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Protein kinase C-zeta reverts v-raf transformation of NIH-3T3 cells
1Institut für Klinische Molekularbiologie und Tumorgenetik, Forschungszentrum für Umwelt and Gesundheit, München, Germany.
Abstract:
We have identified protein kinase C-zeta (PKC-zeta) as a novel suppressor of neoplastic transformation caused by the v-raf oncogene. PKC-zeta overexpression drastically retards proliferation, abolishes anchorage-independent growth, and reverts the morphological transformation of v-raf-transformed NIH-3T3 cells. The molecular basis for this effect appears to be a specific induction of junB and egr-1 expression, triggered synergistically by PKC-zeta via a Raf/Mek/MAPK-independent mechanism and v-raf. junB-promoter/CAT assays revealed that PKC-zeta directly targets the junB promoter. The induction of junB and egr-1 is linked to the v-raf transformation-suppressing effect of PKC-zeta as constitutive expression of junB and egr-1 but not of c-jun also abolishes anchorage-independent growth of v-raf-transformed NIH-3T3 cells. Moreover, junB overexpression leads to a retardation of proliferation in these cells. PKC-zeta interferes with the serum inducibility of an AP-1 reporter plasmid in v-raf-transformed NIH-3T3 cells, indicating that PKC-zeta antagonizes transformation and proliferation by down-modulating AP-1 function via induction of junB. In summary, our data suggest that PKC-zeta counteracts v-raf transformation by modulating the expression of the transcription factors junB and egr-1.
Insights
Protein kinase C-zeta (PKC-zeta) suppresses cancer-causing v-raf oncogene activity. It halts cell growth and transformation by increasing junB and egr-1 gene expression, inhibiting cancer progression.
Area of Science:
- Molecular Biology
- Oncology
- Cell Signaling
Background:
- Neoplastic transformation driven by oncogenes like v-raf is a hallmark of cancer.
- Understanding the regulatory mechanisms that suppress oncogenic transformation is crucial for developing targeted therapies.
Purpose of the Study:
- To identify novel suppressors of v-raf-induced neoplastic transformation.
- To elucidate the molecular mechanisms by which PKC-zeta exerts its tumor-suppressive effects.
Main Methods:
- Overexpression of protein kinase C-zeta (PKC-zeta) in v-raf-transformed NIH-3T3 cells.
- Analysis of cell proliferation, anchorage-independent growth, and morphological changes.
- Investigation of gene expression using junB-promoter/CAT assays and AP-1 reporter plasmids.
- Assessment of transcription factor involvement (junB, egr-1, c-jun).
Main Results:
- PKC-zeta overexpression significantly inhibited proliferation and anchorage-independent growth of v-raf-transformed cells.
- PKC-zeta specifically induced the expression of junB and egr-1 via a Raf/Mek/MAPK-independent pathway.
- PKC-zeta directly targeted the junB promoter, and junB/egr-1 induction was essential for suppressing v-raf transformation.
- PKC-zeta antagonized AP-1 activity, thereby down-modulating transformation and proliferation.
Conclusions:
- PKC-zeta acts as a novel suppressor of v-raf-induced neoplastic transformation.
- The tumor-suppressive function of PKC-zeta is mediated by the induction of junB and egr-1, leading to the down-regulation of AP-1 activity.
- These findings highlight PKC-zeta as a potential therapeutic target for cancers driven by v-raf or related oncogenes.