CMA mediates resistance in breast cancer models

BACKGROUND

Breast cancer (BC) is the most common malignancy in women and the second leading cause of cancer-related death; chemoresistance is still a clinical challenge mainly because of the different molecular features of this kind of tumour. Doxorubicin (Doxo) is widely used despite its adverse effects and the common onset of resistance. Chaperone-Mediated Autophagy (CMA) has been identified as an important mechanism through which chemotherapeutics can exert their cytotoxic effects and, in this context, LAMP-2A, the key player of CMA, can be a useful biomarker.

METHODS

A cohort of patients and breast cancer cells have been screened for Doxo effect and CMA activation by analysing the LAMP-2A level. Molecular silencing has been used to clarify CMA role in BC responsiveness to treatments. Low Doxo doses were combined with other drugs (TMZ or PX-478, a HIF-1α inhibitor) to evaluate their cytotoxic ability and their role in modulating CMA.

RESULTS

In this paper, we showed that CMA is an important mechanism mediating the responsiveness of breast cancer cell to different treatments (Doxo and TMZ, as suggested by triple negative cells that are TMZ-resistant and fails to activate CMA). The LAMP-2A expression level was specific for different cell lines and patient-derived tumour subtypes, and was also useful in discriminating patients for their survival rates. Moreover, molecular silencing or pharmacological blockage of HIF-1α activity reverted BC resistance to TMZ. The combination of low-dose Doxo with TMZ or PX-478 showed that the drug associations have synergistic behaviours.

CONCLUSION

Here, we demonstrated that CMA activity exerts a fundamental role in the responsiveness to different treatments, and LAMP-2A can be proposed as a reliable prognostic biomarker in breast cancer. In this context, HIF-1α, a potential target of CMA, can also be assessed as a valuable therapeutic target in BC in view of identifying new, more efficient and less toxic therapeutic drug combinations. Moreover, the possibility to combine Doxo with other drugs acting on different but coherent molecular targets could help overcome resistance and open the way to a decrease in the dose of the single drugs.

Diagnostic Circulating miRNAs in Sporadic Amyotrophic Lateral Sclerosis

Amyotrophic Lateral Sclerosis (ALS) is a fatal neurodegenerative disease characterized by the neurodegeneration of motoneurons. About 10% of ALS is hereditary and involves mutation in 25 different genes, while 90% of the cases are sporadic forms of ALS (sALS). The diagnosis of ALS includes the detection of early symptoms and, as disease progresses, muscle twitching and then atrophy spreads from hands to other parts of the body. The disease causes high disability and has a high mortality rate; moreover, the therapeutic approaches for the pathology are not effective. miRNAs are small non-coding RNAs, whose activity has a major impact on the expression levels of coding mRNA. The literature identifies several miRNAs with diagnostic abilities on sALS, but a unique diagnostic profile is not defined. As miRNAs could be secreted, the identification of specific blood miRNAs with diagnostic ability for sALS could be helpful in the identification of the patients. In the view of personalized medicine, we performed a meta-analysis of the literature in order to select specific circulating miRNAs with diagnostic properties and, by bioinformatics approaches, we identified a panel of 10 miRNAs (miR-193b, miR-3911, miR-139-5p, miR-193b-1, miR-338-5p, miR-3911-1, miR-455-3p, miR-4687-5p, miR-4745-5p, and miR-4763-3p) able to classify sALS patients by blood analysis. Among them, the analysis of expression levels of the couple of blood miR-193b/miR-4745-5p could be translated in clinical practice for the diagnosis of sALS.

Involvement of a cell size control mechanism in the induction and maintenance of oscillations in continuous cultures of budding yeast

Spontaneous oscillations occur in glucose-limited continuous cultures of Saccharomyces cerevisiae under aerobic conditions. The oscillatory behavior is detectable as a periodic change of many bioparameters such as dissolved oxygen, ethanol production, biomass concentration, as well as cellular content of storage carbohydrates and is associated to a marked synchronization of the yeast population. These oscillations may be related to a periodic accumulation of ethanol produced by yeast in the culture medium.The addition of ethanol to oscillating yeast cultures supports this hypothesis: indeed, no effect was observed if ethanol was added when already present in the medium, while a marked phase oscillation shift was obtained when ethanol was added at any other time. Moreover, the addition of ethanol to a nonoscillating culture triggers new oscillations. An accurate analysis performed at the level of nonoscillating yeast populations perturbed by addition of ethanol showed that both the growth rate and the protein content required for cell division increased in the presence of mixed substrate (i.e., ethanol plus limiting glucose). A marked synchronization of the yeast population occurred when the added ethanol was exhausted and the culture resumed growth only on limiting glucose. A decrease of protein content required for cell division was also apparent. These experimental findings support a new model for spontaneous oscillations in yeast cultures in which the alternative growth on limiting glucose and limiting glucose plus ethanol modifies the critical protein content required for cell division.

Higher levels of melanin and inhibition of cdk2 activity in primary human melanoma cells WM115 overexpressing nPKCdelta

Many studies have attempted to define the state of differentiation of melanoma cells and to correlate it with other critical parameters of malignancy such as the tumorigenic and metastatic nature of the cells. In the present paper we focused on the possible relationships between the novel protein kinase C isoform nPKCdelta, melanin synthesis and proliferative capacity in a primary human melanoma cell line WM115. Cells were transfected to produce overexpression of this isoform and the effects on melanin synthesis, cyclin-E dependent kinase (cdk2) activity and cyclin E expression were studied. It was shown that translocation of nPKCdelta into the nucleus affects melanin synthesis and inhibits cdk2 activity. As a compensatory effect, the level of cyclin E increases. In view of these results we suggest a model for the role of nPKCdelta in melanoma cells that may offer a new therapeutic perspective.

Efficient homolactic fermentation by Kluyveromyces lactis strains defective in pyruvate utilization and transformed with the heterologous LDH gene

A high yield of lactic acid per gram of glucose consumed and the absence of additional metabolites in the fermentation broth are two important goals of lactic acid production by microrganisms. Both purposes have been previously approached by using a Kluyveromyces lactis yeast strain lacking the single pyruvate decarboxylase gene (KlPDC1) and transformed with the heterologous lactate dehydrogenase gene (LDH). The LDH gene was placed under the control the KlPDC1 promoter, which has allowed very high levels of lactate dehydrogenase (LDH) activity, due to the absence of autoregulation by KlPdc1p. The maximal yield obtained was 0.58 g g(-1), suggesting that a large fraction of the glucose consumed was not converted into pyruvate. In a different attempt to redirect pyruvate flux toward homolactic fermentation, we used K. lactis LDH transformant strains deleted of the pyruvate dehydrogenase (PDH) E1alpha subunit gene. A great process improvement was obtained by the use of producing strains lacking both PDH and pyruvate decarboxylase activities, which showed yield levels of as high as 0.85 g g(-1) (maximum theoretical yield, 1 g g(-1)), and with high LDH activity.

Isolation and sequence analysis of the gene encoding triose phosphate isomerase from Zygosaccharomyces bailii

The ZbTPI1 gene encoding triose phosphate isomerase (TIM) was cloned from a Zygosaccharomyces bailii genomic library by complementation of the Saccharomyces cerevisiae tpi1 mutant strain. The nucleotide sequence of a 1.5 kb fragment showed an open reading frame (ORF) of 746 bp, encoding a protein of 248 amino acid residues. The deduced amino acid sequence shares a high degree of homology with TIMs from other yeast species, including some highly conserved regions. The analysis of the promoter sequence of the ZbTPI1 revealed the presence of putative motifs known to have regulatory functions in S. cerevisiae. The GenBank Accession No. of ZbTPI1 is AF325852.

Alterations of the glucose metabolism in a triose phosphate isomerase-negative Saccharomyces cerevisiae mutant

The absence of triose phosphate isomerase activity causes an accumulation of only one of the two trioses, dihydroxyacetone phosphate, and this produces a shift in the final product of glucose catabolism from ethanol to glycerol (Compagno et al., 1996). Alterations of glucose metabolism imposed by the deletion of the TPI1 gene in Saccharomyces cerevisiae were studied in batch and continuous cultures. The Deltatpi1 null mutant was unable to grow on glucose as the sole carbon source. The addition of ethanol or acetate in media containing glucose, but also raffinose or galactose, relieved this effect in batch cultivation, suggesting that the Crabtree effect is not the primary cause for the mutant's impaired growth on glucose. The addition of an energy source like formic acid restored glucose utilization, suggesting that a NADH/energy shortage in the Deltatpi1 mutant could be a cause of the impaired growth on glucose. The amount of glycerol production in the Deltatpi1 mutant could represent a good indicator of the fraction of carbon source channelled through glycolysis. Data obtained in continuous cultures on mixed substrates indicated that different contributions of glycolysis and gluconeogenesis, as well as of the HMP pathway, to glucose utilization by the Deltatpi1 mutant may occur in relation to the fraction of ethanol present in the media.

Current awareness

In order to keep subscribers up-to-date with the latest developments in their field, this current awareness service is provided by John Wiley & Sons and contains newly-published material on yeasts. Each bibliography is divided into 10 sections. 1 Books, Reviews & Symposia; 2 General; 3 Biochemistry; 4 Biotechnology; 5 Cell Biology; 6 Gene Expression; 7 Genetics; 8 Physiology; 9 Medical Mycology; 10 Recombinant DNA Technology. Within each section, articles are listed in alphabetical order with respect to author. If, in the preceding period, no publications are located relevant to any one of these headings, that section will be omitted. (4 weeks journals - search completed 7th Mar. 2001)

Towards a blueprint of the cell cycle

The understanding of the organisation of cell cycle events is of utmost importance to devise effective therapeutic strategies for cancer. In this article we gather evidences from the literature in support of a system model of the cell cycle, in which a growth-sensitive threshold controls entry into S phase and the sequential activation of cyclin-dependent kinases. The cycle is terminated by an End function, that comprises events from the onset of mitosis to cell division and that may also be modulated by the increase of cell size. This blueprint allows quantitative predictions by computer simulations of steady and transitory states. In fact, we show that the proposed control system applies to budding yeast populations during nutritional shift-up and following hyperactivation of the cAMP signalling pathway. Besides the growth-sensitive control system it is shown to apply to mammalian cells both in the exit from quiescence and in active proliferation. The putative molecular determinants that set the threshold controlling S phase entry are consistently altered in cancer cells. Finally, we discuss an input/output analysis based on the simulated behaviour derived from the blueprint as a new tool to investigate the road to cancer.

Relation between growth dynamics and diffusional limitations in Saccharomyces cerevisiae cells growing as entrapped in an insolubilised gelatin gel

Flow-cytometric analysis was employed to investigate growth dynamics of a yeast cell population immobilised in an insolubilised gelatin gel by means of the quantitative determination of the average protein content per cell. This analysis was carried out on both the immobilised cell population considered as a whole and the subpopulations colonising the gelatin matrix at different depths. The results show that growth of the gelatin-immobilised yeast population was affected by the existence of a gradient of nutrient concentrations through the matrix and are in agreement with the unsteady-state diffusion model employed for the description of glucose transfer in the gel.

Improved secretion of native human insulin-like growth factor 1 from gas1 mutant Saccharomyces cerevisiae cells

We studied the secretion of recombinant human insulin-like growth factor 1 (rhIGF-1) from transformed yeast cells. The hIGF-1 gene was fused to the mating factor alpha prepro- leader sequence under the control of the constitutive ACT1 promoter. We found that the inactivation of the GAS1 gene in the host strain led to a supersecretory phenotype yielding a considerable increase, from 8 to 55 mg/liter, in rhIGF-1 production.

Real-time flow cytometric quantification of GFP expression and Gfp-fluorescence generation in Saccharomyces cerevisiae

A genetic and analytical methodology was developed based on a green fluorescent mutant protein (Gfp(S65T)) that allows the real-time quantification of gene expression in Saccharomyces cerevisiae. Using the UAS(GAL)(1-10)/CYC1 promoter and plasmids that are maintained in different copy numbers per cell, wild-type GFP and mutant GFP(S65T) were expressed in low to high concentration. Flow cytometric analysis was then applied to directly quantify Gfp((S65T)) (both wild type and mutant protein) expression at the single-cell level, and to indirectly measure the concentrations of non-fluorescent apoGfp((S65T)) and fluorescent Gfp((S65T)), which is autocatalytically formed from the apoprotein. Kinetics of apoGfp((S65T))/Gfp((S65T)) conversion during aerobic growth showed that the time required for complete apoGfp((S65T)) conversion is limited only by the amount of apoprotein that is expressed. When GFP(S65T) was expressed in single copy, the apoprotein did not accumulate and was instantly converted into its fluorescent form. The data indicate that an instant quantification of gene expression in S. cerevisiae is achievable based on Gfp(S65T), even if the gene is transcribed from a very strong promoter.

Relating growth dynamics and glucoamylase excretion of individual Saccharomyces cerevisiae cells

We have developed a novel flow cytometric procedure that allows determinations of properties of protein excretion in the growth medium on a cell-by-cell basis in Saccharomyces cerevisiae. The procedure is based on labelling of a periplasmically secreted protein with antibodies conjugated to a fluorescent marker such as fluorescein isothiocyanate (FITC). The staining conditions did not perturb cell growth after resuspension of stained cells in growth medium. Decrease in fluorescence was found to correlate with excretion of glucoamylase into the growth medium. The analysis of the staining pattern over time provides information on the behaviour of individual cells belonging to different cell-cycle phases and can be used to calculate the specific excretion rate of the overall population.

Overexpression of novel protein kinase C delta in BL6 murine melanoma cells inhibits the proliferative capacity in vitro but enhances the metastatic potential in vivo

In this study we analysed the effect of overexpressing novel protein kinase C delta isoform (n-PKC delta) on melanin synthesis and metastatic potential in the highly metastatic BL6 murine melanoma cells. The proliferative capacity in vitro and into matrigel in vivo were also examined. Although murine melanocytes express the n-PKC delta isoform, BL6 cells do not express this isoform at levels detectable by Western blot analysis. In untransfected and transfected cells we also studied the effect of 12-O-tetradecanoylphorbol-13-acetate (TPA), a modulator of specific isoforms of PKC, and of bryostatin 1, a potent immunomodulator and antineoplastic drug and a partial agonist of PKC. Our results demonstrate a pivotal role for this isoform in melanin synthesis and the close relationship between n-PKC delta expression and its association with the particulate fraction, melanogenesis and metastatic potential. In fact, heterogeneous BL6 cells overexpressing n-PKC delta and all the clones isolated showed increased intracellular melanin and metastatic capacity. TPA and bryostatin 1 decreased n-PKC delta expression, the intracellular melanin level and metastatic capacity in both cell lines. Therefore both treatments were able to abolish the effects of overexpressing n-PKC delta.

Replacement of a metabolic pathway for large-scale production of lactic acid from engineered yeasts

Interest in the production of L-(+)-lactic acid is presently growing in relation to its applications in the synthesis of biodegradable polymer materials. With the aim of obtaining efficient production and high productivity, we introduced the bovine L-lactate dehydrogenase gene (LDH) into a wild-type Kluyveromyces lactis yeast strain. The observed lactic acid production was not satisfactory due to the continued coproduction of ethanol. A further restructuring of the cellular metabolism was obtained by introducing the LDH gene into a K. lactis strain in which the unique pyruvate decarboxylase gene had been deleted. With this modified strain, in which lactic fermentation substituted completely for the pathway leading to the production of ethanol, we obtained concentrations, productivities, and yields of lactic acid as high as 109 g liter(-1), 0.91 g liter(-1) h(-1), and 1.19 mol per mole of glucose consumed, respectively. The organic acid was also produced at pH levels lower than those usual for bacterial processes.

Isolation, nucleotide sequence, and physiological relevance of the gene encoding triose phosphate isomerase from Kluyveromyces lactis

Lack of triose phosphate isomerase activity (TIM) is of special interest because this enzyme works at an important branch point of glycolytic flux. In this paper, we report the cloning and sequencing of the Kluyveromyces lactis gene encoding TIM. Unlike Saccharomyces cerevisiae DeltaTPI1 mutants, the K. lactis mutant strain was found to be able to grow on glucose. Preliminary bioconversion experiments indicated that, like the S. cerevisiae TIM-deficient strain, the K. lactis TIM-deficient strain is able to produce glycerol with high yield.

In budding yeast, reactive oxygen species induce both RAS-dependent and RAS-independent cell cycle-specific arrest

The role of mild oxidative stresses elicited by diethylmaleate (DEM)-induced glutathione depletion in the progression of the yeast cell cycle has been investigated. We found that different wild-type strains are sensitive to oxidative stresses induced by similar DEM doses: approximately 1 mM on YPD plates, 5-10 mM in shaken flasks. At lower doses, DEM caused a transient decrease in growth rate, largely because of a decreased G1-to-S transition. Treatment with higher DEM doses leads to complete growth arrest, with most cells found in the unbudded G1 phase of the cell cycle. DEM treatment resulted in transcriptional induction of stress-responsive element (STRE)-controlled genes and was relieved by treatment with the antioxidant N-acetyl cysteine. Reciprocal shift experiments with cdc25 and cdc28 mutants showed that the major cell cycle arrest point was located in the Start area, at or near the CDC25-mediated step, before the step mediated by the CDC28 cyclin-dependent kinase. The DEM-induced G1 arrest requires a properly regulated RAS pathway and can be bypassed by overexpressing the G1-specific cyclin CLN2. However, cells with either a deregulated RAS pathway or overexpressing CLN2 failed to grow and arrested as budded cells, indicating that a second DEM-sensitive cell cycle step exists.

NADH reoxidation does not control glycolytic flux during exposure of respiring Saccharomyces cerevisiae cultures to glucose excess

Introduction of the Lactobacillus casei lactate dehydrogenase (LDH) gene into Saccharomyces cerevisiae under the control of the TPI1 promoter yielded high LDH levels in batch and chemostat cultures. LDH expression did not affect the dilution rate above which respiro-fermentative metabolism occurred (Dc) in aerobic, glucose-limited chemostats. Above Dc, the LDH-expressing strain produced both ethanol and lactate, but its overall fermentation rate was the same as in wild-type cultures. Exposure of respiring, LDH-expressing cultures to glucose excess triggered simultaneous ethanol and lactate production. However, the specific glucose consumption rate was not affected, indicating that NADH reoxidation does not control glycolytic flux under these conditions.

Opposite effects of TPA on G1/S transition and on cell size in the low metastatic B16F1 with respect to high metastatic BL6 murine melanoma cells

Phorbol esters, known activators of c- and n-protein kinase C (PKC) isoforms, play a pivotal role in tumor promotion. In order to better understand the relationships between PKC activation, the metastatic potential and the proliferative capacity, we have analyzed the effect of 12-O-tetradecanoylphorbol-13-acetate (TPA) treatment on the proliferative as well as on the cell cycle distribution and on the cell size of low and high metastatic murine B16F1 and B16-BL6 (BL6) melanoma cells, respectively. TPA-treated B16F1 cells showed an increased proliferative capacity up to 72 h, the cytofluorimetric analysis revealing an increased number of cells in the S + G2-M phase of the cell cycle. In contrast, TPA-treated BL6 cells reached a plateau at 48 h and showed an increased cell volume in the G1 and S phases of the cell cycle, with a reduction in the percentage of cells in the S + G2-M phase. Taken together, our results indicate opposite effects of TPA treatment in murine melanoma cells of different metastatic potential. TPA could cause a block in the G1 phase of the cell cycle with enhanced cell volume in high metastatic BL6 cells. The same treatment, on the contrary, induced an increased entry into the cell cycle of low metastatic B16F1 cells, suggesting a relationship between cell proliferation and the metastatic potential of B16 murine melanoma cells. Moreover, under the present conditions, classical PKC isoforms were inactivated, suggesting the involvement of the TPA-dependent novel PKCs.

A mutation in a novel yeast proteasomal gene, RPN11/MPR1, produces a cell cycle arrest, overreplication of nuclear and mitochondrial DNA, and an altered mitochondrial morphology

We report here the functional characterization of an essential Saccharomyces cerevisiae gene, MPR1, coding for a regulatory proteasomal subunit for which the name Rpn11p has been proposed. For this study we made use of the mpr1-1 mutation that causes the following pleiotropic defects. At 24 degreesC growth is delayed on glucose and impaired on glycerol, whereas no growth is seen at 36 degreesC on either carbon source. Microscopic observation of cells growing on glucose at 24 degreesC shows that most of them bear a large bud, whereas mitochondrial morphology is profoundly altered. A shift to the nonpermissive temperature produces aberrant elongated cell morphologies, whereas the nucleus fails to divide. Flow cytometry profiles after the shift to the nonpermissive temperature indicate overreplication of both nuclear and mitochondrial DNA. Consistently with the identification of Mpr1p with a proteasomal subunit, the mutation is complemented by the human POH1 proteasomal gene. Moreover, the mpr1-1 mutant grown to stationary phase accumulates ubiquitinated proteins. Localization of the Rpn11p/Mpr1p protein has been studied by green fluorescent protein fusion, and the fusion protein has been found to be mainly associated to cytoplasmic structures. For the first time, a proteasomal mutation has also revealed an associated mitochondrial phenotype. We actually showed, by the use of [rho degrees] cells derived from the mutant, that the increase in DNA content per cell is due in part to an increase in the amount of mitochondrial DNA. Moreover, microscopy of mpr1-1 cells grown on glucose showed that multiple punctate mitochondrial structures were present in place of the tubular network found in the wild-type strain. These data strongly suggest that mpr1-1 is a valuable tool with which to study the possible roles of proteasomal function in mitochondrial biogenesis.

Control by nutrients of growth and cell cycle progression in budding yeast, analyzed by double-tag flow cytometry

To gain insight on the interrelationships of the cellular environment, the properties of growth, and cell cycle progression, we analyzed the dynamic reactions of individual Saccharomyces cerevisiae cells to changes and manipulations of their surroundings. We used a new flow cytometric approach which allows, in asynchronous growing S. cerevisiae populations, tagging of both the cell age and the cell protein content of cells belonging to the different cell cycle set points. Since the cell protein content is a good estimation of the cell size, it is possible to follow the kinetics of the cell size increase during cell cycle progression. The analysis of the findings obtained indicates that both during a nutritional shift-up (from ethanol to glucose) and following the addition of cyclic AMP (cAMP), two important delays are induced. The preexisting cells that at the moment of the nutritional shift-up were cycling before the Start phase delay their entrance into S phase, while cells that were cycling after Start are delayed in their exit from the cycle. The combined effects of the two delays allow the cellular population that preexisted the shift-up to quickly adjust to the new growth condition. The effects of a nutritional shift-down were also determined.

Identification of different daughter and parent subpopulations in an asynchronously growing Saccharomyces cerevisiae population

Under all growth conditions, a growing Saccharomyces cerevisiae yeast population is extremely heterogeneous, since individual cells differ in their cell size; this is due to their position in the cell division cycle and their genealogical age. To gain insight into the structure of a growing yeast population, we used a recently developed flow cytometric approach which enables, in asynchronously growing S. cerevisiae populations, tagging of both the cell age and the protein content of individual cells. This approach enabled the identification of daughter cells belonging to different cell cycle positions (i.e. newborn, G1, S + G2 + M + G1*, and dividing), thus yielding information about the relative fraction in the whole population, cell size and variability. More limited information could be obtained for the parent subpopulation; however, we were able to identify and characterize the dividing parent cells. The coefficient of variation (CV) of the protein content distribution for the dividing parents (27) was much higher than the CV of dividing daughters (18). Further findings obtained indicated a large overlap between the cell protein content distributions of daughter and parent cells as well as between the protein content of cells of the same subpopulation but belonging to different stages of the cell division cycle. The analysis of these differences enables a better understanding of the complex structure of an asynchronously growing yeast population.

Selection of yeast cells with a higher plasmid copy number in a Saccharomyces cerevisiae autoselection system

Autoselection systems allow the selection of a genetically engineered population independently of the growth medium composition. The structure of a Saccharomyces cerevisiae population transformed with an autoselection plasmid, in which a carbon-source-dependent modulation of the plasmid copy number occurs, was analysed. By means of flow cytometric procedures we tested the cell viability, dynamics of growth and heterologous protein production at single cell level. Such analyses allow the identification and the tracking of a specific cellular sub-population with a higher plasmid copy number which arises after the carbon source shift. The effects of the cellular plasmid distribution on the dynamics of growth are also discussed.

Development of RAPD protocol for typing of strains of lactic acid bacteria and enterococci

A protocol for typing strains of lactic acid bacteria and enterococci based on randomly amplified polymorphic DNA (RAPD) fragments has been developed. Using a single 10-mer primer, fingerprints were achieved without the need to isolate genomic DNA. Different conditions of DNA release and amplification were investigated in order to obtain reproducible results and high discrimination among strains. This RAPD protocol was successfully applied for the typing of strains belonging to the species Lactobacillus acidophilus, Lact. helveticus, Lact. casei, Lact. reuteri, Lact. plantarum, Enterococcus faecalis, Ent. faecium and Streptococcus thermophilus.

Fermentation of whey and starch by transformed Saccharomyces cerevisiae cells

Among the main agro-industrial wastes, whey and starch are of prime importance. In previous work we showed that strains of Saccharomyces cerevisiae transformed with the episomal plasmid pM1 allow production of yeast biomass and ethanol from whey/lactose. Ethanol production from whey and derivatives has been improved in computer-controlled bioreactors, while fermentation studies showed that the composition of the medium greatly modulates the productivity (g ethanol produced/l in 1 h of fermentation). A yeast strain for the simultaneous utilization of lactose and starch has also been developed. Biotechnological perspectives are discussed.

A double flow cytometric tag allows tracking of the dynamics of cell cycle progression of newborn Saccharomyces cerevisiae cells during balanced exponential growth

Studies on the dynamics of growth of single eukaryotic cells and their relationships with cell cycle regulations are generally carried out following cell synchronization procedures or, on a relatively low number of cells, by time-lapse studies. Establishment of both time-lapse studies and synchronous cell populations usually requires elaborate experimental efforts and is prone to perturb the physiological state of the cell. In this paper we use a new flow cytometric approach which allows, in asynchronous growing Saccharomyces cerevisiae populations, tagging of both the cell age and the cell protein content of a cohort of daughter cells at the different cell cycle set points. Since the cell protein content is a good estimation of the cell size, it is possible to follow the kinetics of the cell size increase during cell cycle progression. The experimental findings obtained indicate an exponential increase of the cell size during growth, that the daughter and the parent subpopulations grow with the same specific growth rate, that the average cell size increase rate of each individual cell is almost identical to the specific growth rate of the overall population and provide the opportunity to estimate the cell cycle length for the daughter cell population as well as the identification of the complex structure of asynchronously growing yeast populations.

Tracking of individual cell cohorts in asynchronous Saccharomyces cerevisiae populations

A novel flow cytometric procedure has been developed with the aim to obtain the growth properties of individual Saccharomyces cerevisiae cells in asynchronous culture. The method is based on labeling of the cell surface with FITC-conjugated concanavalin A and detection of the single-cell fluorescence with flow cytometry after cell exposure to growth conditions. Because the formation of new cell wall material in budded cells is restricted to the bud tip, exposure of the stained cells to growth conditions results in three cell types: (i) stained cells, (ii) partially stained cells, and (iii) unstained cells. Analysis of the staining pattern over time permits the determination of the specific growth rate of the cell population, the length of the budded cell cycle phase, and the growth pattern during the cell cycle of newly formed, partially stained daughter cells. The procedure has been tested with yeast cell populations growing at different rates. The data suggest an exponential increase in the size of individual cells during the cell cycle, as reflected by the forward angle light scattering (FALS) signals. It has been found that the apparent single-cell specific cell size growth rates, determined by FALS intensity, are significantly lower than the specific growth rates of the overall population. This could indicate that the tracking of a cohort of cells is significantly perturbed by a distribution of staining levels of daughter cells at cell division and that FALS may not be a good indicator of the cell size.

Development of metabolically engineered Saccharomyces cerevisiae cells for the production of lactic acid

Interesting challenges from metabolically engineered Saccharomyces cerevisiae cells arise from the opportunity to obtain yeast strains useful for the production of chemical(s). In this paper, we describe the accumulation of lactic acid in the culture medium of growing, engineered yeast cells expressing a mammalian lactate dehydrogenase gene (LDH-A). High and reproducible productions (20 g/L) and productivities (up to 11 g/L/h) of lactic acid have been obtained by modulating the physiological growth conditions. Since yeast cells are acid tolerant and survive at very low pH values, the production of lactate can be avoided. In perspective, the approaches described could be useful for the production of lactic acid, outflanking the problems related to the synthesis from bacteria cells. In fact, during industrial productions, there is an inhibitory effect on the metabolic activities of the growing bacteria (i.e., Lactobacillus spp.) caused by the acid produced and by the low pH value. Thus, strategies to prevent the lowering of pH are conventional operations. These processes allow the production of lactate(s) and require the purification of the acid from its salt. The biotechnological implications of this study are also discussed.

Involvement of the alpha isoenzyme of protein kinase C in the growth inhibition induced by phorbol esters in MH1C1 hepatoma cells

MH1C1 rat hepatoma cells express the alpha isoenzyme as the only phorbol-ester sensitive isoform of protein kinase C (PKC). In this cell line, phorbol 12-myristate 13-acetate (PMA) induced a marked, dose-dependent growth inhibition. The administration of the PKC inhibitor staurosporine was able to mimic the effect of the phorbol ester on cell growth in a dose-dependent fashion, whereas the PKC activator arachidonic acid stimulated cell proliferation. Exposure of cells to an antisense oligonucleotide specific for alpha PKC caused a significant impairment of cell growth. These data suggest that the alpha PKC activity is required for proliferation of MH1C1 cells.

Alteration of cell population structure due to cell lysis in Saccharomyces cerevisiae cells overexpressing the GAL4 gene

Transformed Saccharomyces cerevisiae cells overexpressing the Escherichia coli LacZ gene and the transcriptional activator GAL4, release in the external medium a fraction (from 2 to 10%) of the total beta-galactosidase activity (Porro et al., 1992b). It is known that this abnormal release of a cytoplasmic protein is related to a partial cell lysis of the yeast population, which is likely to be caused by the overexpression of the transcriptional activator GAL4. In the present paper we have characterized the GAL4-induced cell lysis phenomenon. The expression of the GAL4 gene causes morphological modifications and alteration of the cell size distribution. The cell lysis is independent of the expression of the heterologous LacZ gene and occurs in a specific subpopulation of cells (the parent cells) independently of the genealogical age, growth phase conditions and cell cycle progression. Lysis is preceded by a loss of the plasma membrane integrity as indicated by the uptake of ethidium bromide in unfixed cells. Computer analysis of simulated protein distributions indicates that cell lysis takes place in a sizeable aliquot (about 50%) of the parent cells, therefore profoundly altering the age structure of the population.

In Saccharomyces cerevisiae, protein secretion into the growth medium depends on environmental factors

In the budding yeast Saccharomyces cerevisiae the cell wall, mainly composed of mannoproteins and glucans, constitutes a barrier to protein excretion in the growth medium. In this paper we have studied the effects of different environmental parameters on excretion of Escherichia coli beta-galactosidase obtained by exploiting the glucoamylase II signal sequence. Excretion of the unglycosylated beta-galactosidase was detectable only in cells grown in rich medium, was affected by temperature (36 degrees C > 30 degrees C >> 24 degrees C) and slightly stimulated by reducing agents. On the contrary, glycosylated proteins, such as alpha-galactosidase and glucoamylase II, were excreted to a good extent under all tested conditions of medium composition, growth temperature and pH. These data indicate that optimization of environmental parameters may help the excretion of heterologous proteins, offering advantages for protein purification.

Expression of high levels of human tissue plasminogen activator in yeast under the control of an inducible GAL promoter

The human tissue plasminogen activator (h-tPA) cDNA was fused either with the leader sequence of the killer toxin of Kluyveromyces lactis or with the Saccharomyces diastaticus glucoamylase leader peptide and cloned in the yeast expression vector under the control of the inducible USAgal/CYC1 promoter. The recombinant tPA is produced in yeast as a single-chain glycosylated polypeptide of 66-72 kDa, which accumulates intracellularly associated with a membrane fraction. Using two-step fed-batch fermentation, a productivity up to 100 mg/l of active intracellular tPA was obtained.

Enhanced expression of heterologous proteins by the use of a superinducible vector in budding yeast

We report the effects of a strong overexpression of the GAL4 activator protein on the expression of UASGAL regulated genes, obtained by cloning the GAL4 gene and the GAL1-10 upstream activating sequence (UASGAL)-lacZ fusion in the same high copy number plasmid. Comparable amounts of active enzyme were obtained by host strains usually producing different levels of cloned proteins due to their different genetic background. The transformed cells constitutively produced low levels of beta-galactosidase (1-2% of total proteins) both in glucose and in raffinose minimal media. Nevertheless, expression was still inducible and a tenfold induction could be rapidly obtained by the addition of 0.5% (w/v) galactose to the culture, even when glucose was still present in the medium.

Efficient production of recombinant DNA proteins in Saccharomyces cerevisiae by controlled high-cell-density fermentation

High levels of expression of heterologous proteins (from 5 to 15% of total cell proteins) in the budding yeast Saccharomyces cerevisiae have been obtained previously by the use of the inducible strong hybrid promoter UASGAL/CYC1, in batch as well in continuous cultures. However, in order to maximize the yield of heterologous proteins, a computer controlled fed-batch fermentation is essential. For this reason we have developed a fed-batch system based on a semiconductor gas detector that measures ethanol in the outflow gases. The optimal conditions are described for very high production (up to 1550 mg/liter), with both high productivity (up to 100-120 mg/liter/h) and high yield (up to 15 mg of protein/g of dry biomass), of heterologous protein driven by the UASGAL/CYC1 promoter in a completely computer controlled fed-batch fermentation of budding yeast. However, high production was dependent upon the addition of a large amount of galactose. The process was improved by developing a new, more easily inducible, vector system obtained by subcloning the GAL4 gene.

Heterologous gene expression in continuous cultures of budding yeast

In a previous paper we have studied the expression of beta-galactosidase from Escherichia coli, driven from the inducible GAL1-10/CYC1 hybrid promoter, in batch cultures of budding Saccharomyces cerevisiae and have described operating conditions for maximal productivity. In this paper we show that the plasmid instability in continuous cultures can be overcome by utilizing appropriate selection markers and a high copy number vector. The maximal level of expression is influenced by the dilution rate. Moreover, enzyme accumulation appears to depend also upon the degree of oxygenation. A possible explanation of these modulations is discussed, taking into account the interactions of the UAS-GAL and TATA-CYC1 elements.

Flow cytometry and cell cycle kinetics in continuous and fed-batch fermentations of budding yeast

Cell size distributions, obtained either as protein distribution by flow cytometry or as cell volume distribution by a Coulter counter, give relevant information about the growth conditions of populations of budding yeast Saccharomyces cerevisiae. We have previously found a good correlation between these distributions and the growth rate in continuous cultures (Ranzi et al., Biotechnol. Bioeng. 1986, 28, 185-190). We now present determinations of the protein distributions and cell volume distributions during different fed-batch fermentations performed with a simple on/off controller. Since during the fed-batch fermentation a true steady state is not obtained, the distributions continuously change with time, but nevertheless we observed a good correlation between the average of both distributions and the actual growth rate. The behavior of the cell size distributions can be interpreted on the basis of a two-threshold cell cycle model in which both the critical protein content at budding (Ps) and the critical protein content for cell division (Pm) are differently modulated by the growth rate. Additional findings will be presented showing that this model can be used to successfully explain the insurgence and the maintenance of oscillatory states in continuous cultures.

Development of a pH-controlled fed-batch system for budding yeast

In the manufacturing of baker's yeast by aerobic fed-batch systems, continuous assessment of the state of the process is necessary for regulating the flow rate (on/off) for growth medium addition. A new, simple method for the fed-batch yeast process has been developed. It is based on pH changes as a suitable parameter for regulating the feed of fresh concentrated medium in response to metabolic activities of the yeast population. Experimental results have shown that it enables the attaining of high cell density with both high productivity and high yields.

Secretion of Escherichia coli beta-galactosidase in Saccharomyces cerevisiae using the signal sequence from the glucoamylase-encoding STA2 gene

The budding yeast Saccharomyces cerevisiae is a safe and widely used host for the production of recombinant DNA-derived proteins. We have used the signal sequence from the S. diastaticus STA2 gene, encoding glucoamylase II, to secrete Escherichia coli beta-galactosidase, encoded by the lacZ gene. In frame STA2/lacZ gene fusions have been constructed and expressed in S. cerevisiae under the control of either the STA2 or the galactose inducible GAL1-10 upstream promoters. Fairly high amounts of the enzyme (up to 76% of total activity, depending on the growth conditions) are secreted in the periplasmic space. Adding yeast extract and peptone to the growth medium results in a dramatic increase in both synthesis and secretion of beta-galactosidase.