Degradation of Tob1 mediated by SCFSkp2-dependent ubiquitination

Area of Science:

• Molecular and Cellular Biology
• Biochemistry
• Oncology

Background:

• Tob1, a Tob/BTG family member, functions as a tumor suppressor by inhibiting G1-S phase transition and suppressing cyclin D1 expression.
• Tob1 exhibits rapid turnover via the ubiquitin-proteasome pathway, yet the specific proteins mediating this degradation remain unidentified.

Purpose of the Study:

• To identify the proteins responsible for Tob1 ubiquitination and degradation.
• To elucidate the role of the SCF-Skp2 ubiquitin ligase complex in Tob1 regulation.

Main Methods:

• Investigated the interaction between Tob1 and Skp2 using co-immunoprecipitation assays.
• Assessed Tob1 ubiquitination in vitro and in intact cells.
• Utilized Skp2 knockout mouse fibroblasts and Skp2 knockdown HeLa cells to study Tob1 stability and cyclin D1 expression.

Main Results:

• Skp2 directly interacts with Tob1 and promotes its ubiquitination.
• Skp2 mutants lacking the F-box or leucine-rich repeat failed to bind Tob1 or enhance its ubiquitination.
• Tob1 levels were significantly increased in Skp2-deficient cells, and cyclin D1 expression was suppressed in Skp2-depleted cells.

Conclusions:

• Tob1 is a novel substrate targeted for degradation by the SCF-Skp2 ubiquitin ligase complex.
• The SCF-Skp2-mediated degradation of Tob1 plays a role in regulating cyclin D1 expression and cell cycle progression.