Characterization of human mesoderm induction early response 1 (hMIER1) as a coregulator of the estrogen receptors, ERα and ERβ

Fifield, Heather (2008) Characterization of human mesoderm induction early response 1 (hMIER1) as a coregulator of the estrogen receptors, ERα and ERβ. Masters thesis, Memorial University of Newfoundland.

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Abstract

The human mesoderm induction early response gene 1 (hmier1) is a growth factor induced gene encoding a novel transcription factor. There are two major isoforms of hMIER1, hMIER1α and hMIER1β, which differ in their C-termini (Paterno et al, 2002). In particular, hMIER1α, but not hMIER1β, contains a conserved motif important for interaction with nuclear hormone receptors, the LXXLL motif. Further analysis revealed that hMIER1 was differentially expressed in normal human breast compared to breast carcinoma cell lines and tissues, implying it may have a role in the neoplastic state (Paterno et al., 1998; Paterno et al., 2002). -- In this study, the role of hMIER1 as a coregulator of the estrogen receptor (ER) was investigated. The physiological effects of estrogen are mediated by two receptors: estrogen receptor alpha (ERα) and estrogen receptor beta (ERβ). It has previously been shown that both ERα and ERβ interact with hMIER1α and hMIER1β in vitro (Fifield, Honours dissertation). Electrophoretic mobility shift assays (EMSAs) were performed to determine if hMIER1α or hMIER1β interaction with ERα or ERβ affected the ability of the ER to bind a consensus ERE in the absence and presence of specific ligands. These studies revealed that hMIER1α inhibited DNA binding of both ER subtypes in the absence or presence of ligand. In contrast, hMIER1β inhibited the DNA binding of the ERβ in presence and absence of ligand, but has little effect on the DNA binding of ERα. -- Further studies were performed to determine if the in vitro interaction and effect on DNA binding would be translated into functional effects in vivo. Experiments in HEK 293 cells showed that in the absence of ligand, hMIER1α and hMIER1β enhanced ERE-driven transcription with the ERα, but not ERβ. In the presence of ligand, such as estrogen or the ERα-specific agonist, propylpryazole-triol (PPT), neither hMIER1α nor hMIERβ significantly affected ERE-driven transcription with ERα In the presence of diarylpropionitrile (DPN), an ERβ specific agonist, neither hMIER1α nor hMIER1β affected ERE-driven transcription with ERβ. -- Overall these results imply that hMIER1α and hMIER1β are involved in ligand independent activation of ERα, but have no functional effect on the ERβ. This ER subtype selectivity, along with activation of ER signalling in the absence of estrogen or other ligands, warrant further investigation of the role that hMIER1 plays in estrogen receptor signalling.

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