The Rb gene suppresses the growth of normal cells.

The suppression of tumor formation, first demonstrated by somatic cell hybrid and microcell fusion experiments, suggests the existence of a class of genes that selectively suppress the growth of tumor cells but not normal cells. The reintroduction of these genes into tumor cells presumably renders the cells responsive to in vivo growth inhibitory environment. As the inheritance of a defective retinoblastoma gene (Rb-1) allele results in a predisposition to the development of various cancers, and since inactivation of both alleles are observed in tumor cells, the Rb gene has been suspected to have the ability to suppress tumor growth. Data presented here demonstrated that different types of normal cells, which have a limited life span, were also growth arrested by a transfected Rb gene. Cell lines which are resistant to the growth suppression effect of the Rb gene in vitro, retain the ability to form tumors in nude mice even in the presence of a stable and highly expressed wild type Rb protein. We conclude that while the Rb gene can suppress the growth of many tumor cell lines, its growth suppression effect is not tumor specific.