CONSTRUCTION AND CHARACTERIZATION OF LCK-SPECIFIC AND FYN-SPECIFIC TRANSFER-RNA-RIBOZYME CHIMERAS

Two src-family protein tyrosine kinases (PTKs), p56(lck) and p59(fyn), are thought to play an important role in the antigen-specific T cell receptor (TCR)/CD3-initiated signaling pathway, but their relative contribution to these events is not clearly defined. Here, we have explored the potential of catalytic RNA molecules, or ribozymes, as tools for selectively inhibiting expression of the corresponding target genes in T cells. Several lck- or fyn-specific hammerhead ribozymes were synthesized, cloned into a bacterial transcription vector, and found to display specific catalytic activity in vitro. In order to achieve stable high-level ribozyme expression in intact cells, selected ribozymes were subsequently cloned into a retroviral vector (DC-T5T) immediately downstream of a tRNA(met) transcription unit. Upon retroviral transduction of a human leukemic T cell line (Jurkat), two out of four chimeric tRNA:ribozymes, fyn-1 and lck-1, were stably expressed at levels of similar to 10,000 or similar to 25,000 copies/cell, respectively. Ribozyme expression was associated with a reduction of up to 80% (lck) or 61% (fyn) in endogenous target mRNA by comparison to the corresponding transcript levels in control clones transfected with vector alone. By contrast, expression of the corresponding target proteins was not reduced, suggesting a post-transcriptional compensatory mechanism that increases translation or stability of the p56(lck) and/or p59(fyn) proteins.