doubling of the phospholipid mass occurs in S phase due to continued phospholipid synthesis but with drastically reduced phospholipid turnover. The turnover of nuclear polyphosphoinositides is an additional S phase event that may be a component of a regulatory network that governs DNA replication. The G2 and M phases are characterized by the cessation of phospholipid metabolism.
Cellular localization
Phosphatidylcholine and phosphatidylethanolamine are the two main phospholipids in eukaryotic
cells comprising
50 and 25% of phospholipid mass, respectively. Phosphatidylcholine is synthesized almost exclusively through the CDP-choline pathway in essentially all mammalian cells. Phosphatidylethanolamine is synthesized through either the CDP-ethanolamine pathway or by the decarboxylation of phosphatidylserine, with the contribution of each pathway being cell type dependent. Two human genes, CEPT1 and CPT1, code for the total compliment of activities that directly synthesize phosphatidylcholine and phosphatidylethanolamine through the CDP-alcohol pathways. CEPT1 transfers a phosphobase from either CDP-choline or CDP-ethanolamine to diacylglycerol to synthesize both phosphatidylcholine and phosphatidylethanolamine, whereas CPT1 synthesizes phosphatidylcholine
exclusively. We show through immunofluorescence that brefeldin A treatment relocalizes
CPT1, but not CEPT1, implying CPT1 is found in the Golgi. A combination of oimmunofluorescence and subcellular fractionation experiments with various endoplasmic reticulum, Golgi, and nuclear markers confirmed that CPT1 was found in the Golgi and CEPT1 was found in both the endoplasmic reticulum and nuclear membranes. The rate-limiting step for phosphatidylcholine synthesis is catalyzed by the amphitropic CTP:phosphocholine cytidylyltransferase
, which is found in the nucleus in most cell types. CTP:phosphocholine cytidylyltransferase
is found immediately upstream cholinephosphotransferase,
and it translocates from a soluble nuclear location to the nuclear membrane in
response to activators of the CDP-choline pathway. Thus, substrate channeling of the CDP-choline produced by CTP:phosphocholine cytidylyltransferase
to nuclear located CEPT1 is the mechanism by which upregulation of the CDP-choline pathway increases de novo phosphatidylcholine biosynthesis.
In addition, a series of CEPT1 site-directed mutants was generated that allowed for the
assignment of specific amino acid residues as structural requirements that directly alter either phospholipid head group or fatty acyl composition. This pinpointed glycine 156 within the catalytic motif as being responsible for the dual CDP-alcohol specificity of CEPT1, whereas mutations within helix 214–228 allowed for the orientation of transmembrane helices surrounding the catalytic site to be definitively positioned.