Repression of the prolactin promoter: a functional consequence of the heterodimerization between Pit-1 and Pit-1 beta

The POU-homeodomain transcription factor Pit-1 is required for the differentiation of the anterior pituitary cells and the expression of their hormone products. Pit-1beta, an alternate splicing isoform, has diametrically different outcomes when it is expressed in different cell types. Pit-1beta acts as a transcriptional repressor of prolactin (PRL) and growth hormone genes in pituitary cells, and as a transcriptional activator in non-pituitary cells. In order to explore these differences, we: (1) identified the transcriptional cofactors necessary for reconstitution of repression in non-pituitary cells; (2) tested the effect of the beta-domain on heterodimerization with Pit-1 and physical interaction with the co-activator CREB binding protein (CBP); and (3) determined the beta-domain sidechain chemistry requirements for repression. Co-expression of both Pit-1 isoforms reconstituted the repression of the PRL promoter in non-pituitary cells. The beta-domain allowed heterodimerization with Pit-1 but blocked physical interaction with CBP, and specific chemical properties of the beta-domain beyond hydrophobicity were dispensable. These data strongly suggest that Pit-1beta represses hormone gene expression by heterodimerizing with Pit-1 and interfering with the assembly of the Pit-1-CBP complex required for PRL promoter activity in pituitary cells.

Basement membrane induced differentiation of HEC-1B(L) endometrial adenocarcinoma cells affects both morphology and gene expression

In vitro studies of endometrial carcinogenesis have been hampered by dedifferentiation of the cells in culture. Using the endometrial carcinoma cell line HEC-1B(L), we aimed to establish and characterize culture conditions that preserve a more differentiated state of the tumor cells. HEC-1B(L) cells grown in a serum-free defined medium on plastic (PL/SFDM) on top of a reconstituted basement membrane (Matrigel, MG/SFDM) or in a thick layer of Matrigel showed pronounced morphological differentiation as compared with HEC-1B(L) cells cultured on plastic in a medium containing serum (PL/10% FCS). Features of differentiation included cuboidal to columnar cell shape and an increase of rough endoplastic reticulum in Matrigel cultures. Gene expression of HEC-1B(L) cells was studied by metabolic [35S]methionine labeling and SDS-gel electrophoresis. HEC-1B(L) cells cultured in the presence of Matrigel showed two additional secretory proteins approximately 31 kD and 77 kD in size. rt-PCR was used to screen cell cultures for the presence of estrogen receptor, progesterone receptor, and lactoferrin-mRNA, genes typically expressed by normal endometrial epithelium. We found no expression of the estrogen receptor or progesterone receptor. Lactoferrin-mRNA was present under all culture conditions tested. Our results suggest a regulatory role of the extracellular matrix for the differentiation of the HEC-1B(L) cell line.

The role of interleukin-1 in interactive senescence and age-related human endometrial cancer

The causes of the age-related increase in cancer rates are poorly understood. One cause could be age-related changes in the stromal/epithelial cell interactions that facilitate tumorigenesis. We tested the hypothesis that aging of human endometrial stromal fibroblasts (ESF) alters their influence over endometrial epithelial cells. ESF from adults were found to inhibit anchorage-independent proliferation, to restrain colony outgrowth, and to induce formation of normal tissue architecture by human endometrial cancer cells. As ESF age, these inhibitory influences on malignant-like behaviors by epithelial cells are altered, becoming stimulatory. Age-related change in interleukin-1alpha (IL-1alpha) expression is a molecular determinant of ESF/epithelial cell interactions. Levels of IL-1alpha and IL-1-induced mRNAs increase in ESF with age. Treatment with IL-1 accelerates age-related changes in mRNA abundance and loss of ESF restraint over malignancy-associated behaviors by epithelial cells. Transfection of ESF with the intracellular IL-1 receptor antagonist preserved the young phenotype with respect to interactions with epithelial cells and prevented age-associated increases in groalpha and IL-8 mRNA levels. Our results indicate that aging of ESF is accompanied by an interactive senescence that alters ESF signaling to cancer cells and could contribute to increased cancer rates by providing a microenvironment that is more conducive to tumorigenesis.

Age-related expression of PEDF/EPC-1 in human endometrial stromal fibroblasts: implications for interactive senescence

Aging is the major risk factor for many cancers, and age-related changes in the tissue microenvironment can facilitate tumor growth. This study uses human endometrial cells to begin to test the hypothesis that age-related changes in pigment epithelium-derived factor/early population doubling cDNA-1 (PEDF/EPC-1) levels create an environment that is more permissive to tumor growth. Endometrial stromal fibroblasts (ESF) are the predominant cell type in the human endometrium and exert regulatory control over the glandular epithelial cells, which are the source of most tumors. As ESF age in vitro, their ability to regulate appropriate growth and differentiation of epithelial cells declines. Endometrial epithelial cells in primary culture expressed relatively low levels of PEDF/EPC-1 mRNA. In contrast, early passage quiescent ESF from adult donors produce higher levels of the 1.5-kb PEDF/EPC-1 mRNA and 50-kDa secreted protein than epithelial cells. As ESF age in vitro the relative abundance of PEDF/EPC-1 mRNA declines, as does the level of PEDF/EPC-1 protein secreted into cell culture medium. Treatment with PEDF/EPC-1 protein had no effect on ESF proliferation but did inhibit anchorage-dependent and anchorage-independent proliferation of endometrial carcinoma cells in a dose- and time-dependent manner. These findings imply that an age-related loss of PEDF/EPC-1 expression by ESF could eliminate a negative regulator of cancer cell growth and, thereby, contribute to the age-related increase in cancer incidence.

Regulation of keratinocyte growth factor expression in human endometrium: implications for hormonal carcinogenesis

Estrogen is thought to be an important etiologic agent in endometrial and breast cancers. However, the mechanism or mechanisms by which estrogen acts as a hormonal carcinogen are not well understood. We hypothesize that in response to chronic exposure to estrogens, human endometrial stromal fibroblasts (ESF) produce factors that facilitate neoplastic transformation in epithelial cells. To test this hypothesis, we assessed the regulation of keratinocyte growth factor (KGF) mRNA and protein in ESF by interleukin-1 (IL-1) and diethylstilbestrol (DES). Short-term treatments with IL-1 but not with DES increased the abundance of KGF mRNA in ESF. However, chronic treatment with DES significantly increased KGF mRNA levels and protein production. KGF protein in medium conditioned by ESF chronically treated with 1 nM DES reached concentrations of approximately 100 ng/mL. At this concentration, KGF increased endometrial epithelial cell numbers fourfold and enhanced anchorage independence tenfold. These results suggest that KGF may play a role in hormonal carcinogenesis by mediating estrogen-induced changes in the interactions between stromal and epithelial cells. To address the potential role of nuclear transcription factor kappa B (NF-kappaB) in regulating KGF expression, we determined the effect of increased expression of its inhibitor, IkappaBalpha, on KGF mRNA and protein levels. Transfection with IkappaBalpha blocked induction of KGF expression by IL-1 but had no effect on the increase in KGF mRNA caused by chronic treatment with DES. These results suggest that IL-1 exerts its effects on KGF by an NF-kappaB-mediated pathway but that chronic treatment with DES stimulates KGF expression by some other mechanism.

Selective potentiation of gynecologic cancer cell growth in vitro by electromagnetic fields

OBJECTIVE

Epidemiological data suggest that exposure to electromagnetic fields (EMF) may increase the risk of various cancers. We evaluated EMF effects on the in vitro growth response of human cell lines isolated from various reproductive tract tissues. We also assessed the effects of EMF on cisplatin- or paclitaxel-induced cytotoxicity.

METHODS

Endometrial, ovarian, and prostate cancer cell lines as well as immortalized endometrial stromal cells and immortalized ovarian epithelial cells were exposed continually to EMF. Proliferation was assessed by the metabolic activity assay, MTT, direct cell counting, and anchorage-independent colony formation in soft agar. Cytotoxicity induced by cisplatin or paclitaxel was assessed using the MTT assay.

RESULTS

Continuous exposure to EMF at field strengths of 2 G enhanced proliferation of two human prostate and three endometrial, but only one ovarian, cancer cell lines. EMF enhanced metabolic activity of cancer cells within 96 h and increased absolute cell number (anchorage-dependent proliferation) and colony-forming efficiency (anchorage-independent proliferation) over sham-treated controls. EMF had no effect on cytotoxicity induced by the chemotherapeutic agents Taxol or cisplatin.

CONCLUSIONS

Continuous exposure to EMF can enhance growth rates of transformed cells for some human epithelial cancers. Cancer cells from the steroid sex hormone regulated tissues of endometrium and prostate appeared to be more responsive to EMF than cells from ovarian cancers.

Identification of the structural region of taxol that may be responsible for cytokine gene induction and cytotoxicity in human ovarian cancer cells

PURPOSE

Interleukin-8 (IL-8) is a pleiotropic chemokine with both chemoattractant and angiogenic properties. In addition to its cytotoxic effects on ovarian cancer cells, taxol can transcriptionally activate genes such as IL-8 that may play a role in tumorigenesis. Utilizing IL-8 as a prototypic marker of tumor-derived modulators of growth, we undertook a systematic study of taxol and 11 structurally modified taxol analogs to identify the region of the taxane skeleton responsible for IL-8 gene induction.

METHODS

The human ovarian cancer cell line OVCA-420 was exposed to taxol or taxol analogs. IL-8 gene induction was assessed by Northern blot analysis after 6 h and cytotoxicity after 72 h.

RESULTS

Changes in the southern hemisphere (C-1 to C-4) of the taxane skeleton had greater effects on IL-8 induction than changes in the northern hemisphere (C-7 to C-11). Some of the taxol analogs modified at positions C-1 and/or C-2 with increased hydrophobicity induced IL-8 expression more than threefold over that induced by taxol or taxotere and more than 20-fold over control cells. Cells that failed to induce IL-8 gene expression in response to taxol were only marginally responsive to the analogs unless first primed with IL-1beta. Modifications to the northern hemisphere did not alter taxol's effect on IL-8 expression in human cells, but did influence TNFalpha expression in murine macrophage cells, suggesting species and/or gene specificity. We found a direct correlation between IL-8 induction and cytotoxicity, in that analogs that dramatically upregulated IL-8 expression proved to be the most cytotoxic, inhibiting cell survival by > 90%.

CONCLUSION

Taken together our results demonstrate that changes in the southern hemisphere of the taxane skeleton influence both the gene induction and cytotoxic potential of taxol in human ovarian cancer cells.

Diethylstilbestrol-induced immortalization of human endometrial cells: alterations in p53 and estrogen receptor

Carcinogenesis is a process requiring multiple steps. Immortalization is one step in this process and may be rate limiting. To further our understanding of estrogen-induced carcinogenesis, we evaluated diethylstilbestrol (DES)-induced immortalization of human endometrial stromal cells. This was achieved by assessing at the restrictive temperature the colony-forming efficiency of cells that were conditionally immortalized with a temperature-sensitive simian virus 40 large T antigen. Treatment with DES for 1 wk did not increase the immortalization frequency; however, cultures that were treated for 20 wk had a twofold increase in immortalization frequency, and continued treatment for a total of 44 wk produced a threefold increase in immortalization frequency that was dose dependent. DES-treated restrictive temperature variants (RTVs) but not spontaneous RTVs lost the temperature-sensitive phenotype. DES-RTVs also had a shorter doubling time than spontaneous RTVs did. p53 expression was increased in DES-RTVs, and its localization within the cell was altered. Conversely, expression of the estrogen receptor was decreased in DES-immortalized cells. These changes in gene expression often occur in estrogen-related malignancies, and our results are consistent with a causal role for estrogens in these p53 and the estrogen receptor alterations. Immortalization of human cells may be analogous to initiation of rodent cells, and our results suggest that estrogen-induced alterations in p53 or other genes that regulate life span could contribute to estrogen-induced initiation.

Tumor cell invasion of basement membrane in vitro is regulated by amino acids

Because most cancer deaths result from disseminated disease, understanding the regulation of tumor invasion and metastasis is a central theme in tumor cell biology. Interactions between extracellular matrices (ECM) and cellular microenvironment play a crucial role in this process. We have tested selected amino acids and polyamines for their ability to regulate RL95-2 cell invasion through both intact human amniotic basement membrane and a novel human ECM (Amgel). Three major systems for neutral amino acid transport, systems L, A, and ASC, are operational in these neoplastic cells. Amino acids entering the cell via transport system A or N, i.e., (methyl amino)-isobutyrate (MeAIB) or Asn, markedly enhanced invasiveness of these human adenocarcinoma cells as measured by a standard 72-hr amnion or Amgel invasion assay. Addition of 2-amino-2-norborane carboxylic acid (BCH; 1 mM), a model substrate of the L transport system, caused a significant decrease in invasive activity when tested in the Amgel assay. Interestingly, Val lowers steady-state levels of MeAIB uptake and blocks the increase in cell invasion elicited by MeAIB. At the same time, these amino acids do not influence cell proliferation activity. Neither the charged amino acid Lys or Asp (not transported by A/N/L systems) nor the polyamines putrescine, spermidine, or spermine modulate invasiveness under similar experimental conditions. Moreover, the observed time-dependent stimulation of system A activity (cellular influx of MeAIB) by substrate depletion is prevented by the addition of actinomycin D (5 microM) or cycloheximide (100 microM), suggesting the involvement of de novo RNA and protein synthesis events in these processes. MeAIB treatment of tumor cells selectively increased the activities of key invasion-associated type IV collagenases/gelatinases. These results indicate that in the absence of defined regulators (growth factors or hormones), certain amino acids may contribute to the epigenetic control of human tumor cell invasion and, by extension, metastasis. We propose that amino acids, acting via specific signaling pathways, modulate phenotypic cell behavior by modulating the levels of key regulatory enzymatic proteins.

The intracellular IL-1 receptor antagonist alters IL-1-inducible gene expression without blocking exogenous signaling by IL-1 beta

The epithelium-associated tissue distribution of the intracellular IL-1R antagonist (icIL-1Ra) suggests that it functions as a novel regulatory molecule for IL-1 in somatic tissues. We examined the role of the icIL-1Ra in IL-1 beta-induced responses in human ovarian cancer cells because ovarian surface epithelium expresses transcripts for the icIL-1Ra, and the majority of ovarian cancers arise from these cells. Several human ovarian and cervical cancer cell lines spontaneously express the icIL-1Ra. icIL-1Ra-expressing cells did not have altered growth characteristics or altered short term responses to IL-1 compared with icIL-1Ra-nonexpressing cells. While a 90-min exposure to IL-1 beta resulted in increased steady state cytokine mRNA levels in all cells, icIL-1Ra-positive cells were incapable of maintaining IL-1-beta-induced expression of GRO mRNA. This did not result from decreased transcriptional activity of the GRO gene, but reflected differences in mRNA stability and/or degradation. To determine whether the icIL-1Ra altered mRNA stability, we used a retroviral expression vector to express the icIL-1Ra in an icIL-1Ra-negative cell line. The resulting cells displayed a profile of IL-1 beta-induced genes analogous to that found in cells spontaneously expressing icIL-1Ra. These data show for the first time an intrinsic biologic activity for the icIL-1Ra. The capacity to selectively alter IL-1-induced gene expression suggests that this version of the IL-1Ra is a unique intracellular inhibitor that attenuates IL-1 responses at a point downstream of the initial IL-1/IL-1 receptor interaction.

The intracellular IL-1 receptor antagonist alters IL-1-inducible gene expression without blocking exogenous signaling by IL-1 beta

The epithelium-associated tissue distribution of the intracellular IL-1R antagonist (icIL-1Ra) suggests that it functions as a novel regulatory molecule for IL-1 in somatic tissues. We examined the role of the icIL-1Ra in IL-1 beta-induced responses in human ovarian cancer cells because ovarian surface epithelium expresses transcripts for the icIL-1Ra, and the majority of ovarian cancers arise from these cells. Several human ovarian and cervical cancer cell lines spontaneously express the icIL-1Ra. icIL-1Ra-expressing cells did not have altered growth characteristics or altered short term responses to IL-1 compared with icIL-1Ra-nonexpressing cells. While a 90-min exposure to IL-1 beta resulted in increased steady state cytokine mRNA levels in all cells, icIL-1Ra-positive cells were incapable of maintaining IL-1-beta-induced expression of GRO mRNA. This did not result from decreased transcriptional activity of the GRO gene, but reflected differences in mRNA stability and/or degradation. To determine whether the icIL-1Ra altered mRNA stability, we used a retroviral expression vector to express the icIL-1Ra in an icIL-1Ra-negative cell line. The resulting cells displayed a profile of IL-1 beta-induced genes analogous to that found in cells spontaneously expressing icIL-1Ra. These data show for the first time an intrinsic biologic activity for the icIL-1Ra. The capacity to selectively alter IL-1-induced gene expression suggests that this version of the IL-1Ra is a unique intracellular inhibitor that attenuates IL-1 responses at a point downstream of the initial IL-1/IL-1 receptor interaction.

Estrogen-induced anchorage-independence in human endometrial stromal cells

Estrogens are important etiologic agents for most gynecologic malignancies, and chronic exposure to estrogen that is unopposed by progestins conveys the greatest risk. Treatments with estrogen facilitate the process of malignant transformation in rodents, but relatively few studies of estrogen-induced carcinogenesis have been performed using human cells. Most malignancies in estrogen-responsive tissues arise from epithelial cells, but an increasing body of evidence emphasizes the role of stromal cells as mediators of the effects of estrogens on epithelial cells. Our studies were designed to assess estrogens as carcinogens for human endometrial stromal cells and to provide a basis for studies of the role of stroma in estrogen-induced carcinogenesis in humans. Acute treatments with the estrogens diethylstilbestrol (DES), 17 beta-estradiol (E2) and beta-dienestrol enhance anchorage-independent proliferation (AIP) of SV40-immortalized human endometrial stromal cells in the rank order of DES > E2 > beta-dienestrol. The anti-estrogenic compound tamoxifen inhibits DES-induced AIP. The magnitude of DES-induced AIP increases with prolonged duration of treatment. After 11 months of chronic treatment with 0.1 nM DES, AIP was 20-fold higher than in vehicle-treated control cultures. Expression of the estrogen receptor was altered by treatments with DES in parallel with increased capacity for AIP. These conditionally immortal human endometrial stromal cells appear to be a good model for estrogen-induced transformation of human cells.

Productive infection of human endometrial stromal cells by human cytomegalovirus

Cultured endometrial stromal cells were susceptible to productive human cytomegalovirus (HCMV) infection. Infection of endometrial stromal cells resulted in pronounced cytopathic effects including cell rounding and aggregation, fusions, and some lysis, although not in the synchronous fashion observed in infected fibroblasts. The aggregation events were reminiscent of normal endometrial stromal cell responses to cyclical estrogen/progesterone levels. Immunofluorescence analysis demonstrated expression of viral gene products suggesting a productive virus infection. One-step growth analysis showed that infectious virus was produced but the titers were two logs lower than those obtained in fibroblasts even though HCMV DNA accumulated to similar levels in both cell types. In contrast, viral DNA replication was greatly reduced in endometrial stromal cells immortalized with a temperature-sensitive SV40 large T gene at both permissive and nonpermissive temperatures. A more detailed analysis of viral gene expression by Northern blotting revealed earlier appearances and greater initial levels of viral transcripts in endometrial stromal cells. No HCMV gene expression was observed at 120 hpi in these cells even though half of the cells were still intact and cellular gene expression was functional. Since this was the time of peak virus production, it seems plausible that reduced viral gene expression at late times p.i. was a major contributor to the reduced titers observed in endometrial stromal cells. These in vitro results coupled with in vivo observations by others of endometritis associated with HCMV suggest that further investigation into the effects of HCMV on the endometrium is warranted.

In vitro interactions of endometrial stromal and epithelial cells in Matrigel: reorganization of the extracellular matrix

Fragments of human endometrial glands and dispersed endometrial stromal cells were cultured together in a thick layer of reconstituted basement membrane (Matrigel). Epithelial cells kept their glandular morphology whereas stromal cells grew into round clusters of mainly fusiform cells. Transmission electron micrographs showed collagen fibers between stromal cells as well as in surrounding extracellular matrix after 2.5 weeks. A well-defined basement membrane was found when epithelial and stromal cells were in close proximity to each other. Beneath the lamina densa there was a loose network of collagen fibers or a dense fibrillar network arranged parallel to the cell layers. Epithelial cells showed hemidesmosomes at their basal surface where they were close to stromal cells.

H-ras codon 12 mutation in cervical dysplasia

A mutation in codon 12 of the H-ras oncogene has been implicated in the pathogenesis of cervical cancer. To determine if mutational activation of H-ras is an early event in carcinogenesis, we looked for the presence of codon 12 H-ras mutation in precancerous cervical dysplasia. We analyzed cervical DNA from 63 normal patients and 72 patients with biopsy-proven cervical dysplasia [CIN I (48), CIN II (9), CIN III (15)]. HPV typing was performed on these samples by Viratype and analysis and polymerase chain reaction (PCR). To detect H-ras codon 12 mutation, DNA was isolated and amplified by PCR with primers for H-ras. A unique restriction site for MspI contained within the wild-type ras PCR product allows discrimination between unmutated and mutated sequences. Restriction enzyme analysis with MspI was performed on PCR products to distinguish between wild-type and mutated sequences. HPV 16 or 18 was present in 33% of CIN I, 56% of CIN II, and all CIN III samples. No codon 12 mutations were detected in any sample. We conclude that while HPV is associated with cervical dysplasia and its prevalence increases in more advanced lesions, it is unlikely that H-ras codon 12 mutations are an early occurrence in the progression of precancerous lesions to cervical carcinoma.

Papilloma virus immortalized tracheal epithelial cells retain a well-differentiated phenotype

Human airway epithelial cell lines that retain phenotypic properties representative of the native tissue will be useful physiological models. Human papilloma viral (HPV) genes can immortalize human genital keratinocytes and breast and bronchial epithelia. We transfected cystic fibrosis (CF) and normal tracheobronchial epithelial cell cultures with DNA encoding the HPV-18 E6 and E7 genes and characterized phenotypic properties of resultant cell lines. Of the 11 CF clones isolated, 6 developed a polarized phenotype with vectorial ion transport and membrane-specific expression of histamine and purinergic receptors. The ion transport properties of these lines differed from the normal lines and approximated those of primary CF airway epithelial cell cultures more closely than do those of cell lines transformed with the simian virus 40 large T gene. When transplanted into denuded tracheal grafts, these cells can differentiate into ciliated and secretory phenotypes. We conclude that HPV-18 E6 and E7 genes are sufficient to transform human airway epithelial cells and that the resultant cell lines express differentiated phenotypic properties that approximate those of the native epithelium.

Conditional immortalization of human endometrial stromal cells with a temperature-sensitive simian virus 40

The study of immortalization and other alterations associated with neoplastic transformation of endometrial stromal cells is important to understanding the development of uterine sarcomas and mixed tumors. Because stromal cells are important regulators of associated epithelial cells, alterations in the regulation of stromal cell proliferation that influence epithelial cells may also contribute to the development of endometrial carcinomas. To study immortalization and associated phenotypic and genetic alterations of human endometrial stromal cells, cultures were transfected with a plasmid containing an ori-, temperature-sensitive mutant SV40, A209 (tsSV40). Morphologically transformed colonies were selected and propagated at the permissive temperature until they entered 'crisis'. In contrast to human fibroblasts, every clone tested was immortalization competent. The frequency of immortalization was approximately 1 x 10(-6). One uncloned and six cloned cell lines escaped from crisis and appear to be immortal. Two clones, M4 and B10T1, were selected for further study. Immortalization is conditional; proliferative arrest occurs at the restrictive temperature for large T antigen function. Furthermore, withdrawal of the large T antigen results in expression of the senescent phenotype of enlarged, flattened cells. Colony-forming efficiency at the restrictive temperature was undetectable. Immortalization is also associated with several genetic alterations. The DNA content of tsSV40 transfected cells was either diploid or tetraploid in the precrisis stage of proliferation, but became aneuploid upon immortalization. Several structural rearrangements of chromosomes were detected in the immortalized stromal cells which differ from those found in SV40 immortalized fibroblasts. Although their capacity for anchorage-independent proliferation (AIP) is variable, tsSV40-immortalized endometrial stromal cells have a higher capacity for AIP than their tsSV40-transfected progenitor cells in the period of proliferation prior to 'crisis'.

Development of a novel human extracellular matrix for quantitation of the invasiveness of human cells

During the crucial stages of tumor cell invasion and metastasis, neoplastic cells must traverse extracellular matrices for their migration to distant sites. Because basement membranes (BM) serve as a critical barrier to such passages, most previous in vitro assay models have utilized either an intact BM or a reconstituted rodent or avian BM-matrix to study this process. We have created a gel-like extracellular matrix derived from human amnions which contained type IV collagen, laminin, entactin, tenascin and heparan sulfate proteoglycan. This matrix, which we called Amgel, was used to study selected steps of invasion including cell attachment to matrix, degradation of it by proteolytic enzymes and movement of human tumor cells through matrix defects. An efficient tumor invasion assay system was developed utilizing filter-supported uniform coatings of this matrix in chambers. Human tumor cells (HT-1080 fibrosarcoma and RL-95 adenocarcinoma), when seeded onto Amgel-coated membranes, attached to matrix within 2 h and initiated a time-dependent migration and invasion process, as verified by biochemical analysis and both light and electron microscopy. In an optimized invasion assay 12-15% of tumor cells completely traversed the matrix during a 72-h period with > 90% viability. In contrast to these highly-invasive cells, normal human foreskin fibroblasts and normal human endometrial stromal cells exhibited minimal migration/matrix penetration during the same time period. When the Amgel-selected tumor cells (i.e. those penetrating the barrier) were isolated, subcultured, and re-exposed to Amgel, they had heightened invasiveness (2-3-fold) as compared to the parental cells. Thus, this improved 'all human' system for quantitating the invasive ability of tumor cells may provide a valuable tool in dissecting out the mechanistic underpinnings of human metastasis. In addition, this assay has the ability to screen agents which have potential anti-invasive and by extension anti-metastatic, activity or chemotactic properties.

Expression of tissue kallikrein in normal and SV40-transfected human endometrial stromal cells

The polymerase chain reaction with specific tissue kallikrein primers was utilized to demonstrate the presence of tissue kallikrein mRNA in human endometrial stromal cells. Enzymatic analysis measured with a specific tripeptide nitroanilide substrate demonstrated the presence of tissue kallikrein in the conditioned medium obtained from both normal stromal cells and stromal cells transfected with an origin-defective temperature-sensitive SV40 large T antigen. The transfected stromal cell supernatant exhibited approximately twice as much tissue kallikrein activity as normal stromal cells at 60-100% of cell confluence. The release of tissue kallikrein from transfected stromal cells was confirmed by Western blot analysis and [35S]-methionine incorporation into a 35-kD protein which retains tissue kallikrein activity. These results demonstrate for the first time the expression and secretion of tissue kallikrein in human endometrial stromal cells and provide evidence of possible involvement of tissue kallikrein in cell transformation.

Interleukin-1 inhibits growth of normal human endometrial stromal cells

OBJECTIVE

To understand growth regulation of the endometrium by studying the effect of interleukin-1 beta (IL-1) on human endometrial stromal cell proliferation in vitro.

METHODS

Endometrial stromal cells from human endometrium were separated and purified and placed in culture. Fresh and first- and sixth-passage cells were incubated with IL-1 (0.025, 0.25, and 2.5 ng/mL) for 24, 48, and 72 hours, respectively. Proliferation as a function of DNA synthesis was assessed by measuring 3H-thymidine incorporation. Experiments were then repeated in the presence of indomethacin to determine whether IL-1 effects were dependent upon prostaglandin synthesis. We evaluated overall growth by adding IL-1 to cell cultures of sixth-passage stromal cells every 3 days and by performing cell count studies.

RESULTS

Interleukin-1 beta significantly inhibited 3H-thymidine uptake in freshly explanted endometrial stromal cells at all doses in a dose-dependent manner; a 44% inhibition was seen at 2.5 ng/mL IL-1 after 72 hours of incubation. In first- and sixth-passage cells, 3H-thymidine uptake was inhibited only at intermediate and high doses of IL-1. Cell count studies showed that sixth-passage cells were significantly inhibited by IL-1 after 23 days of growth (22%; P less than .01). Adding indomethacin did not affect inhibition of growth.

CONCLUSION

Interleukin-1 beta inhibits growth of normal human endometrial stromal cells in vitro and does not appear to be mediated by arachidonic acid metabolites. This inhibition of growth may be important for maintenance of a normal endometrial phenotype.

Alterations of DNA content in human endometrial stromal cells transfected with a temperature-sensitive SV40: tetraploidization and physiological consequences

The normal genomic stability of human cells is reversed during neoplastic transformation. The SV40 large T antigen alters the DNA content in human endometrial stromal cells in a manner that relates to neoplastic progression. Human endometrial stromal cells were transfected with a plasmid containing the A209 temperature-sensitive mutant of SV40 (tsSV40), which is also defective in the viral origin of replication. Ninety-seven clonal transfectants from seven different primary cell strains were isolated. Initial analysis revealed that 20% of the clonal populations (19/97) had an apparent diploid DNA content, 35% (34/97) had an apparent tetraploid DNA content, and the remainder were mixed populations of diploid and tetraploid cells. No aneuploid populations were observed. Diploid tsSV40 transformed cells always give rise to a population of cells with a tetraploid DNA content when continuously cultured at the permissive temperature. The doubling of DNA content can be vastly accelerated by the sudden reintroduction of large T antigen activity following a shift from non-permissive to permissive temperature. Tetraploid tsSV40 transfected cells have a lower capacity for anchorage-independent growth and earlier entry into 'crisis' than diploid cells. These results indicate that during the pre-crisis, extended lifespan phase of growth, the SV40 large T antigen causes a doubling of DNA content. This apparent doubling of DNA content does not confer growth advantage during the extended lifespan that precedes 'crisis'.

Extended life span of human endometrial stromal cells transfected with cloned origin-defective, temperature-sensitive simian virus 40

Human endometrial stromal cells transfected with an origin-defective, temperature-sensitive simian virus 40 recombinant plasmid are dependent on T-antigen function for proliferation and at the permissive temperature have an extended life span in culture. Southern blot analysis indicates that the transfected gene is present in low copy number, possibly at a single integration site. Normal stromal cells are capable of 10 to 20 population doublings in culture. Transfected cultures have been carried at the permissive temperature to 80 population doublings before crisis. In the multistep model of malignant transformation of human cells, these cells represent one of the earliest stages: extended but finite life span. We have used these cells to investigate alterations in signal transduction that may be responsible for this early stage of transformation caused by the large T antigen. Temperature shift experiments indicate that the expression of ornithine decarboxylase (ODC) but not of c-fos is altered by the large T antigen. Induction of c-fos by serum or 12-O-tetradecanoylphorbol-13-acetate is independent of temperature. However, in the transfected cells, the induction of ODC by asparagine or serum is greatly enhanced at the permissive temperature. This result indicates that the large T antigen acts downstream of c-fos but upstream of ODC expression in the signal-transducing cascade.

Automated fluorescence image cytometry. DNA quantification and detection of chlamydial infections

Digitized fluorescence microscopy in conjunction with automated image segmentation is a promising approach for screening clinical specimens quickly and reliably. This paper describes the hardware and software of a prototype image-based cytometer that can identify fluorescent objects, discriminate true objects from artifacts and divide overlapping pairs of objects. The use of this image cytometer is discussed for: (1) the measurement of the DNA ploidy distribution of isolated mature rat liver nuclei labeled with 4',6-diamidine-2-phenylindole; (2) the comparison of the DNA ploidy distributions of the same samples measured by image cytometry (ICM) and flow cytometry (FCM); and (3) the quantification of chlamydial infection by double labeling cells with antichlamydiae antibody and Hoechst 33258 for nuclear DNA analysis. Ploidy distributions measured by the automated image cytometer compared favorably to those obtained by FCM. All pairs of overlapping nuclei were automatically detected by an additional computer algorithm, and those pairs that were clearly more than one nucleus by visual inspection were correctly divided. The irregular morphology of the chlamydiae-infected cells meant that 26% of them were not correctly identified in the fluorescein-stained images (as judged by manual inspection), but all cells were nevertheless detected correctly from the images of the Hoechst-stained samples. Automated fluorescence ICM yielded results similar to those obtained with FCM and had the additional benefit of maintaining cell and tissue architecture while preserving the opportunity for subsequent manual inspection of the specimen.

Fluorescent laser scanning microscopy of F-actin disruption in human endometrial stromal cells expressing the SV40 large T antigen and the EJ ras oncogene

To attempt to understand the effects of the SV40 large T antigen and an activated EJ ras oncogene on F-actin organization, we compared normal human endometrial stromal cells (HESC; proliferating, short life span) to cells transfected with the SV40 large T antigen either alone or in combination with the EJ ras oncogene. Normal HESC displayed numerous bundles of actin filaments (stress fibers) evenly distributed throughout the cell. In HESC transfected with a plasmid containing the gene for a temperature-sensitive SV40 large T antigen, stress fibers were disrupted and the remaining F-actin was also disrupted and clumped near the plasma membrane. Cells expressing both the SV40 large T antigen and the EJ ras oncogene sometimes appeared rounded, with stress fibers organized mainly near the cell periphery. Under restrictive temperature conditions for the function of the SV40 large T antigen, cells with or without the EJ ras oncogene reorganize actin stress fibers to resemble those of normal HESC. Therefore, the EJ ras oncogene alone does not disrupt F-actin organization. When operating in cooperation with the SV40 large T antigen, however, it leads to the reorganization of F-actin at the cell periphery and confers a rounded structure on the cells.

Ultrastructural characterization of two new human endometrial carcinoma cell lines and normal human endometrial epithelial cells cultured on extracellular matrix

Two new lines of human endometrial carcinoma (HEC) cells, one from an adenocarcinoma and one from a highly metastatic serous papillary carcinoma, were established in culture. Structural and morphologic properties of these cells at early passage were compared with those of cultured normal human endometrial epithelial (NHEE) cells. For these studies, cells were grown on a conventional plastic surface or on an extracellular matrix substrate (Matrigel), and examined by transmission electron microscopy and immunofluorescent light microscopy. The HEC cells appeared morphologically similar on plastic and Matrigel, whereas the NHEE cells showed significantly greater epithelial morphologic differentiation on Matrigel than on plastic. On extracellular matrix, the morphologic differences observed between HEC cells and NHEE cells were primarily of an architectural nature, which may be in part explained by differences between NHEE and HEC cells in the arrangement of actin microfilaments and cytokeratin intermediate filaments. Furthermore, HEC cells displayed extensive networks of vimentin intermediate filaments, which were absent from the NHEE cells. These observations support the hypothesis that architectural deregulation is a prominent feature of endometrial carcinoma, and that cytoskeletal alterations may uncouple HEC cell ultrastructural morphology from the influence of extracellular matrix.

Gland formation from human endometrial epithelial cells in vitro

We have developed methods for the culture of human endometrial glandular epithelia in vitro. The culture medium is serum-free and is used in combination with Matrigel, an extracellular matrix material applied as a coating on cell culture plates. Cell growth begins as a monolayer, but the cells subsequently form glandular or organoid structures. The glands are composed of polar columnar cells facing a central lumen, which is enclosed by the apical surfaces of cells displaying numerous microvilli and sealed by tight junction complexes. The ability to study in vitro the complex process of glandular morphogenesis represents an important new tool in cell biology which may be used to investigate growth regulation, hormone production and dependency, and cellular recognition and interactions. Ultimately, these characteristics may be applied to study the alterations of glandular epithelia associated with neoplasia.

Sequence and organization of southern bean mosaic virus genomic RNA

The genomic RNA sequence of the cowpea strain of southern bean mosaic virus (SBMV-C) has been determined. The genome is 4194 nucleotides in length and has four open reading frames. A 5' proximal open frame, from base 49 to base 603, corresponds to the length of the P4 proteins translated in cell-free extracts from full-length and smaller virion RNA. The largest open frame extends from base 570 to base 3437 and encodes the two largest proteins translated in cell-free extracts from full-length virion RNA. Segments of this open reading frame's predicted amino acid sequence resemble those of known viral RNA polymerases, ATP-binding proteins, and viral genome-linked proteins. A third open frame extends from base 1895 to base 2380 and has not been correlated with an in vitro translation product. The fourth open reading frame is located in the 3' terminal region of the genome extending from base 3217 to base 4053. This frame encodes the SBMV capsid protein which is translated from subgenomic, virion RNA.

Induction of ornithine decarboxylase activity by insulin and growth factors is mediated by amino acids

The polypeptide growth factors, nerve growth factor, epidermal growth factor, and platelet-derived growth factor, as well as insulin do not induce ornithine decarboxylase (L-ornithine carboxy-lyase, EC 4.1.1.17) unless a minimal concentration of an ornithine decarboxylase-inducing amino acid, such as asparagine, is present in the medium. The effects of the growth factors were studied in appropriately responsive cell lines: pheochromocytoma (PC12) cells for nerve and epidermal growth factors, fibroblasts (NIH 3T3) for platelet-derived growth factor, and fibroblasts and hepatoma (KRC-7) cells for insulin. The nonmetabolizable amino acid analog alpha-aminoisobutyric acid can replace asparagine, indicating that the covalent modification of the inducing amino acid is not necessary for the induction of ornithine decarboxylase by these growth factors. For the same intracellular concentration of the inducing amino acid, the presence of the growth factors induces higher levels of ornithine decarboxylase. The evidence indicates that these growth factors do not induce ornithine decarboxylase by raising the intracellular concentration of amino acids but rather act synergistically with the inducing amino acid. Evidence is provided that the induction of polyamine-dependent growth by these growth factors is mediated by amino acids. The relationship of these results to the A and N amino acid transport systems and to the Na+ influxes in relation to growth is discussed.

The effect of transport system A and N amino acids and of nerve and epidermal growth factors on the induction of ornithine decarboxylase activity

The induction of ornithine decarboxylase (EC 4.1.1.17) (ODC) by amino acids and by the peptide hormones nerve growth factor (NGF) and epidermal growth factor (EGF) in salts-glucose media has been studied. Only those neutral amino acids taken into the cell via one of the Na+ dependent transport systems stimulate ODC activity. Asparagine and the nonmetabolizable alpha-amino-isobutyric acid (AIB) were used as representatives of this class of inducing amino acids, and their intracellular concentrations were related to the levels of ODC induced. A threshold intracellular concentration of asparagine or AIB has to be attained before ODC can be induced. Further slight increases in intracellular concentrations of asparagine or AIB produce disproportionately large increases of ODC, resulting in a sigmoidal curve of ODC induction. These results, and the fact that the decrease in ODC levels caused by valine is associated with a concurrent decrease in the intracellular level of the inducing amino acid, suggest that the intracellular amino acid level is causally related to the induction of ornithine decarboxylase. Glutamic acid, EGF, and NGF do not induce ODC except in the presence of an inducing amino acid. They act synergistically with the inducing amino acid and produce higher ODC levels at the same intracellular concentration of the inducing amino acid.

Immunological determination of phosphoenolpyruvate carboxylase and the large and small subunits of ribulose 1,5-bisphosphate carboxylase in leaves of the c(4) plant pearl millet

The light-dependent development of the photosynthetic apparatus in the first leaf of the C(4) plant pearl millet (Pennisetum americanum) was monitored by immunologically determining the concentration of phospho-enolpyruvate carboxylase and ribulose 1,5-bisphosphate carboxylase. A competitive enzyme-linked immunosorbent assay procedure using antibodies to the monomeric subunit of phosphoenolpyruvate carboxylase and the large and small subunit of ribulose 1,5-bisphosphate carboxylase was used to quantitate the amounts of these polypeptides in the first leaf of etiolated seedlings and etiolated seedlings exposed to light for varying periods of time. Phosphoenolpyruvate carboxylase was present in etiolated tissue; however, light stimulated its synthesis nearly 23-fold. Maximum accumulation of phosphoenolpyruvate carboxylase occurred approximately 4 days after etiolated plants were placed in the light. Both the large subunit and the small subunit of ribulose 1,5-bisphosphate carboxylase were present in leaves of etiolated seedlings. Light also stimulated the synthesis of both of these polypeptides, but at different rates. In etiolated leaves there was approximately a 3-fold molar excess of the small subunit to large subunit. Exposure of the etiolated leaves to light resulted in the molar ratio of the large subunit to the small subunit increasing to approximately 0.72. These data indicate that the net synthesis of these two polypeptides is not coordinately regulated at all times.

Regulation of polyamine biosynthesis by antizyme and some recent developments relating the induction of polyamine biosynthesis to cell growth. Review

This review considers the role of antizyme, of amino acids and of protein synthesis in the regulation of polyamine biosynthesis. The ornithine decarboxylase of eukaryotic cells and of Escherichia coli can be non-competitively inhibited by proteins, termed antizymes, which are induced by di- and poly- amines. Some antizymes have been purified to homogeneity and have been shown to be structurally unique to the cell of origin. Yet, the E. coli antizyme and the rat liver antizyme cross react and inhibit each other's biosynthetic decarboxylases. These results indicate that aspects of the control of polyamine biosynthesis have been highly conserved throughout evolution. Evidence for the physiological role of the antizyme in mammalian cells rests upon its identification in normal uninduced cells, upon the inverse relationship that exists between antizyme and ornithine decarboxylase as well as upon the existence of the complex of ornithine decarboxylase and antizyme in vivo. Furthermore, the antizyme has been shown to be highly specific; its Keq for ornithine decarboxylase is 1.4 X 10(11) M-1. In addition, mammalian cells contain an anti-antizyme, a protein that specifically binds to the antizyme of an ornithine decarboxylase-antizyme complex and liberates free ornithine decarboxylase from the complex. In E. coli, in which polyamine biosynthesis is mediated both by ornithine decarboxylase and by arginine decarboxylase, three proteins (one acidic and two basic) have been purified, each of which inhibits both these enzymes. They do not inhibit the biodegradative ornithine and arginine decarboxylases nor lysine decarboxylase. The two basic inhibitors have been shown to correspond to the ribosomal proteins S20/L26 and L34, respectively. The relationship of the acidic antizyme to other known E. coli proteins remains to be determined. In mammalian cells, ornithine decarboxylase can be induced by a broad spectrum of compounds. These range from hormones and growth factors to natural amino acids such as asparagine and to non-metabolizable amino acid analogues such as alpha-amino-isobutyric acid. The amino acids that induce ornithine decarboxylase as well as those that promote polyamine uptake utilize the sodium dependent A and N transport systems. Consequently, they act in concert and increase intracellular polyamine levels by both mechanisms. The induction of ornithine decarboxylase by growth factors, such as NGF, EGF, and PDGF as well as by insulin requires the presence of these same amino acids and does not occur in their absence. However, the inducing amino acid need not be incorporated into protein nor covalently modified.(ABSTRACT TRUNCATED AT 400 WORDS)

Identification of the insulin receptor in undifferentiated and differentiated NB-15 mouse neuroblastoma cells by affinity labeling

Plasma membranes prepared from clonal NB-15 mouse neuroblastoma cells were sequentially incubated with 125I-labeled insulin (10 nM) and the bifunctional cross-linking agent disuccinimidyl suberate. This treatment resulted in the cross-linking of 125I-labeled insulin to a polypeptide that gave an apparent Mr of 135 000 on a sodium dodecyl sulfate-polyacrylamide gel electrophoresed in the presence of 10% beta-mercaptoethanol. Affinity labeling of this polypeptide was inhibited by the presence of 5 microM unlabeled insulin, but not by 1 microM unlabeled nerve growth factor. Using the same affinity labeling technique, 125I-labeled nerve growth factor (1 nM) did not label any polypeptide appreciably in the plasma membranes of NB-15 cells but labeled an Mr 145 000 and an Mr 115 000 species in PC-12 rat pheochromocytoma cells. The number of insulin binding sites per cell in the intact differentiated NB-15 mouse neuroblastoma cells was approx. 6-fold greater than that in the undifferentiated NB-15 mouse neuroblastoma cells as measured by specific binding assay, suggesting an increase of the number of insulin receptors in NB-15 mouse neuroblastoma cells during differentiation.

Characterization of the polyamine transport system in mouse neuroblastoma cells. Effects of sodium and system A amino acids

The biochemical properties of polyamine transport system have been studied in detail in NB-15 mouse neuroblastoma cells in culture by measuring the uptake of [14C]putrescine under various experimentally imposed pharmacological conditions. Putrescine uptake in the NB-15 mouse neuroblastoma cells appeared to be a sodium-dependent process. Iso-osmotic displacement of Na+ in the assay medium with either choline or Li+ resulted in a linear decrease of putrescine uptake. Gramicidin, a channel-former ionophore, inhibited putrescine uptake by more than 90% at 20 nM. N-Ethylmaleimide at 5 mM or p-chloromercuribenzene sulfonate at 50 microM completely abolished putrescine uptake. Conversely, oxidized glutathione at 10 mM or 5,5'-dithiobis-(2-nitrobenzoic acid) at 5 microM gave a 1.3-1.4-fold stimulation after a 1-h incubation. This polyamine transport system appeared to be subjected to adaptive regulation. Polyamine antimetabolites such as alpha-difluoromethyl ornithine stimulated putrescine uptake whereas preloading of cells with polyamines inhibited putrescine uptake. Preloading cells with neutral amino acids that belong to sodium-dependent transport System A stimulated putrescine uptake by more than 8-10-fold. These results suggested that the polyamine transport system in NB-15 mouse neuroblastoma cells was sodium dependent and shared some characteristics common to other known sodium-dependent transport systems. These characteristics included (a) sensitivity to ionophores, (b) sensitivity to sulfhydryl reagents, and (c) sensitivity to intracellular contents of substrate molecules. Our data also indicated that polyamine transport may be regulated by transport System A amino acids.

Variability of Reaction Kinetics for Ribulose-1,5-bisphosphate Carboxylase in a Barley Population

The photosynthetic enzyme ribulose bisphosphate carboxylase-oxygenase [EC 4.1.1.39] (RuBPCase) plays a key role in the carbon reduction system of plants. In this study, we determined the kinetic variability of RuBPCase among 46 varieties of Hordeum vulgare L. at two ages. The V(max) CO(2) and K(m) CO(2) of RuBPCase was determined for each cultivar. Varietal differences were found in K(m) CO(2) and V(max) CO(2) for one and four genotypes, respectively. One variety exhibited atypical behavior in both K(m) and V(max). A comparison of varieties and age showed a significant interaction between these factors for K(m) but not for V(max). These data indicate the presence of kinetic variability in RuBPCase within the H. vulgare population and perhaps between plant ages.

Identification of exposed surface glycoproteins in undifferentiated and differentiated mouse N-18 neuroblastoma cells

A simple method is described that permitted rapid isolation of plasma membranes from mouse N-18 neuroblastoma cells. The purified plasma membranes gave a 10-fold increase in the specific activity of incorporated [3H]fucose over that of the cell homogenate. The specific activities of two other membrane markers, 5'-nucleotidase and alkaline phosphatase, increased 11-fold and 15-fold, respectively. Metabolic labeling with [3H]fucose identified a major fucosyl glycoprotein with apparent molecular weight of 92 000. Three surface labeling methods together with SDS-polyacrylamide gel electrophoresis and fluorography were used to characterize and compare the surface glycoproteins of undifferentiated and differentiated N-18 cells. The galactose oxidase/NaB3H4 method labeled two major galactoproteins (Mr = 52 000, 42 000) in both undifferentiated and differentiated cells. The neuraminidase/galactose oxidase/NaB3H4 method revealed many sialylgalactoproteins. Among them, the 220-kdalton, 150-kdalton and 130-kdalton bands were at least 100% more prominently labeled in the differentiated cells whereas the 76-kdalton and 72-kdalton bands were less prominently labeled in the differentiated cells when compared to their undifferentiated counterparts. The prominently iodinated protein bands in the undifferentiated cells had apparent molecular weights of 130 000, 92 000, 76 000 and 72 000 as compared to 150-, 130-, 92- and 76-kdalton bands in the differentiated cells. The labeling data obtained will enable us to further study the changes of these identified surface glycoproteins, both quantitatively and topologically, during the differentiation of neuroblastoma cells.

Energy coupling in the active transport of proline and glutamate by the photosynthetic halophile Ectothiorhodospira halophila

When illuminated, washed cell suspensions of Ectothiorhodospira halophila carry out a concentrative uptake of glutamate or proline. Dark-exposed cells accumulate glutamate but not proline. Proline transport was strongly inhibited by carbonylcyanide-m-chlorophenylhydrazone (CCCP), a proton permeant that uncouples photophosphorylation, and by 2-heptyl-4-hydroxyquinoline-n-oxide (HQNO), an inhibitor of photosynthetic electron transport. A stimulation of proline uptake was effected by N,N'-dicyclohexylcarbodiimide (DCCD), an inhibitor of membrane adenosine triphosphatase (ATPase) which catalyzes the phosphorylation. These findings suggest that the driving force for proline transport is the proton-motive force established during photosynthetic electron transport. Glutamate uptake in the light was inhibited by CCCP and HQNO, but to a lesser extent than was the proline system. DCCD caused a mild inhibition of glutamate uptake in the light, but strongly inhibited the uptake by dark-exposed cells. CCCP strongly inhibited glutamate uptake in the dark. The light-dependent transport of glutamate is apparently driven by the proton-motive force established during photosynthetic electron transport. Hydrolysis of adenosine triphosphate (ATP) by membrane ATPase apparently establishes the proton-motive force to drive the light-independent transport. These conclusions were supported by demonstrating that light- or dark-exposed cells accumulate [3H]triphenylmethylphosphonium, a lipid-soluble cation. Several lines of indirect evidence indicated that the proline system required higher levels of energy than did the glutamate system(s). This could explain why ATP hydrolysis does not drive proline transport in the dark. Membrane vesicles were prepared by the sonic treatment of E. halophila spheroplasts. The vesicles contained active systems for the uptake of proline and glutamate.

Bacteriorhodopsin formation in Halobacterium halobium

Systematic examinations were made of factors influencing bacteriorhodopsin formation during the growth of Halobacterium halobium. Light-induced adenosine triphosphate (ATP) production and [14C]proline uptake were used as measures of functional ability of the purple membrane. Maximum bacteriorhodopsin formation occurred under growth conditions of illumination and limited aeration. The purple membrane -ATP production system did not confer an appreciable growth advantage. Growth in the dark or with adequate aeration partially suppressed bacteriorhodopsin formation and the effects were additive. Nicotine effectively inhibited bacteriorhodopsin formation. A rapid synthesis of functional pigment occurred when washed suspensions of cells which had been grown under illumination with nicotine present were incubated under dark, aerobic conditions. The alleviation of this nicotine inhibition was not blocked by chloramphenicol or bacitracin. Bacteriorhodopsin formation was negligible when washed suspensions of cells from dark, limited aeration or light, adequate aeration cultures were incubated in the light with limited aeration. A nutritionally complex medium was needed to elicit appreciable bacteriorhodopsin formation by the cells from the dark or adequately aerated cultures. Bacitracin partially inhibited this bacteriorhodopsin formation by cells form the light, adequately aerated culture.

Energy coupling in the active transport of amino acids by bacteriohodopsin-containing cells of Halobacterium holobium

Growth of Halobacterium halobium under illumination with limiting aeration induces bacteriorhodopsin formation and renders the cells capable of photophosphorylation. Cells depleted of endogenous reserves by a starvation treatment were used to investigate the means by which energy is coupled to the active transport of [14C]proline, -leucine, and -histidine. Proline was readily accumulated by irradiated cells under anaerobiosis even when the photophosphorylation was abolished by the adenosine triphosphatase inhibitor N,N'-dicyclohexylcarbodimiide (DCCD). The uptake of proline in the dark was limited except when the cells were allowed to accumulate adenosine 5'-triphosphate (ATP) by prior light exposure or by the oxidation of glycerol. DCCD inhibited this dark uptake. These findings essentially support Mitchell's chemiosmotic theory of active transport. The driving force is apparently the proton-motive force developed when protons are extruded from irradiated bacteriorhodopsin or by the dydrolysis of ATP by membrane adenosine triphosphatase. Carbonylcyanide m-chlorophenylhydrazone (CCCP), a proton permeant known to abolish membrane potential, was a strong inhibitor of proline uptake. Leucine transport was also apparently driven by proton-motive force, although its kinetic properties differed from the proline system. Histidine transport is apparently not a chemiosmotic system. Dark- or light-exposed cells show comparable initial rats of histidine uptake, and these processes were only partially inhibited by DCCD or CCCP. The histidine system apparently does not utilize ATP per se since comparable rates of uptake were exhibited by cells of differing intracellular ATP levels. Irradiated cells did effect a greater total accumulation of histidine than dark-exposed cells. These findings suggest that ATP is needed for sustained transport.