The RB1 Story: Characterization and Cloning of the First Tumor Suppressor Gene

Abstract

The RB1 gene is the first described human tumor suppressor gene and plays an integral role in the development of retinoblastoma, a pediatric malignancy of the eye. Since its discovery, the stepwise characterization and cloning of RB1 have laid the foundation for numerous advances in the understanding of tumor suppressor genes, retinoblastoma tumorigenesis, and inheritance. Knowledge of RB1 led to a paradigm shift in the field of cancer genetics, including widespread acceptance of the concept of tumor suppressor genes, and has provided crucial diagnostic and prognostic information through genetic testing for patients affected by retinoblastoma. This article reviews the long history of RB1 gene research, characterization, and cloning, and also discusses recent advances in retinoblastoma genetics that have grown out of this foundational work.

Keywords: cancer genetics; gene cloning; genetic testing; retinoblastoma; tumor suppressor gene.

Figure 1

The RB1 story. (A) Knudson evaluated age at diagnosis vs. proportion not diagnosed; two hits initiated unilateral retinoblastoma and only one hit was required for bilateral patients predisposed to retinoblastoma [1]. (B) A rare third form of unilateral, non-hereditary retinoblastoma has normal RB1 alleles and instead is driven by one hit: high-level amplification of the oncogene MYCN (reproduced from [23], with permission). (C) Inactivation in tumor of esterase D alleles near the retinoblastoma susceptibility locus suggested regional somatic inactivation was the second hit in some retinoblastoma tumors [10]. (D) Mitotic recombination results in loss of heterozygosity around RB1 locus so that cells that form the retinoblastoma tumor have lost both copies of normal RB1 [11,12]. (E) Retinoblastoma tumor 9 (of 22) has homozygous deletion of H-38 probe (*) that mapped in the 13q14 genomic region [16]. (F) The RB1 tumor suppressor gene is cloned: a conserved DNA sequence near H-38 probe hybridized to a 4.7 kb messenger RNA found in all normal tissues but not in retinoblastoma or osteosarcoma tumors [17]. (G) Persons carrying a RB1 pathogenic variant are H1 (at risk for retinoblastoma and second cancers); prenatal detection and early term delivery facilitates detection and laser treatment of invisible tumors with minimal scarring (reproduced from [60], with permission). (H) Cell-free DNA from fluid behind the cornea (aqueous humor) shows the same pattern of copy number changes characteristic of retinoblastoma as the tumor from the removed eye (reproduced from [62], with permission).