Cloning of hHRI, Human Heme-regulated Eukaryotic Initiation Factor 2α Kinase: Down-regulated in Epithelial Ovarian Cancers

Abstract

Protein synthesis is regulated in response to environmental stimuli by covalent modification, phosphorylating the components of the translational machinery. Phosphorylation of the α subunit of eIF-2 is one of the bestcharacterized mechanisms for down-regulating protein synthesis in higher eukaryotes in response to various stress conditions. One of mammalian eIF-2α kinases is a hemeregulated inhibitor kinase (HRI), which is activated by heme deficiency and plays an important role in translational control. In this work, we have analyzed the differentially expressed genes between epithelial ovarian cancer and normal ovary. We have screened a total of 1,408 genes isolated from a human dermal papilla cell cDNA library by cDNA array hybridization. Among many differentially expressed genes, eIF2α kinase, a heme regulated inhibitor was down-regulated in ovarian epithelium cancer. The down-regulation of hHRI was also confirmed in other ovarian cancer tissues by Northern blot hybridization. The hHRI gene is 2,887 bp in length and the amino acid sequence deduced from the cDNA clone encodes a protein of 630 amino acids with molecular mass of 73 kDa. It contains all 12 catalytic domains of the protein kinases with consensus sequences of the proteinserine/threonine kinases. The expression pattern of hHRI mRNA showed approximately 3.0 kb bands which were expressed ubiquitously in all human tissues examined, which indicates that eIF-2α kinase could play an important role in the translational regulation of nonerythroid tissues.