Role of Raf and MEK-1 in skin homeostasis and tumorigenesis

Raf kinases have been intensely studied as the link between active Ras and the MEK/ERK module signaling proliferation. This pathway is activated in human tumors, and Raf kinases are considered excellent therapeutic targets. We concentrate on determining the essential roles of Raf-1, B-Raf, and MEK-1 in the healthy and diseased mouse by using conditional knock-out strains established in our lab (Raf-1, MEK-1) or obtained as a result of collaboration (B-Raf) to gain information about the function of Raf and MEK-1 in specific tissues and in the adult animal. One of the experimental systems we use is the epidermis, chosen because of its eminent amenability to the study of tissue remodeling and neoplasia, and because constitutive activation of the pathway at study is reportedly associated with regulated and deregulated skin proliferation. In a previous project, we have investigated the role of Raf-1 and B-Raf in the epidermis and showed that neither kinase is necessary for normal skin homeostasis. Both are, however, essential for the development of Ras-induced tumors, and at least one, Raf-1, is required for tumor maintenance. The molecular basis of the role of Raf-1 in tumorigenesis was traced to a kinase-independent cross- talk with TGF-ß signaling. We could further show that epidermis-restricted ablation of both Raf-1 and B-Raf massively perturbs skin homeostasis, resulting in a condition of chronic dermatitis. The present project has three specific aims: 1. to further characterize the role of B-Raf in Ras-induced tumorigenesis and to identify the molecular changes involved; 2. to characterize the phenotype of the b-raf;c-raf-1ep animals in detail and analyze the pathways underlying disease development; and 3. to investigate the impact, if any, of MEK-1 ablation in the development of Ras-induced tumors. The work described in the proposal will break new scientific ground by identifying essential biological function(s) of B-Raf, Raf-1 and MEK-1 in the epidermis, and the targets that mediate them. In addition, the information obtained will be instrumental in directing the design and use of pharmacological kinase inhibitors.

Raf kinases have been intensely studied as the link between active Ras and the MEK/ERK module signaling proliferation. This pathway is activated in human tumors, and Raf kinases are considered excellent therapeutic targets. We concentrate on determining the essential roles of Raf-1, B-Raf, and MEK-1 in the healthy and diseased mouse by using conditional knock-out strains established in our lab (Raf-1, MEK-1) or obtained as a result of collaboration (B-Raf) to gain information about the function of Raf and MEK-1 in specific tissues and in the adult animal. One of the experimental systems we use is the epidermis, chosen because of its eminent amenability to the study of tissue remodeling and neoplasia, and because constitutive activation of the pathway at study is reportedly associated with regulated and deregulated skin proliferation. In a previous project, we have investigated the role of Raf-1 and B-Raf in the epidermis and showed that neither kinase is necessary for normal skin homeostasis. Both are, however, essential for the development of Ras-induced tumors, and at least one, Raf-1, is required for tumor maintenance. The molecular basis of the role of Raf-1 in tumorigenesis was traced to a kinase-independent cross- talk with TGF-ß signaling. We could further show that epidermis-restricted ablation of both Raf-1 and B-Raf massively perturbs skin homeostasis, resulting in a condition of chronic dermatitis. The present project has three specific aims: 1. to further characterize the role of B-Raf in Ras-induced tumorigenesis and to identify the molecular changes involved; 2. to characterize the phenotype of the b-raf;c-raf-1ep animals in detail and analyze the pathways underlying disease development; and 3. to investigate the impact, if any, of MEK-1 ablation in the development of Ras-induced tumors. The work described in the proposal will break new scientific ground by identifying essential biological function(s) of B-Raf, Raf-1 and MEK-1 in the epidermis, and the targets that mediate them. In addition, the information obtained will be instrumental in directing the design and use of pharmacological kinase inhibitors.