Restoration of hydroxyindole O-methyltransferase levels in human cancer cells induces a tryptophan-metabolic switch and attenuates cancer progression

Abstract

5-Methoxytryptophan (5-MTP) is a tryptophan metabolite with recently discovered anti-inflammatory and tumor-suppressing activities. Its synthesis is catalyzed by a hydroxyindole -methyltransferase (HIOMT)-like enzyme. However, the exact identity of this HIOMT in human cells remains unclear. Human HIOMT exists in several alternatively spliced isoforms, and we hypothesized that 5-MTP-producing HIOMT is a distinct isoform. Here, we show that human fibroblasts and cancer cells express the HIOMT298 isoform as contrasted with the expression of the HIOMT345 isoform in pineal cells. Sequencing analysis of the cloned isoforms revealed that HIOMT298 is identical to the sequence of a previously reported truncated HIOMT isoform. Of note, HIOMT298 expression was reduced in cancer cells and tissues. Stable transfection of A549 cancer cells with HIOMT298 restored HIOMT expression to normal levels, accompanied by 5-MTP production. Furthermore, HIOMT298 transfection caused a tryptophan-metabolic switch from serotonin to 5-MTP production. To determine the relevance of this alteration, we compared growth and lung metastasis of HIOMT298-transfected A549 cells with those of vector- or untransfected A549 cells as controls in a murine xenograft model. Of note, the HIOMT298-transfected A549 cells exhibited slower growth and lower metastasis than the controls. Our findings provide insight into the crucial role of HIOMT298 in 5-MTP production in cells and in inhibiting cancer progression and highlight the potential therapeutic value of 5-MTP for managing cancer.

5-methoxytryptophan: an arsenal against vascular injury and inflammation

“…It is not entirely certain as to which isoform of HIOMT catalyzes 5-MTP synthesis. Recent published data suggest that HIOMT298 isoform is the active isoform in 5-MTP synthesis [ 10 ]. HIOMT is known to catalyze the final step of melatonin synthesis in pineal and retinal cells.…”

“…ASMT345 is the major isoform expressed in pineal cells and retinoblastoma cell line Y-79. By contrast, only isoform 298 mRNA is detected in human ECs and fibroblasts [ 10 ]. Cancer cells express a very low level of HIOMT298 and are deficient in 5-MTP synthesis.…”

“…Cancer cells express a very low level of HIOMT298 and are deficient in 5-MTP synthesis. Stable transfection of HIOMT298 in A549 lung cancer cells restores 5-MTP synthesis [ 10 ]. These results suggest that HIOMT298 is the active isoform catalyzing 5-MTP synthesis [ 10 ].…”

Persistent elevation of blood pressure by ambient coarse particulate matter after recovery from pulmonary inflammation in mice

“…Angiotensin II (AngII) and serotonin were measured using ultra‐performance liquid chromatography (UPLC) coupled with a Xevo‐TQ mass spectrometer (MS) as previously described . In brief, liquid chromatography was performed using an Acquity UPLC system (Waters Corporation) with a BEH C18 column (1.7 μM, 2.1 mm × 100 mm; Waters Corporation).…”

Hydroxyindole-O-methyltransferase (HIOMT) activity in the retina of melatonin-proficient mice

“…In humans, HIOMT also localizes within the PAR region (Yi et al., 1993), and display a high inter-individual enzyme variance (Bernard et al., 1995). Besides these genetic features, the possible expression of HIOMT isoforms, even truncated, has been proposed (Chen et al., 2018). It is thus possible that currently available analytical methods are not sensitive enough to detect HIOMT variants in the retinal counterpart, preventing the investigation of its function and regulation in the native tissue (Tosini and Menaker, 1998; Żmijewski et al., 2009; Tosini et al., 2012).…”