p150 expression and its prognostic value in squamous-cell carcinoma of the esophagus

Identification of a 170-kDa protein over-expressed in lung cancers

Lung cancer is the leading cause for cancer death in both male and female populations. Although many molecular markers for lung cancer have been developed and useful for early detection of lung cancer, their function remains unknown. In this paper, we report our findings that a 170-kDa protein (p170) is over-expressed in all types of human lung cancers compared with normal tissues and it is identified as a subunit of translation initiation factor eIF3 by cDNA cloning. Translation initiation factors are a family of proteins that promote the initiation step of protein synthesis and are regulators of cell growth at the translational level. Further studies showed that p170 mRNA is ubiquitously expressed with higher levels in adult proliferating tissues (e.g. bone marrow) and tissues during development (e.g. fetal tissues). This study suggests that p170 and eIF3 may be important factors for cell growth, development, and tumorigenesis.

Molecular interaction between human tumor marker protein p150, the largest subunit of eIF3, and intermediate filament protein K7

The human tumor marker protein p150 was identified as the largest subunit of eukaryotic translation initiation factor 3 (eIF3) (also known as p170/p180). Its expression level is not only upregulated in many transformed cell lines, but also in several human cancers including breast, cervical, esophageal, and stomach carcinomas. The function of p150 in cancer and initiation of translation are not well understood. Using the yeast two-hybrid genetic screen, we found that a portion of p150 interacts with hPrt1, another subunit of eIF3, and cytokeratin 7, an intermediate filament protein. The interactions between p150 and hPrt1, and between p150 and cytokeratin 7 were verified both in vivo and in vitro. The interaction site for hPrt1 was mapped to the carboxyl half of the coiled-coil region of the p150 protein between amino acids 664-835. The expression of hPrt1 was clearly upregulated in cancer tissue, similarly to that of p150. By contrast, no substantial difference in the expression level of cytokeratin 7 was observed between cancer and normal breast tissue, suggesting that cytokeratin 7 expression is not co-regulated with p150. Taken together, our studies suggest a new role for p150 in translation initiation, possibly by acting as an adapter molecule between the translation initiation apparatus and the cytoskeleton structure in the cell.