The common acute lymphoblastic leukemia antigen (CALLA) is a glycoprotein expressed on the majority of acute lymphoblastic leukemia tumor cells. Despite the recognition for more than a decade of the importance of this surface structure in diagnostic and therapeutic considerations related to hematopoietic malignancies, the primary structure of CALLA has not been resolved and its function remains unknown. Recently, we have employed protein microsequencing of intact CALLA and derived tryptic and V8 fragments to obtain primary structural information, design oligonucleotides complementary to CALLA and isolate cDNAs encoding portions of the CALLA protein. Homology searches at DNA and protein levels indicate that CALLA is a novel structure. At least three CALLA related RNA forms are detected in leukemic cells (5.8, 4.5 and 3.7Kb). In the present proposal, we plan to first isolate complete cDNA sequences of the 100KD CALLA molecule, determine the intron-exon organization of the CALLA gene and its chromosomal location in the human genome. The structural nature of the putative murine CALLA homologue and its chromosomal location will be investigated and monoclonal antibodies against murine CALLA equivalent produced. Second, RNA analysis will be utilized to examine the differential expression of the three CALLA related transcripts in normal lymphoid and non-lymphoid tissues and characterize the various species of CALLA RNA which are expressed. Cloning of individual RNAs in cDNA form and genomic analysis will be used to determine whether these represent alternative splicing of the same gene or related but distinct genes. Third, as CALLA is expressed on early T and B cell lineages, in vitro bone marrow culture systems will be utilized to assess whether CALLA expression is necessary for commitment of lymphoid progenitors. In vivo studies employing transgenic animals which constitutively express CALLA or whose CALLA+ cells are deleted via novel CALLA promoter/toxin transgenes will be examined. Finally, CALLA expression in neoplastic and normal cells will be compared for quantitative as well as qualitative differences. As southern blot analysis already suggests that there are restriction pattern differences among certain CALLA+ malignancies, investigation of potential chromosomal translocation vs. restriction fragment length polymorphisms will be undertaken.
Showing the most recent 10 out of 13 publications
