Protein expression of double-stranded RNA-activated protein kinase in thyroid carcinomas: correlations with histologic types, pathologic parameters, and Ki-67 labeling.

There have been no reports evaluating double-stranded RNA-activated protein kinase (PKR) in thyroid carcinomas. Therefore, we investigated the protein expression of PKR and its correlations with several pathologic parameters and Ki-67 labeling in 86 thyroid carcinomas, using a semiquantitative scoring method. Western blot analysis showed a specific band of 68 kDa corresponding to PKR molecular weight in 9 selected fresh samples. In immunohistochemistry of archival samples, PKR was expressed in 77 of 86 (90%) cases. The positive rate and PKR score were significantly higher in papillary carcinoma (75 of 80, 94%, PKR score = 4.47 +/- 2.17) than in nonpapillary carcinomas (2 of 6, 33%, PKR score = 1.50 +/- 2.81). Nontumorous thyroid showed no or faint "baseline" PKR expression. There were no significant differences between the PKR score and tumor size, tumor invasion, capsular invasion, or lymph node metastasis. However, there were significant differences between the PKR score and vascular invasion or presence of satellite tumor nodules, the PKR score being higher in cases with more vascular invasion and in cases with satellite tumor nodules than in cases without them. Ki-67 labeling showed a reverse correlation with the PKR score, being the highest in cases with low PKR scores. These results suggest that follicular cells newly express PKR during thyroid carcinogenesis, that PKR is more expressed in papillary carcinoma than in nonpapillary carcinoma, that PKR expression may be associated with high vascular invasion and satellite nodules, and that PKR expression is linked to low cell proliferative activity.