Transforming growth factor-B3 protects murine small intestinal crypt stem cells and animal survival after irradiation, possibly by reducing stem-cell cycling.

Damage to the normal replacing tissues of the body, specifically the gastro-intestinal tract, limits the treatment and hence, cure rate of cancer patients. Here, we investigate the possibility that the sensitivity of the gastro-intestinal tract can be manipulated by transforming growth factor beta3 (TGF-beta3), making it more resistant to radiation in a murine model. The effects of TGF-beta3 were assessed using the crypt microcolony assay, a test of crypt stem-cell functional competence, in animal survival studies examining diarrhoea severity, labelling index and crypt size. Prior treatment with TGF-beta3 can result in a 3- to 4-fold increase (protection factor, PF) in surviving crypts, whilst longer exposure can raise the PF to almost 12. Protection of intestinal clonogenic stem cells results in marked protection of survival with a corresponding reduction in the duration and level of diarrhoea and ultimate restoration of normal histology in surviving mice. Inhibition of proliferation can be demonstrated when sufficient TGF-beta3 exposure is studied. Crypt size is also reduced. In conclusion, TGF-beta3 protects small intestinal clonogenic stem cells from radiation damage, reducing diarrhoea and animal mortality. The mode of action is believed to be specific inhibition of stem-cell proliferation.

A p53 growth arrest protects fibroblasts from anticancer agents.

Reversible inhibitors of the cell cycle such as the TGF-betas have been exploited to protect dividing cells from exposure to anticancer drugs and radiation. Here, rat embryo fibroblast (REF) lines expressing different p53 mutations were used to test whether the p53 growth arrest could also chemoprotect cells from high doses of anticancer drugs. Whereas the doubling times of the different REF lines at 37 degrees C were similar, cells bearing temperature-sensitive mutations (mouse 135V or human 143A) were growth arrested at 31 degrees C. Temperature-dependent p53 activity was associated with increased levels of MDM2 and p21/WAF1, and the induction of an integrated p53-responsive luciferase gene. The REF lines exhibited similar sensitivities to common anticancer drugs when grown at 37 degrees C. However, when exposed to the same agents following transient incubation at 31 degrees C, the p53-arrested cells exhibited a marked survival advantage as shown by colony-forming assays. Chemoprotection was not universal, in that colony formation was not enhanced significantly after treatment with cisplatin or 5-fluorouracil, two drugs which can cause cellular damage throughout the cell cycle. Like other negative growth regulators, an activated p53 checkpoint may mediate the survival of cells exposed to drugs that target DNA synthesis or mitosis.

Transforming growth factor-beta 3 mediated modulation of cell cycling and attenuation of 5-fluorouracil induced oral mucositis.

Mucositis is a common, dose-limiting complication in patients receiving cancer chemotherapy, which derives from damage to the epithelial cell layer. We have shown that transforming growth factor-beta 3 (TGF-beta 3) negatively regulates epithelial cell proliferation and reduces the incidence of oral mucositis. Here, we report the findings of a large study examining the effects of TGF-beta 3 administration in a hamster model on oral epithelial cell cycling in vivo, on oral mucositis, on weight retention and on survival. Topical application of TGF-beta 3 to the buccal mucosa significantly reduced basal cell proliferation, as measured by proliferating cell nuclear antigen (PCNA) immunohistochemistry and DNA ploidy. Administration of topical TGF-beta 3 prior to chemotherapy with 5-fluorouracil (5-FU) significantly reduced the severity of mucositis with respect to time, reduced chemotherapy-associated weight loss and increased survival.

Effect of protein tyrosine phosphatase 1B expression on transformation by the human neu oncogene.

Many oncogenes encode proteins with a tyrosine kinase activity that appears to be directly involved in the process of transformation. Because these kinases are themselves activated for transformation by tyrosine phosphorylation, proteins which remove phosphate from tyrosine residues, protein tyrosine phosphatases (also termed phosphotyrosine phosphatases and protein phosphotyrosyl phosphatases), are intuitive candidate transformation suppressors. The human PTP1B gene, previously cloned in our laboratory and encoding the low molecular weight protein tyrosine phosphatase PTPase 1B, was introduced into NIH 3T3 cells. Subsequent transformation of these PTPase 1B-expressing cells by an oncogenic form of the human neu gene was suppressed relative to control NIH 3T3 cells. This suppression of transformation was observed in assays for focus formation, anchorage-independent growth, and tumorigenicity. Tumorigenicity assays indicated a complex effect of PTPase 1B expression on transformation.

Requirements for the internalization of a murine monoclonal antibody directed against the HER-2/neu gene product c-erbB-2.

A murine monoclonal antibody, TA1, is directed against an epitope on the extracellular domain of the HER-2/neu (c-erbB-2) gene product. Requirements for TA1-induced internalization of c-erbB-2 have been studied using the SKBr3 human breast cancer cell line and several rat fibroblast cell lines that express either wild-type or mutant human c-erbB-2. Internalization of TA1 was monitored by assaying protease-resistant uptake of 125I-labeled TA1, by electron microscopy of gold-labeled TA1, and by inhibition of clonogenic growth of cells incubated with TA1 that had been conjugated with blocked ricin. Similar rates of internalization of TA1 were observed in SKBr3 and in rat fibroblasts that expressed human c-erbB-2. The route of endocytosis was the same as that observed with antibodies against other membrane receptors. Anti-c-erbB-2 and anti-transferrin receptor cointernalized through clathrin-coated pits, coated vesicles, endosomes, and multivesicular bodies. Products of mutant c-erbB-2 that lacked a portion of the tyrosine kinase domain or that lacked most of the cytoplasmic domain were endocytosed in the presence of TA1 as promptly as the wild-type c-erbB-2 product. Slightly more rapid internalization of TA1 was observed in rat cells that expressed c-erbB-2 with a single point mutation in the transmembrane domain. Taken together, our data suggest that neither the intracytoplasmic domain nor receptor phosphorylation is required for antibody-mediated endocytosis of c-erbB-2.

Structure of the Spec1 gene encoding a major calcium-binding protein in the embryonic ectoderm of the sea urchin, Strongylocentrotus purpuratus.

We have identified and characterized the structure of the Spec1 gene in the sea urchin Strongylocentrotus purpuratus. In earlier studies we demonstrated that a small family of messenger RNAs, termed Spec mRNAs for S. purpuratus ectodermal mRNAs, begins to accumulate 20 hours after fertilization in ectoderm cells of the sea urchin embryo. The Spec mRNAs code for a group of low molecular weight proteins belonging to the troponin C superfamily. Spec1 transcripts, the predominant mRNAs of the family, are heterogeneous in their 3' untranslated sequences but code for a single protein, recently shown to be a calcium-binding protein. Spec complementary DNA clones were used to isolate genomic clones from two lambda libraries. These genomic clones comprise a 41 kb (kb = 10(3) bases or base-pairs) region of the S. purpuratus genome and contain a Spec1 gene closely linked to another Spec gene, Spec2c. The Spec1 gene is 10.3 kb in length and contains six exons. The genomic clones containing the Spec1 gene can be placed into two groups based on restriction fragment length differences and differences in hybridization strengths using probes derived from Spec1 3' untranslated regions. Evidence that these groups probably correspond to two alleles of the Spec1 gene was obtained by probing genomic DNA blots of sperm DNA from different individuals with 3' untranslated sequences of Spec1 complementary DNA clones. These blots show that two of the Spec1 mRNAs we have characterized, and probably a third, are alleles of the Spec1 gene. Thus, there appears to be a single polymorphic Spec1 gene in the sea urchin genome. We used S1 protection and primer extension procedures to map the 5' end of the Spec1 gene. Results from these experiments indicate that the initiation of transcription of the Spec1 mRNA begins at an A residue 220 bases from the 3' end of the first exon. Adding support to this claim, cannonical T-A-T-A and C-A-A-T sequences, indicative of many eukaryotic promoters, are found 23 bases and 60 bases upstream from this site, respectively. Analysis of sequences within a few kb of the Spec1 gene show that there are five members of a repetitive sequence family near the gene, three upstream and two downstream. The 5' leader sequence of another Spec mRNA, Spec2a, also contains a member of this repeat family.(ABSTRACT TRUNCATED AT 400 WORDS)

Novel proteins belonging to the troponin C superfamily are encoded by a set of mRNAs in sea urchin embryos.

The properties of several cDNA clones representing a family of mRNAs found in the embryonic ectoderm of Strongylocentrotus purpuratus are described. We have previously shown that these mRNAs (termed Spec for Strongylocentrotus purpuratus ectoderm) accumulate in the presumptive dorsal ectoderm of post-cleavage stage embryos and code for a group of 10 to 12 low molecular weight acidic proteins. We demonstrate here, using antibodies raised against the major Spec proteins, that the proteins are localized in the cytoplasm of dorsal ectoderm cells. Hybridization analysis and DNA sequencing show that the mRNAs coding for these proteins, although all related, can be divided into two subfamilies. Comparison of the translational reading frames of the Spec mRNAs with known protein sequences shows a significant homology with troponin C-related proteins, especially in the calcium-binding domains. We suggest that the Spec proteins are previously uncharacterized members of the troponin C superfamily.

Localization of a family of MRNAS in a single cell type and its precursors in sea urchin embryos.

Spec 1 mRNAs increase 100-fold in abundance per embryo during early sea urchin development. Previous studies indicated an enrichment of this mRNA in ectoderm fractions of gastrulae and plutei. We have determined the precise localization of this mRNA by in situ hybridization techniques. In pluteus larvae, the mRNA is highly restricted to a set of morphologically uniform ectoderm cells in the dorsal part of the embryo. The mRNA is not detectable in other regions of ectoderm or in endoderm and mesoderm. The pattern of localization is already established at the gastrula stage, before these cells are distinguishable by morphological criteria. This pattern of distribution of Spec 1 mRNA is distinct from that of bulk poly(A)+ mRNA. Measurements of the amount of Spec 1 mRNA per embryo and the number of cells containing this RNA indicate that there are about 500 Spec 1 mRNA molecules per cell at the pluteus stage and probably twice as many at the gastrula stage. These results indicate that the sensitivity of the in situ hybridization method allows detection of sequences that comprise approximately equal to 0.05% of the embryo mRNA nucleotides.

The 3' untranslated regions of two related mRNAs contain an element highly repeated in the sea urchin genome.

Two closely related cDNA clones, pSpec1 and pSpec2, specifying two developmentally regulated tissue specific mRNAs from sea urchin embryos were used to probe a sea urchin genomic lambda library. Screening 10,000 phage by plaque hybridization yielded several hundred positive signals. With more stringent wash procedures, only two to three phage were positive. Three of these phage, one isolated by stringent wash procedures and two isolated by standard wash procedures were further investigated by restriction analysis, RNA gel blots, and DNA sequencing. The phage isolated by the stringent wash procedure appears to be a gene coding for the Specl mRNA. The other phage contain only partial homology to pSpec1 and pSpec2, 150 to 200 base pairs of the 3' untranslated region of the Spec1 and Spec2 mRNAs. It is concluded that the Spec1 and Spec2 mRNAs contain a highly repetitive element near their 3' end. The element is present at 2000 to 3000 copies per genome and may be transcribed at some sites other than those coding for the Spec1 and Spec2 genes. The possible function and evolutionary origin of the repetitive element is discussed.

Energization of glucose transport by Pseudomonas fluorescens.

We have measured the capacity of Pseudomonas fluorescens to transport the glucose analog 2-deoxy-d-glucose and the amino acids l-alanine and alpha-aminoisobutyric acid under conditions in which the cells could generate (i) both a membrane proton motive force and high-energy phosphate compounds, (ii) a proton motive force but not high-energy phosphate compounds, and (iii) neither a proton motive force nor high-energy phosphate compounds. This was done by depleting cells of adenosine triphosphate stores by treatment with sodium arsenate and then suspending them in a phosphate-free medium, where they could generate a proton motive force but not phosphate bond energy, or in a phosphate-containing medium, where they could generate both a proton motive force and phosphate bond energy. Inclusion of the proton-conducting ionophore carbonyl cyanide-m-chlorophenyl hydrazone under either condition precluded the generation of both a proton motive force and phosphate bond energy. The amino acids l-alanine and alpha-aminoisobutyric acid were transported independently of phosphate bond energy and required only a proton motive force. 2-Deoxy-d-glucose was transported only under conditions in which phosphate bond energy could be generated. These results are consistent with the findings of others that Pseudomonas aeruginosa produces an inducible shock-sensitive glucose-binding protein and conform to the generalization that binding protein-associated transport systems are energized by phosphate bond energy.