Characterization of Ras-driven human epidermal neoplasia
Final Report Abstract
Epidermal squamous cell carcinoma (SCC) represents one of the two most abundant cancers in the USA. Ras is supposed to play a major role in the development of murine and human SCC. Induction of Ras and CDK4 could be demonstrated in a subset of human SCO's. Furthermore, co-expression of Ras with CDK4 or IkappaBa led to the induction of invasive human epidermal neoplasia indistinguishable from SCC at all stages analyzed but the underlying mechanistic basis is largely unknown. This work was aimed towards studying the functional role of Ras in the development of human epidermal neoplasia by analyzing three Ras effectors named Raf, PI3K and RalGEF as well as the corresponding signal transduction pathways. To elucidate mechanisms of cancer progression, we generated inducible human neoplasia in three-dimensionally intact epithelial tissue. In order to analyze which of the tree major Ras effector pathways is sufficient for induction of human epidermal neoplasia, we selectively activated either of the three signaling cascades by overexpressing Raf (Erk/MAPK pathway), Ral/GDS (RalGEF/Ral pathway), or PI3K p110a(PI3K/Akt pathway), in our human epidermal neoplasia model system. We could show that Raf - and not Ral/GDS or PI3K p110a can mimic Ras-induced invasive epidermal neoplasia. This finding helped us to optimize our Ras gene expression profile by using the increased signaling specificity of the Ras downstream effector Raf to generate a core cancer progression signature. The potential clinical relevance of this core signature was shown by blockade of one of the most central genes in this signature, ß1 integrin (detected by network modeling analysis). Ablation of ß1 integrin attenuated tumorigenesis in vivo. Although the Erk/MAPK cascade is among the most conserved signaling pathways in eukaryotes, the effectors of its tumor-enabling processes, such as suppression of differentiation, are still largely unidentified. Long noncoding RNAs have recently emerged as powerful regulators of gene expression and cell fate. We identified NEDCR1, a noncoding RNA within the epidermal differentiation complex (EDC) on chromosome 1q21 that seems to be Erk/MAPK-regulated. NEDCR1 is expressed only in differentiating epidermal keratinocytes, and is dramatically suppressed by MAPK signaling and in SCC tumor specimens. Initial experiments show that NEDCR1 depletion blocks differentiation while over-expression induces differentiation within epidermal tissue. NEDCR1 might therefore be the first long noncoding RNA that regulates epidermal differentiation and thus may represent a new class of MAPK-regulated mediators of tissue homeostasis and neoplasia.
Publications
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Truong A.B., Kretz M., Ridky T.W., Kimmel R., Khavari P.A.
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Reuter JA, Ortiz-Urda S, Kretz M, Garcia J, Scholl FA, Pasmooij AM, Cassarino D, Chang HY, Khavari PA
