A human integrin beta 1 subunit with a unique cytoplasmic domain generated by alternative mRNA processing.

The integrin subunit (beta 1) is common to a group of plasma membrane glycoprotein heterodimers that include the fibronectin, laminin and collagen receptors. These receptors span the plasma membrane, providing a transmembrane linkage between the extracellular matrix and the cytoskeleton. Here, we describe a variant of the human beta 1 differing from the previously described beta 1 in the cytoplasmic domain. The variant beta 1 transcript (beta 13'v) is present in different cell types and is synthesized at lower levels compared to the beta 1 mRNA. The cytoplasmic domain of the beta 13'v is characterized by a unique 12-amino acid C-terminal sequence. A Tyr residue present in this region, and known to be phosphorylated in the beta 1, is no longer part of a consensus sequence for phosphorylation by Tyr kinases. The integrin cytoplasmic domain anchors actin fibrils to the plasma membrane by interacting with cytoskeletal proteins such as talin and fibulin. The integrin beta 13'v with the variant cytoplasmic domain is likely to mediate a new type of membrane-cytoskeleton interaction during cell-cell and cell-matrix adhesion. Analysis of genomic clones showed that the new sequences of the variant mRNA are identical to an intron located between the last two exons of the beta 1 gene, indicating that the alternative message is generated either by premature transcription termination or by lack of splicing at this site.

Cloning of cDNA for a novel mouse membrane glycoprotein (gp42): shared identity to histocompatibility antigens, immunoglobulins and neural-cell adhesion molecules.

A full-length clone encoding a murine membrane glycoprotein, gp42, was selected from a mouse fibroblast cDNA expression library by screening with a polyclonal antiserum. The deduced amino acid (aa) sequence indicates that gp42 is a transmembrane protein of 273 aa with a large N-terminal portion exposed outside the cell and a short cytoplasmic domain. Computer assisted analysis shows that gp42 is distinct from previously characterized proteins, but shares a number of structural features with the class II histocompatibility antigens. The sizes of the extracellular domains of gp42 and of class II histocompatibility antigens are similar, the position of four cysteines and the location of several aa residues are conserved. Some of these conserved residues are also present in immunoglobulins (Ig) and in the neural-cell adhesion molecule, thus indicating that gp42 is a new member of the Ig superfamily.

An intronic deletion in TP53 gene causes exon 6 skipping in breast cancer.

Six hundred and thirty primary breast cancer were screened for abnormalities in exons 5, 6, 7 and 8 of the TP53 tumour suppressor gene. Analysis of the structure of the TP53 gene exons was performed with the polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) method and with direct sequencing of amplified DNA. In a breast tumour case from a postmenopausal patient, we found a deletion of 36 bp in intron 5 and no immunohistochemical staining for p53. We amplified and sequenced the cDNA region between exons 4 and 7 and showed that the deletion causes the skipping of exon 6. The resulting mRNA sequence had a frameshift that yields an inactive protein with a truncated C terminus. These results show the first example of intronic deletion causing exon skipping at the TP53 gene level.

Analysis of regulatory regions of the ciliary neutrophic factor gene in transgenic mice.

In order to study the regulatory regions of the human ciliary neurotrophic factor (CNTF) gene we made constructs containing sequences upstream and downstream of CNTF coding regions and the lacZ gene and analysed their expression in transgenic mice. We show that 240 bp upstream of the translation start codon are sufficient for the transcription of the lacZ gene. A further 4 kb upstream sequence is required for the expression of the transgene in Schwann cells. These two upstream regions together with a 2 kb downstream fragment drive high level of expression of the lacZ gene in the sciatic nerve. Our results indicate that these three fragments contain regulatory regions able to mimic the CNTF expression pattern in the mouse peripheral nervous system.

Evaluation of commercial kits for the detection and typing of human papillomavirus in cervical swabs.

Human papillomaviruses (HPV) detection by MY consensus primers amplification within the L1 region and typing of prevalent genital HPVs by reference and commercial sets of probes was compared by PCR-ELISA systems. The specificity of commercial probes used in the L1 HPV Geno-Kit with respect to the reference probes proved to be 100%, with an overall agreement of 97.6%. The discordant results concerned only the detection of HPV 16, both as single genotype present in the sample and as multiple infections. The analytical sensitivity of the commercial probe for HPV 16 proved to be slightly less sensitive than the reference probe in the hybridisation conditions of the PCR-ELISA system. The L1 PCR-ELISA reference system was evaluated further in comparison with commercial E6/E7 consensus PCR and microplate hybridisation by typing kit. Amplified products of both the L1 and E6/E7 consensus regions were also analysed by agarose gel electrophoresis. An overall concordance of 95.2% was found. On account of its specificity and sensitivity the E6/E7 commercial system proved to be particularly useful for diagnostic laboratory, as it detects only the prevalent high risk genotypes. The agarose gel detection can therefore be used as screening test, thus reducing the costs, while the E6 E7 HPV Geno-Kit High Risk can be used when specific typing is required.

Tumor necrosis factor alpha and interferon gamma modulate the expression of the vitronectin receptor (integrin beta 3) in human endothelial cells.

In this paper we show that tumor necrosis factor alpha (TNF alpha) and interferon gamma (IFN gamma) alter the expression of extracellular matrix receptors (integrins) in cultured human endothelial cells. Endothelial cells express at their surface integrins of the beta 1 and beta 3 groups that include receptors for fibronectin, collagen, laminin, and vitronectin. After treatment for 72 h with a combination of TNF alpha and IFN gamma, the level of the vitronectin receptor (alpha v beta 3) at the cell surface decreases by 70%, whereas the amounts of the beta 1 integrins remain unchanged. The decreased expression of the alpha v beta 3 complex at the cell surface is due to a selective effect of TNF alpha and IFN gamma on the regulation of the beta 3 subunit synthesis at the translational level. In fact, although the steady state levels of the mRNA for the beta 3 subunit are comparable in control and treated cells, the overall synthesis of the beta 3 subunit is decreased by a factor of 70%. No significant alteration of the synthesis of the companion alpha v subunit is detectable in cytokine-treated cells. As a consequence of the decreased expression of the receptor, cytokine-treated cells show decreased ability to adhere to vitronectin but adhere normally to fibronectin. These data show that two important inflammatory mediators, TNF alpha and IFN gamma, can modify the interaction of endothelial cells with the extracellular matrix by selectively altering the expression of specific cell surface integrin complexes.

Expression of receptors for extracellular matrix proteins in human endothelial cells.

The interaction with matrix components of the basal membrane is an important factor in the control of vascular endothelial cell function in both normal and pathological conditions. In the present work we define integrin receptors in vascular endothelial cells and analyze whether their expression is affected by endothelial cell activators. Using in vitro adhesion tests we show that human endothelial cells (HEC) can attach and spread on substrates coated with several matrix components including fibronectin, laminin, collagen type IV, fibrinogen and vitronectin. Using specific antibodies we detect integrin receptor complexes of the beta 1 and beta 3 families that can support adhesion of HEC to the above matrix proteins. These are the alpha 2/beta 1 collagen receptor, the alpha 3/beta 1 receptor for fibronectin, collagens and laminin, the alpha 5/beta 1 fibronectin receptor, the alpha 6/beta 1 laminin receptor and the alpha V/beta 3 receptor for vitronectin and fibrinogen. When HEC are exposed to a combination of tumor necrosis factor alpha (TNF alpha) and immune interferon (IFN-gamma) the amount of the alpha V/beta 3 vitronectin receptor at the cell surface was decreased by a factor of 50-70%, while the beta 1 integrin complexes were not affected. HEC cells thus express receptors for several matrix components and inflammatory mediators such as TNF alpha and IFN-gamma can selectively alter the expression of some of them.

Ciliary neurotrophic factor constitutively expressed in the nervous system of transgenic mice protects embryonic dorsal root ganglion neurons from apoptosis.

Ciliary neurotrophic factor (CNTF) is a potent survival factor for several neuronal populations. It is expressed postnatally by Schwann cells in the peripheral nervous system and by some glial and neuronal cells in the central nervous system. We used the promoter of the neurofilament light chain gene to produce transgenic mice that express CNTF in neurons from the beginning of neuronal differentiation. These transgenic animals may represent a suitable model to identify neuronal cell types responsive to CNTF in vivo and to study the mechanism of action of this neurotrophic factor. We show that dorsal root ganglion neurons of transgenic mice expressing CNTF in neurons are protected from apoptosis during embryonic development: 40% of these cells undergo apoptosis between embryonic day 12.5 and postnatal day 5 in transgenic mice whereas 60% do so in control animals. However, protection from apoptosis does not result in an increase in the total number of neurons at the end of development. We discuss our results with regard to CNTF potentialities in vivo and the significance of programmed cell death during development.