Many genes have been described and characterized which result in alternative polyadenylation site use at the 3'-end of their mRNAs based on the cellular environment. In this survey and summary article 95 genes are discussed in which alternative polyadenylation is a consequence of tandem arrays of poly(A) signals within a single 3'-untranslated region. An additional 31 genes are described in which polyadenylation at a promoter-proximal site competes with a splicing reaction to influence expression of multiple mRNAs. Some have a composite internal/terminal exon which can be differentially processed. Others contain alternative 3'-terminal exons, the first of which can be skipped in some cells. In some cases the mRNAs formed from these three classes of genes are differentially processed from the primary transcript during the cell cycle or in a tissue-specific or developmentally specific pattern. Immunoglobulin heavy chain genes have composite exons; regulated production of two different Ig mRNAs has been shown to involve B cell stage-specific changes in trans -acting factors involved in formation of the active polyadenylation complex. Changes in the activity of some of these same factors occur during viral infection and take-over of the cellular machinery, suggesting the potential applicability of at least some aspects of the Ig model. The differential expression of a number of genes that undergo alternative poly(A) site choice or polyadenylation/splicing competition could be regulated at the level of amounts and activities of either generic or tissue-specific polyadenylation factors and/or splicing factors.

Previous studies on the regulation of polyadenylation of the immunoglobulin (Ig) heavy-chain pre-mRNA argued for trans-acting modifiers of the cleavage-polyadenylation reaction operating differentially during B-cell developmental stages. Using four complementary approaches, we demonstrate that a change in the level of hnRNP F is an important determinant in the regulated use of alternative polyadenylation sites between memory and plasma stage B cells. First, by Western analyses of cellular proteins, the ratio of hnRNP F to H or H was found to be higher in memory B cells than in plasma cells. In memory B cells the activity of CstF-64 binding to pre-mRNA, but not its amount, was reduced. Second, examination of the complexes formed on input pre-mRNA in nuclear extracts revealed large assemblages containing hnRNP H, H, and F but deficient in CstF-64 in memory B-cell extracts but not in plasma cells. Formation of these large complexes is dependent on the region downstream of the AAUAAA in pre-mRNA, suggesting that CstF-64 and the hnRNPs compete for a similar region. Third, using a recombinant protein we showed that hnRNP F could bind to the region downstream of a poly(A) site, block CstF-64 association with RNA, and inhibit the cleavage reaction. Fourth, overexpression of recombinant hnRNP F in plasma cells resulted in a decrease in the endogenous Ig heavychain mRNA secretory form-to-membrane ratio. These results demonstrate that mammalian hnRNP F can act as a negative regulator in the pre-mRNA cleavage reaction and that increased expression of F in memory B cells contributes to the suppression of the Ig heavy-chain secretory poly(A) site.The immunoglobulin (Ig) heavy-chain transcription unit and the two heavy-chain mRNAs it encodes are shown in Fig. 1A (reviewed in reference 8). In mature and memory B cells the promoter-distal membrane-specific poly(A) site (mb-pA) is selected and splicing to the downstream M1 exon occurs via a 5Ј splice site within the coding region of CH4. The secretoryspecies-specific poly(A) (sec-pA) and mb-pA sites are used with equal frequency in mature and memory B cells and their tumor analogs, lymphoma cells. Plasma cells are terminally differentiated B cells; myeloma cells are their tumor counterparts, which accurately reflect their pattern of Ig gene expression. In plasma and myeloma lines polyadenylation takes place preferentially at the weaker, promoter-proximal sec-pA site, precluding the splicing to membrane-specific exons; the sec-pA site is used up to 100-fold more often than the mb-pA site in plasma cells (23). Polyadenylation at the promoter-proximal secretory site and splicing of CH4 to M1 are mutually exclusive events; consequently, it is the balance between these two that determines the final ratio of secretory-form to membrane mRNA (sec-to-mb mRNA ratio) (26). Previous experiments demonstrated that regulation of Ig heavy-chain mRNA production occurs primarily at the level of polyadenylation, not message stability, transcription termination, or splicing efficiency (14-16, 19, 2...

Fibroproliferative disorders such as idiopathic pulmonary fibrosis and systemic sclerosis have no effective therapies and result in significant morbidity and mortality due to progressive organ fibrosis. We examined the effect of peptides derived from endostatin on existing fibrosis and fibrosis triggered by two potent mediators, transforming growth factor–β (TGF-β) and bleomycin, in human and mouse tissues in vitro, ex vivo, and in vivo. We identified one peptide, E4, with potent antifibrotic activity. E4 prevented TGF-β–induced dermal fibrosis in vivo in a mouse model, ex vivo in human skin, and in bleomycin-induced dermal and pulmonary fibrosis in vivo, demonstrating that E4 exerts potent antifibrotic effects. In addition, E4 significantly reduced existing fibrosis in these preclinical models. E4 amelioration of fibrosis was accompanied by reduced cell apoptosis and lower levels of lysyl oxidase, an enzyme that cross-links collagen, and Egr-1 (early growth response gene–1), a transcription factor that mediates the effects of several fibrotic triggers. Our findings identify E4 as a peptide with potent antifibrotic activity and a possible therapeutic agent for organ fibrosis.

We have determined that the DNA sequence downstream of the well-characterized gonococcal fbp gene contains two open reading frames: one designated fbpB, which encodes a protein proposed to function as a cytoplasmic permease, and one designated fbpC, which encodes a protein proposed to function as a nucleotidebinding protein. The fpbABC operon composes an iron transport system that is homologous to the sfu and hit operons previously reported for Serratia marcescens and Haemophilus influenzae, respectively, and displays elements characteristic of ATP binding cassette transporters. The fpbABC operon differs from these loci in that it is lethal when overexpressed in Escherichia coli.