Identification and functional analysis of choline transporter in tongue cancer: A novel molecular target for tongue cancer therapy

Abstract

We examined the functional characteristics of choline uptake in human tongue carcinoma using the cell line HSC-3. Furthermore, we explored the possible correlation between the inhibition of choline uptake and apoptotic cell death. Both choline transporter-like protein 1 (CTL1) and CTL2 mRNAs and proteins were expressed, and were located in plasma membrane and mitochondria, respectively. Choline uptake was saturable and mediated by a single transport system, which is pH-dependent. Several cationic drugs inhibited cell viability and [(3)H]choline uptake. Choline uptake inhibitors and choline deficiency inhibited cell viability and increased caspase-3/7 activity. We conclude that extracellular choline is mainly transported via a CTL1 that relies on a directed H(+) gradient as a driving force. The functional inhibition of CTL1 by cationic drugs could promote apoptotic cell death. Furthermore, CTL2 may be the major site for the control of choline oxidation in mitochondria and hence for the supply of endogenous betaine and S-adenosyl methionine, which serves as a major methyl donor. Identification of this CTL1- and CTL2-mediated choline transport system provides a potential new target for tongue cancer therapy.

Choline transport for phospholipid synthesis: An emerging role of choline transporter-like protein 1

“…Similar to the high-affinity choline transporter CHT1, CTL1 is selectively inhibited by the choline analogue hemicholinium-3 (CH-3), yet with a much lower sensitivity. In recent years, further choline uptake studies confirmed the expression and choline transporter function of CTL1/SLC44A1 in human lung alveolar cells, 28 mouse bone marrow-derived macrophages, 42 rat renal tubule epithelial cells, 30 human keratinocytes, 31 human brain microvascular endothelial cells, 14 rheumatoid arthritis synovial fibroblasts, 40 mouse muscle and liver cell lines, 32,33 and numerous cancer cell lines 26,28,[34][35][36][37][38][39]41 as summarized in Table 1.…”

“…In choline-deficient skin fibroblast from the postural orthostatic tachycardia syndrome (POTS) patient mentioned above, CTL1/SLC44A1 protein is reduced, and at the same time, oxygen consumption, mitochondrial potential, and glycolytic activity are diminished and mitochondrial function therefore impaired. 43 Recent studies could also localize CTL2/SLC44A2 protein to the mitochondria of human esophageal cells, 41 renal tubule epithelial cells, 30 human tongue carcinoma cells, 39 and human brain microvascular epithelial cells. 14 The purpose of a widely expressed choline transporter in the mitochondrial membrane is not clear yet, but it is likely that there is a link between CTL1/SLC44A1-mediated choline transport and mitochondrial phospholipid metabolism.…”

“…Brain, breast, prostate, and colon cancer cells have been characterized by elevated choline and phosphocholine levels and abnormal choline metabolism, which correlates with malignancy of the cancer. In recent years, CTL/SLC44A protein overexpression was detected in various cancer cell lines 25,39,41,50 , and the proteins are involved in choline transport in these cells. 15 For example, expression of CTL1/SLC44A1, CTL2/SLC44A2, and CTL4/SLC44A4 messenger RNA is higher in cancerous MCF7 breast epithelial cells than in the MCF10A non-cancerous comparative cell line.…”

Protein kinase�C promotes choline transporter‑like protein�1 function via improved cell surface expression in immortalized human hepatic cells

“…PMA and 4α-phorbol 12-myristate 13-acetate (4α-PMa) were acquired from wako Pure chemical industries, ltd., and hemicholinium-3 (Hc-3) was obtained from Sigma-aldrich, Merck Kgaa. we assessed the properties of [methyl-3 H]choline chloride uptake according to a previous study (13). radioactivity was measured using a liquid scintillation counter (Tri-carb ® 2100Tr, Packard) and [methyl-3 H]choline specific uptake was calculated as the difference between total [methyl-3 H]choline uptake in the presence and absence of 30 mM of unlabeled choline.…”

“…anti-β-actin pab-HrP-direcT antibody (PM053-7) was obtained from MBL. Fa2N-4 cell culture was performed according to a previously published procedure (13). in brief, membranes were incubated with rabbit anti-cTl1 polyclonal (ab110767) and anti-cTl2 monoclonal (clone 3d11) antibodies.…”