The retinoid signalling molecule, TRIM16, is repressed during squamous cell carcinoma skin carcinogenesis in vivo and reduces skin cancer cell migration in vitro.

Retinoid therapy is used for chemo-prevention in immuno-suppressed patients at high risk of developing skin cancer. The retinoid signalling molecule, tripartite motif protein 16 (TRIM16), is a regulator of keratinocyte differentiation and a tumour suppressor in retinoid-sensitive neuroblastoma. We sought to determine the role of TRIM16 in skin squamous cell carcinoma (SCC) pathogenesis. We have shown that TRIM16 expression was markedly reduced during the histological progression from normal skin to actinic keratosis and SCC. SCC cell lines exhibited lower cytoplasmic and nuclear TRIM16 expression compared with primary human keratinocyte (PHK) cells due to reduced TRIM16 protein stability. Overexpressed TRIM16 translocated to the nucleus, inducing growth arrest and cell differentiation. In SCC cells, TRIM16 bound to and down regulated nuclear E2F1, this is required for cell replication. Retinoid treatment increased nuclear TRIM16 expression in retinoid-sensitive PHK cells, but not in retinoid-resistant SCC cells. Overexpression of TRIM16 reduced SCC cell migration, which required the C-terminal RET finger protein (RFP)-like domain of TRIM16. The mesenchymal intermediate filament protein, vimentin, was directly bound and down-regulated by TRIM16 and was required for TRIM16-reduced cell migration. Taken together, our data suggest that loss of TRIM16 expression plays an important role in the development of cutaneous SCC and is a determinant of retinoid sensitivity.

PHLDA1 expression marks the putative epithelial stem cells and contributes to intestinal tumorigenesis.

Studies employing mouse models have identified crypt base and position +4 cells as strong candidates for intestinal epithelial stem cells. Equivalent cell populations are thought to exist in the human intestine; however robust and specific protein markers are lacking. Here, we show that in the human small and large intestine, PHLDA1 is expressed in discrete crypt base and some position +4 cells. In small adenomas, PHLDA1 was expressed in a subset of undifferentiated and predominantly Ki-67-negative neoplastic cells, suggesting that a basic hierarchy of differentiation is retained in early tumorigenesis. In large adenomas, carcinomas, and metastases PHLDA1 expression became widespread, with increased expression and nuclear localization at invasive margins. siRNA-mediated suppression of PHLDA1 in colon cancer cells inhibited migration and anchorage-independent growth in vitro and tumor growth in vivo. The integrins ITGA2 and ITGA6 were downregulated in response to PHLDA1 suppression, and accordingly cell adhesion to laminin and collagen was significantly reduced. We conclude that PHLDA1 is a putative epithelial stem cell marker in the human small and large intestine and contributes to migration and proliferation in colon cancer cells.

The estrogen-responsive B box protein (EBBP) restores retinoid sensitivity in retinoid-resistant cancer cells via effects on histone acetylation.

Retinoids have significant clinical activity in several human cancers, yet the factors determining retinoid sensitivity in cancer cells are still unclear. Retinoid-induced expression of retinoic acid receptor (RAR) beta(2) is a necessary component of the retinoid anticancer signal in cancer cells. We have previously identified the Estrogen-responsive B Box Protein (EBBP), a member of the Tripartite Motif (TRIM) protein family, as a novel RARbeta2 transcriptional regulator in the retinoid signal. Here we examined the mechanism of the EBBP effect on the retinoid anticancer signal. We assessed retinoid-responsive RARbeta2 transcription in retinoid-resistant breast and lung cancer cells in the presence of chromatin modifying agents. A histone deacetylase (HDAC) inhibitor alone, or in combination with retinoid, was more effective than a demethylating agent in restoring RARbeta2 transcription in resistant cells. Overexpression of EBBP alone markedly increased histone acetylation. The effect of EBBP on retinoid-responsive transcription appeared to be limited to genes with the retinoic acid response element (betaRARE) regulatory sequence, such as CYP26A1. EBBP inhibited cell growth by effects on cyclin D1 and Phospho-Rb, and, reduced cell viability in retinoid-resistant cancer cells. The viability of non-cancer cells was unaffected by EBBP overexpression. Taken together our data suggests that EBBP acts to de-repress transcription of RARbeta2 and CYP26A1, by modifying histone acetylation in retinoid-resistant cancer cells, and, is an important target for drug discovery in retinoid-resistant cancers.