Differential expression and characterization of proto-oncogene product Ha-Ras GTPase in camel tissues

Pas proto-oncogene product is known to be involved in transducing signals for growth, differentiation and oncogenesis in mammalian cells. Using a monoclonal antibody to human Ha-Ras, a camel homolog of Ha-Ras protein having an apparent molecular mass of 21 kDa was identified. The expression level of Ha-Ras protein in various tissues of camel was compared with that of mouse tissues. In camel it was found that expression of Ha-Ras protein was highest in the kidney and moderate in the liver. Expression of Ha-Ras in camel lung, testis, spleen, heart, brain, intestine and muscle was found to be very low. While Ha-Ras expression in mouse was found to be highest in the intestine. A moderate expression of Ha-Ras was found in mouse testis, kidney and heart. The kidney tissue extract of camel was immunoprecipitated using the same human Ha-Ras antibody. Biochemical characterization of the immunoprecipitate revealed that like most other G proteins, the camel homolog of Ras is a GTPase. The GTPase activity was found to be stimulated specifically by recombinant human Ras GAP p120 and neurofibromin. It suggests that both camel and human share the same Ras mediated growth signaling process and that human Ras GAP might be able to complement camel Ras GAP function. Camel homolog of Raf-1 and MAP kinase (member of Ras signaling pathway) were also identified by immunoblot. This is the first demonstration showing the existence of a Ras mediated growth signal transduction pathway in camel.