Induction of indoleamine 2,3-dioxygenase 1 expression in neurons of the central nervous system through inhibition of histone deacetylases blocks the progression of experimental autoimmune encephalomyelitis.

BACKGROUND: A wide array of histone deacetylase (HDAC) inhibitors and aryl hydrocarbon receptor (AHR) agonists commonly arrest experimental autoimmune encephalomyelitis (EAE). However, it is not known whether HDAC inhibition is linked to the AHR signaling pathway in EAE. METHODS: We investigated how the pan-HDAC inhibitor SB939 (pracinostat) exerted immunoregulatory action in the myelin oligodendrocyte glycoprotein 35-55 (MOG35-55)-induced EAE mouse model by evaluating changes in of signal transducer and activator of transcription 3 (STAT3) acetylation and the expression of indoleamine 2,3-dioxygenase 1 (IDO1) and AHR in inflamed spinal cords during EAE evolution. We proved the involvement of IDO1 and the AHR in SB939-mediated immunosuppression using Ido1-/- and Ahr-/- mice. RESULTS: Administration with SB939 halted EAE progression, which depended upon IDO1 expression in neurons of the central nervous system (CNS). Our in vitro and in vivo studies demonstrated that SB939 sustained the interleukin-6-induced acetylation of STAT3, resulting in the stable transcriptional activation of Ido1. The therapeutic effect of SB939 also required the AHR, which is expressed mainly in CD4+ T cells and macrophages in CNS disease lesions. Finally, SB939 was shown to markedly reduce the proliferation of CD4+ T cells in inflamed neuronal tissues but not in the spleen or draining lymph nodes. CONCLUSIONS: Overall, our results suggest that IDO1 tryptophan metabolites produced by neuronal cells may act on AHR in pathogenic CD4+ T cells in a paracrine fashion in the CNS and that the specific induction of IDO1 expression in neurons at disease-afflicted sites can be considered a therapeutic approach to block the progression of multiple sclerosis without affecting systemic immunity.

Histone modification-dependent production of peptide hormones facilitates acquisition of pluripotency during leaf-to-callus transition in Arabidopsis.

Chromatin configuration is critical for establishing tissue identity and changes substantially during tissue identity transitions. The crucial scientific and agricultural technology of in vitro tissue culture exploits callus formation from diverse tissue explants and tissue regeneration via de novo organogenesis. We investigated the dynamic changes in H3ac and H3K4me3 histone modifications during leaf-to-callus transition in Arabidopsis thaliana. We analyzed changes in the global distribution of H3ac and H3K4me3 during the leaf-to-callus transition, focusing on transcriptionally active regions in calli relative to leaf explants, defined by increased accumulation of both H3ac and H3K4me3. Peptide signaling was particularly activated during callus formation; the peptide hormones RGF3, RGF8, PIP1 and PIPL3 were upregulated, promoting callus proliferation and conferring competence for de novo shoot organogenesis. The corresponding peptide receptors were also implicated in peptide-regulated callus proliferation and regeneration capacity. The effect of peptide hormones in plant regeneration is likely at least partly conserved in crop plants. Our results indicate that chromatin-dependent regulation of peptide hormone production not only stimulates callus proliferation but also establishes pluripotency, improving the overall efficiency of two-step regeneration in plant systems.

Machine learning based prediction for oncologic outcomes of renal cell carcinoma after surgery using Korean Renal Cell Carcinoma (KORCC) database.

We developed a novel prediction model for recurrence and survival in patients with localized renal cell carcinoma (RCC) after surgery and a novel statistical method of machine learning (ML) to improve accuracy in predicting outcomes using a large Asian nationwide dataset, updated KOrean Renal Cell Carcinoma (KORCC) database that covered data for a total of 10,068 patients who had received surgery for RCC. After data pre-processing, feature selection was performed with an elastic net. Nine variables for recurrence and 13 variables for survival were extracted from 206 variables. Synthetic minority oversampling technique (SMOTE) was used for the training data set to solve the imbalance problem. We applied the most of existing ML algorithms introduced so far to evaluate the performance. We also performed subgroup analysis according to the histologic type. Diagnostic performances of all prediction models achieved high accuracy (range, 0.77-0.94) and F1-score (range, 0.77-0.97) in all tested metrics. In an external validation set, high accuracy and F1-score were well maintained in both recurrence and survival. In subgroup analysis of both clear and non-clear cell type RCC group, we also found a good prediction performance.

Germline DNA-Repair Genes and HOXB13 Mutations in Korean Men with Metastatic Prostate Cancer: Data from a Large Korean Cohort.

PURPOSE: Germline mutations in DNA damage repair (DDR) genes such as BRCA2 have been associated with prostate cancer (PC) risk but has not been thoroughly evaluated for metastatic prostate cancer (mPC) in Asian men. This study attempts to evaluate frequency of DDR mutations in the largest cohort of Koreans. MATERIALS AND METHODS: We recruited 340 patients with mPC unselected for family history of cancer and compared to 495 controls. Whole genome sequencing was applied to assess germline pathogenic/likely pathogenic variants (PV/LPVs) in 26 DDR genes and HOXB13, including 7 genes (ATM, BRCA1/2, CHEK2, BRIP1, PALB2, and NBN) associated with hereditary PC. Comparisons to published Caucasian and Japanese cohorts were performed. RESULTS: Total of 28 PV/LPVs were identified in 30 (8.8%) patients; mutations were found in 13 genes, including BRCA2 (15 men [4.41%]), ATM (2 men [0.59%]), NBN (2 men [0.59%], and BRIP1 (2 men [0.59%]). Only one patient had HOXB13 mutation (0.29%). A lower rate of overall germline variant frequency was observed in Korean mPC compared to Caucasians (8.8% vs. 11.8%), but individual variants notably differed from Caucasian and geographically similar Japanese cohorts. PV/LPVs in DDR genes tended to increase gradually with higher Gleason scores (GS 7, 7.1%; GS 8, 7.5%; GS 9-10, 9.9%). CONCLUSIONS: BRCA2 was the most frequently mutated gene common to different cohorts supporting its importance, but differences in variant distribution in Korean mPC underscore the need for ethnic-specific genetic models. Future ethnic-specific analyses are warranted to verify our findings.

Polygenic risk score for tumor aggressiveness and early-onset prostate cancer in Asians.

We attempted to assess the performance of an ethnic-specific polygenic risk score (PRS) designed from a Korean population to predict aggressive prostate cancer (PCa) and early-onset (age < 60). A PRS score comprised of 22 SNPs was computed in 3695 patients gathered from one of 4 tertiary centers in Korea. Males with biopsy or radical prostatectomy-proven PCa were included for analysis, collecting additional clinical parameters such as age, BMI, PSA, Gleason Group (GG), and staging. Patients were divided into 4 groups of PRS quartiles. Intergroup differences were assessed, as well as risk ratio and predictive performance based on GG using logistic regression analysis and AUC. No significant intergroup differences were observed for BMI, PSA, and rate of ≥ T3a tumors on pathology. Rate of GG ≥ 2, GG ≥ 3, and GG ≥ 4 showed a significant pattern of increase by PRS quartile (p < 0.001, < 0.001, and 0.039, respectively). With the lowest PRS quartile as reference, higher PRS groups showed sequentially escalating risk for GG ≥ 2 and GG ≥ 3 pathology, with a 4.6-fold rise in GG ≥ 2 (p < 0.001) and 2.0-fold rise in GG ≥ 3 (p < 0.001) for the highest PRS quartiles. Combining PRS with PSA improved prediction of early onset csPCa (AUC 0.759) compared to PRS (AUC 0.627) and PSA alone (AUC 0.736). To conclude, an ethnic-specific PRS was found to predict susceptibility of aggressive PCa in addition to improving detection of csPCa when combined with PSA in early onset populations. PRS may have a role as a risk-stratification model in actual practice. Large scale, multi-ethnic trials are required to validate our results.

Melatonin attenuates MPP+-induced apoptosis via heat shock protein in a Parkinson's disease model.

Heat shock proteins (HSPs) play an essential role as molecular chaperones to prevent abnormal protein aggregation and misfolding. Moreover, they protect dopamine neurons from oxidative stress, inflammation, and apoptosis, all well-known pathomechanisms of Parkinson's disease (PD). Melatonin is a potent antioxidant that has the beneficial ability to prevent neurodegenerative diseases like PD. We aimed to explore the protective properties of melatonin in an in vitro PD model, focusing on its underlying mechanism using HSPs. A 1-methyl-4-phenylpyridimium (MPP+)-induced toxin model was established with retinoic acid (RA)-differentiated SH-SY5Y cells. Cell viability and apoptosis were measured using MTT and DAPI. Intracellular reactive oxygen species (ROS) levels were measured by the cell-permeant fluorescent probe DCFH-DA. The level of malondialdehyde and the activities of superoxide dismutase and glutathione peroxidase were assessed using ELISA kits. Apoptotic markers of Bax, Bcl2, and cleaved caspase-3, as well as HSP70 and heat shock factor-1 (HSF1), were measured by Western blot. The melatonin effect through HSP70 was tested with silencing of HSF1 in the MPP + -treated SH-SY5Y cells. Melatonin can protect against MPP + -induced neuronal toxicity by promoting anti-oxidative and anti-apoptotic properties. SH-SY5Y cells exposed to melatonin with MPP + showed increased expression of HSP70 and HSF1 compared with those exposed to MPP + alone. However, siRNA-mediated downregulation of HSF1 significantly attenuated the protective effects of melatonin in the MPP + -induced in vitro PD model. Our findings revealed the protective roles of melatonin in an in vitro PD model. Melatonin can hinder the toxic effects of MPP + on dopaminergic neuronal cells via upregulation of the HSF1/HSP70 pathway. Further experimental studies would verify the therapeutic relevance of melatonin with HSP70 and HSF1 to prevent and decelerate PD-like neurodegeneration.

Zika virus baculovirus-expressed envelope protein elicited humoral and cellular immunity in immunocompetent mice.

Zika virus (ZIKV) is a mosquito-borne virus that has a high risk of inducing Guillain-Barré syndrome and microcephaly in newborns. Because vaccination is considered the most effective strategy against ZIKV infection, we designed a recombinant vaccine utilizing the baculovirus expression system with two strains of ZIKV envelope protein (MR766, Env_M; ZBRX6, Env_Z). Animals inoculated with Env_M and Env_Z produced ZIKV-specific antibodies and secreted effector cytokines such as interferon-γ, tumor necrosis factor-α, and interleukin-12. Moreover, the progeny of immunized females had detectable maternal antibodies that protected them against two ZIKV strains (MR766 and PRVABC59) and a Dengue virus strain. We propose that the baculovirus expression system ZIKV envelope protein recombinant provides a safe and effective vaccine strategy.

Effects of particulate matter and nicotine for the MPP+-induced SH-SY5Y cells: Implication for Parkinson's disease.

Exposure to particulate matter (PM) has been considered a potential risk factor for various neurodegenerative diseases, whereas nicotine has protective effects on Parkinson's disease (PD). However, it is still unclear whether or how PM alone and in combination with nicotine affects the pathogenesis of PD. We investigated the potential neurotoxicity of PM and the protective properties of nicotine in an in vitro PD model. A 1-methyl-4-phenylpyridimium (MPP+)-induced neurotoxicity model was established with SH-SY5Y cells. Cell viability and apoptosis were measured using MTT and TUNEL assays, respectively. Intracellular reactive oxygen species (ROS) levels were analyzed using the cell-permeant fluorescent probe DCFH-DA. We investigated mitochondrial apoptotic markers such as Bax, Bcl2, cytochrome C, and cleaved caspase-3 and analyzed their levels by Western blotting. SH-SY5Y cells exposed to PM and MPP+ exhibited significantly increased intracellular ROS and decreased cell viability with those exposed to PM alone. PM strikingly exacerbated MPP+-induced mitochondrial dysfunction, including an increase in the Bax/Bcl2 ratio and the release of cytochrome C and cleaved caspase-3. On the other hand, pretreatment of SH-SY5Y cells with nicotine reduced the MPP+-induced loss of cell viability and levels of intracellular ROS and mitochondrial apoptotic signaling proteins. However, pretreatment with nicotine did not prevent PM-induced toxicity in MPP+-treated SHSY5Y cells. PM and MPP+ synergistically increased ROS levels and mitochondrial apoptosis, which led to SH-SY5Y cell death. The protective effect of nicotine cannot rescue PM-induced synergistic neurotoxicity in the MPP+-induced PD model. Our findings verified the opposing roles of PM and nicotine in a model of PD pathogenesis. A large number of in vivo and in vitro studies would verify the roles of PM and nicotine in the future.

BCG Cell Wall Skeleton As a Vaccine Adjuvant Protects Both Infant and Old-Aged Mice from Influenza Virus Infection.

Bacillus Calmette-Guerin (BCG) and the cell wall skeleton (CWS) derived from BCG are known to enhance nonspecific immune activation and anti-cancer immunity; however, their roles as a vaccine adjuvant are largely unknown. Here, we report that BCG-CWS acts as a strong immune adjuvant by promoting the protective immune responses in mouse models with influenza vaccination. The different aged mice immunized with inactivated split vaccine with or without BCG-CWS were challenged with an influenza pandemic virus. When protective immune responses were compared, even a single immunization of adult mice with a BCG-CWS-adjuvanted vaccine showed significantly enhanced humoral immune responses with increased IgG1 and IgG2a isotype antibodies. Importantly, the protective effects by the BCG-CWS adjuvant for influenza vaccination upon humoral and cellular immunogenicity were comparable between infants (6 days and 2 weeks old) and aged (20 months old) mice. Moreover, BCG-CWS dramatically augmented vaccine-mediated protective responses, including decreased viral loads, lung damage, and airway resistance, as well as increased mouse survival, amelioration of weight loss, and proinflammatory cytokine expression in all experimental groups including infant, adults, and old aged mice. We further provided the evidence that the BCG-CWS adjuvant effects were mediated through Toll-like receptors (TLR) 2 and TLR4 signaling pathways. Together, these data suggest that BCG-CWS can be promising as a potential influenza vaccine adjuvant in both young and old aged population through TLR2/4-mediated immune-boosting activities.

Rapamycin Promotes ROS-Mediated Cell Death via Functional Inhibition of xCT Expression in Melanoma Under γ-Irradiation.

Although many cancer patients are administered radiotherapy for their treatment, the interaction between tumor cells and macrophages in the tumor microenvironment attenuates the curative effects of radiotherapy. The enhanced activation of mTOR signaling in the tumors promotes tumor radioresistance. In this study, the effects of rapamycin on the interaction between tumor cells and macrophages were investigated. Rapamycin and 3BDO were used to regulate the mTOR pathway. In vitro, tumor cells cocultured with macrophages in the presence of each drug under normoxic or hypoxic conditions were irradiated with γ-rays. In vivo, mice were irradiated with γ-radiation after injection with DMSO, rapamycin and 3BDO into tumoral regions. Rapamycin reduced the secretion of IL-4 in tumor cells as well as YM1 in macrophages. Mouse recombinant YM1 decreased the enhanced level of ROS and the colocalized proportion of both xCT and EEA1 in irradiated tumor cells. Human recombinant YKL39 also induced results similar to those of YM1. Moreover, the colocalized proportion of both xCT and LC3 in tumor tissues was elevated by the injection of rapamycin into tumoral regions. Overall, the suppression of mTOR signaling in the tumor microenvironment might be useful for the improvement of tumor radioresistance.

Cyclooxygenase-2 induces neoplastic transformation by inhibiting p53-dependent oncogene-induced senescence.

Much in vivo evidence indicates that cyclooxygenase-2 (COX-2) is deeply involved in tumorigenesis. Although it has been proposed that COX-2-derived pro-inflammatory prostanoids mediate the tumorigenic activity of COX-2, the tumorigenic mechanisms of COX-2 are not yet fully understood. Here, we investigated the mechanism by which COX-2 causes transformation from normal cells to malignant cells by using normal murine or human cells. We found that COX-2 inhibits the pro-senescent function of p53 under oncogenic RAS activation, by which it prevents oncogene-induced senescence (OIS) and induces neoplastic transformation. We also found that COX-2 physically interacts with p53 in the nucleus under oncogenic RAS activation, and that this COX-2-p53 interaction rather than the catalytic activity is involved in the COX-2-mediated inhibition of the pro-senescent function of p53 and OIS, and induction of neoplastic transformation. These findings strongly suggest that the oncogenic property of COX-2 is closely related to its ability to inactivate p53 under strong mitogenic signals, and that aberrant activation of the COX-2/a mitogenic oncogene combination can be a potent driving force for tumorigenesis. This study might contribute to our understanding of the molecular basis for the tumorigenic activity of COX-2 and the development of novel anti-tumor drugs targeting COX-2-p53 interactions.

Study of the Pathogen Inactivation Mechanism in Salt-Coated Filters.

As COVID-19 exemplifies, respiratory diseases transmitted through aerosols or droplets are global threats to public health, and respiratory protection measures are essential first lines of infection prevention and control. However, common face masks are single use and can cause cross-infection due to the accumulated infectious pathogens. We developed salt-based formulations to coat membrane fibers to fabricate antimicrobial filters. Here, we report a mechanistic study on salt-induced pathogen inactivation. The salt recrystallization following aerosol exposure was characterized over time on sodium chloride (NaCl), potassium sulfate (K2SO4), and potassium chloride (KCl) powders and coatings, which revealed that NaCl and KCl start to recrystallize within 5 min and K2SO4 within 15 min. The inactivation kinetics observed for the H1N1 influenza virus and Klebsiella pneumoniae matched the salt recrystallization well, which was identified as the main destabilizing mechanism. Additionally, the salt-coated filters were prepared with different methods (with and without a vacuum process), which led to salt coatings with different morphologies for diverse applications. Finally, the salt-coated filters caused a loss of pathogen viability independent of transmission mode (aerosols or droplets), against both DI water and artificial saliva suspensions. Overall, these findings increase our understanding of the salt-recrystallization-based technology to develop highly versatile antimicrobial filters.

GSK3 Restrains Germinal Center B Cells to Form Plasma Cells.

B cells in the germinal center (GC) are programmed to form plasma cells (PCs) or memory B cells according to signals received by receptors that are translated to carry out appropriate activities of transcription factors. However, the precise mechanism underlying this process to complete the GC reaction is unclear. In this study, we show that both genetic ablation and pharmacological inhibition of glycogen synthase kinase 3 (GSK3) in GC B cells of mice facilitate the cell fate decision toward PC formation, accompanied by acquisition of dark zone B cell properties. Mechanistically, under stimulation with CD40L and IL-21, GSK3 inactivation synergistically induced the transcription factors Foxo1 and c-Myc, leading to increased levels of key transcription factors required for PC differentiation, including IRF4. This GSK3-mediated alteration of transcriptional factors in turn facilitated the dark zone transition and consequent PC fate commitment. Our study thus reveals the upstream master regulator responsible for interpreting external cues in GC B cells to form PCs mediated by key transcription factors.

Regulated Necrotic Cell Death in Alternative Tumor Therapeutic Strategies.

The treatment of tumors requires the induction of cell death. Radiotherapy, chemotherapy, and immunotherapy are administered to kill cancer cells; however, some cancer cells are resistant to these therapies. Therefore, effective treatments require various strategies for the induction of cell death. Regulated cell death (RCD) is systematically controlled by intracellular signaling proteins. Apoptosis and autophagy are types of RCD that are morphologically different from necrosis, while necroptosis, pyroptosis, and ferroptosis are morphologically similar to necrosis. Unlike necrosis, regulated necrotic cell death (RNCD) is caused by disruption of the plasma membrane under the control of specific proteins and induces tissue inflammation. Various types of RNCD, such as necroptosis, pyroptosis, and ferroptosis, have been used as therapeutic strategies against various tumor types. In this review, the mechanisms of necroptosis, pyroptosis, and ferroptosis are described in detail, and a potential effective treatment strategy to increase the anticancer effects on apoptosis- or autophagy-resistant tumor types through the induction of RNCD is suggested.

Lysophosphatidylcholine Enhances Bactericidal Activity by Promoting Phagosome Maturation via the Activation of the NF-κB Pathway during Salmonella Infection in Mouse Macrophages.

Salmonella enterica serovar Typhimurium (S. Typhimurium) is a facultative intracellular pathogen that causes salmonellosis and mortality worldwide. S. Typhimurium infects macrophages and survives within phagosomes by avoiding the phagosome-lysosome fusion system. Phagosomes sequentially acquire different Rab GTPases during maturation and eventually fuse with acidic lysosomes. Lysophosphatidylcholine (LPC) is a bioactive lipid that is associated with the generation of chemoattractants and reactive oxygen species (ROS). In our previous study, LPC controlled the intracellular growth of Mycobacterium tuberculosis by promoting phagosome maturation. In this study, to verify whether LPC enhances phagosome maturation and regulates the intracellular growth of S. Typhimurium, macrophages were infected with S. Typhimurium. LPC decreased the intracellular bacterial burden, but it did not induce cytotoxicity in S. Typhimuriuminfected cells. In addition, combined administration of LPC and antibiotic significantly reduced the bacterial burden in the spleen and the liver. The ratios of the colocalization of intracellular S. Typhimurium with phagosome maturation markers, such as early endosome antigen 1 (EEA1) and lysosome-associated membrane protein 1 (LAMP-1), were significantly increased in LPC-treated cells. The expression level of cleaved cathepsin D was rapidly increased in LPCtreated cells during S. Typhimurium infection. Treatment with LPC enhanced ROS production, but it did not affect nitric oxide production in S. Typhimurium-infected cells. LPC also rapidly triggered the phosphorylation of IκBα during S. Typhimurium infection. These results suggest that LPC can improve phagosome maturation via ROS-induced activation of NF-κB pathway and thus may be developed as a therapeutic agent to control S. Typhimurium growth.

Smoking Cessation, Weight Change, and Risk of Parkinson's Disease: Analysis of National Cohort Data.

BACKGROUND AND PURPOSE: To determine whether the postcessation weight gain modifies the protective effect of smoking on the development of Parkinson's disease (PD). METHODS: This nationwide cohort study included 3,908,687 Korean males aged ≥40 years who underwent at least 2 health checkups biennially between 2009 and 2015. They were grouped into current smokers; quitters with body mass index (BMI) increase, maintenance, and decrease; and never smokers. The occurrence of incident PD was tracked, and Cox proportional-hazard models were used to adjust for potential confounding factors. We also analyzed the impact of weight change regardless of smoking status in the study population. RESULTS: There were 6,871 incident PD cases observed during the 13,059,208 person-years of follow-up. The overall risk of PD was significantly lower in quitters than in never smokers [hazard ratio (HR)=0.78, 95% confidence interval (CI)=0.70-0.86]. The risk of PD was still lower in quitters with BMI increase (HR=0.80, 95% CI=0.65-0.98) and in those with BMI maintenance (HR=0.77, 95% CI=0.68-0.87). This tendency was also observed in quitters with BMI decrease (HR=0.76, 95% CI=0.55-1.06), although it was not as robust as in the other two groups. With respect to weight change alone, BMI increase (HR=1.10, 95% CI=1.02-1.18) but not BMI decrease (HR=1.06, 95% CI=0.98-1.14) significantly increased the PD risk compared to BMI maintenance. CONCLUSIONS: Postcessation weight gain in males did not offset the protective impact of smoking on PD development, although overall weight gain predicted an increased risk of PD.

Two-Dimensional Theranostic Nanomaterials in Cancer Treatment: State of the Art and Perspectives.

As the combination of therapies enhances the performance of biocompatible materials in cancer treatment, theranostic therapies are attracting increasing attention rather than individual approaches. In this review, we describe a variety of two-dimensional (2D) theranostic nanomaterials and their efficacy in ablating tumors. Though many literature reports are available to demonstrate the potential application of 2D nanomaterials, we have reviewed here cancer-treating therapies based on such multifunctional nanomaterials abstracting the content from literature works which explain both the in vitro and in vivo level of applications. In addition, we have included a discussion about the future direction of 2D nanomaterials in the field of theranostic cancer treatment.

DNAJB9 Inhibits p53-Dependent Oncogene-Induced Senescence and Induces Cell Transformation.

DNAJB9 is known to be a member of the molecular chaperone gene family, whose cellular function has not yet been fully characterized. Here, we investigated the cellular function of DNAJB9 under strong mitogenic signals. We found that DNAJB9 inhibits p53-dependent oncogene-induced senescence (OIS) and induces neoplastic transformation under oncogenic RAS activation in mouse primary fibroblasts. In addition, we observed that DNAJB9 interacts physically with p53 under oncogenic RAS activation and that the p53-interacting region of DNAJB9 is critical for the inhibition of p53-dependent OIS and induction of neoplastic transformation by DNAJB9. These results suggest that DNAJB9 induces cell transformation under strong mitogenic signals, which is attributable to the inhibition of p53-dependent OIS by physical interactions with p53. This study might contribute to our understanding of the cellular function of DNAJB9 and the molecular basis of cell transformation.