Endocrine Abstracts

The malignant phenotype of small cell lung cancer (SCLC) cells critically relies on the autocrine stimulation of G_12/13- and G_q/11-coupled neuropeptide receptors. By this means, G_12/13- and G_q/11-dependent signalling pathways are constitutively activated in these cells. While G_q/11-dependent signalling has been shown to promote proliferation of SCLC cells, the role of signalling pathways via G_12/13 is still elusive. Thus, we employed shRNA-mediated down-regulation of Gα₁₂, Gα₁₃, or both, in human SCLC cell lines. The use of a lentiviral expression system rather than non-viral transfection resulted in robust, specific, and stable knockdown of both target proteins. This decrease in Gα₁₂ or Gα₁₃ levels markedly reduced proliferation in SCLC cell lines in normal culture medium as well as colony formation in semi-solid medium. However, double targeting of both Gα₁₂ and Gα₁₃ did not exert a synergistic anti-proliferative effect in vitro. In a subcutaneous tumor xenograft mouse model, the downregulation of Gα₁₂ or Gα₁₃ resulted in decreased tumor growth, which was due to reduced tumor cell proliferation. More importantly, double knock-down of Gα₁₂ and Gα₁₃ completely abolished tumorigenicity in mice. Thus, intact G_12/13 signalling is a prerequisite for proliferation of SCLC cells in vitro and tumorigenicity in vivo.