Expression and Functional Characterization of Choline Transporter in Human Keratinocytes

Abstract

Abstract. Choline is essential for synthesis of the major membrane phospholipid phosphatidylcholine. Moreover, it serves as a precursor for synthesis of the neurotransmitter acetylcholine (ACh). Keratinocytes of the epidermis synthesize and release ACh. The uptake of choline is the rate-limiting step in both ACh synthesis and choline phospholipid metabolism, and it is a prerequisite for keratinocyte proliferation. However, the nature of the choline transport system in keratinocytes is poorly understood. In this study, we examined the molecular and functional characterization of choline uptake into cultured human keratinocytes. Choline uptake into keratinocytes was independent of extracellular Na + , saturable, and mediated by a single transport system with an apparent Michaelis-Menten constant of 12.3 μM. Choline uptake was reduced when the keratinocyte membrane potential was depolarized by high K + . These results provide evidence that the choline transport activity is potential-sensitive. Various organic cations inhibit the choline transport system. RT-PCR demonstrated that keratinocytes expressed mRNA for choline transporter-like protein 1 (CTL1), mainly the CTL1a subtype. The present biochemical and pharmacological data suggest that CTL1a is functionally expressed in human keratinocytes and is responsible for the uptake of choline and organic cations in these cells.

The Discovery and Preclinical Development of ASG-5ME, an Antibody–Drug Conjugate Targeting SLC44A4-Positive Epithelial Tumors Including Pancreatic and Prostate Cancer

“…Tumor fragments were implanted or cells were injected s.c. into the flank of ICR-SCID mice, and animals were randomized into treatment groups (n ¼ 10) when tumors reached a size of approximately 150 mm 3 . IHC staining of SLC44A4 expression is shown in A-C. A, in vivo efficacy of ASG-5ME in an androgen-independent patient-derived prostate tumor xenograft model LAPC-9AI.…”

Guide to Receptors and Channels (GRAC), 5th edition

“…CTL3-5 remain to be characterized functionally. (Inazu et al, 2005); rat renal tubule epithelial cells (Yabuki et al, 2009); human colon carcinoma cells (Kouji et al, 2009); human keratinocytes (Uchida et al, 2009) and human neuroblastoma cells (Yamada et al, 2011). Choline uptake by CLT1 is inhibited by numerous organic cations (e.g.…”

Cholinergic Targets in Lung Cancer

“…The CTLs are Na + -independent and have an intermediate-affinity for choline and hemicholinium-3 (HC-3) as compared to CHT1 [23,25]. CTL1, in particular, has been shown to transport choline in renal tubule epithelia [26], keratinocytes [27], and lung adenocarcinoma cells [28]. CTL2 has also been shown to transport choline in lung adenocarcinoma cells [28].…”