Cancer cells bypass replicative senescence, the major barrier to tumor progression, by using telomerase or alternative lengthening of telomeres (ALT) as telomere maintenance mechanisms (TMMs). Correlation between ALT and patient survival was demonstrated for high-grade astrocytomas. Transcription from subtelomeres produces telomeric repeat-containing RNA (TERRA), a natural inhibitor of telomerase activity (TA). This led us to evaluate correlations of TERRA and TMM with tumor grade and outcome in astrocytoma patients. SYBR Green real-time reverse transcription-polymerase chain reaction assays for quantitation of total and chromosome 2p and 18p specific TERRA levels were developed. Tumor samples from 46 patients with astrocytoma grade 2 to 4, tissue controls, and cell lines were assessed. TMMs were evaluated by measuring TA and by detecting long telomeres due to ALT. In glioblastoma multiforme (GBM) grade 4, total TERRA levels were similar to cell lines but 14-, 31-, and 313-fold lower compared with grade 3, grade 2, and nonmalignant tissue, respectively. Total TERRA levels differed from chromosomal levels. Low 2p TERRA levels correlated with dense promoter methylation of subtelomeric CpG islands, indicating that TERRA expression in gliomas may be chromosome specific and epigenetically regulated. Total TERRA levels correlated with diagnosis, with low or absent TA and the presence of ALT, and were tentatively associated with favorable patient prognosis in our cohort (P = .06). TA and short telomeres identified a subset of GBM with a median survival of only 14.8 months. TERRA and TA may be prognostic in astrocytic tumors.

Alternative splicing of the IgIII loop of fibroblast growth factor receptors (FGFRs) 1–3 produces b- and c-variants of the receptors with distinctly different biological impact based on their distinct ligand-binding spectrum. Tissue-specific expression of these splice variants regulates interactions in embryonic development, tissue maintenance and repair, and cancer. Alterations in FGFR2 splicing are involved in epithelial mesenchymal transition that produces invasive, metastatic features during tumor progression. Recent research has elucidated regulatory factors that determine the splice choice both on the level of exogenous signaling events and on the RNA-protein interaction level. Moreover, methodology has been developed that will enable the in depth analysis of splicing events during tumorigenesis and provide further insight on the role of FGFR 1–3 IIIb and IIIc in the pathophysiology of various malignancies. This paper aims to summarize expression patterns in various tumor types and outlines possibilities for further analysis and application.

A hallmark of cancer cells is an activated telomere maintenance mechanism, which allows prolonged survival of the malignant cells. In more than 80% of tumours, telomeres are elongated by the enzyme telomerase, which adds de novo telomere repeats to the ends of chromosomes. Cancer cells are also characterized by expression of active LINE-1 elements (L1s, long interspersed nuclear elements-1). L1 elements are abundant retrotransposons in the eukaryotic genome that are primarily known for facilitating aberrant recombination. Using L1-knockdown (KD), we show for the first time that L1 is critical for telomere maintenance in telomerase-positive tumour cells. The reduced length of telomeres in the L1-KD-treated cells correlated with an increased rate of telomere dysfunction foci, a reduced expression of shelterin proteins and an increased rate of anaphase bridges. The decreased telomere length was associated with a decreased telomerase activity and decreased telomerase mRNA level; the latter was increased upon L1 overexpression. L1-KD also led to a decrease in mRNA and protein expression of cMyc and KLF-4, two main transcription factors of telomerase and altered mRNA levels of other stem-cell-associated proteins such as CD44 and hMyb, as well as a corresponding reduced growth of spheroids. The KD of KLF-4 or cMyc decreased the level of L1-ORF1 mRNA, suggesting a specific reciprocal regulation with L1. Thus, our findings contribute to the understanding of L1 as a pathogenicity factor in cancer cells. As L1 is only expressed in pathophysiological conditions, L1 now appears to be target in the rational treatment of telomerase-positive cancer.

Fibroblast growth factor receptors (FGFRs) are important in malignant progression of several human epithelial tumors. However, little is known about FGFRs in canine or human soft tissue sarcomas. Thus, our aim was to investigate expression of FGFRs and their involvement in cell survival in sarcomas of both species. FGFR1-4 and FGFRL1 transcripts as well as IIIb/IIIc splice variants of FGFR1-3 were evaluated in 3 canine- and 6 human sarcoma cell lines and 19 spontaneous canine sarcomas by SYBRqPCR. FGFR1 protein expression was assessed by immunohistochemistry. Growth inhibitory effects of FGFR1 inhibitor PD166866 and dominant negative recombinant FGFR adenoviral expression constructs (dnFGFR) on tumor cell lines were analyzed. Profiling of multiple FGFR transcripts detected comparable co-expression in most of human and canine sarcoma cell lines and canine tumor specimens. This indicates existence of closely related regulation mechanisms for FGFR expression in sarcomas of both species. FGFR1 with splice variant IIIc was consistently expressed with highest transcript levels. In 88% of the spontaneous tumor samples a heterogeneous FGFR1 protein expression was observed. Significant growth inhibition and cell death was seen after infection with dnFGFR1 in canine and human sarcoma cells, but not with dnFGFR3 and 4. PD166866 showed selective cytotoxicity with IC50 values between 12.1 and 26.4 μM. FGFR1 inhibition blocked ligand-induced tyrosine phosphorylation of ERK1/2 mitogen-activated protein kinase isoforms. This study emphasizes the important role FGFR1, especially splice variant IIIc, likely plays in sarcomas. Inhibitory small molecules could be of potential use for targeted therapy in aggressive sarcomas of both species.