Recently we proposed the hypothesis that extensive telomeric association of chromosomes is an early manifestation of cell death and asked whether there are extensive telomeric associations present in metaphases of the spontaneously regressing Sinclair swine cutaneous
melanoma (SSCM). Our results indicate that early passage SSCMs, in the accelerated growth phase, do not show telomeric associations but do have numerical and other specific structural abnormalities. However, the same
melanoma cell lines at late passages or
melanomas obtained from middle- and old-aged Sinclair swine show extensive telomeric associations in the form of dicentric, multicentric, and ring configurations. Such abnormal structures are present mostly in metaphases that are hyperploids. Increasing frequencies of apoptotic bodies were also observed in higher passage tumor cell lines obtained from younger animals or in
melanomas obtained from older animals. The polymerase chain reaction (PCR)-based telomeric repeat amplification protocol (TRAP) assay shows no detectable
telomerase activity in any of these regressing swine
melanoma cell lines, neither in normal swine skin fibroblasts nor in
nevi. However, the fetal swine (i.e., non-regressing)
melanoma cells show
telomerase activity. Fluorescence in situ hybridization (FISH) results using the commercially available human telomeric repeat
DNA probe indicate a reduction of telomeric signals in metaphase and interphase cells of regressing
melanomas. From these observations we conclude that
spontaneous regression of SSCM is associated with the loss of
telomerase activity and a reduction of telomeric repeats that results in the formation of multicentric and ring configurations. Such abnormal chromosome configurations are lost, following the breakage-fusion-bridge-cycles, and result in extensive DNA fragmentation, as shown by laddering experiments, and, finally, cell death.