The members of the large keratin family of cytoskeletal proteins are expressed in a carefully regulated tissueand differentiation-specific manner. Although these proteins are thought to be involved in imparting mechanical integrity to epithelial cells, the functional significance of their complex differential expression is still unclear. Here we provide new data suggesting that the expression of particular keratins may influence cell proliferation. Specifically, we demonstrate that the ectopic expression of K10 inhibits the proliferation of human keratinocytes in culture, while K16 expression appears to promote the proliferation of these cells. Other keratins, such as K13 or K14, do not significantly alter this parameter. K10-induced inhibition is reversed by the coexpression of K16 but not that of K14. These results are coherent with the observed expression pattern of these proteins in the epidermis: basal, proliferative keratinocytes express K14; when they terminally differentiate, keratinocytes switch off K14 and start K10 expression, whereas in response to hyperproliferative stimuli, K16 replaces K10. The characteristics of this process indicate that K10 and K16 act on the retinoblastoma (Rb) pathway, as (i) K10-induced inhibition is hampered by cotransfection with viral oncoproteins which interfere with pRb but not with p53; (ii) K10-mediated cell growth arrest is rescued by the coexpression of specific cyclins, cyclindependent kinases (CDKs), or cyclin-CDK complexes; (iii) K10-induced inhibition does not take place in Rbdeficient cells but is restored in these cells by cotransfection with pRb or p107 but not p130; (iv) K16 efficiently rescues the cell growth arrest induced by pRb in HaCaT cells but not that induced by p107 or p130; and (v) pRb phosphorylation and cyclin D1 expression are reduced in K10-transfected cells and increased in K16-transfected cells. Finally, using K10 deletion mutants, we map this inhibitory function to the nonhelical terminal domains of K10, hypervariable regions in which keratin-specific functions are thought to reside, and demonstrate that the presence of one of these domains is sufficient to promote cell growth arrest.Keratins are a large family of proteins which form the intermediate filament (IF) cytoskeleton of epithelial cells and their appendages, hairs and nails (reviewed in references 8 and 15). These proteins are subdivided according to biochemical criteria into two subfamilies: type I, or acidic keratins, and type II, or neutral-basic keratins. This division also has important structural and functional implications, since to build up a wellorganized IF cytoskeleton, tetramers containing equimolar amounts of each keratin subtype are required. Like all IF proteins, keratins consist of a central ␣-helical rod domain responsible for dimerization and higher-order polymerization. The rod domain is flanked by globular head (amino) and tail (carboxyl) domains, the functions of which are still unclear. Variations in these nonhelical end domains largely account for the differe...
BackgroundBladder cancer (BC) is one of the most common cancers in the western world and ranks as the most expensive to manage, due to the need for cystoscopic examination. BC shows frequent changes in DNA methylation, and several studies have shown the potential utility of urinary biomarkers by detecting epigenetic alterations in voided urine. The aim of this study is to develop a targeted bisulfite next-generation sequencing assay to diagnose BC from urine with high sensitivity and specificity.ResultsWe defined a 150 CpG loci biomarker panel from a cohort of 86 muscle-invasive bladder cancers and 30 normal urothelium. Based on this panel, we developed the UroMark assay, a next-generation bisulphite sequencing assay and analysis pipeline for the detection of bladder cancer from urinary sediment DNA. The 150 loci UroMark assay was validated in an independent cohort (n = 274, non-cancer (n = 167) and bladder cancer (n = 107)) voided urine samples with an AUC of 97%. The UroMark classifier sensitivity of 98%, specificity of 97% and NPV of 97% for the detection of primary BC was compared to non-BC urine.ConclusionsEpigenetic urinary biomarkers for detection of BC have the potential to revolutionise the management of this disease. In this proof of concept study, we show the development and utility of a novel high-throughput, next-generation sequencing-based biomarker for the detection of BC-specific epigenetic alterations in urine.Electronic supplementary materialThe online version of this article (doi:10.1186/s13148-016-0303-5) contains supplementary material, which is available to authorized users.
The pRb pathway is inactivated in most, if not all, human and mouse tumors, including skin tumors. However, a relatively low frequency of Rb gene alterations is found. The embryonic lethality of pRb-deficient animals restricts the analysis of these mice to midgestation and precludes the analysis of the roles of pRb in mouse cancer models. To solve this problem, we used the Cre/LoxP technology to induce the tissue-specific deletion of pRb. In epidermis, pRb deletion leads to altered proliferation and differentiation but these alterations do not induce the development of spontaneous skin tumors. To gain insight in the possible roles of pRb in mouse skin carcinogenesis, we have performed chemical tumorigenesis experiments in mice bearing epidermal-specific inactivation of Rb gene. Unexpectedly, these mice develop fewer and smaller tumors than control animals, but showing increased malignant conversion to squamous cell carcinomas. Detailed biochemical analysis demonstrates that, in the absence of pRb, multiple pathways are activated leading to increased tumor apoptosis. In particular, we characterized the aberrant p53 activation mediated by E2F/p19(ARF) and other transduction pathways. This may generate a selective pressure in the tumor leading to premature p53 loss of function, which ultimately results in increased malignancy. Overall, these data highlights the role of pRb during the malignant conversion in the mouse skin carcinogenesis, and the intimate relationships between pRb and multiple tumor suppressor networks in this system.
Different chemicals that specifically and selectively inhibit or activate protein kinases have been used to define the possible roles of these enzymes in the different steps of epidermal differentiation. Using HaCaT keratinocytes as a model, and under conditions in which cell proliferation is minimally affected, we found that tyrosine kinase inhibition leads to an inhibition of early (spinous; keratin k10 expression) and late (granulosum; involucrin expression) differentiation processes. cGMP- and cAMP-dependent protein kinases appear to modulate the transition from spinous to granular differentiation, a process which seems to be negatively controlled by protein phosphatases. Finally, enzymes belonging to the protein kinase C family appear to facilitate the transition from spinous to granular differentiation programmes while inhibiting the early steps of epidermal differentiation.
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