EXPRESSION PROFILE OF miR-145, -182, -21, -27a, -29b, and -34a IN BREAST CANCER PATIENTS OF YOUNG AGE

BACKGROUND

Breast cancer (BC) in young women remains a significant public health concern. While progress has been made in understanding the etiology, diagnosis, and treatment of BC in this population, challenges persist. The identification and utilization of prognostic biomarkers offer valuable tools for tailoring treatment strategies and improving outcomes for BC patients.

AIM

To evaluate the relationship between the expression of tumor-associated microRNAs and the clinical and pathological features of BC in young patients.

MATERIALS AND METHODS

The work is based on the results of the examination and treatment of 50 women younger than 45 years with stage I-II BC. miR-145, -182, -21, -27a, -29b, and -34a expression in tumor samples was analyzed by the real-time reverse transcription polymerase chain reaction.

RESULTS

Higher expression of miR-182, -21, and -29b and lower levels of miR-27a were associated with tumor stage in young BC patients. Patients without lymph node metastases (N0) had significantly higher levels of miR-182, -27a, and -34a and lower levels of miR-29b compared to N1 cases (p < 0.05). Expression of miR-145, -182, -21, -27a, and -29b was associated with molecular BC subtypes.

CONCLUSION

Obtained results show that a high malignancy degree of BC in young women is associated with an increase in the miR-182, -21, -29b, and -34a expressions and a decrease in the miR-27a level in the tumor tissue, which indicates the prospects of the use of them for predicting the aggressiveness of the disease.

MATERIALS OF NOBEL SYMPOSIUM 175: PRECISION MEDICINE TRANSFORMS HEALTHCARE: A NEW TRAJECTORY FOR RESEARCH AND INNOVATION SEPTEMBER 20-22, 2023, STOCKHOLM, SWEDEN

Nobel Symposium 175 was organized by Professor Richard Rosenquist Brandell of Karolinska Institutet and was supported by the Royal Swedish Academy of Sciences. The focus of the symposium was a discussion on the development of precision medicine in infectious and rare diseases, cancer, and complex diseases. Presentations and discussions concerned new technologies, bioinformatics, and new diagnostic and therapeutic approaches based on findings in basic research. Organization of precision medicine models and their implementation in medical practice at the national and international levels were also on the agenda. 29 scientists from different fields of medicine presented their work during a three-day exciting trip into the future of patient' care. Panel discussions shed light on the development of precision medicine for better treatment of patients.

FEATURES OF COL1A1 EXPRESSION IN BREAST CANCER TISSUE OF YOUNG PATIENTS

BACKGROUND

In the last decades, the incidence of breast cancer (BCa) in young women has been increasing steadily. The quantitative indicators of expression of collagen, which play important role in stromal microenvironment, and their association with the age and survival rates of BCa patients have not been yet definitively clarified.

AIM

To investigate the relationship between the COL1A1 gene expression at the mRNA and protein levels in BCa tissue and the clinicopatological features and survival rates of BCa patients of different age groups.

MATERIALS AND METHODS

The study was conducted on the clinical material of 50 patients with stage I-III BCa. COL1A1 gene expression at the mRNA and protein levels in BCa tissue were studied using the real-time PCR and immunohistochemical methods, as well as the bioinformatic analysis (UALCAN and Kaplan - Meier Plotter databases).

RESULTS

The bioinformatic analysis showed that BCa tissue is characterized by 6.0 times (p < 0.05) higher level of COL1A1 mRNA compared to normal breast tissue. The correlation of COL1A1 expression at the mRNA and protein levels with the molecular subtype of neoplasms was demonstrated. According to Kaplan - Meier Plotter database, a low level of expression of COL1A1 protein level in BCa tissue is associated with lower rates of relapse-free survival of patients. The ex vivo study of the clinical material revealed a decrease in COL1A1 protein expression in tumor tissue of young patients with BCa of T3 category (p < 0.0374), low differentiation grade (p < 0.0163) and basal molecular subtype (p < 0.0001). A correlation between the expression of COL1A1 at the mRNA and protein levels and the expression status of estrogen receptors (p < 0.0001) and progesterone receptors (p < 0.0040) was established. The relapse-free 3-year survival rate of young BCa patients is significantly lower in the presence of a low COL1A1 optical density index in the tumor tissue.

CONCLUSIONS

The identified relationship between COL1A1 expression and such indicators of BCa malignancy as tumor size, differentiation grade, molecular subtype, receptor status, and the recurrencefree survival of patients indicates the prospects of its use to predict the aggressiveness of the BCa course in young patients.

DIFFERENTIAL EXPRESSION PATTERN OF AIP, UCKL1, AND PKN1 GENES IN PROSTATE CANCER PATIENTS

BACKGROUND

The evolution of research on the therapy of prostate cancer (PC) depends on a study of molecules that are involved in the progression of this disease. Nevertheless, there is a need for additional biomarkers that would help to refine the molecular profile of PC and propose the personalized therapeutic approach.

AIM

To study differential expression patterns of the AIP, UCKL1, and PKN1 genes in blood sera and tumor tissue of patients with PC with different Gleason scores.

MATERIALS AND METHODS

The total extracellular RNA was isolated from blood sera of 44 PC patients and 4 healthy donors. cDNAs were synthesized and quantitative polymerase chain reaction (qPCR) was performed. Immunohistochemical study of the UCKL, AIP and PKN1 proteins was performed on deparaffinized sections of tumors. The study was supplemented by a bioinformatic analysis of the publicly available databases.

RESULTS

The UCKL1, AIP, PKN1 genes were overexpressed at the mRNA level in blood sera of PC patients, compared to healthy donors. Extracellular mRNA levels of AIP and UCKL-1 were 100-1000-fold increased in all PC samples compared to the healthy donors but without significant inequality between the groups of PC cases differing by the Gleason score. The highest levels were detected in the samples from PC patients with the Gleason score > 9. The PKN1 expression was higher in PC patients compared with healthy donors but without significant difference between the groups.

CONCLUSIONS

From the three chosen genes, AIP and UCKL1 showed similar pattern of expression assessed either by extracellular mRNA levels in patient sera or the protein in PC tissues. AIP was up to 1000-fold increased in all PC samples, compared to the healthy donors, with the highest levels in PC cases with Gleason score > 9. Expression levels of the AIP and UCKL1 genes in the PC patient sera may be used as an additional criterion for prognosis of tumor progression.

EXPRESSION OF MARKERS OF BONE TISSUE REMODELING IN BREAST CANCER AND PROSTATE CANCER CELLS IN VITRO

The aim of the study was to compare the expression of markers of bone remodeling in vitro in breast cancer (BCa) cells and prostate cancer (PCa) cells varying in their malignancy phenotype.

MATERIALS AND METHODS

The study was performed on human BCa cells (MCF-7 and MDA-MB-231 lines) and PCa cells (LNCaP and DU-145 lines). Expression levels of bone tissue remodeling proteins (osteopontin (OPN), osteonectin (ON) and bone morphogenetic protein 7 (BMP-7) were determined immunocytochemically. The mRNA levels of bone tissue remodeling proteins OPN (SPP1), ON (SPARC), BMP-7 (BMP7)) and miRNA-10b, -27a, -29b, -145, -146a were assessed by quantitative reverse transcription polymerase chain reaction. To search for miRNAs involved in the regulation of target genes, miRNet v. 2.0 resource was used.

RESULTS

We have shown that highly malignant MDA-MB-231 cells are characterized by significantly higher expression of OPN and ON on the background of decreased SPARC and BMP7 mRNA expression. In highly malignant DU-145 cells, ON and SPP1, SPARC, and BMP7 mRNA expression was significantly higher compared with low malignant LNCaP cells. MDA-MB-231 line was characterized by significantly higher expression of miRNA-10b, -27a, -29b, -145 and -146a. In DU-145 cells, significantly lower levels of expression of miRNAs-27a and -145 against the background of increasing levels of miRNAs-29b and -146a were recorded.

CONCLUSION

High malignancy phenotype of the BCa and PCa cells is characterized by high levels of expression of bone remodeling proteins, which may be caused by impaired regulation of their expression at the epigenetic level.

Differential expression patterns of AIP, UCKL1, and PKN1 genes in breast cancer of different molecular subtypes

BACKGROUND

Classification of breast cancer (BC) in the molecular subtypes had the enormous impact on the development of the individualized therapy. Nevertheless, there is a need for additional biomarkers that would help to refine molecular subtypes of BC and propose the therapeutic approach for each patient.

AIM

To study differential expression patterns of AIP, UCKL1, and PKN1 genes in blood sera and tumor tissue of patients with BC of different molecular subtypes.

MATERIALS AND METHODS

The total extracellular RNA was isolated from serum of 26 BC patients. cDNAs was synthesized and quantitative polymerase chain reaction was performed. Also, immunohistochemical studies of UCKL, AIP and PKN1 were performed on deparaffined tissue sections. The study was supplemented by a bioinformatic analysis of the publicly available databases.

RESULTS

AIP and UCKL-1 extracellular mRNA levels were 100-1000-fold increased in blood sera of all BC patients, compared to the healthy donors. The highest levels were detected in the luminal A and HER2 (ERRB2) BC subtypes. The highest levels of PKN1 were detected blood sera of the patients with luminal B and basal subtypes; its expression levels were just 10-100-fold higher in BC samples compared to healthy donors.

CONCLUSIONS

The UCKL1, AIP, PKN1 genes are overexpressed at the mRNA level in blood sera of BC patients compared to the sera of healthy individuals. Among three genes under study, only for the AIP gene, the pattern of extracellular mRNA expression in sera paralleled to protein expression in BC tissues of each specified molecular subtype.

Expression pattern of MRPS18 family genes in malignantly transformed b-cells

AIM

To compare expression patterns of proteins of a family of mitochondrial ribosomal protein S18 (MRPS18) in tumor cell lines of the B-cell origin.

MATERIALS AND METHODS

The study has been performed on different subsets of tonsil B-cells and tumor cell lines of the B-cell origin using quantitative polymerase chain reaction analysis, western blot analysis, immunohistochemistry, bioinformatic analysis of the publicly available data bases on expression.

RESULTS

We have found that genes of the MRPS18 family (1-3) show different expression patterns in tumor cell lines of the B-cell origin. The highest levels of expression were shown for MRPS18-3, the lowest - for MRPS18-1. MRPS18-2 was expressed at the highest levels in germinal center cells, Burkitt lymphoma and Hodgkin lymphoma cell lines. At the protein levels, MRPS18-2 showed the highest expression in Burkitt lymphoma and B-cell precursor acute lymphoblastic leukemia cell lines. In lymphoblastoid cell lines, and in germinal center B-cells MRPS18-2 levels were somewhat lower, but higher than in memory and plasma B-cells.

CONCLUSIONS

The differential expression pattern of the MRPS18 family proteins suggests that they play various roles in cellular processes.

The TGF-beta - SMAD pathway is inactivated in cronic lymphocytic leukemia cells

AIM

To study the status of the tumor growth factor beta (TGFB) pathway in chronic lymphocytic leukemia (CLL) cells and to uncover molecular details underlying CLL cell genesis.

OBJECTS AND METHODS

The study was conducted on peripheral blood samples of patients with CLL using the following methods: RNA isolation, analysis of expression of transcription factors using RT2 profiler assay, bioinformatics analysis of publicly available data bases on expression.

RESULTS

We have shown that the TGFB - SMAD canonical pathway is not active in CLL cells. SMAD-responsive genes, such as BCL2L1 (BCL-XL), CCND2 (Cyclin D2), and MYC, are down-regulated in CLL cells compared with peripheral blood B cells of healthy donors.

CONCLUSIONS

The TGFB-mediated signaling is not active in CLL cells due to low (or absent) expression of SMAD1, -4, -5, -9, and ATF-3. Expression and phosphorylation status of SMAD2 and -3 should be further elucidated in the future studies.

Expression Levels of the Uridine-Cytidine Kinase Like-1 Protein As a Novel Prognostic Factor for Hepatitis C VirusAssociated Hepatocellular Carcinomas

The expression levels of the two novel oncoproteins uridine-cytidine kinase like-1 (UCKL-1) and mitochondrial ribosomal protein S18-2 (MRPS18-2) were assessed in samples of hepatitis C virus (HCV)-associated hepatocellular carcinoma (HCC) using immunohistochemistry. Tissue microarray (TMA) paraffin blocks were prepared from 42 HCC tumor samples with the corresponding peri-tumor tissues and from 11 tissues of a liver with HCV-induced cirrhosis. We found that the UCKL-1 signal in the liver tissues of the peri-tumor zone in the HCC samples was stronger than that in cirrhosis (50 49.44 vs. 24.27 14.53; p = 0.014). The MRPS18-2 expression was weak, and there was no differences between the groups (p = 0.26). Noteworthy, the UCKL-1 protein was expressed at higher levels in peri-tumor tissues in the cases of HCC recurrence; this was confirmed for 27 older patients (63.78 9.22 vs. 53.53 4.07 years, p 0.001), in parallel with enhanced UCKL-1 staining in former HCC nodules (62.69 50.4 vs. 26.0 30.19, p = 0.006) and microvascular invasion (p = 0.02). A multivariate analysis of prognostic factors for HCC recurrence showed that the best predictive factors for these conditions were UCKL-1 expression in tumor, vascular invasion, and HCC treatment modality, other than liver transplantation (odds ratios: 1.029, 18.143 and 11.984, R = 0.633, p = 0.002). In conclusion, the high UCKL-1 expression might be a prognostic factor for HCC relapse, in combination with age and microvascular invasion. MRPS18-2 protein expression has no prognostic significance in the cases of HCV-associated HCC.

Do MRPS18-2 and RB proteins cooperate to control cell stemness and differentiation, preventing cancer development?

In childhood tumors, including retinoblastoma, osteosarcoma, and neuroblastoma, the RB-E2F1 pathway is inactivated, as a rule. These tumors arise from precursor cells that fail to undergo the terminal differentiation. Noteworthy, the RB1-encoded protein (RB) does not control the cell cycle in embryonic stem cells. It has not been yet well understood how RB controls cell stemness and differentiation. The question arises why "inactive" RB is required for the survival and stemness of cells? Recently, we have found that overexpression of the RB-binding protein MRPS18-2 (S18-2) in primary fibroblasts leads to their immortalization, which is accompanied by the induction of embryonic stem cell markers and, eventually, malignant transformation. We suggest that cell stemness may be associated with high expression levels of both proteins, RB and S18-2. There must be a strict regulation of the expression levels of S18-2 and RB during embryogenesis. Disturbances in the expression of these proteins would lead to the abnormalities in development. We think that the S18-2 protein, together with the RB, plays a crucial role in the control on cell stemness and differentiation. We hope to uncover the new mechanisms of the cell fate determination. The S18-2 may serve as a new target for anticancer medicines, which will help to improve human health.

Expression Levels of the Uridine-Cytidine Kinase Like-1 Protein As a Novel Prognostic Factor for Hepatitis C Virus-Associated Hepatocellular Carcinomas

The expression levels of the two novel oncoproteins uridine-cytidine kinase like-1 (UCKL-1) and mitochondrial ribosomal protein S18-2 (MRPS18-2) were assessed in samples of hepatitis C virus (HCV)-associated hepatocellular carcinoma (HCC) using immunohistochemistry. Tissue microarray (TMA) paraffin blocks were prepared from 42 HCC tumor samples with the corresponding peri-tumor tissues and from 11 tissues of a liver with HCV-induced cirrhosis. We found that the UCKL-1 signal in the liver tissues of the peri-tumor zone in the HCC samples was stronger than that in cirrhosis (50 ± 49.44 vs. 24.27 ± 14.53; p = 0.014). The MRPS18-2 expression was weak, and there was no differences between the groups (p = 0.26). Noteworthy, the UCKL-1 protein was expressed at higher levels in peri-tumor tissues in the cases of HCC recurrence; this was confirmed for 27 older patients (63.78 ± 9.22 vs. 53.53 ± 4.07 years, p < 0.001), in parallel with enhanced UCKL-1 staining in former HCC nodules (62.69 ± 50.4 vs. 26.0 ± 30.19, p = 0.006) and microvascular invasion (p = 0.02). A multivariate analysis of prognostic factors for HCC recurrence showed that the best predictive factors for these conditions were UCKL-1 expression in tumor, vascular invasion, and HCC treatment modality, other than liver transplantation (odds ratios: 1.029, 18.143 and 11.984, R² = 0.633, p = 0.002). In conclusion, the high UCKL-1 expression might be a prognostic factor for HCC relapse, in combination with age and microvascular invasion. MRPS18-2 protein expression has no prognostic significance in the cases of HCV-associated HCC.

Number of Langerhans cells is decreased in premalignant keratosis and skin cancers

BACKGROUND

It was shown earlier that a number of CD207 positive Langerhans cells was lower in basal cell carcinomas than in the normal epidermis. Moreover, benign skin lesions presented a higher number of Langerhans cells when they were compared to malignant tumors.

AIM

To count Langerhans cells, assessing expression levels of CD1A and CD207 markers in actinic keratosis, basal and squamous cell carcinomas, compared with the normal skin. Comparison of Langerhans cells might give a valuable prognostic marker for skin cancer.

METHODS

Immunohistochemistry and methods of statistics were used.

RESULTS

Expression of CD1A and CD207 markers was assessed in tumor samples of actinic keratosis, cutaneous basal and squamous cell carcinomas, in comparison with the normal skin. In each cohort there were 40 patients (and 11 healthy individuals). We have shown that the number of Langerhans cells is considerably lower in cutaneous basal and squamous cell carcinomas, compared with their number in the normal skin (p < 0.0001).

CONCLUSIONS

CD1A expression correlated with CD207 expression only in the control group. There was no correlation in actinic keratosis, basal and squamous cell carcinoma. This may suggest an alteration of Langerhans cells phenotype in skin neoplastic diseases, making the number of Langerhans cells a valuable prognostic factor for skin tumors.

Stem cell gene expression in MRPS18-2-immortalized rat embryonic fibroblasts

We have recently found that primary rat embryonic fibroblasts (REFs) could be immortalized by overexpression of the human mitochondrial ribosomal protein MRPS18-2 (S18-2). A derived cell line, designated 18IM, expressed the embryonic stem cell markers SSEA-1 and Sox2. Upon inoculation into severe combined immunodeficiency mice, 18IM cells differentiated to express pan-keratin. They were not tumorigenic. Here we report the gene profiling of 18IM, compared with REF cells. Pathways involved in oxidative phosphorylation, ubiquinone (Coenzyme Q 10) biosynthesis, fatty acid elongation in mitochondria, PI3K/AKT signaling, a characteristic of rapidly proliferating cells, were upregulated in 18IM. Genes involved in the transcription/translation machinery and redox reactions, like elongation factors, ATP synthases, NADH dehydrogenases, mitogen activated kinases were upregulated as well. 18IM cells produced more pyruvate, indicating enhanced ATP synthesis. The expression of Oct4, Sox2, and Nanog that can contribute to the experimental induction of pluripotency in primary fibroblasts was also elevated, in contrast to Klf4 and C-myc that were downregulated. Subsequently, three new immortalized cell lines were produced by S18-2 overexpression in order to check the representativeness of 18IM. All of them showed anchorage-independent growth pattern. Two of three clones lost vimentin and smooth muscle actin, and expressed Sox2 and Oct4. We suggest that S18-2 is involved in the developmental regulation.

CD150-mediated Akt signalling pathway in normal and malignant B cells

AIM

To study upstream and downstream events in CD150-mediated Akt signaling pathway in normal human B cells, EBV-transformed lymphoblastoid (LCL) and malignant Hodgkin's lymphoma (HL) B cell lines.

METHODS

To access protein-protein interaction we applied immunoprecipitation, Western blot analysis and surface plasmon resonance (SPR) technique. A novel modification of SPR technique using reduced glutathione bound to golden surface was proposed. Immunostaining and isolation of cytoplasmic fractions and nuclear extracts were performed to detect proteins' localization in cells. Western blot analysis was performed to follow up the phosphorylation of proteins on specific sites and proteins' expression level.

RESULTS

It was shown that CD150 ligation induced Akt activation in normal tonsillar B cells (TBC), SH2D1A positive LCL and HL B cell lines. The p85α subunit of PI3K co-precipitated with CD150 cytoplasmic tail. This direct association depends on tyrosine phosphorylation and is mediated by N terminal SH2 domain of p85α. CD150 initiated phosphorylation of FoxO1 transcription factor in normal B cells as well as in LCL MP-1 and HL cell line L1236. At the same time, CD150 ligation triggered GSK-3β kinase phosphorylation only in immortalized LCL MP-1 and HL cell line L1236.

CONCLUSIONS

We have demonstrated that CD150 receptor could trigger PI3K-mediated Akt signaling pathway in normal, EBV-transformed and malignant B cells. CD150-mediated phosphorylation of Akt downstream targets GSK-3β and FoxO1 in EBV-transformed and HL cells could be one of the mechanisms to avoid apoptosis and support survival program in these immortalized B cells.

Nuclear receptors and their role in Epstein -- Barr virus induced B cell transformation

Epstein - Barr virus (EBV) is a lymphotropic virus that infects more than 90% of the human population, and targets B cells for infection. Infection of human B cells leads to the malignant transformation and eventual immortalization. In latency III infection six EBV-encoded nuclear antigens (EBNAs) and three latent membrane proteins (LMPs) are expressed in the transformed cells that can grow as a lymphoblastoid cell lines in vitro . These proteins hijack the normal B cell growth pathways by activating the constitutive growth promotion and external survival signals. We have determined a set of the nuclear receptors that are up- (and down-) regulated in the latency III infected cells at the mRNA level. In the present paper we discussed the possible role of these receptors in B cell transformation upon EBV infection based on the literature data.

Expression profile of nuclear receptors upon Epstein -- Barr virus induced B cell transformation

BACKGROUND

Infection of human B cells with Epstein - Barr virus (EBV) induces metabolic activation, morphological transformation, cell proliferation and eventual immortalization.

AIM

To identify the nuclear receptors, which are the cellular interaction partners of EBNAs, that will help to elucidate the mechanism of B cell transformation.

METHODS

We have compared the nuclear receptor profile in the naïve and EBV-transformed B-lymphocytes, using TaqMan LDA microfluidic card technology.

RESULTS

Out of 48 nuclear receptor, 17 showed differential expression at the mRNA level. The expression of 5 genes was elevated in EBV-transformed cells, whereas 12 genes were downregulated in lymphoblastoid cells (LCLs). 7 genes were studied at the protein level; 2 genes were up regulated (Nr2F2 and RARA) and 4 genes were down regulated (ERB, NUR77, PPARG, and VDR) in LCLs.

CONCLUSION

The nuclear receptor profiling on EBV infected B cells showed alterations of nuclear receptors expression at both mRNA and protein levels compared with non infected peripheral blood cells. Further analysis on a possible role of each nuclear receptor in EBV induced cell transformation should be performed.

Immunofluorescence staining of paraffin sections: creating DAB staining like virtual digital images using CMYK color conversion

Crystal violet treatment of formalin fixed paraffin embedded tissue slides greatly reduces the endogenous autofluorescence, and allows immunofluorescence (IF) staining with FITC or Alexa488 conjugated antibodies. Using cold CCD camera to capture the fluorescence images makes this staining method very sensitive. Here we show that combination of IF with the simultaneous recording of crystal violet induced red and Hoechst 33258 induced blue fluorescence permits the localization of the IF signal over a cytoplasmic: nuclear red:blue stain that visualizes the microscopic anatomy of the underlying tissue. To make the visual interpretation of the IF staining easier for microscopists, who are used to DAB staining over weak hematoxilin-eosin background, we created a simple color conversion procedure that turns the captured three-color fluorescence RGB (red, green, blue) images over a black background into four color CMYK (cyan, magenta, yellow, key color (black)) images.

Epstein-Barr virus encoded nuclear protein EBNA-3 binds XAP-2, a protein associated with Hepatitis B virus X antigen

EBNA-3 (also called EBNA-3A) is one of the EBV encoded nuclear antigens that are necessary for B-cell transformation. EBNA-3 is known to target RBPs, nuclear proteins that also interacts with EBNA-2, EBNA-4 and EBNA-6. In order to identify additional EBNA-3 targets, an EBV-transformed human lymphocyte cDNA library was screened in the yeast two-hybrid system with N-terminus truncated EBNA-3 that cannot interact with RBP-Jkappa. A clone, encoding Xap-2 protein, a cellular partner of Hepatitis B virus X-antigen was isolated. This protein is also known as the p38 subunit of the aryl hydrocarbon receptor complex (ARA9). The specific binding to EBNA-3 was confirmed by showing that the GST-Xap-2 precipitated EBNA-3 from CV1 cells that were infected with recombinant vaccinia virus expressing EBNA-3. Deletion of the C-terminus of Xap-2 eliminated the binding. Fusion with green fluorescent protein showed that Xap-2 is preferentially cytoplasmic but translocates to the nucleus upon expression of EBNA-3.

Epstein-Barr virus infection and mitogen stimulation of normal B cells induces wild-type p53 without subsequent growth arrest or apoptosis

Infection of human B lymphocytes with Epstein-Barr virus (EBV) in vitro induces a G0 to G1 transition followed by DNA synthesis and cell division. The virus activation of the cell cycle closely mimics the antigen-dependent normal B cell activation pathway. Infected B cells undergo blast transformation followed by the emergence of immortalized lymphoblastoid cell lines. Numerous cellular proteins are switched on in the infected cells, including p53. In view of the frequent association of wild-type p53 (wtp53) expression with growth arrest and apoptosis, p53 expression, cell viability (absence of apoptosis) and cell cycle progression at the single cell level during the first week after EBV infection were assessed. The rate of EBV infection was scored by EBNA-5 staining between 20 and 72 h after infection and varied between 20 and 25% of the cell population. All EBNA-5-positive blasts were p53-positive as well. Double staining for p53 and for DNA ends (TUNEL) revealed that p53-positivity and apoptosis were mutually exclusive. Quantification of the DNA content by Hoechst staining and computer-assisted image analysis showed that a fraction of the p53-positive blasts had a DNA content higher than 2N, indicating entry into the S/G2 phases. Double p53 and BrdU staining of the cells, pulse-labelled with BrdU, revealed that 65% of the p53-positive blasts were in S phase 3 days after infection. Similarly, B cell activation by CD40L and IL-4 induced p53 expression without any adverse effect on cell cycle progression. Therefore, the phenomenon is not EBV-specific but correlates with immunoblast activation.

Epstein-Barr virus-encoded nuclear protein EBNA-3 interacts with the epsilon-subunit of the T-complex protein 1 chaperonin complex

OBJECTIVE

To find cellular proteins that associate with EBNA-3 (also called EBNA-3A), one of the Epstein-Barr virus (EBV)-encoded growth transformation-associated nuclear proteins.

METHODS

Screening human cDNA libraries in the yeast two-hybrid system and performing an analysis of interaction in vitro as well as in cell lysates.

RESULTS

EBNA-3 binds to the epsilon subunit of the chaperonin containing T-complex protein 1 (epsilon-TCP-1) in the yeast two-hybrid system. The cDNA clone isolated from a human lymphocyte library was found to encode the middle and C-terminal part of epsilon-TCP-1. The interaction was confirmed by showing that a GST fusion protein specifically precipitated EBNA-3 from CV1 cells infected with recombinant vaccinia virus expressing EBNA-3. The interacting region was mapped to the putative apical domain of epsilon-TCP-1.

CONCLUSIONS

This study shows that large, virus-encoded transforming proteins such as EBNA-3 may receive help for their initial folding by chaperonin complexes. The recognition of the chaperonin complex likely occurs through specific interaction with one of the subunits. We suggest that nascent EBNA-3 may recognize the TCP-1 complex by interacting with the apical region of the epsilon subunit.

Role of p53 mutation in polyomavirus-induced tumorigenesis

Small DNA tumour viruses, such as simian virus 40 (SV40), papilloma viruses and adenoviruses, encode proteins that form complexes with and inactivate the p53 and retinoblastoma (RB) proteins. This convergent evolution reflects the common need of these viruses to inactivate these two important regulators of cell cycle progression and cell survival. Polyomavirus, a close relative of SV40, is different. Its large T protein complexes only with RB, not with p53. We have examined whether this is compensated by the frequent appearance of p53 mutations in polyomavirus-induced tumours. We tested the p53 status of 15 polyomavirus-induced sarcomas. Two sarcomas were p53-negative while six carried mutant p53. Another six sarcomas expressed low levels of wild-type p53. One tumour expressed high levels of wild-type p53 protein as shown by DNA sequencing and immunofluorescence staining. MDM2 amplification was not detected in any of the tumours, but Northern blotting showed that MDM2 was overexpressed in at least two tumours that expressed wild-type p53 and in one tumour that expressed both wild-type and mutant p53. Treatment with the DNA-damaging agent mitomycin C caused p53 protein accumulation followed by induction of MDM2 and WAF1/p21 mRNA in four of the tumours expressing wild-type p53, indicating that p53-mediated transcriptional activation was unaltered in these tumours. However, p53-mediated transactivation of WAF1/p21 was impaired in the wild-type p53-expressing tumours that expressed elevated levels of MDM2. These results demonstrate that p53 mutation and inactivation are frequently but not invariably involved in polyomavirus-induced tumorigenesis.

Infrequent MDM2 gene amplification and absence of gross WAF1 gene alterations in nasopharyngeal carcinoma

We have investigated the possible involvement of MDM2 and WAF1 gene alterations in the development of nasopharyngeal carcinoma (NPC). MDM2 and WAF1 were analysed in 46 primary NPCs by Southern blot analysis. Forty-five tumours showed a normal EcoRI hybridisation pattern and hybridisation intensity with a human MDM2 cDNA probe. One tumour had more intense normal size MDM2 hybridising bands. Densitometric scanning revealed a 10-12-fold MDM2 gene amplification, as compared with human placenta DNA. All 46 tumours showed normal size WAF1 EcoRI bands that hybridised with normal intensity. This is the first demonstration of MDM2 gene amplification in NPC. Nonetheless, our analysis indicates that gross structural alterations of the MDM2 and WAF1 genes are infrequent events in the genesis of NPC.

p53 binds single-stranded DNA ends through the C-terminal domain and internal DNA segments via the middle domain

We have previously reported that wild-type p53 can bind single-stranded (ss) DNA ends and catalyze renaturation of ss complementary DNA molecules. Here we demonstrate that p53 can also bind to internal segments of ss DNA molecules via a binding site (internal DNA site) distinct from the binding site for DNA ends (DNA end site). Using p53 deletion mutants, the internal DNA site was mapped to the central region (residues 99-307), while the DNA end site was mapped to the C-terminal domain (residues 320-393) of the p53 protein. The internal DNA site can be activated by the binding of ss DNA ends to the DNA end site. The C-terminal domain alone was sufficient to catalyze DNA renaturation, although the central domain was also involved in promotion of renaturation by the full-length protein. Our results suggest that the interaction of the C-terminal tail of p53 with ss DNA ends generated by DNA damage in vivo may lead to activation of non-specific ss DNA binding by the central domain of p53.