Related Experiment Videos
Ca2+/calmodulin regulation of prolactin gene expression
Abstract:
Despite the extensive literature on the biological actions of Ca2+ and calmodulin, very little is known about their involvement in nuclear functions, e.g., regulation of specific gene expression. To date, the only genes other than prolactin and growth hormone shown to be regulated by perturbations in cell Ca2+ are those coding for two glucose-regulated proteins. However, there is a growing body of indirect evidence for nuclear functions of Ca2+ and calmodulin, and we suspect that other examples of Ca2+-regulated genes will emerge. We have described in this chapter several different experimental approaches which we have employed to examine first whether prolactin gene expression is regulated by changes in cell Ca2+ content, and then to begin searching for the components of the mechanism by which Ca2+ exerts its effects on the prolactin gene. The tentative identification of 56-kDa nuclear matrix protein as both a calmodulin-binding protein and a substrate of a Ca2+-calmodulin-dependent protein kinase suggests that NMP 56 may be a subunit of a multifunctional Ca2+-calmodulin-protein kinase. This enzyme was recently detected in the nuclear matrix fraction of neuronal nuclei, and was shown to phosphorylate a chromatin protein similar to high mobility group protein 17 (HMG 17). Since HMG 17 is associated with actively transcribed chromatin, its phosphorylation in GH3 cells might play a role in the Ca2+-calmodulin-dependent regulation of prolactin gene expression by hormones and growth factors.
Insights
Calcium (Ca2+) and calmodulin play roles in nuclear functions, including gene expression regulation. Research suggests a 56-kDa nuclear matrix protein may be involved in Ca2+-calmodulin-dependent prolactin gene regulation.
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.