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Selective monoclonal antibody recognition and cellular localization of an unphosphorylated form of connexin43
1Department of Physiology, Faculty of Medicine, University of Manitoba, Winnipeg, Canada. nagyji@ms.umanitoba.ca
Insights
A new monoclonal antibody specifically detects the unphosphorylated form of connexin43 (Cx43), a gap junction protein. This finding advances research into Cx43 phosphorylation and its role in cellular processes.
Area of Science:
- Cell Biology
- Biochemistry
- Molecular Biology
Background:
- Connexin43 (Cx43) is a key gap junction protein involved in intercellular communication.
- Cx43 undergoes phosphorylation, altering its function and localization.
- Understanding Cx43 phosphorylation states is crucial for studying its role in various tissues.
Purpose of the Study:
- To characterize a novel monoclonal antibody targeting connexin43 (Cx43).
- To determine the specificity of this antibody for different phosphorylation states of Cx43.
- To investigate the presence and distribution of unphosphorylated Cx43 in various cell types.
Main Methods:
- Western blotting using native and alkaline phosphatase-treated samples.
- Immunohistochemistry on cultured cardiac myocytes, tracheal smooth muscle cells, and Cl-9 epithelial cells.
- Comparison with a polyclonal antibody recognizing all Cx43 forms.
Main Results:
- The monoclonal antibody specifically recognizes the unphosphorylated form of Cx43.
- Unphosphorylated Cx43 was detected in tracheal smooth muscle and Cl-9 cells, but not significantly in cardiac myocytes.
- Both phosphorylated and unphosphorylated Cx43 exist in assembled gap junctions, and dephosphorylation is not strictly required for annular gap junction degradation.
Conclusions:
- A novel antibody tool is available for studying unphosphorylated Cx43.
- Cx43 phosphorylation is a complex, multi-site process.
- The antibody's specificity provides insights into Cx43 phosphorylation dynamics and gap junction turnover.
Abstract:
A sequence-specific monoclonal antibody directed against the gap junction protein connexin43 (Cx43) is shown here to be specific for the unphosphorylated form of this protein. In tissues and cultured cells containing different phosphorylated and unphosphorylated forms of Cx43, the antibody detected only the latter as shown by Western blotting of native and alkaline phosphatase-treated samples. Immunohistochemically, this monoclonal antibody did not recognize gap junctions in the vast majority of cultured cardiac myocytes, where nearly all detectable Cx43 is phosphorylated. In contrast, it was able to detect some intracellular Cx43 in tracheal smooth muscle cells and an epithelial cell line (Cl-9 cells), producing patterns of labeling consistent with those seen using a polyclonal antibody that recognizes both phosphorylated and unphosphorylated forms of Cx43. Immunostaining of gap junctions in the cultured cells indicates that both phosphorylated and unphosphorylated Cx43 are present in some assembled gap junctions, suggesting that assembled junctions do not contain exclusively the phosphorylated form of the protein. Annular gap junctions, believed to form as part of the pathway for internalization and degradation of gap junctions, were only occasionally and sparsely labeled by the monoclonal antibody, indicating that complete protein dephosphorylation is not required for uptake and degradation of gap junctions. Furthermore, the ability of this antibody to recognize only unphosphorylated Cx43, and not any of the phosphorylated forms present in the tissues and cell types examined, suggests that a unique phosphorylation site, perhaps present in the epitope recognized by this antibody, must be phosphorylated prior to phosphorylation of Cx43 at other sites.
