We are interested in the fundamental signaling pathways responsible for cellular growth in the skin. Cellular growth in the skin can occur in response to immune mediators as in psoriasis, as a result of infection with viruses as in verruca vulgaris, and secondary to UV radiation and DNA damage as in skin cancer. One signaling pathway known to have a key role in cellular growth in all mammalian cells is the cAMP pathway. We study a novel source of cAMP in mammalian cells discovered 10 years ago called soluble adenylyl cyclase (sAC). This enzyme is unique in that it is present throughout the cell including the nucleus and mitochondria and, unlike other mammalian adenylyl cyclases, is not tethered to the plasma membrane. Investigation of this enzyme has proven useful for understanding the pathogenesis of diseases in organs such as the pancreas, kidney, brain, lung, and testes. We are currently exploring the role of this enzyme in pathogenesis of diseases of keratinocytes and melanocytes. In addition, we study the subcellular localization of this enzyme as a potential diagnostic for melanocytic proliferations.
Keratinocyte Hyperproliferative Skin Diseases
We have established that sAC is present in the cytoplasm of normal epidermal keratinocytes; but when these keratinocytes are stimulated to divide, sAC migrates into the nucleus. This phenomenon occurs in a variety skin diseases such as psoriasis, verruca vulgaris, seborrheic keratoses, actinic keratoses, and squamous cell carcinoma. In each of these diseases the inciting stimulus driving the cell to proliferate is distinct. This implies that nuclear sAC marks a key signaling cascade important for cellular proliferation. We are actively exploring the role of sAC and other adenylyl cyclases in the pathogenesis of these diseases. We have recently demonstrated that small molecule inhibitors of sAC are capable of blocking IL-22-induced hyperproliferation in mice. Because IL-22 is a cytokine important in psoriasis pathogenesis, we feel that small molecule inhibitors of sAC may represent novel therapeutics for keratinocyte hyperproliferative diseases of the skin.
Our observations in keratinocytes prompted us to explore the localization of sAC in melanocytes. Similar to keratinocytes, normal human melanocytes have a cytoplasmic perinuclear staining pattern; however, when we immunostained melanoma cells in culture we found that sAC was predominately nuclear. Because most melanomas are associated with RAS and RAF disregulation and because cAMP is a key regulator of RAS and RAF signaling, we asked whether sAC biology was altered in melanoma cells harboring mutations in RAS and RAF. We found that sAC expression is greatly elevated in RAS/RAF mutated melanoma lines as compared to melanoma lines without these mutations and normal human melanocytes. We are actively exploring the role of sAC in melanoma pathogenesis.
sAC localization as a diagnostic tool
As outlined above, we have observed that sAC moves into the nucleus of proliferating keratinocytes and melanocytes. In the case of human melanocyte proliferations, there is a paucity of objective metrics that are universally accepted by both dermatologists and pathologists. We posited that if sAC’s localization coincided with different states of proliferation, we might provide such a metric. Currently we have observed four specific subcellular localizations for soluble adenylyl cyclase: perinuclear golgi, diffuse cytoplasmic, diffuse nuclear, and nucleolar. Specific combinations of these subcellular localizations provide a immunostaining pattern that can differentiate between benign nevi, dysplastic nevi, superficial spreading melanoma, nodular melanoma, acral lentiginous melanoma, and lentigo maligna melanoma. We are currently exploring borderline melanocytic proliferations in an attempt to provide a better means of diagnosing these entities, and we are evaluating patient outcome to establish whether this immunostain will provide any prognostic information. We are also exploring sAC as a diagnostic marker in other skin diseases.
Zippin JH, Chadwick P, Levin LR, Buck J, and Magro C. (2010) "Soluble adenylyl cyclase defines a nuclear cAMP microdomain in keratinocyte hyperproliferative skin diseases" J Invest Dermatol. May;130(5):1279-87.
Zippin JH, Farrell J, Huron D, Kamenetsky M, Hess KC, Fischman D, Levin LR and Buck J (2004) "Bicarbonate-responsive ‘soluble’ adenylyl cyclase defines a cAMP signaling microdomain" J Cell Biol. Feb 16;164(4):527-34. Highlighted as Editor’s choice for paper of the week (Sci. STKE, Vol. 2004, Issue 221, pp. tw67) and in a news and views by Richard A. Bundey and Paul A. Insel (Sci. STKE 2004 (231), pe19) in Science’s Signal Transduction Knowledge Environment (STKE).
Zippin JH, Chen Y, Nahirney P, Kamenetsky M, Wuttke MS, Fischman DA, Levin LR, Buck J. (2002) "Compartmentalization of bicarbonate-sensitive adenylyl cyclase in distinct signaling microdomains". FASEB J. Jan; 17(1):82-84.