Ablation of Goalpha overrides G1 restriction point control through Ras/ERK/cyclin D1-CDK activities

We have generated stable IIC9 cell lines, Goa1 and Goa2, that overexpress full-length antisense Goalpha RNA. As shown previously, expression of antisense Goalpha RNA ablated the alpha subunit of the heterotrimeric G protein, Go, resulting in growth in the absence of mitogen. To better understand this change in IIC9 phenotype, we have characterized the signaling pathway and cell cycle events previously shown to be important in control of IIC9 G1/S phase progression. In this paper we clearly demonstrate that ablation of Goalpha results in growth, constitutively active Ras/ERK, elevated expression of cyclin D1, and constitutively active cyclin D1-CDK complexes, all in the absence of mitogen. Furthermore, these characteristics were abolished by the transient overexpression of the transducin heterotrimeric G protein alpha subunit strongly suggesting the transformation of Goalpha-ablated cells involves Gobetagamma subunits. This is the first study to implicate a heterotrimeric G protein in tumor suppression.