The hypusine cascade promotes cancer progression and metastasis through the regulation of RhoA in squamous cell carcinoma.

Metastasis is a critical factor contributing to poor prognosis in cancer, but the underlying mechanisms of metastasis are still poorly understood. We established a highly metastatic cell subline (HOC313-LM) derived from an oral squamous cell carcinoma cell line (HOC313) for uncovering the mechanisms of metastasis, and identified deoxyhypusine synthase (DHPS) as a metastasis-associated gene within the specific amplification at 19p13.2-p13.13 in HOC313-LM. DHPS-mediated hypusine-modification of eukaryotic translation factor 5A facilitated the translation of RhoA, resulting in the activation of the RhoA signaling pathway and leading to not only increased cell motility, invasion and metastasis of cancer cells in vitro, but also increased tumor growth in vivo. Moreover, the use of N1-Guanyl-1,7-diaminoheptane, a DHPS inhibitor, resulted in a significant decrease in tumor formation in vivo. In patients with esophageal squamous cell carcinoma (ESCC), overexpression of DHPS in ESCC tumors was significantly associated with worse recurrence-free survival, and correlated with distant metastasis. The elucidation of these molecular mechanisms within the hypusine cascade suggests opportunities for novel therapeutic targets in SCC.

Distinct distribution of protein disulfide isomerase family proteins in rat tissues.

We investigated the distribution of protein disulfide isomerase (PDI) family proteins PDI, ERp72, and ERp61 in rat tissues and compared their localization by immunohistochemical double staining. The extent of their expression was diverse in different cell types, although they were ubiquitously distributed in a wide variety of cell types. Prominent staining for all three proteins was detected in thyroid follicular epithelia, tracheal mucous gland cells and chondrocytes, and chief cells and mucous neck cells of the stomach. Hepatocytes, neuronal cells in brain and spinal cord, and pancreatic acinar cells were also consistently and uniformly stained, but with low intensity. On the other hand, distinct differences were observed for the expression of the three proteins in plasma cells, pancreatic islet cells, goblet cells, and Paneth's cells of intestines, seminiferous epithelia, and salivary gland ductal epithelia. The similarities and differences in the distribution of the three proteins provide helpful clues to their biological functions.

PRTFDC1, a possible tumor-suppressor gene, is frequently silenced in oral squamous-cell carcinomas by aberrant promoter hypermethylation.

Array-based comparative genomic hybridization (array-CGH) has good potential for the high-throughput identification of genetic aberrations in cell genomes. In the course of a program to screen a panel of oral squamous-cell carcinoma (OSCC), cell lines for genomic copy-number aberrations by array-CGH using our in-house arrays, we identified a 3-Mb homozygous deletion at 10p12 in 1 of 18 cell lines (5.6%). Among seven genes located within this region, expression of PRTFDC1 mRNA was not detected in 50% (9/18) or decreased in 5.6% (1/18) of OSCC cell lines, but detected in normal oral epithelia and restored in gene-silenced OSCC cells without its homozygous loss after treatment with 5-aza-2'-deoxycytidine. Among 17 cell lines without a homozygous deletion, the hypermethylation of the PRTFDC1 CpG island, which showed promoter activity, was observed in all nine cell lines with no or reduced PRTFDC1 expression (52.9%). Methylation of this CpG island was also observed in primary OSCC tissues (8/47, 17.0%). In addition, restoration of PRTFDC1 in OSCC cells lacking its expression inhibited cell growth in colony-formation assays, whereas knockdown of PRTFDC1 expression in OSCC cells expressing the gene promoted cell growth. These results suggest that epigenetic silencing of PRTFDC1 by hypermethylation of the CpG island leads to a loss of PRTFDC1 function, which might be involved in squamous cell oral carcinogenesis.