Abstract 2542: c-Jun and FOXO1 play key roles in the overexpression of oncogenic PKC-ι in human prostate and melanoma cell lines

Protein Kinase C-ι (PKC-ι) is an anti-apoptotic oncogene overexpressed in multiple cancers including prostate, melanoma, ovarian, breast, and glioma. We have previously shown that PKC-ι is part of a cycle that helps cancer cells avoid senescence by releasing the transcription factor NF-kB. Additionally, PKC-ι has an anti-apoptotic effect while promoting epithelial-mesenchymal transition in melanoma {Ratnayake, et al. Int. J. Oncol. 51(5), (2017), 1370-1382}. PKC-ι is activated externally by factors like loss of PTEN and TGFβ stimulation. However treatment with PKC-ι specific inhibitors downregulate expression of both PKC-ι and phosphorylated PKC-ι, suggesting PKC-ι plays a role in regulating its own expression. A previous study showed the ELK1 transcription factor to be a regulator of PKC-ι (Gustafson, et al. J. Biol. Chem 279(10), (2003), 9400-8}. In this study, transcription factors c-Jun, ISGF3, PAX3, EGR1, and FOXO1 which bind on or near the promoter sequence of the PRKCI gene, were analyzed for their role in PKC-ι regulation in prostate cancer cell lines (DU145 and PC3) and melanoma cell lines (SK-MEL-2 and MeWo). Each transcription factor was systematically silenced. Western blots revealed that treatment with either c-Jun or FOXO1 siRNA significantly altered expression of PKC-ι. Results showed c-Jun followed by FOXO1 are the two major transcription factors which involve in PKC-ι expression in prostate cells compared to FOXO1 in melanoma cells. This suggests that these transcription factors act as activators that regulate PKC-ι expression and can be downstream targets of PKC-ι. We found that regulation of PKC-ι expression was governed mainly through NF-κB pathway. siRNA knockdown of NF-κB p65 and application of NF-κB inhibitors confirmed the above observation. We have also used immuno-paired-antibody detection assay to determine which pathways were affected with PKC-ι inhibitor treatments other than NF-κB pathway. qPCR and microarray were performed to analyze the transcriptome of treated cells to match protein levels with mRNA levels. We have analyzed multiple targets both up and downstream of PKC-ι to determine the mechanism of PKC-ι self-regulation. Overall results suggest that PKC-ι inhibition downregulates its own expression making it a novel target in prostate and melanoma cancer treatment. Citation Format: Andre H. Apostolatos, Wishrawana S. Ratnayake, Anisul Islam, Christopher Apostolatos, Tracess Smalley, Mildred Acevedo-Duncan. c-Jun and FOXO