α-Synuclein Expression Selectively Affects Tumorigenesis in Mice Modeling Parkinson's Disease

Alpha Synuclein (α-Syn) is a protein implicated in mechanisms of neuronal degeneration in Parkinson's disease (PD). α-Syn is primarily a neuronal protein, however, its expression is found in various tumors including ovarian, colorectal and melanoma tumors. It has been hypothesized that neurodegeneration may share common mechanisms with oncogenesis. We tested whether α-Syn expression affects tumorigenesis of three types of tumors. Specifically, B16 melanoma, E0771 mammary gland adenocarcinoma and D122 Lewis lung carcinoma. For this aim, we utilized transgenic mice expression the human A53T α-Syn form. We found that the in vivo growth of B16 and E0771 but not D122 was enhanced in the A53T α-Syn mice. The effect on tumorigenesis was not detected in age-matched APP/PS1 mice, modeling Alzheimer's disease (AD), suggesting a specific effect for α-Syn- dependent neurodegeneration. Importantly, transgenic α-Syn expression was detected within the three tumor types. We further show uptake of exogenously added, purified α-Syn, by the cultured tumor cells. In accord, with the affected tumorigenesis in the young A53T α-Syn mice, over- expression of α-Syn in cultured B16 and E0771 cells enhanced proliferation, however, had no effect on the proliferation of D122 cells. Based on these results, we suggest that certain forms of α-Syn may selectively accelerate cellular mechanisms leading to cancer

Tumorigenicity in old A53T α-Syn +/+ and control mice.

<p>(a). Mice (9–10 months old) were injected with B16 melanoma cells and tumor volumes were determined as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0019622#pone-0019622-g001" target="_blank">Fig. 1a</a>. The experiment was stopped after 20 days, when the tumors in any genotype group reached 1 to 1.2 cm in diameter. The graph represents the means ± standard errors (SE) of 8–9 mice in each group. (b). Mice were injected with D122 Lewis lung carcinoma cells and tumor volume was measured as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0019622#pone-0019622-g001" target="_blank">Fig. 1a</a>. Mean weights of tumors formed in each group at 20 days post- injection ± SE for B16 (c); and D122 (d). *, p<0.05 Mann-Whitney test.</p

Tumorigenicity of B16 melanoma is not affected in APP/PS1 tg mice.

<p>(a). Mice (3–4 months old) were injected subcutaneously with 2.5×10⁵ B16 melanoma cells and tumor volumes were determined every 1–2 days post injection. The experiment was stopped after 14 days, when the tumors in the A53T α-Syn+/+ group reached 1 to 1.2 cm in diameter. The graph represents the means ± standard errors (SE) of 5–7 mice in each group. (b). Mean weights of tumors formed in each group at 14 days post- injection ± SE. *, p<0.05, Mann-Whitney test.</p

α-Syn expression in B16 and E0771 enhances cell proliferation.

<p>(a). Stable poly-clones of B16 cells over expressing either human wt α-Syn, human β-Syn, amyloid precursor protein carrying the Swedish mutation (APPsw) or mock-transfected, were seeded in a 96-well plates at 5×10³ cells per well. Proliferation was determined by the fluorescence ratio at 560ex/590em and normalized to the mock-transfected cells. A representative result of cells 48 hours post seeding. Mean ± SE of n = 6 wells out of three repeats. (b) Stable poly-clones of E0771 and (c) D122, seeded and measured as in (a). *, p<0.05, Mann-Whitney test.</p

Tumorigenicity in young A53T α-Syn +/+ and control F1 B6/C3H mice.

<p>(a). Mice (3–4 months old) were subcutaneously injected with 0.25×10⁶ B16 melanoma cells. Tumor volumes were determined every 1–2 days post injection. The experiment was stopped after 15 days, when the tumors in the A53T α-Syn +/+ group reached 1 to 1.2 cm in diameter. The graph represents the means ± standard errors (SE) of 5–8 mice in each group. A representative growth curve out of three independent experiments. (b). Mice were injected with 1×10⁵ E0771 mammary gland adenocarcinoma cells and tumor volume was measured as in (a). (c). Mice were injected with 5×10⁴ D122 Lewis lung carcinoma and tumor volume was measured as in (a). (d). Mean weights of tumors formed in each genotype group at 15 days post- injection ± SE for B16, *,p = 0.015, t-test; (e). E0771, *, p = 0.012, t-test; (f). D122; (g). Mean weights of tumors formed in each genotype group at 15 days post- injection ± SE, n = 6–7, *, p<0.05 Mann-Whitney test.</p