Cyclin-dependent kinase 11 (CDK11; also named PITSLRE) is part of the large family of p34 cdc2 -related kinases whose functions appear to be linked with cell cycle progression, tumorigenesis, and apoptotic signaling. However, substrates of CDK11 during apoptosis have not been identified. We used a yeast two-hybrid screening strategy and identified eukaryotic initiation factor 3 p47 protein (eIF3 p47) as an interacting partner of caspase-processed C-terminal kinase domain of CDK11 (CDK11 p46 ). We demonstrate that the eIF3 p47 can interact with CDK11 in vitro and in vivo, and the interaction can be strengthened by stimulation of apoptosis. EIF3 p47 contains a Mov34/JAB domain and appears to interact with CDK11 p46 through this motif. We show in vitro that the caspase-processed CDK11 p46 can phosphorylate eIF3 p47 at a specific serine residue (Ser 46 ) and that eIF3 p47 is phosphorylated in vivo during apoptosis. Purified recombinant CDK11 p46 inhibited translation of a reporter gene in vitro in a dose-dependent manner. In contrast, a kinase-defective mutant CDK11 p46M did not inhibit translation of the reporter gene. Stable expression of CDK11 p46 in vivo inhibited the synthesis of a transfected luciferase reporter protein and overall cellular protein synthesis. These data provide insight into the cellular function of CDK11 during apoptosis.

Accumulating evidence indicates that elevated levels of prostaglandin E 2 (PGE 2 ) can increase intestinal epithelial cell proliferation, and thus play a role in colorectal tumorigenesis. PGE 2 exerts its effects through four G-protein coupled PGE receptor (EP) subtypes, named the EP1, EP2, EP3, and EP4. Increased phosphorylation of extracellular regulated kinases (ERK1/2) is required for PGE 2 to stimulate cell proliferation of human colon cancer cells. However, the EP receptor(s) that are involved in this process remain unknown. We provide evidence that L-161,982, a selective EP4 receptor antagonist, completely blocks PGE 2 -induced ERK phosphorylation and cell proliferation of HCA-7 cells. In order to identify downstream target genes of ERK1/2 signaling, we found that PGE 2 induces expression of early growth response gene-1 (EGR-1) downstream of ERK1/2 and regulates its expression at the level of transcription. PGE 2 treatment induces phosphorylation of cyclic AMP response element binding protein (CREB) at Ser133 residue and CRE-mediated luciferase activity in HCA-7 cells. Studies with dominant negative CREB mutant (ACREB) provide clear evidence for the involvement of CREB in PGE 2 driven egr-1 transcription in HCA-7 cells. In conclusion, this study reveals that egr-1 is a target gene of PGE 2 in HCA-7 cells and is regulated via the newly identified EP4/ERK/CREB pathway. Finally our results support the notion that antagonizing EP4 receptors may provide a novel therapeutic approach to the treatment of colon cancer.

Selenomethionine (SeMet) is being tested alone and in combination with other agents in cancer chemoprevention trials. However, the molecular targets and the signaling mechanism underlying the anticancer effect of this compound are not completely clear. Here, we provide evidence that SeMet can induce cell-growth arrest and that the growth inhibition is associated with S-G2/M cell-cycle arrest. Coincidentally with the cell-cycle arrest, we observed a striking increase in cyclin B as well as phosphorylation of the cyclin-dependent kinase Cdc2. Since activation of the mitogen-activated protein kinase (MAPK) cascade has been associated with cell-cycle arrest and growth inhibition, we evaluated the activation of extracellular signal-regulated kinase (ERK). We found that SeMet induced phosphorylation of the MAPK ERK in a dose-dependent manner. We also demonstrate phosphorylation of ribosomal S6 kinase (p90RSK) by SeMet. Additionally, we show phosphorylation of histone H3 in a concentration-dependent manner. Furthermore, the phosphorylation of p90RSK and histone H3 were both antagonized by the MEK inhibitor U0126, implying that SeMet-induced phosphorylation of p90RSK and histone H3 are at least in part ERK pathway dependent. Based on these results, we propose that SeMet induced growth arrest and phosphorylation of histone H3 are mediated by persistent ERK and p90RSK activation. These new data provide valuable insights into the biological effects of SeMet at clinically relevant concentrations.

Prostate cancer is the most common cancer diagnosed and the second leading cause of cancer-related deaths in men in the United States. The etiological factors that give rise to prostate cancer are not known. Therefore, it is not possible to develop primary intervention strategies to remove the causative agents from the environment. However, secondary intervention strategies with selenium (Se) compounds and other agents represent a viable option to reduce the morbidity and mortality of prostate cancer. In this review, we discuss ongoing clinical trials. In addition, we discuss preclinical mechanistic studies that provide insights into the biochemical and molecular basis for the anti-carcinogenic activity of both inorganic and organic forms of Se.

Translocations and unique chromosome break points in melanoma will aid in the identification of the genes that are important in the neoplastic process. We have previously shown a unique translocation in malignant melanoma cells der(12)t(12;20). The transcription factor E2F1 maps to 20q11. Increased expression of E2F has been associated with the autonomous growth of melanoma cells, however, the molecular basis has not yet been elucidated. To this end, we investigated E2F1 gene copy number and structure in human melanoma cell lines and metastatic melanoma cases. Fluorescent in situ hybridization (FISH) analysis using a specific E2F1 probe indicated increased E2F1 gene copies in melanoma cell lines compared to normal melanocytes. We also observed increased copies of the E2F1 gene in lymph node metastases of melanoma. In addition, Western blot analysis demonstrated increased E2F1 protein levels in 8 out of 9 melanoma cell lines relative to normal melanocytes. Inhibition of E2F1 expression with RNAi also reduced melanoma cell growth. Our results suggest that the release of E2F activity by elevated E2F1 gene copy numbers may play a functional role in melanoma growth.