Isolation and partial characterization of a transformation‐associated sequence from human nasopharyngeal carcinoma

A transforming activity associated with Chinese nasopharyngeal carcinoma (NPC) cell line CNE 2 DNA has been identified by transfer into nontransformed promotion‐sensitive mouse JB6(P + ) C141 cells. To clone this transformation‐associated sequence, we carried out three cycles of transfection, followed by cloning of anchorage‐independent transformants in soft agar. A tertiary CNE/JB6 clonal transfectant cell line 625 whose DNA showed transforming activity, as indicated in both soft‐agar assay and nude‐mice implantation, was used to make a genomic library in the vector λ dash. Using the human repeated sequence Blur 8 to screen the library, we obtained 10 human Alu‐positive clones. A cloned Alu‐positive insert of 16 kbp, CNE 323, was characterized in detail. CNE 323 transferred moderate transforming activity when introduced into JB6 P + cells and showed no homology to Ha‐, Ki‐, or N‐ ras genes; human promotion sensitivity genes; src, myb, jun, myc, fos, raf, or int ‐2 oncogenes; or epidermal growth factor receptor. The isolated CNE 323 DNA sequence appeared to preserve the genomic structure of the original sequence found in CNE 2 cells and in nude mouse tumors induced by CNE 2 cells or by CNE/JB6 transfectant cells, indicating that the cloned NPC sequence was activated during NPC carcinogenesis and not during transfection or construction of the library, and that the cloned sequence or a larger sequence of which it was part played a role in tumor formation. Finally, we identified a 1.3‐kb mRNA that hybridizes to a subclone of the 16‐kb NPC sequence in CNE 2 cell poly (A) + RNA.