A novel cis-acting element from the 3'UTR of DNA damage-binding protein 2 mRNA links transcriptional and post-transcriptional regulation of gene expression.

The DNA damage-binding protein 2 (DDB2) is an adapter protein that can direct a modular Cul4-DDB1-RING E3 Ligase complex to sites of ultraviolet light-induced DNA damage to ubiquitinate substrates during nucleotide excision repair. The DDB2 transcript is ultraviolet-inducible; therefore, its regulation is likely important for its function. Curiously, the DDB2 mRNA is reportedly short-lived, but the transcript does not contain any previously characterized cis-acting determinants of mRNA stability in its 3' untranslated region (3'UTR). Here, we used a tetracycline regulated d2EGFP reporter construct containing specific 3'UTR sequences from DDB2 to identify novel cis-acting elements that regulate mRNA stability. Synthetic 3'UTRs corresponding to sequences as short as 25 nucleotides from the central region of the 3'UTR of DDB2 were sufficient to accelerate decay of the heterologous reporter mRNA. Conversely, these same 3'UTRs led to more rapid induction of the reporter mRNA, export of the message to the cytoplasm and the subsequent accumulation of the encoded reporter protein, indicating that this newly identified cis-acting element affects transcriptional and post-transciptional processes. These results provide clear evidence that nuclear and cytoplasmic processing of the DDB2 mRNA is inextricably linked.

Lovastatin inhibits VEGFR and AKT activation: synergistic cytotoxicity in combination with VEGFR inhibitors.

BACKGROUND: In a recent study, we demonstrated the ability of lovastatin, a potent inhibitor of mevalonate synthesis, to inhibit the function of the epidermal growth factor receptor (EGFR). Lovastatin attenuated ligand-induced receptor activation and downstream signaling through the PI3K/AKT pathway. Combining lovastatin with gefitinib, a potent EGFR inhibitor, induced synergistic cytotoxicity in a variety of tumor derived cell lines. The vascular endothelial growth factor receptor (VEGFR) and EGFR share similar activation, internalization and downstream signaling characteristics. METHODOLOGY/PRINCIPAL FINDINGS: The VEGFRs, particularly VEGFR-2 (KDR, Flt-1), play important roles in regulating tumor angiogenesis by promoting endothelial cell proliferation, survival and migration. Certain tumors, such as malignant mesothelioma (MM), also express both the VEGF ligand and VEGFRs that act in an autocrine loop to directly stimulate tumor cell growth and survival. In this study, we have shown that lovastatin inhibits ligand-induced VEGFR-2 activation through inhibition of receptor internalization and also inhibits VEGF activation of AKT in human umbilical vein endothelial cells (HUVEC) and H28 MM cells employing immunofluorescence and Western blotting. Combinations of lovastatin and a VEGFR-2 inhibitor showed more robust AKT inhibition than either agent alone in the H28 MM cell line. Furthermore, combining 5 µM lovastatin treatment, a therapeutically relevant dose, with two different VEGFR-2 inhibitors in HUVEC and the H28 and H2052 mesothelioma derived cell lines demonstrated synergistic cytotoxicity as demonstrated by MTT cell viability and flow cytometric analyses. CONCLUSIONS/SIGNIFICANCE: These results highlight a novel mechanism by which lovastatin can regulate VEGFR-2 function and a potential therapeutic approach for MM through combining statins with VEGFR-2 inhibitors.

Lovastatin enhances gefitinib activity in glioblastoma cells irrespective of EGFRvIII and PTEN status.

The epidermal growth factor receptor (EGFR) is commonly amplified and mutated in glioblastoma, making it a compelling therapeutic target. Recent reports have demonstrated clinical activity of the EGFR inhibitors gefitinib and erlotinib in a subset of glioblastoma patients. Co-expression of EGFRvIII, a constitutively active mutant receptor expressed in 50% of tumours, and PTEN, an inhibitor of PI3K activity, by glioblastoma cells is associated with clinical response to these EGFR kinase inhibitors. PTEN loss and resulting increased PI3K pathway activity appears to act as a resistance factor. A critical therapeutic challenge is to identify agents that enhance the anti-cancer effects of these agents and promote responsiveness to EGFR kinase inhibitors in a broader spectrum of glioblastoma patients. For example, combining gefitinib with inhibitors of the PI3K/AKT pathway show enhanced cytotoxicity in glioblastoma derived cell lines. Here, we show that targeting HMG-CoA reductase with lovastatin, that can affect the activity of multiple cell signaling pathways, significantly enhanced the sensitivity of glioblastoma cells to the EGFR kinase inhibitor gefitinib in the five cell lines tested. In an isogenic model system, U87MG glioblastoma cells expressing EGFRvIII and PTEN in relevant combinations, we show that combined gefitinib and lovastatin treatments induce potent synergistic cytotoxicity irrespective of EGFRvIII and PTEN status. These studies demonstrate the potential of lovastatin to augment the cytotoxic effects of gefitinib and provide a rationale for combined statin/EGFR targeted therapies in glioblastoma patients.