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Loss of Keratin Expression in Anaplastic Carcinoma Cells Due to Posttranscriptional Down-Regulation Acting in trans¹

Department of Medical Oncology, University of Sydney, Westmead Centre, Westmead, New South Wales 2145 [M. L. P., R. F. K.], and Department of Pathology, University of Sydney, Sydney, New South Wales 2006 [M. L. P., J. R. G., K. E. C., A. D.], Australia

² To whom requests for reprints should be addressed, at Department of Medical Oncology, University of Sydney, Westmead Centre, Westmead, New South Wales 2145, Australia.

Rat keratin K5 and vimentin complementary DNAs have been isolated, identified, and used to study keratin and vimentin expression as markers for cell differentiation. Isologous rat neoplastic epithelial cell lines used were based on a clonal benign epithelial line (A5P/B10) and a clonal anaplastic malignant derivative line (T952/F7). Stable cytoplasmic mRNA was detected for keratin but not vimentin in the benign cells. The anaplastic derivative cells expressed vimentin but showed a 1000-fold reduction in the keratin message, which nuclear run-on assays identified as being due to posttranscriptional down-regulation. An identical pattern of posttranscriptional down-regulation was found in independent malignant somatic cell hybrids of the benign and anaplastic cells. trans-acting regulatory mechanisms implicated in posttranscriptional (pretranslational) keratin down-regulation in these anaplastic malignant cells may play a role in the apparent loss of differentiation evident in tumor progression.

¹ Supported by a grant from the University of Sydney Cancer Research Fund. M. L. P. is supported by National Health and Medical Research Council Dental Post-graduate Research Scholarship Grant 908007, and the work reported forms part of material to be submitted for the degree of Ph.D. in the Faculty of Medicine, University of Sydney.

The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

Received 4/13/92. Accepted 9/23/92.