Growth of persistent foci of DNA damage checkpoint factors is essential for amplification of G1 checkpoint signaling.

Several DNA damage checkpoint factors form nuclear foci in response to ionizing radiation (IR). Although the number of the initial foci decreases concomitantly with DNA double-strand break repair, some fraction of foci persists. To date, the physiological role of the persistent foci has been poorly understood. Here we examined foci of Ser1981-phosphorylated ATM in normal human diploid cells exposed to 1Gy of X-rays. While the initial foci size was approximately 0.6microm, the one or two of persistent focus (foci) grew, whose diameter reached 1.6microm or more in diameter at 24h after IR. All of the grown persistent foci of phosphorylated ATM colocalized with the persistent foci of Ser139-phosphorylated histone H2AX, MDC1, 53BP1, and NBS1, which also grew similarly. When G0-synchronized normal human cells were released immediately after 1Gy of X-rays and incubated for 24h, the grown large phosphorylated ATM foci (> or =1.6microm) were rarely (av. 0.9%) observed in S phase cells, while smaller foci (<1.6microm) were frequently (av. 45.9%) found. We observed significant phosphorylation of p53 at Ser15 in cells with a single grown phosphorylated ATM focus. Furthermore, persistent inhibition of foci growth of phosphorylated ATM by an ATM inhibitor, KU55933, completely abrogated p53 phosphorylation. Defective growth of the persistent IR-induced foci was observed in primary fibroblasts derived from ataxia-telangiectasia (AT) and Nijmegen breakage syndrome (NBS) patients, which were abnormal in IR-induced G1 checkpoint. These results indicate that the growth of the persistent foci of the DNA damage checkpoint factors plays a pivotal role in G1 arrest, which amplifies G1 checkpoint signals sufficiently for phosphorylating p53 in cells with a limited number of remaining foci

Human antigen R as a predictive marker for response to gemcitabine?based chemotherapy in advanced cisplatin?resistant urothelial cancer

In patients with advanced urothelial cancer (UC), a combination of cisplatin (CDDP) and gemcitabine (GEM) is the most commonly used first-line systematic chemotherapy regimen. Although no standard regime for the treatment of CDDP-resistant UC has been established, GEM-based regimens are frequently used in these patients. In other types of cancer, human antigen R (HuR) status in cancer cells is closely associated with patient response to GEM. The aim of the present study was to establish the predictive potential of HuR expression for disease progression and survival in patients with UC who were treated with GEM-based regimens as a first or second-line chemotherapy. A total of 50 patients with advanced UC were enrolled in the current study. As first-line chemotherapy, methotrexate, vinblastine, epirubicin and CDDP (MVEC) combination therapy and GEM and CDDP combination therapy were administered in 34 (68.0%) and 16 patients (32.0%), respectively. Following progression, 45 patients (90.0%) were treated with combined GEM and paclitaxel therapy, and 5 patients (10.0%) were treated with GEM monotherapy. Cytoplasmic and nuclear HuR expression was evaluated using immunohistochemical techniques. The associations between HuR expression levels and local tumor response and treatment outcomes were analyzed. In first-line chemotherapy, no anticancer effects were observed to be significantly associated with nuclear or cytoplasmic HuR expression. In second-line chemotherapy nuclear HuR expression also exhibited no significant association with anticancer effects; however, the local tumor response was significantly improved if positive cytoplasmic HuR expression was present (P=0.002). Multivariate analyses revealed that cytoplasmic HuR expression levels were a significant predictive marker for longer OS (hazard ratio, 0.22; 95% confidence interval, 0.09-0.56; P=0.001). No significant association was observed between nuclear HuR expression levels and the overall survival. Therefore, cytoplasmic HuR expression is a significant predictive marker of response to GEM-based chemotherapy in patients with CDDP-resistant UC. Despite the limitations of a small and retrospective study, the results of the present study may facilitate the development of novel treatment strategies and provide a focus for additional basic and clinical studies