PHF2 histone demethylase acts as a tumor suppressor in association with p53 in cancer

Plant homeodomain finger 2 (PHF2) has a role in epigenetic regulation of gene expression by demethylating H3K9-Me2. Several genome-wide studies have demonstrated that the chromosomal region including the PHF2 gene is often deleted in some cancers including colorectal cancer, and this finding encouraged us to investigate the tumor suppressive role of PHF2. As p53 is a critical tumor suppressor in colon cancer, we tested the possibility that PHF2 is an epigenetic regulator of p53. PHF2 was associated with p53, and thereby, promoted p53-driven gene expression in cancer cells under genotoxic stress. PHF2 converted the chromatin that is favorable for transcription by demethylating the repressive H3K9-Me2 mark. In an HCT116 xenograft model, PHF2 was found to be required for the anticancer effects of oxaliplatin and doxorubicin. In PHF2-deficient xenografts, p53 expression was profoundly induced by both drugs, but its downstream product p21 was not, suggesting that p53 cannot be activated in the absence of PHF2. To find clinical evidence about the role of PHF2, we analyzed the expressions of PHF2, p53 and p21 in human colon cancer tissues and adjacent normal tissues from patients. PHF2 was downregulated in cancer tissues and PHF2 correlated with p21 in cancers expressing functional p53. Colon and stomach cancer tissue arrays showed a positive correlation between PHF2 and p21 expressions. Informatics analyses using the Oncomine database also supported our notion that PHF2 is downregulated in colon and stomach cancers. On the basis of these findings, we propose that PHF2 acts as a tumor suppressor in association with p53 in cancer development and ensures p53-mediated cell death in response to chemotherapy.

beta-Catenin expression in the transitional cell zone of pilomatricoma

BACKGROUND

beta-Catenin, a participant in the Wnt pathway, has been shown to play an important role in the morphogenesis of hair follicles and the formation of hair follicle-related tumours, including pilomatricomas. It has been observed that at least 75% of human pilomatricomas possess activating mutations in beta-catenin. These findings suggested that beta-catenin plays an important role in the tumorigenesis of pilomatricomas. However, the pattern of beta-catenin expression in pilomatricoma tissues is still unclear. Objectives To examine the expression of beta-catenin in human pilomatricomas by immunohistochemical staining.

METHODS

Twenty-six formalin-fixed and paraffin-embedded samples of pilomatricoma tissue were studied.

RESULTS

Most transitional cells of pilomatricoma expressed beta-catenin strongly, but the basophilic cells and shadow cells did not. beta-Catenin showed a prominent membranous immunoreactivity and a small amount of condensed cytoplasmic staining, but there was definitely no evidence of nuclear positivity.

CONCLUSIONS

These findings imply that beta-catenin is primarily involved in cell-cell adhesion rather than cellular proliferation during pilomatricoma pathogenesis, and suggest that if beta-catenin is involved in pilomatricoma tumorigenesis and tumour growth, it plays an indirect role.

Activating signal cointegrator 1, a novel transcription coactivator of nuclear receptors, and its cytosolic localization under conditions of serum deprivation

Activating signal cointegrator 1 (ASC-1) harbors an autonomous transactivation domain that contains a putative zinc finger motif which provides binding sites for basal transcription factors TBP and TFIIA, transcription integrators steroid receptor coactivator 1 (SRC-1) and CBP-p300, and nuclear receptors, as demonstrated by the glutathione S-transferase pull-down assays and the yeast two-hybrid tests. The ASC-1 binding sites involve the hinge domain but not the C-terminal AF2 core domain of nuclear receptors. Nonetheless, ASC-1 appears to require the AF2-dependent factors to function (i.e., CBP-p300 and SRC-1), as suggested by the ability of ASC-1 to coactivate nuclear receptors, either alone or in cooperation with SRC-1 and p300, as well as its inability to coactivate a mutant receptor lacking the AF2 core domain. By using indirect immunofluorescence, we further show that ASC-1, a nuclear protein, is localized to the cytoplasm under conditions of serum deprivation but is retained in the nucleus when it is serum starved in the presence of ligand or coexpressed CBP or SRC-1. These results suggest that ASC-1 is a novel coactivator molecule of nuclear receptors which functions in conjunction with CBP-p300 and SRC-1 and may play an important role in establishing distinct coactivator complexes under different cellular conditions.