The Role of RASSF1A in Uveal Melanoma

1, 5, 6 PURPOSE. RASSF1A inactivation in uveal melanoma (UM) is common and methylation-induced. We investigated the effect of RASSF1A re-expression on the UM phenotype in vivo and in vitro. METHODS. The phenotypic effect of methylation-induced inactivation of RASSF1A in UM was explored using a stable RASSF1A-expressing UM-15 clone. RASSF1A expression was assessed using QRT-PCR. Proliferation was evaluated in vitro using MTT assays. Additionally, athymic NOD/SCID mice were injected subcutaneously or intraocularly with RASSF1A-expressing and -non-expressing UM-15 clones, and euthanized when tumors reached a volume of 1500 mm 3 , or at 56 or 46 days, respectively. Tumor tissues, eyes, and livers were analyzed histologically. RESULTS. In vitro analysis confirmed the lack of RASSF1A expression and full methylation of the RASSF1A promoter region in the UM-15 cell line, which was reversible following treatment with 5-Aza-2-deoxycytidine. Cells expressing exogenous RASSF1A showed slower proliferation than controls and regained sensitivity to cisplatin. Compared to mice injected with control cells, mice treated with UM-15 cells expressing exogenous RASSF1A did not acquire intraocular tumors, and their subcutaneous tumors were relatively delayed and small. Neither group had liver metastases. CONCLUSIONS. UM cells reduced tumorigenicity in the presence of activated RASSF1A. RASSF1A apparently has an important role in the development of UM, and its reactivation might be applied in the development of new treatments. (Invest Ophthalmol Vis Sci. 2012;53:2611-2619) DOI:10.1167/ iovs.11-7730 U veal melanoma (UM) is the most common form of primary eye cancer in adults, with an annual incidence of 6-7 cases per million per year. 1 It accounts for 80% of all noncutaneous melanomas and 13% of all deaths caused by melanoma. The tumor carries up to 50% 5-year mortality from metastasis. 3,4 However, their biological and clinical behaviors differ. 2 Additionally, although alterations of chromosomes 1 and 6 are common to both tumors, aberrations, such as monosomy of chromosome 3 and gain of 8q, in addition to other aberrations, typically are found only in UM. 9 Studies revealed that a mutation in the alpha subunit of the heterotrimeric G gene (GNAQ) was present in almost half of all UMs examined, 9-15 and that UM metastatic spread was related to mutations in the BRCA associated protein 1 (BAP1) gene on chromosome 3. 9 Aberrant promoter hypermethylation of CpG islands is thought to have an important role in the inactivation of tumor suppressor genes (TSGs) in cancer. 21 From th

Photoperiod-induced increases in bone mineral apposition rate in Siberian hamsters and the involvement of seasonal leptin changes

The adipokine leptin regulates energy balance, appetite, and reproductive maturation. Leptin also acts on bone growth and remodeling, but both osteogenic and anti-osteogenic effects have been reported depending on experimental conditions. Siberian hamsters (Phodopus sungorus) have natural variation in circulating leptin concentrations, where serum leptin is significantly decreased during the short day (SD)-induced winter state. In summer long day (LD) photoperiods, appetite and body adiposity increase with associated central leptin insensitivity. This natural change in leptin secretion was exploited to investigate leptin’s effect on bone growth. Hamsters were injected with calcium-chelating fluorescent dyes to measure bone mineral apposition rate (MAR). Measurements were initially obtained from 5-week and 6-month-old animals maintained in low leptin (SD) or high leptin (LD) states. A further study investigated effects of chronic administration of recombinant mouse leptin to hamsters housed in SD and LD conditions; growth plate thickness and bone density were also assessed. As expected, a reduction in body mass was seen in hamsters exposed to SD, confirming the phenotype change in all studies. Serum leptin concentrations were significantly reduced in SD animals in all studies. MAR was reproducibly and significantly increased in the femurs of SD animals in all studies. Vitamin D and growth plate thickness were significantly increased in SD animals at 6 months. No effect on bone density was observed in any study. Taken together these data suggest that bone growth is associated with the low leptin, winter, lean state. In leptin-treated animals, there was a significant interaction effect of leptin and photoperiod. In comparison to their vehicle counterparts, SD animals had decreased and LD animals had increased MAR, which was not apparent prior to leptin administration. In conclusion, increased MAR was associated with low serum leptin levels in early life and sustained over 6 months, implying that leptin has a negative effect on bone growth in this model. The unexpected finding that MAR increased after peripheral leptin administration in LD suggests that leptin exerts different effects on bone growth dependent on initial leptin status. This adds further weight to the hypothesis that leptin-treated LD animals display central leptin resistance