Ultraviolet (UV) light-induced pyrimidine photodimers are repaired by the nucleotide excision repair pathway. Photolesions have biophysical parameters closely resembling undamaged DNA, impeding discovery through damage surveillance proteins. The DDB1-DDB2 complex serves in the initial detection of UV lesions in vivo. Here we present the structures of the DDB1-DDB2 complex alone and bound to DNA containing either a 6-4 pyrimidine-pyrimidone photodimer (6-4PP) lesion or an abasic site. The structure shows that the lesion is held exclusively by the WD40 domain of DDB2. A DDB2 hairpin inserts into the minor groove, extrudes the photodimer into a binding pocket, and kinks the duplex by approximately 40 degrees. The tightly localized probing of the photolesions, combined with proofreading in the photodimer pocket, enables DDB2 to detect lesions refractory to detection by other damage surveillance proteins. The structure provides insights into damage recognition in chromatin and suggests a mechanism by which the DDB1-associated CUL4 ubiquitin ligase targets proteins surrounding the site of damage.

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The expression of pancreatic secretory trypsin inhibitor (PSTI) was studied immunohistochemically in 106 cases of gastric carcinoma. Of the 45 intestinal-type carcinomas, 34 cases (76%) expressed PSTI: 15 (63%) of 24 early carcinomas and 19 (90%) of 21 advanced carcinomas, the incidence being significantly different (P less than 0.05). Furthermore, in the intestinal-type carcinomas, a significant correlation was observed between PSTI expression and clinical stage or nodal involvement. On the other hand, of the 61 diffuse-type carcinomas, including 27 early and 34 advanced carcinomas, 54 cases (89%) were positive for PSTI; a high incidence of the PSTI expression was observed in both early and advanced carcinomas, being 93% and 85%, respectively. Moreover, PSTI-positive cells were localized in more than half of the early diffuse-type gastric carcinomas at the invading zone of the surrounding tissues. The incidence of PSTI expression in advanced scirrhous-type carcinomas (100%) was significantly higher than that (76%) in medullary-type ones (P less than 0.05). Thus, the present findings, together with the previous reports that PSTI stimulates 3H-thymidine incorporation into DNA in human fibroblasts, suggest that the PSTI expressed in gastric carcinomas may possibly possess a biologic function responsible for the tumor growth and progression and for the stromal proliferation of fibrous tissues.

Summary We examined the expression of pancreatic secretory trypsin inhibitor (PSTI) in colorectal cancer by immunohistochemical staining using an anti-PSTI antiserum, an in situ hybridisation technique utilising sulphonated PSTI cDNA probe, and a Northern blot hybridisation method, using a 32P-labelled PSTI Pancreatic secretory trypsin inhibitor (PSTI) consists of a single polypeptide chain, and is known to be a specific trypsin inhibitor in the pancreas. Its physiological role has been considered to prevent the premature activation of trypsin in the pancreatic acini and ducts (Kazal et al., 1948). However, PSTI has also been demonstrated in various malignant cell lines and tissues, including pancreatic cancer, lung cancer, gynaecological cancer, and gastric cancer (Higashiyama et al., 1990;Ogata, 1988;Ogawa et al., 1987;Tomita et al., 1987;Ueda et al., 1989); the physiological role of PSTI in neoplastic tissue remains unknown. Nevertheless, several investigators have recently shown that PSTI may have functions other than the inhibition of trypsin activity, such as growth factor action (Niinobu et al., 1986;Ogawa et al., 1985Ogawa et al., , 1987. In fact, we have shown that the expression of PSTI in gastric cancer may possibly be associated with tumour growth and progression (Higashiyama et al., 1990).Although it has been reported that PSTI may be expressed in villous adenoma of the colon (Bohe et al., 1986;Tomita et al., 1987), there has been-u-study of the expression of PSTI in colorectal cancer, except for the preliminary report (Ogawa et al., 1987). In the present study, we demonstrate that colorectal cancer may also express PSTI, not only by immunohistochemical analysis for detection at the product level but also by in situ hybridisation and Northern blot hybridisation for detection at the transcriptional level. In addition, the possible biological and clinical significance of PSTI expression in colorectal cancer is also discussed. Materials and methods Tissue preparationThe tissues were supplied from surgical specimens resected at the 2nd Dept of Surgery, Osaka University Hospital. Preparation of anti-PSTI antiserum and immunohistochemical study Anti-PSTI antiserum used in this study was produced in rabbits as previously described (Kitahara et al., 1980). Its sensitivity and specificity were also confirmed by radioimmunoassay.Immunohistochemical study was performed according to a modified method of Hsu et al. (1981). Briefly, sections were dewaxed in xylene, rehydrated with a series of ethanol solutions, and endogenous peroxidase activity was blocked using 0.3% hydrogen peroxide in methanol for 30 min. After immersion in 3% normal goat serum for 30 min, in order to block non-specific binding, the sections were incubated with primary anti-PSTI antiserum at a dilution of 1:400 overnight at 4°C, and subsequently with biotinylated goat anti-rabbit IgG (Vector) and avidin-biotin peroxidase complex (Vectastain ABC kit, Vector) for 30 min each at room temperature. They were washed in PBS between each incubation...

Expression of p53, a tumor-suppressor gene product, was studied immunohistochemically in microwave-fixed, paraffin-embedded sections of 84 colorectal carcinomas and 44 adenomas. Using a monoclonal antibody (PAb1801), nuclear p53 was detected successfully in 51 of 84 (60.7%) cases of carcinomas, and no stain for p53 was demonstrated in the adjacent normal mucosa. The results in the microwave-fixed, paraffin-embedded sections correlated with those in the frozen sections. The incidence of p53 expression in colorectal carcinomas was high in the cases with distant metastasis, but it was not affected by clinicopathologic features such as tumor size or depth of invasion. In colorectal adenomas, only 4 of 44 (9%) adenomas expressed p53. This expression of p53, however, was restricted to only a few glands within tubular adenomas with mild dysplasia. Thus, p53 protein was expressed preferably by malignant tumors of the colorectum. The present study demonstrated the usefulness of microwave fixation to preserve p53. The immunohistochemical detection of p53 in microwave-fixed, paraffin-embedded sections of colorectal carcinoma and adenoma can provide valuable information about the mechanism of carcinogenesis in colorectal epithelium.