Activation of the glycoprotein hormone alpha-subunit promoter by a LIM-homeodomain transcription factor.

Recently, a pituitary-specific enhancer was identified within the 5' flanking region of the mouse glycoprotein hormone alpha-subunit gene. This enhancer is active in pituitary cells of the gonadotrope and thyrotrope lineages and has been designated the pituitary glycoprotein hormone basal element (PGBE). In the present studies, we sought to isolate and characterize proteins which interact with the PGBE. Mutagenesis experiments identified a 14-bp imperfect palindrome that is required for binding of a factor which is present in cells of gonadotrope and thyrotrope lineages but not in other cells. Screening of a mouse cDNA library with a DNA probe containing the imperfect palindrome resulted in the isolation of a LIM-homeodomain transcription factor. The cDNA predicts a mouse protein which is 94% identical to the recently described rat LIM-homeodomain protein LH-2. LH-2 contains two zinc fingers (LIM domain) and a consensus homeodomain. Hybridization analysis revealed relatively high expression of LH-2 mRNA in the central nervous system and in pituitary cells of the gonadotrope and thyrotrope lineages. Lower or nondetectable levels of LH-2 mRNA were found in other pituitary cells and tissues, including placental cells. Recombinant LH-2 homeodomain was found to selectively bind to the previously identified imperfect palindrome in the PGBE. Point mutations in the PGBE resulted in parallel losses in the binding of a nuclear factor from a cell line of the gonadotrope lineage and recombinant LH-2-binding activity. Use of an antibody to LH-2 provided evidence that endogenous PGBE-binding activity from cells of the gonadotrope lineage involves a protein which is immunologically related to LH-2. Expression of LH-2 in two heterologous cell types resulted in activation of a reporter gene containing the mouse alpha promoter. These data suggest that the LIM-homeodomain factor LH-2 plays a role in stimulating tissue-specific expression of the mouse glycoprotein hormone alpha subunit. The finding that a LIM-homeodomain protein can stimulate expression of one of the earliest markers of pituitary differentiation raises the possibility that this factor plays a role in cell lineage determination in the pituitary.

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Activation of the glycoprotein hormone alpha-subunit promoter by a LIM-homeodomain transcription factor

Molecular and Cellular Biology ◽

10.1128/mcb.14.5.2985-2993.1994 ◽

1994 ◽

Vol 14 (5) ◽

pp. 2985-2993

Author(s):

M S Roberson ◽

W E Schoderbek ◽

G Tremml ◽

R A Maurer

Keyword(s):

Transcription Factor ◽

Binding Activity ◽

Alpha Subunit ◽

Homeodomain Protein ◽

Pituitary Cells ◽

Glycoprotein Hormone ◽

Homeodomain Transcription Factor ◽

Imperfect Palindrome ◽

Recombinant Lh ◽

Lim Homeodomain

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Cofactor CLIM2 promotes the repressive action of LIM homeodomain transcription factor Lhx2 in the expression of porcine pituitary glycoprotein hormone α subunit gene

Biochimica et Biophysica Acta (BBA) - Gene Structure and Expression ◽

10.1016/j.bbaexp.2006.08.004 ◽

2006 ◽

Vol 1759 (8-9) ◽

pp. 403-409 ◽

Cited By ~ 8

Author(s):

Takao Susa ◽

Takanobu Sato ◽

Tetsuo Ono ◽

Takako Kato ◽

Yukio Kato

Keyword(s):

Transcription Factor ◽

Subunit Gene ◽

Glycoprotein Hormone ◽

Α Subunit ◽

Homeodomain Transcription Factor ◽

Lim Homeodomain

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Activation of the Thyroid-Stimulating Hormone β-Subunit Gene by LIM Homeodomain Transcription Factor Lhx2

Endocrinology ◽

10.1210/en.2006-1088 ◽

2007 ◽

Vol 148 (7) ◽

pp. 3468-3476 ◽

Cited By ~ 15

Author(s):

Kee K. Kim ◽

Seok B. Song ◽

Kwang I. Kang ◽

Myungchull Rhee ◽

Kyoon Eon Kim

Keyword(s):

Transcription Factor ◽

Reporter Gene ◽

Thyroid Stimulating Hormone ◽

Β Subunit ◽

Subunit Gene ◽

Mobility Shift ◽

Glycoprotein Hormone ◽

Α Subunit ◽

Homeodomain Transcription Factor ◽

Lim Homeodomain

Although there is evidence that the LIM homeodomain transcription factor, Lhx2, can stimulate transcription of the glycoprotein hormone α-subunit gene, the role of Lhx2 in regulating TSH β-subunit has not been established. In the present studies, the ability of Lhx2 to regulate transcription of the TSH β-subunit gene was examined. In the thyrotrope-derived TαT1 cell line, Lhx2 expression was found to be induced by treatment with either TRH or cAMP, consistent with the possibility that Lhx2 may play a role in mediating the ability of this signaling pathway to stimulate TSH gene expression. Transient, forced overexpression of Lhx2 stimulated activity of a TSH β-subunit reporter gene. Deletion studies provided evidence that the −177 to −79 region of the TSH β-subunit promoter was necessary for stimulation of reporter gene activity by Lhx2. A gel mobility shift assay provided the evidence that Lhx2 can bind to this region of DNA. DNase I footprinting studies demonstrated that two distinct regions of the TSHβ promoter, −118 to −108 and −86 to −68, are protected by Lhx2 from nuclease digestion. These regions contain repeats of the sequence, 5′-(G/T)CAAT(T/A)-3′. Mutation of this sequence, especially in the −86 to −68 region, substantially decreased Lhx2 responsiveness of the TSH β-subunit reporter gene. In addition, a DNA fragment containing the −177 to −79 region of the TSHβ promoter was found to confer Lhx2 responsiveness to a minimal promoter. These results provide multiple lines of evidence consistent with a role for Lhx2 in modulating expression of the TSH β-subunit gene.

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