Cell-cycle-dependent, differential prenylation of proteins

Area of Science:

• Cell Biology
• Biochemistry
• Molecular Biology

Background:

• Isoprenylated proteins are crucial for cell growth and proliferation.
• Cholesterogenesis, the synthesis of cholesterol and isoprenoids, is essential for cell division.
• The precise role of protein prenylation timing during the cell cycle remains to be fully elucidated.

Purpose of the Study:

• To investigate the cell-cycle-phase-dependent pattern of protein prenylation.
• To correlate protein prenylation with specific stages of the cell division cycle and cholesterol synthesis.
• To determine if protein prenylation is an obligatory step for DNA replication and cell cycle progression.

Main Methods:

• Synchronization of HepG2 cells to study the cell division cycle.
• Measurement of [3H]mevalonate incorporation into proteins to assess protein prenylation.
• Measurement of [14C]acetate incorporation into cholesterogenic lipid intermediates to track isoprenoid synthesis.

Main Results:

• A distinct cell-cycle-dependent pattern of protein prenylation was observed for cytosolic and nuclear matrix proteins.
• Mevalonate incorporation into proteins increased in mid-to-late G1 phase, peaking around mid-S phase.
• Cholesterol synthesis peaked in early-to-mid G1, followed by increased incorporation into the farnesyl moiety during late G1/S phase.

Conclusions:

• Protein prenylation, particularly involving the farnesyl moiety, is a cell-cycle-regulated process.
• The timing suggests that cholesterol-pathway-dependent protein prenylation is a prerequisite for DNA replication.
• This process may be an obligatory step driving cell cycle transit and supporting continuous proliferation, as seen in tumors.