Ca2+/calmodulin regulation of prolactin gene expression

Area of Science:

• Molecular Biology
• Cell Biology
• Biochemistry

Background:

• Calcium (Ca2+) and calmodulin are known for biological actions but their nuclear functions, particularly in gene expression, are less understood.
• While prolactin and growth hormone genes are known to be Ca2+-regulated, other examples are emerging.
• Indirect evidence suggests Ca2+ and calmodulin have nuclear roles.

Purpose of the Study:

• To investigate if prolactin gene expression is regulated by cellular Ca2+ levels.
• To identify the molecular mechanisms through which Ca2+ influences prolactin gene expression.
• To explore the nuclear functions of Ca2+ and calmodulin in gene regulation.

Main Methods:

• Experimental approaches to examine Ca2+ regulation of prolactin gene expression.
• Identification of calmodulin-binding proteins within the nuclear matrix.
• Characterization of Ca2+-calmodulin-dependent protein kinase activity in the nuclear matrix.

Main Results:

• A 56-kDa nuclear matrix protein (NMP 56) was tentatively identified as a calmodulin-binding protein and a substrate for Ca2+-calmodulin-dependent protein kinase.
• This enzyme was found in the nuclear matrix of neuronal nuclei and phosphorylates a chromatin protein similar to high mobility group protein 17 (HMG 17).
• Phosphorylation of HMG 17, associated with active transcription, may mediate Ca2+-calmodulin-dependent regulation of prolactin gene expression.

Conclusions:

• Ca2+ and calmodulin are implicated in the regulation of prolactin gene expression.
• A 56-kDa nuclear matrix protein may be a component of a Ca2+-calmodulin-dependent protein kinase involved in nuclear functions.
• This pathway, involving HMG 17 phosphorylation, could be crucial for hormone and growth factor-mediated gene regulation.