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Detection of an Altered Form of Cell-CAM 105 on Rat Transplantable and Primary Hepatocellular Carcinomas¹

Department of Medical Oncology, Rhode Island Hospital-Brown University, Providence, Rhode Island [D. C. H.]; and the University of Texas System Cancer Center, Science Park Research Division, Smithville, Texas [K. D. M.]

Monoclonal (MAb 362.50) and polyclonal (anti-gp105-2) antibodies have been used to examine the expression by transplantable (THC) and primary (PHC) hepatocellular carcinomas of a 105 kd rat hepatocyte cell adhesion molecule designated cell-CAM 105. Two-dimensional gel analysis of components immunoprecipitated with MAb 362.50 or anti-gp105-2 antibodies from detergent extracts of cells surface labeled with ¹²⁵I showed that cell-CAM 105 from three different THC exhibited a more basic pI than its counterpart from normal rat hepatocytes. Immunoprecipitation of detergent extracts from radioiodinated hepatocytes with anti-THC antisera raised in rabbits by four immunizations with THC cells showed that six THC lines which were negative when stained by indirect immunofluorescence with MAb 362.50 expressed sufficient levels of cell-CAM 105 to induce precipitating antibodies. In contrast, antisera collected after eight immunizations with THC 253.1 and THC 252.2, showed no detectable reactivity with cell-CAM 105 suggesting that these THC lines had completely lost the expression of this molecule. Immunofluorescence analysis of normal rat tissues indicated that cell-CAM 105 was also present in the brush border of the small intestine and a subset of tubules in the kidney, raising the possibility that THC cells were expressing an isoform normally found in nonhepatic tissues. However, cell-CAM 105 isolated from kidney showed a mobility on two-dimensional gels that was distinct from both the THC and hepatocyte forms of this molecule. Indirect immunofluorescence analysis of PHC induced by ethionine in a choline-deficient diet or by the Solt/Farber protocol showed that 52% and 65% of the persistent hepatic nodules induced by ethionine in a choline-deficient diet and by the Solt/Farber protocol, respectively, were unreactive with MAb 362.50. Immunoprecipitation analysis of PHC induced by ethionine or diethylnitrosamine and choline-deficient diet showed that one of four PHC was expressing an altered form of cell-CAM 105 with the more basic pI characteristic of the THC form of this molecule. Taken together, these results suggest that quantitative and qualitative changes in the expression of cell-CAM 105 may constitute an important step in the acquisition of the malignant phenotype.

¹ Supported by Grant CA-42715 from the National Cancer Institute.

² To whom all requests for reprints should be sent: Medical Oncology Department, Rhode Island Hospital, 593 Eddy Street, Providence, RI 02903.

Received 5/ 9/88. Revised 2/14/89. Revised 6/16/89. Accepted 8/22/89.

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