Involvement Of Tumor Suppressor Genes Research Articles

Abstract 5839: Identification of low-dose ligand dependent drug-resistance in ALK/ROS1 positive NSCLC via CRISPR library screening

Abstract Tyrosine kinase inhibitor (TKI) therapy has displayed significant effectiveness in treating patients with anaplastic lymphoma kinase (ALK) and ROS proto-oncogene 1 (ROS1)-positive non-small cell lung cancer (NSCLC). Nonetheless, the emergence of acquired resistance in most patients presents a major challenge. Drug-tolerant persister (DTP) cells have recently gained attention as potential sources of resistance, highlighting the need for a deeper understanding of drug resistance mechanisms. To address this issue, a comprehensive genome-wide CRISPR-Cas9 knockout screening was conducted using an ALK-positive NSCLC cell line derived from pleural effusion in a patient who had not been exposed to ALK-TKI treatment. Following a 9-day ALK-TKI treatment, sequencing analysis was performed to identify sgRNAs in DTP cells. Notably, this analysis detected the involvement of tumor suppressor genes, including NF2, BAX, and ERRFI1.NF2 depletion was found to induce a substantial resistance to ALK-TKIs, and a combination therapy involving mTOR inhibitors showed promise in partially overcoming this resistance. Moreover, knockout of ERRFI1 or BAX led to an increase in DTP cells, drawing particular attention to ERRFI1, also known as MIG6, which is known for negatively regulating EGFR signaling. One intriguing discovery was that the loss of MIG6 induced resistance to ALK-TKIs when exposed to a relatively low dose of EGF, comparable to concentrations in plasma of healthy adults. This resistance was attributed to the upregulation of the MAPK and PI3K/Akt/mTOR pathways. Similar to ALK-rearranged NSCLC, ROS1 fusion-positive NSCLC cell lines also showed resistance by MIG6 knockout. Interestingly, some cell lines with reduced MIG6 expression tended to develop resistance with low-dose EGF, even without prior treatment, and overexpression of MIG6 restored sensitivity to TKIs. We further explored the potential of combination therapy, combining ALK-TKIs with anti-EGFR antibodies, and this approach effectively addressed acquired resistance in both in vivo and in vitro models. Furthermore, an analysis of clinical samples revealed that individuals resistant to ALK-TKIs displayed decreased mRNA MIG6 levels in comparison to their sensitive counterparts. Investigating the mechanisms behind MIG6 expression, we confirmed that ALK-TKI therapy suppressed MIG6 expression levels, while factors such as corticosteroid usage or exposure to hypoxia induced the upregulation of MIG6, potentially influencing the formation of DTP cells. In conclusion, this research has unveiled a novel factor contributing to resistance in ALK and ROS1-TKI therapies by activating the EGFR pathway through exposure to low-dose ligands, shedding light on potential therapeutic strategies to combat acquired resistance. Citation Format: Nobuyuki Kondo, Takahiro Utsumi, Ken Uchibori, Yasunari Miyazaki, Ryohei Katayama. Identification of low-dose ligand dependent drug-resistance in ALK/ROS1 positive NSCLC via CRISPR library screening [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 5839.

Mutational landscape of cancer-driver genes across human cancers

The genetic mutations that contribute to the transformation of healthy cells into cancerous cells have been the subject of extensive research. The molecular aberrations that lead to cancer development are often characterised by gain-of-function or loss-of-function mutations in a variety of oncogenes and tumour suppressor genes. In this study, we investigate the genomic sequences of 20,331 primary tumours representing 41 distinct human cancer types to identify and catalogue the driver mutations present in 727 known cancer genes. Our findings reveal significant variations in the frequency of cancer gene mutations across different cancer types and highlight the frequent involvement of tumour suppressor genes (94%), oncogenes (93%), transcription factors (72%), kinases (64%), cell surface receptors (63%), and phosphatases (22%), in cancer. Additionally, our analysis reveals that cancer gene mutations are predominantly co-occurring rather than exclusive in all types of cancer. Notably, we discover that patients with tumours displaying different combinations of gene mutation patterns tend to exhibit variable survival outcomes. These findings provide new insights into the genetic landscape of cancer and bring us closer to a comprehensive understanding of the underlying mechanisms driving the development of various forms of cancer.

Germline large genomic alterations on 7q in patients with multiple primary cancers

Patients with multiple primary cancers (MPCs) are suspected to have a hereditary cancer syndrome. However, only a small proportion may be explained by mutations in high-penetrance genes. We investigate two unrelated MPC patients that met Hereditary Breast and Ovaria Cancer criteria, both presenting triple negative breast tumors and no mutations in BRCA1, BRCA2 and TP53 genes. Germline rearrangements on chromosome 7q, involving over 40 Mb of the same region, were found in both patients: one with mosaic loss (80% of cells) and the other with cnLOH (copy-neutral loss of heterozygosity) secondary to maternal allele duplication. Five children tested had no alterations on 7q. The patients shared 330 genes in common on 7q22.1-q34, including several tumor suppressor genes (TSGs) previously related to breast cancer risk and imprinted genes. The analysis of the triple negative BC from one patient revealed a mosaic gain of 7q translated for over-expressed cancer-related genes. The involvement of TSGs and imprinted genes, mapped on 7q, has the potential of being associated to MPC risk, as well as cancer progression. To our knowledge, this is the first description of patients with MPCs that harbor constitutive large alterations on 7q.

WWOX: a fragile tumor suppressor.

WWOX, the WW domain-containing oxidoreductase gene at chromosome region 16q23.3-q24.1, spanning chromosomal fragile site FRA16D, encodes the 46 kDa Wwox protein, a tumor suppressor that is lost or reduced in expression in a wide variety of cancers, including breast, prostate, ovarian, and lung. The function of Wwox as a tumor suppressor implies that it serves a function in the prevention of carcinogenesis. Indeed, in vitro studies show that Wwox protein interacts with many binding partners to regulate cellular apoptosis, proliferation, and/or maturation. It has been reported that newborn Wwox knockout mice exhibit nascent osteosarcomas while Wwox(+/-) mice exhibit increased incidence of spontaneous and induced tumors. Furthermore, absence or reduction of Wwox expression in mouse xenograft models results in increased tumorigenesis, which can be rescued by Wwox re-expression, though there is not universal agreement among investigators regarding the role of Wwox loss in these experimental models. Despite this proposed tumor suppressor function, the overlap of the human WWOX locus with FRA16D sensitizes the gene to protein-inactivating deletions caused by replication stress. The high frequency of deletions within the WWOX locus in cancers of various types, without the hallmark protein inactivation-associated mutations of "classical" tumor suppressors, has led to the proposal that WWOX deletions in cancers are passenger events that occur in early cancer progenitor cells due to fragility of the genetic locus, rather than driver events which provide the cancer cell a selective advantage. Recently, a proposed epigenetic cause of chromosomal fragility has suggested a novel mechanism for early fragile site instability and has implications regarding the involvement of tumor suppressor genes at chromosomal fragile sites in cancer. In this review, we provide an overview of the evidence for WWOX as a tumor suppressor gene and put this into the context of fragility associated with the FRA16D locus.

SDF-1/CXCR4 signal is involved in decreased expression of p57kip2 in de novo MDS patients

P57kip2 is considered as a candidate tumor suppressor gene involvement in cell cycle control. In this study, we explored the expression of p57kip2 in various myelodysplastic syndrome (MDS) subsets by real-time quantitative PCR, as well as the relationship between p57kip2 and CXC receptor 4 (CXCR4). We also searched the role of stromal cell-derived factor-1 (SDF-1)/CXCR4 signal in p57kip2 expression in vitro. The expression of p57kip2 decreased in MDS cases (low grade MDS, P<0··001, n = 46; high grade MDS, P<0··001, n = 21), compared with that in control group. Patients with poor karyotype (according to IPSS) had lower p57kip2 than that in the normal group (P<0··05). P57kip2 expression increased after treatment with decitabine in the cases that had achieved response (P = 0··009, n = 7). Additionally, a positive correlation between p57kip2 and CXCR4 was investigated (r = 0··652, P<0··001, n = 67). P57kip2 expression in bone marrow mononuclear cells of normal controls increased significantly when co-cultured with SDF-1 in vitro, which could be blocked by AMD3100, whereas SDF-1 only induced a mild increase in p57kip2 in MDS. In conclusion, low expression of p57kip2 is common in MDS, which may play an important role in MDS pathogenesis. Reduced response to SDF-1 contributed to low expression of p57kip2 in MDS cases.

The biology of ovarian cancer development.

In theory, all the cell types that comprise the human ovary have the potential for malignant transformation. The vast majority of malignant ovarian tumors in the human, however, arise from the ovarian surface epithelium. These cells have important functions during reproductive life; they contribute to follicular rupture and by cell division repair the wound that accompanies ovulation. There has been much speculation that the rapid cycles of cell division associated with wound repair contribute significantly to the development of ovarian cancer. Such speculation is based on the observation that ovarian cancer occurs most frequently at the end of a woman's reproductive life and is associated with nulliparity. It is of potential significance that, unlike most epithelia, these cells are not replaced through replenishment stem cells with the development of one end-stage cell and one cell with continued growth potential. Rather, the division of an ovarian surface epithelial cell yields two daughter cells with equal potential for subsequent growth. Thus, all potential mutations as they accumulate are passed on to near-exponentially expanding subsequent generations of cells that can acquire additional mutations that could confer the malignant phenotype. We have developed a model to test the hypothesis that repeated cell division by ovarian surface epithelial cells contributes to development of malignancy. In this model, rat ovarian surface epithelial cells are isolated and subjected in vitro to repetitious cell division to mimic in a simple way growth of the surface epithelium in vivo. These cells develop a malignant phenotype based on loss of contact inhibition, the ability for substrate independent growth, tumorigenicity in athymic mice, and cytogenetic changes. Our data support the involvement of tumor suppressor genes in the development of ovarian cancer.

Molecular pathways in myelodysplastic syndromes and acute myeloid leukemia: relationships and distinctions–a review

The myelodysplastic syndromes (MDS) and acute myeloid leukemia (AML) are both hematopoietic stem cell disorders. However, while leukemic stem cells have been revealed by clonal tracking experiments, dysplastic stem cells have never been demonstrated by xeno-transplantation assays because of poor engraftment problems. These engraftment difficulties may be due to the unique nature of MDS genetic lesions that are truly able to recapitulate the disease phenotype. MDS and AML of younger patients harbour clonal yet different chromosomal markers, whereas MDS and AML of the elderly present similar defects. Potential involvement of tumor suppressor genes in MDS has been hypothesized but never confirmed, while cooperation between class I and class II mutations has been identified in AML. The reciprocal interactions between stromal cells and neoplastic clones are disrupted in both MDS and AML. In early MDS, stromal and neoplastic cells produce high levels of inhibitory cytokines, whereas in advanced MDS and AML they produce high levels of anti-apoptotic molecules.

Whole Genome Association Study in Acute Myeloid Leukemia with a Normal Karyotype, Using a Single-Nucleotide Polymorphism (SNP) Analysis.

As a result of numerous genetic aberrations, acute myeloid leukemia (AML) present with very heterogeneous clinical features. Moreover, structural and numerical chromosome aberrations currently comprise the most important basis for predicting these heterogeneous outcomes. However, 30 to 50 percent of AML patients have cytogenetically normal karyotypes. Though submicroscopic genetic alterations (such as NPM1, CEBPA, MLL-PTD) are increasingly being used for clinical purposes, additional markers with prognostic or predictive value are still lacking in this group. In this study, we performed a genome-wide, single-nucleotide polymorphism (SNP) study in order to identify novel genomic regions of interest in normal karyotype AML. 54 untreated AML patients with normal karyotypes were analyzed with an Illumina infinium 317K SNP chip assay. SNP genotype call rate was 99.8 percent, resulting in a resolution of 1 SNP/Mb. In a genome-wide SNP analysis, 317 SNP loci, having a significant difference between AML and normal control, were found. In addition, about 300 loci were also identified, showing a significant difference between patients who achieved CR and those who did not. Some of these were found to be related with drug metabolism and MDR family. Also we used the SNP assay to screen a loss of heterozygosity (LOH), suggesting possible involvement of tumor suppressor genes. In summary, 38 LOH regions larger than 1Mb were observed in 23 cases (43%) among 54 AML patients having normal karyotypes. Most (55%) of them were copy-neutral events and the most frequently identified alterations were located at 3p, 8p, 13q and 22q. 11 (29%) out of 38 LOH regions had overlapping parts among them. Some LOHs were correlated with response to chemotherapy. Various genetic changes were discovered by use of an SNP-based chip array in normal karyotype AML patients. Moreover, some of these were related with CR acquisition and drug metabolism. These results can be used to differentiate normal karyotype AML and warrant further study.

Exclusion of APC and VHL gene deletions by array-based comparative hybridization in two patients with microscopically visible chromosomal aberrations

Karyotyping is a major component of the genetic work-up of patients with dysmorphism. Cytogenetic aberrations close to a known tumor suppressor gene raise important clinical issues because deletion of that tumor suppressor gene can cause genetic predisposition to cancer. We present two cancer-free dysmorphic patients with karyotypes of 46,XX,del(5)(q15q22.3) and 46,XX,del(3)(p25.2∼pter). These deletions are close to the APC and VHL genes that confer susceptibility to familial Adenomatous polyposis (OMIM #17510) and von-Hippel-Lindau syndrome (OMIM #193300), respectively. The array-based comparative genomic hybridization (array-CGH) analysis using a custom Agilent 44K oligonucleotide array demonstrated an interstitial 20.7-megabase (Mb) deletion on 5q (chr5: 89,725,638-110,491,345) and a terminal 9.45-Mb deletion on 3p (chr3:pter-9,450,984). According to the March 2006 human reference sequence, the APC gene is located at chr5: 112,101,483-112,209,835 and the VHL gene is located at chr3: 10,158,319-10,168,746. These results indicate that the APC gene is 2,300 kilobases (kb) and the VHL gene is 700 kb away from deleted regions. Southern blot analysis for APC and VHL genes were negative, consistent with array-CGH findings. These results demonstrate the power of array-CCH to assess potential tumor suppressor gene involvement and cancer risk in patients with microscopically visible deletions in areas near tumor suppressors.

Photocarcinogenesis inXiphophorusHybrid Models

The poeciliid fish genus Xiphophorus provides important models for investigating the etiology and genetics of sunlight-induced melanoma. Interspecific hybrids generated among platyfish and swordtails have been used as genetic tumor models, particularly for cutaneous malignant melanoma (CMM), for more than 6 decades. Oncogene and tumor suppressor gene involvement in a variety of spontaneous and carcinogen-induced tumors has been and continues to be extensively studied. Select hybrids develop melanoma spontaneously or after acute or chronic exposure to ultraviolet radiation. Many scientists believe that the etiology of CMM and particularly its initiation is different from other types of sunlight-induced skin cancers, and may involve free radical chemistry rather than the direct absorption of UVB by DNA. Xiphophorus offers a unique platform to scrutinize this question and determine the types of DNA damage that are involved, the solar wavelength ranges that are important, and the role of DNA repair genes in early tumorigenesis. The diverse photochemical and photobiological responses observed in the different Xiphophorus species and interspecies hybrids suggest that heritable traits governing DNA damage induction and repair may be involved in the susceptibility of Xiphophorus hybrids to melanomagenesis.

Analysis of Loss of heterozygosity and immunohistochemistry in BRCA1 gene in sporadic breast cancers

BRCA1 is a tumour suppressor gene (TSG), which predisposes cancer to both breast and ovary. The primary objective of the present study is to ascertain the involvement of BRCA1 gene in the pathogenesis of sporadic breast cancer women in Chennai (South India) by analysing its protein expression by immunohistochemistry (IHC) and loss of heterozygosity (LOH) for confirmation of the involvement of TSG in the study population. We found down regulation of BRCA1 protein (54%) in IHC and it was correlated with the clinicopathological parameters of the patients. We found near significant correlation (P < 0.063) between BRCA1 protein expression and clinicopathological parameters. We found 30% LOH in our study and it was also correlated with the clinicopathological parameters. No correlation was found between LOH and clinicopathological parameters. Though we found no correlation, the results revealed in this study support the involvement of BRCA1 TSG in the pathogenesis of sporadic breast cancer women in Chennai (South India).

Tumor suppressor genes in normal and malignant hematopoiesis.

Over the last decade, a growing number of tumor suppressor genes have been discovered to play a role in tumorigenesis. Mutations of p53 have been found in hematological malignant diseases, but the frequency of these alterations is much lower than in solid tumors. These mutations occur especially as hematopoietic abnormalities become more malignant such as going from the chronic phase to the blast crisis of chronic myeloid leukemia. A broad spectrum of tumor suppressor gene alterations do occur in hematological malignancies, especially structural alterations of p15(INK4A), p15(INK4B) and p14(ARF) in acute lymphoblastic leukemia as well as methylation of these genes in several myeloproliferative disorders. Tumor suppressor genes are altered via different mechanisms, including deletions and point mutations, which may result in an inactive or dominant negative protein. Methylation of the promoter of the tumor suppressor gene can blunt its expression. Chimeric proteins formed by chromosomal translocations (i.e. AML1-ETO, PML-RARalpha, PLZF-RARalpha) can produce a dominant negative transcription factor that can decrease expression of tumor suppressor genes. This review provides an overview of the current knowledge about the involvement of tumor suppressor genes in hematopoietic malignancies including those involved in cell cycle control, apoptosis and transcriptional control.

Loss of heterozygosity in childhood de novo acute myelogenous leukemia

A genome-wide screening for loss of heterozygosity (LOH), a marker for possible involvement of tumor suppressor genes, was conducted in 53 children with de novo acute myelogenous leukemia (AML). A total of 177 highly polymorphic microsatellite repeat markers were used in locus-specific polymerase chain reactions. This comprehensive allelotyping employed flow-sorted cells from diagnostic samples and whole-genome amplification of DNA from small, highly purified samples. Nineteen regions of allelic loss in 17 patients (32%) were detected on chromosome arms 1q, 3q, 5q, 7q (n = 2), 9q (n = 4), 11p (n = 2), 12p (n = 3), 13q (n = 2), 16q, 19q, and Y. The study revealed a degree of allelic loss underestimated by routine cytogenetic analysis, which failed to detect 9 of these LOH events. There was no evidence of LOH by intragenic markers for p53, Nf1, or CBFA2/AML1. Most lymphocytes lacked the deletions, which were detected only in the leukemic myeloid blast population. Analysis of patients' clinical and biologic characteristics indicated that the presence of LOH was associated with a white blood cell count of 20 x 10(9)/L or higher but was not correlated with a shorter overall survival. The relatively low rate of LOH observed in this study compared with findings in solid tumors and in pediatric acute lymphoblastic leukemia and adult AML suggests that tumor suppressor genes are either infrequently involved in the development of pediatric de novo AML or are inactivated by such means as methylation and point mutations. Additional study is needed to determine whether these regions of LOH harbor tumor suppressor genes and whether specific regions of LOH correlate with clinical characteristics. (Blood. 2001;98:1188-1194)

Tumor suppressor loss in pituitary tumors.

The current model of human neoplasia invokes a number of potential genomic alterations that impact cellular phenotype and proliferative rates. In the majority of human tumor models, the transformation from normal cells to neoplastic lesion is a multistep process. This review offers a specific overview of the involvement of tumor suppressor genes (TSGs) in the pathogenesis of human pituitary adenomas. TSG genetic lesions, such as BRCA1 in breast cancer and p53 in Li-Fraumeni Syndrome, have been identified in both sporadic and heritable human endocrine tumors. Familial neoplastic syndromes like multiple endocrine neoplasia type 1 (MEN1) that include pituitary tumor formation as part of a broad clinical spectrum of disease represent a unique opportunity to investigate the general mechanisms of tumorigenesis, and well as genes responsible for sporadic endocrine tumors. Similarly, homologous recombination knockout mice with selectively ablated candidate TSGs have also shed light on the molecular mechanisms of pituitary cell proliferation and tumor suppression. However, despite insights into pituitary tumorigenesis generated by heritable neoplasia syndromes and mouse knockout of critical TSGs that display a pituitary tumor phenotype, the molecular pathogenesis of human pituitary adenomas remains largely an enigma. Thus, the role of TSGs, if any, in sporadic pituitary adenoma formation has yet to be determined, despite our greater understanding of the molecular mechanisms underlying pituitary cell function and phenotype.

Identification and refinement of two regions on chromosomal arm 15q involved in breast cancer progression

Loss of heterozygosity constitutes a major mechanism of genetic abberations in breast cancer, and strongly indicates the involvement of tumor-suppressor genes in the affected chromosomal regions. Ascertainment and refinement of such deleted regions by highly polymorphic microsatellite markers is a prerequisite for the identification of candidate genes and the isolation of novel genes. Prelimary results from our group indicate the existence of genes located on chromosomal arm 15q that may be involved in breast cancer progression to metastatic stage (Wick et al, Oncogene 1996). In this study a panel of 210 primary breast carcinomas, 28 metastases and 17 local recurrencies from primary breast carcinomas were analyzed for loss of heterozygosity by the use of 16 highly polymorphic markers spanning the chromosomal region 15q11-21. After PCR amplification, microsatellite markers were separated by PAGE. LOH15q was seen in 30 out of 45 (67%) metastases and recurrences, but only in 50 out of 210 (24%) primary tumors (P < 0.01). We identified two subregions defined by microsatellite markers D15S514 (15q15) and CYP19 (15q21.1). LOH15q21.1 was most frequently detected in progressive tumor stages. Importantly, analysis of LOH in several other chromosomal regions (ie BRCA1 and BRCA2, TP53, RB1, ATM) did not demonstrate a general increase in LOH frequencies, indicating that LOH15q is a specific event associated with tumor progression. We are currently analyzing candidate genes located in the regions of interest.

Genetic aberrations in oral or head and neck squamous cell carcinoma 2: chromosomal aberrations.

Carcinogenesis is the result of a series of genetic mutations resulting in unregulated growth of a clone of cells and the development of malignant lesion that is largely monoclonal though, with the evolution of further genetic changes, there develops a degree of heterogeneity in the tumour. DNA technology, especially allelic imbalance (loss of heterozygosity) studies have identified chromosomal changes in oral carcinoma and head and neck squamous cell carcinoma (SCCHN), suggestive of the involvement of tumour suppressor genes (TSGs), particularly in chromosomes 3, 9, 11 and 17. The regions most commonly identified have included 3p, especially 3p14.2 (FHIT); 3p24, and 3p21.3, where the TSGs involved are as yet unidentified; 9p21 where p16 (INK4A/MTS-1] is the main target TSG; and 17p13 where p53 is the major target TSG. Over-expression of oncogenes, genes mainly involved in cell signalling, especially those on chromosome 11 (PRAD-1 in particular) and 17 (H-ras) and mutations in DNA repair genes, have also been implicated in the carcinogenesis of SCCHN.

Three new regions on chromosome 17p13.3 distal to p53 with possible tumor suppressor gene involvement in lung cancer.

We investigated loss of heterozygosity (LOH) at the distal portion of the p53 gene on the short arm of chromosome 17 in lung cancers in order to search for new tumor suppressor genes. The roles of the putative genes were also studied in terms of pathological features. One hundred and forty‐five resected non‐small cell lung cancers were examined for LOH using 11 markers mapped on, and distal to the p53 locus, and deletion maps were constructed. Four commonly deleted regions were found: one from TP53 to ENO3, where the p53 gene resides, and three others from ENO3 to D17S1566, D17S379 to D17S1574 and distal to ABR, with LOH frequencies almost the same as, or higher than, at the TP53 locus. Examination of the relationship between LOH of the latter three regions and histopathological parameters of adenocarcinomas (genetically negative for p53 mutation) revealed allelic losses on D17S379 to be associated with advanced lesions, while D17S513 was more frequently deleted in poorly differentiated tumors. These results indicate that new tumor suppressor gene(s) may reside on these three distinctly deleted regions on chromosome 17p13.3 distal to the p53 gene in lung cancer, with possible roles in progression and differentiation of adenocarcinomas.

Absence of p16, p21 and p53 gene alterations in hepatocellular carcinomas induced by N-nitrosodiethylamine or a choline-deficient l-amino acid-defined diet in rats

To clarify the involvement of tumor suppressor genes in exogenous and endogenous liver carcinogenesis, alterations of p16, p21 and p53 in hepatocellular carcinomas (HCCs) induced by N-nitrosodiethylamine (DEN) and a choline deficient l-amino acid-defined (CDAA) diet in rats were investigated. Male Fischer 344 rats received DEN at 6-week of age followed by partial hepatectomy (PH), with colchicine to induce cell cycle disturbance, and a selection pressure regimen. Sacrifice was after 42 weeks. Other animals continuously received a CDAA diet for 75 weeks and were then killed. Eleven and 15 HCCs were obtained, respectively. Total RNA was extracted from and cDNA was synthesized with reverse transcriptase to allow investigation of mutations in p16, p21 and p53 by polymerase chain reaction single strand conformation polymorphism (PCR-SSCP) analysis. Expression of p16 and p21 mRNA was also analyzed by reverse transcription (RT)-PCR. The results showed no mutations or deletions of p16, p21 and p53 in any of the HCCs induced by DEN or CDAA. Loss or decrease of p16 and p21 expression were also not found, suggesting that p16, p21 and p53 alteration may not be necessary for either exogenous or endogenous liver carcinogenesis in rats.

Loss of Heterozygosity on Chromosome 10 Is More Extensive in Primary (De Novo) Than in Secondary Glioblastomas

Glioblastomas develop de novo (primary glioblastomas) or through progression from low-grade or anaplastic astrocytoma (secondary glioblastomas). There is increasing evidence that these glioblastoma subtypes develop through different genetic pathways. Primary glioblastomas are characterized by EGFR and MDM2 amplification/overexpression, PTEN mutations, and p16 deletions, whereas secondary glioblastomas frequently contain p53 mutations. Loss of heterozygosity (LOH) on chromosome 10 (LOH#10) is the most frequent genetic alteration in glioblastomas; the involvement of tumor suppressor genes, other than PTEN, has been suggested. We carried out deletion mappings on chromosome 10, using PCR-based microsatellite analysis. LOH#10 was detected at similar frequencies in primary (8/17; 47%) and secondary glioblastomas (7/13; 54%). The majority (88%) of primary glioblastomas with LOH#10 showed LOH at all informative markers, suggesting loss of the entire chromosome 10. In contrast, secondary glioblastomas with LOH#10 showed partial or complete loss of chromosome 10q but no loss of 10p. These results are in accordance with the view that LOH on 10q is a major factor in the evolution of glioblastoma multiform as the common phenotypic end point of both genetic pathways, whereas LOH on 10p is largely restricted to the primary (de novo) glioblastoma.

Genetic alterations on 3p, 11q13, and 18q in nonfamilial and MEN 1-associated pancreatic endocrine tumors

Pancreatic endocrine tumors occur sporadically and as part of the multiple endocrine neoplasia type 1 (MEN 1) and von Hippel-Lindau (VHL) syndromes. The MEN1 locus on 11q13 and a candidate tumor suppressor locus on 3p are known to be hemi- or homozygously mutated in a subset of these tumors. Chromosome arm 18q harbors the SMAD4/DPC4 tumor suppressor gene that is frequently deleted and inactivated in tumors of the exocrine pancreas. We have analyzed 22 nonfamilial and 16 MEN 1-associated pancreatic endocrine tumors for loss of heterozygosity (LOH) at 3p, 11q13, and 18q. LOH at 3p was revealed in 45% and 36% of tumors from 31 patients with nonfamilial and MEN 1-associated disease, respectively. The corresponding proportions for 11q13 were 55% and 91%, and for 18q 27% and 25%, respectively. A striking relation between LOH at 11q13 and 3p and a malignant phenotype was found for the nonfamilial tumors. None of the six benign tumors (all of them insulinomas) had allelic loss at 3p or 11q13, whereas 92% (P < 0.01) of the malignant tumors (including malignant insulinomas) had such deletions. Besides the 11q13 abnormality, more than half of the MEN 1-associated tumors had additional genetic lesions affecting 3p or 18q. LOH analysis of several tumors from two MEN 1 patients suggested different clonal origin of the lesions. Sequencing of the SMAD4/DPC4 gene did not identify mutations in coding regions or at exon/intron boundaries in tumors with LOH at 18q. The data indicate involvement of tumor suppressor genes on 3p and 18q, in addition to the MEN1 gene at 11q13, in the tumorigenesis of both nonfamilial and MEN 1-associated pancreatic endocrine tumors.