Carcinogenesis Advance Access originally published online on October 18, 2005
Carcinogenesis 2006 27(4):693-707; doi:10.1093/carcin/bgi235
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Evidence that sequence homologous region in LRAT-like proteins possesses anti-proliferative activity and DNA binding properties: translational implications and mechanism of action
Laboratory of Cellular Carcinogenesis and Tumor Promotion, Center for Cancer Research, National Cancer Institute, NIH, Bethesda, MD 20892, USA, 1 Basic Research Program, SAIC-Frederick, and 2 Laboratory of Medicinal Chemistry, Center for Cancer Research, NCI-Frederick, Frederick, MD 21702, USA
* To whom correspondence should be addressed. Tel: +1 301 496 2698; Fax: +1 301 496 8709; Email: delucal{at}mail.nih.gov
LRAT (lecithin:retinol acyltransferase), an enzyme whose levels are modulated during malignant conversion, has been reported as the founder member of a new LRAT-like family that includes tumor suppressors TIG-31–164 and Ha-Rev1071-162. The mechanisms that link these three proteins to carcinogenesis as well as the significance of a reported shared sequence homologous region remain unclear. This begs the question if the tumor suppressors possess enzyme properties and/or if the LRAT enzyme possesses tumor suppressor properties. We use the reported homologous region as a first approach to address the question from the perspective that all three proteins can possess tumor suppressor properties. We postulated that the homologous sequence harbors an anti-proliferation domain within the full-length proteins and that dodecapeptides of this sequence possess anti-proliferative activity. We report that H-TIG-3111–123, H-Ha-Rev107-1111–123 and H-LRAT160–171:C168L exhibited in vitro growth inhibitory activity in a human cutaneous melanoma (HCM) model and affected tumor growth in a nude mouse model. Further, in peptide-sensitive HCM cells, these peptides crossed the plasma membrane and localized to the nucleus, where they could bind and activate promoters of transcription factors involved in G1
S transition. Moreover, peptide-induced abrogation of cyclin dependent kinase-2 expression was concomitant with sub-cellular re-distribution of cyclins E and A. Indeed, the sequence homologous region within each full-length wild-type protein as well as the growth inhibitory peptides can form alpha helices, a likely configuration for binding to DNA. This is the first report that this sequence homologous region (AA111–123) within these LRAT-like proteins harbors an anti-proliferative domain with DNA binding properties. Sequences from this sequence homologous region can be used as templates for anti-tumor drug design and as probes to investigate disease-related mechanisms and structure-activity relationships of the full-length proteins, TIG-31–164, Ha-Rev1071–162 and LRAT160–171.