Genome structure and gene expression depend on a multitude of chromatin-binding proteins. The binding properties of these proteins to native chromatin in intact cells are largely unknown. Here, we describe an approach based on combined in vivo photobleaching microscopy and kinetic modeling to analyze globally the dynamics of binding of chromatin-associated proteins in living cells. We have quantitatively determined basic biophysical properties, such as off rate constants, residence time, and bound fraction, of a wide range of chromatin proteins of diverse functions in vivo. We demonstrate that most chromatin proteins have a high turnover on chromatin with a residence time on the order of seconds, that the major fraction of each protein is bound to chromatin at steady state, and that transient binding is a common property of chromatin-associated proteins. Our results indicate that chromatin-binding proteins find their binding sites by three-dimensional scanning of the genome space and our data are consistent with a model in which chromatin-associated proteins form dynamic interaction networks in vivo. We suggest that these properties are crucial for generating high plasticity in genome expression.Organization of DNA into higher-order chromatin structure serves to accommodate the genome within the spatial confines of the cell nucleus and acts as an important regulatory mechanism (22,36,46,60). Establishment, maintenance, and alterations of global and local chromatin states are modulated by the combined action of a multitude of chromatin-binding proteins. The nucleosome, containing histone proteins, acts as a structural scaffold and as an entry point for regulatory mechanisms (60, 63). Nonhistone proteins, including the HMG proteins, further contribute to the structural maintenance and regulation of chromatin regions (6, 61). In heterochromatin, specific factors such as HP1 convey a transcriptionally repressed state, possibly by influencing higher-order chromatin structure (19,27). Histone-modifying enzymes such as histone acetyl-and methyltransferases are instrumental in generating epigenetic marks on chromatin domains (60). Chromatin remodeling factors act on specific sites to facilitate access to regulatory DNA elements. Once accessible, transcriptional activators bind specific sequences on DNA and recruit the basal transcription machinery (37,44,46). All of these steps involve binding of proteins to chromatin.Due to their functional significance, chromatin-associated proteins have been extensively characterized-mostly by biochemical extraction and in vitro binding assays. Little is known about the dynamics of how chromatin proteins bind to their target sites in native chromatin in living cells. In vivo microscopy techniques are providing novel tools to study chromatin proteins in living cells (32,39,41,50). Qualitative analysis of photobleaching experiments has revealed a wide range of dynamic behavior for chromatin-associated proteins. The bulk of core histones is immobile on DNA, whereas the linker histone H1...

We have identified a critical role for amplified FGFR2 in gastric cancer cell proliferation and survival. In a panel of gastric cancer cell lines, fibroblast growth factor receptor 2 (FGFR2) was overexpressed and tyrosine phosphorylated selectively in FGFR2-amplified cell lines KatoIII, Snu16, and OCUM-2M. FGFR2 kinase inhibition by a specific smallmolecule inhibitor resulted in selective and potent growth inhibition in FGFR2-amplified cell lines, resulting in growth arrest in KatoIII cells and prominent induction of apoptosis in both Snu16 and OCUM-2M cells. FGFR2-amplified cell lines also contained elevated phosphotyrosine in EGFR, Her2, and Erbb3, but the elevated phosphorylation in EGFR could not be inhibited by gefitinib or erlotinib. We show that the elevated EGFR, Her2, and Erbb3 phosphotyrosine is dependent on FGFR2, revealing EGFR family kinases to be downstream targets of amplified FGFR2. Moreover, shRNA to Erbb3 resulted in a loss of proliferation, confirming a functional role for the activated EGFR signaling pathway. These results reveal that both the FGFR2 and EGFR family signaling pathways are activated in FGFR2-amplified gastric cancer cell lines to drive cell proliferation and survival. Inhibitors of FGFR2 or Erbb3 signaling may have therapeutic efficacy in the subset of gastric cancers containing FGFR2 amplification.

We have identified a novel gene, six transmembrane protein of prostate 2 (STAMP2), named for its high sequence similarity to the recently identified STAMP1 gene. STAMP2 displays a tissue-restricted expression with highest expression levels in placenta, lung, heart, and prostate and is predicted to code for a 459-amino acid six transmembrane protein. Using a form of STAMP2 labeled with green flourescent protein (GFP) in quantitative time-lapse and immunofluorescence confocal microscopy, we show that STAMP2 is primarily localized to the Golgi complex, trans-Golgi network, and the plasma membrane. STAMP2 also localizes to vesicular-tubular structures in the cytosol and colocalizes with the Early Endosome Antigen1 (EEA1) suggesting that it may be involved in the secretory/endocytic pathways. STAMP2 expression is exquisitely androgen regulated in the androgen-sensitive, androgen receptor-positive prostate cancer cell line LNCaP, but not in androgen receptornegative prostate cancer cell lines PC-3 and DU145. Analysis of STAMP2 expression in matched normal and tumor samples microdissected from prostate cancer specimens indicates that STAMP2 is overexpressed in prostate cancer cells compared with normal prostate epithelial cells. Furthermore, ectopic expression of STAMP2 in prostate cancer cells significantly increases cell growth and colony formation suggesting that STAMP2 may have a role in cell proliferation. Taken together, these data suggest that STAMP2 may contribute to the normal biology of the prostate cell, as well as prostate cancer progression.

We have identified a novel gene, six transmembrane protein of prostate 1 (STAMP1), which is largely specific to prostate for expression and is predicted to code for a 490-amino acid six transmembrane protein. Using a form of STAMP1 labeled with green fluorescent protein in quantitative time-lapse and immunofluorescence confocal microscopy, we show that STAMP1 is localized to the Golgi complex, predominantly to the trans-Golgi network, and to the plasma membrane. STAMP1 also localizes to vesicular tubular structures in the cytosol and colocalizes with the early endosome antigen 1 (EEA1), suggesting that it may be involved in the secretory/endocytic pathways. STAMP1 is highly expressed in the androgen-sensitive, androgen receptor-positive prostate cancer cell line LNCaP, but not in androgen receptor-negative prostate cancer cell lines PC-3 and DU145. Furthermore, STAMP1 expression is significantly lower in the androgen-dependent human prostate xenograft CWR22 compared with the relapsed derivative CWR22R, suggesting that its expression may be deregulated during prostate cancer progression. Consistent with this notion, in situ analysis of human prostate cancer specimens indicated that STAMP1 is expressed exclusively in the epithelial cells of the prostate and its expression is significantly increased in prostate tumors compared with normal glands. Taken together, these data suggest that STAMP1 may have an important role in the normal prostate cell as well as in prostate cancer progression.The prostate gland is a major secretory organ whose precise function is still not known (1). Through secretions into the male ejaculate, it is thought that the prostate protects the lower urinary tract from infection and increases fertility. Despite the unknown specific function, the prostate is the most common site of neoplastic transformation in men. Prostate cancer is the most commonly diagnosed cancer and the second leading cause of cancer mortality in men other than skin cancer (2). In the initial stages, prostate cancer is dependent on androgens for growth, which is the basis for androgen ablation therapy (3). However, in most cases, prostate cancer progresses to an androgen-independent phenotype for which there is no effective therapy available at present (for reviews, see Refs. 4 and 5).Currently, there is limited information regarding the molecular details of normal prostate function as well as prostate cancer initiation and progression. Several independent approaches resulted in the identification of a few highly prostateenriched genes that may have unique roles in these processes. The first such gene discovered was prostate-specific antigen (PSA) 1 (for a review, see Ref. 6), which is currently used as a diagnostic tool and also as a marker for the progression of prostate cancer, albeit with significant limitations (7,8). More recently, several additional prostate-enriched genes were identified including prostate-specific membrane antigen (PSMA) (9), prostate carcinoma tumor antigen 1 (PCTA-1) (10), NKX3.1 (11, 12), pros...