Esterification of all-trans-retinol in normal human epithelial cell strains and carcinoma lines from oral cavity, skin and breast: reduced expression of lecithin:retinol acyltransferase in carcinoma lines

Abstract

When exogenous [(3)H]retinol (vitamin A) was added to culture medium, normal human epithelial cells from the oral cavity, skin, lung and breast took up and esterified essentially all of the [(3)H]retinol within a few hours. As shown by [(3)H]retinol pulse-chase experiments, normal epithelial cells then slowly hydrolyzed the [(3)H]retinyl esters to [(3)H]retinol, some of which was then oxidized to [(3)H]retinoic acid (RA) over a period of several days. In contrast, cultured normal human fibroblasts and human umbilical vein endothelial cells (HUVEC) did not esterify significant amounts of [(3)H]retinol; this lack of [(3)H]retinol esterification was correlated with a lack of expression of lecithin:retinol acyltransferase (LRAT) transcripts in normal fibroblast and HUVEC strains. These results indicate that normal, differentiated cell types differ in their ability to esterify retinol. Human carcinoma cells (neoplastically transformed epithelial cells) of the oral cavity, skin and breast did not esterify much [(3)H]retinol and showed greatly reduced LRAT expression. Transcripts of the neutral, bile salt-independent retinyl ester hydrolase and the bile salt-dependent retinyl ester hydrolase were undetectable in all of the normal cell types, including the epithelial cells. These experiments suggest that retinoid-deficiency in the tumor cells could develop because of the lack of retinyl esters, a storage form of retinol.

Reduced Lecithin

“…In addition, we showed that LRAT mRNA and protein decrease in TCC of the bladder with increasing pathological tumor stage. These data extend our previous research, which has shown that several types of human carcinomas, including breast, head and neck, skin, prostate, and kidney, exhibit major alterations in LRAT transcripts and a reduced ability to accumulate retinyl esters (25)(26)(27)(28)(29). We have also recently demonstrated differential LRAT protein expression in subtypes of renal cell carcinoma; specifically, LRAT expression was found to be higher in renal tumors, such as chromophobe renal cell carcinoma and renal oncocytoma, with an indolent biological behavior (30).…”

“…Two enzymes have been reported to catalyze retinyl ester synthesis, LRAT and acylCoA:ROL acyltransferase. LRAT levels are reduced in many types of carcinoma specimens and cell lines (25)(26)(27)(28)(29). Given the stated importance of retinyl esterification, then, it is likely that reduced expression of LRAT would result in reduced levels of RA, and thereby render the affected cells at least in part functionally retinoid deficient.…”

“…LRAT mRNA and protein expression have, in addition, been shown in select tissues to be regulated by exogenous retinoids (24). We have demonstrated previously that the metabolism of ROL to retinyl esters is greatly reduced in various human carcinoma cell lines, including prostate, kidney, skin, breast, and oral cavity, as compared with normal human cultured epithelial cell strains from these same human tissues (25)(26)(27)(28)(29). In addition, we have shown that LRAT levels were reduced in the tumor tissue from patients with renal cell carcinoma and prostate cancer compared with adjacent, normal tissue from these organs (25,26,30).…”

Expression of estrogen receptor α, retinoic acid receptor α and cellular retinoic acid binding protein II genes is coordinately regulated in human breast cancer cells

“…Likewise, our conclusion does not exclude the possibility that, under some circumstances, CRAB-PII expression may be dissociated from RARa expression. A case in point is the ERa-negative MDA-MB-468 cell line, which expresses low RARa but high CRABPII mRNA levels (Guo et al, 2000). In human keratinocytes, RARg has been shown to drive CRABPII expression (Astrom et al, 1992;Di et al, 1998) suggesting that in MDA-MB-468 cells, which express RARg (Widschwendter et al, 1995), this receptor may account for CRABPII expression.…”

Cytochrome P450 Cyp26a1 Alters Spinal Motor Neuron Subtype Identity in Differentiating Embryonic Stem Cells

“…After the final wash, PBS was removed, and 0.5 ml of fresh PBS was added to each sample for harvesting. The retinoids were extracted from 350 l of organic phase from both the cell and medium samples of each sample in a dark environment as described (19,20). The HPLC was performed using a Waters Millennium system (Waters Corp., Milford, MA).…”