We have studied the expression of TIMP-1 in a series of Burkitt cell lines. Burkitt's lymphoma, common in AIDS patients, is an aggressive neoplasm without effective therapy in the immunocompromised host. Northern blot analysis reveals that TIMP-1 is expressed at the RNA level by 4 out of 9 lines studied. Cell lines from both African and American Burkitt's express TIMP-1, as do Burkitt cells with t(8;14) and t(8;22) translocations. All of the Burkitt cell lines studied with demonstrable TIMP-1 RNA transcripts secreted TIMP-1 protein (as determined by Western blot analysis) into the culture media. TIMP-1 expression does not correlate with EBV involvement, p53 mutations, or levels of myc expression in these lines. The cell lines that express TIMP-1 have a higher rate of cell proliferation in vitro compared to those negative for TIMP-1 transcripts. We are purifying TIMP-1 protein and intend to study the effect of TIMP-1 on growth kinetics in vitro. The TIMP-1 expressing Burkitt cell lines are also more tumorigenic and invasive in the nude mouse model. Invasion of skin and nerve is seen in only in TIMP-1 expressing lines. This aggressive behavior may be due to high growth rate, enhanced invasive behavior or a combination of the two. We are currently studying four cell lines (two expressing TIMP-1 and two negative) in invasion assays to assess invasive behavior. We plan to infect TIMP-1 negative cell lines with a retroviral construct containing TIMP-1 to cause TIMP-1 expression in order to study the effect of TIMP-1 on growth rate and invasiveness. In four of the Burkitt cell lines studied, Gelatinase B activity can be demonstrated by zymogram but not by Northern blot analysis. TIMP-1 and Gelatinase B coexpression is seen in only one cell line, with very low enzyme expression noted. The remainder of the Gelatinase B activity was demonstrated in TIMP-1 negative cell lines. Gelatinase A expression was not observed in any Burkitt cell lines. If TIMP-1 functions in Burkitt's lymphoma by blocking gelatinase activity, we would have expected to be able to demonstrate gelatinase expression by Northern blot or zymogram in the TIMP-1 positive cell lines. As gelatinase expression may occur in these cells in response to the extracellular matrix, we are studying the expression of Gelatinase A and Gelatinase B in Burkitt cell tumors grown in nude mice.
