Identification of the coding sequences responsible for Tsc2-mediated tumor suppression using a transgenic rat system

Area of Science:

• Genetics and Molecular Biology
• Oncology
• Developmental Biology

Background:

• Hereditary renal carcinomas in Eker rats stem from retrotransposon insertion in the tuberous sclerosis-2 (Tsc2) gene.
• Previous studies established a transgenic Eker rat model that suppressed tumor development and embryonic lethality by introducing a wild-type Tsc2 gene.
• The precise in vivo functions of the Tsc2 protein, tuberin, remain incompletely understood.

Purpose of the Study:

• To elucidate the functional domains of Tsc2 in vivo using a transgenic Eker rat model.
• To identify the minimal region of tuberin required for tumor suppression and rescue from embryonic lethality.

Main Methods:

• Generation of transgenic Eker rats carrying deletion mutants of the Tsc2 gene.
• Analysis of renal carcinogenesis suppression and embryonic lethality rescue in these mutant rats.
• Assessment of Tsc2 deletion mutant protein expression levels and Tsc1 (hamartin) binding capability.

Main Results:

• A transgene encoding the C-terminal region (amino acids 1425-1755) of tuberin suppressed renal carcinogenesis, with suppression level correlating to expression.
• This C-terminal Tsc2 transgene product did not bind to Tsc1 (hamartin).
• A transgene lacking the C-terminus (amino acids 1-1755) completely suppressed renal carcinogenesis and partially rescued homozygous mutants from embryonic lethality.

Conclusions:

• The minimal region of tuberin necessary for tumor suppression has been determined, demonstrating a quantitative suppressive effect.
• Tuberin can function as a tumor suppressor even without binding to hamartin.
• The functional domains of tuberin required for preventing embryonic lethality may differ from those for suppressing renal carcinogenesis.