International Immunology, Vol. 14, No. 5, pp. 481-491,
May 2002
© 2002 Japanese Society for Immunology
MHC class II-deficient tumor cell lines with a defective expression of the class II transactivator
1 Departamento de Biologia, Facultad de Ciencias, Universidad de Chile, and Millennium Institute for Fundamental and Applied Biology, Casilla 653, Santiago, Chile 2 Unité d‘Immunogénétique Humaine, INSERM U276, Institut Pasteur, 25 rue du Dr Roux, 75724 Paris Cedex 15, France 3 INSERM U396, Centre de Recherches Biomédicales des Cordeliers, 15 rue de l‘Ecole de Médecine, 75006 Paris, France 4 Permanent address: Istituto di Biologia dello Sviluppo, CNR 152 via Ugo La Malfa, 90146 Palermo, Italy
The first two authors contributed equally to this work
Correspondence to: M. R. Bono; E-mail: mrbono{at}uchile.cl
Transmitting editor: D. R. Littman
MHC class II expression defects have been evidenced in several human tumor cell lines originating from lung cancers or retinoblastoma. Accordingly, the mouse adenocarcinoma and fibrosarcoma cell lines, RAG and L(tk–), do not express I-A and I-E molecules even when treated with IFN-
. Here we show that fusion of both cell lines restores the inducible expression of MHC class II, thereby demonstrating that they present different and recessive alterations outside the MHC class II locus. CIITA, the MHC class II transactivator, controls the tissue-specific expression of MHC class II genes and creates the architecture of the transcriptional complex that binds to the MHC class II gene promoters. In L(tk–) cells, C2ta transcripts, expressed from the gene encoding CIITA, were indeed detected in severely limited amounts, with a defect in C2ta transcription initiation. In agreement we show here that the L(tk–) cell line does not express the CIITA protein. In contrast, in the RAG cell line, C2ta transcripts were expressed at normal levels, from the proper initiation site. The nucleotide sequencing of the CIITA cDNA from RAG did not reveal any mutation. However, the CIITA protein was not detected. These data evidence a new type of defect in a MHC class II-defective tumor cell line, as we show here that the alteration in the RAG cells occurs downstream of C2ta transcription. The RAG mutation might therefore reside in the C2ta transcript nuclear export or translation, or in the stability of the CIITA protein.
Keywords: CIITA, MHC class II, tumor cell line, transcription
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