P53 In Melanoma Cells Research Articles

Transparent Adult Zebrafish as a Tool for In Vivo Transplantation Analysis

The zebrafish is a useful model for understanding normal and cancer stem cells, but analysis has been limited to embryogenesis due to the opacity of the adult fish. To address this, we have created a transparent adult zebrafish in which we transplanted either hematopoietic stem/progenitor cells or tumor cells. In a hematopoiesis radiation recovery assay, transplantation of GFP-labeled marrow cells allowed for striking in vivo visual assessment of engraftment from 2 hr-5 weeks posttransplant. Using FACS analysis, both transparent and wild-type fish had equal engraftment, but this could only be visualized in the transparent recipient. In a tumor engraftment model, transplantation of RAS-melanoma cells allowed for visualization of tumor engraftment, proliferation, and distant metastases in as little as 5 days, which is not seen in wild-type recipients until 3 to 4 weeks. This transparent adult zebrafish serves as the ideal combination of both sensitivity and resolution for in vivo stem cell analyses.

A Novel BH3 Mimetic Reveals a Mitogen-Activated Protein Kinase–Dependent Mechanism of Melanoma Cell Death Controlled by p53 and Reactive Oxygen Species

The RAS/BRAF/MEK/ERK mitogen-activated protein kinase (MAPK) pathway is emerging as a key modulator of melanoma initiation and progression. However, a variety of clinical studies indicate that inhibiting the MAPK pathway is insufficient per se to effectively kill melanoma cells. Here, we report on a genetic and pharmacologic approach to identify survival factors responsible for the resistance of melanoma cells to MEK/ERK antagonists. In addition, we describe a new tumor cell-selective means to bypass this resistance in vitro and in vivo. By generating a panel of isogenic cell lines with specific defects in the apoptotic machinery, we found that the ability of melanoma cells to survive in the absence of functional MEK relies on an ERK-independent expression of the antiapoptotic factor Mcl-1 (and to a lesser extent, Bcl-x(L) and Bcl-2). Using computer-based modeling, we developed a novel Bcl-2 homology domain 3 (BH3) mimetic. This compound, named TW-37, is the first rationally designed small molecule with high affinity for Mcl-1, Bcl-x(L), and Bcl-2. Mechanistic analyses of the mode of action of TW-37 showed a synergistic tumor cell killing in the presence of MEK inhibitors. Importantly, TW-37 unveiled an unexpected role of the MAPK pathway in the control of reactive oxygen species (ROS). This function was critical to prevent the activation of proapoptotic functions of p53 in melanoma cells, but surprisingly, it was dispensable for normal melanocytes. Our results suggest that this MAPK-dependent ROS/p53 feedback loop is a point of vulnerability of melanoma cells that can be exploited for rational drug design.

P53 plays a central role in UVA and UVB induced cell damage and apoptosis in melanoma cells

We investigated whether p53 plays a role in UV induced apoptosis in melanoma. UVA and UVB induced apoptosis in dose dependent and wild type p53 melanoma cells were much more vulnerable than the mutant cells, indicating that p53 played a role in UV-induced apoptosis in melanoma. No difference in p53 expression pattern between the primary and matched metastatic melanomas was noticed in tumour tissue or cell lines from the same patients. Our findings indicate that expression of p53 plays a role in UV-induced apoptosis in melanoma cells, but not important in melanoma progression from primary to metastasis.

Survivin protein in UVB induced apoptosis of melanoma cells and in melanoma progression

A model system of cultivated melanoma cells and melanomas from patients were used in this study to clarify whether survivin protein was involved in UVB induced cell damage and in melanoma progression. The melanoma cells in culture were exposed to different doses of UVB and post-cultivated for various periods of time. Cell viability, apoptotic index and expression of survivin proteins were estimated. Expression of the survivin in normal tissue, nevi, primary and metastatic melanomas from the patients were also examined by immunohistochemistry. Results showed that UVB induced cell damage and apoptosis in melanoma cells. Primary and wt p53 cells were more sensitive than metastatic and mutant p53 melanoma cells. Expression of survivin protein was markedly decreased in the primary melanoma cells after exposure to UVB compared to the metastasis. The expression was markedly decreased in wt p53 melanoma cells, but not in the mutant p53 melanoma cells. Survivin protein was expressed in nevi, primary and metastatic melanomas. However, the normal tissues were not expressed in the survivin protein. Survivin plays an important role in UVB-induced apoptosis. Overexpression of survivin might be a biomarker for early diagnosis for melanoma.