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The disruption of adherens junctions is associated with a decrease of E-cadherin phosphorylation by protein kinase
M Serres1, O Filhol, H Lickert
1INSERM U 346, Hôpital E. Herriot, Lyon Cedex 03, 69437, France. serres@lyon151.inserm.fr
Abstract:
The down-regulation of E-cadherin is a common event in carcinogenesis. Phosphorylation/dephosphorylation is one posttranscriptional process which may regulate intercellular junctions. Here we show that in okadaic acid-treated keratinocytes, E-cadherin expression is shifted from the membrane to the cytoplasm, preventing cells from forming aggregates. These changes of E-cadherin localization and function are associated with a decrease in its phosphorylation state. The decrease in E-cadherin phosphorylation was essentially detected in okadaic acid-treated cell lysates isolated from 0.5% Triton-soluble fraction and not in the Triton-insoluble fraction linked to the cytoskeleton, suggesting a role of E-cadherin phosphorylation in cell-cell interactions. E-cadherin was markedly phosphorylated by CK2, either the purified recombinant enzyme or the endogenous enzyme. Using specific CK2 inhibitors such as heparin and 5, 6-dichloro-1-beta-d-ribofuranosylbenzimidazole, endogenous CK2 was confirmed as the main enzyme phosphorylating E-cadherin. The decrease in E-cadherin phosphorylation by endogenous CK2 was not restored by the addition of purified CK2, confirming that it is not due to a defect in CK2 expression or to its reduced activity, but rather to the incapacity of CK2 to phosphorylate E-cadherin. The co-immunoprecipitation and colocalization of E-cadherin and CK2 suggests that CK2 may play a critical role in the maintenance of epidermis cohesion.
Insights
E-cadherin phosphorylation by CK2 is crucial for maintaining skin cell adhesion. Decreased phosphorylation disrupts cell junctions, impacting epidermal cohesion and potentially contributing to cancer development.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- Down-regulation of E-cadherin is a hallmark of carcinogenesis.
- Posttranscriptional modifications, like phosphorylation, regulate E-cadherin function.
- E-cadherin mediates cell-cell adhesion, essential for tissue integrity.
Purpose of the Study:
- To investigate the role of E-cadherin phosphorylation in keratinocyte cell-cell adhesion.
- To identify the kinase responsible for E-cadherin phosphorylation.
- To elucidate the mechanism by which phosphorylation affects E-cadherin localization and function.
Main Methods:
- Treatment of keratinocytes with okadaic acid to induce dephosphorylation.
- Fractionation of cell lysates to analyze Triton-soluble and insoluble components.
- Western blotting and co-immunoprecipitation to detect E-cadherin and CK2.
- Use of specific CK2 inhibitors (heparin, DRB) to assess kinase activity.
Main Results:
- Okadaic acid treatment decreased E-cadherin phosphorylation, leading to membrane-to-cytoplasm shift and impaired cell aggregation.
- Reduced phosphorylation was observed in the Triton-soluble fraction, indicating a role in cell-cell interactions.
- Casein kinase 2 (CK2) was identified as the primary kinase phosphorylating E-cadherin.
- CK2 inhibition or impaired CK2 phosphorylation capacity disrupted E-cadherin function.
Conclusions:
- E-cadherin phosphorylation by CK2 is vital for maintaining epidermal cohesion.
- Dysregulation of this phosphorylation process can lead to loss of cell-cell adhesion.
- CK2's role in E-cadherin phosphorylation is critical for skin integrity and may be relevant in carcinogenesis.