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c-myc gene-induced alterations in protein kinase C expression: a possible mechanism facilitating myc-ras gene
L F Barr1, M Mabry, B D Nelkin
1Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205.
Abstract:
The mechanism(s) by which the c-myc nuclear protein and the membrane-associated ras protein interact to mediate phenotypic changes is unknown. We now find that c-mcy gene expression is associated with alterations in the principal signal transduction pathway through which the ras protein is thought to function. We studied the transcript and protein expression of protein kinase C (PKC) isoforms in a culture line of human small cell lung cancer cells (NCI H209) in which expression of inserted c-myc and Ha-ras genes together, but not alone, causes a transition to a large cell phenotype. In control H209 cells, at the transcript and cell membrane protein levels, PKC-alpha is the dominant PKC species. In this cell line, the expression of an exogenous c-myc gene, but not of a viral Ha-ras gene, causes a 5- to 10-fold increase in the PKC-beta isoform transcript and protein. The insertion of ras into the exogenous myc-expressing 209 cells, in addition to causing phenotypic transition, results in the translocation of the PKC-beta protein from the cytosol to the membrane fraction and a decrease in membrane-associated PKC-alpha. Concomitant with these changes, the increased PKC isoform transcript levels induced by myc alone are completely reversed. These observations suggest that a complex set of PKC transcript and protein alterations, most prominently involving an increased PKC-beta protein level in the cell membrane, a decrease in PKC-alpha protein, and a decrease in all PKC isoform transcripts, may represent a fundamental event(s) for c-myc collaboration with Ha-ras to alter cell phenotype.
Insights
The c-myc and ras proteins collaborate to change cell appearance by altering protein kinase C (PKC) signaling. Specifically, c-myc increases PKC-beta, while ras and c-myc together shift PKC-beta to the membrane and decrease PKC-alpha.
Area of Science:
- Cellular Biology
- Molecular Oncology
- Signal Transduction
Background:
- The interaction between c-myc and ras proteins in mediating phenotypic changes is not fully understood.
- Ras proteins are known to function through specific signal transduction pathways.
Purpose of the Study:
- To investigate the role of protein kinase C (PKC) isoforms in the phenotypic transition induced by c-myc and Ha-ras co-expression.
- To elucidate the molecular mechanisms underlying the collaboration between c-myc and Ha-ras in human small cell lung cancer cells.
Main Methods:
- Studied transcript and protein expression of PKC isoforms in NCI H209 human small cell lung cancer cells.
- Analyzed changes in PKC isoform expression and localization upon introduction of exogenous c-myc and Ha-ras genes, individually and together.
- Quantified PKC-beta transcript and protein levels, as well as PKC-alpha protein localization.
Main Results:
- c-myc gene expression alone increased PKC-beta isoform transcript and protein levels 5- to 10-fold.
- Co-expression of c-myc and Ha-ras led to phenotypic transition, translocation of PKC-beta to the cell membrane, and decreased membrane-associated PKC-alpha.
- The increase in PKC isoform transcripts induced by c-myc alone was reversed upon Ha-ras insertion.
Conclusions:
- Altered PKC signaling, including increased membrane-bound PKC-beta and decreased PKC-alpha, is a key event in c-myc and Ha-ras mediated phenotypic changes.
- These findings suggest a complex interplay between c-myc, Ha-ras, and PKC isoforms in regulating cell phenotype.
- The study highlights the importance of PKC signaling in oncogenic transformations involving c-myc and ras.