Research

Identification of the B-Raf/Mek/Erk MAP kinase pathway as a target for all-trans retinoic acid during skin cancer promotion

Satish B Cheepala^1,2 , Weihong Yin^1,3 , Zanobia Syed¹ , Jennifer N Gill¹ , Alaina McMillian¹ , Heather E Kleiner⁴ , Mark Lynch⁵ , Rasiah Loganantharaj⁶ , Marjan Trutschl⁷ , Urska Cvek⁷ and John L Clifford¹

¹  Department of Biochemistry, Louisiana State University Health Sciences Center-Shreveport and Feist-Weiller Cancer Center, 1501 Kings Hwy, Shreveport, Louisiana, 17730, USA

²  St Jude Children's Research Hospital, Memphis, TN 38105, USA

³  Wake Forest University School of Medicine, Winston-Salem, NC 27157, USA

⁴  Pharmacology, Louisiana State University Health Sciences Center-Shreveport and Feist-Weiller Cancer Center, 1501 Kings Hwy, Shreveport, Louisiana, 17730, USA

⁵  Department of Cancer Biology, Bayer HealthCare Pharmaceuticals, West Haven, Connecticut, USA

⁶  Bioinformatics Research Lab, University of Louisiana at Lafeyette, PO Box 44330, Lafayette, LA 70504, USA

⁷  Department of Computer Science, Louisiana State University-Shreveport, USA

author email corresponding author email

Molecular Cancer 2009, 8:27doi:10.1186/1476-4598-8-27

Published:	11 May 2009

Abstract

Background

Retinoids have been studied extensively for their potential as therapeutic and chemopreventive agents for a variety of cancers, including nonmelanoma skin cancer (NMSC). Despite their use for many years, the mechanism of action of retinoids in the prevention of NMSC is still unclear. In this study we have attempted to understand the chemopreventive mechanism of all-trans retinoic acid (ATRA), a primary biologically active retinoid, in order to more efficiently utilize retinoids in the clinic.

Results

We have used the 2-stage dimethylbenzanthracene (DMBA)/12-O-tetradecanoylphorbol-13-acetate (TPA) mouse skin carcinogenesis model to investigate the chemopreventive effects of ATRA. We have compared the gene expression profiles of control skin to skin subjected to the 2-stage protocol, with or without ATRA, using Affymetrix 430 2.0 DNA microarrays. Approximately 49% of the genes showing altered expression with TPA treatment are conversely affected when ATRA is co-administered. The activity of these genes, which we refer to as 'counter-regulated', may contribute to chemoprevention by ATRA. The counter-regulated genes have been clustered into functional categories and bioinformatic analysis has identified the B-Raf/Mek/Erk branch of the MAP kinase pathway as one containing several genes whose upregulation by TPA is blocked by ATRA. We also show that ATRA blocks signaling through this pathway, as revealed by immunohistochemistry and Western blotting. Finally, we found that blocking the B-Raf/Mek/Erk pathway with a pharmacological inhibitor, Sorafenib (BAY43-9006), induces squamous differentiation of existing skin SCCs formed in the 2-stage model.

Conclusion

These results indicate that ATRA targets the B-Raf/Mek/Erk signaling pathway in the 2-stage mouse skin carcinogenesis model and this activity coincides with its chemopreventive action. This demonstrates the potential for targeting the B-Raf/Mek/Erk pathway for chemoprevention and therapy of skin SCC in humans. In addition our DNA microarray results provide the first expression signature for the chemopreventive effect of ATRA in a mouse skin cancer model. This is a potential source for novel targets for ATRA and other chemopreventive and therapeutic agents that can eventually be tested in the clinic.