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Microarray analyses uncover UBE1L as a candidate target gene for lung cancer chemoprevention
Ian Pitha-Rowe1, W Jeffrey Petty, Qing Feng
1Department of Pharmacology and Toxicology, Dartmouth Medical School, Hanover, New Hampshire 03755, USA.
Abstract:
Retinoids, natural and synthetic derivatives of vitamin A, are active in cancer therapy and chemoprevention. We reported previously that all-trans-retinoic acid (RA) treatment prevented carcinogen-induced transformation of immortalized human bronchial epithelial (HBE) cells. To identify cancer chemopreventive mechanisms, immortalized (BEAS-2B), carcinogen-transformed (BEAS-2B(NNK)), and RA-chemoprevented (BEAS-2B(NNK/RA)) HBE cells were used to conduct microarray analyses independently. Species increased in chemoprevented as compared with immortalized HBE cells (group I) and those augmented in chemoprevented as compared with transformed HBE cells (group II) included known RA-target genes as well as previously unrecognized RA-target genes in HBE cells. Unexpectedly, both groups were also enriched for interferon-stimulated genes. One interferon-stimulated gene of particular interest was UBE1L, the ubiquitin-activating enzyme E1-like protein. UBE1L expression was also induced after prolonged RA-treatment of immortalized HBE cells. UBE1L mRNA was shown previously as repressed in certain lung cancer cell lines, directly implicating UBE1L in lung carcinogenesis. Notably, UBE1L immunoblot expression was reduced in a subset of malignant as compared with adjacent normal lung tissues that were examined. Immunohistochemical analyses were performed using a new assay developed to detect this species using rabbit polyclonal anti-UBE1L antibodies independently raised against the amino- or carboxyl-termini of UBE1L. Studies done on paraffin-embedded and fixed tissues revealed abundant UBE1L, but low levels of cyclin D1 expression in the normal human bronchial epithelium, indicating an inverse relationship existed between these species. To study this further, cotransfection into HBE cells of wild-type or mutant UBE1L species was accomplished. In a dose-dependent manner, wild-type but not mutant UBE1L species repressed cyclin D1 expression. This implicated UBE1L in a retinoid chemoprevention mechanism involving cyclin D1 repression described previously. Taken together, these findings directly implicate UBE1L as a candidate-pharmacologic target for lung cancer chemoprevention. These findings also provide a mechanistic basis for the tumor suppressive effects of UBE1L through cyclin D1 repression.
Insights
Retinoids like all-trans-retinoic acid (RA) prevent lung cancer by upregulating UBE1L, a gene that represses cyclin D1. This mechanism offers a new target for lung cancer chemoprevention.
Area of Science:
- Oncology
- Molecular Biology
- Biochemistry
Background:
- Retinoids (vitamin A derivatives) show promise in cancer therapy and chemoprevention.
- All-trans-retinoic acid (RA) has been shown to prevent carcinogen-induced transformation in human bronchial epithelial (HBE) cells.
Purpose of the Study:
- To identify molecular mechanisms underlying retinoid chemoprevention of lung cancer.
- To investigate the role of UBE1L (ubiquitin-activating enzyme E1-like protein) in retinoid-mediated chemoprevention.
Main Methods:
- Microarray analysis of immortalized, carcinogen-transformed, and RA-chemoprevented HBE cells.
- Gene expression analysis (mRNA and protein levels) of UBE1L and cyclin D1.
- Immunohistochemistry on human lung tissues.
- Cell transfection studies with wild-type and mutant UBE1L.
Main Results:
- RA treatment upregulated known and novel RA-target genes, including interferon-stimulated genes like UBE1L.
- UBE1L expression was induced by RA and repressed in some lung cancers.
- UBE1L expression was inversely correlated with cyclin D1 expression in normal bronchial epithelium.
- Wild-type UBE1L repressed cyclin D1 expression in HBE cells, while mutant UBE1L did not.
Conclusions:
- UBE1L is implicated as a key mediator in retinoid chemoprevention of lung cancer.
- UBE1L's tumor-suppressive effects are partly mediated through the repression of cyclin D1.
- UBE1L represents a potential pharmacologic target for lung cancer chemoprevention strategies.
