Downregulation of specific protein carboxylmethyltransferase immunoreactivity in human endometrial carcinoma

Protein carboxylmethyltransferases (PCMT), enzymes that methylate free carboxyl groups of proteins, are involved in functional modification of various proteins including those of age‐damaged proteins and the oncogenic ras proteins. Several species of PCMT are associated with these modifications. By using western blot analysis and specific antibodies raised against one type of PCMT, a 30‐kilodalton (KD) cytosolic enzyme from Torpedo electric organ was identified in human erythrocytes and endometrium. The high specificity of the antibodies made it possible to compare levels of immunoreactive 30‐KD PCMT protein in normal human endometria and endometrial carcinomas. Assays done on samples from 23 patients indicated the average levels of immunoreactive 30‐KD PCMT in endometrial carcinomas was one fifth that of normal endometrium. The sensitivity of the assay was 83%, and its specificity was 90%. These results suggest that levels and activity of the 30‐KD PCMT may be downregulated to maintain the phenotypic expression of the endometrial carcinoma. These assays may be used to assist in the detection of endometrial carcinomas.