Expression of a novel form of the p56lck protooncogene in rat cerebellar granular neurons.

The src family protein tyrosine kinases (PTKs) are nonreceptor kinases. Some PTKs of this family are ubiquitously expressed, whereas others have a more restricted expression, as in neurons. Lymphoid cell kinase (lck) p56lck is highly expressed in tissues of lymphoid origin and believed to be specific for hematopoietic cells. Reports suggesting that CD4 is expressed in neurons prompted us to analyze the possibility that p56lck is also expressed in these cells. By western blot and immunoprecipitations using anti-lck antibody, an lck-like protein was detected in lysates from primary cultures of rat cerebellar granular neurons. This 56-kDa phosphoprotein was autophosphorylated in vitro and also phosphorylated enolase, similarly to p56lck. It was shown to be located actually in the neurons by immunocytofluorescence. Partial proteolysis mapping showed that the 56-kDa phosphoprotein had a peptide pattern very similar to the p56lck protein. Retrotranscription-PCR allowed the detection of an lck RNA in the neurons. The lck kinase domain was completely identical to the lymphocyte lck kinase domain, but the 5' end was modified in the neurons. These results show that p56lck is not lymphoid specific as is widely believed; its expression in neurons might underlie the toxicity of the HIV glycoprotein gp120 to neurons.