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Mad1 Upregulation in Breast Cancer: Causes & Consequences
Author(s) -
Copeland Sarah,
Wan Jun,
Roopra Avtar,
Weaver Beth
Publication year - 2021
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.2021.35.s1.02910
Subject(s) - trichostatin a , downregulation and upregulation , cancer research , biology , microbiology and biotechnology , histone deacetylase , histone , genetics , gene
Mitotic arrest deficient‐1 (Mad1), an essential component of the mitotic checkpoint, is upregulated in 20% of breast cancer patients. Upregulation of Mad1 causes chromosome missegregation during mitosis, a hallmark of cancer, as well as destabilization of the p53 tumor suppressor. Upregulation of Mad1 is sufficient to promote orthotopic tumor growth in immunocompromised animals. Patients with high levels of Mad1 mRNA expression have a poorer prognosis than patients with intermediate or low levels of Mad1. Unlike many core kinetochore proteins, Mad1 is not transcriptionally regulated by the transcription factor FoxM1. Thus, the mechanism for upregulating Mad1 in cancer, as well as the functional consequences, remain unknown. Bioinformatics analysis identified Histone Deacetylase 1 (HDAC1) as a likely cofactor involved in Mad1 transcriptional regulation. Consistent with this, HDAC inhibition with Trichostatin A (TSA) or Valproic Acid (VPA) increases Mad1 mRNA and protein levels 6‐ to 10‐fold in multiple breast cancer cell lines. HDAC inhibition also induces Mad1 nuclear puncta, a localization pattern seen in primary breast cancer and breast cancer cell lines following Mad1 upregulation. Genetic approaches are currently being used to validate that HDAC1 negatively regulates Mad1 expression. To determine the consequences of Mad1 upregulation, we have generated a tetracycline (tet)‐inducible Mad1 mouse model by inserting a tet responsive promoter and HA tag before the first coding exon of the Mad1 gene. Doubly heterozygous mice containing one allele of tet‐inducible Mad1 and one allele of a ubiquitously expressed tet‐transactivator (rtTA‐M2) show inducible expression of HA‐Mad1 following one week or one month of exposure to the tet analog doxycycline. Ongoing experiments will define the impact of Mad1 upregulation on mitotic fidelity and p53 levels and determine whether upregulation of Mad1 is sufficient to induce tumorigenesis in an immunocompetent setting.