The membrane-anchored MMP inhibitor RECK is a key regulator of extracellular matrix integrity and angiogenesis

Matrix metalloproteinases (MMPs) are essential for proper extracellular matrix remodeling. We previously found that a membrane-anchored glycoprotein, RECK, negatively regulates MMP-9 and inhibits tumor invasion and metastasis. Here we show that RECK regulates two other MMPs, MMP-2 and MT1-MMP, known to be involved in cancer progression, that mice lacking a functional RECK gene die around E10.5 with defects in collagen fibrils, the basal lamina, and vascular development, and that this phenotype is partially suppressed by MMP-2 null mutation. Also, vascular sprouting is dramatically suppressed in tumors derived from RECK-expressing fibrosarcoma cells grown in nude mice. These results support a role for RECK in the regulation of MMP-2 in vivo and implicate RECK downregulation in tumor angiogenesis.

Cytotoxicity and mutagenicity of UVB assessed using cultured rat fibroblast

A retroviral vector carrying both positive (neo) and negative (herpes simplex virus thymidine kinase or HSV-tk) selection markers was constructed as a substrate for mutational assay in mammalian cells. Using a population of rat fibroblast cells carrying a single copy per cell of retroviral DNA randomly integrated in their chromosomes, we examined the cytotoxic and mutagenic activities of ultraviolet light (UV) at four wavelengths (254, 290, 300, and 320 nm). The action spectra for these activities are similar to some of the previously reported spectra for photochemical DNA modifications, erythema, cell killing, and mouse skin carcinogenesis, except at 290 and 320 nm. At 290 nm, no significant mutagenicity was observed. At 320 nm, both cytotoxic and mutagenic activities were 10 times higher than the values expected from the absorption spectrum for DNA and the action spectrum for bacterial inactivation and mutagenesis. Structural comparison of some of the HSV-tk mutants obtained after irradiation with 300 and 320 nm UV revealed partially different patterns of mutation specificity, suggesting the involvement of multiple molecular mechanisms in the genotoxicity associated with this range of UV.

Glucocorticoid-induced functional polarity of growth factor responsiveness regulates tight junction dynamics in transformed mammary epithelial tumor cells

The synthetic glucocorticoid, dexamethasone, induces the "normal-like" differentiated property of tight junction formation and suppresses growth of the Con8 mammary epithelial tumor cell line, derived from a 7,12-dimethylbenz(alpha)anthracene-induced rat mammary adenocarcinoma. Characterization of the transepithelial electrical resistance of Con8 mammary tumor cells cultured on permeable supports revealed that a novel response to dexamethasone is the generation of a polarized cell monolayer with respect to epidermal growth factor receptor responsiveness. Administration of transforming growth factor-alpha (TGF-alpha) to the basolateral, but not the apical, plasma membrane compartment disrupted the glucocorticoid-stimulated tight junction barrier. Confocal immunofluorescence microscopy revealed that dexamethasone caused the ZO-1 tight junction-associated protein to localize exclusively to the apical border of laterally adjacent membranes of the cell periphery, whereas basolateral administration of TGF-alpha caused the redistribution of ZO-1 back to disorganized aggregates along the cell periphery. In contrast, TGF-alpha was able to exert its mitogenic effects equally on both sides of the cell monolayer independent of its polarized disruption of tight junction formation. Our results represent the first evidence for a functional polarization of the epidermal growth factor receptor and strongly implicate the glucocorticoid-regulated formation of tight junctions in policing the polarized responsiveness of mammary cells to growth factors.

Transforming growth factor-alpha abrogates glucocorticoid-stimulated tight junction formation and growth suppression in rat mammary epithelial tumor cells

The glucocorticoid and transforming growth factor-alpha (TGF-alpha) regulation of growth and cell-cell contact was investigated in the Con8 mammary epithelial tumor cell line derived from a 7,12-dimethylbenz(alpha)anthracene-induced rat mammary adenocarcinoma. In Con8 cell monolayers cultured on permeable filter supports, the synthetic glucocorticoid, dexamethasone, coordinately suppressed [3H]thymidine incorporation, stimulated monolayer transepithelial electrical resistance (TER), and decreased the paracellular leakage of [3H]inulin or [14C]mannitol across the monolayer. These processes dose dependently correlated with glucocorticoid receptor occupancy and function. Constitutive production of TGF-alpha in transfected cells or exogenous treatment with TGF-alpha prevented the glucocorticoid growth suppression response and disrupted tight junction formation without affecting glucocorticoid responsiveness. Treatment with hydroxyurea or araC demonstrated that de novo DNA synthesis is not a requirement for the growth factor disruption of tight junctions. Immunofluorescence analysis revealed that the ZO-1 tight junction protein is localized exclusively at the cell periphery in dexamethasone-treated cells and that TGF-alpha caused-ZO-1 to relocalize from the cell periphery back to a cytoplasmic compartment. Taken together, our results demonstrate that glucocorticoids can coordinately regulate growth inhibition and cell-cell contact of mammary tumor cells and that TGF-alpha, can override both effects of glucocorticoids. These results have uncovered a novel functional "cross-talk" between glucocorticoids and TGF-alpha which potentially regulates the proliferation and differentiation of mammary epithelial cells.

Regulation of methylthioribose kinase by methionine in Klebsiella pneumoniae

5-Methylthioribose (MTR) kinase catalyses a key step in the recycling of methionine from 5'-methylthioadenosine, a co-product of polyamine biosynthesis, in Klebsiella pneumoniae. In defined medium lacking methionine, K. pneumoniae exhibits abundant MTR kinase activity. When the bacterium is transferred to a medium containing 10 mM-methionine, the specific activity of MTR kinase decreases in a fashion consistent with repression of new enzyme synthesis and dilution of existing enzyme by cell division. The specific activity of methionine synthase decreases to a similar degree under the same conditions. In Escherichia coli and Salmonella typhimurium, the gene for methionine synthase is co-ordinately controlled as part of the methionine regulon. Taken together, our results indicate that a methionine regulon may function in K. pneumoniae and that expression of MTR kinase may be under its control.

Glucocorticoids coordinately disrupt a transforming growth factor alpha autocrine loop and suppress the growth of 13762NF-derived Con8 rat mammary adenocarcinoma cells

We have demonstrated previously that the synthetic glucocorticoid dexamethasone suppresses the growth of Con8 rat mammary tumor cells, which are derived from the 13762NF transplantable, hormone-responsive rat mammary adenocarcinoma. Dexamethasone inhibited [3H]thymidine incorporation into Con8 cells at high cell density under both serum and serum-free conditions. Fractionation in nonreducing sodium dodecyl sulfate-polyacrylamide gels of proteins secreted from dexamethasone-treated and untreated Con8 mammary tumor cells revealed two size classes of glucocorticoid inhibited mitogenic activities; a larger M(r) 27,000-33,000 and a smaller M(r) 5,000-12,000 activity. Both size classes of mitogens restimulated the growth of glucocorticoid-suppressed Con8 cells suggesting that they can act in an autocrine fashion. The smaller mitogen was identified as transforming growth factor alpha (TGF-alpha) since this activity competed with 125I-epidermal growth factor (EGF) for EGF receptor binding and was selectively immunodepleted with monoclonal TGF-alpha antibodies but not with EGF antibodies. Western blots and radioreceptor assay of Con8-secreted proteins revealed that glucocorticoids inhibited the production of a M(r) 5500 immunoreactive TGF-alpha protein by 10-fold. Consistent with a steroid effect on the level of TGF-alpha production, rather than on its activity, the specific mitogenic activities of the TGF-alpha s secreted by dexamethasone-treated and untreated Con8 cells were identical to that of recombinant human TGF-alpha. Treatment of intact cells with suramin, which dissociates ligand-receptor complexes, revealed that the EGF receptor-mediated mitogenic response is functional in both glucocorticoid-treated and untreated cells. Taken together, our results demonstrate that glucocorticoids suppress Con8 mammary tumor cell growth and disrupt a potential TGF-alpha autocrine loop which results in a dramatic reduction in the level of extracellular TGF-alpha.

Overexpression of transforming growth factor alpha overrides the glucocorticoid-mediated suppression of Con8 mammary tumor cell growth in vitro and in vivo

In a preceding paper (D. B. Alexander et al., Cancer Res., 53: 1808-1815, 1993), we demonstrated that the in vitro glucocorticoid inhibition of Con8 mammary tumor cell growth is accompanied by the disruption of a transforming growth factor alpha (TGF-alpha) autocrine loop. This growth suppression response functions in vivo since proliferation of Con8-derived tumors was inhibited in rats treated with the synthetic glucocorticoid, dexamethasone. The effect of dexamethasone on Con8-derived tumor growth was reversible in that tumors rapidly grew at the site of inoculation after discontinuing injections of dexamethasone. To test the in vivo relationship between the glucocorticoid growth suppression response and the TGF-alpha autocrine loop, Con8 cells were transfected with a TGF-alpha expression vector and single cell-derived neomycin-resistant subclones were recovered. [3H]Thymidine incorporation of cultured monolayers of transfected Con8 mammary cells and measurement of tumor diameters in rats revealed that dexamethasone failed to suppress the in vitro proliferation or in vivo tumor growth of Con8-derived cells producing high constitutive levels of secreted TGF-alpha. In contrast, both the in vivo and in vitro growth of Con8 cells transfected with vector controls were fully suppressible by glucocorticoids. Consistent with our in vitro observations, these results demonstrate that the regulation of TGF-alpha production plays a key role in the in vivo glucocorticoid suppression of Con8-derived mammary tumor growth.

Identification of the glucocorticoid suppressible mitogen from rat hepatoma cells as an angiogenic platelet-derived growth factor A-chain homodimer

We have previously shown that BDS.1 rat hepatoma cells are hypersensitive to the antiproliferative effects of glucocorticoids, and secrete a glucocorticoid suppressible mitogenic activity (denoted GSM). Sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed that GSM purified to near homogeneity migrated as a 28-kDa protein under nonreducing conditions and as a single 15-kDa polypeptide in the presence of sulfhydryl reducing agents suggesting a homodimeric structure. Anti-platelet-derived growth factor (PDGF) A-chain specific antibodies selectively immunodepleted the mitogenic activity which can be extracted from nonreducing gels in the 26-30-kDa fraction and, in Western blots, recognized the 15-kDa reduced form of GSM. Western blot analysis further showed that dexamethasone suppressed the level of secreted PDGF A-chain protein in BDS.1 cells but not in glucocorticoid receptor-deficient hepatoma cells. Northern blots revealed that dexamethasone reduced expression of the PDGF A-chain 2.3- and 1.7-kilobase transcripts in proportion to the level of detectable PDGF-AA protein. Similarly to PDGF-AA, the hepatoma cell-derived GSM has a potent angiogenic activity. Taken together, our results demonstrate that the predominant glucocorticoid suppressible mitogen secreted from rat hepatoma cells is a PDGF A-chain homodimer and suggest that in vivo glucocorticoids may potentially regulate hepatoma growth by modulating PDGF-stimulated tumor vascularization.

15 N 2 Fixation by Bacteria Associated with Maize Roots at a Low Partial O 2 Pressure

Nitrogen fixation by bacteria associated with roots of intact maize plants was measured by exposing the roots to 15 N 2 at a partial O 2 pressure (pO 2 ) of 2 or 10 kPa. The plants were grown in a mixture of Weswood soil and sand and then transferred to plastic cylinders containing an N-free plant nutrient solution. The solution was sparged continuously with a mixture of air and N 2 at a pO 2 of 2 or 10 kPa. Acetylene reduction was measured after the roots were exposed to the low pO 2 overnight. The air-N 2 atmosphere in the cylinders was then replaced with an O 2 -He atmosphere at the same pO 2 , and the roots were exposed to 20 kPa of 15 N 2 for 20 to 22 h. Incorporation of 15 N into the roots was 200 times greater at 2 kPa of O 2 than at 10 kPa of O 2 . Adding l -malate (1 g of C liter −1 ) to the nutrient solution increased root-associated nitrogenase activity, producing a strong 15 N label which could be traced into the shoots. Fixed 15 N was detected in the shoots within 5 days after the plants were returned to unfertilized soil. In a similar experiment with undisturbed plants grown in fritted clay, movement of fixed 15 N into the shoots was evident within 4 days after the roots were exposed to 15 N 2 at 2 kPa of O 2 . Inoculation with Azospirillum lipoferum yielded no significant differences in shoot dry weight, total nitrogen content, percent nitrogen, or 15 N enrichment of plant tissues. Inoculated plants did exhibit greater root dry weight than uninoculated plants, however.