Lin-9 Homolog (LIN9)

LIN9 encodes a 542-amino acid protein that contains 2 regions highly conserved between C. elegans Lin9 and 2 Drosophila orthologs. Immunoprecipitation experiments with GST fusion proteins showed that LIN9 binds via its amino-terminal portion to RB protein both in vitro and in vivo. Coexpression of LIN9 with RB protein in Saos-2 cells enhanced the formation of flat (senescent-like) cells.

Transactivation assays with a panel of incompletely penetrant RB mutants demonstrated that LIN9 enhances RB-dependent transactivation. LIN9 inhibited oncogenic transformation of mouse fibroblasts in an RB-dependent manner, and that inactivation of LIN9 substituted for inactivation of RB protein in the transformation of human fibroblasts.