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Induction of a less aggressive breast cancer phenotype by protein kinase C-alpha and -beta overexpression
A Manni1, E Buckwalter, R Etindi
1Department of Medicine, Pennsylvania State University College of Medicine, Hershey 17033, USA.
Abstract:
To address the isoenzyme-specific involvement of protein kinase C (PKC) in breast cancer biology, hormone-responsive MCF-7 breast cancer cells were infected with either PKC-alpha or -beta 1 cDNAs subcloned in the retroviral expression vector pMV7. Several stable clones of PKC-overexpressing cells were generated. Western analysis revealed cross-regulation between the alpha and beta isoforms, because induction of overexpression of one up-regulated the other. Overexpression of the alpha and beta isoenzymes, on the other hand, did not affect the already high endogenous expression of the novel delta, epsilon, eta, and zeta isoforms. Compared with control clones, PKC-alpha- and -beta-overexpressing MCF-7 cells exhibited more drastic morphological changes in response to phorbol 12-myristate 13-acetate administration characterized by cellular flattening and vacuolization. More importantly, induction of PKC-alpha and -beta overexpression induced a less aggressive biological behavior, which was characterized by reduced in vitro invasiveness and markedly diminished tumor formation and growth in nude mice. These in vivo findings can probably best be explained by the dramatic down-regulation of estrogen receptor levels observed in tumors derived from PKC-alpha-infected MCF-7 cells. Our data clearly show that it is possible to induce a less aggressive breast cancer phenotype by altering PKC isoenzyme expression.
Insights
Altering protein kinase C (PKC) isoenzyme expression in breast cancer cells reduced tumor growth and invasiveness. This suggests a potential therapeutic strategy for less aggressive breast cancer phenotypes.
Area of Science:
- Molecular Biology
- Oncology
- Cell Biology
Background:
- Protein kinase C (PKC) isoenzymes play a role in cancer cell biology.
- Understanding the specific roles of PKC isoforms in breast cancer is crucial for targeted therapies.
Purpose of the Study:
- To investigate the specific involvement of PKC-alpha and PKC-beta 1 in breast cancer cell behavior.
- To determine if altering PKC isoenzyme expression can modify breast cancer aggressiveness.
Main Methods:
- Stable MCF-7 breast cancer cell lines overexpressing PKC-alpha or PKC-beta 1 were generated using retroviral vectors.
- Western blot analysis was used to assess PKC isoenzyme expression and cross-regulation.
- In vitro invasiveness assays and in vivo tumor formation studies in nude mice were performed.
- Estrogen receptor levels were analyzed in tumors derived from modified cells.
Main Results:
- Overexpression of PKC-alpha or -beta 1 led to cross-regulation between these isoforms.
- PKC-overexpressing cells showed altered morphology upon phorbol ester treatment.
- Induction of PKC-alpha and -beta overexpression significantly reduced in vitro invasiveness and in vivo tumor growth.
- Down-regulation of estrogen receptor levels was observed in tumors from PKC-alpha-overexpressing cells.
Conclusions:
- Altering protein kinase C (PKC) isoenzyme expression can induce a less aggressive breast cancer phenotype.
- PKC-alpha and -beta 1 overexpression contribute to reduced breast cancer aggressiveness.
- Down-regulation of estrogen receptors may be a mechanism by which PKC affects tumor growth.