The HBP1 transcriptional repressor and the p38 MAP kinase: unlikely partners in G1 regulation and tumor suppression

The Antioxidant Potential and Anticancer Activity of Halodule uninervis Ethanolic Extract against Triple-Negative Breast Cancer Cells

Natural remedies have been indispensable to traditional medicine practices for generations, offering therapeutic solutions for various ailments. In modern times, these natural products continue to play a pivotal role in the discovery of new drugs, especially for cancer treatment. The marine ecosystem offers a wide range of plants with potential anticancer activities due to their distinct biochemical diversity and adaptation to extreme situations. The seagrass Halodule uninervis is rich in diverse bioactive metabolites that bestow the plant with various pharmacological properties. However, its anticancer activity against invasive triple-negative breast cancer (TNBC) is still poorly investigated. In the present study, the phytochemical composition of an ethanolic extract of H. uninervis (HUE) was screened, and its antioxidant potential was evaluated. Moreover, the anticancer potential of HUE against MDA-MB-231 cells was investigated along with the possible underlying mechanisms of action. Our results showed that HUE is rich in diverse phytochemicals that are known for their antioxidant and anticancer effects. In MDA-MB-231 cells, HUE targeted the hallmarks of cancer, including cell proliferation, adhesion, migration, invasion, and angiogenesis. The HUE-mediated anti-proliferative and anti-metastatic effects were associated with the downregulation of the proto-oncogenic STAT3 signaling pathway. Taken together, H. uninervis could serve as a valuable source for developing novel drugs targeting TNBC.

MAP3K4 kinase action and dual role in cancer

It is commonly known that the MAPK pathway is involved in translating environmental inputs, regulating downstream reactions, and maintaining the intrinsic dynamic balance. Numerous essential elements and regulatory processes are included in this pathway, which are essential to its functionality. Among these, MAP3K4, a member of the serine/threonine kinases family, plays vital roles throughout the organism's life cycle, including the regulation of apoptosis and autophagy. Moreover, MAP3K4 can interact with key partners like GADD45, which affects organism's growth and development. Notably, MAP3K4 functions as both a tumor promotor and suppressor, being activated by a variety of factors and triggering diverse downstream pathways that differently influence cancer progression. The aim of this study is to provide a brief overview of physiological functions of MAP3K4 and shed light on its contradictory roles in tumorigenesis.

HNF1α maintains pancreatic α and β cell functions in primary human islets

HNF1A haploinsufficiency underlies the most common form of human monogenic diabetes (HNF1A-maturity onset diabetes of the young [HNF1A-MODY]), and hypomorphic HNF1A variants confer type 2 diabetes risk. But a lack of experimental systems for interrogating mature human islets has limited our understanding of how the transcription factor HNF1α regulates adult islet function. Here, we combined conditional genetic targeting in human islet cells, RNA-Seq, chromatin mapping with cleavage under targets and release using nuclease (CUT&RUN), and transplantation-based assays to determine HNF1α-regulated mechanisms in adult human pancreatic α and β cells. Short hairpin RNA-mediated (shRNA-mediated) suppression of HNF1A in primary human pseudoislets led to blunted insulin output and dysregulated glucagon secretion after transplantation in mice, recapitulating phenotypes observed in patients with diabetes. These deficits corresponded with altered expression of genes encoding factors critical for hormone secretion, including calcium channel subunits, ATPase transporters, and extracellular matrix constituents. Additionally, HNF1A loss led to upregulation of transcriptional repressors, providing evidence for a mechanism of transcriptional derepression through HNF1α. CUT&RUN mapping of HNF1α DNA binding sites in primary human islets imputed a subset of HNF1α-regulated genes as direct targets. These data elucidate mechanistic links between HNF1A loss and diabetic phenotypes in mature human α and β cells.

Targeting of HBP1/TIMP3 axis as a novel strategy against breast cancer

Malignant proliferation and metastasis are the main causes of breast cancer death. The transcription factor high mobility group (HMG) box-containing protein 1 (HBP1) is an important tumor suppressor whose deletion or mutation is closely related to the appearance of tumors. Here, we investigated the role of HBP1 in breast cancer suppression. HBP1 enhances the activity of the tissue inhibitors of metalloproteinases 3 (TIMP3) promoter, thereby increasing protein and mRNA levels of TIMP3. TIMP3 increases the phosphatase and tensin homolog (PTEN) protein level by inhibiting its degradation and acts as a metalloproteinase inhibitor to inhibit the protein levels of MMP2/9. In this study, we demonstrated that the HBP1/TIMP3 axis plays a crucial role in inhibiting the tumorigenesis of breast cancer. HBP1 deletion interferes with the regulation of the axis and induces the occurrence and malignant progression of breast cancer. In addition, the HBP1/TIMP3 axis promotes the sensitivity of breast cancer to radiation therapy and hormone therapy. Our study opens new perspectives on the treatment and prognosis of breast cancer.

DYRK2 maintains genome stability via neddylation of cullins in response to DNA damage

Neural precursor cell-expressed developmentally down-regulated 8 (NEDD8), an ubiquitin-like protein, is an essential regulator of the DNA damage response. Numerous studies have shown that neddylation (conjugation of NEDD8 to target proteins) dysfunction causes several human diseases, such as cancer. Hence clarifying the regulatory mechanism of neddylation could provide insight into the mechanism of genome stability underlying the DNA damage response (DDR) and carcinogenesis. Here, we demonstrate that dual-specificity tyrosine-regulated kinase 2 (DYRK2) is a novel regulator of neddylation and maintains genome stability. Deletion of DYRK2 leads to persistent DNA double-strand breaks (DSBs) and subsequent genome instability. Mechanistically, DYRK2 promotes neddylation through forming a complex with NAE1, which is a component of NEDD8-activating enzyme E1, and maintaining its protein level by suppressing polyubiquitylation. The present study is the first to demonstrate that DYRK2 controls neddylation and is necessary for maintaining genome stability. This article has an associated First Person interview with the first author of the paper.

CRISPR interference and activation of the microRNA-3662-HBP1 axis control progression of triple-negative breast cancer

MicroRNA-3662 (miR-3662) is minimally expressed in normal human tissues but is highly expressed in all types of cancers, including breast cancer. As determined with The Cancer Genome Atlas dataset, miR-3662 expression is higher in triple-negative breast cancers (TNBCs) and African American breast cancers than in other breast cancer types. However, the functional role of miR-3662 remains a topic of debate. Here, we found that inhibition or knockout of endogenous, mature miR-3662 in TNBC cells suppresses proliferation and migration in vitro and tumor growth and metastasis in vivo. Functional analysis revealed that, for TNBC cells, knockout of miR-3662 reduces the activation of Wnt/β-catenin signaling. Furthermore, using CRISPR-mediated miR-3662 activation and repression, dual-luciferase assays, and miRNA/mRNA immunoprecipitation assays, we established that HMG-box transcription factor 1 (HBP-1), a Wnt/β-catenin signaling inhibitor, is a target of miR-3662 and is most likely responsible for miR-3662-mediated TNBC cell proliferation. Our results suggest that miR-3662 has an oncogenic function in tumor progression and metastasis via an miR-3662-HBP1 axis, regulating the Wnt /β-catenin signaling pathway in TNBC cells. Since miR-3662 expression occurs a tumor-specific manner, it is a promising biomarker and therapeutic target for patients who have TNBCs with dysregulation of miR-3662, especially African Americans.

A Warburg-like metabolic program coordinates Wnt, AMPK, and mTOR signaling pathways in epileptogenesis

Epilepsy is a complex neurological condition characterized by repeated spontaneous seizures and can be induced by initiating seizures known as status epilepticus (SE). Elaborating the critical molecular mechanisms following SE are central to understanding the establishment of chronic seizures. Here, we identify a transient program of molecular and metabolic signaling in the early epileptogenic period, centered on day five following SE in the pre-clinical kainate or pilocarpine models of temporal lobe epilepsy. Our work now elaborates a new molecular mechanism centered around Wnt signaling and a growing network comprised of metabolic reprogramming and mTOR activation. Biochemical, metabolomic, confocal microscopy and mouse genetics experiments all demonstrate coordinated activation of Wnt signaling, predominantly in neurons, and the ensuing induction of an overall aerobic glycolysis (Warburg-like phenomenon) and an altered TCA cycle in early epileptogenesis. A centerpiece of the mechanism is the regulation of pyruvate dehydrogenase (PDH) through its kinase and Wnt target genes PDK4. Intriguingly, PDH is a central gene in certain genetic epilepsies, underscoring the relevance of our elaborated mechanisms. While sharing some features with cancers, the Warburg-like metabolism in early epileptogenesis is uniquely split between neurons and astrocytes to achieve an overall novel metabolic reprogramming. This split Warburg metabolic reprogramming triggers an inhibition of AMPK and subsequent activation of mTOR, which is a signature event of epileptogenesis. Interrogation of the mechanism with the metabolic inhibitor 2-deoxyglucose surprisingly demonstrated that Wnt signaling and the resulting metabolic reprogramming lies upstream of mTOR activation in epileptogenesis. To augment the pre-clinical pilocarpine and kainate models, aspects of the proposed mechanisms were also investigated and correlated in a genetic model of constitutive Wnt signaling (deletion of the transcriptional repressor and Wnt pathway inhibitor HBP1). The results from the HBP1^-/- mice provide a genetic evidence that Wnt signaling may set the threshold of acquired seizure susceptibility with a similar molecular framework. Using biochemistry and genetics, this paper outlines a new molecular framework of early epileptogenesis and advances a potential molecular platform for refining therapeutic strategies in attenuating recurrent seizures.

Down-regulation of Polo-like kinase 4 (PLK4) induces G1 arrest via activation of the p38/p53/p21 signalling pathway in bladder cancer

Polo-like kinase 4 (PLK4) has been reported to contribute to tumor growth, invasion, and metastasis. However, the role of PLK4 in human bladder cancer (BC) remains unclear. Here, we demonstrate the regulatory function of PLK4 in human BC progression. PLK4 is overexpressed in BC cell lines and tissues, and its overexpression correlated with poor prognosis. Our transcriptome analysis combined with subsequent functional assays indicated that PLK4 inhibition can suppress BC cell growth and induce cell cycle arrest at G1 phase via activation of the p38/p53/p21 pathway in vitro and in vivo. Overall, our data suggest that PLK4 is a critical regulator of BC cell proliferation, and thus it may have potential as a novel molecular target for BC treatment.

Ras Isoforms from Lab Benches to Lives-What Are We Missing and How Far Are We?

The central protein in the oncogenic circuitry is the Ras GTPase that has been under intense scrutiny for the last four decades. From its discovery as a viral oncogene and its non-oncogenic contribution to crucial cellular functioning, an elaborate genetic, structural, and functional map of Ras is being created for its therapeutic targeting. Despite decades of research, there still exist lacunae in our understanding of Ras. The complexity of the Ras functioning is further exemplified by the fact that the three canonical Ras genes encode for four protein isoforms (H-Ras, K-Ras4A, K-Ras4B, and N-Ras). Contrary to the initial assessment that the H-, K-, and N-Ras isoforms are functionally similar, emerging data are uncovering crucial differences between them. These Ras isoforms exhibit not only cell-type and context-dependent functions but also activator and effector specificities on activation by the same receptor. Preferential localization of H-, K-, and N-Ras in different microdomains of the plasma membrane and cellular organelles like Golgi, endoplasmic reticulum, mitochondria, and endosome adds a new dimension to isoform-specific signaling and diverse functions. Herein, we review isoform-specific properties of Ras GTPase and highlight the importance of considering these towards generating effective isoform-specific therapies in the future.

Expression of the miR-302/367 microRNA cluster is regulated by a conserved long non-coding host-gene

MicroRNAs are important regulators of cellular functions. MiR-302/367 is a polycistronic miRNA cluster that can induce and maintain pluripotency. Here we investigate the transcriptional control and the processing of the miR-302 host-gene in mice. Our results indicate that the mmu-miR-302 host-gene is alternatively spliced, polyadenylated and exported from the nucleus. The regulatory sequences extend at least 2 kb upstream of the transcription start site and contain several conserved binding sites for both transcriptional activators and repressors. The gene structure and regulatory elements are highly conserved between mouse and human. So far, regulating miR-302 expression is the only known function of the miR-302 host-gene. Even though we here only provide one example, regulation of microRNA transcription might be a so far little recognized function of long non-coding RNA genes.

Treating exuberant, non-resolving inflammation in the lung; Implications for acute respiratory distress syndrome and COVID-19

While COVID-19, the disease driven by SARS-CoV-2 has ignited interest in the host immune response to this infection, it has also highlighted the lack of treatment options for the damaging inflammatory responses driven by pathogens that precipitate the acute respiratory distress syndrome (ARDS). With the global prevalence of SARS-CoV-2 and the likelihood of a second winter spike alongside seasonal flu, the need for effective and targeted anti-inflammatory agents is even more pressing. Here we discuss the aetiology of COVID-19 and the common signalling pathways driven by SARS-CoV-2, namely p38 MAP kinase. We highlight that p38 MAP kinase becomes elevated with increasing age, thereby driving many of the inflammatory pathways that precipitate death in old people with the added drawback of impairing vaccine efficacy in this susceptible age group. Finally, we review drugs available to inhibit p38 MAP kinase, their risks-versus-benefits as well as suggested dosing regimen to combat over-exuberant innate immune responses and potentially reverse vaccine inefficacy in older patients.

miR-335-5P contributes to human osteoarthritis by targeting HBP1

MicroRNA (miR)-335-5P has the ability to regulate chondrogenic differentiation and promote chondrogenesis in mouse mesenchymal stem cells. It is also abnormally elevated in human osteoarthritic chondrocytes. However, the biological function of miR-335-5P in osteoarthritis (OA) is not well understood. The present study investigated the mechanism of miR-335-5P in the pathogenesis of OA. To investigate the effect of miR-335-5P on the pathogenesis of OA in vitro, a miR-335-5P mimic and inhibitor were transfected into chondrocytes. Cell Counting kit-8 assay and flow cytometry were used to observe the effects of miR-335-5P on chondrocyte apoptosis and the expression of cartilage-specific genes, such as aggrecan, collagen II, matrix metalloproteinase 13 and collagen X, were detected by reverse transcription-quantitative PCR and western blot analysis. Moreover, the current study assessed whether HMG-box transcription factor 1 (HBP1) is a novel target of miR-335-5P with dual luciferase reporter assays. Finally, a rescue experiment was used to prove the regulation between miR-335-5P and HBP1. The results revealed that HBP1 was a novel target of miR-335-5P, and that miR-335-5P mediated the apoptosis of chondrocytes and changes in cartilage-specific genes via targeting HBP1. Overall, the present study revealed that miR-335-5P mediated the development of OA by targeting the HBP1 gene and promoting chondrocyte apoptosis. These data suggested that miR-335-5P may be used to develop novel early-stage diagnostic and therapeutic strategies for OA.

TLR4-TAK1-p38 MAPK pathway and HDAC6 regulate the expression of sigma-1 receptors in rat primary cultured microglia

Microglia maintain brain homeostasis as the main immune cells in the central nervous system. Activation of sigma-1 receptor (Sig1R) plays neuroprotective and anti-inflammatory roles in microglia. Recent studies showed that Sig1R expression level has been reduced in the brain of the patients with neurodegenerative diseases including Alzheimer's disease. However, the mechanisms underlying the down regulation of the Sig1R has not been clear. Treatment of rat primary cultured microglia with the inflammogen lipopolysaccharide (LPS) significantly decreased the expression of Sig1R mRNA in a concentration and time-dependent manner. The effects of LPS were blocked by pretreatment with TAK-242, a toll-like receptor 4 (TLR4) antagonist. Furthermore, inhibitors of transforming growth factor beta-activated kinase 1 (TAK1), p38 mitogen-activated protein kinase (MAPK) and histone deacetylase 6 (HDAC6) restored the LPS-induced downregulation of Sig1R. Thus, the current findings demonstrate that TLR4 activation leads to the downregulation of the Sig1R expression via TLR4-TAK1-p38 MAPK pathway and the inhibition of HDAC6 can increase Sig1R expression in microglia. The current findings suggest that downregulation of Sig1R may contribute to neuroinflammation-induced microglial dysfunction, regulation of microglial Sig1R may be novel therapeutic drug candidates for neurodegenerative and neuroinflammatory diseases.

Expression Levels of the Immune-Related p38 Mitogen-Activated Protein Kinase Transcript in Response to Environmental Pollutants on Macrophthalmus japonicus Crab

Environmental pollution in the aquatic environment poses a threat to the immune system of benthic organisms. The Macrophthalmus japonicus crab, which inhabits tidal flat sediments, is a marine invertebrate that provides nutrient and organic matter cycling as a means of purification. Here, we characterized the M. japonicus p38 mitogen-activated protein kinase (MAPK) gene, which plays key roles in the regulation of cellular immune and apoptosis responses. M. japonicusp38 MAPK displayed the characteristics of the conserved MAPK family with Thr-Gly-Tyr (TGY) motif and substrate-binding site Ala-Thr-Arg-Trp (ATRW). The amino acid sequence of the M. japonicus p38 MAPK showed a close phylogenetic relationship to Eriocheir sinensis MAPK14 and Scylla paramamosainp38 MAPK. The phylogenetic tree displayed two origins of p38 MAPK: crustacean and insect. The tissue distribution patterns showed the highest expression in the gills and hepatopancreas of M. japonicus crab. In addition, p38 MAPK expression in M. japonicus gills and hepatopancreas was evaluated after exposure to environmental pollutants such as perfluorooctane sulfonate (PFOS), irgarol, di(2-ethylhexyl) phthalate (DEHP), and bisphenol A (BPA). In the gills, p38 MAPK expression significantly increased after exposure to all concentrations of the chemicals on day 7. However, on day 1, there were increased p38 MAPK responses observed after PFOS and irgarol exposure, whereas decreased p38 MAPK responses were observed after DEHP and BPA exposure. The upregulation of p38 MAPK gene also significantly led to M. japonicus hepatopancreas being undertested in all environmental pollutants. The findings in this study supported that anti-stress responses against exposure to environmental pollutants were reflected in changes in expression levels in M. japonicusp38 MAPK signaling regulation as a cellular defense mechanism.

The Global Phosphorylation Landscape of SARS-CoV-2 Infection

The causative agent of the coronavirus disease 2019 (COVID-19) pandemic, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has infected millions and killed hundreds of thousands of people worldwide, highlighting an urgent need to develop antiviral therapies. Here we present a quantitative mass spectrometry-based phosphoproteomics survey of SARS-CoV-2 infection in Vero E6 cells, revealing dramatic rewiring of phosphorylation on host and viral proteins. SARS-CoV-2 infection promoted casein kinase II (CK2) and p38 MAPK activation, production of diverse cytokines, and shutdown of mitotic kinases, resulting in cell cycle arrest. Infection also stimulated a marked induction of CK2-containing filopodial protrusions possessing budding viral particles. Eighty-seven drugs and compounds were identified by mapping global phosphorylation profiles to dysregulated kinases and pathways. We found pharmacologic inhibition of the p38, CK2, CDK, AXL, and PIKFYVE kinases to possess antiviral efficacy, representing potential COVID-19 therapies.

Regulatory role of transcription factor HBP1 in anticancer efficacy of EGFR inhibitor erlotinib in HNSCC

BACKGROUND

Epidermal growth factor receptor (EGFR) is often hyperactivated in head and neck squamous cell carcinoma (HNSCC); however, its downstream mediators are not fully identified. Here, we investigate the role of transcription factor HBP1 in the anticancer efficacy of EGFR inhibitor erlotinib in HNSCC.

METHODS

The effect of erlotinib and HBP1 on cell proliferation and invasion was examined by flow cytometric analysis and a Matrigel invasion assay, respectively. Oral tumor specimens were used to evaluate the association between the expression level of EGFR and HBP1, and metastatic potential.

RESULTS

Erlotinib caused cell growth arrest in the G1 phase and sluggish invasion with a concomitant increase in HBP1 and p27 expression. The erlotinib effect was attenuated upon HBP1 knockdown. Analysis of oral tumor specimens revealed that the low HBP1/high EGFR status can predict metastatic potential.

CONCLUSIONS

Our data support HBP1 as a crucial mediator of EGFR-targeting inhibitors in HNSCC.

An overview of mammalian p38 mitogen-activated protein kinases, central regulators of cell stress and receptor signaling

The p38 family is a highly evolutionarily conserved group of mitogen-activated protein kinases (MAPKs) that is involved in and helps co-ordinate cellular responses to nearly all stressful stimuli. This review provides a succinct summary of multiple aspects of the biology, role, and substrates of the mammalian family of p38 kinases. Since p38 activity is implicated in inflammatory and other diseases, we also discuss the clinical implications and pharmaceutical approaches to inhibit p38.

Dexmedetomidine protects intestinal ischemia-reperfusion injury via inhibiting p38 MAPK cascades

Intestinal ischemia-reperfusion (I/R) is a life-threatening condition associated with high morbidity and mortality. Dexmedetomidine (DEX), an agonist of α2-adrenoceptor with sedation and analgesia effect, has recently been identified with protective function against I/R injury in multiple organs. However, the mechanism underlying the beneficial effect of DEX on intestine after I/R injury remained poorly understood. In the present study, using in both in vitro and in vivo models, we found that intestinal I/R injury was associated with the activation of p38 MAPK cascade, while DEX was capable of deactivating p38 MAPK and thus protect intestinal cells from apoptosis by inhibiting p38 MAPK-mediated mitochondrial depolarization and cytochrome c (Cyto C) release. Moreover, through inhibiting p38 MAPK activity, the downstream production of pro-inflammatory cytokines-regulated by NF-κB was also suppressed by DEX treatment, leading to the resolution of I/R-induced inflammation in intestine. In general, our study provided evidence that DEX protected intestine from I/R injury by inhibiting p38 MAPK-mediated mitochondrial apoptosis and inflammatory response.

DNA damage response manages cell cycle restriction of senile multipotent mesenchymal stromal cells

Multipotent mesenchymal stromal cells (MMSCs) are promising to treat a variety of traumatic and degenerative diseases. However, in vitro-passage aging induces cell cycle arrest and a series of genetic and biological changes, which greatly limits ex vivo cell number expansion and further clinical application of MMSCs. In most cases, DNA damage and DNA damage response (DDR) act as the main cause and executor of cellular senescence respectively. Mechanistically, DNA damage signals induce cell cycle arrest and DNA damage repair via DDR. If the DNA damage is indelible, MMSCs would entry into a permanent cell cycle arrest. It should be noted that apart from DDR signaling, certain proliferation or metabolism pathways are also occupied in DNA damage related cell cycle arrest. New findings of these aspects will also be summarized in this study. In summary, we aim to provide a comprehensive review of DDR associated cell cycle regulation and other major molecular signaling in the senescence of MMSCs. Above knowledge could contribute to improve the limited capacity of in vitro expansion of MMSCs, and then promote their clinical applications.

Ethanol extract of asiasari radix preferentially induces apoptosis in G361 human melanoma cells by differential regulation of p53

Background

In Korea and China, asiasari radix (AR) is widely used as a traditional anti-inflammatory and analgesic agent. After its skin-regenerating and hair loss-preventing activities were identified, several types of AR extracts were used for aesthetic purposes. Nevertheless, the effect of ARE on various types of skin cancers was not fully studied yet.

Methods

In this study, we tested the effect of an ethanolic AR extract (ARE) on G361 human melanoma and HaCaT human keratinocyte cell lines. After ARE exposure, cell growth and the expression patterns of proteins and genes were monitored.

Results

The ARE-mediated cell growth inhibition was greater in G361 cells than in HaCaT cells due to differences in its cell growth regulation effects. Interestingly, ARE treatment induced caspase-3-mediated apoptosis in G361 cells, but not in HaCaT cells. Furthermore, ARE reduced the expression of p53 and p21 proteins in G361 cells, whereas it induced their expression in HaCaT cells. ARE induced cell death in G361 cells through the reactive oxygen species (ROS)-dependent regulation of p53 and p21 in G361 cells. Microarray analysis showed that ARE regulates Mouse double minute 2 homolog (MDM2) and CASP8 and FADD-like apoptosis regulator (CFLAR) gene expression in G361 and HaCaT cells differently.

Conclusion

The treatment of ARE preferentially induces apoptosis in melanoma cells by the ROS-dependent differential regulation of p53 level. Therefore, ARE can be used as a new medicinal option for melanoma.

Selective activation of tumor-suppressive MAPKP signaling pathway by triptonide effectively inhibits pancreatic cancer cell tumorigenicity and tumor growth

The mitogen-activated protein kinase (MAPK, 1K) family members ERK, JNK, and p38 play a divergent role in either promoting tumorigenesis or tumor-suppression. Activation of ERK and JNK promotes tumorigenesis; whereas, escalation of p38 inhibits carcinogenesis. As these three MAPK members are controlled by the common up-stream MAPK signaling proteins which consist of MAPK kinases (2K) and MAPK kinase kinases (3K), how to selectively actuate tumor-suppressive p38, not concurrently stimulate tumorigenic ERK and JNK, in cancer cells is a challenge for cancer researchers, and a new opportunity for novel anti-cancer drug discovery. Using human pancreatic cancer cells and xenograft mice as models, we found that a small molecule triptonide first discerningly activated the up-stream MAPK kinase kinase MEKK4, not the other two 3K members ASK1 and GADD45; and then selectively actuated the middle stream MAPK kinase MKK4, not the other two 2K members MKK3 and MKK6; and followed by activation of the MAPK member p38, not the other two members ERK and JNK. These data suggest that triptonide is a selective MEKK4-MKK4-p38 axis agonist. Consequently, selective activation of the MEKK4-MKK4-p38 signaling axis by triptonide activated tumor suppressor p21 and inhibited CDK3 expression, resulting in cancer cell cycle arrest at G2/M phase and marked inhibition of pancreatic cancer cell tumorigenic capability in vitro and tumor growth in xenograft mice. Our findings support the notion that selective activation of tumor-suppressive MEKK4-MKK4-p38-p21signaling pathway by triptonide is a new approach for pancreatic cancer therapy, providing a new drug candidate for development of novel anti-cancer therapeutics.

Molecular Characterization of Two Mitogen-Activated Protein Kinases: p38 MAP Kinase and Ribosomal S6 Kinase From Bombyx mori (Lepidoptera: Bombycidae), and Insight Into Their Roles in Response to BmNPV Infection

Proteins p38 map kinase and ribosomal S6 kinase (S6K) as members of mitogen-activated protein kinases (MAPKs) play important roles against pathogens. In this study, Bmp38 and BmS6K were identified as differentially expressed proteins from iTRAQ database. Bmp38 and BmS6K were expressed, and recombinant proteins were purified. The bioinformatics analysis showed that both proteins have serine/threonine-protein kinases, catalytic domain (S_TKc) with 360 and 753 amino acids, respectively. The real-time quantitative polymerase chain reaction (RT-qPCR) results suggest that Bmp38 and BmS6K had high expression in the midgut and hemolymph. The comparative expression level of Bmp38 and BmS6K in BC9 was upregulated than in P50 in the midgut after Bombyx mori nucleopolyhedrovirus (BmNPV) infection. Western bolt results showed a positive correlation between RT-qPCR and iTRAQ data for Bmp38, but BmS6K data showed partial correlation with iTRAQ. Injection of anti-Bmp38 and anti-BmS6K serum suggested that Bmp38 may be involved against BmNPV infection, whereas BmS6K may require phosphorylation modification to inhibit BmNPV infection. Taken together, our results suggest that Bmp38 and BmS6k might play an important role in innate immunity of silkworm against BmNPV.

Matrix metalloproteinase-13 is a target gene of high-mobility group box-containing protein 1 in modulating oral cancer cell invasion

Transcription factor high-mobility group box-containing protein 1 (HBP1) may function as a tumor suppressor in various types of cancer. In a previous study, we demonstrated that HBP1 suppressed cell invasion in oral cancer. To further understand the underlying mechanism, the current study is aimed at investigating how HBP1 exerts its antimetastatic potential in oral cancer. In a cell model, ectopic expression of HBP1 potently suppressed epithelial-mesenchymal transition, cellular migration, and invasion; conversely, HBP1 knockdown promoted these malignant phenotypes. The matrix metalloproteinase (MMP) family is highly implicated in tumor metastasis. Therefore, we examined the effect of HBP1 on the activation of the MMP members, MMP-2, -9, and -13 that are highly associated with the aggressiveness of oral cancer. Ectopic expression of HBP1 resulted in a mild reduction in the expression and activity of MMP-2 and -9, yet it had a potent inhibitory effect on MMP-13. In contrast, HBP1 knockdown strongly enhanced the activation of MMP-13. Further, we demonstrated that MMP-13 is a target of HBP1 transcription repression as evidenced by the identification of an HBP1 binding site in the cis proximal region of the MMP-13 promoter. More important, MMP-13 knockdown significantly alleviated HBP1 small interfering RNA-mediated promotion in cell invasion. Analysis of oral tumor specimens revealed that the low HBP1 (<0.3-fold)/high MMP-13 (>3-fold) status was associated with metastatic potential. All told, our study provides evidence supporting the idea that the HBP1-MMP-13 axis is a key regulator of the aggressiveness in oral cancer.

Size uniformity of animal cells is actively maintained by a p38 MAPK-dependent regulation of G1-length

Animal cells within a tissue typically display a striking regularity in their size. To date, the molecular mechanisms that control this uniformity are still unknown. We have previously shown that size uniformity in animal cells is promoted, in part, by size-dependent regulation of G1 length. To identify the molecular mechanisms underlying this process, we performed a large-scale small molecule screen and found that the p38 MAPK pathway is involved in coordinating cell size and cell cycle progression. Small cells display higher p38 activity and spend more time in G1 than larger cells. Inhibition of p38 MAPK leads to loss of the compensatory G1 length extension in small cells, resulting in faster proliferation, smaller cell size and increased size heterogeneity. We propose a model wherein the p38 pathway responds to changes in cell size and regulates G1 exit accordingly, to increase cell size uniformity.

High mobility group box transcription factor 1 (HBP1) from Lampetra japonica affects cell cycle regulation

High mobility group (HMG) box-containing protein 1 (HBP1) is a member of the HMG family of chromosomal proteins. Previous studies have shown that human HBP1 exhibits tumor-suppressor activity. Here, we identified a homologue of HBP1, L-hbp1, in Lampetra japonica. The L-hbp1 gene shared high sequence similarity with its homologues in jawed vertebrates, as shown by bioinformatics analyses. L-hbp1 contains a 1,584-bp open reading frame that encodes 527 amino acids. A pAdenox-L-HBP1 plasmid was constructed and transfected successfully in Raji cells, as revealed by real-time PCR. The overexpression of L-HBP1 reduced cell growth rates, inhibited G1 phase progression, decreased cyclin D1 and c-Myc protein expression, and increased p53 protein expression. Western blot and immunohistochemical assays showed that L-HBP1 was primarily distributed in the heart, kidney, gill and liver of lamprey. Cell cycle analysis revealed that decreased L-HBP1 expression in HBP1 morpholino oligonucleotide-transfected lamprey cells resulted in a decreased fraction of cells in the G1 phase and corresponding increases in the S and G2/M phases. Additionally, treatment of lamprey cardiac cells with pharmacological inhibitors of p38 MAP kinase released the cells from G1 arrest. Together, these results indicated that HBP1 expression in lamprey was correlated with the onset of mitotic arrest in these cells, which have implications for cell cycle regulation.

HMG-box transcription factor 1: a positive regulator of the G1/S transition through the Cyclin-CDK-CDKI molecular network in nasopharyngeal carcinoma

HMG-box transcription factor 1 (HBP1) has been reported to be a tumor suppressor in diverse malignant carcinomas. However, our findings provide a conclusion that HBP1 plays a novel role in facilitating nasopharyngeal carcinoma (NPC) growth. The Kaplan-Meier analysis indicates that high expression HBP1 and low miR-29c expression both are negatively correlated with the overall survival rates of NPC patients. HBP1 knockdown inhibits cellular proliferation and growth, and arrested cells in G1 phase rather than affected cell apoptosis via flow cytometry (FCM) analysis. Mechanistically, HBP1 induces the expression of CCND1 and CCND3 levels by binding to their promoters, and binds to CDK4, CDK6 and p16^INK4A promoters while not affects their expression levels. CCND1 and CCND3 promote CCND1-CDK4, CCND3-CDK6, and CDK2-CCNE1 complex formation, thus, E2F-1 and DP-1 are activated to accelerate the G1/S transition in the cell cycle. MiR-29c is down-regulated and correlated with NPC tumorigenesis and progression. Luciferase assays confirms that miR-29c binds to the 3' untranslated region (3'-UTR) of HBP1. Introduction of pre-miR-29c decreased HBP1 mRNA and protein levels. Therefore, the high endogenous HBP1 expression might be attributed to the low levels of endogenous miR-29c in NPC. In addition, HBP1 knockdown and miR-29c agomir administration both decrease xenograft growth in nude mice in vivo. It is firstly reported that HBP1 knockdown inhibited the proliferation and metastasis of NPC, which indicates that HBP1 functions as a non-tumor suppressor gene in NPC. This study provides a novel potential target for the prevention of and therapies for NPC.

Transcription factor HMG box-containing protein 1 (HBP1) modulates mitotic clonal expansion (MCE) during adipocyte differentiation

Transcription factor HMG box-containing protein 1 (HBP1) has been found to be up-regulated in rat adipose tissue and differentiated preadipocyte; however, how HBP1 is involved in adipocyte formation remains unclear. In the present study, we demonstrated that under a standard differentiation protocol HBP1 expression fluctuates with down-regulation in the mitotic clonal expansion (MCE) stage followed by up-regulation in the terminal differentiation stage in both 3T3-L1 and MEF cell models. Also, HBP1 knockdown accelerated cell cycle progression in the MCE stage, but it impaired final adipogenesis. To gain further insight into the role of HBP1 in the MCE stage, we found that the HBP1 expression pattern is reciprocal to that of C/EBPβ, and ectopic expression of HBP1suppresses C/EBPβ expression. These data indicate that HBP1 functions as a negative regulator of MCE. In contrast, when HBP1 expression was gradually elevated along with a concomitant induction of C/EBPα at the end of the MCE, HBP1 knockdown leads to a significant reduction of C/EBPα expression, suggesting that HBP1-mediated C/EBPα expression may be needed for the termination of the cell cycle at the end of MCE for terminal differentiation. All told, our findings show that HBP1 is a key transcription factor in the already complicated regulatory cascade during adipocyte differentiation.

Transcription factor HBP1 is a direct anti-cancer target of transcription factor FOXO1 in invasive oral cancer

Either FOXO1 or HBP1 transcription factor is a downstream effector of the PI3K/Akt pathway and associated with tumorigenesis. However, the relationship between FOXO1 and HBP1 in oral cancer remains unclear. Analysis of 30 oral tumor specimens revealed that mean mRNA levels of both FOXO1 and HBP1 in non-invasive and invasive oral tumors were found to be significantly lower than that of the control tissues, and the status of low FOXO1 and HBP1 (< 0.3 fold of the control) was associated with invasiveness of oral tumors. To investigate if HBP1 is a direct transcription target of FOXO1, we searched potential FOXO1 binding sites in the HBP1 promoter using the MAPPER Search Engine, and two putative FOXO1 binding sites located in the HBP1 promoter –132 to –125 bp and –343 to –336 bp were predicted. These binding sites were then confirmed by both reporter gene assays and the in cellulo ChIP assay. In addition, Akt activity manipulated by PI3K inhibitor LY294002 or Akt mutants was shown to negatively affect FOXO1-mediated HBP1 promoter activation and gene expression. Last, the biological significance of the FOXO1-HBP1 axis in oral cancer malignancy was evaluated in cell growth, colony formation, and invasiveness. The results indicated that HBP1 knockdown potently promoted malignant phenotypes of oral cancer and the suppressive effect of FOXO1 on cell growth, colony formation, and invasion was alleviated upon HBP1 knockdown in invasive oral cancer cells. Taken together, our data provide evidence for HBP1 as a direct downstream target of FOXO1 in oral cancer malignancy.

Mice Lacking Hbp1 Function Are Viable and Fertile

Fetal germ cell development is tightly regulated by the somatic cell environment, and is characterised by cell cycle states that differ between XY and XX gonads. In the testis, gonocytes enter G1/G0 arrest from 12.5 days post coitum (dpc) in mice and maintain cell cycle arrest until after birth. Failure to correctly maintain G1/G0 arrest can result in loss of germ cells or, conversely, germ cell tumours. High mobility group box containing transcription factor 1 (HBP1) is a transcription factor that was previously identified in fetal male germ cells at the time of embryonic cell cycle arrest. In somatic cells, HBP1 is classified as a tumour suppressor protein, known to regulate proliferation and senescence. We therefore investigated the possible role of HBP1 in the initiation and maintenance of fetal germ cell G1/G0 arrest using the mouse model. We identified two splice variants of Hbp1, both of which are expressed in XY and XX fetal gonads, but only one of which is localised to the nucleus in in vitro assays. To investigate Hbp1 loss of function, we used embryonic stem (ES) cells carrying a Genetrap mutation for Hbp1 to generate mice lacking Hbp1 function. We found that Hbp1-genetrap mouse mutant germ cells proliferated correctly throughout development, and adult males were viable and fertile. Multiple Hbp1-LacZ reporter mouse lines were generated, unexpectedly revealing Hbp1 embryonic expression in hair follicles, eye and limbs. Lastly, in a model of defective germ cell G1/G0 arrest, the Rb1-knockout model, we found no evidence for Hbp1 mis-regulation, suggesting that the reported RB1-HBP1 interaction is not critical in the germline, despite co-expression.

Molecular characterization of a p38 mitogen-activated protein kinase gene from Scylla paramamosain and its expression profiles during pathogenic challenge

A novel p38 MAPK gene from S. paramamosain was cloned and characterized by rapid amplification of cDNA ends (RACE) technology. S. paramamosain p38 (Sp-p38) MAPK gene consists of an open reading frame of 1095bp encoding a 365-amino-acid protein, which showed close phylogenetic relationship to Litopenaeus vannamei p38 MAPK. The tissue distribution patterns showed that Sp-p38 MAPK was widely expressed in all examined tissues, with the highest expression in hemocytes and intestines. The expression levels of Sp-p38 MAPK in hemocytes was up-regulated post-stimulation, which reached the peak at 6h and 12h after bacteria (S. aureus and V. harveyi) and WSSV infection, respectively. In conclusion, our data contributed to define the biological characteristics of Sp-p38 MAPK and further demonstrated the critical role of Sp-p38 MAPK in vivo during the viral and bacterial infection.

Effects of herbal Epimedium on the improvement of bone metabolic disorder through the induction of osteogenic differentiation from bone marrow-derived mesenchymal stem cells

Herbal Epimedium (HE) has been commonly used as a tonic, antirheumatic agent and in the treatment of bone-associated diseases including osteoporosis. Treatment for osteoporosis is important to increase bone mass density and maintain to balance of bone remodeling. The present study was performed to investigate the effects of HE on mouse bone marrow mesenchymal stem cell (mBMMSC) proliferation and osteogenic differentiation, using MTT assays, proliferating cell nuclear antigen (PCNA) detection and apoptosis and differentiation assays. HE was demonstrated to inhibit the proliferation of mBMMSCs up to 45.43±3.33% and to decrease the level of PCNA expression compared with untreated cells. HE also induced late apoptosis at 24 and 48 h after treatment up to 71.93 and 67.03%, respectively, while only 14.93% of untreated cells exhibited apoptosis. By contrast, HE induced differentiation of mBMMSCs into an osteogenic lineage at the beginning of three weeks after commencement of treatment. This suggested that HE is a candidate as an inducer of osteogenesis from bone marrow mesenchymal stem cells, and additionally has potential for use in the treatment of bone metabolic disorders such as osteoporosis.

Focused screening of mitochondrial metabolism reveals a crucial role for a tumor suppressor Hbp1 in ovarian reserve

Granulosa cells (GCs) are tightly associated with fertility and the fate of ovarian follicles. Mitochondria are the central executers of apoptosis. However, the genetic basis underlying mitochondrial modulation in GCs during the ovarian development is poorly understood. Here, CRISPR/Cas9-mediated genetic screening was used to identify genes conferring mitochondrial metabolism in human GCs. The results uncovered roles for several tumor suppressors, including HBP1, in the augmentation of mitochondrial function. Focused analysis revealed that high-mobility group (HMG)-box transcription factor 1 (Hbp1) levels regulate mitochondrial biogenesis, which is associated with global changes in transcription including Tfam. The systemic or granulosa-specific but not oocyte-specific ablation of Hbp1 promoted follicle growth and oocyte production, and is associated with the reduced apoptotic signals in mouse GCs. Consistent with increased mitochondrial function and attenuated GC apoptosis, the regulation of Hbp1 conferred substantial protection of ovarian reserve. Thus, the results of the present study provide a critical target to understand the control of the reproductive lifespan.

Inhibition of Phosphatase Activity Follows Decline in Sulfatase Activity and Leads to Transcriptional Effects through Sustained Phosphorylation of Transcription Factor MITF

Arylsulfatase B (B-acetylgalactosamine 4-sulfatase; ARSB) is the enzyme that removes 4-sulfate groups from the non-reducing end of the glycosaminoglycans chondroitin 4-sulfate and dermatan sulfate. Decline in ARSB has been shown in malignant prostate, colonic, and mammary cells and tissues, and decline in ARSB leads to transcriptional events mediated by galectin-3 with AP-1 and Sp1. Increased mRNA expression of GPNMB (transmembrane glycoprotein NMB) in HepG2 cells and in hepatic tissue from ARSB-deficient mice followed decline in expression of ARSB and was mediated by the microphthalmia-associated transcription factor (MITF), but was unaffected by silencing galectin-3. Since GPNMB is increased in multiple malignancies, studies were performed to determine how decline in ARSB increased GPNMB expression. The mechanism by which decline in ARSB increased nuclear phospho-MITF was due to reduced activity of SHP2, a protein tyrosine phosphatase with Src homology (SH2) domains that regulates multiple cellular processes. SHP2 activity declined due to increased binding with chondroitin 4-sulfate when ARSB was reduced. When SHP2 activity was inhibited, phosphorylations of p38 mitogen-associated phosphokinase (MAPK) and of MITF increased, leading to GPNMB promoter activation. A dominant negative SHP2 construct, the SHP2 inhibitor PHSP1, and silencing of ARSB increased phospho-p38, nuclear MITF, and GPNMB. In contrast, constitutively active SHP2 and overexpression of ARSB inhibited GPNMB expression. The interaction between chondroitin 4-sulfate and SHP2 is a novel intersection between sulfation and phosphorylation, by which decline in ARSB and increased chondroitin 4-sulfation can inhibit SHP2, thereby regulating downstream tyrosine phosphorylations by sustained phosphorylations with associated activation of signaling and transcriptional events.

Transcription Factor HBP1 Enhances Radiosensitivity by Inducing Apoptosis in Prostate Cancer Cell Lines

Radiotherapy for prostate cancer has been gradually carried out in recent years; however, acquired radioresistance often occurred in some patients after radiotherapy. HBP1 (HMG-box transcription factor 1) is a transcriptional inhibitor which could inhibit the expression of dozens of oncogenes. In our previous study, we showed that the expression level of HBP1 was closely related to prostate cancer metastasis and prognosis, but the relationship between HBP1 and radioresistance for prostate cancer is largely unknown. In this study, the clinical data of patients with prostate cancer was compared, and the positive correlation was revealed between prostate cancer brachytherapy efficacy and the expression level of HBP1 gene. Through research on prostate cancer cells in vitro, we found that HBP1 expression levels were negatively correlated with oncogene expression levels. Furthermore, HBP1 overexpression could sensitize prostate cancer cells to radiation and increase apoptosis in prostate cancer cells. In addition, animal model was employed to analyze the relationship between HBP1 gene and prostate cancer radiosensitivity in vivo; the result showed that knockdown of HBP1 gene could decrease the sensitivity to radiation of xenograft. These studies identified a specific molecular mechanism underlying prostate cancer radiosensitivity, which suggested HBP1 as a novel target in prostate cancer radiotherapy.

Meso-dihydroguaiaretic acid induces apoptosis and inhibits cell migration via p38 activation and EGFR/Src/intergrin β3 downregulation in breast cancer cells

AIMS

Meso-dihydroguaiaretic acid (MDA) is known for its anti-inflammatory, anti-oxidant, anti-bacterial, and anti-tumor activity. However, the anti-breast cancer effect and the mechanism of MDA remain undefined.

MAIN METHODS

In this study, we examined the anti-cancer activity and the mechanisms of action of MDA in breast cancer cell lines, 4T-1 and MCF-7 cells; and 4T-1 bearing mouse model.

KEY FINDINGS

MDA showed cytotoxic effects on 4T-1 and MCF-7 cells in a dose-dependent manner. Moreover, MDA increased the amount of Annexin V-positive apoptotic bodies, phosphorylated JNK and p38 in 4T-1 cells. MDA also down-regulated cell-cycle dependent proteins, CDK-4 and cyclin D1; and induced cleaved caspase-3 in MDA-treated 4T-1 cells. We further verified that MDA-induced apoptosis is mediated by p38 and caspase-3 activation in 4T-1 cells. Next, we studied the effect of MDA treatment on cell migration and found that MDA significantly reduced cell migration. Moreover, MDA reduced EGFR and intergrin β3 expression, and dephosphorylated Src in a dose-dependent manner in 4T-1 cells. Furthermore, we observed in vivo effect of MDA in 4T-1 cell inoculated mice. MDA (20mg/kg/day) significantly suppressed mammary tumor volume and activated caspase-3 in tumor tissues.

SIGNIFICANCE

These results suggest novel targets of MDA in breast cancer in vitro and in vivo, making it a potential candidate as a chemotherapeutic drug.

Suppression of centrosome protein TACC3 induces G1 arrest and cell death through activation of p38-p53-p21 stress signaling pathway

The centrosome regulates diverse cellular processes, including cell proliferation and differentiation. TACC3, a member of the human transforming acidic coiled-coil protein family, is a key centrosomal protein that is up-regulated in many cancers. Previous studies have demonstrated that TACC3 is essential for the survival of vertebrates and is involved in cell cycle regulation in human cells. However, the details of the underlying mechanisms in its cell cycle regulatory activity remain poorly understood. In this study, we showed that suppression of TACC3 expression induced G1 cell cycle arrest and triggered cell death in human cells. TACC3 depletion-induced G1 arrest and cell death were significantly reduced in cells either lacking p53 or with pharmacologically-inhibited p38, indicating that G1 arrest and cell death induction both require p53 and p38. TACC3 depletion up-regulated the levels of p53 and p21 and induced the accumulation of p53 both in the nucleus and at the centrosome. Interestingly, TACC3 depletion led to the activation of p38 and stimulated the recruitment of activated p38 to the centrosome. Depletion of TACC3 up-regulated the phosphorylation of p53 at Serine 33, a site known to be phosphorylated by p38 under cellular stress and further induced the accumulation of phosphorylated p53 to the centrosome. Loss of TACC3 affected centrosome integrity by disrupting the localization of components of the γ-tubulin ring complex at the centrosome. The results demonstrate that TACC3 depletion induces G1 arrest and cell death by activating p38-p53-p21 signaling and triggering a centrosome-mediated cellular stress response.

MAPK signaling mediates sinomenine hydrochloride-induced human breast cancer cell death via both reactive oxygen species-dependent and -independent pathways: an in vitro and in vivo study

Sinomenine, the main alkaloid extracted from the medicinal plant Sinomenium acutum, is known for its anti-inflammatory effects. Recent studies have suggested its anti-cancer effect in synovial sarcoma, lung cancer and hepatic cancer. However, the underlying molecular mechanism for its anti-cancer effect still remains unclear. This study investigated the anti-tumor activity of sinomenine hydrochloride (SH), a hydrochloride form of sinomenine, in human breast cancer cells in vitro and in vivo. We found that SH potently inhibited cell viability of a broad panel of breast cancer cell lines. Two representative breast cancer cell lines, namely ER(-)/PR(-) MDA-MB-231 and ER(+)/PR(+) MCF-7, were used for further investigation. The results showed that SH induced G1/S cell cycle arrest, caused apoptosis and induced ATM/Chk2- and ATR/Chk1-mediated DNA-damage response in MDA-MB-231 and MCF-7. The anti-cancer effect of SH was regulated by increased expression levels of p-ERK, p-JNK and p-38 MAPK. Further studies showed that SH resulted in an increase in reactive oxygen species (ROS) and inhibition of ROS by N-acetyl-L-cysteine (NAC) almost blocked SH-induced DNA damage but only mitigated SH-induced MAPK expression changes, suggesting that both ROS-dependent and -independent pathways were involved in MAPK-mediated SH-induced breast cancer cell death. The in vivo study demonstrated that SH effectively inhibited tumor growth without showing significant toxicity. In conclusion, SH induced breast cancer cell death through ROS-dependent and -independent pathways with an upregulation of MAPKs, indicating that SH may be a potential anti-tumor drug for breast cancer treatment.

Cooperativity of oncogenic K-ras and downregulated p16/INK4A in human pancreatic tumorigenesis

Activation of K-ras and inactivation of p16 are the most frequently identified genetic alterations in human pancreatic epithelial adenocarcinoma (PDAC). Mouse models engineered with mutant K-ras and deleted p16 recapitulate key pathological features of PDAC. However, a human cell culture transformation model that recapitulates the human pancreatic molecular carcinogenesis is lacking. In this study, we investigated the role of p16 in hTERT-immortalized human pancreatic epithelial nestin-expressing (HPNE) cells expressing mutant K-ras (K-ras^G12V). We found that expression of p16 was induced by oncogenic K-ras in these HPNE cells and that silencing of this induced p16 expression resulted in tumorigenic transformation and development of metastatic PDAC in an orthotopic xenograft mouse model. Our results revealed that PI3K/Akt, ERK1/2 pathways and TGFα signaling were activated by K-ras and involved in the malignant transformation of human pancreatic cells. Also, p38/MAPK pathway was involved in p16 up-regulation. Thus, our findings establish an experimental cell-based model for dissecting signaling pathways in the development of human PDAC. This model provides an important tool for studying the molecular basis of PDAC development and gaining insight into signaling mechanisms and potential new therapeutic targets for altered oncogenic signaling pathways in PDAC.

Mitogen-activated protein kinase p38 and retinoblastoma protein signalling is required for DNA damage-mediated formation of senescence-associated heterochromatic foci in tumour cells

DNA-damaging agents are able to induce irreversible cell growth arrest and senescence in some types of tumour cells, thus contributing to the static feature of cancer. However, senescent tumour cells may re-enter the cell cycle, leading to tumour relapse. Understanding the mechanisms that control the viability of senescent cells may be critical for tumour suppression. Primary human fibroblasts undergoing oncogene-induced or replicative senescence are known to form senescence-associated heterochromatin foci (SAHF), which contribute to the stability of the senescent state. However, it is unclear whether SAHF formation is universal in tumour cells. We report that the DNA-damaging agents doxorubicin and 7-ethyl-10-hydroxycamptothecin were able to induce the formation of SAHF in some tumour cell types, and this induction was accompanied by activation of the retinoblastoma protein pathway. By contrast, tumour cells in which the retinoblastoma protein pathway could not be activated by doxorubicin or 7-ethyl-10-hydroxycamptothecin failed to form SAHF. In parallel, tumour cells with deficient retinoblastoma protein were also unable to form SAHF. In addition, we show that the mitogen-activated protein kinase p38 pathway was involved in tumour cell SAHF formation in response to doxorubicin and 7-ethyl-10-hydroxycamptothecin. Furthermore, HMG box transcription factor 1 (HBP1), a downstream target of the mitogen-activated protein kinase p38-mediated senescence pathway, was required for SAHF formation. Taken together, the results of the present study highlight the roles of the mitogen-activated protein kinase p38/retinoblastoma protein pathway in tumour cell SAHF formation in response to DNA-damaging agents, and provide new insights into the mechanisms of DNA damage-mediated tumour suppression.

HBP1-mediated transcriptional regulation of DNA methyltransferase 1 and its impact on cell senescence

The activity of DNA methyltransferase 1 (DNMT1) is associated with diverse biological activities, including cell proliferation, senescence, and cancer development. In this study, we demonstrated that the HMG box-containing protein 1 (HBP1) transcription factor is a new repressor of DNMT1 in a complex mechanism during senescence. The DNMT1 gene contains an HBP1-binding site at bp -115 to -134 from the transcriptional start site. HBP1 repressed the endogenous DNMT1 gene through sequence-specific binding, resulting in both gene-specific (e.g., p16(INK4)) and global DNA hypomethylation changes. The HBP1-mediated repression by DNMT1 contributed to replicative and premature senescence, the latter of which could be induced by Ras and HBP1 itself. A detailed investigation unexpectedly revealed that HBP1 has dual and complex transcriptional functions, both of which contribute to premature senescence. HBP1 both repressed the DNMT1 gene and activated the p16 gene in premature senescence. The opposite transcriptional functions proceeded through different DNA sequences and differential protein acetylation. While intricate, the reciprocal partnership between HBP1 and DNMT1 has exceptional importance, since its abrogation compromises senescence and promotes tumorigenesis. Together, our results suggest that the HBP1 transcription factor orchestrates a complex regulation of key genes during cellular senescence, with an impact on overall DNA methylation state.

N-acetylcysteine (NAC) inhibits cell growth by mediating the EGFR/Akt/HMG box-containing protein 1 (HBP1) signaling pathway in invasive oral cancer

OBJECTIVES

Overexpression of the epidermal growth factor (EGF) receptor (EGFR) gene in the squamous cell carcinomas of the head and neck (SCCHN) is often associated with inauspicious prognosis and poor survival. N-acetylcysteine (NAC), a compound from some vegetables and allium species, appears anti-tumorigenesis, but the underlying mechanism is unclear. The objective of this study is to investigate the role of NAC in EGFR-overexpressing oral cancer.

MATERIALS AND METHODS

Both HSC-3 and SCC-4 human tongue squamous carcinoma cell lines and an HSC-3 xenograft mouse model were used to test the anti-growth efficacy of NAC in vitro and in vivo, respectively.

RESULTS

NAC treatment suppressed cell growth, with concomitantly increased expression of HMG box-containing protein 1 (HBP1), a transcription suppressor, and decreased EGFR/Akt activation, in EGFR-overexpressing HSC-3 oral cancer cells. HBP1 knockdown attenuated the growth arrest and apoptosis induced by NAC. Lastly, NAC and AG1478, an EGFR inhibitor, additively suppressed colony formation in HSC-3 cells.

CONCLUSION

Taken together, our data indicate that NAC exerts its growth-inhibitory function through modulating EGFR/Akt signaling and HBP1 expression in EGFR-overexpressing oral cancer.

The acetylation of transcription factor HBP1 by p300/CBP enhances p16INK4A expression

HBP1 is a sequence-specific DNA-binding transcription factor with many important biological roles. It activates or represses the expression of some specific genes during cell growth and differentiation. Previous studies have exhibited that HBP1 binds to p16^INK4A promoter and activates p16^INK4A expression. We found that trichostatin A (TSA), an inhibitor of HDAC (histone deacetylase), induces p16^INK4A expression in an HBP1-dependent manner. This result was drawn from a transactivation experiment by measuring relative luciferase activities of p16^INK4A promoter with HBP1-binding site in comparison with that of the wild-type p16^INK4A promoter by transient cotransfection with HBP1 into HEK293T cells and 2BS cells. HBP1 acetylation after TSA treatment was confirmed by immunoprecipitation assay. Our data showed that HBP1 interacted with histone acetyltransferase p300 and CREB-binding protein (CBP) and also recruited p300/CBP to p16^INK4A promoter. HBP1 was acetylated by p300/CBP in two regions: repression domain (K297/305/307) and P domain (K171/419). Acetylation of Repression domain was not required for HBP1 transactivation on p16^INK4A. However, luciferase assay and western blotting results indicate that acetylation of P domain, especially K419 acetylation is essential for HBP1 transactivation on p16^INK4A. As assayed by SA-beta-gal staining, the acetylation of HBP1 at K419 enhanced HBP1-induced premature senescence in 2BS cells. In addition, HDAC4 repressed HBP1-induced premature senescence through permanently deacetylating HBP1. We conclude that our data suggest that HBP1 acetylation at K419 plays an important role in HBP1-induced p16^INK4A expression.

Antiproliferative activity of melanoidins isolated from heated potato fiber (potex) in glioma cell culture model

Potex constitutes a potato fiber preparation widely used as an ingredient to meat and bakery products which thermal treatment results in creation of new compounds. Melanoidins are high molecular weight brown end products of Maillard reaction, and few data presenting tumor cell growth inhibiting activity of melanoidins have been reported. Thus, in present study we utilized water extract of Potex roasted (180 °C for 2 h), whose chemical characterization revealed the presence of melanoidin complexes. Heated Potex extract inhibited C6 glioma cell proliferation in a dose-dependent manner measured by MTT method. High molecular weight components present in initial extract were responsible for stronger antiproliferative effect compared with low molecular weight fraction. Impaired MAPK (mitogen-activated protein kinase) and Akt signaling was found in cells treated with the extract. Moreover, flow cytometry analyses revealed the extract to induce G1/S arrest in glioma cells. Simultaneously, Western blot analysis showed elevated levels of p21 protein with concomitant decrease of cyclin D1. In conclusion, observed antiproliferative activity of melanoidins present in heated Potex was linked to disregulated MAPK and Akt signaling pathways, as well as to cell cycle cessation. These results suggest potential application of Potex preparation as a functional food ingredient and chemopreventive agent.