We used immunochemistry to demonstrate expression of acetylcholine's nicotinic α7-receptor subtype in human colon cancer cell line HT-29. Moreover, RT-PCR and immunochemistry showed that choline acetyltransferase and acetylcholine esterase, the enzymes responsible for acetylcholine synthesis and degradation, respectively, localise in HT-29 cells. Bromoacetylcholine bromide, an inhibitor of choline acetyltransferase, significantly attenuated basal cell growth. Our findings suggest that acetylcholine might serve as an autocrine/paracrine–or speculatively, even intracrine–signalling molecule in cell line HT-29, thus contributing to carcinogenesis/cancer progression.

The secreted mammalian Ly-6⁄urokinase plasminogen activator receptor-related protein-1 (SLURP-1) is an endogenous ligand at the α7 subunit of the nicotinic acetylcholine receptor (nAChR). SLURP-1 has anti-tumourigenic properties. In the current study, we demonstrate that the challenge of HT-29 human colon cancer cells with nicotine for 24 h to increase cell growth via the α7nAChRs, caused a marked reduction of the protein expression of SLURP-1. We suggest that there is an interplay between acetylcholine and SLURP-1 in the HT-29 cells, both molecules serving as autocrine growth controlling ligands at the α7nAChR, where acetylcholine regulates the release of SLURP-1.

1. Secreted mammalian Ly-6/urokinase plasminogen activator receptor-related protein-1 (SLURP-1) is a recently discovered endogenous ligand at the alpha7 subunit of the nicotinic acetylcholine receptors. Previous reports have shown that SLURP-1 is expressed in normal human keratinocytes seemingly with a pro-apoptotic function. Conversely, such expression was markedly attenuated in transformed cells and it was suggested that the molecule could convey protection against malignant transformation. 2. In this study, we demonstrated the mRNA expression (by RT-PCR) and protein expression (by Western blotting and immunocytochemistry) of SLURP-1 in the human colon cancer cell line, HT-29. 3. Furthermore, we demonstrated the expression of SLURP-1 (by immunohistochemistry) in tumour cells of human colon cancer tissue, and, to a greater extent, in immune and smooth muscle cells of adjacent, macroscopically tumour-free colon tissue. 4. The current findings suggest that SLURP-1 participates in the regulation of gut immune functions and motility, as well as possibly playing a role in colon carcinogenesis/cancer progression.

We have investigated the functional expression of μ-opioid receptors (MORs) in the human colon cancer cell line, HT-29. As revealed by immunocytochemistry, immunoreactivity was present in both the cytoplasm and nuclei of the cells. Challenge with morphine for 24 h (1 nM to 1 μM) barely affected cell proliferation, while the secretion of urokinase type plasminogen activator (a protease involved in invasion/metastasis) was markedly augmented by a concentration of 0.1 μM. Human colon cancer tissue from 14 consecutively operated patients was investigated by immunohistochemistry. MORs were found in the nuclei of colonocytes and immune cells of the lamina propria in tumor-free tissue. In tumor tissue, immunoreactivity was found in the membrane and often in the nuclei of tumor cells. The current findings suggest that morphine administration could affect tumor progression by interfering with, for example, invasive properties. Our demonstration of a nuclear expression of the MORs appears to be a novel finding.