Transcriptional pausing induced by ionizing radiation enables the acquisition of radioresistance in nasopharyngeal carcinoma.

Lesions on the DNA template can impact transcription via distinct regulatory pathways. Ionizing radiation (IR) as the mainstay modality for many malignancies elicits most of the cytotoxicity by inducing a variety of DNA damages in the genome. How the IR treatment alters the transcription cycle and whether it contributes to the development of radioresistance remain poorly understood. Here, we report an increase in the paused RNA polymerase II (RNAPII), as indicated by the phosphorylation at serine 5 residue of its C-terminal domain, in recurrent nasopharyngeal carcinoma (NPC) patient samples after IR treatment and cultured NPC cells developing IR resistance. Reducing the pool of paused RNAPII by either inhibiting TFIIH-associated CDK7 or stimulating the positive transcription elongation factor b, a CDK9-CycT1 heterodimer, attenuates IR resistance of NPC cells. Interestingly, the poly(ADP-ribosyl)ation of CycT1, which disrupts its phase separation, is elevated in the IR-resistant cells. Mutation of the major poly(ADP-ribosyl)ation sites of CycT1 decreases RNAPII pausing and restores IR sensitivity. Genome-wide chromatin immunoprecipitation followed by sequencing analyses reveal that several genes involved in radiation response and cell cycle control are subject to the regulation imposed by the paused RNAPII. Particularly, we identify the NIMA-related kinase NEK7 under such regulation as a new radioresistance factor, whose downregulation results in the increased chromosome instability, enabling the development of IR resistance. Overall, our results highlight a novel link between the alteration in the transcription cycle and the acquisition of IR resistance, opening up new opportunities to increase the efficacy of radiotherapy and thwart radioresistance in NPC.

The role of GATA switch in benzene metabolite hydroquinone inhibiting erythroid differentiation in K562 cells.

The phenolic metabolite of benzene, hydroquinone (HQ), has potential risks for hematological disorders and hematotoxicity in humans. Previous studies have revealed that reactive oxygen species, DNA methylation, and histone acetylation participate in benzene metabolites inhibiting erythroid differentiation in hemin-induced K562 cells. GATA1 and GATA2 are crucial erythroid-specific transcription factors that exhibit dynamic expression patterns during erythroid differentiation. We investigated the role of GATA factors in HQ-inhibited erythroid differentiation in K562 cells. When K562 cells were induced with 40 µM hemin for 0-120 h, the mRNA and protein levels of GATA1 and GATA2 changed dynamically. After exposure to 40 µM HQ for 72 h, K562 cells were induced with 40 µM hemin for 48 h. HQ considerably reduced the percentage of hemin-induced Hb-positive cells, decreased the GATA1 mRNA, protein, and occupancy levels at α-globin and ß-globin gene clusters, and increased the GATA2 mRNA and protein levels significantly. ChIP-seq analysis revealed that HQ reduced GATA1 occupancy, and increased GATA2 occupancy at most gene loci in hemin-induced K562 cells. And GATA1 and GATA2 might play essential roles in the erythroid differentiation protein interaction network. These results elucidate that HQ decreases GATA1 occupancy and increases GATA2 occupancy at the erythroid gene loci, thereby downregulating GATA1 and upregulating GATA2 expression, which in turn modulates the expression of erythroid genes and inhibits erythroid differentiation. This partially explains the mechanism of benzene hematotoxicity.

Malignant glomus tumor of prostate: A case report.

We reported an 85-year-old patient with malignant glomus tumor (GT) of the prostate. He presented with urinary frequency for more than 2 years and gross hematuria for 7 days. Computed tomography scan showed that the prostate was markedly irregularly enlarged, and the boundary between the prostate and the posterior wall of the bladder was unclear. Bilateral kidneys and ureters were dilated. Biochemical examinations showed that the serum potassium was 7.24 mmol/L and the serum creatinine was 974.6 µmol/L. Transurethral diagnostic resection was performed after restoring homeostasis through several times of bedside blood filtration. The pathological diagnosis was malignant GT. The patient's renal function recovered after bilateral nephrostomy, and he refused further treatment and was out of contact after 9 months. We summarize the clinical and histopathological features of malignant GT of the prostate in order to improve the early recognition of the disease by clinicians.

A patent and literature review of CDK12 inhibitors.

INTRODUCTION: Cyclin-dependent kinase 12 (CDK12) belongs to the CDK family of serine/threonine protein kinases and is associated with cyclin K to exert its biological functions, including regulating gene transcription, mRNA processing, and translation. Increasing evidences demonstrate the importance of CDK12 in various human cancers, illustrating its potential as both biomarker and therapeutic target. In addition, CDK12 is also a promising target for the treatment of myotonic dystrophy type 1. Efforts have been taken to discover small molecule inhibitors to validate this important therapeutic target. AREAS COVERED: This review covers the patented CDK12 inhibitors from 2016 to present, as well as these from peer-reviewed literature. It provides the reader an update of the discovery strategies, chemical structures, and molecular profiling of all available CDK12 inhibitors. EXPERT OPINION: CDK12 inhibitors with various mechanism of actions have been discovered, and it is a great set of tools to evaluate the therapeutic potential of CDK12 in different disease models. CDK12 inhibitors have shown promising results in myotonic dystrophy type 1 mouse model and several preclinical cancer models either as single agent or combination with other anti-cancer agents. Its therapeutic value awaits more rigorous preclinical testing and further clinical investigation.

Can preoperative ureteral stents reduce the incidence of ureteral stricture after radiotherapy in patients with cervical cancer?

OBJECTIVE: To determine the impact of preoperative stent placement on postradiotherapy stricture rate in patients with cervical cancer after radical resection. METHODS: This study was a retrospective analysis of data collected from 55 cervical cancer patients treated with radiotherapy between June 2016 and June 2020. Patients were divided into the stent and control groups. After 3 months, the stricture rate and the complications related to stent placement between the two groups were compared. RESULTS: There were 12 (46.2%) and 10 (34.5%) cases of ureteral stricture in the stent (n = 26) and control (n = 29) groups, respectively, three months after the end of radiotherapy. The incidence rates of ureter stricture in the two groups were not significantly different (P = 0.378). Moreover, there were 20 units (38.5%) and 15 units (25.9%) ureteral strictures in the stent and control groups, respectively. No significant difference in the incidence rates of ureteral strictures was found between the two groups (P = 0.157). There were 13 (50.0%) and 10 (34.5%) cases of ureteral stricture in the stent (n = 26) and control (n = 29) groups, respectively, six months after the end of the radiotherapy. The incidence rates of ureter stricture in the two groups were not significantly different (P = 0.244). Moreover, there were 21 units (40.4%) and 15 units (25.9%) ureteral strictures in the stent and control groups, respectively. No significant difference in the incidence rates of ureteral strictures was found between the two groups (P = 0.105). Complications related to stent placement such as urinary tract infections and bladder irritation were statistically significant (P = 0.006 and P = 0.036) between the two groups; while the other complications were not significantly different (P = 0.070, P = 0.092 and P = 0.586). CONCLUSIONS: Ureteral stents may not reduce the incidence of ureteral stricture after radiotherapy in patients with cervical cancer. The stent needs to be replaced regularly, and the complications related to stent placement may occur at any time. Thus, preoperative stent placement should be cautious for the clinical management of cervical cancer patients treated with postoperative radiotherapy.

ARID1A loss derepresses a group of human endogenous retrovirus-H loci to modulate BRD4-dependent transcription.

Transposable elements (TEs) through evolutionary exaptation have become an integral part of the human genome, offering ample regulatory sequences and shaping chromatin 3D architecture. While the functional impacts of TE-derived sequences on early embryogenesis have been recognized, their roles in malignancy are only starting to emerge. Here we show that many TEs, especially the pluripotency-related human endogenous retrovirus H (HERVH), are abnormally activated in colorectal cancer (CRC) samples. Transcriptional upregulation of HERVH is associated with mutations of several tumor suppressors, particularly ARID1A. Knockout of ARID1A in CRC cells leads to increased transcription at several HERVH loci, which involves compensatory contribution by ARID1B. Suppression of HERVH in CRC cells and patient-derived organoids impairs tumor growth. Mechanistically, HERVH transcripts colocalize with nuclear BRD4 foci, modulating their dynamics and co-regulating many target genes. Altogether, we uncover a critical role for ARID1A in restraining HERVH, whose abnormal activation can promote tumorigenesis by stimulating BRD4-dependent transcription.

The novel mechanism of Med12-mediated drug resistance in a TGFBR2-independent manner.

Inevitable emergence of drug resistance is the biggest hurdle to both chemotherapies and targeted therapies. Understanding the resistance mechanisms will contribute to identification of biomarkers for predicting response to therapy and design new therapeutic strategies to overcome drug resistance in human cancers. The type II transforming growth factor (TGF)-ß receptor gene (TGFBR2) is frequently frameshift mutated in several cancer types, especially in colorectal, endometrium and gastric cancers cells. Here, we found that Med12, a component of the transcriptional mediator complex, plays a role in modulating chemosensitivity in TGFBR2 deficient cancer cells. Loss of Med12 leads to chemoresistance in multiple TGFBR2 deficient cancer cells. Interestingly, RNA sequencing data revealed that interferon IFN-related DNA damage resistance signature (IRDS) is upregulated in Med12 knockdown cancer cells. And the expression of IRDS pattern is negatively correlated with chemosensitivity. Therefore, our study identifies a novel mechanism of Med12-mediated drug resistance, which is a TGFBR-independent manner.

Identification of potential pathways and microRNA-mRNA networks associated with benzene metabolite hydroquinone-induced hematotoxicity in human leukemia K562 cells.

BACKGROUND: Hydroquinone (HQ) is a phenolic metabolite of benzene with a potential risk for hematological disorders and hematotoxicity in humans. In the present study, an integrative analysis of microRNA (miRNA) and mRNA expressions was performed to identify potential pathways and miRNA-mRNA network associated with benzene metabolite hydroquinone-induced hematotoxicity. METHODS: K562 cells were treated with 40 µM HQ for 72 h, mRNA and miRNA expression changes were examined using transcriptomic profiles and miRNA microarray, and then bioinformatics analysis was performed. RESULTS: Out of all the differentially expressed genes (DEGs) and differentially expressed miRNAs (DEMs) induced by HQ, 1482 DEGs and 10 DEMs were up-regulated, and 1594 DEGs and 42 DEMs were down-regulated. HQ-induced DEGs were involved in oxidative stress, apoptosis, DNA methylation, histone acetylation and cellular response to leukemia inhibitory factor GO terms, as well as metabolic, Wnt/ß-catenin, NF-κB, and leukemia-related pathways. The regulatory network of mRNAs and miRNAs includes 23 miRNAs, 1108 target genes, and 2304 potential miRNAs-mRNAs pairs. MiR-1246 and miR-224 had the potential to be major regulators in HQ-exposed K562 cells based on the miRNAs-mRNAs network. CONCLUSIONS: This study reinforces the use of in vitro model of HQ exposure and bioinformatic approaches to advance our knowledge on molecular mechanisms of benzene hematotoxicity at the RNA level.

Role of microRNA-regulated cancer stem cells in recurrent hepatocellular carcinoma.

Among the most common cancers, hepatocellular carcinoma (HCC) has a high rate of tumor recurrence, tumor dormancy, and drug resistance after initial successful chemotherapy or radiotherapy. A small subset of cancer cells, cancer stem cells (CSCs), exhibit stem cell characteristics and are present in various cancers, including HCC. The dysregulation of microRNAs (miRNAs) often accompanies the occurrence and development of HCC. miRNAs can influence tumorigenesis, progression, recurrence, and drug resistance by regulating CSCs properties, which supports their clinical utility in managing and treating HCC. This review summarizes the regulatory effects of miRNAs on CSCs in HCC with a special focus on their impact on HCC recurrence.

Bergenin inhibits bladder cancer progression via activating the PPARγ/PTEN/Akt signal pathway.

Bladder cancer is one of the most common malignant tumors in the urinary system with high mortality and morbidity. Evidence revealed that bergenin could affect the development of cancer. Here, we aimed to investigate the effect of bergenin on bladder cancer progression and its mechanism. The effect of bergenin on cell function was first detected, followed by assessing the changes of the epithelial-mesenchymal transition (EMT) in bergenin-treated cells. The effect of bergenin on peroxisome proliferator-activated receptor γ (PPARγ)/phosphatase and tensin homolog (PTEN)/Akt signal pathway was measured by Western blotting, followed by the rescue experiments. The results showed that bergenin treatment significantly decreased cell viability and increased G1 phase arrest, accompanied by reduced expression of Ki67, cycling D1, and cycling B1 in bladder cancer cells. Apoptosis was induced by bergenin in bladder cancer cells, as evidenced by increased Bax and cleaved caspase 3 protein levels and decreased Bcl-2 level in bergenin-treated cells. Meanwhile, the inhibition of the invasion, migration, and EMT was also observed in bergenin-treated cells. Mechanism studies showed that bergenin treatment could activate PPARγ/PTEN/Akt signal pathway, as evidence by the increased nucleus PPARγ and phosphatase and tensin homolog (PTEN) expression and decreased Akt expression. Moreover, PPARγ inhibitor administration inverted the effects of bergenin on bladder cancer cell function, including the proliferation, apoptosis, invasion, and migration in bladder cancer cells. Our findings revealed that bergenin could inhibit bladder cancer progression via activating the PPARγ/PTEN/Akt signal pathway, indicating that bergenin may be a potential therapeutic medicine for bladder cancer treatment.

Influences of Different Operative Methods on the Recurrence Rate of Non-Muscle-Invasive Bladder Cancer.

PURPOSE: To compare the influence of three operative approaches [transurethral en bloc resection of bladder tumor by pin-shaped electrode (pin-ERBT), transurethral resection of bladder tumor (TURBT) and transurethral holmium laser resection of bladder tumor (HoLRBT)] on the recurrence rate of non-muscle-invasive bladder cancer (NMIBC) at low dimension (i.e. diameter below 3 cm). MATERIALS AND METHODS: A retrospective analysis was conducted for a total of 115 patients affected by solitary NMIBC, with a diameter <3 cm, who were submitted to operation between March 2013 to May 2017. The patients were divided according to the operative method applied (pin-ERBT, TURBT and HoLRBT groups, respectively). The 2-year recurrence rate was compared among the three groups, and multivariat Cox hazard model analysis was applied to analyze the influencing factor(s) for postoperative recurrence. RESULTS: The 2-year recurrence rate was 10.0% in ERBT, 38.5% in TURBT and 40.0% in HoLRBT group, with a significant difference (P =0.014). According to the Cox hazard model analysis, age(HR=1.058, 95% CI: 1.019~1.098，P=0.003), operative method(HR=2.974,6.508, 95% CI: 0.862~10.255,1.657~25.566, P=0.023), smoking(HR=2.399, 95% CI: 1.147~5.017, P=0.020) and pathological grade(HR=2.012,95% CI: 1.279~3.165, P=0.002) were risk factors for postoperative recurrence of bladder cancer. CONCLUSION: Pin-ERBT can prominently decrease the postoperative recurrence rate of solitary NMIBC with a diameter <3 cm.

Circular RNA cir-ITCH Is a Potential Therapeutic Target for the Treatment of Castration-Resistant Prostate Cancer.

cir-ITCH, a well-known tumor-suppressive circular RNA, plays a critical role in different cancers. However, its expression and functional role in prostate cancer (PCa) are unclear. Herein, we explored the potential mechanism and tumor-inhibiting role of cir-ITCH in PCa. Using reverse transcriptase polymerase chain reaction assay, we analyzed the expression of cir-ITCH in PCa and paired adjacent nontumor tissue samples resected during surgical operation, as well as in two cell lines of human PCa (LNCaP and PC-3) and the immortalized normal prostate epithelial cell line (RWPE-1). Cell viability and migration of PCa cell lines were evaluated using CCK-8 and wound-healing assays. Expression of key proteins of the Wnt/ß-catenin and PI3K/AKT/mTOR pathways was detected using western blotting. We found that cir-ITCH expression was typically downregulated in the tissues and cell lines of PCa compared to that in the peritumoral tissue and in RWPE-1 cells, respectively. The results showed that cir-ITCH overexpression significantly inhibits the proliferation, migration, and invasion of human PCa cells and that reciprocal inhibition of expression occurred between cir-ITCH and miR-17. Proteins in the Wnt/ß-catenin and PI3K/AKT/mTOR pathways were downregulated by overexpression of cir-ITCH both in androgen receptor-positive LNCaP cells and androgen receptor-negative PC-3 cells. Taken together, these data demonstrated that cir-ITCH plays a tumor-suppressive role in human PCa cells, partly through the Wnt/ß-catenin and PI3K/AKT/mTOR pathways. Thus, cir-ITCH may serve as a novel therapeutic target for the treatment of PCa, especially castration-resistant prostate cancer.

CircPDE4B inhibits retinal pathological angiogenesis via promoting degradation of HIF-1α though targeting miR-181c.

Retinopathy of prematurity is a major cause of childhood blindness worldwide. Hence, exploring the proper treatment methods is a must in tacking this disease. qRT-PCR and western blot were used to detect the expression of genes and proteins, respectively. The proliferation of human retinal vascular endothelial cells (HRECs) was ensured by MTT assay. The luciferase activity was measured through luciferase assay. The inverted phase-contrast light microscope was used to observe the formation of a vascular tube. In the present study, our data demonstrated that circPDE4B was downregulated, while hypoxia-inducible factor-1α (HIF-1α) and VEGFA were upregulated in the retinopathy of prematurity model in vitro and in vivo. CircPDE4B increasing remarkably inhibited the expression of HIF-1α and VEGFA in hypoxia-induced HRECs and subsequent repressed cell proliferation and pathological angiogenesis. We further found that miR-181c suppressed the expression of von Hippel-Lindau (VHL), while circPDE4B could promote VHL expression via binding to miR-181c. Finally, our results revealed that circPDE4B inhibited the expression of VEGFA and pathological angiogenesis via facilitating VHL-mediated ubiquitin degradation of HIF-1α. In conclusion, circPDE4B suppressed the expression of VEGFA and pathological angiogenesis via promoting VHL-mediated ubiquitin degradation of HIF-1α through binding to miR-181c. Our study indicated that circPDE4B might be an effective therapeutic target of retinopathy of prematurity.

MYC predetermines the sensitivity of gastrointestinal cancer to antifolate drugs through regulating TYMS transcription.

BACKGROUND: Thymidylate synthase (TYMS) is a successful chemotherapeutic target for anticancer therapy. Numerous TYMS inhibitors have been developed and used for treating gastrointestinal cancer now, but they have limited clinical benefits due to the prevalent unresponsiveness and toxicity. It is urgent to identify a predictive biomarker to guide the precise clinical use of TYMS inhibitors. METHODS: Genome-scale CRISPR-Cas9 knockout screening was performed to identify potential therapeutic targets for treating gastrointestinal tumours as well as key regulators of raltitrexed (RTX) sensitivity. Cell-based functional assays were used to investigate how MYC regulates TYMS transcription. Cancer patient data were used to verify the correlation between drug response and MYC and/or TYMS mRNA levels. Finally, the role of NIPBL inactivation in gastrointestinal cancer was evaluated in vitro and in vivo. FINDINGS: TYMS is essential for maintaining the viability of gastrointestinal cancer cells, and is selectively inhibited by RTX. Mechanistically, MYC presets gastrointestinal cancer sensitivity to RTX through upregulating TYMS transcription, supported by TCGA data showing that complete response cases to TYMS inhibitors had significantly higher MYC and TYMS mRNA levels than those of progressive diseases. NIPBL inactivation decreases the therapeutic responses of gastrointestinal cancer to RTX through blocking MYC. INTERPRETATION: Our study unveils a mechanism of how TYMS is transcriptionally regulated by MYC, and provides rationales for the precise use of TYMS inhibitors in the clinic. FUNDING: This work was financially supported by grants of NKRDP (2016YFC1302400), STCSM (16JC1406200), NSFC (81872890, 81322034, 81372346) and CAS (QYZDB-SSW-SMC034, XDA12020210).

Benzene metabolite 1,2,4-benzenetriol changes DNA methylation and histone acetylation of erythroid-specific genes in K562 cells.

1,2,4-Benzenetriol (BT) is one of the phenolic metabolites of benzene, a general occupational hazard and ubiquitous environmental air pollutant with leukemogenic potential in humans. Previous studies have revealed that the benzene metabolites phenol and hydroquinone can inhibit hemin-induced erythroid differentiation in K562 cells. We investigated the roles of DNA methylation and histone acetylation in BT-inhibited erythroid differentiation in K562 cells. When K562 cells were treated with 0, 5, 10, 15 or 20 µM BT for 72 h, hemin-induced hemoglobin synthesis decreased in a concentration-dependent manner. Both 5-aza-2'-deoxycytidine (5-aza-CdR, DNA methyltransferase inhibitor) and trichostatin A (TSA, histone deacetylases inhibitor) could prevent 20 µM BT from inhibiting hemin-induced hemoglobin synthesis and the mRNA expression of erythroid genes. Exposure to BT changed DNA methylation levels at several CpG sites of erythroid-specific genes, as well as the acetylation of histone H3 and H4, chromatin occupancy of GATA-1 and recruitment of RNA polymerase II at α-globin and ß-globin gene clusters after hemin induction. These results demonstrated that BT could inhibit hemin-induced erythroid differentiation, where DNA methylation and histone acetylation also played important roles by down-regulating erythroid-specific genes. This partly explained the mechanisms of benzene hematotoxicity.

High glucose induced endothelial to mesenchymal transition in human umbilical vein endothelial cell.

BACKGROUND: Studies have shown that endothelial-to-mesenchymal transition (EndMT) could contribute to the progression of diabetic nephropathy, diabetic renal fibrosis, and cardiac fibrosis. The aim of this study was to investigate the influence of high glucose and related mechanism of MAPK inhibitor or specific antioxidant on the EndMT. METHODS: In vitro human umbilical vein endothelial cells (HUVEC) were cultured with 11mM, 30mM, 60mM and 120mM glucose for 0, 24, 48, 72 and 168h. Endothelial cell morphology was observed with microscope, and RT-PCR was used to detect mRNA expression of endothelial markers VE-cadherin and CD31, mesenchymal markers α-SMA and collagen I, and transforming growth factor TGF-ß1. Immunofluorescence staining was performed to detect the expression of CD31 and α-SMA. The concentration of TGF-ß1 in the supernatant was detected by ELISA. ERK1/2 phosphorylation level was detected by Western blot analysis. RESULTS: High glucose induced EndMT and increased the TGF-ß1 level in HUVEC cells. Cells in high glucose for 7 days showed a significant decrease in mRNA expression of CD31 and VE-cadherin, and a significant increase in that of α-SMA and collagen I, while lost CD31 staining and acquired α-SMA staining. ERK signaling pathway blocker PD98059 significantly attenuated the high glucose-induced increase in the ERK1/2 phosphorylation level. PD98059 and NAC both inhibited high glucose-induced TGF-ß1 expression and attenuated EndMT marker protein synthesis. CONCLUSION: High glucose could induce HUVEC cells to undergo EndMT. NAC and ERK signaling pathway may play important role in the regulation of the TGF-ß1 biosynthesis during high glucose-induced EndMT.

Phenolic metabolites of benzene induced caspase-dependent cytotoxicities to K562 cells accompanied with decrease in cell surface sialic acids.

Benzene-induced erythropoietic depression has been proposed to be due to the production of toxic metabolites. Presently, the cytotoxicities of benzene metabolites, including phenol, catechol, hydroquinone, and 1,2,4-benzenetriol, to erythroid progenitor-like K562 cells were investigated. After exposure to these metabolites, K562 cells showed significant inhibition of viability and apoptotic characteristics. Each metabolite caused a significant increase in activities of caspase-3, -8, and -9, and pretreatment with caspase-3, -8, and -9 inhibitors significantly inhibited benzene metabolites-induced phosphatidylserine exposure. These metabolites also elevated expression of Fas and FasL on the cell surface. After exposure to benzene metabolites, K562 cells showed an increase in reactive oxygen species level, and pretreatment with N-acetyl-l-cysteine significantly protected against the cytotoxicity of each metabolite. Interestingly, the control K562 cells and the phenol-exposed cells aggregated together, but the cells exposed to other metabolites were scattered. Further analysis showed that hydroquione, catechol, and 1,2,4-benzenetriol induced a decrease in the cell surface sialic acid levels and an increase in the cell surface sialidase activity, but phenol did not cause any changes in sialic acid levels and sialidase activity. Consistently, an increase in expression level of sialidase Neu3 mRNA and a decrease in mRNA level of sialyltransferase ST3GAL3 gene were detected in hydroquione-, catechol-, or 1,2,4-benzenetriol-treated cells, but no change in mRNA levels of two genes were found in phenol-treated cells. In conclusion, these benzene metabolites could induce apoptosis of K562 cells mainly through caspase-8-dependent pathway and ROS production, and sialic acid metabolism might play a role in the apoptotic process.