PROJECT SUMMARY
Telomeres are specialized protein-DNA structures that protect the ends of linear chromosomes and
maintain genomic stability. Maintenance of adequate telomere length is thus essential for cellular
immortalization and tumorigenesis. While most human cancers achieve this through telomerase
activation, ~ 5% - 10% of them adopt a recombination-based mechanism termed alternative lengthening
of telomeres (ALT) to elongate their telomeres. Although the ALT-driven cancers are generally aggressive
with poor prognosis, there are currently no targeted therapies. In human cancers, ALT is strongly
associated with genetic alterations that affect histone H3.3 chaperone ATRX-DAXX complex. We and
others previously demonstrated that the ATRX-DAXX complex is essential for normal telomere
maintenance. We showed that ATRX or DAXX loss, while promoting tumorigenesis by potentiating the
ALT-driven immortalization, also creates a persistent telomere replication dysfunction. We therefore
hypothesize that ALT-immortalized cancers must have adopted special mechanism(s) to offset their
innate telomere DNA replication defects, and thus would be selectively vulnerable to the inhibition of
those compensatory pathways. By combining our unique isogenic ALT-immortalization model system
and customized domain-focused CRISPR screen platform, we have uncovered a list of selective
molecular vulnerabilities including histone lysine demethylase KDM2A for ALT-dependent cells. We
demonstrate that KDM2A-mediated H3K36me2 demethylation is required for ALT-directed telomere
maintenance. Inactivation of KDM2A impairs ALT-specific multitelomere cluster dissolution, leading to
chromosome missegregation and mitotic cell death. The objectives of this proposal are to delineate the
molecular mechanism underlying ALT-directed telomere maintenance and to identify mechanism-based
therapeutic targets against ALT-driven human cancers. To meet those goals, we will pursue the following
three specific aims. In Aim 1, we will investigate the molecular functions of KDM2A in ALT-directed
telomere maintenance. In Aim 2, we will define the potential adverse effects and off-tumor toxicities of
future KDM2A-targeted therapies. In Aim 3, we will establish an in vivo platform to explore the synthetic-
lethal interactions of ALT-driven ATRX-mutant malignant gliomas. Completion of the proposed studies
will uncover the molecular mechanisms and critical dependencies underlying ALT-directed telomere
maintenance and thus drive the development of novel mechanism-based therapeutics against ALT-
dependent cancers including the ATRX mutant malignant gliomas.