Telomerase Recruitment Requires both TCAB1 and Cajal Bodies Independently

Abstract

The ability of most cancer cells to grow indefinitely relies on the enzyme telomerase and its recruitment to telomeres. In human cells, recruitment depends on the Cajal body RNA chaperone TCAB1 binding to the RNA subunit of telomerase (hTR) and is also thought to rely on an N-terminal domain of the catalytic subunit, hTERT. We demonstrate that coilin, an essential structural component of Cajal bodies, is required for endogenous telomerase recruitment to telomeres but that overexpression of telomerase can compensate for Cajal body absence. In contrast, recruitment of telomerase was sensitive to levels of TCAB1, and this was not rescued by overexpression of telomerase. Thus, although Cajal bodies are important for recruitment, TCAB1 has an additional role in this process that is independent of these structures. TCAB1 itself localizes to telomeres in a telomerase-dependent but Cajal body-independent manner. We identify a point mutation in hTERT that largely abolishes recruitment yet does not affect association of telomerase with TCAB1, suggesting that this region mediates recruitment by an independent mechanism. Our results demonstrate that telomerase has multiple independent requirements for recruitment to telomeres and that the function of TCAB1 is to directly transport telomerase to telomeres.

SUPPLEMENTAL MATERIAL

Supplemental material for this article may be found at http://dx.doi.org/10.1128/MCB.00379-12.

ACKNOWLEDGMENTS

We thank A. Neumann for help with microscopic analysis and J. Jurczyluk and N. Sasaki for plasmid construction. We thank Titia de Lange (Rockefeller University, New York, NY) and Christopher Counter (Duke University Medical Centre, Durham, NC) for the gift of plasmids. We are grateful to Timothy Adams and George Lovrecz (CSIRO, Melbourne, Australia) for assistance in establishing the telomerase overexpression system.

J.L.S. was supported by a National Health and Medical Research Council (NHMRC) Biomedical Research scholarship, the Cancer Institute of New South Wales Research Scholar Award, and the Judith Hyam Memorial Trust. This work was also supported by a Cancer Institute NSW Career Development and Support Fellowship (to T.M.B.); an Australian Postgraduate Award and a Cancer Institute of New South Wales Research Scholar Award (to K.G.Z.); a Cure Cancer Australia project grant (to H.A.P.); and NHMRC, Cancer Council NSW, and Association for International Cancer Research project grants (to T.M.B. and S.B.C.).