Intestinal cell cycle regulation

Spirulina Crude Protein Promotes the Migration and Proliferation in IEC-6 Cells by Activating EGFR/MAPK Signaling Pathway

Spirulina is a type of filamentous blue-green microalgae known to be rich in nutrients and to have pharmacological effects, but the effect of spirulina on the small intestine epithelium is not well understood. Therefore, this study aims to investigate the proliferative effects of spirulina crude protein (SPCP) on a rat intestinal epithelial cells IEC-6 to elucidate the mechanisms underlying its effect. First, the results of wound-healing and cell viability assays demonstrated that SPCP promoted migration and proliferation in a dose-dependent manner. Subsequently, when the mechanisms of migration and proliferation promotion by SPCP were confirmed, we found that the epidermal growth factor receptor (EGFR) and mitogen-activated protein (MAPK) signaling pathways were activated by phosphorylation. Cell cycle progression from G0/G1 to S phase was also promoted by SPCP through upregulation of the expression levels of cyclins and cyclin-dependent kinases (Cdks), which regulate cell cycle progression to the S phase. Meanwhile, the expression of cyclin-dependent kinase inhibitors (CKIs), such as p21 and p27, decreased with SPCP. In conclusion, our results indicate that activation of EGFR and its downstream signaling pathway by SPCP treatment regulates cell cycle progression. Therefore, these results contribute to the research on the molecular mechanism for SPCP promoting the migration and proliferation of rat intestinal epithelial cells.

Withaferin A and sulforaphane regulate breast cancer cell cycle progression through epigenetic mechanisms

Little is known about the effects of combinatorial dietary compounds on the regulation of epigenetic mechanisms involved in breast cancer prevention. The human diet consists of a multitude of components, and there is a need to elucidate how certain compounds interact in collaboration. Withaferin A (WA), found in the Indian winter cherry and documented as a DNA methyltransferase (DNMT) inhibitor, and sulforaphane (SFN), a well-known histone deacetylase (HDAC) inhibitor found in cruciferous vegetables, are two epigenetic modifying compounds that have only recently been studied in conjunction. The use of DNMT and HDAC inhibitors to reverse the malignant expression of certain genes in breast cancer has shown considerable promise. Previously, we found that SFN + WA synergistically promote breast cancer cell death. Herein, we determined that these compounds inhibit cell cycle progression from S to G2 phase in MDA-MB-231 and MCF-7 breast cancer. Furthermore, we demonstrate that this unique combination of epigenetic modifying compounds down-regulates the levels of Cyclin D1 and CDK4, and pRB; conversely, the levels of E2F mRNA and tumor suppressor p21 are increased independently of p53. We find these events coincide with an increase in unrestricted histone methylation. We propose SFN + WA-induced breast cancer cell death is attributed, in part, to epigenetic modifications that result in the modulated expression of key genes responsible for the regulation of cancer cell senescence.

Green Tea Induced Cellular Proliferation and the Expression of Transforming Growth Factor-β1 in the Jejunal Mucosa of Fasting Rats

OBJECTIVE

The aim of this study was to understand whether or not the protective effect of green tea after fasting-induced damage in the jejunal mucosa of rat is dependent on cell proliferation and the stimulation of specific growth factors.

MATERIALS AND METHODS

Sixty adult male Wistar rats were used in this study. The animals were divided randomly into 5 groups, with 12 in each group (G1-5). The animals in G1 (control group) were fed a rat chow diet and water ad libitum. The animals in G2 (fasting group) were fasted for 3 days. The animals in the G3, G4, and G5 groups were fasted for 3 days as G2, but were given water (G3), green tea (G4), or a vitamin E (G5) solution, respectively, for another 7 days. The animals were euthanized, and the jejunum was removed and processed for histological and immunohistochemical analysis.

RESULTS

Compared to the G3 group, the jejunal mucosa of G4 rats showed a 70.6% higher level (p < 0.001) of expression of proliferating cell nuclear antigen and 98% higher level (p = 0.0001) of the expression of transforming growth factor-β1 (TGF-β1), whereas the level of fibroblast growth factor-1 (FGF-1) and insulin-like growth factor-1 (IGF-1) expression was 22 and 11% lower, respectively, in G4 animals as compared to G3 rats. These differences in the expression of FGF-1 and IGF-1 in G4 animals were not statistically significant.

CONCLUSION

In this study, green tea repaired the fasting-induced damage in the jejunal mucosa of rats, mainly by inducing a significant expression of TGF-β1 in the jejunal mucosa.

Ghrelin promotes intestinal epithelial cell proliferation through PI3K/Akt pathway and EGFR trans-activation both converging to ERK 1/2 phosphorylation

Little is known about ghrelin's effects on intestinal epithelial cells even though it is known to be a mitogen for a variety of other cell types. Because ghrelin is released in close proximity to the proliferative compartment of the intestinal tract, we hypothesized that ghrelin may have potent pro-proliferative effect on intestinal epithelial cells as well. To test this hypothesis, we characterized the effects of ghrelin on FHs74Int and Caco-2 intestinal epithelial cell lines in vitro. We found that ghrelin has potent dose dependent proliferative effects in both cell lines through a yet to be characterized G protein coupled growth hormone secretagogue receptor (GHS-R) subtype. Consistent with above findings, cell cycle flowcytometric analyses demonstrated that ghrelin shifts cells from the G1 to S phase and thereby promotes cell cycle progression. Further characterization of subcellular events, suggested that ghrelin mediates its pro-proliferative effect through Adenylate cyclase (AC)-independent epidermal growth factor receptor (EGFR) trans-activation and PI3K-Akt phosphorylation. Both these pathways converge to stimulate MAPK, ERK 1/2 downstream. The role of ghrelin in states where intestinal mucosal injury and rapid mucosal repair occur warrants further investigation.

MPK-1 ERK controls membrane organization in C. elegans oogenesis via a sex-determination module

Tissues that generate specialized cell types in a production line must coordinate developmental mechanisms with physiological demand, although how this occurs is largely unknown. In the Caenorhabditis elegans hermaphrodite, the developmental sex-determination cascade specifies gamete sex in the distal germline, while physiological sperm signaling activates MPK-1/ERK in the proximal germline to control plasma membrane biogenesis and organization during oogenesis. We discovered repeated utilization of a self-contained negative regulatory module, consisting of NOS-3 translational repressor, FEM-CUL-2 (E3 ubiquitin ligase), and TRA-1 (Gli transcriptional repressor), which acts both in sex determination and in physiological demand control of oogenesis, coordinating these processes. In the distal germline, where MPK-1 is not activated, TRA-1 represses the male fate as NOS-3 functions in translational repression leading to inactivation of the FEM-CUL-2 ubiquitin ligase. In the proximal germline, sperm-dependent physiological MPK-1 activation results in phosphorylation-based inactivation of NOS-3, FEM-CUL-2-mediated degradation of TRA-1 and the promotion of membrane organization during oogenesis.

Anticancer activity of a low immunogenic protein toxin (BMP1) from Indian toad (Bufo melanostictus, Schneider) skin extract

Earlier, a protein (BMP1, MW-79kDa) had been isolated from Indian toad (Bufo melanostictus) skin aqueous extract possessed anticancer activity against EAC bearing mice (Bhattacharjee et al., 2011). In the present study, the anti-proliferative and apoptogenic activities of BMP1 have been evaluated in leukemic (U937 and K562) and hepatoma (HepG2) cells. BMP1 dose dependently inhibited U937 and K562 cell growth having IC₅₀ values of 49 μg/ml and 30 μg/ml respectively. The anti-proliferative activity of BMP1 was observed in MTT assay, proliferating cell nuclear antigen (PCNA) expression and cell cycle arrest study. Flow-cytometric data revealed that BMP1 arrested cell cycle in U937 and K562 cells at Sub-G1 and G1 phases. The BMP1-induced dose dependent expressions of CDKIs (p21(cip1) and p27(kip1)) and inhibition of CDK2 and PCNA expression in HepG2 cells support the inhibition of cell proliferation due to G1 arrest. BMP1-induced apoptosis analyzed by annexin-V binding study and the DNA fragmentation by comet assay were correlated with the sub-G1 arrest. The parallel induction of bax and p53 expression in HepG2 cells and the up-regulation of caspase 3 and caspase 9 due to BMP1 treatment indicated the involvement of p53-dependent intrinsic pathway of apoptosis. BMP1 was found to be low immunogenic in nature.

Fused Toes Homolog modulates radiation cytotoxicity in uterine cervical cancer cells

Radiotherapy is the major treatment modality for uterine cervical cancer, but in some cases, the disease is radioresistant. Defining the molecular events that contribute to radioresistance and progression of cancer are of critical importance. Here we evaluated the role of Fused Toes Homolog (FTS) in radiation resistance of cervical carcinoma. Immunostaning of cervical cancer cells and tissues revealed that FTS localization and expression was changed after radiation. Targeted stable knockdown of FTS in HeLa cells led to the growth inhibition after radiation. Radiation induced AKT mediated cytoprotective effect was countered by FTS knockdown which leads to PARP cleavage and caspase-3 activation leading to cell death. FTS knockdown promotes radiation induced cell cycle arrest at G0/G1 and apoptosis of HeLa cells with concurrent alterations in the display of cell cycle regulatory proteins. This study revealed FTS is involved in radioresistance of cervical cancer. Targeted inhibition of FTS led to the shutdown of key elemental characteristics of cervical cancer and could lead to an effective therapeutic strategy.

Bombesin enhances TGF-beta growth inhibitory effect through apoptosis induction in intestinal epithelial cells

Mammalian intestinal epithelium undergoes continuous cell turn over, with cell proliferation in the crypts and apoptosis in the villus. Both transforming growth factor (TGF)-beta and gastrin-releasing peptide (GRP) are involved in the regulation of intestinal epithelial cells for division, differentiation, adhesion, migration and death. Previously, we have shown that TGF-beta and bombesin (BBS) synergistically induce cyclooxygenase-2 (COX-2) expression and subsequent prostaglandin E(2) (PGE2) production through p38(MAPK) in rat intestinal epithelial cell line stably transfected with GRP receptor (RIE/GRPR), suggesting the interaction between TGF-beta signaling pathway and GRPR. The current study examined the biological responses of RIE/GRPR cells to TGF-beta and BBS. Treatment with TGF-beta1 (40 pM) and BBS (100 nM) together synergistically inhibited RIE/GRPR growth and induced apoptosis. Pretreatment with SB203580 (10 microM), a specific inhibitor of p38(MAPK), partially blocked the synergistic effect of TGF-beta and BBS on apoptosis. In conclusion, BBS enhanced TGF-beta growth inhibitory effect through apoptosis induction, which is at least partially mediated by p38(MAPK).

TGF-beta repression of Id2 induces apoptosis in gut epithelial cells

Transforming growth factor-beta (TGF-beta) regulates epithelial tissue homeostasis by activating processes that control cell cycle arrest, differentiation and apoptosis. Disruption of the TGF-beta signaling pathway often occurs in colorectal cancers. Earlier, we have shown that TGF-beta induces apoptosis through the transcription factor Smad3. Affymetrix oligonucleotide microarrays were used to identify TGF-beta/Smad3 target genes that regulate apoptosis in rat intestinal epithelial cells (RIE-1). We found that TGF-beta repressed the expression of the inhibitor of differentiation (Id) gene family. Knockdown of Id1 and Id2 gene expression induced apoptosis in RIE-1 cells, whereas overexpression of Id2 attenuated TGF-beta-induced apoptosis. TranSignal Protein/DNA arrays were used to identify the hypoxia-inducing factor-1 (HIF-1) as a downstream target of TGF-beta. HIF-1 is a basic helix-loop-helix protein, and overexpression of Id2 blocked HIF-1 activation by TGF-beta. Furthermore, knockdown of HIF-1 blocked TGF-beta-induced apoptosis. Thus, we have identified HIF-1 as a novel mediator downstream of Id2 in the pathway of TGF-beta-induced apoptosis.

Using genomics to understand intestinal biology

The use of microarrays to evaluate the transcriptome has transformed our view of biology. In addition to the focused, hypothesis-testing studies that we have traditionally conducted in cell biology, we are now able to see global changes within the entire system of the cell in response to a treatment. By examining a biological question under multiple complementary perturbations model systems (e.g. yeast, C. Elegans) have revealed new complexity that would have been impossible to see on a gene-by-gene approach. Unfortunately, beyond the use of transcript profiles to define the molecular signature of diseases (e.g. cancer), transcriptomics has not been extensively used to study intestinal biology. This review will provide a roadmap for effective use of gene expression profiling for biological research and will review some of the microarray work that has been done to better understand the nature of intestinal development and enterocyte differentiation.

Differential subcellular targeting of PKC-epsilon in response to pharmacological or ischemic stimuli in intestinal epithelia

Ischemia is the central pathogenic factor underlying a spectrum of intestinal disorders. The study of the cellular signaling responses to ischemic stress in nonepithelial cells has progressed substantially in the previous several years, but little is known about the response in epithelial cells. Unique features of the epithelial response to ischemic stress suggest differential regulation with regards to signaling. The PKC family of proteins has been implicated in ischemic stress in nonepithelial systems. The role of PKC isoforms in chemical ischemia in intestinal epithelial cells is evaluated in this study. Additionally, the phosphorylation of the F-actin cross-linking protein myristoylated alanine-rich C kinase substrate (MARCKS) is also studied. Chemical ischemia resulted in the transient activation of only the isoform PKC-epsilon as detected by translocation employing the subcellular fractionation technique. The pharmacological agonists phorbol 12-myristate 13-acetate and carbachol also led to the translocation of PKC-epsilon. By immunofluoresence, MARCKS is noted to be located at the lateral membrane under control conditions. In response to carbachol, MARCKS translocates to the cytosol, indicating its phosphorylation, which is additionally confirmed biochemically. Consistent with this observation, carbachol induces the translocation of PKC-epsilon to proximity with MARCKS at the lateral membrane. In response to chemical ischemia, MARCKS fails to translocate and phosphorylation does not increase. Additionally, the translocation of PKC-epsilon is not to the lateral membrane but rather basally. The data suggest that the differential translocation of PKC-epsilon in response to pharmacological agonists versus ischemic stress may lead to different effects on downstream targets.

TGFbeta down-regulation of the CFTR: a means to limit epithelial chloride secretion

Transforming growth factor beta (TGFbeta) is a multifunctional cytokine with effects on many cell types. We recently showed that in addition to epithelial barrier enhancing properties, TGFbeta causes diminished cAMP-driven chloride secretion in colonic epithelia, in a manner that is p38 MAPK-dependent. In this study, we sought to further delineate the mechanism behind TGFbeta diminution of chloride secretion. Using colonic and kidney epithelial cell lines, we found that exposure to TGFbeta causes dramatic changes in the expression and localization of the apical membrane chloride channel, cystic fibrosis transmembrane conductance regulator (CFTR). In TGFbeta-treated colonic epithelia (T84 and HT-29), CFTR mRNA was significantly reduced 2-24 h post-cytokine exposure. At a time consistent with decreased colonic epithelial secretory responses (16 h), TGFbeta treatment caused diminished intracellular CFTR protein expression (confocal microscopy) and reduced channel expression in the apical membrane during stimulated chloride secretion (biotinylation assay). In comparison, polarized kidney epithelia (MDCK) treated with TGFbeta displayed similarly reduced secretory responses to cAMP stimulating agents; however, a perinuclear accumulation of CFTR was observed, contrasting the diffuse cytoplasmic CFTR expression of control cells. Our data indicate that TGFbeta has profound effects on the expression and subcellular localization of an important channel involved in cAMP-driven chloride secretion, and thus suggest TGFbeta represents a key regulator of fluid movement.

Prevention of mucosal atrophy: role of glutamine and caspases in apoptosis in intestinal epithelial cells

Glutamine starvation induces apoptosis in enterocytes; therefore glutamine is important in the maintenance of gut mucosal homeostasis. However, the molecular mechanisms are unknown. The caspase family of proteases constitutes the molecular machinery that drives apoptosis. Caspases are selectively activated in a stimulus-specific and tissue-specific fashion. The aims of this study were to (1) identify specific caspases activated by glutamine starvation and (2) determine whether a general caspase inhibitor blocks glutamine starvation-induced apoptosis in intestinal epithelial cells. Rat intestinal epithelial (RIE-1) cells were deprived of glutamine. Specific caspase activation was measured using fluorogenic substrate assay. Apoptosis was quantified by DNA fragmentation and Hoechst nuclear staining. Glutamine starvation of RIE-1 cells resulted in the time-dependent activation of caspases 3 (10 hours) and 2 (18 hours), and the induction of DNA fragmentation (12 hours). Caspases 1 and 8 remained inactive ZVAD-fluoromethyl ketone, a general caspase inhibitor, completely blocked glutamine starvation-induced caspase activation, DNA fragmentation, and nuclear condensation. These results indicate that glutamine starvation selectively activates specific caspases, which leads to the induction of apoptosis in RIE-1 cells. Furthermore, inhibition of caspase activity blocked the induction of apoptosis, suggesting that caspases are potential molecular targets to attenuate apoptotic responses in the gut.

p21 (WAF1/CIP1) is required for the mitogenic response to intestinal resection

BACKGROUND

Increased enterocyte proliferation and apoptosis characterize the intestinal adaptive response to massive small bowel resection (SBR). Since p21 (WAF1/CIP1) has been implicated to play a role in cellular differentiation and apoptosis, this study tested the hypothesis that p21 is obligatory for adaptation to occur.

MATERIALS AND METHODS

p21-null (n = 36) and wild-type (C57B1/6, n = 19) mice underwent a 50% SBR or sham operation. After 3 days, parameters of adaptation (ileal wet weight, villus/crypt morphology, and ileal protein content), an enterocyte proliferation index (PI), and an apoptotic index (AI) were determined in the residual ileum. In a separate set of experiments, p21-null (n = 11) and control (n = 20) mice underwent the aforementioned operative procedures and the remnant intestine was subjected to a reverse transcription polymerase chain reaction for p27 (KIP1).

RESULTS

Both AI and PI increased after SBR in the wild-type mice. In the p21-null mice, SBR increased AI, but did not affect the PI. After SBR, adaptive parameters increased in the wild-type mice, but failed to increase in the p21-null mice. The absence of p21 caused a baseline increase in p27 mRNA, which did not change after SBR.

CONCLUSION

p21 appears to be required to increase enterocyte proliferation and to augment the other parameters of intestinal adaptation. In the absence of p21, the proliferative and apoptotic responses to SBR are uncoupled. These results suggest a differential mechanism for the regulation of enterocyte proliferation and apoptosis in the adapting intestine.

Characterization and regulation of E2F activity during Caco-2 cell differentiation

The specific mechanisms controlling intestinal cell differentiation remain largely undefined. The retinoblastoma (Rb) proteins (pRb, p130, and p107) appear crucial to the terminal differentiation process of certain cells through their association and repression of E2F transcription factors. We have examined the expression of pRb-related proteins p130 and p107 as well as the regulation of E2F during spontaneous differentiation of the Caco-2 intestinal cell line. Nuclear protein levels of p130 and p107 were increased with Caco-2 differentiation. Induction of a slower-migrating E2F complex was noted in postconfluent (i.e., differentiated) Caco-2 cells; p130 protein was the predominant component of this E2F complex with a minor contribution from cyclin-dependent kinase-2. A small component of p107 binding was identified by deoxycholate release gel shift assays. In contrast, no pRb binding to E2F was noted in Caco-2 cells. In addition to increased association with p130, E2F-4 phosphorylation was markedly decreased in differentiated Caco-2 cells, whereas E2F protein levels remained unchanged. Taken together, our findings suggest that the regulation of E2F function may be an important contributing factor in the cell cycle block and spontaneous differentiation of Caco-2 cells. This regulation of E2F occurs most likely through its increased association with p130 as well as decreased phosphorylation.

Induction of G(1) checkpoint in the gastric mucosa of aged rats

Although in Fischer 344 rats aging is found to be associated with increased gastric mucosal proliferative activity, little is known about specific changes in the regulatory mechanisms of this process. To determine whether changes in cell cycling events could partly contribute to the age-related rise in gastric mucosal proliferative activity, the present investigation examines changes in cyclin-dependent kinase (Cdk2) activity and the regulation of this process in the gastric mucosa of Fischer 344 rats aged 4 (young), 13 (middle aged), and 24 (old) mo. We observed that aging is associated with a progressive rise in activity and protein levels of Cdk2 in the gastric mucosa. This is also found to be accompanied by a concomitant increase in cyclin E but not cyclin D1 levels. On the other hand, the levels of p21(Waf1/Cip1) (total as well as the fraction associated with Cdk2), a nuclear protein that is known to inhibit different cyclin-Cdk complexes, are found to decline in the gastric mucosa with advancing age. In contrast, with aging, there was a steady rise in p53 levels in the gastric mucosa. We have also observed that the levels of phosphorylated retinoblastoma protein, a form that participates in regulating progression through the S phase, are markedly elevated in the gastric mucosa of aged rats. In conclusion, our data suggest that, in the gastric mucosa, aging enhances transition of G(1) to S phase as well as progression through the S phase of the cell cycle. However, the age-related decline in p21(Waf1/Cip1) in the gastric mucosa appears to be independent of p53 status.

Caco-2 intestinal cell differentiation is associated with G1 arrest and suppression of CDK2 and CDK4

The cellular mechanisms regulating intestinal proliferation and differentiation remain largely undefined. Previously, we showed an early induction of the cyclin-dependent kinase (CDK) inhibitor p21(Waf1/Cip1) in Caco-2 cells, a human colon cancer line that spontaneously differentiates into a small bowel phenotype. The purpose of our present study was to assess the timing of cell cycle arrest in relation to differentiation in Caco-2 cells and to examine the mechanisms responsible for CDK inactivation. Caco-2 cells undergo a relative G1/S block and cease to proliferate at day 3 postconfluency; an increase in the activity of terminally differentiated brush-border enzymes (sucrase and alkaline phosphatase) was noted at day 6 postconfluency. Cell cycle block was associated with suppression of both CDK2 and CDK4 activities, which are important for G1/S progression. Treatment of the CDK immune complexes with the detergent deoxycholate (DOC) resulted in restoration of CDK2, but not CDK4, activity at day 3 postconfluency, suggesting the presence of inhibitory protein(s) binding to the cyclin/CDK2 complex at this time point. An increased binding of p21(Waf1/Cip1) to CDK2 complexes at day 3 postconfluency was noted, suggesting a potential role for p21(Waf1/Cip1) in CDK2 inactivation; however, immunodepletion of p21(Waf1/Cip1) from Caco-2 protein extracts demonstrated that p21(Waf1/Cip1) is only partially responsible for CDK2 suppression at day 3 postconfluency. A decrease in the cyclin E/CDK2 complex appears to contribute to the CDK2 inactivation noted at days 6 and 12 postconfluency. Taken together, our results suggest that multiple mechanisms contribute to CDK suppression during Caco-2 cell differentiation. Inhibition of CDK2 and CDK4 leads to G1 arrest and inhibition of proliferation that precede Caco-2 cell differentiation.