Mechanisms of telomere maintenance in liposarcomas (LPS)

Abstract

9017 Background: Maintenance of telomeres is essential for the continued cellular proliferation that is a hallmark of cancer. Accordingly, the components of the pathways regulating telomere length have been the subjects of intense study. In most epithelial tumors, telomeric DNA is replicated and maintained by telomerase. In contrast, sarcomas often utilize a telomerase-independent pathway for telomere maintenance, Alternative Lengthening of Telomeres (ALT). Methods: LPS were characterized for presence of telomerase activity using the telomere repeat amplification protocol (TRAP) assay. As an independent assay for telomerase activity we carried out RT-PCR to detect mRNA encoding the telomerase catalytic subunit, hTERT. Southern analysis was used to determine telomere length. Indirect immunofluorescence was done to detect association of telomeric components with the PML nuclear body in ALT-associated PML bodies (APBs), structures characteristic of cells that use ALT for telomere maintenance. Results: Thirty LPS were analyzed, of which 8 (27%) had evidence of telomerase activity by either TRAP or RT-PCR. Telomerase activity was present in all grades of tumor. Telomeres characteristic of ALT were found in 4 of the 22 (18%) telomerase-negative tumors. “ALT-type” telomeres were also observed in 2 of the telomerase-positive LPS. Low or intermediate grade telomerase-negative tumors had telomeres within the size range more commonly associated with telomerase-positive samples (<15kb). APBs were present in all of the telomerase-negative tumors with ALT-type telomeres, as well as in one telomerase-negative tumor with shorter telomeres. APBs were not observed in any telomerase positive LPS. APBs were also not detected in some telomerase negative tumors that had telomeres of intermediate length, 9 kb to 12 kb. Conclusions: Telomerase is only active in a subset of tumors limiting the potential efficacy of telomerase inhibitors. ALT is active in a significant fraction of LPS. We have not found evidence of the two pathways, telomerase and ALT, being active in a single LPS. A proportion of tumors that can not be classified as either ALT or telomerase, suggesting that neither pathway is constitutively active in some LPS. No significant financial relationships to disclose.