141 All-trans Retinoic Acid Inhibits Cell Proliferation through Upregulation of TET2 in Squamous Cell Cancer

Abstract

Cutaneous squamous cell carcinoma (cSCC) is the second most frequent non-melanoma skin cancer. All-trans retinoic acid (ATRA) has been previously proposed anti-tumor potential via inhibiting cancer cell growth by binding to the intracellular retinoic acid receptors (RAR). The ten-eleven translocation 2 (TET2) proteins oxidize the epigenetic mark 5-methylcytosine to 5-hydroxymethylcytosine (5hmC) and loss-functions of TET2 leading to hypermethylation have been established in various cancers. However, its role in cSCC remains unknown. In the present study, we detected the expression of 5hmC, TET2 and retinoic acid receptor B (RARb) in normal skin, actinic keratosis (AK), Bowen disease and cSCC clinical samples by immunohistochemical staining. It’s significant downregulation of 5hmC and TET2 were observed in the AK, Bowen disease and cSCC tissues compared with normal skin, while expression of RARb was reduced. Human primary keratinocytes and cSCC cell lines (Scl-1 and HSC-1) were cultured in vitro, receiving stimulation of retinoic acid. The results showed that treatment with ATRA inhibited the proliferation of cSCC cell lines and increased the expressions of TET2 and RARb in cSCC cell lines. Moreover, ectopic overexpression of TET2 in cSCC cell lines induce upregulation of RARB while no obvious expression changes of TET2 were observed in RARB overexpressed cSCC cell lines. Our results suggest that TET2 and 5hmC were decreased in cSCC tissue and cSCC cell lines compared to normal tissues and human primary keratinocytes. In addition, ATRA promotes the expression of TET2 in cSCC cell lines, which is closely related to RARb. This study provides evidence that 5hmC and TET2 have the potentials to serve as biomarkers that identified presence and progression of cSCC. It identified a novel function of ATRA in promoting a TET-mediated epigenetic regulation suggesting that the availability of ATRA in cancer cells will have various effects on different epigenetic targets.