Figure 5.

Model of telomeres as platform for cell signaling. (A) In the presence of telomerase, telomeres remain stable. In the absence of Wnt, cytosolic β-catenin (β-ctn, green particle) associates with the APC (red particle) and the kinase GSK3β (blue particle). Free β-catenin is rapidly degraded by the proteasome. The majority of β-catenin is bound to the cell membrane in a complex with E-cadherin (yellow element at the plasma membrane). (B) In the absence of telomerase, telomeres shorten and the protective effect of shelterin is eventually lost (yellow dots). Telomere shortening affects epigenetics marks in sub-telomeric regions and at the global genome level (small blue arrow). Signals emanating from telomeres, directly or indirectly, can alter cell signaling. One sign of this influence is the accumulation of β-catenin in the cytosol as result of proteasome impairment or higher nuclear export by APC. Cell signaling changes may also affect proteins expressed at the cell membrane and influence cell adhesion properties (larger blue arrow).