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The protein kinase C-related PKC-L(eta) gene product is localized in the cell nucleus
H Greif1, J Ben-Chaim, T Shimon
1Department of Chemical Immunology, Weizmann Institute of Science, Rehovot, Israel.
Abstract:
The tumor promoters phorbol esters are thought to induce changes in cell growth and gene expression by direct activation of protein kinase C (PKC). However, the molecular mechanisms by which PKC molecules transduce signals into the cell nucleus are unknown. In this study, we provide evidence for a direct target for phorbol esters in the nucleus. We demonstrate that the new PKC-related family member, PKC-L, recently isolated by us, is expressed specifically in the cell nucleus. Localization of PKC-L in the cell nucleus is shown both by immunofluorescence staining and by subcellular fractionation experiments of several human cell lines, including the human epidermoid carcinoma line A431. Treatment of these cells by phorbol esters does not induce the down-regulation of PKC-L, in contrast to their effect on classical PKC family members. This is the only PKC isoenzyme described so far that resides permanently and specifically in the cell nucleus. PKC-L may function as an important link in tumor promoting, e.g., as a nuclear regulator of gene expression that changes the phosphorylation state of transcriptional components such as the AP-1 complex.
Insights
Phorbol esters activate protein kinase C (PKC) but nuclear pathways are unclear. Researchers identified PKC-L, a novel nuclear PKC, as a direct target for phorbol esters, potentially regulating gene expression in tumor promotion.
Area of Science:
- Molecular Biology
- Cell Biology
- Cancer Research
Background:
- Tumor promoters like phorbol esters activate protein kinase C (PKC) pathways.
- The specific nuclear mechanisms of PKC signaling remain largely unknown.
- Understanding nuclear PKC targets is crucial for elucidating tumor promotion.
Purpose of the Study:
- To identify direct nuclear targets of phorbol esters within the protein kinase C family.
- To characterize the subcellular localization and regulation of novel PKC family members.
- To investigate the role of nuclear PKC in gene expression and tumor promotion.
Main Methods:
- Immunofluorescence staining to determine protein localization.
- Subcellular fractionation to isolate nuclear components.
- Analysis of human cell lines (e.g., A431) treated with phorbol esters.
- Western blot analysis to assess protein expression and regulation.
Main Results:
- A novel PKC-related protein, PKC-L, was identified and found to be specifically localized to the cell nucleus.
- PKC-L expression was confirmed in multiple human cell lines, including A431 carcinoma cells.
- Unlike classical PKC members, PKC-L levels were not reduced by phorbol ester treatment.
- PKC-L is the first described PKC isoenzyme with permanent and specific nuclear residence.
Conclusions:
- PKC-L is a unique nuclear-resident PKC isoenzyme.
- PKC-L represents a direct nuclear target for phorbol esters.
- PKC-L may act as a nuclear regulator of gene expression, influencing transcriptional components like AP-1, and play a role in tumor promotion.