Inhibitory and stimulatory effects of somatostatin on two human pancreatic cancer cell lines: a primary role for tyrosine phosphatase SHP-1.

Somatostatin (SS-14) and its structural analogue SMS 201-995 (SMS) are recognized as physiological inhibitors of multiple organs and tissue functions through specific membrane receptors (sst1-sst5). The effects of SS-14 and SMS in the growth control of the pancreatic cancer cell lines MIA PaCa-2 and PANC-1 were investigated to identify and clarify the intracellular events involved. In PANC-1 cells, SS-14 and SMS caused inhibition of their basal growth, and that stimulated by epidermal growth factor, with a maximal effect at 0.1-1 microM. To understand the inhibitory mechanisms, we investigated the effects of SS-14 and SMS on phosphotyrosine phosphatase (PTPase) activity and, more specifically, that of tyrosine phosphatase SHP-1 (PTP1C). SS-14 and SMS caused significant increases in total cellular PTPase activity, and particularly SHP-1, with maximal activation within 1 min. Inhibition of membrane tyrosine kinase and p42 MAP kinase activities was also observed, in response to SS-14 and SMS. In MIA PaCa-2 cells, SS-14 and SMS were associated with a positive growth response at 1-10 nM, after 4 days of culture in serum-free medium. Total cellular PTPase activity was slightly increased, but SHP-1 activity could not be detected; its absence in this cell line was confirmed by Western blot. Membrane tyrosine kinase activities were significantly increased by SS-14 and SMS at concentrations needed for maximal growth. p44/p42, which are constitutively active in this cell line, and p38 activities were not affected by somatostatin. In conclusion, somatostatin can exert different effects on human pancreatic cancer cell growth, depending upon the presence or absence of SHP-1. This enzyme can play a key role in the control of cell proliferation, and its cellular presence may determine the therapeutic potential of somatostatin in the control of cancer cell growth.

Molecular cloning of IgE-binding fragments of Alternaria alternata allergens.

Exposure to the hyphomycete Alternaria alternata is recognized as an important risk factor for asthma. IgE immunoblotting has been used to catalogue the number and Mr of allergens in A. alternata extracts, with estimates ranging from 10 to 30, although few are present in nearly all extracts studied. Several A. alternata allergens have been cloned, including a subunit of the major allergen Alt a 1, ribosomal P2 phosphoprotein, aldehyde dehydrogenase and a yeast YCP4 homolog. We have cloned two sequences encoding IgE-binding fragments of allergens from an A. alternata lambda gt11 cDNA library using pooled atopic sera from A. alternata-sensitive individuals. One is homologous to a region near the C-terminus of hsp70 from Cladosporium herbarum; a near-complete isoallergen variant of A. alternata ribosomal P2 protein was also cloned. Their lacZ fusion proteins had reactivities of 5 and 14%, respectively, with individual atopic sera, indicating that the corresponding allergens are both minor. This study describes one new A. alternata allergen candidate and implicates ribosomal P2 protein as an allergen thtat is stable between independently isolated clones.

Isolation and expression of a cDNA clone encoding an Alternaria alternata Alt a 1 subunit.

Alternaria alternata is recognized as an important source of fungal aeroallergens. Alt a 1, the major allergen of this mold, is a dimer of disulfide-linked subunits that migrate in SDS-PAGE under reducing conditions at apparent M(r)s of 14,500 and 16,000. IgE antibodies to this protein are present in the sera of >90% of A. alternata-sensitive individuals. Previous studies from this laboratory showed that the N-termini twenty amino acids of the purified subunits are nearly identical. We now report the isolation of clones from an A. alternata (strain 34-016) cDNA library constructed in lambda(gt)11, using rabbit IgG antiserum against partially purified Alt a 1. One of nineteen clones selected from screens totalling 305,000 pfu (rb51) was sequenced, and determined to harbor an insert of 660 bp. An in-frame open reading frame within the cloned insert encodes a peptide of M(r) 16,960 that bears no significant homology to known allergens or proteins. The size of the rb51 transcript was determined to be approximately 0.7 kb by Northern analysis of A. alternata total RNA. The largely hydrophobic N-terminal region of the peptide contains an alpha-helical domain and other features characteristic of membrane targeting or secretory signals. The peptide sequence downstream of this region matches previously sequenced Alt a 1 N-terminal from two independent sources at 17 of 20, and 24 of 26 positions. Recombinant Alt a 1 expressed as a secreted protein in Pichia pastoris exists as a dimer in conditioned medium, as shown by immunoblotting under nonreducing conditions. Recombinant Alt a 1, like the natural allergen in A. alternata extracts, is also reactive with serum IgE from A. alternata-sensitive individuals.

An allergenic polypeptide representing a variable region of hsp 70 cloned from a cDNA library of Cladosporium herbarum.

BACKGROUND: Extracts of Cladosporium herbarum, a major source of fungal aeroallergens, exhibit a complex profile of IgE-binding proteins. Yields of conventionally purified allergens from this mold have been insufficient to permit further molecular analyses. OBJECTIVE: To enhance and simplify the purification of allergens from C. herbarum, we have sought to use recombinant DNA techniques to clone, identify and bacterially express immunoselected C. herbarum allergens. METHODS: We constructed a cDNA library in lambda ZAP II using mRNA isolated from C. herbarum. From this library, phage clones encoding a new allergen were immunoselected using pooled human atopic IgE. The cloned cDNA was excised from the phage vector as a recombinant pBluescript II SK-phagemid and sequenced. Expression of the recombinant allergen was carried out in E. coli XL1-blue transformants of the phagemid. Bacterial lysates from cells induced to express the cloned allergen were immunoblotted and probed with individual human atopic IgEs. RESULTS: The cDNA clone encodes a 278 amino acid polypeptide homologous to the C-terminal portion of 70 kDa heat shock protein (hsp 70). The polypeptide possesses features common to other hsps 70, i.e. a similar hydropathic profile and a variable C-terminal region with conserved sequence at the very C-terminus. Binding of the recombinant peptide to IgE from 38% of atopic sera or plasma from individuals allergic to C. herbarum was demonstrated. CONCLUSION: These results indicate that amino acid substitutions are relatively conserved even in the variable C-terminal regions of hsp 70 species. Thus, this study should draw attention to the possibility of induction of anaphylactic responses in a sensitized individual when hsp 70 from any pathogenic species is administered for vaccination.

N-terminus of a major allergen, Alt a I, of Alternaria alternata defined to be an epitope.

A 20mer peptide representing the N-terminus of a major allergen, Alt a I, of Alternaria alternata was synthesized and examined for its antibody binding and antibody induction activities. Alt a I peptide-BSA conjugate reacted with both human IgE and rabbit anti-Alt a I IgG in ELISA, albeit the binding of the peptide to IgE was relatively weak. Control conjugate showed no antibody binding. These results indicated that the N-terminus of Alt a I is an antibody binding site. Moreover, peptide-KLH conjugate and nonconjugated peptide induced both IgG and IgE antibodies in Balb/c mice that recognized both native Alt a I allergen and peptide-BSA conjugate. Since the free peptide was able to induce antibodies in vivo, the peptide may also possess a T cell epitope.

A cDNA clone coding for a novel allergen, Cla h III, of Cladosporium herbarum identified as a ribosomal P2 protein.

Mold allergens represent a major cause of atopic disorders. Progress in the molecular characterization of allergens has been hampered by batch-to-batch variation and poor yields in mold extracts. In the present study, we established a cDNA library in lambda ZAP II by using mRNA isolated from a major allergen-producing mold, Cladosporium herbarum. From this library, a novel allergen has been cloned and sequenced. The clone encodes a full length protein of 111 amino acids with a molecular mass of 11.1 kDa and pI of 3.94. By using sequence homology analysis, the allergen was found to belong to the ribosomal P2 protein family. Approximately 60% peptide sequence homology was found between the cloned protein and other known fungal ribosomal P2 proteins. In addition to conserved C-terminal sequences and serine blocks for phosphorylation in all eukaryotic ribosomal P2 proteins, this protein also contains a potential N-glycosylation site at position 15-17. Northern blots demonstrated that mRNA molecules of this gene are present even at late stages of culture. The gene was expressed in Escherichia coli by using the pMAL-2c system, and murine antisera against the recombinant allergen (rCh2.1) were generated. The antisera revealed that the native allergen corresponding to rCh2.1 was present in extracts prepared by grinding mycelia under liquid nitrogen in the presence of protease inhibitors, but absent in extracts prepared by conventional methods. This result indicates the usefulness of recombinant allergens in characterization and standardization of mold allergenic extracts.

Two-dimensional immunoblot analysis of allergens of Cladosporium herbarum.

In the present study, allergens of Cladosporium herbarum were analysed by SDS-PAGE, two-dimensional gel electrophoresis and immunoblot. The SDS-PAGE under reduced conditions followed by western blotting analysis revealed 10 human IgE-binding components with molecular masses ranging from 15 to 143 kDa. Within the same molecular mass range, five components were detected under non-reduced conditions. Examination of the specificities of 10 individual sera revealed that two patients were sensitive to almost all the allergens, whereas the majority reacted with only some components. Two-dimensional immunoblot was employed to further analyse the allergens in the extract. A silver-stain of the two-dimensional gel revealed that there were more than 30 different protein components visible in the extract. Immunoblot of the proteins separated under denatured conditions disclosed that 17 spots were reactive with human atopic sera.