AP-1 complexes containing cJun and JunB cause cellular transformation of Rat1a fibroblasts and share transcriptional targets

Abstract

To investigate the role of individual Jun proteins in cell growth and transformation, we have used a doxycyclineinducible retroviral vector to regulate their expression in rat fibroblasts. AP-1 complexes enriched with cJun and JunB result in morphological alterations and anchorageindependent cell growth consistent with a transformationlike phenotype, whereas complexes enriched with JunD had an antiproliferative effect. These results suggest that genes regulated by both cJun and JunB are potentially involved in transformation and that they can be distinguished from those regulated by AP-1 complexes containing JunD. To identify genes regulated by cJun and JunB that may have a role in anchorage-independent growth, we investigated differential gene expression by each of the Jun family members using the Affymetrix Rat oligonucleotide microarray, RG_U34A containing approximately 8000 genes. Differentially regulated genes were identified and grouped for correlation with regulation by the different Jun proteins. A total of 33 candidate genes were found to be differentially regulated by both cJun and JunB and not by JunD. These genes have roles in cell metabolism, growth, signal transduction, migration and adhesion. We validated the differential regulation by cJun and JunB of 10 candidate genes by Northern blot analysis. Of these, eight were further characterized as potential direct targets of AP-1 regulation based on Northern blot results showing differential regulation that correlate with cJun expression. Our results show that inducible cJun and JunB expression result in anchorage-independent growth of Rat1a cells, distinct from JunD-expressing cells. This model system and a functional genomic approach enabled us to differentiate AP-1-regulated genes involved in transformation from AP-1-regulated genes known as bystander genes. This approach significantly reduces the number of bystanders and allows for the targeting of genes specifically involved in transformation.

TAF4b and Jun/Activating Protein-1 Collaborate to Regulate the Expression of Integrin α6 and Cancer Cell Migration Properties

“…Although, c-Jun and JunB may induce opposite effects (43), they also have gene targets in common (44). Interestingly, JunB has been suggested to substitute c-Jun during mouse development and cell proliferation when c-Jun is depleted (45), further supporting our suggestion that AP-1 family members take their promoter-specific interaction with TAF4b into their own hands and follow with regulation of transcription.…”

Simultaneous blockade of AP-1 and phosphatidylinositol 3-kinase pathway in non-small cell lung cancer cells

“…Although the role of c-Jun in human cancers remains to be defined, substantial evidence suggests that it is involved in cellular proliferation and transformation. Deregulated expression of c-Jun induces immortalised rat fibroblasts to grow in an anchorage-independent fashion (Schütte et al, 1989) depending on the induction of multiple c-Jun target genes Leaner et al, 2003Leaner et al, , 2005Hommura et al, 2004;Katabami et al, 2005). Recent studies reported that specific AP-1 blockade by a dominantnegative mutant of c-Jun, TAM67, inhibited the growth of some types of human cancer cells by causing G1 arrest (Ludes-Meyers et al, 2001;Liu et al, 2004;Suto et al, 2004).…”

Identification of integrins α6 and β7 as c‐Jun‐ and transformation‐relevant genes in highly invasive fibrosarcoma cells

“…As c-Jun/AP-1 can additionally regulate many other genes participating in different steps of transformation (Refs. 7,14,20,32,33,51, and this study), it could offer a good target for cancer therapeutic trials. However, as we did not find TAM67 to fully inhibit the expression of the three invasion/metastasis-regulating molecules, it is possible that some kind of combination therapy, consisting of a cocktail of inhibitors for integrins, cysteine cathepsins, and thymosin b4, could result in a more effective therapeutic (anti-metastatic) response in the aggressive human/animal fibrosarcomas and other sarcomas/ tumors overexpressing these molecules.…”