Sporadic basal-like cancers (BLC) are a distinct class of human breast cancers that are phenotypically similar to BRCA1-associated cancers. Like BRCA1-deficient tumors, most BLC lack markers of a normal inactive X chromosome (Xi). Duplication of the active X chromosome and loss of Xi characterized almost half of BLC cases tested. Others contained biparental but nonheterochromatinized X chromosomes or gains of X chromosomal DNA. These abnormalities did not lead to a global increase in X chromosome transcription but were associated with overexpression of a small subset of X chromosomal genes. Other, equally aneuploid, but non-BLC rarely displayed these X chromosome abnormalities. These results suggest that X chromosome abnormalities contribute to the pathogenesis of BLC, both inherited and sporadic.

There are currently two distinct models proposed to explain why both MDM2 and MDMX are required in p53 control, with a key difference centered on whether these two p53 inhibitors work together or independently. To test these two competing models, we generated knockin mice expressing a point mutation MDMX mutant (C462A) that is defective in MDM2 binding. This approach allowed a targeted disassociation of the MDM2/MDMX heterocomplex without affecting the ability of MDMX to bind to p53, and while leaving the MDM2 protein itself completely untouched. Significantly, Mdmx C462A/C462A homozygous mice died at approximately day 9.5 of embryonic development, as the result of a combination of apoptosis and decreased cell proliferation, as shown by TUNEL and BrdU incorporation assays, respectively. Interestingly, even though the MDMX mutant protein abundance was found slightly elevated in the Mdmx C462A/C462A homozygous embryos, both the abundance and activity of p53 were markedly increased. A p53-dependent death was demonstrated by the finding that concomitant deletion of p53 completely rescued the embryonic lethality in Mdmx C462A/C462A homozygous mice. Our data demonstrate that MDM2 and MDMX function as an integral complex in p53 control, providing insights into the nonredundant nature of the function of MDM2 and MDMX.knockin mouse model | p53 regulation U nder normal physiological conditions, wild-type p53 protein levels must be kept low owing to its growth-inhibitory activities, and this control is mainly modulated via regulation of p53 protein stability. Although a number of different regulators have been reported to be involved in this protein regulation, MDM2 has been shown to be the principal player in control of p53 turnover (1). MDM2 primarily functions as an E3 ubiquitin ligase targeting p53 for ubiquitination and subsequent degradation. At the same time, p53 induces the expression of the Mdm2 gene, forming a negative feedback loop (1). The importance of MDM2 in p53 control is highlighted by the finding that Mdm2 knockout results in p53-dependent embryonic lethality in mice (2, 3).MDMX (also known as MDM4), which was originally isolated as a novel p53-interacting protein, shares substantial structural homology with MDM2 (4, 5). The highest sequence similarity between MDM2 and MDMX lies at the N terminus and contains a p53-binding domain, and the two also share high sequence homology in a RING-finger domain, a region that mediates the association between MDMX and MDM2 (6,7). Genetic studies have demonstrated that like MDM2, MDMX is another essential negative regulator of p53 (8-10). Although it remains unclear why both MDM2 and MDMX are required for p53 control, a model has been proposed that these two proteins function independently. On the basis of the fact that unlike MDM2, MDMX lacks an intrinsic ubiquitin E3 ligase activity, it has been proposed that MDMX inhibits p53 chiefly by binding to the p53 transactivation domain and antagonizing p53 transcription activity, whereas MDM2 inactivates p53 primarily by wo...

Telomeres cap the ends of eukaryotic chromosomes and prevent them from being recognized as DNA breaks. We have shown that certain DNA damage responses induced during senescence and, at times of telomere uncapping, also can be induced by treatment of cells with small DNA oligonucleotides homologous to the telomere 3 single-strand overhang (T-oligos), implicating this overhang in generation of these telomere-based damage responses. Here, we show that T-oligo-treated fibroblasts contain ␥H2AX foci and that these foci colocalize with telomeres. T-oligos with nuclease-resistant 3 ends are inactive, suggesting that a nuclease initiates T-oligo responses. We therefore examined WRN, a 3 3 5 exonuclease and helicase mutated in Werner syndrome, a disorder characterized by aberrant telomere maintenance, premature aging, chromosomal rearrangements, and predisposition to malignancy. Normal fibroblasts and U20S osteosarcoma cells rendered deficient in WRN showed reduced phosphorylation of p53 and histone H2AX in response to T-oligo treatment. Together, these data demonstrate a role for WRN in processing of telomeric DNA and subsequent activation of DNA damage responses. The T-oligo model helps define the role of WRN in telomere maintenance and initiation of DNA damage responses after telomere disruption.exonuclease ͉ ␥-H2AX foci ͉ Werner syndrome ͉ senescence ͉ oligonucleotide

Chemoresistance contributes to cancer relapse and increased mortality in a variety of cancer types, raising a pressing need to better understand the underlying mechanism. MUC1 is abnormally overexpressed in numerous carcinomas and associated with poor prognosis. However, the functional significance of MUC1 in chemoresistance has not been fully elucidated. Here, we showed that MUC1 expression was considerably induced in cells that had acquired chemoresistance at both transcriptional and post-translational levels. Using gain- and loss-of function approaches, we demonstrated a critical role of MUC1 in induction of drug resistance. Through stimulation of EGFR activation and nuclear translocation, MUC1 increased the expression of ATP-binding cassette transporter B1 (ABCB1). Remarkably, targeted suppression of EGFR or ABCB1 by both shRNAs and inhibitors effectively reversed chemoresistance. Moreover, co-administration of the inhibitors of MUC1–EGFR–ABCB1 with paclitaxel significantly blocked not only tumor growth but also relapse in xenograft mouse model. Our data collectively support a model in which MUC1 induces acquired chemotherapy resistance by upregulating ABCB1 in an EGFR-dependent manner, providing a novel molecular basis of using the EGFR inhibitor in MUC1-positive cancers to prevent chemotherapy resistance.

Esophagus squamous cell carcinoma (ESCC) is one of the most deadly malignances because of its high frequency of metastasis. Given the associations of MUC1 with ESCC and tumor metastasis, we explored a potential role of MUC1 in ESCC metastasis. Among 40 ESCC and 20 paired normal tissue specimens examined, we found a significant increase of MUC1 expression in ESCC and more importantly, that expression of MUC1 and MMP13 are strongly correlated in patients who had lymph node metastasis. Studies with cell models indicated that overexpression of MUC1 upregulates the expression of MMP13, leading to increased cell migration. In support of a mode of transcriptional regulation, promoter analysis revealed that MUC1 stimulates MMP13 expression through the Runx-2-binding site. The link of MUC1 to cell motility was further confirmed by the finding that depletion of MUC1 resulted in reduced expression of MMP13 and cell migration, invasion and adhesion. Moreover, the loss of cell metastatic potential was rescued by overexpression of MMP13 completely. Collectively, our findings indicate that MUC1 contributes to ESCC metastasis by stimulating MMP13 expression, suggesting MUC1 as a novel diagnostic biomarker and therapeutic target in ESCC. Esophageal squamous cell carcinoma (ESCC) frequently exhibits extensive local invasion or regional lymph node metastasis at the time of initial diagnosis; therefore, it is one of the most common aggressive diseases with poor outcome. 1 Tumor invasion and metastasis involve degradation of different components of the extracellular matrix and require the actions of proteolytic enzymes, such as matrix metalloproteinases (MMPs), which are produced either by the tumor cells or surrounding stromal cells.2,3 MMP13 is a highly regulated zinc-dependent endopeptidase and has been reported to be associated with vascular invasion and lymph node metastasis in ESCC. 4 Mechanisms involved in regulation of MMP13 in ESCC are likely complex and poorly understood.Mucins are high-molecular-weight glycoproteins that have been identified as markers of adverse prognosis and as attractive therapeutic targets.5 MUC1, one of transmembrane mucins, is normally expressed in esophageal epithelium.Patients with MUC1 high expression often appear with advanced stage or lymph node metastasis suggesting correlation of the MUC1 expression and the invasion or metastasis of ESCC.6 In this study, we investigated the expression of MUC1 and MMP13 in ESCC patients and the potential functional relationship in tumor metastasis and prognosis. MATERIALS AND METHODS Tissue Sample CollectionA total of 40 paraffin-embedded archival specimens of primary ESCC cases were enrolled in this study: 20 with lymph node metastasis and 20 without lymph node metastasis. A total of 20 paired normal esophageal tissue specimens distant from the cancerous lesion in patients without lymph node metastasis were used as control. These patients did not receive any preoperative adjuvant radiation or chemotherapy.

Liver regeneration is a very complex and well-orchestrated process associated with signaling cascades involving cytokines, growth factors, and metabolic pathways. Adiponectin is an adipocytokine secreted by mature adipocytes, and its receptors are widely distributed in many tissues, including the liver. Adiponectin has direct actions in the liver with prominent roles to improve hepatic insulin sensitivity, increase fatty acid oxidation, and decrease inflammation. To test the hypothesis that adiponectin is required for normal progress of liver regeneration, 2/3 partial hepatectomy (PH) was performed on wild-type and adiponectin-null mice. Compared to wild-type mice, adiponectin-null mice displayed decreased liver mass regrowth, impeded hepatocyte proliferation, and increased hepatic lipid accumulation. Gene expression analysis revealed that adiponectin regulated the gene transcription related to lipid metabolism. Furthermore, the suppressed hepatocyte proliferation was accompanied with reduced signal transducer and activator of transcription protein 3 (STAT3) activity and enhanced suppressor of cytokine signaling 3 (Socs3) transcription. In conclusion, adiponectin-null mice exhibit impaired liver regeneration and increased hepatic steatosis. Increased expression of Socs3 and subsequently reduced activation of STAT3 in adiponectin-null mice may contribute to the alteration of the liver regeneration capability and hepatic lipid metabolism after PH. The liver has a central role in metabolic homeostasis, as it is responsible for the metabolism, synthesis, storage, and redistribution of nutrients, carbohydrates, fats, and vitamins. Paradoxically, it is also the main detoxifying organ of the body, which is frequently challenged by chemical, traumatic, or infectious injuries. Consequently, the liver has evolved a unique ability to regenerate in respond to liver mass loss because of injuries. 1,2 Liver regeneration, which is driven by the replication of existing hepatocytes, is a process of compensatory hyperplasia rather than a differentiation process of stem cells. 3 One of the most effective models for studying liver regeneration after hepatocellular loss is partial hepatectomy (PH) in rodents. This technique, which was first described by Higgins and Anderson and performed in rats, 4 can be modified to be safely and reproducibly performed in mice. 5 After PH, resection of about 2/3 of liver mass results in quiescent hepatocytes rapidly re-entering the cell cycle. This highly regulated process is primed by different cytokines and growth factors that activate the downstream kinases and transcription factors. As a result, the hepatocytes initiate the transcription of more than 100 early genes, accumulate triglyceride and cholesterol to supply the energy and materials required for restore the liver mass. After one or two rounds of replication of hepatocytes, the original liver mass is restored within 5-7 days. Thus, liver regeneration constitutes a unique model to study signal transduction, lipid metabolism, and cell cycl...

The ataxia-telangiectasia mutated (ATM) kinase is activated in the cellular response to ionizing radiation (IR) and is of importance to the repair of DNA double strand breaks (DSBs). The MUC1 oncoprotein is aberrantly overexpressed in human breast carcinomas. The present work demonstrates that the MUC1 C-terminal subunit (MUC1-C) constitutively interacts with ATM in human breast cancer cells. We show that the MUC1-C cytoplasmic domain binds directly to ATM HEAT repeats. Our results also demonstrate that the MUC1-C cytoplasmic domain binds to the ATM substrate H2AX. The functional significance of these interactions is supported by the finding that MUC1-C promotes removal of IR-induced nuclear γH2AX foci. MUC1-C also protects against IR-induced chromosomal aberrations. In concert with these results, MUC1-C blocks IR-induced death by promoting repair of potentially lethal DNA damage. These findings indicate that the overexpression of MUC1 can protect against IR-induced DNA DSBs and may represent a physiologic response that has been exploited by malignant cells.

Cancer stem cells (CSCs) are often enriched after chemotherapy and contribute to tumor relapse. While epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs) are widely used for the treatment of diverse types of cancer, whether EGFR-TKIs are effective against chemoresistant CSCs in cervical cancer is largely unknown. Here, we reveal that EGFR correlates with reduced disease-free survival in cervical cancer patients with chemotherapy. Erlotinib, an EGFR-TKI, effectively impedes CSCs enrichment in paclitaxel-resistant cells through inhibiting IL-6. In this context, MUC1 induces CSCs enrichment in paclitaxel-resistant cells via activation of EGFR, which directly enhances IL-6 transcription through cAMP response element-binding protein (CREB) and glucocorticoid receptor β (GRβ). Treatment with erlotinib sensitizes CSCs to paclitaxel therapy both in vitro and in vivo. More importantly, positive correlations between the expressions of MUC1, EGFR, and IL-6 were found in 20 cervical cancer patients after chemotherapy. Mining TCGA data sets also uncovered the expressions of MUC1-EGFR-IL-6 correlates with poor disease-free survival in chemo-treated cervical cancer patients. Collectively, our work has demonstrated that the MUC1-EGFR-CREB/GRβ axis stimulates IL-6 expression to induce CSCs enrichment and importantly, this effect can be abrogated by erlotinib, uncovering a novel strategy to treat paclitaxel-resistant cervical cancer.