Changes In Doubling Time Research Articles

Overexpression or Deletion of Ergosterol Biosynthesis Genes Alters Doubling Time, Response to Stress Agents, and Drug Susceptibility in Saccharomyces cerevisiae.

ABSTRACTErgosterol (ERG) is a critical sterol in the cell membranes of fungi, and its biosynthesis is tightly regulated by 25 known enzymes along the ERG production pathway. The effects of changes in expression of each ERG biosynthesis enzyme in Saccharomyces cerevisiae were analyzed by the use of gene deletion or plasmid-borne overexpression constructs. The strains overexpressing the ERG pathway genes were examined for changes in doubling time and responses to a variety of stress agents. In addition, ERG gene overexpression strains and ERG gene deletion strains were tested for alterations in antifungal drug susceptibility. The data show that disruptions in ergosterol biosynthesis regulation can affect a diverse set of cellular processes and can cause numerous phenotypic effects. Some of the phenotypes observed include dramatic increases in doubling times, respiratory deficiencies on glycerol media, cell wall insufficiencies on Congo red media, and disrupted ion homeostasis under iron or calcium starvation conditions. Overexpression or deletion of specific enzymes in the ERG pathway causes altered susceptibilities to a variety of classes of antifungal ergosterol inhibitors, including fluconazole, fenpropimorph, lovastatin, nystatin, amphotericin B, and terbinafine. This analysis of the effect of perturbations to the ERG pathway caused by systematic overexpression of each of the ERG pathway genes contributes significantly to the understanding of the ergosterol biosynthetic pathway and its relationship to stress response and basic biological processes. The data indicate that precise regulation of ERG genes is essential for cellular homeostasis and identify several ERG genes that could be exploited in future antifungal development efforts.

Effect and regulation of metformin on endometrial carcinoma subline of progestin-resistance

To investigate the effect and mechanism of metformin on endometrial carcinoma subline of progestin-resistance and find whether metformin could regulate progestin-resistance in endometrial carcinoma. Ishikawa endometrial carcinoma cells were cultured for a long period in the presence of the synthetic medroxyprogesterone 17-acetate (MPA) to generate a subline refractory to the growth-suppressive effects of MPA, named Ishikawa/MPA cells. The effect of MPA (1, 5, 10, 20, 40 and 60 μmol/L) or metformin (1, 10, 20, 40, 60, 70 and 80 mmol/L) on proliferation of the Ishikawa/MPA and parental Ishikawa cells was detected by cell counting kit-8 (CCK-8) method. Western blot was used to detect the effect of metformin and (or) MPA on the expression of PR-B in the Ishikawa/MPA and Ishikawa cells. The Ishikawa/MPA showed that growth stimulation rather than inhibition in the Ishikawa cells after low MPA concentration treatment. The doubling time of Ishikawa/MPA cell lines were (43±4) hours and that of Ishikawa cell line were (47 ± 3) hours. No changes in doubling time were observed (t=0.349, P= 0.572). Low concentration (1 and 5 μmol/L) of MPA could promote the growth of Ishikawa/MPA cells (by 3% and 13%). High concentration (10, 20, 40 and 60 μmol/L) of MPA could inhibited the growth of Ishikawa/MPA cells (by 4%, 3%, 9% and 40%) and the growth of Ishikawa cells (by 41%, 55%, 65% and 66% ). At the same concentration, the difference of inhibition rates between the two cell lines were statistically significant (P<0.01). Metformin (1, 10, 20, 40, 60, 70 and 80 mmol/L) could inhibite the growth of Ishikawa/MPA (by -10%, 20%, 56%, 89%, 97%, 98% and 99%) greater than those in parental Ishikawa cells (by -6%, 19%, 37%, 54%, 70%, 72% and 83%), and the inhibitory effect was dose-dependent manner. Western blot assay showed that for Ishikawa cells, the protein expression levels of PR-B in metformin group and MPA+metformin group were respectively (53.5±4.0)% and (37.7±5.2)%, which were higher than that in the control group [(23.4 ± 3.0)%], and there were significant the differences (P<0.01). For Ishikawa/MPA cells, the protein expression levels of PR-B in metformin group and MPA+metformin group were respectively (38.6±1.7)%, (36.3±2.5)%, which were higher than those in the control group [(6.4±1.6)%], and there were also significant differences (P<0.01). Metformin may regulate the progestin-resistance in endometrial carcinoma by increasing the expression of PR-B.

Pressure and Temperature Dependence of Growth and Morphology of Escherichia coli: Experiments and Stochastic Model

We have investigated the growth of Escherichia coli, a mesophilic bacterium, as a function of pressure (P) and temperature (T). Escherichia coli can grow and divide in a wide range of pressure (1–400 atm) and temperature (23–40°C). For T > 30°C, the doubling time of E. coli increases exponentially with pressure and exhibits a departure from exponential behavior at pressures between 250 and 400 atm for all the temperatures studied in our experiments. The sharp change in doubling time is followed by a sharp change in phenotypic transition of E. coli at high pressures where bacterial cells switch to an elongating cell type. We propose a model that this phenotypic change in bacteria at high pressures is an irreversible stochastic process, whereas the switching probability to elongating cell type increases with increasing pressure. The model fits well the experimental data. We discuss our experimental results in the light of structural and thus functional changes in proteins and membranes.

A Critical Assessment of Post-Prostatectomy Prostate Specific Antigen Doubling Time Acceleration—Is it Stable?

We examined a retrospective cohort of patients with biochemical recurrence after prostatectomy to determine whether prostate specific antigen doubling time would remain stable with time. We also examined the relationship between other clinical parameters and the change in prostate specific antigen doubling time. We retrospectively reviewed the prostate cancer database from 1989 to 2008 to identify patients treated with radical prostatectomy for prostate cancer who experienced prostate specific antigen recurrence. Of the 2,237 patients identified 329 had biochemical recurrence. Prostate specific antigen doubling time was calculated at each visit and linear regression of prostate specific antigen doubling time with time was fit. Rate of change in prostate specific antigen doubling time was defined as the slope of the least squares regression line. Median followup was 5 years (range 0.2 to 18). High Gleason score and local recurrence within 5 years were significantly associated with shorter 2-year prostate specific antigen doubling time and a decreased rate of change in doubling time (p = 0.0096, 0.0119, 0.0195 and 0.0258, respectively). Metastasis within 5 years was significantly associated with shorter 2 and 5-year doubling time (p = 0.0006 and 0.0014, respectively). Using all prostate specific antigen values within 5 years of initial biochemical recurrence yielded an overall median prostate specific antigen doubling time of 52.8 months (range 5.4 to 100.0). The median rate of change in doubling time was -1.05 (range -64.7 to 27.0). Median time to metastasis after biochemical recurrence was 12.9 years. Median prostate specific antigen doubling time decreases with time. This may influence the decision to offer secondary therapy to patients with biochemical recurrence sooner since initial prostate specific antigen doubling time is long and may not accurately reflect the biological nature of the disease.

Downregulation of both p21/Cip1 and p27/Kip1 produces a more aggressive prostate cancer phenotype

Roles of cyclin dependent kinase inhibitors, p21/Cip1 (p21) and p27/Kip1 (p27) in prostate cancer (PCa) progression is still not clear. Lower p27 protein expression in PCa tissues is often associated with poor prognosis, but prognostic significance of p21 is still controversial. Herein, we investigated the role of these molecules in determining PCa growth characteristics. We generated human PCa DU145 cell variants with knocked down levels of p21 (DU-p21) or p27 (DU-p27), or both (DU-p21+p27) via retroviral transduction of respective shRNAs and compared their various characteristics with empty vector-transduced DU145 (DU-EV) cells in vitro as well as in vivo. Knocking down either p21 or p27 did not show any significant change in doubling time, clonogenicity and cell cycle progression in DU145 cells, but simultaneous knock-down of both p21 and p27 significantly enhanced these parameters. In athymic mice, DU-p21+p27 tumors showed higher growth rate than the comparable growth of DU-EV, DU-p21 and DU-p27 tumors. Concurrently, DU-p21+p27 tumors had significantly higher proliferation rate, showing 54% and 48% increase in proliferating cell nuclear antigen (PCNA) and Ki-67-positive cells, respectively, compared to DU-EV tumors. DU-p21+p27 tumors also showed higher microvessel density and increased expression of vascular endothelial growth factor (VEGF). Proliferation and angiogenic status of DU-p21 and DU-p27 tumors was comparable to DU-EV tumors. Both in vitro and in vivo results implicate that p21 and p27 have compensatory roles in advanced prostate cancer cells, and ablation or down-modulation of both these molecules essentially enhances the aggressive prostate carcinoma phenotype.

Extinction of the weakest

Purpose: To examine whether changes in the effective doubling time of tumor cells during irradiation of head-and-neck cancer are linked to accumulating dose.Methods and Materials: Optimal fitting of the results of four apparently iso-effective regimens in three recently reported randomized controlled trials (continuous hyperfractionated accelerated radiation therapy [CHART], Radiation Therapy Oncology Group [RTOG] 90-03, and Trans-Tasman Radiation Oncology Group [TROG] 91.01) was attempted using two different types of model of the change in effective doubling time that may occur during treatment. The first involved the traditional approach where doubling time changes at specific times after the start of treatment regardless of fractionation used (“fixed response time” models). The second is where changes in doubling time are linked to accumulating biologic dose (“cellular depletion” models).Results: Changes in effective doubling time occur during radiotherapy for head-and-neck cancer. Data from the three trials can be fitted successfully by functions that imply a continuous reduction in effective doubling time. Models linking the reductions in effective doubling time to the cellular depletion that occurs in the tumor during radiotherapy fit the data satisfactorily. Effective doubling time ultimately reduces to 2 days, or slightly less, during high-dose radiotherapy regimens designed to cure squamous head-and-neck cancer.Conclusions: If the assumption of iso-effectivity is justified then this study indicates that the “repopulation phenomenon” may be best described by a function that depicts a reduction in effective tumor cell doubling time that decreases continuously during treatment down to a certain minimum value. Furthermore, this reduction may be linked to cellular depletion.

Autocrine Transforming Growth Factor α Provides a Growth Advantage to Malignant Cells by Facilitating Re-entry into the Cell Cycle from Suboptimal Growth States

CBS human colon carcinoma cells are poorly tumorigenic in athymic nude mice, whereas FET colon carcinoma cells are non-tumorigenic. Both cell lines have well differentiated properties in tissue culture. Transforming growth factor alpha (TGF-alpha) was ectopically expressed by stable transfection of a TGF-alpha cDNA under repressible tetracycline control. The TGF-alpha-transfected cells showed enhanced clonal initiation and shortened lag phase growth in tissue culture without an alteration in doubling time in exponential phase relative to untransfected cells. Furthermore, the TGF-alpha transfectants showed increased independence from exogenous growth factors in clonal growth assays and induction of DNA synthesis after release from quiescence. Growth factor independence was associated with sustained epidermal growth factor receptor activation in quiescent TGF-alpha-transfected cells and the requirement of exogenous insulin for stimulation of quiescent cells to re-enter the cell cycle. Higher cloning, reduced lag time in tissue, and the acquisition of growth factor independence for DNA synthesis without a change in doubling time of TGF-alpha-transfected cells indicate that autocrine TGF-alpha functions by facilitating re-entry into the cell cycle from sub-optimal growth states rather than promoting or controlling the proliferation of actively cycling cells. The modulation of growth regulation by autocrine TGF-alpha was associated with increased malignant properties as TGF-alpha transfectants showed increased tumorigenicity in athymic nude mice. The administration of tetracycline reversed the effects of TGF-alpha expression in these cells both in vivo and in vitro, indicating that the alterations of the biological properties were due to the expression of TGF-alpha. Since these cells are continuously grown in a completely chemically defined medium without serum supplementation, it was possible to assign the mechanism underlying the generation of growth factor independence to the replacement of a requirement for exogenous insulin in parental cells by autocrine TGF-alpha.

A possible change in doubling time of haemopoietic progenitor cells with stem cell development.

We separated haemopoietic progenitors derived from marrow cells of 5-fluorouracil (5-FU)-treated mice into three groups, based on the stages of stem cell development and studied doubling time, using a serum-free clonal culture system. Stage I progenitors were those present in primary marrow cells from 5-FU-treated mice. Stages II and III progenitors were early and late progenies in culture of stage I progenitors respectively. The morphological analysis of colonies derived from stage I, II and III progenitors demonstrated an association of progression of stages with loss of multipotentiality. The doubling time of haemopoietic progenitors was estimated by sequential analysis of colony formation and studies of growth fraction. The time required for haemopoietic progenitors to double shortened as their stage of development progressed. Alteration in one doubling time of haemopoietic progenitors at progressive stages of stem cell development was seen in cultures supported by various combinations of growth factors, including interleukin-3 (IL-3), IL-11. and steel factor (SF), Cell-cycle analysis suggested that reduction of the doubling time of haemopoietic progenitors is probably due to a decrease in the time spent in the G1 phase of the cell cycle. Our results suggest that in early haemopoiesis the doubling time of haemopoietic progenitors may change with stem cell development.

TGF-beta 1 is an autocrine-negative growth regulator of human colon carcinoma FET cells in vivo as revealed by transfection of an antisense expression vector.

Transforming growth factor-beta 1 (TGF-beta 1) has previously been implicated as a potential negative autocrine or paracrine growth regulator of certain cell types (Arteaga, C. L., R. J. Coffey, Jr., T. C. Dugger, C. M. McCutchen, H. L. Moses, and R. M. Lyons. 1990. Cell Growth & Differ. 1:367-374; Hafez, M. M., D. Infante, S. Winawer, and E. Friedman. 1990. Cell Growth & Differ. 1:617-626; Glick, A. B., K. C. Flanders, D. Danielpour, S. H. Yuspa, and M. B. Sporn. 1989. Cell Regulation. 1:87-97). This is based mainly on experiments assessing the effects of exogenous TGF-beta 1 or neutralizing antibodies to TGF-beta 1 on normal or tumor cell proliferation in vitro. However, direct evidence demonstrating such a negative regulation of tumor cell growth in vivo is still lacking. To overcome this problem we have constructed and used an antisense expression vector for TGF-beta 1 as a means of regulating endogenous TGF-beta 1 expression in tumor cells. Antisense-transfected FET human colon carcinoma cells showed a fivefold reduction in TGF-beta 1 mRNA and 15-fold reduction in TGF-beta 1 secretion. Antisense mRNA was detected in transfected cells by an RNase protection assay. Compared to control cells, cultured antisense-transfected cells showed a reduction in lag phase time rather than a change in doubling time. Cloning efficiencies of transfected cells were four times greater than control cells in anchorage-independent assays. Control cells did not form tumors at 5 x 10(5) in athymic nude mice. Antisense-transfected cells formed tumors in 40% of animals injected. At higher inocula (1 x 10(6) cells) antisense-transfected cells formed tumors in 100% of animals injected, but control cells still failed to form tumors. These results show that TGF-beta 1 acts as a negative growth regulator of human colon carcinoma cells in vivo as well as in vitro. Acquisition of partial or full resistance to such inhibitory effects may therefore contribute to tumor development and progression.

The effect of aging on the growth of colon cancer

Reports on the effect of patient age on the prognosis for colon cancer vary. We have tested the effect of aging using a model of murine colon adenocarcinoma in groups of mice of different ages. In experiment A, Balb/c mice of age groups 3–4 weeks, 10–12 weeks, 24–32 weeks and 40–48 weeks (13 mice/group) were injected with 5 × 10 4MC-26 cells subcutaneously in the right flank. Tumors were measured twice weekly, and the rate of occurrence of tumor, mortality rate, and growth rate were calculated. In experiment B, the same plan as experiment A was used, except mice of age groups I (14 days), II (3–4 weeks), and III (20–22 months) were used with tumor doses of 1 × 10 4 cells and 5 × 10 5 cells (9–15 mice/group). In both experiments, the rate of growth of tumor, mortality rate, and sizes of tumors obtained were the same. In experiment A, the rate of occurrence of the tumors was the same in all groups, but in experiment B the occurrence of the tumor varied. A palpable tumor appeared earliest in the weanling mice (14 days), next in old mice (20–22 months), and last in the young adult group (3–4 weeks). Tumor doubling time was longest in the young adult mice (7 days), intermediate in the old mice (6.1 days), and shortest in the weanling mice (5.5 days). Established tumors grew at similar rates (as assessed by doubling time), independent of host age. Mortality rates were similar. Subtle changes in doubling time and rate of occurrence of tumor are apparent only during the “low” dose of tumor (1 × 10 4) cells, which suggests a host-immune response that is able to cope with a relatively small burden of tumor cells. Any immune system can be overwhelmed. The use of low doses of cell inoculum allows differentiation of small, but important age-related differences of colon cancer growth.

Temperature-induced differences in growth rate and fatty acid composition in two strains of Escherichia coli 15T−

The saturated/unsaturated fatty acid ratio of Escherichia coli 15T- decreases almost threefold as growth temperature decreases from 43 to 27 degrees C, wheras the ratio of a fast-growing mutant derived from 15T- changes only half as much. Strain 15T- experiences a 2.4-fold change in doubling time across this temperature range, but doubling time in the mutant changes 3.3-fold.