No abstract

Non-melanoma skin cancers, in particular keratoacanthomas (KAs) and squamous cell carcinomas (SCCs), have become highly frequent tumor types especially in immunesuppressed transplant patients. Nevertheless, little is known about essential genetic changes. As a paradigm of 'early' changes, that is, changes still compatible with tumor regression, we studied KAs by comparative genomic hybridization and show that gain of chromosome 11q is not only one of the most frequent aberration (8/18), but in four tumors also the only aberration. Furthermore, 11q gain correlated with amplification of the cyclin D1 locus (10/14), as determined by fluorescence in situ hybridization, and overexpression of cyclin D1 protein (25/31), as detected by immunohistochemistry. For unraveling the functional consequence, we overexpressed cyclin D1 in HaCaT skin keratinocytes. These cells only gained little growth advantage in conventional and in organotypic cocultures. However, although the control vector-transfected cells formed a well-stratified and orderly differentiated epidermis-like epithelium, they showed deregulation of tissue architecture with an altered localization of proliferation and impaired differentiation. The most severe phenotype was seen in a clone that additionally upregulated cdk4 and p21. These cells lacked terminal differentiation, exhibited a more autonomous growth in vitro and in vivo and even formed tumors in two injection sites with a growth pattern resembling that of human KAs. Thus, our results identify 11q13 gain/cyclin D1 overexpression as an important step in KA formation and point to a function that exceeds its known role in proliferation by disrupting tissue organization and thereby allowing abnormal growth.

Glomerular parietal epithelial cells (PECs) are precursors to podocytes in mature glomeruli; however, as progenitors, the distinct intrinsic mechanisms that allow for repeated periods of cell-cycle arrest and re-entry of PECs after glomerulogenesis are unknown. Here, we show that the Src-suppressed protein kinase C substrate (SSeCKS), a multivalent scaffolding A kinase anchoring protein, sequesters cyclin D1 in the cytoplasm of quiescent PECs. SSeCKS expression is induced in embryonic PECs, but not in embryonic podocytes, starting at the S phase of glomerulogenesis, and is constitutively expressed postnatally by PECs, but not podocytes, in normal glomeruli. Cyclin D1 was immunoprecipitated with SSeCKS from capsulated glomeruli containing PECs, whereas decapsulated glomeruli without PECs lacked SSeCKS and cyclin D1. Cell-cell contact inhibition of proliferation in cultured PECs induced SSeCKS expression and binding of cyclin D1 by SSeCKS in the cytoplasm, whereas phosphorylation of SSeCKS by activated protein kinase C disrupted binding, resulting in nuclear translocation of cyclin D1. SSeCKS À/À mice showed hyperplasia of PECs in otherwise normal glomeruli and developed significantly worse proteinuric glomerular disease, marked by increased PEC proliferation and expression of nuclear cyclin D1, from nephrotoxic nephritis. These results suggest that SSeCKS controls the localization and activity of cyclin D1 in PECs and influences proliferative injury in the glomerulus.