1. Chronic exposure of LLC-PK1 epithelia to the phorbol ester TPA produces polyp-like foci with leaky tight junctions and altered protein kinase C-alpha expression and localization
J M Mullin, A P Soler, K V Laughlin, J A Kampherstein, L M Russo, D T Saladik, K George, R D Shurina, T G O'Brien Exp Cell Res. 1996 Aug 25;227(1):12-22. doi: 10.1006/excr.1996.0244.
Acute exposure (up to 4 h) of LLC-PK1 epithelial cell sheets to the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) causes a rapid decrease of transepithelial electrical resistance (TER) to less than 15% of initial value. As the TPA exposure period is continued by chronically passaging cells in the presence of TPA, TER begins to recover. By 6 weeks of exposure, TER recovers to almost 50% of its initial value, suggesting that tight junctions (TJs) are recovering barrier function even in the continued presence of TPA. Between 6 and 8 weeks, TER then decreases a second time to approximately 20 to 40% of initial values, and TER values remain at this level for at least 18 weeks of exposure. Transepithelial (paracellular) fluxes of D-mannitol inversely correspond with TER changes. Across chronically treated cell sheets, rates are higher than those across control cell sheets, but lower than those across acutely treated cell sheets. The decrease of TER at 6-8 weeks coincides with the appearance of multilayered, polyp-like foci (PLFs) on the otherwise one cell layer thick epithelium. Electron microscopy shows that the electron-dense dye ruthenium red cannot penetrate across TJs of control cells but passes across all of the TJs of a cell sheet treated acutely with TPA. In chronically treated cultures, ruthenium red penetrates TJs between most cells of PLFs, but not TJs of adjacent morphologically normal epithelium. A clonal subline derived from cells of a PLF (clone PLF-A) is multilayered almost throughout and exhibits ruthenium red penetration across nearly all of its tight junctions, monolayer or multilayer. Acute exposure of control cell sheets to TPA induces activation, translocation, and down-regulation of protein kinase C-alpha (PKC-alpha). In chronically TPA-treated and clone PLF-A cells, total PKC-alpha levels are reduced even further and almost all remaining PKC-alpha is found in the membrane-associated and Triton-insoluble fractions. Immunofluorescence shows that PKC-alpha expression is restricted to the PLFs in chronically TPA-treated cells and is more homogeneously distributed in clone PLF-A cultures. In summary, the data show that chronic treatment of epithelial cells with a tumor promoter induces the formation of abnormal cell architecture (PLFs) associated with increased leakiness of TJs and membrane translocation of PKC-alpha. Recovery of barrier function in portions of chronically TPA-treated cultures does not correlate with up-regulation of PKC-alpha nor translocation back to the cytosolic compartment.
2. CD147 mediates epidermal malignant transformation through the RSK2/AP-1 pathway
Xu Zhang, et al. J Exp Clin Cancer Res. 2022 Aug 13;41(1):246. doi: 10.1186/s13046-022-02427-w.
Background: Malignant transformation of the epidermis is an essential process in the pathogenesis of cutaneous squamous-cell carcinoma (cSCC). Although evidence has demonstrated that CD147 plays key roles in various tumors, the role of CD147 in epidermal malignant transformation in vivo remains unclear. Methods: Epidermal CD147-overexpression or knockout (EpiCD147-OE or EpiCD147-KO) transgenic mouse models were generated for in vivo study. RNA-sequencing and q-PCR were performed to identify the differentially expressed genes. Immunohistochemistry and flow cytometry were performed to investigate the role of CD147 in regulating myeloid-derived suppressor cells (MDSCs). Immunoprecipitation, EMSA and ChIP assays were performed to investigate the mechanism of CD147 in cell transformation. Results: We found that specific overexpression of CD147 in the epidermis (EpiCD147-OE) induces spontaneous tumor formation; moreover, a set of chemokines and cytokines including CXCL1, which play essential function in MDSC recruitment, were significantly upregulated in EpiCD147-OE transgenic mice. As expected, overexpression of CD147 in the epidermis remarkably facilitated tumorigenesis by increasing the rate of tumor initiation and the number and size of tumors in the DMBA/TPA mouse model. Interestingly, the expression of CXCL1 and the infiltration of MDSCs were dramatically increased in EpiCD147-OE transgenic mice. Our findings also showed that knockdown of CD147 attenuated EGF-induced malignant transformation as well as CXCL1 expression in HaCaT cells. Consistently, CD147 was found overexpressed in cutaneous squamous cell carcinoma (cSCC), and positively related with the expression of CD33, a myeloid-associated marker. We further identified RSK2, a serine/threonine kinase, as an interacting partner of CD147 at the binding site of CD147D207-230. The interaction of CD147 and RSK2 activated RSK2, thus enhancing AP-1 transcriptional activation. Furthermore, EMSAs and ChIP assays showed that AP-1 could associate with the CXCL1 promoter. Importantly, RSK2 inhibitor suppressed the tumor growth in DMBA/TPA mouse model by inhibiting the recruitment of MDSCs. Conclusion: Our findings demonstrate that CD147 exerts a key function in epidermal malignant transformation in vivo by activating keratinocytes and recruiting MDSCs via the RSK2/AP-1 pathway.
3. Aberrant activation of CYR61 enhancers in colorectal cancer development
Lingzhu Xie, et al. J Exp Clin Cancer Res. 2019 May 22;38(1):213. doi: 10.1186/s13046-019-1217-9.
Background: High expression of secreted matricellular protein cysteine-rich 61 (CYR61) correlates with poor prognosis in colorectal cancer (CRC). Aberrant enhancer activation has been shown to correlate with expression of key genes involved in cancer progression. However, such mechanisms in CYR61 transcription regulation remain unexplored. Methods: Expression of CYR61 was determined by immunohistochemistry (IHC), quantitative real-time PCR (qRT-PCR) and western blotting (WB) in CRC patients paraffin specimens and colon cell lines. ChIP-seq data of enhancer-characteristic histone modifications, in CRC tissues from the Gene Expression Omnibus (GEO) database, were reanalyzed to search for putative enhancers of CYR61. Dual-luciferase reporter assay was used to detected enhancer activity. Physical interactions between putative enhancers and CYR61 promoter were detected by chromosome conformation capture (3C) assay. Histone modification and transcription factors (TFs) enrichment were detected by ChIP-qPCR. Additionally, biological function of enhancers was investigated by transwell migration assays. Results: CRC tissues and cell lines expressed higher level of CYR61 than normal colon mucosa. Three putative enhancers located downstream of CYR61 were found in CRC tissues by ChIP-seq data reanalysis. Consistent with the ChIP-seq analysis results in the GEO database, the normal colon mucosal epithelial cell line NCM460 possessed no active CYR61 enhancers, whereas colon cancer cells exhibited different patterns of active CYR61 enhancers. HCT116 cells had an active Enhancer3, whereas RKO cells had both Enhancer1 and Enhancer3 active. Pioneer factor FOXA1 promoted CYR61 expression by recruiting CBP histone acetyltransferase binding and increasing promoter-enhancer looping frequencies and enhancer activity. CBP knockdown attenuated H3K27ac enrichment, promoter-enhancer looping frequencies, and enhancer activity. Small molecule compound 12-O-tetradecanoyl phorbol-13-acetate (TPA) treatment, which stimulated CYR61 expression, and verteporfin (VP) treatment, which inhibited CYR61 expression, confirmed that the enhancers regulated CYR61 expression. Knockdown and ectopic expression of CYR61 rescued cell migration changes induced by over-expressing and knockdown of FOXA1, respectively. Conclusions: CYR61 enhancer activation, mediated by FOXA1 and CBP, occurs during CRC progression to up-regulate CYR61 expression and promote cell migration in CRC, suggesting inhibition of recruitment of FOXA1 and/or CBP to CYR61 enhancers may have therapeutic implications.
