No abstract

The urothelium is a specialized epithelium that lines the urinary tract. It consists of three different cell types, namely, basal, intermediate and superficial cells arranged in relatively distinct cell layers. Normally, quiescent, it regenerates fast upon injury, but the regeneration process is not fully understood. Although several reports have indicated the existence of progenitors, their identity and exact topology, as well as their role in key processes such as tissue regeneration and carcinogenesis have not been clarified. Here we show that a minor subpopulation of basal cells, characterized by the expression of keratin 14, possesses self-renewal capacity and also gives rise to all cell types of the urothelium during natural and injury-induced regeneration. Moreover, these cells represent cells of origin of urothelial cancer. Our findings support the hypothesis of basally located progenitors with profound roles in urothelial homoeostasis.

No abstract

The DNA damage response (DDR) pathway and ARF function as barriers to cancer development. Although commonly regarded as operating independently of each other, some studies proposed that ARF is positively regulated by the DDR. Contrary to either scenario, we found that in human oncogene-transformed and cancer cells, ATM suppressed ARF protein levels and activity in a transcription-independent manner. Mechanistically, ATM activated protein phosphatase 1, which antagonized Nek2-dependent phosphorylation of nucleophosmin (NPM), thereby liberating ARF from NPM and rendering it susceptible to degradation by the ULF E3-ubiquitin ligase. In human clinical samples, loss of ATM expression correlated with increased ARF levels and in xenograft and tissue culture models, inhibition of ATM stimulated the tumour-suppressive effects of ARF. These results provide insights into the functional interplay between the DDR and ARF anti-cancer barriers, with implications for tumorigenesis and treatment of advanced tumours.

No abstract

Hepatocyte nuclear factor-1 (HNF-1) plays an important role in the regulation of a large number of genes expressed in the liver, kidney, and pancreatic ␤-cells. In exploring the molecular mechanism involved in HNF-1-dependent gene activation in the in vivo chromatin context, we found that HNF-1 can physically interact with the histone acetyltransferases (HATs) CREB-binding protein (CBP), p300/CBP-associated factor (P/CAF), Src-1, and RAC3. The transcriptional activation potential of HNF-1 on a genome integrated promoter was strictly dependent on the synergistic action of CBP and P/CAF, which can independently interact with the Nterminal and C-terminal domain of HNF-1, respectively. Moreover, the HAT activity of both coactivators was important, as opposed to the selective requirement for the HAT activity of P/CAF in activation from a transiently transfected reporter. Interaction of CBP with the N-terminal domain of HNF-1 greatly increased the binding affinity for P/CAF with the C-terminal activation domain, which may represent the molecular basis for the observed functional synergism. The results support a model that involves the combined action of multiple coactivators recruited by HNF-1, which activate transcription by coupling nucleosome modification and recruitment of the general transcription machinery.Tissue-specific expression of hepatic genes is accomplished by the concerted action of a small number of liver-enriched regulatory proteins, including the HNF-1 1 (1-4), the HNF3 (5), the HNF-4 (6), and the C/EBP (7) families of transcription factors. Although the expression of these factors is not restricted to hepatocytes, only these cells express them simultaneously at high levels (8). This pattern is achieved by a complex cross-regulatory network that has been postulated to determine the hepatic phenotype (9 -11). HNF-1 plays a central role in the coordination of this network, via positive regulation of a large number of downstream target genes (12) and via negative regulation of genes activated by HNF-4, including the HNF-1 gene itself (13,14). The key role of HNF-1 in nonhepatic tissues, such as in pancreatic ␤-cells and the kidney, has been recently highlighted by the complex phenotype of HNF-1 Ϫ/Ϫ mice (15-17) and the association of various HNF-1 mutations with an early onset form of noninsulin-dependent diabetes in human subjects (18).HNF-1 contacts DNA via an extra large atypical homeodomain exhibiting distant homology to other known homeoproteins (2, 3). Two features distinguish HNF-1 from other homeodomain transcription factors: it contains an extra 21-amino acid loop within the DNA-binding domain and dimerizes via the N-terminal dimerization domain (2, 3). The dimerization domain can associate with DcoH (19), an 11-kDa protein that has been suggested to be involved in dimer stabilization (20). The C-terminal part of HNF-1 contains at least three regions, ADI, ADII, and ADIII, that have been shown to be indispensable for transcription activation (3,12).Recent studies on the regulatory region of phe...

No abstract

Oncogenic stimuli trigger the DNA damage response (DDR) and induction of the alternative reading frame (ARF) tumor suppressor, both of which can activate the p53 pathway and provide intrinsic barriers to tumor progression. However, the respective timeframes and signal thresholds for ARF induction and DDR activation during tumorigenesis remain elusive. Here, these issues were addressed by analyses of mouse models of urinary bladder, colon, pancreatic and skin premalignant and malignant lesions. Consistently, ARF expression occurred at a later stage of tumor progression than activation of the DDR or p16INK4A , a tumor-suppressor gene overlapping with ARF. Analogous results were obtained in several human clinical settings, including early and progressive lesions of the urinary bladder, head and neck, skin and pancreas. Mechanistic analyses of epithelial and fibroblast cell models exposed to various oncogenes showed that the delayed upregulation of ARF reflected a requirement for a higher, transcriptionally based threshold of oncogenic stress, elicited by at least two oncogenic 'hits', compared with lower activation threshold for DDR. We propose that relative to DDR activation, ARF provides a complementary and delayed barrier to tumor development, responding to more robust stimuli of escalating oncogenic overload.