Altered telomeres in tumors with ATRX and DAXX mutations

Abstract

The proteins encoded by ATRX and DAXX participate in chromatin remodeling at telomeres and other genomic sites. Because inactivating mutations of these genes are common in human pancreatic neuroendocrine tumors (PanNETs), we examined the telomere status of these tumors. We found that 61% of PanNETs displayed abnormal telomeres that are characteristic of a telomerase-independent telomere maintenance mechanism termed ALT (alternative lengthening of telomeres). All of the PanNETs exhibiting these abnormal telomeres had ATRX or DAXX mutations or loss of nuclear ATRX or DAXX protein. ATRX mutations also correlate with abnormal telomeres in tumors of the central nervous system. These data suggest that an alternative telomere maintenance function may operate in human tumors with alterations in the ATRX or DAXX genes.

Fig. 1

Representative images of ALT-positive tumors with ATRX or DAXX mutations. (A) Example of ALT-positive PanNET. Large, ultrabright telomere FISH signals (red) indicative of ALT are marked (arrows). (B)Immunolabeling of the same PanNET shows loss of nuclear DAXX protein in tumor cells. (C) Example of ALT-positive GBM. Large, ultrabright telomere FISH signals (red) indicative of ALT are marked (arrows). (D) Immunolabeling of the same GBM shows loss of nuclear ATRX protein in tumor cells. In (B) and (D), benign endothelial cells (arrowheads) served as positive immunostaining controls. Scale bars, 30 mm.