Loss of 9p leads to p16INK4A down-regulation and enables RB/E2F1-dependent cell cycle promotion in gastrointestinal stromal tumours (GISTs).

Department of Pathology, Georg August University, Göttingen, Germany.
The Journal of Pathology (Impact Factor: 7.59). 07/2008; 215(3):253-62. DOI: 10.1002/path.2352
Source: PubMed

ABSTRACT Loss of chromosome 9p is a reliable predictor of malignant behaviour in gastrointestinal stromal tumours (GISTs). p16INK4A located at 9p21 inhibits the CDK4/6/cyclin D complex from phosphorylating RB. Phosphorylation of RB through CDK4/6/cyclin D in early G(1) phase frees the transcription factor E2F1 from RB and enables mRNA transcription of genes essential for G(1)/S phase transition. This study aims to determine the impact of 9p loss on mRNA and protein expression of p16INK4A and further key cell cycle regulators in the different phases of the cell cycle. Sixty primary GISTs previously characterized for 9p loss by comparative genomic hybridization were analysed for mRNA expression of p16INK4A, p15INK4B, CDK4, CDK6, cyclin D, p21CIP1p27KIP1, CDK2, cyclin E, cyclin B, RB and E2F1, using quantitative RT-PCR. The protein expression of CDK6, CDK2, p21CIP1, p27KIP1 and phosphorylated RB (S807/S811) was evaluated using protein arrays as a novel and highly sensitive platform for profiling of protein abundance and protein phosphorylation. In parallel, the nuclear percentages of immunohistochemical staining for p16INK4A, cyclin D, E2F1 and RB were quantified on a tissue microarray. GISTs with 9p loss had significantly higher proliferation rates, higher metastatic behaviour and shorter disease-free survival. On the molecular level, GISTs with 9p loss had a significantly reduced mRNA as well as nuclear protein expression of p16INK4A. RB was significantly more phosphorylated in these tumours, together with increased mRNA expression and nuclear staining for E2F1. Furthermore, GISTs with 9p loss had up-regulation of the late G1/S phase promoters CDK2 and cyclin E. We conclude that loss of 9p accompanied by early G1 phase inhibitor p16(INK4A) down-regulation in GISTs facilitates phosphorylation of RB, enabling E2F1-dependent transcription of genes essential for late G1/S phase transition. This study provides a possible basis for the accelerated proliferation and particularly malignant behaviour in GISTs with 9p loss.

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: High-grade soft tissue sarcomas are a heterogeneous, complex group of aggressive malignant tumors showing mesenchymal differentiation. Recently, soft tissue sarcomas have increasingly been classified on the basis of underlying genetic alterations; however, the role of aberrant DNA methylation in these tumors is not well understood and, consequently, the usefulness of methylation-based classification is unclear. We used the Infinium HumanMethylation27 platform to profile DNA methylation in 80 primary, untreated high-grade soft tissue sarcomas, representing eight relevant subtypes, two non-neoplastic fat samples and 14 representative sarcoma cell lines. The primary samples were partitioned into seven stable clusters. A classification algorithm identified 216 CpG sites, mapping to 246 genes, showing different degrees of DNA methylation between these seven groups. The differences between the clusters were best represented by a set of eight CpG sites located in the genes SPEG, NNAT, FBLN2, PYROXD2, ZNF217, COL14A1, DMRT2 and CDKN2A. By integrating DNA methylation and mRNA expression data, we identified 27 genes showing negative and three genes showing positive correlation. Compared with non-neoplastic fat, NNAT showed DNA hypomethylation and inverse gene expression in myxoid liposarcomas, and DNA hypermethylation and inverse gene expression in dedifferentiated and pleomorphic liposarcomas. Recovery of NNAT in a hypermethylated myxoid liposarcoma cell line decreased cell migration and viability. Our analysis represents the first comprehensive integration of DNA methylation and transcriptional data in primary high-grade soft tissue sarcomas. We propose novel biomarkers and genes relevant for pathogenesis, including NNAT as a potential tumor suppressor in myxoid liposarcomas.
    Genome biology 12/2013; 14(12):R137. · 10.30 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: We have previously described immune cells in untreated primary gastrointestinal stromal tumors (GIST). Here we compare immune cells in metastatic and primary GIST, and describe their chemoattractants. For this purpose, tissue microarrays from 196 patients, 188 primary and 51 metastasized GIST were constructed for paraffin staining. Quantitative analysis was performed for cells of macrophage lineage (Ki-M1P, CD68), T-cells (CD3, CD56) and B-cells (CD20). Chemokine gene-expression was evaluated by real-time RT-PCR. Immuno-localisation was verified by immunofluorescence. Ki-M1P+ cells were the predominant immune cells in both primary and metastatic GIST (2 8.8% ± 7.1, vs. 26.7% ± 6.3). CD68+ macrophages were significantly fewer, with no significant difference between primary GIST (3.6% ± 2.1) and metastases (4.6% ± 1.5). CD3+ T-cells were the most dominant lymphocytes with a significant increase in metastases (7.3% ± 2.3 vs. 2.2% ± 1.8 in primary GIST, P < 0.01). The percentage of CD56+ NK-cells was 1.1% ± 0.9 in the primary, and 2.4 ± 0.7 (P < 0.05) in the metastases. The number of CD20+ B-cells was generally low with 0.6% ± 0.7 in the primary and 1.8% ± 0.3 (P < 0.05) in the metastases. Analysis of the metastases showed significantly more Ki-M1P+ cells in peritoneal metastases (31.8% ± 7.4 vs. 18.2% ± 3.7, P < 0.01), whilst CD3+ T-cells were more common in liver metastases (11.7% ± 1.8 vs. 4.4% ± 2.6, P < 0.01). The highest transcript expression was seen for monocyte chemotactic protein 1 (MCP1/CCL2), macrophage inflammatory protein 1α (MIP-1α/CCL3) and the pro-angiogenic growth-related oncoprotein 1 (Gro-α/CXCL-1). Whilst the ligands were predominantly expressed in tumor cells, their receptors were mostly present in immune cells. This locally specific microenvironment might influence neoplastic progression of GIST at the different metastatic sites.
    International journal of clinical and experimental pathology. 01/2014; 7(7):3563-79.
  • [Show abstract] [Hide abstract]
    ABSTRACT: Loss of RB1 gene is considered either a causal or an accelerating event in retinoblastoma. A variety of mechanisms inactivates RB1 gene, including intragenic mutations, loss of expression by methylation and chromosomal deletions, with effects which are species- and cell type- specific. RB1 deletion can even lead to aneuploidy thus greatly increasing cancer risk. The RB1gene is part of a larger gene family that includes RBL1 and RBL2, each of the three encoding structurally related proteins indicated as pRb, p107 and p130, respectively. The great interest in these genes and proteins springs from their ability to slow down neoplastic growth. pRb can associate with various proteins by which it can regulate a great number of cellular activities. In particular, its association with the E2F transcription factor family allows the control of the main pRb functions, while the loss of these interactions greatly enhances cancer development. As RB1 gene, also pRb can be functionally inactivated through disparate mechanisms which are often tissue specific and dependent on the scenario of the involved tumor suppressors and oncogenes. The critical role of the context is complicated by the different functions played by the RB proteins and the E2F family members. In this review, we want to emphasize the importance of the mechanisms of RB1/pRb inactivation in inducing cancer cell development. The review is divided in three chapters describing in succession the mechanisms of RB1 inactivation in cancer cells, the alterations of pRb pathway in tumorigenesis and the RB protein and E2F family in cancer. J. Cell. Physiol. © 2013 Wiley Periodicals, Inc.
    Journal of Cellular Physiology 01/2013; · 4.22 Impact Factor