Reactive oxygen species and p21Waf1/Cip1 are both essential for p53-mediated senescence of head and neck cancer cells.

Treatment of head and neck squamous cell carcinoma, HNSCC, often requires multimodal therapy, including radiation therapy. The efficacy of radiotherapy in controlling locoregional recurrence, the most frequent cause of death from HNSCC, is critically important for patient survival. One potential biomarker to determine radioresistance is TP53 whose alterations are predictive of poor radiation response. DNA-damaging reactive oxygen species (ROS) are a by-product of ionizing radiation that lead to the activation of p53, transcription of p21(cip1/waf1) and, in the case of wild-type TP53 HNSCC cells, cause senescence. The expression of p21 and production of ROS have been associated with the induction of cellular senescence, but the intricate relationship between p21 and ROS and how they work together to induce senescence remains elusive. For the first time, we show that persistent exposure to low levels of the ROS, hydrogen peroxide, leads to the long-term expression of p21 in HNSCC cells with a partially functional TP53, resulting in senescence. We conclude that the level of ROS is crucial in initiating p53's transcription of p21 leading to senescence. It is p21's ability to sustain elevated levels of ROS, in turn, that allows for a long-term oxidative stress, and ensures an active p53-p21-ROS signaling loop. Our data offer a rationale to consider the use of either ROS inducing agents or therapies that increase p21 expression in combination with radiation as approaches in cancer therapy and emphasizes the importance of considering TP53 status when selecting a patient's treatment options.

Reciprocal negative regulation between S100A7/psoriasin and beta-catenin signaling plays an important role in tumor progression of squamous cell carcinoma of oral cavity.

Overexpression of S100A7 (psoriasin), a small calcium-binding protein, has been associated with the development of psoriasis and carcinomas in different types of epithelia, but its precise functions are still unknown. Using human tissue specimens, cultured cell lines, and a mouse model, we found that S100A7 is highly expressed in preinvasive, well-differentiated and early staged human squamous cell carcinoma of the oral cavity (SCCOC), but little or no expression was found in poorly differentiated, later-staged invasive tumors. Interestingly, our results showed that S100A7 inhibits both SCCOC cell proliferation in vitro and tumor growth/invasion in vivo. Furthermore, we demonstrated that S100A7 is associated with the beta-catenin complex, and inhibits beta-catenin signaling by targeting beta-catenin degradation via a noncanonical mechanism that is independent of GSK3beta-mediated phosphorylation. More importantly, our results also indicated that beta-catenin signaling negatively regulates S100A7 expression. Thus, this reciprocal negative regulation between S100A7 and beta-catenin signaling implies their important roles in tumor development and progression. Despite its high levels of expression in early stage SCCOC tumorigenesis, S100A7 actually inhibits SCCOC tumor growth/invasion as well as tumor progression. Downregulation of S100A7 in later stages of tumorigenesis increases beta-catenin signaling, leading to promotion of tumor growth and tumor progression.

Signal transduction activator of transcription 5 (STAT5) dysfunction in autoimmune monocytes and macrophages.

Autocrine granulocyte macrophage-colony stimulating factor (GM-CSF) sequentially activates intracellular components in monocyte/macrophage production of the pro-inflammatory and immunoregulatory prostanoid, prostaglandin E2 (PGE2). GM-CSF first induces STAT5 signaling protein phosphorylation, then prostaglandin synthase 2 (COX2/PGS2) gene expression, and finally IL-10 production, to downregulate the cascade. Without activation, monocytes of at-risk, type 1 diabetic (T1D), and autoimmune thyroid disease (AITD) humans, and macrophages of nonobese diabetic (NOD) mice have aberrantly high GM-CSF, PGS2, and PGE2 expression, but normal levels of IL-10. After GM-CSF stimulation, repressor STAT5A and B isoforms (80-77kDa) in autoimmune human and NOD monocytes and activator STAT5A (96-94kDa) and B (94-92kDa) isoforms in NOD macrophages stay persistently tyrosine phosphorylated. This STAT5 phosphorylation persisted despite treatment in vitro with IL-10, anti-GM-CSF antibody, or the JAK2/3 inhibitor, AG490. Phosphorylated STAT5 repressor isoforms in autoimmune monocytes had diminished DNA binding capacity on GAS sequences found in the PGS2 gene enhancer. In contrast, STAT5 activator isoforms in NOD macrophages retained their DNA binding capacity on these sites much longer than in healthy control strain macrophages. These findings suggest that STAT5 dysfunction may contribute to dysregulation of GM-CSF signaling and gene activation, including PGS2, in autoimmune monocytes and macrophages.

IL10 resistant PGS2 expression in at-risk/Type 1 diabetic human monocytes.

Aberrant prostaglandin synthase 2 (PGS2/COX2) expression constitutes an antigen presenting cell (APC) dysfunction seen in monocytes of humans at risk for or with Type 1 diabetes. During endotoxin activation of PGS2 expression in healthy monocytes, granulocyte-monocyte colony stimulating factor (GM-CSF) is activated and, in turn, promotes PGS2 gene activation. GM-CSF is considered a major target the action for IL10 in its suppression of PGS2. We found that the PGS2 expression in monocytes from 47% of at-risk and diabetic humans tested were highly resistant to suppression by IL10 (maintaining > or =50% of their untreated expression), and had significantly increased GM-CSF production in vitro (1043+/-SD2798 pg/10(6)cells, subject n=35, vs 29.7+/-SD91 pg/10(6)cells, control n=20; P=0.0165). The PGS2 insensitivity to IL10 of these cells was not due to a lack of IL10 functionality or its suppression of GM-CSF. In contrast to its effects on PGS2, IL10 regulation of GM-CSF and other monocyte factors (i.e., DR, IL1beta, TNFalpha, IL12, CD54, and CD64) remained intact. These findings suggest that the inability of IL10 to properly downregulate PGS2 gene expression may contribute to its dysregulation in Type 1 diabetes.

Absence of p53-mediated G1 arrest with induction of MDM2 in sterigmatocystin-treated cells.

P53 plays a critical role in G1 checkpoint after DNA damage. MDM2 gene is a p53 target gene and its protein forms a feedback loop with p53 and inhibits p53-mediated G1 arrest. Sterigmatocystin (ST) is a mycotoxin and carcinogen. In this study we show that exposure of cells to ST for 12 or 24 h resulted in failure of G1 arrest at both time points. Accordingly, p53 protein was not increased and p21WAF1 expression was inhibited at 12 h, and both proteins were weakly induced at 24 h after treatment with ST. Meanwhile, MDM2 protein was induced in a p53-dependent fashion by ST at both 12 and 24 h. The induction of MDM2 was coincident with the cellular responses of p53 and p21WAF1, and might contribute to the failure of G1 arrest in ST-treated cells. In addition, ST-treated cells exhibited G2M arrest, regardless of p53 status. Our results indicate that the carcinogenic effects of ST seem to be mediated by failure of p53-mediated G1 checkpoint.

[Effects of extract solution of Aspergillus versicolor on human fetal gastric cells in vitro].

To detect the carcinogenicity of sterigmatocystin for human stomach, the human fetal gastric cells, cultured in vitro, were treated with extract solution of Aspergillus versicolor culture (0.117mg sterigmatocystin per Kg culture of Aspergillus versicolor). The cells showed random arrangement, loss of contact inhibition and cell polarity. Some transformed foci were present in different numbers and times according to the dosages of the extract solution. The cells with such changes were analysed with a flow cytometer and the results showed that the cell number in S phase of cell cycle distribution was greatly increased. The above changes were similar to those of the cells treated with MNNG, but no such changes were noted in the control group. These results indicated that sterigmatocystin could induce some characteristics of neoplastic transformed cells and that sterigmatocystin may be a carcinogen for human gastric cancer.

Studies on pathological morphology, clinical features and nuclear DNA contents by flow cytometry in adrenal neoplasms.

Pathological morphology, clinical features and nuclear DNA contents determined by flow cytometry (FCM) were studied in 11 cases of normal adrenals and 41 cases of adrenal neoplasms. It was found that despite differences in clinical manifestations and in degrees of cellular atypia of the adenomas their DNA contents were the same as in normal adrenals. On the other hand, the pheochromocytomas were benign in nature, but most of them (16/19) showed DNA aneuploidy and the DNA indices were correlated with their clinical and morphological features.

[Sterigmatocystin induced adenocarcinoma of the lung and atypical hyperplasia of glandular stomach in mice].

Aspergillus versicolor was isolated from the gastric juice of patients with chronic stomach diseases in high-risk area of gastric cancer. Mice fed with aspergillus-inoculated corn flour developed adenocarcinoma of the lung in 15 of 35 mice (42.9%) and atypical hyperplasia of the glandular stomach in 13 of 35 mice (37.4%). Sterigmatocystin was identified by HPLC and fluorescence spectrophotometry in the extract of aspergillus-inoculated corn flour. The results suggest that the mycotoxin sterigmatocystin is a potential carcinogen in human.