Genome stability and Chromosome Segregation: a Unique SET of Functions

Aliyah Weinstein, Ph.D.

hSET1, encoded by gene SETD1A, and also known as MLL, is a human lysine methyltransferase. hSET1 functions as a subunit of the histone H3K4 methyltransferase complex and is most functional within the COMPASS complex1. hSET1 interacts with numerous other nuclear proteins to regulate transcription and cellular differentiation through H3K4 methylation, and this function is conserved in SET1 orthologs across eukaryotes including yeast, drosophila, mice, and humans1-4.

Studies of SET1 in yeast identified that methylation of H3K4 is required for non-homologous end joining, a cellular mechanism that repairs double-stranded DNA breaks2. In the yeast Saccharomyces cerevisiae, SET1 can demethylate or trimethylate H3K4, and these methylation states are found in regions of the genome that are actively being transcribed, but not in heterochromatic regions5. During transcription, SET1 plays a crucial role in maintaining genome stability through its interaction with BOD1L. Both SET1 and BOD1L function as replication fork protection factors that facilitate migration of histone proteins to stalled replication forks to protect them from degradation 6. SET1 also physically interacts with phosphorylated RNA polymerase II. This interaction facilitates trimethylation of H3K4 near the transcription start site7, and indicates that trimethylation of H3K4 may be a mark of recently transcribed regions of the genome8 and may functionally suppress the activity of RNA polymerase II9. The ability of SET1 to methylate H3K4 is nonredundant, as ablation of SET1, but not other proteins containing a SET domain, abrogates H3K4 methylation and that this methylation is required for normal cell growth and the regulation of transcription9. SET1 is additionally involved in regulating transcription in telomeric regions by maintaining the integrity of telomeres10,11. In eukaryotes, SET1 silences the transcription of telomere associated satellite-like sequences10,12. The interaction between SET1 and MEC3 is important for telomeric stability, as SET1 requires MEC3 to silence transcription of telomeres13.

Independent of its effects on genome stability, SET1 plays an important role in chromosome segregation during the cell division process in yeast. SET1 impacts chromosome segregation through methylation of the kinetochore protein, Dam1. A balance between methylation of Dam1 by SET1, and phosphorylation of Dam1 by Ip11 is required for proper segregation of chromosomes during mitosis14.

Histone methyltransferases that contain a SET domain have been implicated in several types of cancer 15. hSET1 is being investigated as a novel therapeutic target for colon carcinoma as it was observed that blockade of hSET1 selectively induced apoptosis of cancer cells and led to regression of a transplantable model of colon cancer in a mouse model 16. Rearrangement of the gene encoding MLL, the human homolog to yeast hSET1, has been observed in a variety of hematologic malignancies including B and T cell lymphomas and acute myeloid leukemia 17, 18. In breast cancer, duplication of the gene encoding hSET1 has been observed, and expression of hSET1 maintains the expression of several matrix metalloproteinases that are involved in cancer metastasis19.

Detection of human hSET1 (red) in FFPE ovarian carcinoma by IHC-IF.
Detection of human hSET1 (red) in FFPE ovarian carcinoma by IHC-IF. Antibody: Rabbit anti-hSET1 recombinant monoclonal [BLR024E] (A700-024). Secondary:DyLight® 594-conjugated goat anti-rabbit IgG (A120-201D4). Counterstain: DAPI (blue).
Detection of human hSET1 by WB of immunoprecipitates from HEK293T lysate.
Detection of human hSET1 by WB of immunoprecipitates from HEK293T lysate. Antibodies: Rabbit anti-hSET1 recombinant monoclonal [BLR024E] (A700-024) and rabbit anti-hSET1.
Detection of human hSET1 in FFPE lung carcinoma by IHC.
Detection of human hSET1 in FFPE lung carcinoma by IHC. Antibody: Rabbit anti-hSET1 recombinant monoclonal [BLR024E] (A700-024). Secondary: HRP-conjugated goat anti-rabbit IgG (A120-101P). Substrate: DAB.

Bethyl has an extensive catalog of Recombinant Rabbit Monoclonal Antibodies.


References

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