Deciphering the Role of SLX4IP in Telomere Maintenance Mechanisms

Abstract

Telomeres are protective caps found at chromosomal ends that act to prevent attrition of the genome and aberrant activation of DNA repair mechanisms. In somatic cells, telomeric DNA progressively shortens with rounds of replication until a critically short length is reached triggering the cell to undergo senescence to prevent loss of genomic information. However, some cells express telomerase to elongate telomeres and avoid reaching this critical length, thus instilling additional replicative capacity. Notably, 85% of all cancer cells upregulate telomerase and the remaining 15% primarily utilize the alternative lengthening of telomeres (ALT) pathway which relies upon homologous recombination. There is evidence to suggest that cancer cells have the ability to switch to the ALT pathway, should telomerase activity be compromised, but the molecular switch regulating this process is unknown. A recently identified protein, SLX4IP, appears to play a critical role in telomere homeostasis and the telomerase‐to‐‐ALT conversion. In order to identify the basic function of SLX4IP in telomere homeostasis, the interactome of SLX4IP must be interrogated to identify additional proteins involved under specific conditions. For example, identifying differences between the interactomes in telomerase‐positive and ALT‐positive cells will provide insight regarding SLX4IP in telomere maintenance mechanisms. Initially, immunoprecipitation experiments were carried out to identify discrepancies in the proportion of known SLX4IP binding partners among telomerase‐positive and ALT‐positive cell lines. As expected, SLX4IP interacts with TRF2, a telomeric binding protein, and SLX4, an ALT‐associated nuclease scaffold protein, but with varying degrees among the cell types tested. To further dissect the interactome of SLX4IP, wild type SLX4IP, an N‐terminal mutant being interrogated for structural studies, and a C‐terminal mutant which represents a deletion mutant identified in acute lymphoblastic leukemia patients exhibiting poor prognosis were stably overexpressed in telomerase‐positive and ALT‐positive cell lines followed by subsequent immunoprecipitation and proteomic evaluation. This evaluation will provide valuable information as to which regions of SLX4IP are responsible for orchestrating particular interactions in each cell type. With this knowledge, a greater understanding of SLX4IP's role in telomere homeostasis and the telomerase‐to‐ALT conversion can be elucidated.Support or Funding InformationThis work was supported in part by an NIH T32 (GM008803) grant.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.