An alternative HER-2/neu transcript of 8 kb has an extended 3'UTR and displays increased stability in SKOV-3 ovarian carcinoma cells

Alternative polyadenylation: An enigma of transcript length variation in health and disease

Alternative polyadenylation (APA) is a molecular mechanism during a pre-mRNA processing that involves usage of more than one polyadenylation site (PA-site) generating transcripts of varying length from a single gene. The location of a PA-site affects transcript length and coding potential of an mRNA contributing to both mRNA and protein diversification. This variation in the transcript length affects mRNA stability and translation, mRNA subcellular and tissue localization, and protein function. APA is now considered as an important regulatory mechanism in the pathophysiology of human diseases. An important consequence of the changes in the length of 3'-untranslated region (UTR) from disease-induced APA is altered protein expression. Yet, the relationship between 3'-UTR length and protein expression remains a paradox in a majority of diseases. Here, we review occurrence of APA, mechanism of PA-site selection, and consequences of transcript length variation in different diseases. Emerging evidence reveals coordinated involvement of core RNA processing factors including poly(A) polymerases in the PA-site selection in diseases-associated APAs. Targeting such APA regulators will be therapeutically significant in combating drug resistance in cancer and other complex diseases. This article is categorized under: RNA Processing > 3' End Processing RNA in Disease and Development > RNA in Disease Translation > Regulation.

EGFR/HER-targeted therapeutics in ovarian cancer

Despite decades of research and evolving treatment modalities, survival among patients with epithelial ovarian cancer has improved only incrementally. During this same period, the development of biologically targeted therapeutics has improved survival for patients with diverse malignancies. Many of these new drugs target the human epidermal growth factor receptor (EGFR/HER/ErbB) family of tyrosine kinases, which play a major role in the etiology and progression of many carcinomas, including epithelial ovarian cancer. While several HER-targeted therapeutics are US FDA approved for the treatment of various malignancies, none have gained approval for the treatment of ovarian cancer. Here, we review the published literature on HER-targeted therapeutics for the treatment of ovarian cancer, including novel HER-targeted therapeutics in various stages of clinical development, as well as the challenges that have limited the use of these inhibitors in clinical settings.

Antagonism of the human epidermal growth factor receptor family controls disease severity in murine collagen-induced arthritis

OBJECTIVE

To evaluate the therapeutic potential of the human epidermal growth factor receptor (HER) family inhibitor, herstatin, in an animal model of arthritis.

METHODS

Constructs of herstatin and modified tissue plasminogen activator (tPA)-herstatin were expressed in HEK 293T cells, and secreted protein was analyzed by Western blotting. Tissue PA-herstatin adenovirus (Ad-tPA-Her) was prepared, and titers established. Gene expression of Ad-tPA-Her was determined by polymerase chain reaction using HeLa cells. Pharmacokinetics of gene and protein expression in vivo in liver tissue and serum samples were confirmed via intravenous administration of Ad-tPA-Her. Clinical signs of disease were monitored in arthritic DBA/1 mice after therapeutic administration of Ad-tPA-Her, and histologic analysis of hind foot specimens was performed.

RESULTS

Native herstatin was not secreted in supernatants, while modified tPA-herstatin was detected in abundance. HeLa cells stably expressed the tPA-herstatin gene when infected with virus. Additionally, tPA-herstatin gene and protein expression was observed over time in mice treated with virus. Importantly, Ad-tPA-Her, when administered therapeutically to arthritic mice, controlled clinical and histologic signs of disease and reduced the number of joints with severe damage.

CONCLUSION

Our results support the notion that the human epidermal growth factor receptor family has a role in the progression of collagen-induced arthritis. The novel tPA-herstatin fusion protein could be used as an effective therapeutic tool for control of inflammatory disorders involving an angiogenic component.

Taxol Increases the Amount and T Cell–Activating Ability of Self-Immune Stimulatory Multimolecular Complexes Found in Ovarian Cancer Cells

It has been proposed that chemotherapy enhances tumor antigen (TA)-specific immunity. The molecular form of TA from ovarian tumor that activates cellular immunity is unknown. We report here identification of a novel molecular form of immunogenic TA for CD8(+) cells named self-immune stimulatory multimolecular complexes (ISMMC). ISMMC consist of a molecular complex of polyosome/ribosome-bound ubiquitinated nascent HER-2 polypeptides. This complex is chaperoned by heat shock protein Gp96, which mediates ISMMC uptake by antigen-presenting cells through the scavenger receptor CD91. RNAs in ISMMC stimulate immature dendritic cells to secrete interleukin 12 and induce IFN-gamma in peripheral blood mononuclear cells. ISMMC dissociate, retrotranslocate from the lysosome to cytoplasm, and are processed to peptides by the proteasome. At subpharmacologic doses, Taxol increased the amount of ISMMC by three to four times and modified their composition by inducing the attachment of cochaperones of HSP70, such as the mitotic-phase phosphoprotein 11J. On a total protein basis, Taxol induced ISMMC, expanded more CD8(+) cells, activated more CD56(+) NKG2D(+) cells to produce IFN-gamma, and were more potent inducers of high T-cell receptor density Perforin(+) cells than native ISMMC and peptide E75. Elucidation of the composition of ISMMC and identification of adducts formed by Taxol should be important for developing molecular cancer vaccines.

Derepression of the Her-2 uORF is mediated by a novel post-transcriptional control mechanism in cancer cells

Transcripts harboring 5' upstream open reading frames (uORFs) are often found in genes controlling cell growth including receptors, oncogenes, or growth factors. uORFs can modulate translation or RNA stability and mediate inefficient translation of these potent proteins under normal conditions. In dysregulated cancer cells, where the gene product, for example Her-2 receptor, is overexpressed, post-transcriptional processes must exist that serve to override the inhibitory effects of the uORFs. The 5' untranslated region (UTR) of Her-2 mRNA contains a short uORF that represses translation of the downstream coding region. We demonstrate that in Her-2 overexpressing breast cancer cells, the 3' UTR of the Her-2 mRNA can override translational inhibition mediated by the Her-2 uORF. Within this 3' UTR, a translational derepression element (TDE) that binds to a 38-kDa protein was identified. These results define a novel biological mechanism in which translational control of genes harboring a 5' uORF can be modulated by elements in their 3' UTRs.

Elevated levels of the 64-kDa cleavage stimulatory factor (CstF-64) in lipopolysaccharide-stimulated macrophages influence gene expression and induce alternative poly(A) site selection

Lipopolysaccharide (LPS) activation of murine RAW 264.7 macrophages influences the expression of multiple genes through transcriptional and post-transcriptional mechanisms. We observed a 5-fold increase in CstF-64 expression following LPS treatment of RAW macrophages. The increase in CstF-64 protein was specific in that several other factors involved in 3'-end processing were not affected by LPS stimulation. Activation of RAW macrophages with LPS caused an increase in proximal poly(A) site selection within a reporter mini-gene containing two linked poly(A) sites that occurred concomitant with the increase in CstF-64 expression. Furthermore, forced overexpression of the CstF-64 protein also induced alternative poly(A) site selection on the reporter minigene. Microarray analysis performed on CstF-64 overexpressing RAW macrophages revealed that elevated levels of CstF-64 altered the expression of 51 genes, 14 of which showed similar changes in gene expression with LPS stimulation. Sequence analysis of the 3'-untranslated regions of these 51 genes revealed that over 45% possess multiple putative poly(A) sites. Two of these 51 genes demonstrated alternative polyadenylation under both LPS-stimulating and CstF-64-overexpressing conditions. We concluded that the physiologically increased levels of CstF-64 observed in LPS-stimulated RAW macrophages contribute to the changes in expression and alternative polyadenylation of a number of genes, thus identifying another level of gene regulation that occurs in macrophages activated with LPS.

Postgenomic global analysis of translational control induced by oncogenic signaling

It is commonly assumed that developmental and oncogenic signaling achieve their phenotypic effects primarily by directly regulating the transcriptional profile of cells. However, there is growing evidence that the direct effect on transcription may be overshadowed by differential effects on the translational efficiency of specific existing mRNA species. Global analysis of this effect using microarrays indicates that this mechanism of controlling protein production provides a highly specific, robust, and rapid response to oncogenic and developmental stimuli. The mRNAs so affected encode proteins involved in cell-cell interaction, signal transduction, and growth control. Furthermore, a large number of transcription factors capable of secondarily rearranging the transcriptional profile of the cell are controlled at this level as well. To what degree this translational control is either necessary or sufficient for tumor formation or maintenance remains to be determined.

Different mechanisms are implicated in ERBB2 gene overexpression in breast and in other cancers

The ERBB2 gene is overexpressed in 30% of breast cancers and this has been correlated with poor prognosis. ERBB2 is upregulated in other cancers such as prostate, pancreas, colon and ovary. In breast cancer cells, the mechanisms leading to ERBB2 gene overexpression are increased transcription and gene amplification. In these cancers, AP-2 transcription factors are involved in ERBB2 overexpression, and AP-2 levels are correlated with p185(c-)(erbB-2) levels. In this work, we wanted to know if the same molecular mechanisms are responsible for the ERBB2 upregulation in non-breast cancers. We compared ERBB2 gene copy number, p185(c-)(erbB-2) and mRNA levels with AP-2 levels in several ovary, prostate, colon and pancreas cancer cells. A moderate expression of erbB-2 mRNA and protein were observed in some cells without gene amplification. In contrast to breast cancer cells, AP-2 factors were absent or low in some non-breast cells which did express ERBB2. It is thus likely that AP-2 is not a major player in the increased levels of erbB-2 transcripts in non-breast cancer cells. The transcriptional activity of the ERBB2 promoter in colon and ovary cancer cells was estimated using reporter vectors. The results showed that the promoter regions involved in ERBB2 gene overexpression in breast cancer cells are different from those that lead to the gene upregulation in colon and ovary cancers. In conclusion, our results indicate that different transcriptional and post-transcriptional mechanisms are responsible for the increased levels of erbB-2 transcript and protein in breast and non-breast cancer cells.