The low molecular weight cyclin E isoforms augment angiogenesis and metastasis of human melanoma cells in vivo.

Immunohistochemical analysis has consistently shown that cyclin E is up-regulated in human malignant melanomas in vivo. Here we analyzed such expression in more detail and show that cyclin E is overexpressed and present in low molecular weight (LMW) isoforms in metastatic melanoma and in a subset of primary invasive melanoma tumor tissues, but not in benign nevi. Human metastatic melanoma cell lines, but not normal melanocytes, also expressed the LMW cyclin E forms. The biological significance of these findings was established by showing that overexpression of two LMW cyclin E forms named cyclin E truncated 1 [cyclinE(T1)] and cyclin E truncated 2 [cyclinE(T2)] in a low tumorigenic and non-metastatic primary cutaneous melanoma cell line generated angiogenic tumors with prominent perineural invasion compared with full-length cyclin E. In addition, cyclin E(T1)- and cyclin E(T2)-expressing melanoma cells displayed a dramatic increase in the incidence and number of metastases in an experimental lung metastasis assay. Together, these results indicate that the LMW cyclin E forms are functional and likely act as regulators of human melanoma tumor progression and invasion.

Targeting the epidermal growth factor receptor in epithelial ovarian cancer: current knowledge and future challenges.

The epidermal growth factor receptor is overexpressed in up to 60% of ovarian epithelial malignancies. EGFR regulates complex cellular events due to the large number of ligands, dimerization partners, and diverse signaling pathways engaged. In ovarian cancer, EGFR activation is associated with increased malignant tumor phenotype and poorer patient outcome. However, unlike some other EGFR-positive solid tumors, treatment of ovarian tumors with anti-EGFR agents has induced minimal response. While the amount of information regarding EGFR-mediated signaling is considerable, current data provides little insight for the lack of efficacy of anti-EGFR agents in ovarian cancer. More comprehensive, systematic, and well-defined approaches are needed to dissect the roles that EGFR plays in the complex signaling processes in ovarian cancer as well as to identify biomarkers that can accurately predict sensitivity toward EGFR-targeted therapeutic agents. This new knowledge could facilitate the development of rational combinatorial therapies to sensitize tumor cells toward EGFR-targeted therapies.

The differential staurosporine-mediated G1 arrest in normal versus tumor cells is dependent on the retinoblastoma protein.

Previously, we reported that breast cancer cells with retinoblastoma (pRb) pathway-defective checkpoints can be specifically targeted with chemotherapeutic agents, following staurosporine-mediated reversible growth inhibition in normal cells. Here we set out to determine if the kinetics of staurosporine-mediated growth inhibition is specifically targeted to the G(1) phase of cells, and if such G(1) arrest requires the activity of wild-type pRb. Normal human mammary epithelial and immortalized cells with intact pRb treated with low concentrations of staurosporine arrested in the G(1) phase of the cell cycle, whereas pRb-defective cells showed no response. The duration of G(1) and transition from G(1) to S phase entry were modulated by staurosporine in Rb-intact cells. In pRb(+) cells, but not in Rb(-) cells, low concentrations of staurosporine also resulted in a significant decrease in cyclin-dependent kinase 4 (CDK4) expression and activity. To directly assess the role of pRb in staurosporine-mediated G(1) arrest, we subjected wild-type (Rb(+/+)) and pRb(-/-) mouse embryo fibroblasts (MEFs) to staurosporine treatments. Our results show that whereas Rb(+/+) MEFs were particularly sensitive to G(1) arrest mediated by staurosporine, pRb(-/-) cells were refractory to such treatment. Additionally, CDK4 expression was also inhibited in response to staurosporine only in Rb(+/+) MEFs. These results were recapitulated in breast cancer cells treated with siRNA to pRb to down-regulate the pRb expression. Collectively, our data suggest that treatment of cells with nanomolar concentrations of staurosporine resulted in down-regulation of CDK4, which ultimately leads to G(1) arrest in normal human mammary epithelial and immortalized cells with an intact pRb pathway, but not in pRb-null/defective cells.