Accumulated phosphatidylcholine (16:0/16:1) in human colorectal cancer; possible involvement of LPCAT4

Abstract

The identification of cancer biomarkers is critical for target-linked cancer therapy. The overall level of phosphatidylcholine (PC) is elevated in colorectal cancer (CRC). To investigate which species of PC is overexpressed in colorectal cancer, an imaging mass spectrometry was performed using a panel of non-neoplastic mucosal and CRC tissues. In the present study, we identified a novel biomarker, PC(16:0 ⁄ 16:1), in CRC using imaging mass spectrometry. Specifically, elevated levels of PC(16:0 ⁄ 16:1) expression were observed in the more advanced stage of CRC. Our data further showed that PC(16:0 ⁄ 16:1) was specifically localized in the cancer region when examined using imaging mass spectrometry. Notably, because the ratio of PC(16:0 ⁄ 16:1) to lyso-PC(16:0) was higher in CRC, we postulated that lyso-PC acyltransferase (LPCAT) activity is elevated in CRC. In an in vitro analysis, we showed that LPCAT4 is involved in the deregulation of PC (16: (1) Previous studies have reported that CRC contains increased amounts of phospholipids as well as an altered phospholipid composition of the CRC cell membrane.(2,3) These changes in membrane phospholipid levels can affect cell proliferation, viability and tumor development.(2,4) Moreover, although phosphatidylcholine (PC) is the most dominant phospholipid in both non-neoplastic and cancer tissues,the amount of PC is highly increased in CRC cells.(2) In addition, the changes in membrane potential and the increased PC ⁄ phosphatidylethanolamine (PE) composition rate are related to the grade of CRC malignancy.(3) In higher eukaryotes, PC is synthesized via two pathways: (i) the triple methylation of PE; and (ii) the cytidine diphosphate (CDP)-choline pathway. (6) However, the steady-state composition of PC species is maintained by the remodeling cycle (Lands' cycle).(7) The precise and concerted deacylation by phospholipase A 2 (PLA 2 ) and reacylation by lyso-PC acyltransferase (LPCAT) are required for normal cell functioning. Notably, the elevated expression of LPCAT1 was associated with colon cancer growth. (8) LPCAT1 is a member of the LPCAT family (LPCAT1-4) and shows LPCAT activity, preferentially incorporating palmitate into PC.(8) However, the relationship between PC remodeling and the progression of cancer, as well as the class of LPCAT involved in this process, remains unclear.Direct mass spectrometry (MS) of biological tissue sections using matrix-assisted laser desorption ⁄ ionization (MALDI) can profile many molecules including phospholipid subtypes. (9) Furthermore, this approach can be extended to imaging MS, which can visualize the distribution of biomolecules in the tissue section.(10-13) Because specific antibodies against lipids and macromolecules are often difficult to obtain, MALDI imaging is a suitable option for detecting distinct species of these molecules directly in a tissue section. This technique has already been applied to various human cancers including prostate and gastric cancer. (14,15) Although this emerging analytical technique was initial...

Visualization of sphingolipids and phospholipids in the fundic gland mucosa of human stomach using imaging mass spectrometry

“…For each spectrum, baseline subtraction, smoothing, normalization to the total ion current, and recalibration were conducted using ClinProTools 2.2 software (Bruker Daltonics) [12] . The total ion currents were the sum of all spectrum intensities.…”

“…The treated data was the average spectrum of input data sets. MS/MS analyses were performed to assign the molecular species using QSTAR Elite (Applied Biosystems, Foster City, CA, United States) [12] . The MS/MS spectral data were then verified using the LIPID MAPS database (http://lipidmaps.org).…”

“…Images of these sections were obtained using Keyence BZ9000 (Keyence, Tokyo, Japan). The stained sections were histologically evaluated by experienced pathologists [11,12] .…”

“…Because of its higher resolution compared with other imaging MS apparatuses, it enables us to visualize the localization of many lipids at one time. Using iMScope, we have already demonstrated the exact spatial distribution of lung surfactant and also discovered a specific phosphatidylcholine that is a potential biomarker in colorectal cancer tissue [11,12] . In this study, to investigate the molecular profile of human gastric mucosa in detail, iMScope was used to analyze the lipid distribution in the human gastric mucosa near the fundic glands.…”

Loss of Ypk1, the Yeast Homolog to the Human Serum- and Glucocorticoid-induced Protein Kinase, Accelerates Phospholipase B1-mediated Phosphatidylcholine Deacylation

“…In mammalian cells, increased choline uptake and incorporation into PC is a marker for proliferative growth (25), and conversely, inhibition of choline synthesis results in apoptosis (26). Aberrant PC levels and/or alterations in GroPCho have also been observed in patients with various cancers, such as colorectal (27) and prostate (28) cancer, and in Alzheimer disease (29,30). What has remained unknown, however, is how protein kinases and members of the B-type phospholipases, which deacylate phospholipids to produce GroPCho, are coordinately regulated to ensure lipid homeostasis.…”