LRAT Overexpression Diminishes Intracellular Levels of Biologically Active Retinoids and Reduces Retinoid Antitumor Efficacy in the Murine Melanoma B16F10 Cell Line

Abstract

Background/Aim: Vitamin A (all-trans-retinol, ATRol) serves as a precursor for all-trans-retinoic acid (ATRA), a ligand for the retinoic acid receptor (RAR), representing a potent regulator for many physiological processes. While murine melanoma cells are highly sensitive to retinoid treatment, human melanoma cells have developed still unidentified mechanisms that mediate cellular retinoid resistance. One of the key retinoid metabolizing enzymes is lecithin retinol acyltransferase (LRAT), which catalyzes the transformation of ATRol into inactive retinyl esters. LRAT is highly expressed in human melanoma cells. The aim of this study was to identify the mechanisms in retinol metabolism that are responsible for cellular retinoid sensitivity in the murine melanoma cell line B16F10. Methods: mRNA expression analysis, cell viability assessment and determination of intracellular retinoid levels using HPLC analysis of a generated LRAT-overexpressing B16F10 cell line compared to the control B16F10 cell line. Results: We found that the murine retinoid-sensitive B16F10 cell line does not express the enzyme LRAT. LRAT overexpression decreased the antiproliferative effects of retinoid treatment in these melanoma cells. The RAR-regulated enzyme Cyp26a1 showed a significantly lower expression in LRAT-overexpressing B16F10 cells. Cyp26a1 expression was restored after ATRA incubation. HPLC analysis revealed that the level of inactive retinyl ester increased after ATRol treatment, and levels of the substrate ATRol and biologically active ATRA significantly decreased in LRAT-overexpressing murine melanoma. Consistently with this, levels of 4-oxo-retinoic acid, an ATRA metabolite and Cyp26a1 product, were also decreased in LRAT-overexpressing cells. Conclusion: Our results revealed a direct link between LRAT expression and regulation of ATRA levels indicating that the absence of LRAT-catalyzed retinol esterification is important for mediating retinoid sensitivity in murine melanoma cells. Thus, our data suggest that LRAT overexpression represents a novel mechanism by which tumor cells can escape high supplementary ATRA levels that mediate tumor-suppressive RAR signaling.

Identification of Long Non-coding and Messenger RNAs Differentially Expressed Between Primary and Metastatic Melanoma

“…Other genes such as CYP3A4, CYP2C9, ADH4, ADH1A, and CYP1A2 enriched in the cytochrome P450 pathway are observed as metabolically active procarcinogens to genotoxic intermediates, and an association has been found between CYP enzyme activity and the risk to develop several forms of cancer. Amann et al (2015) found that the retinoic acid receptor (RAR) regulated enzyme CYP26a1 showed a significantly lower expression in the lecithin retinol acyltransferase (LRAT)-overexpressing murine melanoma B16F10 cell line. The absence of LRAT-catalyzed retinol esterification is important for mediating retinoid sensitivity in murine melanoma cells.…”

Early synergistic interactions between the HPV16‑E7 oncoprotein and 17β-oestradiol for repressing the expression of Granzyme�B in a cervical cancer model

“…Furthermore, this synergistic interaction between E7 and E 2 resulted in distinct gene expression profiles even within the same ontological processes compared with that in the groups that did not develop cancer (FVB, FVB+E 2 and K14E7). Although some of these genes have already been implicated in cancer, a number are new in the context of CC; for example, Nppc is expressed in prostate cancer ( 37 – 39 ), GDPD3 is overexpressed in luminal B type breast cancer ( 40 ), MGAT4C is associated with prostate cancer risk ( 41 ), IL1R2 is observed in relation to colon cancer and is associated with enhanced angiogenesis ( 42 ), and LRAT is involved in the metabolism of retinoic acid, which when overexpressed, increases the sensitivity of cells to carcinogens ( 43 ). Most notably, the synergistic effect of the HPV16-E7 oncoprotein and E 2 on the downregulation of the Granzyme gene family was observed in the present study.…”

Intrinsic Disorder in Nuclear Receptor Amino Termini: From Investigational Challenge to Therapeutic Opportunity

“…For some NR, there may be benefit from the reciprocal approach of small molecule facilitation of NR A/B activity. Retinoids in various forms are key to chemotherapy for various dermatologic and non-dermatologic benign hyperproliferative and malignant neoplastic pathologies [133,134]. However, their use is often limited by metabolic inactivation or dose toxicity.…”