# TET enzymes as guardians of genome stability

> **NIH NIH R35** · LA JOLLA INSTITUTE FOR IMMUNOLOGY · 2020 · $1,080,000

## Abstract

Project summary/ abstract
In 2009, my laboratory discovered the enzymatic activities of the three mammalian TET (Ten-Eleven-Translo-
cation) proteins, TET1, TET2 and TET3. Since then, work from our own and other groups has implicated TET
proteins in regulating gene expression, cell lineage specification, embryonic development, neuronal function
and cancer. TET proteins are dioxygenases that oxidize 5-methylcytosine (5mc) to 5-hydroxymethylcytosine
(5hmC) and further oxidized methylcytosines (oxi-mC). They have two biochemical functions: to generate oxi-
mC and to facilitate DNA demethylation. However, the mechanisms by which TET proteins exert their diverse
biological effects are much less understood.
TET2 mutations are frequently observed in myeloid malignancies, but many other cancers are documented to
have low 5hmC levels, implying profound loss of TET function even in the absence of TET coding region muta-
tions. Because TET loss-of-function is associated with increased DNA methylation, the tumor suppressive role
of TET proteins has been assumed to involve their ability to maintain DNA in a demethylated state. However,
in powerful, inducible mouse models developed in our laboratory, we have shown that acute deletion of both
Tet2 and Tet3 rapidly induces an aggressive, transmissible myeloid leukemia within 4 weeks and with 100%
penetrance. Using this system, we have found that while the average level of DNA methylation increases
across expressed genes in early hematopoietic stem/precursor cells as expected, there is little or no correla-
tion of increased or decreased DNA methylation with up- or down-regulation of gene expression or with onco-
genesis. Instead, we observe a strong correlation of oncogenic transformation with increased phospho-H2AX
and impaired DNA damage repair. Here we propose to extend these studies to address the mechanisms
involved.
In this project we will use mouse models as well as in vitro systems to analyze the mechanisms of oncogenesis
induced by TET loss-of-function. We will examine the role of TET catalytic activity, and compare the conse-
quences of loss-of-function of TET proteins versus DNA methyltransferases (DNMTs). We will examine the
kinetic relation between loss of oxi-mC in expanding cells and the development of replication stress, genome
instability and chromosomal aberrations. As feasible, we will perform RNAi/CRISPR screens to identify
important players that regulate cell expansion induced by TET loss-of-function. We will extend our findings to
human cancers with high and low 5hmC. Our studies have the potential to change current paradigms and
suggest new therapeutic approaches, by defining the mechanisms by which TET function is linked to genome
stability.

## Key facts

- **NIH application ID:** 9978730
- **Project number:** 5R35CA210043-05
- **Recipient organization:** LA JOLLA INSTITUTE FOR IMMUNOLOGY
- **Principal Investigator:** Anjana Rao
- **Activity code:** R35 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $1,080,000
- **Award type:** 5
- **Project period:** 2016-09-01 → 2023-08-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/9978730

## Citation

> US National Institutes of Health, RePORTER application 9978730, TET enzymes as guardians of genome stability (5R35CA210043-05). Retrieved via AI Analytics 2026-05-23 from https://api.ai-analytics.org/grant/nih/9978730. Licensed CC0.

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