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Association of calmodulin with lysosomes
T B Nielsen1, J B Field, J R Dedman
1Metabolic Research Branch, Naval Medical Research Institute, Bethesda, MD 20814-5055.
Journal of Cell Science
|March 1, 1987
Summary
Calmodulin, a key calcium-binding protein, is found in cell cytoplasm and acidic vesicles, including lysosomes. Its localization and interaction with acceptor proteins suggest a role in regulating lysosome function, particularly in thyroid cells.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- Calmodulin is a crucial calcium-binding protein involved in numerous cellular processes.
- Understanding calmodulin's subcellular localization is essential for elucidating its diverse functions.
- Previous studies have indicated calmodulin's presence in various cellular compartments.
Purpose of the Study:
- To investigate the subcellular localization of calmodulin in different cultured cell types.
- To identify calmodulin-binding proteins (CAPs) in specific cellular fractions.
- To explore the potential role of calmodulin in lysosome function and calcium regulation.
Main Methods:
- Indirect immunofluorescence using anti-calmodulin antibody.
- Vital staining with Acridine Orange to identify acidic vesicles.
- Differential centrifugation, radioimmunoassay (RIA), and SDS-polyacrylamide gel electrophoresis (SDS-PAGE) to analyze calmodulin and CAPs in cellular fractions.
Main Results:
- Calmodulin exhibited diffuse cytoplasmic localization in resting cells and stained spindle fibers in mitotic cells.
- A distinct vesicular staining pattern was observed under specific lysis and fixation conditions, with vesicles identified as lysosomes or acidic vesicles.
- Calmodulin was found in both cytosolic (89%) and membrane vesicle (11%) fractions of thyroid homogenates, with associated calmodulin acceptor proteins (CAPs) identified in the vesicle fraction.
Conclusions:
- Calmodulin is present in both the cytoplasm and a membrane vesicle fraction, potentially lysosomes.
- Thyrotropin stimulation affected the number of calmodulin-containing vesicles in thyroid cells, suggesting calcium's role in lysosome regulation.
- The presence of calmodulin and CAPs in vesicles indicates their involvement in vesicle-associated functions.