Proteomics Analysis Reveals Involvement of Krt17 in Areca Nut-Induced Oral Carcinogenesis.

The areca nut is a known carcinogen that causes oral cancer in individuals in Southeast Asia, but the molecular mechanism that leads to this malignancy is still unclear. To mimic the habit of areca nut chewing, our laboratory has established four oral cancer cell sublines (SAS, OECM1, K2, C9), which have been chronically exposed to areca nut extract (ANE). To elucidate the molecular basis of areca nut-induced oral carcinogenesis, the differential proteomes between oral cancer cells and the ANE-treated sublines were determined using isobaric mass tag (iTRAQ) labeling and multidimensional liquid chromatography-mass spectrometry (LC-MS/MS). Over 1000 proteins were identified in four sublines, and 196 proteins were found to be differentially expressed in at least two ANE-treated sublines. A bioinformatic analysis revealed that these proteins participate in several pathways, and one of the most prominent pathways was the regulation of epithelial to mesenchymal transition (EMT). In all, 24 proteins including Krt17 were confirmed to be differentially expressed in the ANE-treated sublines. To reveal additional information on the mechanism of ANE-induced carcinogenesis, Krt17 was further investigated. Krt17 knockdown significantly suppressed ANE-induced cell migration and invasion and modulated the EMT process. Furthermore, in a murine model of carcinogen-induced (arecoline cocktail, an active compound of ANE) oral cancer, Krt17 was significantly up-regulated in all hyperplastic tissues and in carcinoma tissues (p < 0.001). In conclusion, we have identified a proteome of oral cancer cells that is associated with chronic areca nut exposure. Krt17 was demonstrated to contribute to areca nut-induced oral malignancy. The results of this study contribute to risk assessment, disease prevention and other clinical applications associated with areca nut-induced oral cancer.

Keratin 17 as a therapeutic target for the treatment of psoriasis.

Keratin 17 (K17) is the only ectopically expressed keratin in psoriatic lesional epidermis. This review focuses mainly on reports that have addressed the mechanism of K17 up-regulation and its biological role in psoriasis. In addition to IFN-γ, IL-17A and IL-22, which are derived from Th17 and Th22 cells, could up-regulate K17 mRNA and protein levels in keratinocytes in a dose-dependent manner. Moreover, these effects are partially blocked with STAT1- and STAT3-specific inhibitors, as well as small interfering RNA (siRNA) targeting STAT1 and STAT3. On the other hand, the HLA DRB1*04 and/or *07 positive patients show significant T cell responses to two peptides from K17 protein selected on the basis of predicted HLA DRB1*04 and/or *07 bindings. One peptide contains the ALEEAN sequence, while the other peptide has an amino acid sequence that has not been previously reported. Analysis of these processes led us to propose the existence of a K17/T cells/cytokine autoimmune loop, in which ectopically expressed K17 impacts on the maintenance of psoriasis by activating autoreactive T cells. Furthermore, it has been found that altered peptide ligands, which are produced through single alanine residue substitutions at a critical TCR contact position, abolish the T cell proliferation and IFN-γ production induced by K17 pathogenic peptides. K17-specific antisense ODNs and RNAi suppress K17 mRNA and protein expression in psoriatic skin in vivo, which coincides with marked clinical and histological improvement. These findings highlight K17 as an attractive target for novel therapies aimed at curtailing psoriasis driven by chronic inflammation.

Epithelial transition zones: merging microenvironments, niches, and cellular transformation.

Transition zones (TZs) are regions in the body where two different types of epithelial tissue meet resulting in the appearance of a distinct abrupt transition. These TZs are found in numerous locations within the body, including the cornea-conjunctiva junction, esophagogastric junction, gastro-duodenal junction, endo-ectocervix junction, ileocecal junction, and anorectal junction. Several of these TZs are often associated with the development of cancer, in some cases due to viral transformation by the human papilloma virus (HPV). The underlying molecular and cellular basis for this tumor susceptibiblity is unknown. The distinct epithelial morphology and location results in unique properties being conferred upon this epithelial tissue, as different signaling cues and cell surface markers are apparent. Importantly, the natural state of TZs closely resembles that of a pre-lesional epithelium, as several proteins that are induced during wounding are expressed specifically within this region, which may contribute to transformation. This region may also act as a stem cell niche, and as such, represents a key location for cellular transformation by accumulated genetic mutations or viral transformation resulting in tumor formation.

Keratin 17 identified by proteomic analysis may be involved in tumor angiogenesis.

Angiogenesis is crucial for solid tumor growth. By secreting angiogenic factors, tumor cells induce angiogenesis. However, targeting these angiogenic factors for cancer therapy is not always successful, suggesting that other factors may be involved in tumor angiogenesis. This work shows that 25 protein spots were differentially expressed by two-dimensional gel electrophoretic analysis when HepG2 cells induced endothelial cell differentiation to tube in vitro, and most of them were upregulated. Twenty-one proteins were identified with MALDI-TOF-MS, and the other four were identified by LTQ-MS/MS. Keratins were identified as one class of these upregulated proteins. Further study indicated that the expression of keratin 17 in cultured endothelial cells is likely microenvironment regulated, because its expression can be induced by HepG2 cells and bFGF as well as serum in culture media. Increased expression of keratins in endothelial cells, such as keratin 17, may contribute to the angiogenesis induced by HepG2 cells.