WTH3 is a direct target of the p53 protein

Low RAB6C expression is a predictor of tamoxifen benefit in estrogen receptor-positive/progesterone receptor-negative breast cancer

Over the last few decades, improved and more individualized treatment has contributed to the increased survival rate of patients with breast cancer. However, certain patients may receive excessive treatment resulting in undesired side effects. In a previous study, it was demonstrated that systemically untreated patients with estrogen receptor (ER)-positive/progesterone receptor (PR)-negative tumors with high Ras-related protein Rab-6C (RAB6C) expression levels (RAB6C⁺) had prolonged distant recurrence-free survival compared with that of patients exhibiting low RAB6C (RAB6C^-)-expressing tumors. The aim of the present study was to investigate whether RAB6C predicts the effectiveness of tamoxifen treatment. The present study used a dataset comprising 486 female patients with ER⁺ tumors from a randomized study conducted by the Stockholm Breast Cancer Study Group between November 1976 and August 1990. The patients were considered as low-risk if their tumor size was ≤30 mm and their lymph node status was negative. Patients were followed up until distant recurrence, mortality or when 25 years after randomization was achieved, whichever occurred first. For patients with ER⁺/PR^-/RAB6C⁺ tumors, prolonged distant recurrence-free survival could not be observed if the patients were treated with tamoxifen [hazard ratio (HR), 1.82; 95% confidence interval (CI), 0.69-4.79; P=0.23], whereas patients with ER⁺/PR^-/RAB6C^- tumors had 75% reduced distant recurrence risk (HR, 0.25; 95% CI, 0.09-0.70; P=0.008). In the ER⁺/PR⁺ subgroup, patients with RAB6C^- and RAB6C⁺ tumors benefited from tamoxifen treatment, though it was most evident in the RAB6C⁺ group (HR, 0.27; 95% CI, 0.13-0.58; P=0.001). The results of the present study indicated that, for patients with ER⁺/PR^- tumors, those with low RAB6C expression benefited from tamoxifen treatment, whereas no benefit was observed in patients with high RAB6C levels.

RAB6C is an independent prognostic factor of estrogen receptor-positive/progesterone receptor-negative breast cancer

The majority of breast cancer tumors are estrogen receptor-positive (ER⁺) and can be treated with endocrine therapy. However, certain patients may exhibit a good prognosis without systemic treatment. The aim of the present study was to identify novel prognostic factors for patients with ER⁺ breast cancer tumors using gene copy data, and to investigate if these factors have prognostic value in subgroups categorized by progesterone receptor status (PR). Public data, including the whole genome gene copy data of 199 systemically untreated patients with ER⁺ tumors, were utilized in the present study. To assess prognostic value, patients were divided into two groups using the median gene copy number as a cut-off for the SNPs that were the most variable. One SNP was identified, which indicated that the Ras-related protein Rab-6C (RAB6C) gene may exhibit prognostic significance. Therefore, RAB6C protein expression was subsequently investigated in a second independent cohort, consisting of 469 systematically untreated patients (of which 310 were ER⁺) who received long term follow-up. In the public data set, a distant recurrence risk reduction of 55% was determined for copy numbers above the median value of RAB6C compared with numbers below [multivariable adjusted hazard ratio (HR), 0.45; 95% CI 0.28–0.72; P=0.001)]. It was also more pronounced in the ER⁺/PR⁻ subgroup (HR, 0.15; 95% CI, 0.05–0.46; P=0.001). In the second cohort, patients of the ER⁺/PR⁻ subgroup who exhibited high RAB6C expression had a reduced distant recurrence risk (HR, 0.17; 95% CI, 0.05–0.60; P=0.006). However, this was not identified among ER⁺/PR⁺ tumors (HR, 1.31; 95% CI, 0.69–2.48; P=0.41). The results of the present study indicated that RAB6C serves as an independent prognostic factor of distant recurrence risk in systemically untreated patients with an ER⁺/PR⁻ tumor.

The transcription factor p53: not a repressor, solely an activator

The predominant function of the tumor suppressor p53 is transcriptional regulation. It is generally accepted that p53-dependent transcriptional activation occurs by binding to a specific recognition site in promoters of target genes. Additionally, several models for p53-dependent transcriptional repression have been postulated. Here, we evaluate these models based on a computational meta-analysis of genome-wide data. Surprisingly, several major models of p53-dependent gene regulation are implausible. Meta-analysis of large-scale data is unable to confirm reports on directly repressed p53 target genes and falsifies models of direct repression. This notion is supported by experimental re-analysis of representative genes reported as directly repressed by p53. Therefore, p53 is not a direct repressor of transcription, but solely activates its target genes. Moreover, models based on interference of p53 with activating transcription factors as well as models based on the function of ncRNAs are also not supported by the meta-analysis. As an alternative to models of direct repression, the meta-analysis leads to the conclusion that p53 represses transcription indirectly by activation of the p53-p21-DREAM/RB pathway.

Expression of WTH3 in breast cancer tissue and the effects on the biological behavior of breast cancer cells

The aim of the present study was to investigate the expression of WTH3 in tumor and normal breast tissue. The mRNA and protein expression levels of WTH3 were detected using reverse transcription quantitative polymerase chain reaction and western blot analysis, respectively. In addition, matrix metalloproteinase (MMP)-2 protein expression was measured. The effect of WTH3 expression on the proliferation activity of breast cancer cells was detected using a Cell Counting Kit-8 assay. Furthermore, the effects of WTH3 on the invasion and migration ability of the breast cancer cells was investigated. The results revealed that WTH3 was able to significantly inhibit the proliferation of the MCF-7 and MDA-MB-231 breast cancer cell lines. In addition, the invasion and migration assay demonstrated that WTH3 was able to inhibit the invasion and migration of breast cancer cells. Western blot analysis revealed that increased expression of WTH3 resulted in decreased expression levels of MMP-2, which has an important function in the metastasis of cancer cells. In conclusion, WTH3 expression differed between the tumor and normal breast tissues. WTH3 was able to inhibit the proliferation of breast cancer cells and decrease their invasion ability. Thus, WTH3 may be a promising target for breast cancer therapy in the future.

Dual functions of autophagy in the response of breast tumor cells to radiation: cytoprotective autophagy with radiation alone and cytotoxic autophagy in radiosensitization by vitamin D 3

In MCF-7 breast tumor cells, ionizing radiation promoted autophagy that was cytoprotective; pharmacological or genetic interference with autophagy induced by radiation resulted in growth suppression and/or cell killing (primarily by apoptosis). The hormonally active form of vitamin D, 1,25D 3, also promoted autophagy in irradiated MCF-7 cells, sensitized the cells to radiation and suppressed the proliferative recovery that occurs after radiation alone. 1,25D 3 enhanced radiosensitivity and promoted autophagy in MCF-7 cells that overexpress Her-2/neu as well as in p53 mutant Hs578t breast tumor cells. In contrast, 1,25D 3 failed to alter radiosensitivity or promote autophagy in the BT474 breast tumor cell line with low-level expression of the vitamin D receptor. Enhancement of MCF-7 cell sensitivity to radiation by 1,25D 3 was not attenuated by a genetic block to autophagy due largely to the promotion of apoptosis via the collateral suppression of protective autophagy. However, MCF-7 cells were protected from the combination of 1,25D 3 with radiation using a concentration of chloroquine that produced minimal sensitization to radiation alone. The current studies are consistent with the premise that while autophagy mediates a cytoprotective function in irradiated breast tumor cells, promotion of autophagy can also confer radiosensitivity by vitamin D (1,25D 3). As both cytoprotective and cytotoxic autophagy can apparently be expressed in the same experimental system in response to radiation, this type of model could be utilized to distinguish biochemical, molecular and/or functional differences in these dual functions of autophagy.

RAB6C is a retrogene that encodes a centrosomal protein involved in cell cycle progression

Rab-GTPases are key regulators of membrane transport, and growing evidence indicates that their expression levels are altered in certain human malignancies, including cancer. Rab6C, a newly identified Rab6 subfamily member, has attracted recent attention because its reduced expression might confer a selective advantage to drug-resistant breast cancer cells. Here, we report that RAB6C is a primate-specific retrogene derived from a RAB6A' transcript. RAB6C is transcribed in a limited number of human tissues including brain, testis, prostate, and breast. Endogenous Rab6C is considerably less abundant and has a much shorter half-life than Rab6A'. Comparison of the GTP-binding motifs of Rab6C and Rab6A', homology modeling, and GTP-blot overlay assays indicate that amino acid changes in Rab6C have greatly reduced its GTP-binding affinity. Instead, the noncanonical GTP-binding domain of Rab6C mediates localization of the protein to the centrosome. Overexpression of Rab6C results in G1 arrest, and its specific depletion generates tetraploid cells with supernumerary centrosomes, revealing a role of Rab6C in events related to the centrosome and cell cycle progression. Thus, RAB6C is a rare example of a recently emerged retrogene that has acquired the status of a new gene, encoding a functional protein with altered characteristics compared to Rab6A'.

Methylation of WTH3, a possible drug resistant gene, inhibits p53 regulated expression

BACKGROUND

Previous results showed that over-expression of the WTH3 gene in MDR cells reduced MDR1 gene expression and converted their resistance to sensitivity to various anticancer drugs. In addition, the WTH3 gene promoter was hypermethylated in the MCF7/AdrR cell line and primary drug resistant breast cancer epithelial cells. WTH3 was also found to be directly targeted and up regulated by the p53 gene. Furthermore, over expression of the WTH3 gene promoted the apoptotic phenotype in various host cells.

METHODS

To further confirm WTH3's drug resistant related characteristics, we recently employed the small hairpin RNA (shRNA) strategy to knockdown its expression in HEK293 cells. In addition, since the WTH3 promoter's p53-binding site was located in a CpG island that was targeted by methylation, we were interested in testing the possible effect this epigenetic modification had on the p53 transcription factor relative to WTH3 expression. To do so, the in vitro methylation method was utilized to examine the p53 transgene's influence on either the methylated or non-methylated WTH3 promoter.

RESULTS

The results generated from the gene knockdown strategy showed that reduction of WTH3 expression increased MDR1 expression and elevated resistance to Doxorubicin as compared to the original control cells. Data produced from the methylation studies demonstrated that DNA methylation adversely affected the positive impact of p53 on WTH3 promoter activity.

CONCLUSION

Taken together, our studies provided further evidence that WTH3 played an important role in MDR development and revealed one of its transcription regulatory mechanisms, DNA methylation, which antagonized p53's positive impact on WTH3 expression.

Establishment and characterization of a bona fide Barrett esophagus-associated adenocarcinoma cell line

Esophageal adenocarcinoma currently has one of the most rapidly increasing tumor incidences in the United States, with the vast majority of cases occurring on the backdrop of metaplastic epithelium (Barrett esophagus). The availability of appropriate cell line models is essential for maintaining the pace of esophageal cancer research and for pre-clinical validation of new therapeutic modalities. The identity of several of the widely utilized esophageal adenocarcinoma cell lines (BIC-1, SEG-1 and TE-7) have recently been called into question. Here we describe the establishment and characterization of a bona fide esophageal cancer cell line, JH-EsoAd1, from a patient with Barrett-associated adenocarcinoma. The rapid dissemination of this cancer cell line to the esophageal cancer research community should help ameliorate the current scarcity of preclinical models in this disease.