Alterations of the p15, p16,and p18 genes in osteosarcoma

Loss of TIP60 (KAT5) abolishes H2AZ lysine 7 acetylation and causes p53, INK4A, and ARF-independent cell cycle arrest

Histone acetylation is essential for initiating and maintaining a permissive chromatin conformation and gene transcription. Dysregulation of histone acetylation can contribute to tumorigenesis and metastasis. Using inducible cre-recombinase and CRISPR/Cas9-mediated deletion, we investigated the roles of the histone lysine acetyltransferase TIP60 (KAT5/HTATIP) in human cells, mouse cells, and mouse embryos. We found that loss of TIP60 caused complete cell growth arrest. In the absence of TIP60, chromosomes failed to align in a metaphase plate during mitosis. In some TIP60 deleted cells, endoreplication occurred instead. In contrast, cell survival was not affected. Remarkably, the cell growth arrest caused by loss of TIP60 was independent of the tumor suppressors p53, INK4A and ARF. TIP60 was found to be essential for the acetylation of H2AZ, specifically at lysine 7. The mRNA levels of 6236 human and 8238 mouse genes, including many metabolism genes, were dependent on TIP60. Among the top 50 differentially expressed genes, over 90% were downregulated in cells lacking TIP60, supporting a role for TIP60 as a key co-activator of transcription. We propose a primary role of TIP60 in H2AZ lysine 7 acetylation and transcriptional activation, and that this fundamental role is essential for cell proliferation. Growth arrest independent of major tumor suppressors suggests TIP60 as a potential anti-cancer drug target.

A murine mesenchymal stem cell model for initiating events in osteosarcomagenesis points to CDK4/CDK6 inhibition as a therapeutic target

Osteosarcoma is a high-grade bone-forming neoplasm, with a complex genome. Tumours frequently show chromothripsis, many deletions, translocations and copy number alterations. Alterations in the p53 or Rb pathway are the most common genetic alterations identified in osteosarcoma. Using spontaneously transformed murine mesenchymal stem cells (MSCs) which formed sarcoma after subcutaneous injection into mice, it was previously demonstrated that p53 is most often involved in the transformation towards sarcomas with complex genomics, including osteosarcoma. In the current study, not only loss of p53 but also loss of p16^Ink4a is shown to be a driver of osteosarcomagenesis: murine MSCs with deficient p15^Ink4b, p16^Ink4a, or p19^Arf transform earlier compared to wild-type murine MSCs. Furthermore, in a panel of nine spontaneously transformed murine MSCs, alterations in p15^Ink4b, p16^Ink4a, or p19^Arf were observed in eight out of nine cases. Alterations in the Rb/p16 pathway could indicate that osteosarcoma cells are vulnerable to CDK4/CDK6 inhibitor treatment. Indeed, using two-dimensional (n = 7) and three-dimensional (n = 3) cultures of human osteosarcoma cell lines, it was shown that osteosarcoma cells with defective p16^INK4A are sensitive to the CDK4/CDK6 inhibitor palbociclib after 72-hour treatment. A tissue microarray analysis of 109 primary tumour biopsies revealed a subset of patients (20-23%) with intact Rb, but defective p16 or overexpression of CDK4 and/or CDK6. These patients might benefit from CDK4/CDK6 inhibition, therefore our results are promising and might be translated to the clinic.

A Novel HCC Prognosis Predictor EEF1E1 Is Related to Immune Infiltration and May Be Involved in EEF1E1/ATM/p53 Signaling

BACKGROUND

EEF1E1 has been reported to play a role in ovarian cancer, breast cancer, non-small cell lung cancer and other cancers, but its role and mechanism in hepatocellular carcinoma (HCC) are still unknown.

METHODS

EEF1E1 expression in human HCC was analyzed via the GTEx and TCGA database. Logistic regression analysis was used to analyze the clinicopathological correlation of EEF1E1 expression. The correlation between EEF1E1 expression and patients' prognosis was analyzed in HCC, shown by forest plots, nomogram and Kaplan-Meier curves. Hazard ratio (HR) with 95% confidence intervals and log-rank p-value were calculated via multivariate/univariate survival analyses. Moreover, the correlation between EEF1E1 and tumor immune infiltration was analyzed using the gsva package with the ssgsea algorithm. Pearson correlation was used to investigate the correlation between EEF1E1 expression and p53 pathway genes expression. Two third-party databases were used to validate the content of EEF1E1 protein and mRNA expression patterns and prognosis analysis. The immunohistochemistry and multiplex immunohistochemistry was used to verify the bio-informatics results.

RESULTS

EEF1E1 mRNA and protein expression in tumor was statistically higher than normal (EEF1E1 mRNA: p < 0.001; EEF1E1 protein: p < 0.01). Results from paired t-test (cancer and adjacent tissues) exhibited consistent trend (t = 7.572, p < 0.001). Immunohistochemistry showed that EEF1E1 is highly expressed in cancer. The expression of EEF1E1 was positively correlated with body weight, BMI, tumor status, vascular invasion, AFP, logistic grade, T stage and pathological stage. The univariate Cox model revealed that high EEF1E1 expression was strongly associated with worse OS (HR=2.581; 95% CI: 1.782-3.739; p < 0.001), as was T stage, pathologic stage, Histologic grade. High EEF1E1 expression was the only independent prognostic factor associated with OS (HR=2.57; 95% CI: 1.715-3.851; p < 0.001) in the multivariate analysis. EEF1E1 was significantly correlated with various immune cells, including cytotoxic cells, DC, macrophages, neutrophils, NK cd56bright, TFH, Tgd, Th17, Th2, Treg. Multiplex immunohistochemistry showed that the EEF1E1 protein level is positively correlated to the CD3, CD4, PD1 and is negatively correlated to the CD8. The expression level of EEF1E1 in HCC was significantly correlated with the key genes involved in the p53 pathway. The expression of EEF1E1, ATM, p53 and CASPASE3 in HCC tissues was significantly higher than that in adjacent tissues.

CONCLUSION

EEF1E1 is highly expressed in cancer tissues in HCC. EEF1E1's high expression is significantly correlated with worse prognosis and immune cell infiltration of HCC. EEF1E1 may be participating in EEF1E1/ATM/p53 signaling pathway in HCC.

Systems Biology Approach Identifies Prognostic Signatures of Poor Overall Survival and Guides the Prioritization of Novel BET-CHK1 Combination Therapy for Osteosarcoma

Osteosarcoma (OS) patients exhibit poor overall survival, partly due to copy number variations (CNVs) resulting in dysregulated gene expression and therapeutic resistance. To identify actionable prognostic signatures of poor overall survival, we employed a systems biology approach using public databases to integrate CNVs, gene expression, and survival outcomes in pediatric, adolescent, and young adult OS patients. Chromosome 8 was a hotspot for poor prognostic signatures. The MYC-RAD21 copy number gain (8q24) correlated with increased gene expression and poor overall survival in 90% of the patients (n = 85). MYC and RAD21 play a role in replication-stress, which is a therapeutically actionable network. We prioritized replication-stress regulators, bromodomain and extra-terminal proteins (BETs), and CHK1, in order to test the hypothesis that the inhibition of BET + CHK1 in MYC-RAD21+ pediatric OS models would be efficacious and safe. We demonstrate that MYC-RAD21+ pediatric OS cell lines were sensitive to the inhibition of BET (BETi) and CHK1 (CHK1i) at clinically achievable concentrations. While the potentiation of CHK1i-mediated effects by BETi was BET-BRD4-dependent, MYC expression was BET-BRD4-independent. In MYC-RAD21+ pediatric OS xenografts, BETi + CHK1i significantly decreased tumor growth, increased survival, and was well tolerated. Therefore, targeting replication stress is a promising strategy to pursue as a therapeutic option for this devastating disease.

Feedback regulation between atypical E2Fs and APC/CCdh1 coordinates cell cycle progression

E2F transcription factors control the oscillating expression pattern of multiple target genes during the cell cycle. Activator E2Fs, E2F1-3, induce an upswing of E2F targets, which is essential for the G1-to-S phase transition, whereas atypical E2Fs, E2F7 and E2F8, mediate a downswing of the same targets during late S, G2, and M phases. Expression of atypical E2Fs is induced by E2F1-3, but it is unknown how atypical E2Fs are inactivated in a timely manner. Here, we demonstrate that E2F7 and E2F8 are substrates of the anaphase-promoting complex/cyclosome (APC/C). Removal of CDH1, or mutating the CDH1-interacting KEN boxes, stabilized E2F7/8 from anaphase onwards and during G1. Expressing KEN mutant E2F7 during G1 impairs S phase entry and eventually results in cell death. Furthermore, we show that E2F8, but not E2F7, interacts also with APC/C(C) (dc20). Importantly, atypical E2Fs can activate APC/C(C) (dh1) by repressing its inhibitors cyclin A, cyclin E, and Emi1. In conclusion, we discovered a feedback loop between atypical E2Fs and APC/C(C) (dh1), which ensures balanced expression of cell cycle genes and normal cell cycle progression.

p16 expression predicts neoadjuvant tumor necrosis in osteosarcomas: reappraisal with a larger series using whole sections

The presence of greater than or equal to 90% necrosis after neoadjuvant chemotherapy is a favorable prognostic factor in osteosarcomas. A recent study using tissue microarrays of 40 conventional osteosarcomas showed that p16 expression independently predicted the necrotic response to neoadjuvant chemotherapy. In this study, we investigated this finding using whole sections in a larger group of osteosarcomas. Cases of 83 patients who had pretreatment biopsies and received neoadjuvant chemotherapy and surgical resection were collected from 3 reference hospital archives. Age, sex, tumor size, tumor subtype, location, and percentage of tumor necrosis were recorded; 4-μm sections from pretreatment biopsies were stained for p16. More than 30% strong nuclear staining was regarded as positive. The median age was 17 years (5-68 years), and male/female ratio was 2.3. The mean tumor diameter was 9.9 cm (2-30 cm). Tumors were most commonly of the osteoblastic type (60%) and located at the femur (47%). p16 positivity was seen in 66% of the patients. The median pathologic necrosis was 65%, and 39% of the patients responded favorably (≥%90 necrosis) to neoadjuvant therapy. In univariate analysis, p16 expression significantly correlated with greater than or equal to 90% response (P = .022). On multivariate analysis, p16 expression (odds ratio [OR], 7.71; P = .008), female sex (OR, 8.62; P = .006), and smaller tumor size (OR, 0.86; P = .023) were independent predictors of favorable response to neoadjuvant chemotherapy. We confirmed the finding that p16 expression predicts postchemotherapy necrotic response in conventional osteosarcomas.

Animal models in osteosarcoma

Osteosarcoma (OS) is the most common non-hematologic primary tumor of bone in children and adults. High-dose cytotoxic chemotherapy and surgical resection have improved prognosis, with long-term survival for non-metastatic disease approaching 70%. However, most OS tumors are high grade and tend to rapidly develop pulmonary metastases. Despite clinical advances, patients with metastatic disease or relapse have a poor prognosis. Toward a better understanding of the molecular pathogenesis of human OS, several genetically modified OS mouse models have been developed and will be reviewed here. However, better animal models that more accurately recapitulate the natural progression of the disease are needed for the development of improved prognostic and diagnostic markers as well as targeted therapies for both primary and metastatic OS.

Osteosarcoma: mouse models, cell of origin and cancer stem cell

Osteosarcoma (OS) is the most common non-hematologic primary tumor of bone in children and adults. High-dose cytotoxic chemotherapy and surgical resection have improved prognosis, with long-term survival for non-metastatic disease approaching 70%. However, most OS tumors are high grade and tend to rapidly develop pulmonary metastases. Despite clinical advances, patients with metastatic disease or relapse have a poor prognosis. Here the cell biology of OS is reviewed with a special emphasis on mouse models as well as the roles of the cell of origin and cancer stem cells. A better understanding of the molecular pathogenesis of human OS is essential for the development of improved prognostic and diagnostic markers as well as targeted therapies for both primary and metastatic OS.

Understanding the Biology of Bone Sarcoma from Early Initiating Events through Late Events in Metastasis and Disease Progression

The two most common primary bone malignancies, osteosarcoma (OS), and Ewing sarcoma (ES), are both aggressive, highly metastatic cancers that most often strike teens, though both can be found in younger children and adults. Despite distinct origins and pathogenesis, both diseases share several mechanisms of progression and metastasis, including neovascularization, invasion, anoikis resistance, chemoresistance, and evasion of the immune response. Some of these processes are well-studies in more common carcinoma models, and the observation from adult diseases may be readily applied to pediatric bone sarcomas. Neovascularization, which includes angiogenesis and vasculogenesis, is a clear example of a process that is likely to be similar between carcinomas and sarcomas, since the responding cells are the same in each case. Chemoresistance mechanisms also may be similar between other cancers and the bone sarcomas. Since OS and ES are mesenchymal in origin, the process of epithelial-to-mesenchymal transition is largely absent in bone sarcomas, necessitating different approaches to study progression and metastasis in these diseases. One process that is less well-studied in bone sarcomas is dormancy, which allows micrometastatic disease to remain viable but not growing in distant sites – typically the lungs – for months or years before renewing growth to become overt metastatic disease. By understanding the basic biology of these processes, novel therapeutic strategies may be developed that could improve survival in children with OS or ES.

Genetically engineered mouse models and human osteosarcoma

Osteosarcoma is the most common form of bone cancer. Pivotal insight into the genes involved in human osteosarcoma has been provided by the study of rare familial cancer predisposition syndromes. Three kindreds stand out as predisposing to the development of osteosarcoma: Li-Fraumeni syndrome, familial retinoblastoma and RecQ helicase disorders, which include Rothmund-Thomson Syndrome in particular. These disorders have highlighted the important roles of P53 and RB respectively, in the development of osteosarcoma. The association of OS with RECQL4 mutations is apparent but the relevance of this to OS is uncertain as mutations in RECQL4 are not found in sporadic OS. Application of the knowledge or mutations of P53 and RB in familial and sporadic OS has enabled the development of tractable, highly penetrant murine models of OS. These models share many of the cardinal features associated with human osteosarcoma including, importantly, a high incidence of spontaneous metastasis. The recent development of these models has been a significant advance for efforts to improve our understanding of the genetics of human OS and, more critically, to provide a high-throughput genetically modifiable platform for preclinical evaluation of new therapeutics.

The arginine methyltransferase PRMT6 regulates cell proliferation and senescence through transcriptional repression of tumor suppressor genes

The protein arginine methyltransferase 6 (PRMT6) is a coregulator of gene expression and executes its repressing as well as activating function by asymmetric dimethylation of histone H3 at R2 (H3 R2me2a). Given that elevated expression levels of PRMT6 have been reported in various cancer types, we explore here its role in cell proliferation and senescence. We find that knockdown of PRMT6 results in proliferation defects of transformed as well as non-transformed cells, causes G1-phase arrest and induces senescence. This phenotype is accompanied by transcriptional upregulation of important cell cycle regulators, most prominently the cyclin-dependent kinase (CDK) inhibitor gene p21 (p21^CIP1/WAF1, CDKN1A) and p16 (p16^INK4A, CDKN2A). Chromatin immuno-precipitation analysis reveals that the p21 gene is a direct target of PRMT6 and the corresponding histone mark H3 R2me2a. Using a cell model of oncogene-induced senescence (OIS), in which p21 is an essential activator of the senescent phenotype, we show that PRMT6 expression declines upon induction of senescence and conversely p21 gene expression increases. Moreover, overexpression of PRMT6 leads to reduced levels of OIS. These findings indicate that the transcriptional repressor activity of PRMT6 facilitates cell proliferation and blocks senescence by regulation of tumor suppressor genes and that this might contribute to the oncogenic capacity of PRMT6.

The genetics of osteosarcoma

Osteosarcoma is a primary bone malignancy with a particularly high incidence rate in children and adolescents relative to other age groups. The etiology of this often aggressive cancer is currently unknown, because complicated structural and numeric genomic rearrangements in cancer cells preclude understanding of tumour development. In addition, few consistent genetic changes that may indicate effective molecular therapeutic targets have been reported. However, high-resolution techniques continue to improve knowledge of distinct areas of the genome that are more commonly associated with osteosarcomas. Copy number gains at chromosomes 1p, 1q, 6p, 8q, and 17p as well as copy number losses at chromosomes 3q, 6q, 9, 10, 13, 17p, and 18q have been detected by numerous groups, but definitive oncogenes or tumour suppressor genes remain elusive with respect to many loci. In this paper, we examine studies of the genetics of osteosarcoma to comprehensively describe the heterogeneity and complexity of this cancer.

USP1 deubiquitinates ID proteins to preserve a mesenchymal stem cell program in osteosarcoma

Inhibitors of DNA binding (IDs) antagonize basic-helix-loop-helix (bHLH) transcription factors to inhibit differentiation and maintain stem cell fate. ID ubiquitination and proteasomal degradation occur in differentiated tissues, but IDs in many neoplasms appear to escape degradation. We show that the deubiquitinating enzyme USP1 promotes ID protein stability and stem cell-like characteristics in osteosarcoma. USP1 bound, deubiquitinated, and thereby stabilized ID1, ID2, and ID3. A subset of primary human osteosarcomas coordinately overexpressed USP1 and ID proteins. USP1 knockdown in osteosarcoma cells precipitated ID protein destabilization, cell-cycle arrest, and osteogenic differentiation. Conversely, ectopic USP1 expression in mesenchymal stem cells stabilized ID proteins, inhibited osteoblastic differentiation, and enhanced proliferation. Consistent with USP1 functioning in normal mesenchymal stem cells, USP1-deficient mice were osteopenic. Our observations implicate USP1 in preservation of the stem cell state that characterizes osteosarcoma and identify USP1 as a target for differentiation therapy.

Epigenetic changes in osteosarcoma

Osteosarcoma is one of the most prevalent primary bone tumors. The pathogenesis and molecular development of this tumor remains elusive. The prognosis is unfavorable due to lack of effective treatment methods. Recent advances in the epigenetics have brought a profound impact on the understanding of molecular mechanisms that lead to osteosarcoma. In this review, we summarized the current literature on epigenetic changes that are thought to contribute to the carcinogenesis of osteosarcoma, and discussed the potential diagnostic and therapeutic applications as well as future areas of research.

Autocrine Transforming Growth Factor-beta Growth Pathway in Murine Osteosarcoma Cell Lines Associated with Inability to Affect Phosphorylation of Retinoblastoma Protein

Purpose. Production of active transforming growth factor-β (TGF-β ) by human osteosarcoma may contribute to malignant progression through mechanisms that include induction of angiogenesis, immune suppression and autocrine growth stimulation of tumor cell growth.To study events associated with induction of cell proliferation by TGF-β , we have evaluated the TGF-β pathway in two murine osteosarcoma cell lines, K7 and K12.

Results. Northern and immunohistochemical analyses show that each cell line expressesTGF-β1 and TGF-β3 mRNA and protein. Both cell lines secrete activeTGF-β 1 and display a 30–50% reduction in growth when cultured in the presence of a TGF-β blocking antibody. Expression of TGF-β receptors TβRI, TβRII and TβRIII is demonstrated by affinity labeling with ¹²⁵ -TGF-β 1, and the intermediates, Smads 2, 3 and 4, are uniformly expressed. Smads 2 and 3 are phosphorylated in response toTGF-β , while pRb phosphorylation in each osteosarcoma cell line is not affected by either exogenousTGF-β or TGF-β antibody.

Conclusions. The data implicate events downstream of Smad activation, including impaired regulation of pRb, in the lack of a growth inhibitory response toTGF-β , and indicate that this murine model of osteosarcoma is valid for investigating the roles of autocrineTGF-β in vivo.

The cyclin-dependent kinase inhibitor SCH 727965 (dinacliclib) induces the apoptosis of osteosarcoma cells

Although rare, osteosarcoma is an aggressive cancer that often metastasizes to the lungs. Toward the goal of developing new treatment options for osteosarcoma, we show that the cyclin-dependent kinase (CDK) inhibitor SCH 727965 (SCH) induces the apoptosis of several osteosarcoma cell lines including those resistant to doxorubicin and dasatinib. Cell lines prepared in our laboratory from patients who had received adjuvant chemotherapy and explants derived from a human osteosarcoma xenograft in mice were also responsive to SCH. Apoptosis occurred at low nanomolar concentrations of SCH, as did CDK inhibition, and was p53-independent. SCH activated the mitochondrial pathway of apoptosis as evidenced by caspase-9 cleavage and accumulation of cytoplasmic cytochrome c. Amounts of the apoptotic proteins Bax and Bim increased in mitochondria, whereas amounts of the antiapoptotic proteins Mcl-1 and Bcl-x(L) declined. Osteosarcoma cells apoptosed when codepleted of CDK1 and CDK2 but not when depleted of other CDK combinations. We suggest that SCH triggers the apoptosis of osteosarcoma cells by inactivating CDK1 and CDK2 and that SCH may be useful for treatment of drug-resistant osteosarcomas. SCH also induced the apoptosis of other sarcoma types but not of normal quiescent osteoblasts or fibroblasts.

Epigenetic regulation of apoptosis and cell cycle in osteosarcoma

The role of genetic mutations in the development of osteosarcoma, such as alterations in p53 and Rb, is well understood. However, the significance of epigenetic mechanisms in the progression of osteosarcoma remains unclear and is increasingly being investigated. Recent evidence suggests that epigenetic alterations such as methylation and histone modifications of genes involved in cell cycle regulation and apoptosis may contribute to the pathogenesis of this tumor. Importantly, understanding the molecular mechanisms of regulation of these pathways may give insight into novel therapeutic strategies for patients with osteosarcoma. This paper serves to summarize the described epigenetic mechanisms in the tumorigenesis of osteosarcoma, specifically those pertaining to apoptosis and cell cycle regulation.

Modeling human osteosarcoma in the mouse: From bedside to bench

Osteosarcoma (OS) is the most common primary tumour of bone, occurring predominantly in the second decade of life. High-dose cytotoxic chemotherapy and surgical resection have improved prognosis, with long-term survival for patients with localized (non-metastatic) disease approaching 70%. At presentation approximately 20% of patients have metastases and almost all patients with recurrent OS have metastatic disease and cure rates for patients with metastatic or recurrent disease remain poor (<20% survival). Over the past 20 years, considerable progress has been made in the understanding of OS pathogenesis, yet these insights have not translated into substantial therapeutic advances and clinical outcomes. Further progress is essential in order to develop molecularly based therapies that target both primary lesions as well as metastatic disease. The increasing sophistication with which gene expression can be modulated in the mouse, both positively and negatively in addition to temporally, has allowed for the recent generation of more faithful OS models than have previously been available. These murine OS models can recapitulate all aspects of the disease process, from initiation and establishment to invasion and dissemination to distant sites. The development and utilisation of murine models that faithfully recapitulate human osteosarcoma, complementing existing approaches using human and canine disease, holds significant promise in furthering our understanding of the genetic basis of the disease and, more critically, in advancing pre-clinical studies aimed at the rational development and trialing of new therapeutic approaches.

TNF-alpha's effects on proliferation and apoptosis in human mesenchymal stem cells depend on RUNX2 expression

RUNX2 is a bone-specific transcription factor that plays a critical role in prenatal bone formation and postnatal bone development. It regulates the expression of genes that are important in committing cells into the osteoblast lineage. There is increasing evidence that RUNX2 is involved in osteoblast proliferation. RUNX2 expression increases during osteoblast differentiation, and recent data even suggest that it acts as a proapoptotic factor. The cytokine tumor necrosis factor alpha (TNF-alpha) is known to modulate osteoblast functions in a manner that depends on the differentiation stage. TNF-alpha affects the rate at which mesenchymal precursor cells differentiate into osteoblasts and induces apoptosis in mature osteoblasts. Thus we sought to establish whether or not the effects of TNF-alpha and fetal calf serum on proliferation and apoptosis in human mesenchymal stem cells (hMSCs) were dependent on RUNX2 level and activity. We transfected hMSCs with small interfering RNAs (siRNAs) directed against RUNX2 and found that they proliferated more quickly than control hMSCs transfected with a nonspecific siRNA. This increase in proliferation was accompanied by a rise in cyclin A1, B1, and E1 expression and a decrease in levels of the cyclin inhibitor p21. Moreover, we observed that RUNX2 silencing protected hMSCs from TNF-alpha's antiproliferative and apoptotic effects. This protection was accompanied by the inhibition of caspase-3 activity and Bax expression. Our results confirmed that RUNX2 is a critical link between cell fate, proliferation, and growth control. This study also suggested that, depending on the osteoblasts' differentiation stage, RUNX2 may control cell growth by regulating the expression of elements involved in hormone and cytokine sensitivity.

RUNX2 regulates the effects of TNFalpha on proliferation and apoptosis in SaOs-2 cells

The runt-related transcriptional factor RUNX2 is an essential mediator of the osteoblast phenotype and plays a pivotal role in the process of osteoblast differentiation. The involvement of RUNX2 includes the regulation of genes that are important in committing cells to the osteoblast lineage. Increasing evidences are consistent with a requirement of RUNX2 for stringent control of osteoblast proliferation and recent data even suggested that RUNX2 might act as a proapoptotic factor. Among the cytokines described as modulators of osteoblast functions, TNFalpha affects both apoptosis and the differentiation rate from mesenchymal precursor cells of osteoblast. Thus we evaluated on the human osteosarcoma cell line SaOs-2 stably transfected with a RUNX2 dominant negative construct (DeltaRUNX2) the effects of serum and TNFalpha on proliferation and apoptosis. In this study we showed that SaOs-2 clones expressing high levels of DeltaRUNX2 presented a higher proliferation rate than clones transfected with an empty vector. This increase in cell growth was accompanied by a rise in cyclins A1, B1 and E1 expression and a decrease in the cyclin inhibitor p21. Moreover we observed that the expression of the RUNX2 transgene protected the SaOs-2 cells from the antiproliferative and the apoptotic effects induced by TNFalpha. This was accompanied by the inhibition of Bax and activation of Bcl2 expression. Experiments done on SaOs-2 cells transiently transfected with siRNA confirmed that RUNX2 represents a critical link between cell fate, proliferation and growth control. This study also suggested that RUNX2 might control osteoblastic growth depending on the differentiation stage of the cells by regulating expression of elements involved in hormones and cytokines sensitivity.

Targets for cancer therapy in childhood sarcomas

Development of chemotherapeutic treatment modalities resulted in a dramatic increase in the survival of children with many types of cancer. Still, in case of some pediatric cancer entities including rhabdomyosarcoma, osteosarcoma and Ewing's sarcoma, survival of patients remains dismal and novel treatment approaches are urgently needed. Therefore, based on the concept of targeted therapy, numerous potential targets for the treatment of these cancers have been evaluated pre-clinically or in some cases even clinically during the last decade. This review gives an overview over many different potential therapeutic targets for treatment of these childhood sarcomas, including receptor tyrosine kinases, intracellular signaling molecules, cell cycle and apoptosis regulators, proteasome, hsp90, histone deacetylases, angiogenesis regulators and sarcoma specific fusion proteins. The large number of potential therapeutic targets suggests that improved comparability of pre-clinical models might be necessary to prioritize the most effective ones for future clinical trials.

Genome-wide transcriptome profile of the human osteosarcoma Sa OS and U-2 OS cell lines

With the use of genome-wide cDNA microarrays, we investigated the transcriptome profile of the human osteosarcoma Sa OS and U-2 OS cell lines. In all, 1,098 chip entries were differentially regulated in the two cell lines; of these, 796 entries corresponded to characterized mRNAs. The identified genes are mostly expressed in epithelial tissues and localize on chromosomes 1, 10, and 20. Furthermore, signaling cascades for cell cycle, glycolysis, and gluconeogenesis, the p53 pathway, cell communication, and focal adhesion were found to be differently regulated in the two cell lines. The transcriptome profiles reported here provide novel information about the considerable molecular differences between these two widely used human osteosarcoma cell lines.

P18 is a tumor suppressor gene involved in human medullary thyroid carcinoma and pheochromocytoma development

In multiple endocrine neoplasia syndrome Type 2 (MEN2), medullary thyroid carcinoma (MTC) and pheochromocytoma (PC) are associated with hereditary activating germ-line mutations in the RET proto-oncogene. Also in a large percentage of sporadic MTCs and PCs, somatic RET mutations appear to be involved in tumor formation. In one single MEN2 family an extensive variety in disease expression may be observed, indicating that additional genetic events are responsible for progression of the disease towards a more aggressive phenotype. However, these additional mutations in both hereditary and sporadic MTC and PC development are largely unknown. Here, we show for the first time the presence of somatic mutations in the cell cycle regulator P18 in human RET-associated MTCs and PCs. Each of these mutations causes an amino acid substitution in the cyclin dependent kinase-interacting region of P18(INK4C). Since these mutations partly inhibited P18(INK4C) function and reduced its stability, our findings implicate P18 as a tumor suppressor gene involved in human MTC and PC development.

Expression of p18(INK4C) is down-regulated in human pituitary adenomas

Cyclin-dependent kinase inhibitors represented by the INK4 family comprising p16(INK4A), p15(INK4B), p18(INK4C), and p19(INK4D) are regulators of the cell cycle shown to be aberrant in many types of cancer. Mice lacking p18(Ink4c) exhibit a series of phenotypes including the development of widespread organomegaly and pituitary adenomas. The objective of our study is to examine the role of p18(INK4C) in the pathogenesis of human pituitary tumors. The protein and mRNA levels of p18(INK4C) were examined by immunohistochemistry and real-time reverse transcription-polymerase chain reaction, respectively. The methylation status of the p18(INK4C) gene promoter and somatic mutations of the p18(INK4C) gene were also investigated. p18(INK4C) protein expression was lost or significantly reduced in 64% of pituitary adenomas compared with levels in normal pituitary glands. p18(INK4C) mRNA levels were low in all ACTH adenomas and non-functioning (NF)-FSH and in 42%, 70% and 66% of GH, PRL, and subtype 3 adenomas, respectively. p18(INK4C) mRNA levels were significantly associated with p18(INK4C) protein levels. Neither methylated promoters in pituitary adenomas, except in one NF-FSH adenoma, nor somatic mutations of the p18(INK4C) gene in any pituitary adenomas were detected. The down-regulation of p18(INK4C) expression may contribute to the tumorigenesis of pituitary adenomas.

Ladder-like amplification of the type I interferon gene cluster in the human osteosarcoma cell line MG63

The organization of the type I interferon (IFN) gene cluster (9p21.3) was studied in a human osteosarcoma cell line (MG63). Array comparative genomic hybridization (aCGH) showed an amplification of approximately 6-fold which ended at both ends of the gene cluster with a deletion that extended throughout the 9p21.3 band. Spectral karyotyping (SKY) combined with fluorescence in-situ hybridization (FISH) identified an arrangement of the gene cluster in a ladder-like array of 5-7 'bands' spanning a single chromosome termed the 'IFN chromosome'. Chromosome painting revealed that the IFN chromosome is derived from components of chromosomes 4, 8 and 9. Labelling with centromeric probes demonstrated a ladder-like amplification of centromeric 4 and 9 sequences that co-localized with each other and a similar banding pattern of chromosome 4, as well as alternating with the IFN gene clusters. In contrast, centromere 8 was not detected on the IFN chromosome. One of the amplified centromeric 9 bands was identified as the functional centromere based on its location at the chromosome constriction and immunolocalization of the CENP-C protein. A model is presented for the generation of the IFN chromosome that involves breakage-fusion-bridge events.

Cause and consequences of genetic and epigenetic alterations in human cancer

Both genetic and epigenetic changes contribute to development of human cancer. Oncogenomics has primarily focused on understanding the genetic basis of neoplasia, with less emphasis being placed on the role of epigenetics in tumourigenesis. Genomic alterations in cancer vary between the different types and stages, tissues and individuals. Moreover, genomic change ranges from single nucleotide mutations to gross chromosomal aneuploidy; which may or may not be associated with underlying genomic instability. Collectively, genomic alterations result in widespread deregulation of gene expression profiles and the disruption of signalling networks that control proliferation and cellular functions. In addition to changes in DNA and chromosomes, it has become evident that oncogenomic processes can be profoundly influenced by epigenetic mechanisms. DNA methylation is one of the key epigenetic factors involved in regulation of gene expression and genomic stability, and is biologically necessary for the maintenance of many cellular functions. While there has been considerable progress in understanding the impact of genetic and epigenetic mechanisms in tumourigenesis, there has been little consideration of the importance of the interplay between these two processes. In this review we summarize current understanding of the role of genetic and epigenetic alterations in human cancer. In addition we consider the associated interactions of genetic and epigenetic processes in tumour onset and progression. Furthermore, we provide a model of tumourigenesis that addresses the combined impact of both epigenetic and genetic alterations in cancer cells.

Osteosarcoma development and stem cell differentiation

Osteosarcoma is the most common nonhematologic malignancy of bone in children and adults. The peak incidence occurs in the second decade of life, with a smaller peak after age 50. Osteosarcoma typically arises around the growth plate of long bones. Most osteosarcoma tumors are of high grade and tend to develop pulmonary metastases. Despite clinical improvements, patients with metastatic or recurrent diseases have a poor prognosis. Here, we reviewed the current understanding of human osteosarcoma, with an emphasis on potential links between defective osteogenic differentiation and bone tumorigenesis. Existing data indicate osteosarcoma tumors display a broad range of genetic and molecular alterations, including the gains, losses, or arrangements of chromosomal regions, inactivation of tumor suppressor genes, and the deregulation of major signaling pathways. However, except for p53 and/or RB mutations, most alterations are not constantly detected in the majority of osteosarcoma tumors. With a rapid expansion of our knowledge about stem cell biology, emerging evidence suggests osteosarcoma should be regarded as a differentiation disease caused by genetic and epigenetic changes that interrupt osteoblast differentiation from mesenchymal stem cells. Understanding the molecular pathogenesis of human osteosarcoma could ultimately lead to the development of diagnostic and prognostic markers, as well as targeted therapeutics for osteosarcoma patients.

Conditional mouse osteosarcoma, dependent on p53 loss and potentiated by loss of Rb, mimics the human disease

Osteosarcoma is the most common primary malignant tumor of bone. Analysis of familial cancer syndromes and sporadic cases has strongly implicated both p53 and pRb in its pathogenesis; however, the relative contribution of these mutations to the initiation of osteosarcoma is unclear. We describe here the generation and characterization of a genetically engineered mouse model in which all animals develop short latency malignant osteosarcoma. The genetically engineered mouse model is based on osteoblast-restricted deletion of p53 and pRb. Osteosarcoma development is dependent on loss of p53 and potentiated by loss of pRb, revealing a dominance of p53 mutation in the development of osteosarcoma. The model reproduces many of the defining features of human osteosarcoma including cytogenetic complexity and comparable gene expression signatures, histology, and metastatic behavior. Using a novel in silico methodology termed cytogenetic region enrichment analysis, we demonstrate high conservation of gene expression changes between murine osteosarcoma and known cytogentically rearranged loci from human osteosarcoma. Due to the strong similarity between murine osteosarcoma and human osteosarcoma in this model, this should provide a valuable platform for addressing the molecular genetics of osteosarcoma and for developing novel therapeutic strategies.

Attenuated Salmonella typhimurium with interleukin 2 gene prevents the establishment of pulmonary metastases in a model of osteosarcoma

PURPOSE

The current management of osteosarcoma (OS) entails an aggressive preoperative and postoperative chemotherapeutic regimen with limb salvage surgery. Despite these efforts, relapse-free survival is less than 60% in patients with classic OS, whereas most patients relapse with pulmonary metastases. In these studies, we sought to prevent the establishment of pulmonary metastases from OS with a single oral dose of SalpIL2.

METHODS

Mice were administered attenuated Salmonella typhimurium with (SalpIL2) and without a gene for human interleukin 2 (Sal-NG) 7 days before challenge with 2 x 10(5) OS cells via tail vein. Three weeks after injection, mice were harvested for splenic lymphocytes and tumor enumeration.

RESULTS

Prophylaxis with attenuated SalpIL2 significantly reduces pulmonary metastases in number and volume (P < .0001 and P < .0001) with respect to saline controls. Furthermore, splenic natural killer cell populations were increased 396% with SalpIL2 (P < .0007) and 426% with Sal-NG (P < .0003) compared to nontreated groups.

CONCLUSIONS

Host natural killer response is greatly amplified and maybe partially responsible for the effective immune response against the formation of pulmonary metastases. A single oral dose of SalpIL2 may be a novel form of adjuvant therapy for patients after early detection of primary OS.

Molecular pathogenesis of osteosarcoma

Osteosarcoma is a devastating but rare disease, whose study has illuminated both the basic biology and clinical management of cancer over the past 30 years. These contributions have included insight into the roles of key cancer genes such as the retinoblastoma tumor suppressor gene and TP53, the identification of familial cancer syndromes implicating DNA helicases, and dramatic improvements in survival by the use of adjuvant chemotherapy. This review provides a synoptic overview of our current understanding of the molecular causes of osteosarcoma, and suggests future directions for study.

Biology of Osteogenic Sarcoma

Osteosarcoma is the most common primary malignant bone tumor in children and adolescents. Despite significant clinical improvements over the past several decades through the use of combination chemotherapy and surgery, patients with metastatic or recurrent disease continue to have a very poor prognosis. Therefore, there is a continued need to study and understand the basic biology of osteosarcoma in order to devise more targeted and rational therapeutic strategies and ultimately to improve survival for these patients. This article reviews several aspects of osteosarcoma biology where data exist to suggest that specific pathways may play a role in the pathogenesis of this tumor. These areas include host genetic predispositions, tumor cytogenetics, molecular genetics (including the Rb, p53, RECQ helicase, and telomere pathways), and metastatic factors (ezrin, annexin 2, chemokine receptor 4, Fas/FasL pathways) that may contribute to both the initiation and the progression of tumor formation. Understanding the mechanisms of and interactions between the various molecular pathways that play a role in osteosarcoma pathogenesis may eventually lead to a more rational strategy for devising therapies targeted specifically toward these pathways.

Osteosarcoma occurring in osteogenesis imperfecta

We describe a case history of a 24-year-old male with osteogenesis imperfecta (OI) who developed osteosarcoma of the left thigh. High-dose ifosfamide therapy caused marked tumor regression of multiple lung metastases. Immunohistochemically, the tumor cells were diffusely positive for the p53 protein. Mutation of the p53 gene was not detected by direct genomic sequencing of exons 4-8. The radiographic characteristics, including irregularly distributed osteolytic lesions and cortical discontinuity, should not be confused with hyperplastic callus formation, a benign process. A biopsy is critical to establish the differential diagnosis between osteosarcoma and common hyperplastic callus formation in OI; however, it must be applied with great care.

Activation of protein kinase C promotes human cancer cell growth through downregulation of p18INK4c

p18(INK4c), a member of INK4 family of cyclin-dependent kinase inhibitors, negatively regulates the cyclin D-cyclin-dependent kinase 4/6 complexes which promote G1/S transition by phosphorylating the retinoblastoma tumor-suppressor gene product. Several recent studies using p18(INK4c)-null mice revealed that the p18(INK4c) plays an important role in cell proliferation and tumor development. We report here that 12-O-tetradecanoylphorbol-13-acetate (TPA), widely used as a protein kinase C (PKC) activator, suppresses the expression of p18(INK4c) through its promoter, accompanied by the induction of human cancer cell growth. Reduction of p18(INK4c) using small interfering RNA (siRNA) also enhanced cell growth, suggesting that p18(INK4c) is a critical target of TPA. Ro 31-8425, a potent and highly specific PKC inhibitor abrogated the suppressive effect of TPA on p18(INK4c) gene expression. However, the expression of dominant-negative c-Jun (TAM-67) did not inhibit the action of TPA on p18(INK4c). These findings suggest that activation of PKC promotes human cancer cell growth through downregulation of p18(INK4c) in an AP-1 activation-independent manner. These results suggest that the accelerated cellular proliferation of some human tumors caused by enhanced PKC activity at least partially involves the suppression of p18(INK4c), which is a ubiquitously expressed cyclin-dependent kinase inhibitor.

Mechanisms of inactivation of the p16INK4a gene in leiomyosarcoma of soft tissue: decreased p16 expression correlates with promoter methylation and poor prognosis

The p16INK4a tumour suppressor gene, encoding p16 protein, plays a crucial role in regulation of the G1 cell-cycle phase. To investigate the potential role of p16 in soft tissue leiomyosarcoma (LMS), an immunohistochemical analysis was performed of 77 LMSs for p16 expression. Decreased expression of the p16 protein was identified in 25 of 77 LMSs (32%). Decreased expression of p16 correlated significantly with large tumour size (p=0.0038). In a univariate analysis, large tumour size and decreased expression of p16 were statistically significant adverse prognostic factors (p=0.025 and p=0.0021, respectively). In a multivariate analysis including conventional clinicopathological parameters, decreased expression of p16 protein was revealed as the only independent unfavourable prognostic factor (p=0.012). To elucidate the mechanisms of inactivation of the p16INK4a gene, 49 LMSs for which genomic DNA was available were examined; analysis for homozygous deletion, mutation, and promoter hypermethylation was conducted using differential PCR, PCR-SSCP, and methylation-specific PCR, respectively. Promoter hypermethylation was detected in 11 of 49 LMS cases (22%); homozygous deletion was detected in 3 of 49 cases (6%); and mutation was not recognized in any of the cases studied. Eight of 15 cases (53%) with decreased expression of p16 protein revealed methylation of the p16INK4a gene promoter. Promoter hypermethylation correlated closely with decreased expression and poor prognosis (p=0.0014 and p=0.0088, respectively). These results suggest that decreased expression of p16 protein can be considered as an independent reliable prognostic parameter in patients with soft tissue LMS. Furthermore, promoter methylation was more frequent than either homozygous deletion or mutation in this tumour, and promoter methylation was also shown to have a strong association with inactivation of the p16INK4a gene.

Genetic and epigenetic alterations of the cell cycle regulators and tumor suppressor genes in pediatric osteosarcomas

PURPOSE

To analyze the genetic and epigenetic alterations affecting the RB1, TP53, p16INK4, and p21WAF1 tumor suppressor genes, loss of heterozygosity (LOH) at 3q and 18q, and the clinical variables of a series of Spanish children with osteosarcoma. These genetic changes were tested for an association with prognosis.

METHODS

Peripheral blood samples and clinical data were available from 76 patients with osteosarcoma. Paired tissue was available from 41 of them. The mutation and methylation status of p16INK4, p21WAF1, TP53, and RB1 was screened as well as LOH at 3q and 18q.

RESULTS

Loss of heterozygosity affecting RB1 (37.2%), TP53 (42.3%), and 18q (30.8%) and TP53 mutation (39%) were frequently encountered. TP53 mutation was associated with diagnosis at a later age. RB1 alteration was associated with reduced survival and event-free survival. The clinical variables associated with poor prognosis were the presence of metastasis at diagnosis (P = 0.035) or during treatment (P = 0.016) and the chondroblastic histologic subtype (P = 0.007); the response to induction chemotherapy (<90% necrosis) also tended to be related to poor prognosis (P = 0.08).

CONCLUSIONS

RB1, TP53, and possibly other tumor suppressor genes located at 18q and other localizations are involved in pediatric osteosarcoma carcinogenesis, together with other genetic alterations not fully understood to date. Based on these results, the presence of an altered RB1 gene should be regarded as a poor prognostic factor for pediatric osteosarcoma.

Frequent amplification and rearrangement of chromosomal bands 6p12-p21 and 17p11.2 in osteosarcoma

Osteosarcoma (OS) is a highly malignant bone neoplasm of children and young adults. It is characterized by chaotic karyotypes with complex marker chromosomes. We applied a combination of molecular cytogenetic techniques including comparative genomic hybridization (CGH), spectral karyotyping (SKY), and fluorescence in situ hybridization (FISH) to decipher the chromosomal complexity in a panel of 25 tumors. Combined SKY and G-banding analysis identified several novel recurrent breakpoint clusters and 9 nonrecurrent reciprocal translocations. CGH identified several recurrent chromosomal losses including 2q, 3p, 9, 10p, 12q, 13q, 14q, 15q, 16, 17p, and 18q, gains including Xp, Xq, 5q, 6p, 8q, 17p, and 20q, and high-level chromosomal amplifications at Xp11.2, 1q21-q22, 4p11, 4q12, 5p15, 6p12.1, 8q13, 8q23, 10q11, 10q22, 11q13, 11q23, 12q13-q14, 13q21-q34, 16q22, 17p11.2, 17q21-q22, 18q22, 20p11.2, and 20q12. Frequent amplification and rearrangement involving chromosomal bands at 6p12-p21 and 17p11.2 were found in 28% and 32% of cases, respectively. In an attempt to identify the genes involved in these amplicons, we used three nonoverlapping BAC clones contained within each amplicon as probes for FISH analysis, leading to a more detailed characterization and quantification of the 6p and 17p amplicons.

Role of tumor suppressor genes in the development of adult T cell leukemia/lymphoma (ATLL)

Adult T cell leukemia/lymphoma (ATLL) is one of the peripheral T cell malignant neoplasms strongly associated with human T cell leukemia virus type-I (HTLV-I). Although the viral transactivating protein Tax has been proposed to play a critical role in leukemogeneis as shown by its transforming activity in various experimental systems, additional cellular events are required for the development of ATLL. One of the genetic events in ATLL is inactivation of tumor suppressor genes. Among many candidates for tumor suppressor genes, the main genetic events have been reported to center around the cyclin-dependent kinase inhibitors ((CDKIs) p15INK4A, p16INK4B, p18INK4C, p19INK4D, p21WAF1, p27KIP1, and p57KIP2), p53 and Rb genes; all of them play a major regulatory role during G1 to S transition in the cell cycle. Acute/lymphomatous ATLL has frequent alterations of p15 (20%) and p16 (28-67%), while chronic/smoldering ATLL has fewer abnormalities of p15 (0-13%) and p16 (5-26%). Most of these changes are deletion of the genes; fewer samples have mutations. ATLL patients with deleted p15 and/or p16 genes have significantly shorter survival than those individuals with both genes preserved. Although genetic alterations of p18, p19, p21, p27 have rarely been reported, inactivation of these genes may contribute to the development of ATLL because low expression levels of these genes seem to mark ATLL. The p53 gene is mutated in 10-50% of acute/lymphomatous ATLL. Functional impairment of the p53 protein, even if the gene has wild-type sequences, has been suggested in HTLV-I infected cells. Each of these genetic events are mainly found in acute/lymphomatous ATLL, suggesting that alterations of these genes may be associated with transformation to an aggressive phenotype. The Rb tumor suppressor gene is infrequently structurally altered, but one half of ATLL cases have lost expression of this key protein. Notably, alterations of one of the CDKIs, p53 and Rb genes appear to obviate the need for inactivation of other genes in the same pathway. A novel tumor suppressor gene on chromosome 6q may also have a critical role in the pathogenesis of ATLL. Taken together, tumor suppressor genes are frequently altered in acute/lymphomatous ATLL and their alteration is probably the driving force fueling the transition from chronic/smoldering to acute/lymphomatous ATLL.

Alterations in the INK4a/ARF locus and their effects on the growth of human osteosarcoma cell lines

Two different proteins, p16(INK4a) and p14(ARF), encoded by the INK4a/ARF locus play important roles in the RB and p53 pathways, respectively. This study was performed to determine genetic and epigenetic alterations in the INK4a/ARF locus and their effects on the growth of osteosarcoma. Among six cell lines examined, both p16(INK4a) and p14(ARF) exons were homozygously deleted in two cell lines, MG63 and HOS, and both p16(INK4a) and p14(ARF) promoters were methylated in one cell line, U2OS. Wild-type mRNA and proteins for p16(INK4a) and p14(ARF) were expressed in three other cell lines, SaOS2, HuO9, and G292. Transfection studies were performed using two cell lines, U2OS and MG63. Both the RB and p53 genes were wild types in U2OS, whereas p53 but not RB was mutated in MG63. Both p16(INK4a) and p14(ARF) suppressed the growth of U2OS, whereas p16(INK4a) but not p14(ARF) suppressed the growth of MG63. p53 only did not suppress the growth of MG63 either; however, coexpression of p14(ARF) with p53 increased the fraction of the G0/G1 phase in MG63 cells. The data presented here demonstrate the importance of genetic and epigenetic alterations in the INK4a/ARF locus for the growth of osteosarcoma and thus will be useful to further understand the biologic behavior of osteosarcoma in association with the defects in the p53 and RB pathways.

Frequent inactivation of the cyclin-dependent kinase inhibitor p18 by homozygous deletion in multiple myeloma cell lines: ectopic p18 expression inhibits growth and induces apoptosis

Multiple myeloma (MM) is a clonal neoplasm of plasma cells which offers an excellent model to study multistep molecular oncogenesis. In 20-25% of primary tumors and cell lines examined, cyclin D1 is overexpressed due to the translocation t(11;14)(q13;q32). We have characterized cyclin-dependent kinase inhibitor p15 (CDKN2B), p16 (CDKN2A) and p18 (CDKN2C) deletions in cyclin D1-expressing and non-expressing MM cell lines. p18 was found to be frequently deleted (38%); in some cases p18 deletions coexisted with hemizygous p16 deletion. To examine the function of p18 as a putative tumor suppressor in myeloma cells, a zinc-inducible p18 construct was stably transfected into KMS12, a MM cell line with biallelic p18 and monoallelic p16 deletions as well as cyclin D1 overexpression. Ectopic expression of p18 caused 40-45% growth suppression as determined by trypan blue exclusion and MTS assays. p18 induction also resulted in apoptosis, suggesting that inhibition of the cyclin D1/CDK/pRb pathway in these tumor cells could be a crucial step toward the induction of tumor regression via apoptotic cell death. This cell cycle pathway is thus frequently mutated and provides a potentially novel target for gene therapeutic or pharmacologic approaches to human myeloma.

P16INK4a protein expression is associated with poor survival of the breast cancer patients after CMF chemotherapy

Immunohistochemical assay for p16 protein expession was performed in 192 breast carcinoma patients treated with adjuvant chemotherapy. p16 expression was observed in 78 cases (40.6%). The frequency of p16 expression significantly decreased in moderately differentiated (histologic grade II) cancers, 20 (19.6%) of 102. In poorly differentiated cancers (histologic grade III), p16 expression was not observed in all 16 cases. p16 expression was significantly associated with histologic grade of the breast carcinomas (p < 0.001). The proliferative index (PI: S + G2/M) of individual tumors was measured by DNA flow cytometry. In 114 tumors with PI less than 20%, p16 expression was observed in 59 tumors (49.1%). In the tumors with PI equal or more than 20%, p16 expression was observed in 22 (28.2%) of 78 cases. p16 expression was significantly decreased in the tumor with higher PI (p =0.003). For the other clinicopathologic variables, no significant association was found with p16 expression status. Immunohistochemical assay for p53 protein expression was performed on the same breast carcinomas. There was no significant association between p16 and p53 expression in breast carcinomas. During median follow-up period of 52 months (range: 40-72 months), 46 patients (25.8%) had recurrent disease and 32 patients (18.91%) died of recurrent disease. p16 expression was observed in 20 (43.5%) of 46 patients with recurrent disease, while its expression was observed in 58 patients (39.7%) of 146 patients who were free of recurrence during the study period. p16 expression had no significant impact on predicting recurrence of breast carcinoma. Fourteen patients (12.2%) of 114 patients whose tumors did not show p16 expression died of recurrent breast carcinoma, whereas 18 patients (23.1%) of 78 patients with p16 expressing tumor died during the follow-up period. There was a significant difference of patient survival according to p16 expression status (p = 0.039). These results indicate that p16 expression is useful in predicting response to chemotherapy in breast cancer patients. p16 protein seems to have a role in tumor growth and differentiation of the breast carcinoma.

Identification of a 1.2 Kb cDNA fragment from a region on 9p21 commonly deleted in multiple tumor types

Chromosome band 9p21 is a frequent target of homozygous deletion in many tumor types. Putative tumor suppressor genes, CDKN2A (p16), p14(ARF) and CDKN2B (p15), were localized to 9p21. However, there have been reports that suggest that there may be other genes targeted for inactivation in the region. We have developed a method to search for transcribed sequences within large genomic regions. We tested our approach in a 100-kilobase region on 9p21, which is 40 kilobases telomeric to CDKN2A. The method, termed expressed sequence selection (ESS), resulted in the isolation of genomic fragments known to be from 9q21 that are homologous to transcribed sequences. One fragment was used to obtain a 1.2 kilobase cDNA. The sequence of the 5' half of the cDNA was almost identical to exons 3-5 of the MTAP gene, which maps to chromosome band 9p21. The 3' portion of the cDNA had sequence homology to the ALA gene, which maps to chromosome arm 9q. Using Northern blot analysis, the 1.2 Kb cDNA identified several widely expressed transcripts ranging from 1 Kb to 8.5 Kb and displayed a complex pattern of alternative splicing in which certain exons of the 1.2 Kb cDNA are excluded from some of the splice products. Using cancer tissue Northern blots, we could show that all of the transcripts are absent from a leukemia cell line and a lung cancer cell line (K562, A549) with homozygous, genomic deletions within chromosome band 9p21. In addition, the 7 Kb transcript is also absent from two additional tumor cell lines (Molt4, a leukemia derived cell line, and in G361, a melanoma derived cell line) with homozygous deletions. Further investigation will determine whether the difference in the expression pattern between the 7 Kb transcript compared with the other sized transcripts could be due to specific targeting for alteration in certain tumor types.