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aPKC function in Hedgehog signaling and basal cell carcinoma

Scott Atwood

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National Institutes of Health (NIH)
Basal cell carcinoma (BCC) is the most prevalent cancer in the world and nearly half of US citizens are likely to develop this cancer before retirement. BCCs are invasive epithelial tumors that originate from activating mutations in the Hedgehog (Hh) pathway, an essential developmental pathway that has been implicated in approximately 25% of all human cancer deaths. Despite the critical nature of Hh signaling, how Hh mediates the impressive proliferative defects in cancers remain poorly understood. Hh pathway activation begins when Hh ligand binds and inhibits transmembrane receptor Patched1, allowing signal transducer Smoothened (Smo) to activate Gli transcription factors and amplify expression of Hh target genes. Smo inhibitors have recently gained approval for treatment of late advanced or metastatic BCC and exhibit potent tumor regression. While these inhibitors are effective in naïve tumors, aggressive tumors tend to develop early resistance to the drug, illustrating the need for new therapeutic targets. I have recently discovered that a critically important oncogene, atypical Protein Kinase C iota/lambda (aPKC-ι/λ), involved in stem cell fate choice during development of nearly all multicellular organisms is essential for high, sustained Hh pathway activation in BCCs. I have also shown pharmacological inhibition of aPKC suppresses murine BCC tumor growth and the growth of naïve and Smo-resistant BCC cells. The goal of my research is to determine the mechanisms that allow the polarity protein aPKC-ι/λ to promote Hh pathway activation and naïve and Smo-resistant BCC growth. During the K99 phase, I will determine how phosphorylation of Gli by aPKC-ι/λ alters target gene specificity to promote tumor growth, how BCC's regulate aPKC-ι/λ activity, and test the therapeutic potential of additional novel aPKC-ι/λ inhibitors for the treatment of naïve and resistant BCC. During the R00 phase, I will determine how aPKC-ι/λ-dependent Gli1 responsive genes regulate tumor invasion and analyze aPKC-ι/λ function in Smo-resistant BCCs. The results of this study will reveal conserved mechanisms that govern cell polarity and Hh signaling during BCC that will prove invaluable in generating novel therapeutics for the treatment of Hh-dependent cancers.

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